SYSTEM AND METHOD FOR CATEGORIZING AND ASSESSING WELLS

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of petroleum production, and more particularly, to a system and method for categorizing and assessing wells within a geologic storage reservoir.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is described in connection with wells within a geologic storage reservoir.

The escalating levels of greenhouse gases, primarily carbon dioxide (CO₂), in the atmosphere are attributed to global climate changes. To mitigate this, Geological Carbon Sequestration (GCS) or Carbon Capture and Storage (CCS) methods have emerged, enabling the capture and permanent storage of CO₂underground [1]. Pilot CCS projects worldwide have capitalized on learnings from CO₂-enhanced oil recovery initiatives, as highlighted in research by Loria and Bright [2]. The core aim of CCS projects is to securely store CO₂underground, preventing its escape to underground sources of drinking water (USDW) or surface leakage, which could contaminate water sources and alter their chemical composition [3, 4]. The leakage of concentrated CO₂or brine to the USDW changes the chemical composition of drinking water by lowering the pH and could increase the concentrations of harmful metals [5]). The leakage through wellbores is mainly caused due to operational challenges (such as mud-space-cement interactions, decreased cement plug effectiveness from mud contamination, and development of micro-annuli) and regulatory factors (which vary depending on the country and year of implementation) [6-9]. Essential to safeguarding groundwater quality is a robust testing and monitoring regimen encompassing various parameters such as mechanical integrity, injection pressure, corrosion, and groundwater assessments [10-11]. Understanding CO₂leakage pathways, classified as artificial penetrations (includes all the wellbores penetrating the confining zones) and geological features (includes faults, fractures, quality and continuity of the confining zones, etc.), is critical for effective monitoring [12-13].

Carbon Capture Utilization & Storage (CCUS) refers to the injection of CO₂to enhance oil recovery with the added benefit of storing some percentage of CO₂in the reservoir. In other words, Enhanced Oil Recovery using CO₂is termed CCUS. Oil and gas companies have the expertise needed to help build the CCS industry. Several incentives and tax credits motivate the companies to perform CCUS and/or CCS [14].

CCS projects can be broadly classified into three parts-capture, transportation, and storage. The storage part can be further classified into separate storage (sequestration) phases based on the activities performed during each phase: characterization and designs (years 1-2); permit (years 2-3); construction (years 3-4); operations (years 12-50); closure and post-closure (defined); and long-term stewardship (indefinite). The risks and uncertainty involved in the CCS projects are initially high and decrease as the project progresses [15]. The success of CCS depends on the capacity, injectivity, and confinement by the storage medium [16]. In geological carbon sequestration, CO₂is captured directly from an industrial source and stored in underground porous mediums mainly saline aquifers and/or depleted oil and gas reservoirs. Their capacity and injectivity are very well-identified and the success of geological sequestration critically depends on the confinement by the confining zone (geologic seals)—low permeability rocks mostly shales [17]. The terminologies used herein like Area of Review (AoR), caprock, confining zone, geologic seal, storage complex, storage reservoir, and storage formation are well defined here [18].

Legacy wellbores, or improperly plugged and abandoned oil and gas wells, act as a threat to the success of the CCS projects if they remain unidentified and/or if remedial actions are not taken. The standards for cement compositions and well-plugging procedures were set up in 1952 by the American Petroleum Institute (API) prior to that mainly wood (logs), mud, animal carcasses, etc. were used as plugging materials. With the standardized plugging procedures and regulations set by the API, cement and mud became the most widely used plugging materials [8]. After the discovery of oil in 1859, several thousands of wells were drilled and left unplugged until the oil and gas divisions for each state were set up [4, 19-20]. As of April 2022, there are 123, 318 documented orphaned oil and gas wells (a sub-category of unplugged abandoned oil and gas wells) in the US that represent ˜3% of the abandoned wells. This count does not take into account the undocumented orphaned wells or potential orphaned wells based on experts' opinions [10]. Cahill and Samano [22] assessed the long-term integrity of onshore decommissioned oil and gas wells in the UK and differentiated them into groups based on their potential of integrity failure. There are several reasons for the improper plugging of wells which could be divided into two broad categories, regulations, and operations. The regulations regarding plug and abandonment of oil and gas wells vary from country to country as well as the year when these regulations were implemented [23]. The operational difficulties include the effects of mud-spacer-cement interactions and the reduction in the effective length of cement plugs due to mud contamination [6-9, 24-25]. The way to mitigate improperly plugged wells is to re-enter the wells and re-plug them using appropriate sealant systems which is a very costly operation depending upon the number of wells to be re-plugged [2627]. If a large number of wells needs to be re-plugged then the operator has another option of geosteering the CO₂plume using active reservoir management techniques to avoid some of the risky wells within the predicted AoR [28-31]. Thus, the density of improperly plugged and abandoned wells within the CCS sites is one of the components that will decide the success of the project.

The cement used to plug these abandoned wells was not CO₂-resistant cement. Much of the research in the previous two decades focuses on the interactions of supercritical CO₂, brine, and oil well cement. The reaction of supercritical CO₂with cement is referred to as the carbonation rate of cement. It is critical to know this rate, as it can be extrapolated to determine how many years the cement can resist the leakage of CO₂, provided the experimental studies are carried out under field conditions [32-37]. Two studies in particular DePaolo and Cole [38] and Teodoriu and Bello [39] have reviewed the experimental work performed by several research groups and summarized their findings related to interactions of supercritical CO₂, brine, and oil well cement. The length of cement coverage across the casings was the main concern of the operators, but several other factors showing the integrity of legacy wells were also highlighted in the survey conducted by Iyer et al. [10-11]. It is therefore critical to evaluate if the well barriers reported in the well documents can resist the attacks of CO₂throughout the lifecycle of the CCS projects or whether the well barriers need to be repaired for wells within the AoR of the CCS projects.

The US Environmental Protection Agency (US EPA) regulates the UIC Class VI wells program in all US states except for three states with primacy, namely Wyoming, North Dakota, and Louisiana. The operators need to have a permit for drilling Class VI wells to store CO₂underground permanently. Two important components of the Class VI permits are corrective action plans and monitoring plans. The operator needs to identify all wells penetrating the confining zones within the AoR and perform corrective actions on the improperly plugged wells or wells that will leak CO₂during the lifecycle of the CCS project [12, 40-41]. AoR refers to the area endangered by CO₂injection activities. The tabulation component of the permit is detailed information of all the borings within the AoR whereas the map component is geospatial mapping of these artificial penetrations with respect to Class VI injection wells, faults, surface bodies of water, springs, mines, quarries, water wells, territory boundaries, roads, etc. To develop the map component, the first step is to build the database of all the information mentioned in the Law 40 Code of Federal Regulation (CFR) § 146.82. The AoR can be calculated using different methodologies mentioned in the literature [42-44]. Once the AoR is calculated, information on all the wells within the AoR penetrating the confining zones can be requested from the respective state geological surveys. The information reported to the states varies based on the regulations of the state as well as the year in which the information was reported. Furthermore, the database can be in digital format or hand-written reports that need to be compiled. Digitization of the handwritten reports is the most critical task. The accuracy of the information extracted from the reports needs to be verified as this is critical information and affects the risk assessment if the extracted information is incorrect.

NORSOK standard D-010 defines well integrity as the application of three different solutions technical, operational, and organizational to prevent the uncontrolled release of fluids to the surface throughout the Lifecycle of the well [45-46]. Considering the lifecycle of a CCS project, the question of whether the oil & gas wells within the AoR will maintain integrity is complicated to answer. These wells within the AoR can be more than one hundred years old. The data reported to the state agencies vary depending on the age of the wells and the regulatory requirements during the completion of the wells. The current technology and regulations related to CO₂leakage through existing wellbores are summarized in: Ide et al. [47], and Syed and Cutler [48].

Qualitative as well as quantitative risk assessment methods of legacy well evaluation are documented in the literature. Qualitative risk evaluations do not determine a numerical score on the likelihood or severity of a certain risk or scenario, but rather they highlight potential dangers and solutions to lower risk. Qualitative risk analysis draws on knowledge gained through experience and expertise to offer a knowledgeable assessment of which risk factors pose the most danger to a project while taking into account compliance with HSE criteria [18], [3] (tabulation of risk assessment tools). When important information is missing or inconsistent, qualitative risk assessment is preferred over quantitative risk assessment methods. Several risk assessment methodologies using data from regional well integrity testing programs have been reported in the literature. These studies have analyzed the occurrence of annular well leakage as indicated by Sustained Casing Pressure (SCP) or Casing-vent Flow (CVF) [49-57]. Lackey et al. [54] searched for 33 US states and found the SCP reports in only three states. Other studies include using cement bond logs (CBL) or good-quality cement coverage in the annulus as an indicator of well integrity [58-61]. CO₂leakage modeling studies through the legacy wellbores can also be found in the literature [62-64]. Buxton et al. [65] have developed a methodology to prioritize the site selection for CO₂storage based on the well integrity of the legacy wells. Some of these studies do not consider the plugged and abandoned wells, but instead focus mainly on the wells currently producing, or recently drilled [52-54, 57, 66]. As discussed earlier, the wells drilled and/or plugged before the API established standardized plugging procedures in 1952 are the riskiest wells with the least documentation for most of them. These wells do not have the SCP reports, CBL data, cementing, and/or casing details. Therefore, there was a need to develop a methodology to assess the integrity of legacy wells without SCP or CBL reports and also focus on all types of legacy wells (including orphaned wells, abandoned wells, active oil and gas wells, stratigraphic wells, disposal wells, etc.).

CO₂storage project locations are densely populated with wells. Identifying the risky wellbores/wells penetrating the geologic seals and predicting their current as well as future well integrity is the most challenging task when limited data is available. The density of these wells within the AoR dictates the corrective actions to be taken for the project to progress. Considering the long-term stewardship, safeguarding the integrity of these risky wells, which require immediate attention, is critical for the success of the CCS projects.

Accordingly, there is a need for a system and method for categorizing and assessing wells within a geologic storage reservoir.

SUMMARY OF THE INVENTION

In one embodiment, the qualitative risk assessment methodology described herein focuses on categorizing the wells within the Area of Review (AoR) based on their status, proximity to the proposed Class VI injection well, existing well barriers reported to the state/government agencies, and penetration into geologic seals, storage reservoir. In another embodiment, the qualitative risk assessment methodology described herein focuses only on the legacy wells within the AoR and needs only well construction details, which are reported to state agencies for all the wells. In another embodiment, the different types of well within the AoR are identified or categorized based on their well construction, penetrations, protections, and accessibility levels. In another embodiment, a risk matrix is used to identify the risky wells within the AoR based only on the well reports submitted to the state agencies. In another embodiment, a standardized qualitative risk assessment technique can be applied to identify the risky wells within the AoR. In another embodiment, the wells which need immediate remedial actions for the success of the CCS projects are identified and/or prioritized.

In another embodiment in accordance with the present disclosure, a method for categorizing and assessing wells within a geologic storage reservoir includes providing a database, a memory and one or more processors communicably coupled to the database and the memory, and one or more wells. A geologic seal penetration data, a geologic storage reservoir penetration data, an underground source of drinking water protection data, a geologic seal protection data and a geologic storage reservoir protection data for the one or more wells are retrieved by the one or more processors from the database. The one or more wells are categorized by the one or more processors as a well type based on the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data and the geologic storage reservoir protection data. A status of the one or more wells is obtained by the one or more processors from the database. An action priority of the one or more wells is assessed by the one or more processors based on the well type and the status. The action priority of the one or more wells is provided by the one or more processors to one or more devices communicably coupled to the one or more processors.

