None.
Unconventional well fracturing impacts on adjacent wells or frac hits, also known as Frac Driven Interactions (FDI), are well-to-well communication events initiated by hydraulic fracturing of an offset well. While some wells show production uplifts after a frac hit, many wells experience production degradation or complete loss of production due to failed casing or plugged up wellbores. This negative parent-child interaction presents challenges to Unconventional Reservoir (UR) operators. As an UR matures with more infill development, the number of frac hit events is set to grow given the increased well density and large completion job sizes. UR fracture hits (FH) characterization, production impact prediction methods and mitigation techniques.
In unconventional plays the initial wells drilled and completed on a lease are referred to as “parent wells”. The parent well multistage hydraulic fracturing process creates a fracture system that can result in depletion of the reservoir proximal to the wellbore. The magnitude and extent of depletion depend on the Stimulated Reservoir Volume (SRV) initially created (Raterman, et al. 2018) and Drained Reservoir Volume (DRV) that reflect productive fracture areas, well operating strategy and well interference (Raterman, et al. 2019; Kasumov et al. 2022).
The depletion surrounding parent wells presents a challenge for operators when drilling and completing subsequent infill wells because the hydraulic fractures created by the infill wells can preferentially propagate towards the depleted rock around parents due to reduced pressure/stress. This can result in asymmetrical fracture growth and lower the effectiveness of the infill stimulation treatment (Gala et al. 2018; Manchanda et al. 2018; Zhang et al. 2020). Infill-to-parent well frac hits or fracture driven interactions occur when infill well fractures intersect with parent well depleted fractures or parent wellbores themselves. As a result, both the parent and infill well production can be negatively impacted. The impact of frac hits on parent wells can vary between plays. For instance, the Bakken and Haynesville show more positive frac hits than the Eagle Ford and Wolfcamp (Miler et al. 2016; Lindsay et al. 2018; Liu et al. 2020). Several factors and mechanisms driving frac hits, including parent-child spacing, completion design, parent well depletion, have recently been studied and presented (King et al. 2017; Guo et al. 2018; Gupta et al. 2021).
Understanding and mitigating frac hits is crucial for unconventional assets since they can impact many aspects of field development, as illustrated in
What is needed is an analysis and methodology to mitigate fracturing impacts on adjacent wells.
With over 12 years of development in the Unconvention Reservoir, we have collected a comprehensive dataset of frac hits and built an integrated database that incorporates frac hit timing, pressure responses, water/sand volume changes, short- to long-term production impacts, associated parent/child well completion and geological information. In-depth analysis has been conducted on extensive development across an UR. A new integrated workflow including empirical assessment, Multivariate Analysis (MVA) and mechanistic modeling was developed to identify key trends, study mechanisms and predict frac hit production impacts on parent wells. Various techniques have been explored and pilots tested in an effort to mitigate parent-child FH impacts.
The key frac hit impact drivers are identified as parent-child well distance and configuration, parent well depletion, completion design and geology. The models and workflows leveraged have improved the predictability of frac hit likelihood and their production impacts with mechanistic modeling providing insights to the physical process of a frac hit. Several mitigation techniques have been piloted with refracturing of the parent well, optimizing drill schedules to increase distance between infills and high-rate parents, as well as post-frac cleanouts proving effective in the study area.
The invention provides an in-depth analysis of the impact of frac hits on parent wells specifically in the Unconvention Reservoir formation. By combining frac hit data, as well as introduce a new empirical and an integrated MVA workflow provides insights into key frac hit drivers. Additionally, various mitigation techniques are provided to minimize the negative effects of frac hits on parent wells.
In one embodiment, an unconventional reservoir is developed by building a database of unconventional reservoir properties that includes well properties and fracturing impacts; empirical assessment of the well data; multivariate analysis of the fracturing impacts; predict fracturing impacts based on current fracturing properties; and mitigate fracturing impacts by adjusting well and fracturing parameters.
In another embodiment, a process for mitigating fracturing impacts by building a database of unconventional reservoir properties that includes well properties and fracturing impacts; empirical assessment of the well data; multivariate analysis of the fracturing impacts; predicting fracturing impacts based on current fracturing properties; and mitigating fracturing impacts by adjusting well and fracturing parameters.
In one embodiment, a computer processor may be configures to calculate fracturing impacts including a database of unconventional reservoir properties that includes well properties and fracturing impacts; an empirical assessment of the well data; a multivariate analysis of the fracturing impacts; configured to predict fracturing impacts based on current fracturing properties; and mitigating fracturing impacts by adjusting well and fracturing parameters.
Unconventional reservoir properties may be selected from incorporates frac hit timing, pressure responses, water/sand volume changes, short- to long-term production impacts, associated parent/child well completion and geological information.
