Patent Grant
11619113
This application relates to the field of water wells and methods used to remedy problematic conditions in such wells including chemical precipitation, biological fouling, and/or scaling, which can diminish the functioning of wells and water quality. Specifically, exemplary embodiments generally relate to a system and method that provides fouling abatement for water wells, although methods have applicability to other types of wells experiencing such fouling.
Fouling of wells is a common problem in nearly all types of wells, not limited to but including residential, public, commercial, and remediation wells. Well fouling can generally be described as the precipitation or deposition of material within or immediately adjacent to a well resulting from one or a combination of physical, chemical, or biological processes. The build-up of material from this precipitation or deposition, within or around the well, may detrimentally affect the intended performance of the well. Non-limiting examples of detrimental effects include damaging of pumps, reducing the pumping capacity of an extraction well, clogging of effluent piping, and affecting the quality or appearance of water produced from a drinking water well.
Various strategies have been employed to alleviate well fouling. Methods employed include: 1) the introduction of chlorine into the well water to mitigate biological growth; 2) the introduction of an acid into the well that has the effect of keeping oxidizable minerals in their dissolved phase; and/or 3) periodic cleaning/flushing of the well, filter pack, and/or surrounding aquifer with brushes, chemicals, and/or heat to remove the build-up of fouling materials. However, these methods address only specific fouling problems and may create undesirable side effects. (1) For example, chlorine can lessen biological growth but can simultaneously enhance oxidative fouling. In addition, creation of undesirable chemical compounds such as disinfection by-products can occur during the use of chlorine in a well. Chlorine and its by-products create concerns for the surrounding environment and receptor's use. (2) Acids decrease the pH of well water and keep in solution minerals that would normally precipitate in the presence of oxygen. Acids, however, generally do not stop all fouling, can potentially damage well components, and must be continually replenished as water moves through a well. (3) Cleaning treatments and/or flushing of a well aim to remove deposited materials that are inhibiting proper function of the well, but these treatments are typically expensive, do not address the root cause of the fouling and scaling, generates waste requiring proper disposal, and requires turning off pumping wells during treatment.
These and other drawbacks exist.
An exemplary embodiment includes a system having a supply of inerting gas; a gas supply line fluidly coupled to the supply of inerting gas that is fluidly coupled to a well through an air-tight seal, the gas supply line extending through the air-tight seal and into the well and terminating at a point above a fluid level in the well, wherein the supply of inerting gas is configured to displace existing atmospheric air in an air column of the well above the liquid level in the well and thereby create an anoxic environment that inhibits biological fouling, chemical precipitation, and scaling in the well; and a regulator positioned in-line on the gas supply line and configured to supply the inerting gas on demand to the well, the regulator being further configured to maintain a pressure of the inerting gas, in the well, greater than atmospheric pressure.
Another exemplary embodiment includes a method of supplying an inerting gas, through a regulator, to an air column of a well; purging the air column, using the inerting gas, to remove existing gas in the air column; measuring an oxygen content of purged gas from the air column; lowering the oxygen content in the air column to a level that inhibits biological fouling, chemical precipitate, and scaling; and maintaining a pressure, greater than atmospheric pressure in the air column, of the inerting gas to maintain the oxygen level at a level that inhibits biological fouling, chemical precipitation, and scaling within the well.
These and other advantages will be described more fully in the following detailed description.
In order to facilitate a fuller understanding of the various embodiments, reference is made to the attached drawings. The drawings should not be construed as limiting the various embodiments but are intended only to illustrate different aspects and embodiments.
The following description is intended to convey an understanding of exemplary embodiments by providing specific embodiments and details. It is understood, however, that various embodiments are not limited to these specific embodiments and details, which are exemplary only. It is further understood that one possessing ordinary skill in the art, in light of known systems and methods, would appreciate the use of various embodiments for its intended purposes and benefits in any number of alternative embodiments, depending upon specific design and other needs.
The following descriptions provide different configurations and features according to exemplary embodiments. While certain nomenclature and types of applications/hardware are described, other names and application/hardware usage is possible, and the nomenclature provided is done so by way of non-limiting examples only. Further, while particular embodiments are described, it should be appreciated that the features and functions of each embodiment may be combined in any combination as is within the capability of one of ordinary skill in the art. The figures provide additional exemplary details regarding the various embodiments. It should also be appreciated that these exemplary embodiments are provided as non-limiting examples only.