In one aspect, the method further comprises physically implementing a corrective action on at least one of the one or more wells based on the action priority. In another aspect, the corrective action comprises relocating of an injection well, or re-entering the at least one of the one or more wells and setting one or more cement plugs/barriers, etc. In another aspect, the method further comprises obtaining by the one or more processors, a sensor data from one or more sensors located near, at or within the one or more wells, and wherein assessing by the one or more processors, the action priority of the one or more wells is further based on the sensor data. In another aspect, the method further comprises installing the one or more sensors located near, at or within the one or more wells. In another aspect, the method further comprises determining by the one or more processors, a location and size of a CO₂plume within the geologic storage reservoir at one or more time periods, and wherein assessing by the one or more processors, the action priority of the one or more wells is further based on the CO₂plume at the one or more time periods. In another aspect, the method further comprises mapping the geographic storage reservoir, the one or more wells and the CO₂plume at the one or more time periods. In another aspect, the method further comprises injecting CO₂into the geologic storage reservoir to store the CO₂in the geologic storage reservoir or enhance oil recovery within the geologic storage reservoir. In another aspect, the method further comprises determining by the one or more processors, if any information for the one or more wells is missing in the database. In another aspect, the method further comprises: obtaining by the one or more processors, any of the information for the one or more wells that is missing in the database and is electronically accessible by the one or more processors from one or more sources; and storing by the one or more processors, the obtained information in the database. In another aspect, the method further comprises providing by the one or more processors, a report identifying the information for the one or more wells that is missing in the database.

In another aspect, categorizing by the one or more processors, the one or more wells as the well type comprises: categorizing by the one or more processors, the one or more wells as a first well type whenever the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells; categorizing by the one or more processors, the one or more wells as a second well type whenever the one or more wells: (1) penetrate a geologic seal as indicated by the geologic seal penetration data, (2) penetrate a geologic storage reservoir as indicated by the geologic storage reservoir data, (3) an underground source of drinking water is not protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is not protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; categorizing by the one or more processors, the one or more wells as a third well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is not protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; categorizing by the one or more processors, the one or more wells as a fourth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; categorizing by the one or more processors, the one or more wells as a fifth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is not protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is not protected as indicated by the geologic seal protection data; categorizing by the one or more processors, the one or more wells as a sixth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is not protected as indicated by the geologic seal protection data; categorizing by the one or more processors, the one or more wells as a seventh well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is protected as indicated by the geologic storage reservoir protection data; categorizing by the one or more processors, the one or more wells as an eighth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is protected as indicated by the geologic seal protection data; and categorizing by the one or more processors, the one or more wells as a ninth well type whenever the one or more wells: (1) do not penetrate the geologic seal as indicated by the geologic seal penetration data, and (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data.

In another aspect, the status of the one or more wells comprises: a first status whenever the one or more wells are dry and abandoned; a second status whenever the one or more wells are plugged and abandoned; a third status whenever the one or more wells are a water injection well or a gas injection well; a fourth status whenever the one or more wells are a production well; and a fifth status whenever the one or more wells are an observation well. In another aspect, the action priority of the one or more wells comprises one of a high priority, a medium priority, a low priority or a least priority.

assessing by the one or more processors, the action priority of the one or more wells as a low priority whenever: (1)(a) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is penetrated, (iii) the underground source of drinking water is protected, (iv) the geologic seal is protected, and (v) the geologic storage reservoir is protected, or (b) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is protected, and (2) the status is: (a) dry and abandoned, or (b) plugged and abandoned; and assessing by the one or more processors, the action priority of the one or more wells as a least priority whenever: (A)(1)(a) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is penetrated, (iii) the underground source of drinking water is protected, (iv) the geologic seal is protected, and (v) the geologic storage reservoir is protected, or (b) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is protected, and (2) the status is: (a) a water injection well, (b) a gas injection well, or (c) a production well, or (B) the well type indicates that (i) the geologic seal is not penetrated, and (ii) the geologic storage reservoir is not penetrated, or (C) the status is the observation well.

In another aspect, the method further comprises: obtaining by the one or more processors, a construction data for the one or more wells from the database; and generating by the one or more processors, a schematic for the one or more wells based on the construction data, the well type and the status. In another aspect, the method further comprises identifying by the one or more processors, one or more potential leakage pathways based on the schematic. In another aspect, the method further comprises: selecting one or more of the action priorities for the one or more wells; and generating by the one or more processors, a geospatial map of the one or more wells having the selected one or more action priorities. In another aspect, the method further comprises: selecting an AoR containing the one or more wells; and prioritizing by the one or more processors, the one or more wells in the AoR by one or more of the action priorities. In another aspect, the method further comprises providing by the one or more processors, a qualitative risk assessment of the one or more wells based on one or more of the action priorities. In another aspect, the method further comprises storing by the one or more processors, the action priority of the one or more wells to the database.

In another embodiment in accordance with the present disclosure, a computerized method for categorizing and assessing wells within a geologic storage reservoir includes providing a database, a memory and one or more processors communicably coupled to the database and the memory, and selecting one or more wells are selected. A geologic seal penetration data, a geologic storage reservoir penetration data, an underground source of drinking water protection data, a geologic seal protection data and a geologic storage reservoir protection data for the one or more wells are retrieved by the one or more processors from the database. The one or more wells are categorized as a well type by the following: (A) categorizing by the one or more processors, the one or more wells as a first well type whenever the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells; (B) categorizing by the one or more processors, the one or more wells as a second well type whenever the one or more wells: (1) penetrate a geologic seal as indicated by the geologic seal penetration data, (2) penetrate a geologic storage reservoir as indicated by the geologic storage reservoir data, (3) an underground source of drinking water is not protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is not protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; (C) categorizing by the one or more processors, the one or more wells as a third well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is not protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; (D) categorizing by the one or more processors, the one or more wells as a fourth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; (E) categorizing by the one or more processors, the one or more wells as a fifth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is not protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is not protected as indicated by the geologic seal protection data; (F) categorizing by the one or more processors, the one or more wells as a sixth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is not protected as indicated by the geologic seal protection data; (G) categorizing by the one or more processors, the one or more wells as a seventh well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is protected as indicated by the geologic storage reservoir protection data; (H) categorizing by the one or more processors, the one or more wells as an eighth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is protected as indicated by the geologic seal protection data; and (I) categorizing by the one or more processors, the one or more wells as a ninth well type whenever the one or more wells: (1) do not penetrate the geologic seal as indicated by the geologic seal penetration data, and (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data. A status of the one or more wells is obtained by the one or more processors from the database. The status of the one or more wells comprises: a first status whenever the one or more wells are dry and abandoned, a second status whenever the one or more wells are plugged and abandoned, a third status whenever the one or more wells are a water injection well or a gas injection well, a fourth status whenever the one or more wells are a production well; and a fifth status whenever the one or more wells are an observation well. The one or more wells are assessed as an action priority by the following: (A) assessing by the one or more processors, an action priority of the one or more wells as a high priority whenever: (1) the well type comprises the first well type, the second well type, the third well type, the fourth well type, the fifth well type or the sixth well type, and (2) the status comprises the first status or the second status; (B) assessing by the one or more processors, the action priority of the one or more wells as a medium priority whenever: (1) the well type comprises the first well type, the second well type, the third well type, the fourth well type, the fifth well type or the sixth well type, and (2) the status comprises the third status or the fourth status; (C) assessing by the one or more processors, the action priority of the one or more wells as a low priority whenever: (1) the well type comprises the seventh well type or the eighth well type, and (2) the status comprises the first status or the second status; and (D) assessing by the one or more processors, the action priority of the one or more wells as a least priority whenever: (A)(1) the well type comprises the seventh well type or the eighth well type, and (2) the status comprises the third status or the fourth status, or (B) the well type comprises the ninth well type, or (C) the status comprises the fifth status. The action priority of the one or more wells is provided by the one or more processors to one or more devices communicably coupled to the one or more processors.

In various aspects, the other aspects described in reference to the first computerized method (paragraphs [0017]-[0021]) are also applicable to the computerized method described in paragraph [0022].

In another embodiment of the present disclosure, a system for categorizing and assessing wells within a geologic storage reservoir includes an input/output interface, a memory, a display communicably coupled to the input/output interface, and one or more processors communicably coupled to the input/output interface and the memory. The following computerized process is performed: (1) one or more wells are selected, (2) a geologic seal penetration data, a geologic storage reservoir penetration data, an underground source of drinking water protection data, a geologic seal protection data and a geologic storage reservoir protection data for the one or more wells are retrieved by the one or more processors from the database, (3) the one or more wells are categorized by the one or more processors as a well type based on the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data and the geologic storage reservoir protection data, (4) a status of the one or more wells is obtained by the one or more processors from the database, (5) an action priority of the one or more wells is assessed by the one or more processors based on the well type and the status, and (6) the action priority of the one or more wells is provided by the one or more processors to one or more devices communicably coupled to the one or more processors.

In one aspect, a corrective action is physically implemented on at least one of the one or more wells based on the action priority. In another aspect, the corrective action comprises relocating of an injection well, or re-entering the at least one of the one or more wells and setting one or more cement plugs/barriers, etc. In another aspect, the one or more processors obtain a sensor data from one or more sensors located near, at or within the one or more wells, and the one or more processors further assess the action priority of the one or more wells based on the sensor data. In another aspect, one or more sensors are installed near, at or within the one or more wells. In another aspect, the one or more processors determine a location and size of a CO₂plume within the geologic storage reservoir at one or more time periods, and the one or more processors further assess the action priority of the one or more wells based on the CO₂plume at the one or more time periods. In another aspect, the one or more processors generate a map of the geographic storage reservoir, the one or more wells and the CO₂plume at the one or more time periods. In another aspect, CO₂is injected into the geologic storage reservoir to store the CO₂in the geologic storage reservoir or enhance oil recovery within the geologic storage reservoir. In another aspect, the one or more processors determine if any information for the one or more wells is missing in the database. In another aspect, the one or more processors obtain any of the information for the one or more wells that is missing in the database and is electronically accessible by the one or more processors from one or more sources, and the obtained information in the database. In another aspect, the one or more processors provide a report identifying the information for the one or more wells that is missing in the database.

In another aspect, the one or more processors categorize the one or more wells as the well type by: categorizing by the one or more processors, the one or more wells as a first well type whenever the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells; categorizing by the one or more processors, the one or more wells as a second well type whenever the one or more wells: (1) penetrate a geologic seal as indicated by the geologic seal penetration data, (2) penetrate a geologic storage reservoir as indicated by the geologic storage reservoir data, (3) an underground source of drinking water is not protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is not protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; categorizing by the one or more processors, the one or more wells as a third well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is not protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; categorizing by the one or more processors, the one or more wells as a fourth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data; categorizing by the one or more processors, the one or more wells as a fifth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is not protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is not protected as indicated by the geologic seal protection data; categorizing by the one or more processors, the one or more wells as a sixth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is not protected as indicated by the geologic seal protection data; categorizing by the one or more processors, the one or more wells as a seventh well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is protected as indicated by the geologic storage reservoir protection data; categorizing by the one or more processors, the one or more wells as an eighth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is protected as indicated by the geologic seal protection data; and categorizing by the one or more processors, the one or more wells as a ninth well type whenever the one or more wells: (1) do not penetrate the geologic seal as indicated by the geologic seal penetration data, and (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data.