Existing parent wells near a new completion pad may be closely monitored, and their pressure, water, or short- and long-term production impacts may be recorded. Existing parent wells may be evaluated within a distance selected from 5000, 4500, 4000, 3500, 3000, 2500, 2000, 1500, 1000, and less than 1000 feet.
Fracturing impact events may be integrated with other relevant information such as geology, completion, and well schedule.
Empirical analysis may be conducted to identify key trends and drivers of fracturing impacts.
Multivariate analysis may be used to model parameters for prediction of fracturing impacts.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. For the purpose of illustration, there is shown in the drawings certain embodiments of the disclosed subject matter. It should be understood, however, that the disclosed subject matter is not limited to the precise embodiments and features shown. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate implementations of systems, methods, and apparatuses consistent with the disclosed subject matter and, together with the description, serve to explain advantages and principles consistent with the disclosed subject matter. A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings.
Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.
Identifying and building a database with frac hit impacts for every parent well has been a significant effort with over 1700 wells drilled in the UR by ConocoPhillips. This provides an excellent foundation where changes to production rate, water cut, yield and pressures are captured. In the example provided in
Parent well surface pressure can also be important data for frac hit analysis. It provides a direct measure of the timing and magnitude of frac hits at the parent well, as shown in
An example of high-frequency pressure responses to frac hits at a parent well is shown in
Since parent well surface pressure is typically acquired as standard, it is widely available across the field and aids an in-depth analysis of pressure data and correlation to production impacts that can provide valuable insights not only to frac hits but also to completion effectiveness, fracture geometry, well interference, and their spatial variation.
Frac hits can also be detected using special hydraulic fracture diagnostic data that are not commonly collected, such as Microseismic, Distributed Acoustic Sensing (DAS), downhole pressure gauges, and tracers. An example is shown in
In addition to the data discussed above, other relevant information is also used for frac hit analysis. This includes well spatial configurations, such as distance, overlap, and landing zone; completion data, such as frac job size, zipper situation, fluid type, stage length, and cluster spacing; reservoir properties, such as initial pressure/stress, fluid property, porosity, clay content, and faults; as well as operational data like mud loss and cleanout data.
The following examples of certain embodiments of the invention are given. Each example is provided by way of explanation of the invention, one of many embodiments of the invention, and the following examples should not be read to limit, or define, the scope of the invention.
Key variables and their correlation to frac hits.
Parent-infill well distance is one of the strongest drivers of frac hits. As the distance between a parent well and an infill well decreases, the risk and severity of production loss caused by frac hits at the parent well increases. This trend is shown in
As discussed earlier, hydraulic fractures preferentially propagate towards depleted areas, which can potentially enhance asymmetric fracture growth and lead to more severe frac hits. The production rate of a parent well prior to a frac hit is used as a proxy for its depletion in this study. The production impact of a frac hit increases if a well is hit at a high rate, as shown in
Many completion design parameters, such as job size, stage length, fluid type, zipper, and sequencing, can be related to frac hits since they can influence the fracture length and complexity. Among them, job size has been found to have the biggest impact where we observe that larger job sizes typically result in higher production impacts as shown in
Several reservoir properties were incorporated into the analysis including porosity, permeability, clay content and geomechanical properties such as Young's Modulus among others. Geomechanical properties and their proxies such as clay content or porosity were the primary geological variables impacting the magnitude of a frac hit. The relationship is not highly correlative.
Within the UR formations faults can be observed, however typically within ConocoPhillips' acreage these are limited and frequently of sub-seismic resolution. To aid identification of structural discontinuities on 3D seismic, we use a fault enhanced volume (FEV) that highlights trace-by-trace discontinuities, with stronger features typically correlating with the presence of faults and/or dip changes. An evaluation was subsequently carried out to evaluate frac hit occurrence and impact relative to the presence and magnitude of these FEV features. While frac hits occur regardless of their presence, there is a subtle correlation between the magnitude of a frac hit and the strength of the seismic feature when intersected along a wellbore, with an increased median negative production impact where stronger features exist (
It had been hypothesized that refracturing parent wells would result in minimal frac hits to offset parent wells, because the pressure is likely to be dissipated into the depleted regions around refrac well(s). However, this study showed that refracturing depleted parent wells induces frac hits to nearby parent wells comparable in magnitude to new infill wells. An example is shown in
Fracture propagation within a multi-well system is dependent on completion design and reservoir properties. For the stimulation of infill wells adjacent to existing wells, the dominant drivers of fracture creation are parent well depletion and existing fracture planes. In this study, fracture propagation in a depleted reservoir has been modeled to understand the interaction of parent well depletion and a pre-existing failure plane and their impact on fracture growth at an infill well. Fracture modeling as shown in
Simulation results show the creation of asymmetric fractures with the longer wing growing into the depleted rock (
The simulation work also reveals the morphology of the fractures from infill wells interacting with existing failure planes which emulate the existing hydraulic fractures from the parent wellbore (
An effective implementation of MVA yields applicable data driven models trained on relevant data. The MVA process couples feature selection with a data driven model which allows simultaneous data and model evaluation.