Various exemplary methods are provided by way of example herein. These methods are exemplary as there are a variety of ways to carry out methods according to the present disclosure. The methods depicted and described can be executed or otherwise performed by one or a combination of various systems and modules. Each block shown in the methods represents one or more processes, decisions, methods or subroutines carried out in the exemplary method, and these processes, decisions, methods or subroutines are not necessarily carried out in the specific order outlined in the methods, nor is each of them required.
Exemplary embodiments provide a system and method that prevents well-fouling from the precipitation, growth, or deposition of material within or immediately adjacent to an extraction well resulting from physical, chemical, and/or biological processes. As a threshold matter, it should be noted that exemplary embodiments are not directed at the prevention of fouling from deposition of particulate material such as clay or silt. Some of the most common chemical and biological well-fouling processes require the presence of dissolved oxygen to occur. Non-limiting examples include: 1) the precipitation of iron or iron rich deposits within well-water resulting from the conversion of dissolved ferrous iron, Fe2+, to ferric iron, Fe3+, 2) the precipitation of dissolved manganese and manganese compounds, such as MnHCO3+, to a precipitate, such as MnCO3, and 3) the accumulation of organic material such as biologically created structures, growth, and biological detritus. Thus, exemplary embodiments address and solve the deficiencies of existing methods and systems in preventing fouling (such as by physical, chemical, and/or biological processes) in extraction wells for ground water as described in the background section above.
Exemplary embodiments differ from existing gas blanketing systems in application, purpose, and chemical process by which they mitigate fouling of extraction wells. For example, gas blanketing systems may be used to reduce corrosion in hydrocarbon storage tanks or as a safety measure to reduce the risk of explosions in storage tanks containing combustible materials. These systems are not used with ground water as in exemplary embodiments. Further, these systems are not used to mitigate or prevent fouling of pumps and equipment through creation and maintenance of atmospheric conditions that prevent chemical deposition of oxidated materials and the growth of bacteria. Creating a non-explosive or inflammable atmosphere within the extraction well is not a goal of exemplary embodiments. Exemplary embodiments do not rely upon the addition of any additives, such as, but not limited to, Volatile Corrosion Inhibitors (VCIs), with the inerting gas. Finally, while exemplary embodiments are directed to ground water extraction wells, other embodiments may have application in other types of wells where fouling, as described herein, is prevalent and causes an impact to well function.
Two common sources of dissolved oxygen in a well are ground water (any water present in the subsurface) and the atmospheric air. Of the two sources, the atmospheric air is typically the primary source of dissolved oxygen because much groundwater is anoxic due to the activity of subsurface biological and chemical reactions that consume available oxygen. Anoxic water does not contain sufficient levels of oxygen to allow most biological fouling. Anoxic ground water also limits or stops chemical oxidation processes that require oxygen within ground water. Through the construction and use of a well, the introduction of atmospheric oxygen may raise dissolved oxygen concentrations in well water high enough for physical and chemical changes and biological fouling to occur from the interaction of the atmospheric oxygen and the well water.
Exemplary embodiments seek to eliminate or reduce fouling enabled by atmospheric oxygen (i.e., O2) entering the airspace of the well column. A well airspace inerting gas, in the sense that it does not contain significant O2 and will slow or stop problematic conditions in the well environment caused or contributed to by oxygen, is used to flush atmospheric oxygen out of the well airspace. Non-limiting examples of such well airspace inerting gases are carbon dioxide (CO2) and nitrogen (N2). Other gas, or mixtures thereof may be used. Once low oxygen conditions in the wellhead airspace have been achieved, the well is sealed and pressurized with the inerting gas. The introduction of atmospheric oxygen back into the system through leaks is overcome by keeping a small, positive pressure-differential between the well column and the atmosphere. A pilot study, as described below, demonstrated the removal of O2 from the system and the replacement with an inerting gas can greatly reduce or eliminate both chemical and biological fouling as well as reduce or eliminate the need for well cleaning treatments. The end-result is improved well performance and decreased long-term maintenance costs associated with biological fouling, and chemical precipitation, and/or scaling.
In the oxic zone 212, oxygen from the airspace moves into the water column as dissolved oxygen, the levels of dissolved oxygen in the system are the highest in this region. Near the bottom of the oxic zone 212, oxygen moves into the water at the air-water boundary. The mixing zone-oxic zone boundary begins where water is no longer in direct connection with air. In the mixing zone, the dissolved oxygen levels in the water are sufficient to allow biological growth to occur and chemical precipitate and scaling to occur. The oxic zone-mixing zone boundary is likely to occur just below the air/water interface.