In another aspect, the one or more processors assess the action priority of the one or more wells by: assessing by the one or more processors, the action priority of the one or more wells as a high priority whenever: (1)(a) the well type indicates that the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells, or (b) the well type indicates that (i) a geologic seal is penetrated, (ii) a geologic storage reservoir is penetrated, (iii) an underground source of drinking water is not protected, (iv) the geologic seal is not protected, and (v) the geologic storage reservoir is not protected, or (c) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (ii) the underground source of drinking water is protected, and (iv) the geologic seal is not protected, or (d) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is not protected, and (iv) the geologic seal is not protected, and (2) the status is: (a) dry and abandoned, or (b) plugged and abandoned; assessing by the one or more processors, the action priority of the one or more wells as a medium priority whenever: (1)(a) the well type indicates that the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells, or (b) the well type indicates that (i) a geologic seal is penetrated, (ii) a geologic storage reservoir is penetrated, (iii) an underground source of drinking water is not protected, (iv) the geologic seal is not protected, and (v) the geologic storage reservoir is not protected, or (c) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is not protected, or (d) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is not protected, and (iv) the geologic seal is not protected, and (2) the status is: (a) a water injection well, (b) a gas injection well, or (c) a production well; assessing by the one or more processors, the action priority of the one or more wells as a low priority whenever: (1)(a) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is penetrated, (iii) the underground source of drinking water is protected, (iv) the geologic seal is protected, and (v) the geologic storage reservoir is protected, or (b) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is protected, and (2) the status is: (a) dry and abandoned, or (b) plugged and abandoned; and assessing by the one or more processors, the action priority of the one or more wells as a least priority whenever: (A)(1)(a) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is penetrated, (iii) the underground source of drinking water is protected, (iv) the geologic seal is protected, and (v) the geologic storage reservoir is protected, or (b) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is protected, and (2) the status is: (a) a water injection well, (b) a gas injection well, or (c) a production well, or (B) the well type indicates that (i) the geologic seal is not penetrated, and (ii) the geologic storage reservoir is not penetrated, or (C) the status is the observation well.

In another aspect, the one or more processors obtain a construction data for the one or more wells from the database, and generate a schematic for the one or more wells based on the construction data, the well type and the status. In another aspect, the one or more processors identify one or more potential leakage pathways based on the schematic. In another aspect, one or more of the action priorities are selected for the one or more wells, and the one or more processors generate a geospatial map of the one or more wells having the selected one or more action priorities. In another aspect, an AoR of review containing the one or more wells is selected, and by the one or more processors prioritize the one or more wells in the AoR by one or more of the action priorities. In another aspect, the one or more processors provide a quantitative risk assessment of the one or more wells based on one or more of the action priorities. In another aspect, the one or more processors store the action priority of the one or more wells to the database.

Note that the invention is not limited to the embodiments described herein, instead it has the applicability beyond the embodiments described herein. The brief and detailed descriptions of this disclosure are given in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

FIG. 1 depicts a table illustrating the types of wells within an Area of Review (AoR) in accordance with one embodiment of the present disclosure;

FIG. 2A depicts schematics illustrating the types of wells within an AoR in accordance with one embodiment of the present disclosure (reprinted with permission from Elsevier);

FIG. 2B shows the distinct types of improperly plugged wells that could be present within an AoR and the possible crossflow paths in accordance with one embodiment of the present disclosure (reprinted with permission from Elsevier);

FIG. 3 depicts schematics illustrating the types of accessibility levels of wells within an AoR in accordance with one embodiment of the present disclosure;

FIG. 4 depicts a risk matrix of wells within an AoR in accordance with one embodiment of the present disclosure;

FIG. 5 depicts a flow chart of a method for categorizing and assessing wells in accordance with one embodiment of the present disclosure;

FIG. 6 depicts a flow chart of a method for categorizing and assessing wells in accordance with another embodiment of the present disclosure;

FIGS. 7A-7D depicts a flow chart of a method for categorizing and assessing wells in accordance with another embodiment of the present disclosure;

FIG. 8 is a block diagram of system for categorizing and assessing wells in accordance with one embodiment of the present disclosure;

FIG. 9A is a map of the first case study location;

FIG. 9B is a stratigraphy of the first case study site;

FIG. 10 is a map showing all the wells that were included in the Petra project;

FIGS. 11A-11C are charts depicting some statistics of the wells evaluated: (11A) age of wells, (11B) depth of seal, and (11C) surface casing depth;

FIGS. 12A-12D are charts depicting some statistics of the wells evaluated: (12A) intermediate casing 1 depths, (12B) cemented intermediate casing 1 lengths, (12C) production casing depths, and (12D) cemented production casing lengths;

FIG. 13 depicts a risk matrix of legacy wells within fifteen mile radius of the OEE site in accordance with one embodiment of the present disclosure;

FIG. 14 is a map of the wells evaluated within a fifteen mile radius of the OEE site;

FIG. 15 is a site formation code summary for the second case study of Lively Grove 1;

FIG. 16 depicts the structural elevation of primary confining seal in the Maquoketa formation;

FIG. 17 depicts the structural elevation of the storage complex at St. Peter Formation;

FIGS. 18A-18B are charts depicting: (18A) the age of wells, and (18B) the availability of well logs;

FIGS. 19A-19B depict hole section depths of: (19A) the surface casings, and (19B) the production casings;

FIGS. 20A-20C depict the length of individual plugs in the P&A reports with: (20A) one plug, (20B) two plugs, and (20C) three plugs;

FIG. 21 depicts a risk matrix of the wells within the LG 1 site assessment in accordance with one embodiment of the present disclosure;

FIG. 22 depicts a risk assessment map of all wells within the AoR in accordance with one embodiment of the present disclosure;

FIG. 23 depicts a qualitative risk assessment of 94 wells penetrating the primary confining seal within the AoR in accordance with one embodiment of the present disclosure;

FIG. 24 depicts a map of the Maquoketa Isopach along with wells of concern (partially penetrating Maquoketa) in accordance with one embodiment of the present disclosure; and

FIG. 25 depicts a hypothetical phased corrective action plan mapping in accordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not limit the invention, except as outlined in the claims.

Various methods are described below to provide an example of each claimed embodiment. They do not limit any claimed embodiment. Any claimed embodiment may cover methods that are different from those described above and below. The drawings and descriptions are for illustrative, rather than restrictive, purposes.

Carbon Capture & Storage (CCS) has gained a lot of importance in the last two decades due to the successful implementation of the technique in pilot projects across the globe. It is one of the most promising techniques developed to address the climate change issue. In simple terms, CCS refers to capturing the anthropogenic CO₂at the source followed by injecting and permanently storing it safely in the subsurface. The success of the CCS projects therefore heavily relies on how efficiently the confining zones (containment seals) prevent migration of the CO₂to the surface and/or to the underground sources of drinking water (USDW) through leakage pathways. CCS projects involve drilling of Underground Injection Control (UIC) Class VI wells. Identifying the risky wellbores/wells penetrating the containment seals and predicting their current as well as future well integrity is the most challenging task when limited data is available.

The six key components of the Class VI permit application include—general administrative project and contact information, site characterization, map, tabulations, project plans and provision for fiscal responsibility. Detailed information on the Legacy wells/wellbores penetrating the confining zones is needed to develop the map and tabulations components of the Class VI permits. Various processes which can be used to develop the dataset necessary for preparing the map and tabulation components of the Class VI permit application will be described herein. The step-by-step procedure from pulling up the relevant information from the state geological website to preliminary risk assessment of the legacy wells/wellbores is discussed.

For example, a dataset of the legacy wells penetrating the confining zones in the Illinois basin was developed using the process flowchart from the publicly available data on the Illinois State Geological Survey (ISGS) website. This dataset acts as an input for the quantitative risk assessment of the legacy wells/wellbores and for identifying the potential leakage pathways. A risk matrix is proposed for risk assessment of legacy wells/wellbores based on well integrity risk, proximity risk, and well accessibility risk. A preliminary risk analysis of the legacy wells/wellbores was carried out based on the dataset developed. This qualitative risk assessment of the legacy wells/wellbores highlights the necessary corrective actions to be taken to prevent leakage of CO₂through the potential leakage pathways.

Sustained Casing Pressure (SCP) and Cement Bond Logs (CBL) are excellent indicators of the well integrity of the legacy wells/wellbores. The qualitative risk assessment methodology described herein can be applied to wells that do not have the SCP data, the cement bond logs, also for the legacy wells/wellbores with the least documentation.

Various embodiments of the present disclosure improve the technology in the field of installing, operating, modifying, and monitoring Carbon Capture Utilization & Storage (CCUS) and CCS projects. The qualitative risk assessment methodology can be integrated into the monitoring and sensor systems of the wells and storage reservoir within the AoR.

In one embodiment, the qualitative risk assessment methodology described herein focuses on categorizing the wells within the AoR based on their status, proximity to the proposed Class VI injection well, existing well barriers reported to the state/government agencies, and penetration into geologic seals, storage reservoir. In another embodiment, the qualitative risk assessment methodology described herein focuses only on the legacy wells within the AoR and needs only well construction details, which are reported to state agencies for all the wells. In another embodiment, the different types of well within the AoR are identified or categorized based on their well construction, penetrations, protections, and accessibility levels. In another embodiment, a risk matrix is used to identify the risky wells within the AoR based only on the well reports submitted to the state agencies. In another embodiment, a standardized qualitative risk assessment technique can be applied to identify the risky wells within the AoR. In another embodiment, the wells which need immediate remedial actions for the success of the CCS projects are identified and/or prioritized.

The following terms are defined below, but are not restricted only to these definitions.

Area of Review (AoR): The region around an injection well, which may be endangered by the injection activity. This endangerment could come from either the increased pressure in the storage reservoir, or the presence of CO₂.

Confining Zone: One or more geologic barriers, typically low-permeability rock units that overlie or enclose a storage reservoir and are capable of preventing upward and/or lateral migration of CO₂or brine out of the reservoir. A confining zone may contain multiple geologic seals.

Geologic Seal: A low-permeability sedimentary or structural unit, such as shale or a sealing fault, which provides a physical barrier to upward or lateral migration of CO₂or brine out of the reservoir.

Injection Interval: The perforated interval, within an injection zone, through which CO₂injectate is pumped into the storage reservoir.

Injection Zone: Specific sedimentary layers, within a storage reservoir, that are targeted for current or future CO₂injection.

Storage Complex: A geologic entity that is physically suitable for long-term storage of CO₂. It consists of: (1) one or more storage reservoirs, with permeability and porosity that allow injection and storage of CO₂; and (2) one or more low-permeability seals, which enclose the reservoir(s) and serve as barriers to migration of CO₂out of the reservoir units.

Storage Formation: An established, named geologic formation that contains known or potential CO₂storage reservoirs.

Storage Reservoir: Layers of porous and permeable rock, within a geologic formation, which are confined by impermeable rock, characterized by a single pressure system, and suitable for long-term storage of CO₂.

Supercritical CO₂: CO₂that is at or above its critical temperature and pressure, or 31.1° C. and 7.39 MPa. In this state it has densities approaching liquid but viscosity approaching gas. This is a very efficient state for transportation and storage.

Wellbores: Boreholes which do not have any cemented casings.

Wells: Boreholes which have cemented casings in place.

As used herein, the term “well” may include wells, wellbores or both wells and wellbores as defined above.

The types of wells within an AoR will now be described in reference to FIGS. 1 and 2. Note that other classifications can be used and implemented using various embodiments of the present disclosure. The confinement by the geologic seals needs to be proved during the phase 1 and 2 studies of the CCS project before submitting the Class VI permit application. Complete documentation of all the wells within the AoR along with the map of these wells need to be submitted with the permit application. All the wells within the AoR must maintain well integrity throughout the lifecycle of the CCS Projects. Thus, wells that need corrective action must be identified and repaired. There is no standardized procedure to categorize the wells within the AoR and identify the wells which need immediate attention. This section describes the distinct types of wells based only on their well construction details reported to state agencies, which helps identify the wells which need immediate attention.

The wells within the AoR can be categorized based on the following two criteria:

Penetrations—whether they are penetrating the confining zone and storage complex, just the confining zone, or neither.