In this study, tree based MVA was used to generate models that predict the implications of future frac hits by effectively ranking features related to geology, completion, well configuration and operating strategy. Specifically, two types of frac hit models were developed and used in conjunction: the likelihood model based on bootstrap forest, and the magnitude model based on boosted trees.
The likelihood model is trained to perform the classification task of predicting the occurrence of a frac hit given a set of features. To clarify, the model outputs a score between 0 and 1, which is used as analog for the likelihood of a frac hit occurring. The response variable is composed of 1's for detected fracs hit and 0's for no frac hits. A simple rounding function converts the model response (0 to 1) into classification (0 or 1). The model performance can be evaluated using the test data and model classification response: the model has a true positive rate (correct detection of a frac hit) of 87% and a true negative rate (correct detection of no frac hit) of 86%. The model is highly sensitive to key variables such as parent to infill overlap and distance.
The magnitude model is trained as a regression model which estimates the production volume impact of frac hits. The model learns from the magnitude of past recorded frac hits and lists the key factors. The volume impacts from frac hit are highly dependent on geological parameters such as Poisson ratio and clay content, parent well cumulative volume produced, and infill completion design (
The MVA model is continuously updated and fine-tuned to improve predictability as new data and understanding become available. This enables the team to quantitatively assess the risk of frac hits and influence project development and field optimization.
Developed a platform for frac hit database update, data integration, empirical and multivariate analysis & prediction to improve FH assessment efficiency and consistency. Various mitigation techniques were tested in the field to minimize production loss impacts caused by frac hits. However, some of these techniques were found to be ineffective. For example:
Pumping water into the parent (PIP) well for re-pressurization. This technique can lead to production degradation of parent wells due to elevated water cuts coupled with the impact of frac hits.
Using far field diverting agents in the infill well fracture treatments. This technique showed mixed results.
On the other hand, there are several proven effective frac hit mitigation techniques, which include:
Refracturing parent wells: Refracturing can dramatically increase the pressure of parent wells and prevent them from experiencing frac hits. Additionally, it can tap into undrained resources and create significant production uplift. However, not all parent wells can be refractured due to economic or well integrity reasons, and refracturing can cause frac hits to offset parents resulting in loss of production that should be accounted for during candidate selection.
Optimize drilling schedules: schedules can be optimized to avoid fracturing too close to high-rate parent wells. This strategy reduces the risk of losing production, however, it can lead to deferral of high-value projects, and is challenging to implement as well density increases.
Post frac hit cleanout: when a frac hit is sustained at the parent well the majority of the lost base production can be restored after removing the solids/obstruction. However, the cost of cleanout can be expensive and depending on the remaining resources, may be uneconomic.
Shutting in parent wells to build up pressure and stress: this technique can provide certain protections to parent wells; however, it results in production deferment and shut-in parents can still experience severe frac hits.
Overall, effective mitigation techniques can help us reduce the negative impacts of frac hits and optimize their production. However, careful evaluation and consideration of the pros and cons are necessary before implementing these techniques.
Frac hits are an important industry challenge that can impact unconventional asset development. The increasing trend of frac hits is expected to continue as more infill wells are drilled and completed.
A rich frac hit data set was built by collating and integrating frac hit events, production impacts, pressure, completion, geology and special frac diagnostic data.
The key drivers of frac hits were identified, including parent-infill well distance (spacing), parent well depletion, parent-infill well overlap, and completion design.
Weaker correlations between geological/geophysical properties and frac hits were observed. Further investigations are needed.
MVA and mechanistic modeling proved to be useful in understanding physics and predicting the occurrence and production impacts of frac hits.
Refracturing a parent well can protect its base production from offset frac hits, but it can also induce frac hits similar to those from the stimulation of new wells.
Refracturing, schedule optimization and post-frac hit cleanout are effective techniques to mitigate production loss. However, their pros and cons should be evaluated before implementation.
While the present disclosure has been described with reference to various implementations, it will be understood that these implementations are illustrative and that the scope of the present disclosure is not limited to them. Many variations, modifications, additions, and improvements are possible. More generally, embodiments in accordance with the present disclosure have been described in the context of particular implementations. Functionality may be separated or combined in blocks differently in various embodiments of the disclosure or described with different terminology. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow.
In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. Each of the references below is incorporated in their entirety for all purposes.
This application is a non-provisional application which claims benefit under 35 USC § 119 (e) to U.S. Provisional Application Ser. No. 63/458,619 filed Apr. 11, 2023, entitled “FRACTURE IMPACT CHARACTERIZATION,” which is incorporated herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63458619 | Apr 2023 | US |