In the mixing zone 210, biological growth occurs, and dissolved oxygen reacts with and oxidizes dissolved Fe2+ to create insoluble Fe3+ minerals. The anoxic zone begins where oxygen levels are low enough that chemical oxidation reactions and biological growth is limited or cannot occur. The anoxic boundary limiting oxidation reactions may not occur at the same depth as the cessation of biological fouling. The minimum oxygen content that creates anoxic conditions is different depending on water conditions; however, the US Geological Survey defines anoxic ground water as ground water with no dissolved oxygen or with dissolved oxygen concentrations of less than 0.5 milligrams per liter (see USGS Circular 1292, Volatile Organic Compounds in the Nation's Ground Water and Drinking-Water Supply Wells, Glossary, April 2006, available at pubs.usgs.gov).
It should be appreciated that other components are not depicted, such as conveyance piping, tubing fittings, additional regulators, manifolds, pressure gauges, pressure-relief valves, shut-off valves, and other equipment to control gas delivery. The components used in exemplary embodiments may include: 40 cubic foot (cf) to 300 cf compressed inerting-gas cylinder(s), a dual-stage regulator with a maximum inlet pressure of 3000 pounds per square inch gauge (psig) that supplies inerting gas in the 0 to 2 (psig) range at 0.5 or greater gallons of gas per minute, 4 cylinder manifold with individual tank shutoff valves, compressed cylinder mounting bracket(s), brass or stainless steel needle valves, brass or stainless steel ball valves, brass or stainless steel compression fittings, brass or stainless steel barb fittings, brass or stainless steel check valve, brass or stainless steel bulkhead NPT to compression fittings, brass or stainless steel “T” compression fittings, rubber or silicon washers, in-line moisture filter with automatic release valve, brass or stainless steel adjustable 0.5 to 5 psig pressure relief valve, 0 to 3 psig pressure gauge, ¼ inch through ½ inch braided poly ethylene tubing, 1-inch MDPE yellow gas piping, 1 to 3 cubic foot reinforced inflatable bag or bladder, an inerting-gas generator such as N2 gas that generates gas at the rate required to replace gas lost through leaks or pressure releases. It should be appreciated that this listing of components is exemplary and non-limiting. As appreciated by one of ordinary skill in the art, other similar components may be used.
The distribution system for the inerting gas (such as that depicted in
Gas may flow from the cylinder into the well through the regulator 306 and the gas supply line 312. The regulator 306 may control the flowrate and pressure. The gas may fluidly move into the well casing through an air-tight seal at connection 314. The gas supply line 312 may be extended down into the well (316) but remain above the top of the fluid level 318.
According to exemplary embodiments, the regulator provides a method to maintain positive air pressure inside the well. The regulator may supply inerting gas only when a minimum positive pressure is reached. For example, if water levels inside the well drop, causing the gas in the well to expand, air pressures can drop to vacuum pressure. With the regulator set to supply gas when minimum positive pressure is reached, gas can be injected into the well as water levels drop to maintain positive gas pressure, stopping the intake of atmospheric oxygen. Conversely, water levels may rise in the well, causing the gas in the well to compress and air pressures to rise. If pressures inside the well are equal to or greater than the supply pressure of the regulator, gas flow into the well from the regulator stops. If pressures in the well are greater than the relief setting of the pressure relief valve, gas from inside the well will be released through the pressure relief valve.
In some embodiments, a baffle or similar expandable compartment may be attached to the system. The additional compartment will expand and fill with gas from the well air-column when a critical airspace pressure is reached within the well. The expansion of the compartment reduces the gas pressure buildup inside the well. When gas air-space pressures drops below the minimum pressure required to keep the expandable compartment open, gas will flow from the compartment back into the well air-column. The use of the expandable compartment may be used in an embodiment that maintains a closed system when a gas release system may not be appropriate.
Shut-off valve 408 may be a ball, needle, gate, globe, or other valve type. The valve may be used to isolate the gas supply from the well. This may allow for the gas supply to be swapped out or changed without losing gas in the well (i.e., pressure may be maintained) or introducing atmospheric gas (i.e., containing oxygen) into the well through the system. In-line pressure gauge 410 may be used to measure in-well pressure for monitoring of pressure variation.
Connection through well-casing 412 may be a fitting that creates a gas-tight seal to allow the supply gas to pass into the well through the well casing. In-well gas supply line 414 may be an extension of the supply line 404 inside the well that delivers the supply gas into the well casing. In exemplary embodiments, the in-well gas supply line 414 may extend to and terminate above the maximum liquid level in the well. This may allow for proper flushing of atmospheric gas (i.e., O2) from the well. According to exemplary embodiments, the supply line should not extend into the liquid, as that may increase the pressure required to inject gas into the well.