Protections—whether the underground source of drinking waters (USDWs) are protected or not. If the primary geologic seal and storage reservoir is penetrated, then whether they are protected or not. Protection refers to the presence of proven barriers to prevent the leakage of CO₂to USDWs or in the worst case to the surface. The primary barriers are casings, cement sheath, and cement plugs.

There has been substantial research done on interactions of cement with supercritical CO₂[33-34, 36, 39] 61, 67-68. Cary [69] summarizes the interaction of CO₂with well construction materials-cement, steel, and brine. The rate of carbonation of several types of cement can be found in the literature [23]. US EPA [40] provides the guidance for materials compatible with supercritical CO₂. The mud contamination of oil well cement proved to be the cause of cement failure jobs while setting plugs in open holes as well as caused other well integrity issues [9, 70-71]. It caused numerous plugging attempts due to incompetent kick-off plug [8]. Arbad and Teodoriu [6] reviewed the cement integrity issues arising due to the mud contamination and also developed correlations to predict the strength of mud contaminated cements [72-73]. The comparison of the well barriers reported in the historical records of abandoned wells along with the literature cited above will provide the necessary assurance of the well barriers to prevent any CO₂leakage. This knowledge must be used when determining the protections of the containment seals, storage reservoir, and USDWs by the well barriers.

It would be fair to assume that wells not penetrating the confining zone should be eliminated from the preliminary evaluation or looked at in detail later [12]. Prioritize the wells penetrating the confining zones and predict the integrity of these wells. The methodology described herein helps in categorizing the wells and identifying the wells, which need immediate attention. The wells within the AoR can be categorized into nine groups 200 based on their penetrations and protections (FIG. 2A, which is not drawn to scale). As the well type number increases the priority for remedial action decreases i.e., it is more favorable to have type 9 wells than to have type 1 or 2. In other words, the corrective actions must be performed first on type 1wells then type 2, and so on. The description of the nine types of wells is as follows:

Type 1 Wells—This category includes the wells which have no documentation available. These are the wells which are mostly drilled before the establishment of the state oil and gas division. The state has little to no records for these wells, and they only know about the wells being drilled. As shown in FIG. 1, documents are not available (orange), and the USDWs, the primary geologic seals and storage reservoirs are uncertain (yellow). Once more information is available on these wells, they can move to other categories based on the penetrations and protections. The schematics for type 1 wells cannot be drawn as the well construction details are not available (FIG. 2A). The undocumented orphaned wells are type 1 wells, and the documented orphaned wells may fall in any of the nine well types based on their penetrations and protections.

Type 2 Wells—This category includes the wells having open holes 202 that are penetrating both the primary geologic seal 204 and the storage reservoir 206. The open holes 202 can also penetrate production formations 208. As shown in FIG. 1, documents are available (green), and the USDWs 210, the primary geologic seals 204 and the storage reservoirs 206 are penetrating and not protected (light gray). The cement 212, casing 214 and cement plug(s) 216 are above the USDAs 210.

Type 3 Wells—This category includes the wells having open holes 202 that are penetrating both the primary geologic seal 204 and the storage reservoir 206. The open holes 202 can also penetrate production formations 208. As shown in FIG. 1, documents are available (green), the USDWs 210 are penetrating and protected (dark gray), and the primary geologic seal 204 and the storage reservoirs 206 are penetrating and not protected (light gray). The cement 212, casing 214 and cement plug(s) 216 extend through and are below the USDAs 210.

Type 4 Wells—This category includes the wells having open holes 202 that are penetrating both the primary geologic seal 204 and the storage reservoir 206. The open holes 202 can also penetrate production formations 208. As shown in FIG. 1, documents are available (green), the USDWs 210 and primary geologic seal 204 are penetrating and protected (dark gray), and the storage reservoirs 206 are penetrating and not protected (light gray). The cement 212, casing 214 and cement plug(s) 216 extend through and are below the USDAs 210. In addition, cement plug(s) 216 protect the primary geologic seal 204 and any production formations 208 above the primary geologic seals 204.

Type 5 Wells—This category includes the wells having open holes 202 that are penetrating only the primary geologic seal 204. The open holes 202 can also penetrate production formations 208. As shown in FIG. 1, documents are available (green), the USDWs 210 and primary geologic seal 204 are penetrating and not protected (light gray), and the storage reservoirs 206 are not penetrating (light blue). The cement 212, casing 214 and cement plug(s) 216 are above the USDAs 210.

Type 6 Wells—This category includes the wells having open holes 202 that are penetrating only the primary geologic seal 204. As shown in FIG. 1, documents are available (green), the USDWs 210 are penetrating and protected (dark gray), the primary geologic seal 204 are penetrating and not protected (light gray), and the storage reservoirs 206 are not penetrating (light blue). The cement 212, casing 214 and cement plug(s) 216 extend through and are below the USDAs 210.

Type 7 Wells—This category includes the wells which are penetrating both the primary geologic seal 204 and the storage reservoir 206. The wells can also penetrate production formations 208. As shown in FIG. 1, documents are available (green), and the USDWs 210, primary geologic seal 204 and storage reservoirs 206 are penetrating and protected (dark gray). The cement 212, casing 214 and cement plug(s) 216 extend through and are below the USDAs 210. In addition, cement plug(s) 216 protect the primary geologic seal 204, any production formations 208 and the storage reservoirs 206.

Type 8 Wells—This category includes the wells which are penetrating only the primary geologic seal 204. The wells can also penetrate production formations 208. As shown in FIG. 1, documents are available (green), and the USDWs 210 and primary geologic seal 204 are penetrating and protected (dark gray), and the storage reservoirs 206 are not penetrating (light blue). The cement 212, casing 214 and cement plug(s) 216 extend through and are below the USDAs 210. In addition, cement plug(s) 216 protect the primary geologic seal 204 and any production formations 208.

Type 9 Wells—This category includes the wells which do not penetrate both the primary geologic seal 204 and the storage reservoir 206. The wells can also penetrate production formations 208. As shown in FIG. 1, documents are available (green), the USDWs 210 are penetrating and protected (dark gray), and the primary geologic seal 204 and storage reservoirs 206 are not penetrating (light blue). The cement 212, casing 214 and cement plug(s) 216 extend through and are below the USDAs 210. In addition, cement plug(s) 216 protect any production formations 208. It would be fair to assume that these are the least risky wells if the confining zone is not penetrated at all.

Once the wells are categorized based on the well barriers, the wells included in categories 1 to 6 need immediate remedial actions if they lie within the predicted CO₂plume radius. The priority to perform remedial actions on these wells depends on the location of these wells from the Class VI injection well as well as the accessibility to these wells. The types of wells within the AoR can be more or less than nine types listed here depending on the level of detail needed to categorize them, but they should to be arranged as described above.

The UIC Class VI injection well is also shown in FIG. 2A. The cement 212, casing 214 and tubing 218 extend through the USDAs 210, production formations 208, primary geologic seal 204 and storage reservoirs 206. A packer 220 seals the tubing 218 and casing 214. The perforations 222 allow the CO₂to be injected into the storage reservoirs 206.

The types of the different accessibility levels to these wells, which will also decide the approximate cost required for corrective actions, will now be described in reference to FIG. 3. The accessibility to wells within the AoR depends on the status of these wells. The status of the wells can be Dry & Abandoned, Plugged & Abandoned, Water or Gas Injection Wells, Oil or Gas Producer Wells, and Observation wells. The key differences between these accessibility levels are described below:

Dry & Abandoned (DA) Wells: These are accessibility level 1 wells that were drilled to tap the oil and gas resources but unfortunately, they did not find oil and gas and/or were not economical enough to produce. Hence, these wells were declared as DA. From a well construction perspective, these wells only have the surface casing cemented to the surface and the plugs are shallow in depth at the bottom of the surface casing and a few meters below the depth of the surface casing shoe (depending upon the regulatory requirements at the time of plugging). The surface plug requirements across the globe are summarized in Van Der Kuip et al. [23]. The top of the surface casing is also cut a few feet below the ground level, and it is filled with land. Some states have markers to identify the dry and abandoned wells, but it will be difficult to locate the wells in states which do not have markers. Further, if these wells are within the AoR and penetrating the storage reservoir and/or confining zone, they need immediate attention as they need to be re-entered and plugged. This will be a more expensive operation as they need to be located first, re-entered, and then plugged. Stratigraphic test wells should be included in this category if they only have surface casings and cement plugs.

Plugged & Abandoned (PA) Wells: These are accessibility level 2 wells that were producing oil and gas reserves and later they were plugged as it was not economical to produce from them. The important distinction between DA and PA wells from the well construction point of view is that the PA wells have a production casing cemented. In some cases, the production casing is cut above the top of cement and removed before plugging these wells. So, these wells have extra barriers as compared to the DA wells. Stratigraphic test wells should be included in this category if they have two or more casings along with cement plugs.

Water or Gas Injection (WIW or GIW) Wells: These are accessibility level 3 wells that are used for the injection of water or gas into the subsurface for EOR purposes or for storing purposes. This also includes the disposal wells (non-water or gas). They have active status and can be easily accessible.

Oil/Gas Producer (Prod.): These are accessibility level 4 wells that are active and currently producing oil and gas. They have similar accessibility like the injection wells.

Observation Wells (OBs): These are accessibility level 5 wells, also called idle wells, that are used for monitoring the pressure changes. They are present in the gas storage fields for observation purposes.

Note that the actual wells might not look exactly the way they are represented in FIGS. 2A and 2B, as the well construction practices vary but finding the answers to the questions discussed herein and categorizing them based on their geologic penetrations and protections would help compare different projects across the globe. Further, there is no information about the near wellbore stresses which makes it difficult to predict whether these DA/PA wells still have open-hole sections or whether the borehole has collapsed over the years.

The well construction differences between the different accessibility levels are shown in FIG. 3. As the accessibility number increases the gas leakage detection possibility increases. In other words, gas leakage can be easily detected in observation wells than in DA wells. The accessibility categories can be more or less than the five listed here but they should be arranged in increasing accessibility order.

Once the wells within the AoR are categorized based on their penetrations, protections, and accessibility they can be counted and tabulated in the risk matrix shown in FIG. 4. As the well type number increase, the priority for remedial action decreases, i.e., it is more favorable to have type 9 wells than to have type 1 or 2 wells. In other words, the corrective actions should be performed first on type 1 wells, then type 2 wells, and so on. Wells which need remedial actions, and their corrective action priority are listed below:

Type 1 to 6 wells with accessibility status DA or PA need immediate attention and remedial actions, which will be the highest cost (red).

Type 1 to 6 wells with accessibility status injection (WIW, GIW) and producer are medium priority wells, which will be at a medium cost (yellow).

Type 7 & 8 wells with accessibility status DA & PA are low priority wells as the geologic seals and reservoir are protected with barriers, which will be at a low cost (light green).

Type 7 & 8 wells with accessibility status injection (WIW, GIW) and producer are the least priority wells as these are active wells and have access to them, which will be a the lowest cost (dark green).

All type 9 wells are the least priority wells with the lowest cost (dark green) as they do not penetrate the confining zone and storage reservoir.

All types of observation wells are the least priority wells with the lowest cost (dark green) as any leakage through them could be easily detected and rectified.

Well Types 1 to 6 need immediate remedial actions if they lie within the predicted CO₂plume radius as there exists the possibility of CO₂cross flow amongst these wells leading to leakage of CO₂to USDWs or surface. The priority to perform remedial actions on different wells within each type depends on the location of these wells with respect to the UIC Class VI injection well as well as the accessibility to these wells. Similarly, the cost of corrective action is qualitatively determined using the accessibility level with DA and PA being highest cost and Obs being the lowest cost. Thus, the risk decreases as both the well type number increases from Type 1 to 9 and accessibility level increases from 1 to 5.

According to US EPA [12], there is a possibility of cross flow of CO₂through these improperly plugged well penetrating the confining zone. These wells within the AoR need to be repaired before the operation phase of the project. The methodology developed herein categorizes the legacy wells within the AoR based on their potential to resist the leakage of CO₂. This categorization of the legacy wells into different types based on their penetrations and protections helps identify the potential crossflow paths. FIG. 2B shows the distinct types of improperly plugged wells that could be present within the AoR, and the possible crossflow paths are shown with black arrows 250. The number and location of these wells within the AoR will dictate the corrective actions plan. The risk matrix described herein helps in prioritizing which corrective actions to take and also helps in planning phased corrective actions if there are a large number of wells to be re-plugged. The geospatial mapping of identified risky wells will help in identifying the locations for drilling groundwater monitoring wells. It is also recommended to evaluate wells outside of the AoR to compensate for the uncertainties involved in AoR prediction.

The remedial actions must be performed on all the risky wells identified by the project owner. Amongst all the risky wells, wells closer to the Class VI injection wells must be prioritized first and this can be done by geospatial mapping of the risky wells within the AoR. The type of remedial action to be performed depends on the barriers present in the well and the leakage pathways. Leakage pathways can be identified using the drawing well schematics of these wells.

Now referring to FIG. 5, a flow chart of a method 500 for categorizing and assessing wells in accordance with one embodiment of the present disclosure is shown. The method 500 includes three phases. Phase 1 is data acquisition and processing (blocks 502-506, 512 and 516-520). Phase 2 is categorization of the legacy well based on geologic penetrations, well barriers and well accessibility (blocks 508, 514, 522-552). Phase 3 is risk assessment, leakage pathways identification and geospatial mapping (blocks 554-564).

An existing database is provided in block 502. A well API number is picked in bock 504. The well is identified, classified or categorized as a type 1 well in block 510 when a well report is not available as determined in decision block 506 and information is not available on a state geological website as determined in decision block 508. If the well report is not available as determined in decision block 506 and the information is available on the state geological website as determined in decision block 508, the documents and/or information is downloaded in block 514 and the existing database is updated with all the necessary information in block 516. If the well report is available, as determined in decision block 506, well reports, logs, tickets or other well information is obtained in block 512, and the existing database is updated with all the necessary information in block 516. Missing information, if any, is estimated, if possible, in bock 518. The updated database is accessed in block 520 to determine additional well types.

The well is identified, classified or categorized as a type 2 well in block 526 when: (1) the well penetrates both a geologic seal and a geologic storage reservoir as determined in decision block 522, (2) the underground source of drinking water is not protected as determined in decision block 524, (3) the underground source of drinking water and the geologic seals are not protected in decision block 530, and (4) the underground source of drinking water, the geologic seals, and the geologic storage reservoir are not protected as determined in decision block 528.

The well is identified, classified or categorized as a type 3 well in block 532 when: (1) the well penetrates both the geologic seal and the geologic storage reservoir as determined in decision block 522, and only the underground source of drinking water is protected as determined in decision block 524.

The well is identified, classified or categorized as a type 4 well in block 534 when: (1) the well penetrates both the geologic seal and the geologic storage reservoir as determined in decision block 522, (2) the underground source of drinking water is not protected as determined in decision block 524, and (3) the underground source of drinking water and the geologic seals are protected as determined in decision block 530.

The well is identified, classified or categorized as a type 5 well in block 542 when: (1) the well does not penetrate both the geologic seal and the geologic storage reservoir as determined in decision block 522, (2) the well penetrates the primary seal but not the geologic storage reservoir as determined in decision block 538, (3) the underground source of drinking water is not protected as determined in decision block 540, and (4) the underground source of drinking water and the geologic seals are not protected as determined in decision block 544.

The well is identified, classified or categorized as a type 6 well in block 546 when: (1) the well does not penetrate both the geologic seal and the geologic storage reservoir as determined in decision block 522, (2) the well penetrates the primary seal but not the geologic storage reservoir as determined in decision block 538, and (3) only the underground source of drinking water is protected as determined in decision block 540.

The well is identified, classified or categorized as a type 7 well in block 536 when: (1) the well penetrates both the geologic seal and the geologic storage reservoir as determined in decision block 522, (2) the underground source of drinking water is not protected as determined in decision block 524, (3) the underground source of drinking water and the geologic seals are not protected in decision block 530, and (4) the underground source of drinking water, the geologic seals, and the geologic storage reservoir are protected as determined in decision block 528.

The well is identified, classified or categorized as a type 8 well in block 548 when: (1) the well does not penetrate both the geologic seal and the geologic storage reservoir as determined in decision block 522, (2) the well penetrates the primary seal but not the geologic storage reservoir as determined in decision block 538, (3) the underground source of drinking water is not protected as determined in decision block 540, and (4) both the underground source of drinking water and the geologic seals are all protected as determined in decision block 544.

The well is identified, classified or categorized as a type 9 well in block 550 when: (1) the well does not penetrate both the geologic seal and the geologic storage reservoir as determined in decision block 522, and (2) the well does not penetrate the geologic seal but does penetrate the geologic storage reservoir as determined in decision block 538.

After the well type as been determined as described above in blocks 510, 532, 534, 526, 536, 548, 542, 546 and 550, the well is identified, classified or categorized based on its status and accessibility type in block 552 using the risk matrix 554 of FIG. 4. The status or accessibility type of the well is: (1) dry and abandoned, (2) plugged and abandoned, (3) a water injection well or a gas injection well, (4) a production well, or (5) an observation well.

Thereafter, well schematics are drawn for the well penetrating the seals in block 556 (see FIGS. 2A, 2B and 3). The potential leakage pathways are identified for all wells penetrating the seal in block 558. Geospatial mapping of the risky well is performed in block 560 (see FIG. 14). The risky wells within the AoR which need remedial actions are identified and prioritized in block 562, and a qualitative risk assessment is performed in block 564.

An alternative flow chart that obtains the same results as FIG. 5 is shown and described in reference to FIG. 5 of U.S. provisional patent application No. 63/465,357 filed on May 10, 2023, which is hereby incorporated by reference in its entirety.

Now referring to FIG. 6, a flow chart of a method 600 for categorizing and assessing wells within a geologic storage reservoir in accordance with one embodiment of the present disclosure is shown. A database, a memory and one or more processors communicably coupled to the database and the memory are provided in block 602. One or more wells are selected in block 604. A geologic seal penetration data, a geologic storage reservoir penetration data, an underground source of drinking water protection data, a geologic seal protection data and a geologic storage reservoir protection data for the one or more wells are retrieving by the one or more processors from the database in block 606. The one or more wells are categorized by the one or more processors in block 608 as a well type based on the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data and the geologic storage reservoir protection data. A status of the one or more wells is obtained by the one or more processors from the database in block 610. An action priority of the one or more wells is assessed by the one or more processors in block 612 based on the well type and the status. The action priority of the one or more wells is provided by the one or more processors to one or more devices communicably coupled to the one or more processors in block 614.

In another aspect, assessing by the one or more processors, the action priority of the one or more wells comprises: assessing by the one or more processors, the action priority of the one or more wells as a high priority whenever: (1)(a) the well type indicates that the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells, or (b) the well type indicates that (i) a geologic seal is penetrated, (ii) a geologic storage reservoir is penetrated, (iii) an underground source of drinking water is not protected, (iv) the geologic seal is not protected, and (v) the geologic storage reservoir is not protected, or (c) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is not protected, or (d) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is not protected, and (iv) the geologic seal is not protected, and (2) the status is: (a) dry and abandoned, or (b) plugged and abandoned; assessing by the one or more processors, the action priority of the one or more wells as a medium priority whenever: (1)(a) the well type indicates that the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells, or (b) the well type indicates that (i) a geologic seal is penetrated, (ii) a geologic storage reservoir is penetrated, (iii) an underground source of drinking water is not protected, (iv) the geologic seal is not protected, and (v) the geologic storage reservoir is not protected, or (c) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is not protected, or (d) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is not protected, and (iv) the geologic seal is not protected, and (2) the status is: (a) a water injection well, (b) a gas injection well, or (c) a production well; assessing by the one or more processors, the action priority of the one or more wells as a low priority whenever: (1)(a) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is penetrated, (iii) the underground source of drinking water is protected, (iv) the geologic seal is protected, and (v) the geologic storage reservoir is protected, or (b) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is protected, and (2) the status is: (a) dry and abandoned, or (b) plugged and abandoned; and assessing by the one or more processors, the action priority of the one or more wells as a least priority whenever: (A)(1)(a) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is penetrated, (iii) the underground source of drinking water is protected, (iv) the geologic seal is protected, and (vv) the geologic storage reservoir is protected, or (b) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is protected, and (2) the status is: (a) a water injection well, (b) a gas injection well, or (c) a production well, or (B) the well type indicates that (i) the geologic seal is not penetrated, and (ii) the geologic storage reservoir is not penetrated, or (C) the status is the observation well.

Referring now to FIGS. 7A-7D, a flow chart of a computerized method 700 for categorizing and assessing wells within a geologic storage reservoir in accordance with one embodiment of the present disclosure is shown. A database, a memory and one or more processors communicably coupled to the database and the memory are provided in block 702. One or more wells are selected in block 704. A geologic seal penetration data, a geologic storage reservoir penetration data, an underground source of drinking water protection data, a geologic seal protection data and a geologic storage reservoir protection data for the one or more wells are retrieved by the one or more processors from the database in block 706. The one or more wells are categorized as a well type by the following:

Block 708—categorizing by the one or more processors, the one or more wells as a first well type whenever the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells;

Block 710—categorizing by the one or more processors, the one or more wells as a second well type whenever the one or more wells: (1) penetrate a geologic seal as indicated by the geologic seal penetration data, (2) penetrate a geologic storage reservoir as indicated by the geologic storage reservoir data, (3) an underground source of drinking water is not protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is not protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data;

Block 712—categorizing by the one or more processors, the one or more wells as a third well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is not protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data;

Block 714—categorizing by the one or more processors, the one or more wells as a fourth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is not protected as indicated by the geologic storage reservoir protection data;

Block 716—categorizing by the one or more processors, the one or more wells as a fifth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is not protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is not protected as indicated by the geologic seal protection data;

Block 718—categorizing by the one or more processors, the one or more wells as a sixth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is not protected as indicated by the geologic seal protection data;

Block 720—categorizing by the one or more processors, the one or more wells as a seventh well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, (4) the geologic seal is protected as indicated by the geologic seal protection data, and (5) the geologic storage reservoir is protected as indicated by the geologic storage reservoir protection data;

Block 722—categorizing by the one or more processors, the one or more wells as an eighth well type whenever the one or more wells: (1) penetrate the geologic seal as indicated by the geologic seal penetration data, (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data, (3) the underground source of drinking water is protected as indicated by the underground source of drinking water protection data, and (4) the geologic seal is protected as indicated by the geologic seal protection data; and

Block 724—categorizing by the one or more processors, the one or more wells as a ninth well type whenever the one or more wells: (1) do not penetrate the geologic seal as indicated by the geologic seal penetration data, and (2) do not penetrate the geologic storage reservoir as indicated by the geologic storage reservoir data.

A status of the one or more wells is obtained by the one or more processors from the database in block 726. The status of the one or more wells comprises: a first status whenever the one or more wells are dry and abandoned, a second status whenever the one or more wells are plugged and abandoned, a third status whenever the one or more wells are a water injection well or a gas injection well, a fourth status whenever the one or more wells are a production well; and a fifth status whenever the one or more wells are an observation well. The one or more wells are assessed as an action priority by the following:

Block 728—assessing by the one or more processors, an action priority of the one or more wells as a high priority whenever: (1) the well type comprises the first well type, the second well type, the third well type, the fourth well type, the fifth well type or the sixth well type, and (2) the status comprises the first status or the second status;

Block 730—assessing by the one or more processors, the action priority of the one or more wells as a medium priority whenever: (1) the well type comprises the first well type, the second well type, the third well type, the fourth well type, the fifth well type or the sixth well type, and (2) the status comprises the third status or the fourth status;

Block 732—assessing by the one or more processors, the action priority of the one or more wells as a low priority whenever: (1) the well type comprises the seventh well type or the eighth well type, and (2) the status comprises the first status or the second status;

Block 734—assessing by the one or more processors, the action priority of the one or more wells as a least priority whenever: (A)(1) the well type comprises the seventh well type or the eighth well type, and (2) the status comprises the third status or the fourth status, or (B) the well type comprises the ninth well type, or (C) the status comprises the fifth status.

The action priority of the one or more wells is providing by the one or more processors to one or more devices communicably coupled to the one or more processors in block 736.

The other aspects described in reference to the computerized method of FIG. 6 are also applicable to other aspects of the computerized method of FIGS. 7A-7D.

Now referring to FIG. 8, a block diagram of a system 800 for categorizing and assessing wells within a geologic storage reservoir is shown. An apparatus 802 includes an input/output interface 804, a memory 806, a display 808 communicably coupled to the input/output interface 804, and one or more processors 810 communicably coupled to the input/output interface 804 and the memory 806. Note that the apparatus 802 may include other components not specifically described herein. The memory 806 can be local, remote or distributed. Likewise, the one or more processors 810 can be local, remote or distributed. Moreover, the apparatus 802 may include database 812 or be communicably coupled to the database 812 via one or more communication links 814. As a result, the database 812 can be local, remote or distributed. The input/output interface 804 can be any mechanism for facilitating the input and/or output of information (e.g., web-based interface, touchscreen, keyboard, mouse, display, printer, etc.) Moreover, the input/output interface 804 can be a remote device communicably coupled to the one or more processors 810 via one or more communication links 814 (e.g., network(s), cable(s), wireless, satellite, etc.). The one or more communication links 814 can communicably couple the apparatus 802 to other devices 816 (e.g., databases, remote devices, controllers, sensors, etc.).

The following computerized process is performed: (1) one or more wells are selected, (2) a geologic seal penetration data, a geologic storage reservoir penetration data, an underground source of drinking water protection data, a geologic seal protection data and a geologic storage reservoir protection data for the one or more wells are retrieved by the one or more processors 810 from the database 812, (3) the one or more wells are categorized by the one or more processors 810 as a well type based on the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data and the geologic storage reservoir protection data, (4) a status of the one or more wells is obtained by the one or more processors 810 from the database 812, (5) an action priority of the one or more wells is assessed by the one or more processors 810 based on the well type and the status, and (6) the action priority of the one or more wells is provided by the one or more processors 810 to one or more devices communicably coupled to the one or more processors 810.

In another aspect, assessing by the one or more processors, the action priority of the one or more wells comprises: assessing by the one or more processors, the action priority of the one or more wells as a high priority whenever: (1)(a) the well type indicates that the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells, or (b) the well type indicates that (i) a geologic seal is penetrated, (ii) a geologic storage reservoir is penetrated, (iii) an underground source of drinking water is not protected, (iv) the geologic seal is not protected, and (v) the geologic storage reservoir is not protected, or (c) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is not protected, or (d) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is not protected, and (iv) the geologic seal is not protected, and (2) the status is: (a) dry and abandoned, or (b) plugged and abandoned; assessing by the one or more processors, the action priority of the one or more wells as a medium priority whenever: (1)(a) the well type indicates that the database does not contain the geologic seal penetration data, the geologic storage reservoir penetration data, the underground source of drinking water protection data, the geologic seal protection data or the geologic storage reservoir protection data for the one or more wells, or (b) the well type indicates that (i) a geologic seal is penetrated, (ii) a geologic storage reservoir is penetrated, (iii) an underground source of drinking water is not protected, (iv) the geologic seal is not protected, and (v) the geologic storage reservoir is not protected, or (c) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is not protected, or (d) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is not protected, and (iv the geologic seal is not protected, and (2) the status is: (a) a water injection well, (b) a gas injection well, or (c) a production well; assessing by the one or more processors, the action priority of the one or more wells as a low priority whenever: (1)(a) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is penetrated, (iii) the underground source of drinking water is protected, (iv) the geologic seal is protected, and (v) the geologic storage reservoir is protected, or (b) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is protected, and (2) the status is: (a) dry and abandoned, or (b) plugged and abandoned; and assessing by the one or more processors, the action priority of the one or more wells as a least priority whenever: (A)(1)(a) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is penetrated, (iii) the underground source of drinking water is protected, (iv) the geologic seal is protected, and (v) the geologic storage reservoir is protected, or (b) the well type indicates that (i) the geologic seal is penetrated, (ii) the geologic storage reservoir is not penetrated, (iii) the underground source of drinking water is protected, and (iv) the geologic seal is protected, and (2) the status is: (a) a water injection well, (b) a gas injection well, or (c) a production well, or (B) the well type indicates that (i) the geologic seal is not penetrated, and (ii) the geologic storage reservoir is not penetrated, or (C) the status is the observation well.

In another aspect, the the one or more processors obtain a construction data for the one or more wells from the database, and generate a schematic for the one or more wells based on the construction data, the well type and the status. In another aspect, the one or more processors identify one or more potential leakage pathways based on the schematic. In another aspect, one or more of the action priorities are selected for the one or more wells, and the one or more processors generate a geospatial map of the one or more wells having the selected one or more action priorities. In another aspect, an AoR containing the one or more wells is selected, and by the one or more processors prioritize the one or more wells in the AoR by one or more of the action priorities. In another aspect, the one or more processors provide a qualitative risk assessment of the one or more wells based on one or more of the action priorities. In another aspect, the one or more processors store the action priority of the one or more wells to the database.

In summary, this disclosure provides a user friendly and easily adaptable risk assessment methodology to assess all the wells within the AoR of CCS projects. A standardized methodology is provided to categorize, assess and identify risky wells that will need corrective actions as well as determine the success of the CCS project. The developed methodology focuses on the abandoned and orphaned wells, which pose the highest risk due to inadequate regulations and policies regarding the materials used for well construction as well as abandonment. A user friendly methodology was developed that identifies and categorizes the wells within the AoR based on their well construction, penetrations, protections and accessibility levels. A risk matrix was developed to identify the risky wells within the AoR based only on the well reports submitted to state agencies. A standardized qualitative risk assessment technique was developed that can be applied to identify the risky well within the AoR. A methodology was developed to identify and prioritize the wells that need immediate remedial actions for the success of CCS projects.

Two case studies will now be described in detail. The first case study is a qualitative risk assessment of legacy wells based on publicly available data for Class VI well permit applications. The second case study is a strategic qualitative risk assessment of thousands of legacy wells within the AoR of a potential CO₂storage site.

First Case Study Details

As a part of the Illinois Storage Corridor project, two different CO₂storage sites were investigated and one of the sites was the One Earth Energy site (OEE)—near an Ethanol Plant. The previously described risk assessment methodology was applied to evaluate the legacy wells within a fifteen-mile radius of the hypothetical injection location (latitude 40.468395, longitude—88.455484) roughly four miles cast of Gibson City, IL (FIG. 9A). The Illinois State Geological Survey (ISGS) identified the Eau Claire formation (lower portion of Knox) approximately at the depth of 1006 m (3300 ft) with a thickness of 177 m (580 ft) as the primary confining unit (seal) for the OEE site. The Knox group will act as the secondary seal and the Maquoketa shale as the tertiary seal. The CO₂storage reservoir for the OEE site is the Mt. Simon formation (Cambrian sandstone) at a depth of approximately 1219 m (4000 ft) and thickness up to 762 m (2500 ft) (FIG. 9B).

Data Collection and Quality Control

A hypothetical AoR with a fifteen-mile radius from the injection well was assumed and the information for 151 wells penetrating the primary confining unit was obtained from the ISGS. These wells were queried from the ISGS database based on their depth and the geologic formations under consideration for this study—Eau Claire and Mt. Simon formations. ISGS provided an existing database of these wells. The existing database provided by the ISGS had generic information about these wells like the location, ownership, target depth, target depth formation code, well category, and well spud/completions details (if available). Well reports and any additional information (completion report, plugging report, well logs, scout tickets, geological report, drill permits, drill time logs, etc.) about the wells were downloaded from the ISGS website. Out of the 555 documents downloaded, 179 were well reports while 376 were well log files (371 TIF files and 5 LAS files). It must be noted that the majority of the reports were hand-written and not all the wells had all the reports, as well as some of the reports submitted were incomplete or data not available with ISGS. The existing database was populated manually with all the information available in the (handwritten) well reports that include well operations history, well deviation data, casing details, cementing details, geologic penetrations, USDW details, drill stem testing details, coring details, completions details, and plugging details. The depths reported in the well reports for geologic penetration of the primary confining unit and storage reservoir were verified using the available logs—Microlog and Laterolog were available. Further, well log correlation on Petra® software was performed to estimate the formation top depths for wells with missing well logs. The structural elevation and thickness maps of the primary confining unit and storage reservoir also helped verify the formation top depths for wells with missing information.

FIG. 10 shows the map of all the wells that were included in the Petra project. Only the wells within 15-mile radius penetrating the primary confining zone (highlighted in red) and/or the storage reservoir (highlighted in yellow) were evaluated in this study (151 wells). The top of cement was estimated for most of the wells using the equation below, the cement volume (sacks) information reported in the well reports and additional information acquired from the cementing service providers for these wells like the neat Class A Portland cement with yield of 0.0334 m³/sack (1.18 ft³/sack) was used for cementing [74]. Cement excess factor was assumed to be one due to lack of information within the reports as well as the service provider. These steps complete phase one of the proposed methodology and the database was ready for risk assessment. The updated database had more information than is required in the tabulations component of the UIC Class VI permit application.

$Cement Length (m) = \frac{Number of cement sacks * Yield (\frac{m^{3}}{sack})}{(\frac{m^{3}}{m})}$

Well Record Evaluation

Currently, there are only two active Class VI wells permitted by US EPA (Archer Daniels Midland CCS1 and CCS2) and there are no legacy wells within the AoR penetrating the primary confining zones except for the characterization wells drilled by operators. SCP and CBL reports were not available for these wells. Van Der Kuip [23] extrapolated penetration depths of aqueous CO₂in cement under in-situ reservoir conditions based on the results reported in the literature. The extrapolated penetration depth after 10,000 years ranges from 0.001 m to 10 m (i.e., a maximum of 32.8 ft). Based on these findings, 12 m (40 ft) of cement plugs and 61 m (200 ft) of cement sheath in the annulus were assumed to be safe to prevent the leakage of CO₂. These conditions were consistently applied to categorize the wells into pre-defined nine categories and five accessibility levels. Well schematics are not available in the well reports for these old legacy wells. The schematics were drawn for all the wells penetrating the primary confining unit using the updated database. These wells were geospatially mapped along with their types and accessibility levels using IHS Markit's Petra® software. Overlaying the actual AoR on the map instead of the hypothetical AoR will indicate the number of wells that need corrective action.

Summary of Wells Evaluated

In this study, 151 wells were evaluated that were penetrating the primary confining unit according to the ISGS database. Out of the 151 wells evaluated, 17 wells were deviated wells and 134 were vertical wells—3 had a “J” type profile while 14 had an “S” type profile (well surveys and schematics were not available/reported to ISGS). Nine wells had two casing policy (Surface and Production casings only), 139 wells had three casing policy (surface, intermediate, and production casings), and 4 wells had four casing policy (surface, two intermediates, and production casings). Three wells have/had dry and abandoned status while their plugging reports were not available in the database. One well had plugged and abandoned status and the length of the plug is 1250 m. The statistics regarding the age of the wells, depth of the seal, and depth of surface casing are shown in FIGS. 11A-11C, respectively. The statistics of intermediate casing (1) depths, estimated length of the cemented intermediate casing (1), production casing depths, and estimated length of cemented production casing section are shown in FIGS. 12A-12D, respectively.

Qualitative Risk Assessment Summary

According to the ISGS database, 151 wells penetrated the primary confining unit (Eau Claire formation) within the fifteen-mile radius that were assessed, and the summary of the risk assessment is presented in FIG. 13. Wells were categorized into nine different types based on their seal/storage reservoir penetrations and the number of well barriers present in the well to prevent the leakage of CO₂. There were 148 type 7 wells within the fifteen-mile radius. Three wells were reported as penetrating the primary confining unit but based on our assessment they did not penetrate the confinement seal and hence were categorized as type 9 wells. It is clear from FIG. 13 that zero wells within the fifteen miles required immediate attention. The accessibility to these wells helped in identifying the time and cost needed to repair the risky wells. For example, it would be easier to repair the producer or observation well than the abandoned wells since they already have access to the well through the wellhead. The proximity of these wells to the injection location and/or the location within the AoR helped in finding which wells needed to be given high priority within each type of well. For example, if there were two type 3 wells, one with a radial distance of five miles from the injector and the other at a radial distance of 0.5 miles, then it is important to repair the one closer to the injector first. However, realistically the CO₂plume would not expand symmetrically, and mapping of risky wells with actual AoR would help in prioritizing the remedial work.

The traditional risk matrix conveys information regarding the impact and probability of occurrences whereas the risk matrix described herein (FIG. 12) conveys additional information regarding the well construction and accessibility details, geologic penetration details, as well as the corrective action priority provided the readers know the pre-defined well types. This will be useful when a lot of wells need corrective action, and the operators have to propose a phased corrective action plan for the project to move forward. The old legacy wells needed to maintain integrity throughout the lifecycle of the CCS project, considering the long-term stewardship of the CCS project. The risk matrix and generalized categorization of legacy wells based on their geologic penetrations and protections will help keep track of the risky legacy wells as some of them might not be risky at the time of permit application but could lose integrity over the years. As the project progresses, the uncertainties would decrease, and more information would be available from the monitoring data that might cause the legacy wells to move from one type to another. Furthermore, law 40 CFR 146.84 required the AoR to be re-evaluated frequently once the project was in the operational phase and the frequency to re-evaluate the AoR should not exceed 5 years. Risk assessment of legacy wells will be a continuous improvement process considering the inadequate data reported for old legacy wells completed before the establishment of regulatory agencies, and the risk matrix needed to be updated by the operator after every re-evaluation of the AoR. Also, the state regulatory agencies would be frequently updating the list of orphaned wells and there might be undocumented orphaned wells within the AoR. The proposed risk matrix considers all types of wells including orphaned wells.

The combined map of risk assessment of the wells penetrating the primary confining unit within the fifteen-mile radius of the OEE site is shown in FIG. 14. The inner circles were color-coded as per their accessibility and outer circles were color-coded as per their well type. This type of map will help easily identify the risky wells as well as propose phased corrective actions if there are a lot of wells needing remedial actions. More information like the faults, surface bodies of water, springs, mines, quarries, water wells, territory boundaries, roads, etc. can also be displayed on the maps using their shape files and Geographic Information System (GIS) software. Currently, the map component of the UIC Class VI Permit application submitted to the US EPA just conveyed the surface location of all wellbores, faults, surface bodies of water, springs, mines, quarries, water wells, territory boundaries, roads, etc. within the AoR. The proposed categorized mapping of risky legacy wells conveyed a lot more information about the geologic penetrations and protections than just the surface locations submitted to the US EPA. It also highlighted the diverse levels of risk involved within the risky wells i.e., the nine pre-defined well types.

The results presented for the OEE have only one improperly plugged well that needed corrective action, assuming a five-mile AoR radius. Upon further investigation of this risky well within the five-mile radius, it was confirmed that the well penetrated the primary confining unit but does not pass through the unit. 30+ m (100+ ft) of Eau Claire formation below the target depth (TD) of the well provided the necessary confinement and no further corrective action was necessary for this well.

If the AoR is the 15-mile radius, then three wells are properly plugged and abandoned, while 129 wells had Water or Gas Injection status, and 18 wells had observation status. The possibility of crossflow of CO₂leakage was almost negligible. National Risk Assessment Partnership Open Source Integrated Assessment Model (NRAP-Open-IAM) tools could be used to quantify the leakage of CO₂through individual wells [62,75-78]. If a more detailed well integrity analysis was required for a well, then the methodology discussed in Romdhane et al. [79] could be applied depending on the availability of data and resources. The Class VI well injection location for this site could be moved to the southwest or southeast to avoid any potentially risky wells within the AoR. Since there were zero type 1 to 6 wells within the hypothetical AoR, no immediate corrective actions were needed for the OEE site. The priority for corrective action was well-defined in the risk matrix described herein. If numerous wells needed corrective action, then the proposed map with highlighted risky legacy wells along with other site selection criteria would help in determining the relocation of UIC Class VI wells to avoid some of the risky wells falling within the AoR thereby reducing the cost of corrective action.

The database was used to draw the well schematics of these wells penetrating the primary confining unit as most of them did not have well schematics and/or proper information reported in the documents. The top of cement (TOC) for most of the casings had to be estimated as they were not reported. These schematics helped in visualizing the well construction details and defined the possible CO₂leakage pathways for individual wells. Schematics also helped in verifying the information reported by operators many years ago for each well. Also, if multiple reports were available for a well, then the possibilities of depth discrepancy were high as the depth reference varies in some of them.

Regulations

In 1859, the modern petroleum industry began with the discovery of oil in Pennsylvania. There were very few regulations in place initially and oil and gas companies were largely left to function on their own. As mentioned previously, a lot of wells were drilled and abandoned before the establishment of regulatory bodies. Further, the regulations vary with countries as well as with the advancement of technology over the years. Some of the wells might be plugged appropriately based on the regulations relevant at the time of abandonment, but when evaluating these abandoned wells based on UIC program criteria, they might be considered improperly plugged wells if there are no barriers ensuring the continuity of the primary confining unit.

Data Quality

The disclosed methodology used publicly available data for risk assessment of legacy wells in the state of Illinois. Unlike Canada or a few other US states, the operators were not mandated to measure the pressure build-up in casing annulus during the production phase commonly termed the SCP. Also, very few wells had CBL which is a great indicator of well integrity. Thus, the well integrity of these wells was predicted from the well construction data reported to the state. The data reported to the state was inconsistent and missed several important pieces of information like the casing details, cementing details, plugging details, etc. for several wells. Appropriate assumptions or estimations had to be made using the available data. For example, the top of cement was calculated for most of the wells if casing details and the number of cement sacks used were reported. The top of the formations was estimated using GIS software and correlating the offset well data for old legacy wells where electrical logs were not run. The quality control of data reported in the handwritten well reports as well as picking the accurate information from different available reports on the same well was critical for risk assessment. It would be right to say that if more data is available, detailed well integrity studies could be carried out, and wells would move from one category to another based on the well integrity evaluations.

Operational Challenges

It was assumed that the data reported regarding plug setting depths for PA or DA wells is accurate as there was no information available on the techniques used for abandoning these wells. Based on the regulations, several wells had shallow surface plugs protecting the ground-water. Further, the length of cement plugs satisfactory for preventing CO₂leakage was assumed based on the extensive literature review of CO₂-Cement-Casing-Formation interactions reported in experimental, modeling, as well as field case studies. Once the risky legacy wells are identified using the proposed methodology, they will further need corrective actions using CO₂-resistant materials. The lead time for these CO₂-resistant materials is long due to high demands. Also, finding these risky wells just based on the coordinates only if all the casings are pulled out of the hole before abandonment as well as getting the necessary permits from landowners for performing corrective actions is another challenging task.

Conclusions

The density of the risky legacy wellbores within the AoR is one of the factors influencing the success of CCS projects as it impacts the site selection and corrective actions. Qualitative risk assessment of these legacy wellbores provides important insights necessary for developing corrective action plans, monitoring plans, as well as the relocation of injection well(s) to avoid many risky wells. The disclosed methodology helps generalize the categorization of the risky legacy wellbores within the AoR. The important highlights of this study are summarized below:

- A step-by-step methodology to develop the tabulations and map component of the Class VI permit was established.
- The risk matrix developed for legacy wellbores within the AoR helps prioritize the corrective actions and prepare a phased corrective action plan if necessary.
- The results of the research showed that the categorization of the legacy wells within AoR as per the risk matrix helps in identifying the potential crossflow leakage of CO₂through improperly plugged wells.
- The disclosed methodology was applied to perform a qualitative risk assessment of legacy wellbores within a hypothetical AoR with fifteen-mile radius at the proposed OEE site.

Second Case Study Details

Southern Illinois is an area that is a historic coal mining area. The legacy of this area is that it is home to several coal-fired plants. These coal-fired plants act as point sources of CO₂. The summary of subsurface evaluations for a Southern Illinois site is presented below in Table 1 which includes the information of the reservoir targets, primary confining units (seals), USDWs, and legacy wellbore information. The reservoir quality of the St. Peter Sandstone is well known for historic potable water production across the upper Midwest and successful natural gas storage operations in Illinois. In the Illinois natural gas storage fields, the St. Peter Sandstone has excellent reservoir quality with porosity values of 5% to over 25% (average 14-16%) and permeability from 10 mD to over 1,000 mD (average 150-400 mD). Maquoketa shale acts as a primary confining seal with average porosity determined by mercury injection of 0.9% and permeabilities near 1.8×10−4 mD indicating its effectiveness as a barrier to vertical migration of fluids [80].

TABLE 1

Summary of Subsurface Evaluations -

Lively Grove #1 well (LG1) Site

Storage
Name
St. Peter Sandstone

Reservoir
Approx. Depth (ft)
3,570

Approx. Thickness (ft)
170

Primary
Name
Ordovician Maquoketa Shale

Confining Seal

Group

Approx. Top (ft)
2,790

Approx. Thickness (ft)
150

Lowermost
Formation Name
Shallow Bedrock Deposits

USDW
Approx. Top (ft)
Within 500 ft

Legacy
Well penetrating lower
300 boring records within 25

Wellbores
most storage reservoir
miles area penetrating through

Maquoketa Shale

Data Collection and Quality Control

Illinois State Geological Survey (ISGS) sent the existing database and the related well reports of legacy wells within a 15-mile radius of the LG1 well. The center of the 15-mile radius is the LG1 location i.e., one of the 10-acre spots in the following quarter: SW quarter of T5W R2W Section 15 roughly (38.353028,−89.644836) WGS84. The data package contained 6,454 documents (well files in PDF format, and logs in either LAS, TIF, or pdf format). The existing database provided information on 4,386 wellbores with a depth greater than 100 ft—well data mainly comprised latitude, longitude, proximity to proposed injection location, completion and plug dates, depths, target formations, formation tops, and other relative information. The quality and quantity of the data within the files varied greatly as the wells were drilled and reported during different years ranging from 1893 to 2018. The wellbores of interest for the qualitative risk assessment were shortlisted based on the following criteria:

Formation code filtering: All the 4,386 wellbores in the existing database well were filtered based on the formation codes i.e., the deepest formation penetrated by the well. All the formation codes for formations below the primary confining seal were selected and all the wells penetrating those formations were shortlisted for evaluation. FIG. 15 provides the list of formations that are classified as primary confining seals, formations below the primary confining seals, and the storage reservoir complex for the target site.

Depth Filtering: As the approximate top of the Maquoketa seal near the LG1 is 2790 ft and its thickness is approximately 150 ft, wells with TD greater than 2470 ft were considered for preliminary risk assessment. This eliminated thousands of wells and only 521 wells with depths greater than 2470 ft were shortlisted.

AoR Filtering: Once the AoR was predicted for a 3-year post-injection differential pressure based on a 20-year injection period by ISGS, the shape files of AoR were imported into Petra to identify the wells within the predicted AoR. Once the above-mentioned filters were applied, 94 wells that were penetrating the primary confining seal (i.e., Maquoketa formation) were evaluated using the qualitative risk assessment (QRA) methodology developed by Arbad et al., (2022a, 2022b).

Well Record Evaluation

The well reports of 521 wells were manually evaluated to extract the necessary information for QRA, such as casing details, cementing data, well depths, plugging information, etc. The log files were uploaded to IHS Markit Petra™ software for geospatial mapping, well log correlation, and for estimating formation tops for wells with missing information. The structural elevation of the Maquoketa formation, mapped with the 94 wells penetrating the primary confining seal as per the ISGS database, is shown in FIG. 16. The yellow circles represent the wells evaluated using the proposed risk assessment methodology. These wells may serve as a potential leakage pathway for CO₂if their well integrity is compromised. Similarly, FIG. 17 shows the structural elevation of the storage complex evaluated for this site, i.e. the St. Peter Sandstone. The red star on all the maps (FIGS. 16 & 17) denotes the LG1 well, and the red solid box indicates the hypothetical injection well location.

Summary of Wells Evaluated

Based on the depth and formation code filtering mentioned in the previous section, 521 wells were thoroughly evaluated, and QRA was performed. FIG. 18A. shows the age distribution of these 521 wells, while FIG. 18B shows the availability of well logs. Most of the wells are between 32 to 52 years old, with 70 wells aged between 62 to 72 years. These wells were drilled and/or plugged before standardization of plugging practices. Approximately 266 wells had electric logs available on the ISGS website, and 203 wells did not run electric logs as mentioned in their well reports. Similarly, logs of 15 wells were missing, and 37 wells did not mention anything about well logs. Out of the 521 wells, 8 wells had three-hole sections (Surface, intermediate, and production), while the rest had just two-hole sections (surface and production). The statistics regarding the depths of hole sections and the Top of Cement (TOC) are presented in FIGS. 19A-19B. Cementing details were inconsistently reported for the wells under evaluation. A cementing service provider was contacted to gain additional insights about the cement slurries like Class A Portland cement used to cement most wells (Yield—1.18 ft3/sack). If the top of cement (TOC) was not reported in the well reports, then it was estimated by multiplying the yield with the number of cement sacks and dividing the product by annular capacity.

Out of 521 wells, 327 were plugged and abandoned status or dry and abandoned status and plugging reports were available for 311 wells. Since some of the wells were plugged before the establishment of plugging standards, the number of plugs within each well varies as described in Table 2. The length of individual plugs for wells with 1, 2, and 3 plugs is depicted in FIGS. 20A-20C.

TABLE 2

Number of Plugs in Abandoned Wells

Number of Cement Plug(s)
Number of Wells

1
135

2
115

3
56

4
3

5
1

6
1

Qualitative Risk Assessment Summary

Out of 521 wells, only 94 wells within the AoR penetrated the primary confining seal, and their QRA results are presented in FIG. 21. Upon detailed investigation, 85 wells penetrated the primary confining seal, and 4 wells reached the storage reservoir. There were two type 1 wells i.e., undocumented wells, zero type 2 and type 4 wells, two type 3 wells, eight type 5 wells, and fifty-two type 6 wells. Fifty-four wells had high priority for corrective action due to lack of documentation and/or uncertainty of barriers across the primary confining seal, while ten wells had medium priority as their status is active. Twenty-nine wells had low or least priority for corrective action as they did not penetrate the primary confining seal. There was a total of 4,312 type 9 wells (not penetrating the primary confining seal) within the AoR, including the 10 listed in FIG. 21. However, the 10 listed in FIG. 21 were reported as penetrating the primary confining seal according to the ISGS database, but they were not actually penetrating the primary confining seal based an evaluation of the well logs and regional stratigraphy.

The combined map of risk assessment of all the wells within the AoR of the LG1 site is displayed in FIG. 22. The inner circles are color-coded according to their accessibility, and the outer circles are color-coded based on their well type. The hollow black circles represent shallow wells that do not penetrate the confining zones and were filtered out. FIG. 23 illustrates the risk assessment of the 94 wells that penetrated the primary confining seal according to the ISGS database. The pink polygon in FIGS. 22 and 23 represents the pressure front of the St. Peter Sandstone (storage reservoir) after 20 years of CO₂injection and a 3-year post-injection period, indicating the maximum size of the AoR. The red star denotes the LG1 well, and the red solid box indicates the hypothetical injection well location. This type of map facilitates easy identification of high-risk wells and suggests phased corrective actions if there are numerous wells requiring remedial actions. Additional information such as faults, surface bodies of water, springs, mines, quarries, water wells, territory boundaries, and roads could also be displayed on the maps using their shapefiles and Geographic Information System (GIS) software. However, this information was not shown in FIGS. 22 and 23 to avoid confusion and to highlight the identification of risky wells with respect to the hypothetical injection location. Presently, the map component of the UIC Class VI Permit application submitted to the US EPA merely conveys the surface location of all wellbores, faults, surface bodies of water, springs, mines, quarries, water wells, territory boundaries, and roads within the AoR. The proposed categorized mapping of risky legacy wells provides much more information about the geological penetrations and protections than solely the surface locations submitted to the US EPA.

Salient Features of Wells Within AoR

The well schematics of all the wells penetrating the primary confining seal were drawn, and leakage pathways were identified. The absence of plugging reports for type 5 wells suggests that had these reports been accessible, these wells could have either retained their type 5 classification or potentially transitioned to less risky categories such as Type 6 or 8, contingent upon their evaluations. Similarly, the well reports for both type 3 wells mention that they were plugged back to TD and produced from shallower depth (Devonian formation) but failed to report the plugging details. These type 3 wells could transition to the less risky category of type 7, contingent upon their evaluations.

Wells With Target Depth (TD) formation Code s 203MQKT

Table 3 lists the wells that have TD formation code as Maquoketa seal (203MQKT). An investigation was conducted to check whether these wells penetrated through the Maquoketa shale and reached the Trenton formation, or if they partially penetrated the Maquoketa seal. These wells are currently listed as penetrating through the Maquoketa seal as there was uncertainty about how much Maquoketa seal below the TD is enough for confinement. Additional caprock integrity study needs to be performed to answer this uncertainty, and it was out of scope for this study. Once an appropriate assumption is made for this, the well type of these wells changes to Type 9. FIG. 24 shows the isopach map of Maquoketa along with these wells under consideration, which helped in estimating the approximate Maquoketa thicknesses below the TD of each well as shown in Table 3.

TABLE 3

Wells with Maquoketa as TD Formation Code

Est.
Trenton
Maquoketa

Current

Maquoketa
Tops Est.
Below TD

Sr. No.
Well Type
API10P
TD (ft)
Thickness (ft)
(ft)
(ft)

1
Type 1
1216329365
2613
155
2655
42

2
Type 1
1216323789
2350
150
2435
85

3
Type 6
1216325631
2614
145
2702
88

4
Type 6
1218924586
3300
155
3327
27

5
Type 6
1218924485
3002
122
3080
78

6
Type 6
1218901772
2712
145
2780
68

7
Type 6
1218902866
3601
105
3655
54

8
Type 8
1215724984
2600
116
2716
116

Phased Corrective Action Plan

For the phased corrective action plan, it is recommended to overlay the CO₂plume for intervals of 3-4 years over the mapped risky wells. Other time periods can be used. This approach prioritizes wells based on their proximity to the expanding CO₂plume over time. The AoR overlay in FIGS. 22 and 23 spans a total of 23 years (20 years injection and 3 years post-injection), and 54 wells that have high priority for corrective action fall within the same period. By overlaying AoR for different time intervals onto the mapped risky wells, it becomes easier to identify which wells require prioritized corrective action before each period. For instance, if the combined CO₂plume and pressure front radius is projected to reach a 2.5-mile radius (red circle) after 4 years of injection as shown in FIG. 25, then wells within the red circle should be prioritized. For this example, there is one type 3 well that has producer status, two type 6 wells each with D&A and P&A status, and one type 8 well with P&A status. Thus, the priority for corrective action in this example would be as follows:

- Type 6 with D&A status: This well has just surface casings and shallow plugs as barriers but no cement plugs across the confining seals.
- Type 6 with P&A status: This well has a cast iron bridge plug set at a shallower depth within the production casing that is cut and retrieved above TOC.
- Type 3 with Producer status: As this well is accessible due to producer status, priority should be given to abandoned wells since locating them and re-entering would be challenging.

Uncertainty Reduction and Future Work

This study is purely based on publicly available data, and inconsistencies in data reporting to the state were observed due to several reasons, such as changes in regulations, advancements in technology, and poor maintenance of the data. The lease operator changed for a lot of wells over the decades, and data was lost in the transition. The uncertainty discussed in this section could be reduced by reaching out to the current operators of these identified risky wells to gain additional insights. Furthermore, National Risk Assessment Partnership-Open-Integrated Assessment Models (NRAP-Open-IAM) tools could be used to estimate the leak rates through these risky wells and reduce uncertainty [42,62,76-78]. These tools help in quantitative risk assessment. The application of active reservoir management techniques for geosteering the CO₂plume and avoiding some of the risky wells should be evaluated [31,81-82]. If there were still numerous wells that required corrective action, then the deeper secondary storage reservoir (Potosi in this case study) should have been evaluated.

Conclusions

Robust risk assessment methodologies are essential for effectively containing anthropogenic CO₂within the subsurface, particularly when dealing with legacy wells within the AoR. Due to lack of data for many old legacy wells, this study strategically categorizes 4,386 such wells within the AoR of a potential CO₂storage site. This study identifies wells posing immediate risks, guiding prioritized corrective actions, and monitoring plans.

- Utilizing publicly available data, including reports and well log submitted to state regulatory agencies, potential risky wells are identified based on criteria such as proximity to the injection well location, depth, and mechanical integrity of well barriers.
- Among the 4,386 wells assessed, 54 are identified as having high priority for corrective action, while 10 have medium priority, and the remaining are of low priority.
- Case study results from the Illinois basin demonstrate the effectiveness and applicability of this approach, showcasing its potential to enhance the safety and success of CCS projects globally.

It is understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. In embodiments of any of the compositions and methods provided herein, “comprising” may be replaced with “consisting essentially of” or “consisting of”. As used herein, the term “consisting” is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), property(ies), method/process steps or limitation(s)) only. As used herein, the phrase “consisting essentially of” requires the specified features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps as well as those that do not materially affect the basic and novel characteristic(s) and/or function of the claimed invention.

The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

As used herein, words of approximation such as, without limitation, “about”, “substantial” or “substantially” refers to a condition that when so modified is understood to not necessarily be absolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skill in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as “about” may vary from the stated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. § 112, U.S.C. § 112 paragraph (f), or equivalent, as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.

For each of the claims, each dependent claim can depend both from the independent claim and from each of the prior dependent claims for each and every claim so long as the prior claim provides a proper antecedent basis for a claim term or element.

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SYSTEM AND METHOD FOR CATEGORIZING AND ASSESSING WELLS

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Provisional Applications (1)