Pressure relief valve 416 may allow for relief of excess pressures above the relief valve set-point. In exemplary embodiments, relief pressures may be set at 5 psig or less. In exemplary embodiments, the relief valve should have a manual release to allow for expulsion of gas during purging of the well during introduction of the inerting gas. An oxygen sensor may be attached to a fitting connected to the pressure relief valve to allow for monitoring of the oxygen level of expelled gas, particularly during the initial purging of the well. Additional piping or tubing may be used to direct purged air volume away from workers or the work area. The pressure relief valve may be located external to the well (see, e.g.,
Air-tight well head seal 418 is a seal that may allow for discharge piping, electrical, and pressure relief valve to pass through the well head and maintain a gas tight seal. According to exemplary embodiments, the seal may be a commercially available well head seal with a rubber gasket between two plates. The two plates may compress the gasket, which may then expand to seal the casing and penetrating components. It should be appreciated that this ordering and interaction of components is exemplary and non-limiting.
It should be appreciated that the sequence of components of
First, at step 502, a system, such as, but not limited to, that depicted in
Next, at step 504, the assembled system may be leak tested and sealed where required. The well may be turned off (if it is currently in operation). The well-head fittings, as well as other supply components, may be tightened and sealed. Gas, such as, but not limited to, the inerting supply gas, may then be injected into the well such that in-well pressure reaches at least a maximum pressure expected during operation. A common method for leak testing involves pressurizing the system and applying soapy water on all connections. Bubbles may form at locations where gas is escaping; these locations should be sealed, or resealed, as appropriate. A leak check is important because stopping or minimizing leaks can help to minimize the usage rate of the inerting gas.
Next, at step 506, once the system has been constructed and leak tested, the well is flushed with inerting gas. The inerting gas may be injected into the well at a small positive pressure (such as 1 psig) through the supply line(s). The gas may enter the well column near the top of or near the surface of the maximum liquid (e.g., water) level. As the inerting gas enters the bottom of the airspace above the fluid level, gas may be manually released from the pressure relief valve. The oxygen level (O2) of the expelled gas may be monitored. An oxygen sensor may be used to monitor the oxygen level. For example, the oxygen content of expelled air can be measured as a percentage of background atmospheric content (i.e., where a 100% reading equals 20.5% atmospheric oxygen content). The flushing of the air column with inerting gas may continue until the oxygen level has at least dropped to a level low enough to inhibit the growth of most aerobic biologic growth in the well water. Removal of atmospheric oxygen from the well column airspace may reduce or stop the mixing of oxygen into the well water column and reduce the overall concentrations of dissolved oxygen in the well water. According to exemplary embodiments, the level of oxygen to inhibit this biological growth, as well as inhibit chemical reactions, may be approximately 5% of dissolved oxygen content (or less) in water (specifically, 5.41% or less). However, it should be appreciated that the exact level of oxygen, or other growth/reaction limiting element, may be site- and nuisance-dependent. Thus, for example, other embodiments may require a different level of oxygen content to achieve the desired results.
At step 508, the well is pressurized with inert gas. The gas supply regulator may be set to the desired pressure (e.g., between 0.1 and 1 psig). The head space is allowed to pressurize until the regulator outlet pressure equals the air-column pressure.
Next, at step 510, well operations may be commenced and pressures can be monitored. The extraction well may be placed back in operation. The pressures in the well column may be monitored by observing the in-line pressure gauge. The regulator outlet pressure may be adjusted if a higher or lower pressure is desired or required. For example, fluid level changes in the well (e.g., the water level rising or falling) may cause the pressure to increase (if the fluid level rises) or decrease (if the fluid level falls). The regulator can allow for appropriate gas flow to compensate for this pressure change. Gas can be manually released from the well through the pressure relief valve. The oxygen level of gas released from the well may be monitored to ensure anoxic conditions are maintained. Periodic sampling of the well atmosphere may be conducted.
At step 512, the inerting gas supply can be replaced. If the supply tank (or equipment) run out of gas, it can be replaced or the cylinder(s) refilled. If the inerting gas is not readily supplied to the well, fluctuating water levels, temperatures, and other factors can create vacuum (less than atmospheric) pressures inside the well. Vacuum pressure can pull in atmospheric oxygen through small leaks in the system and allow fouling to occur. The regulator used to maintain the necessary gas pressure may be as described above with respect to
Pre-treatment conditions of the pumps and piping are shown in
The configuration depicted in
It should be appreciated that the aforementioned embodiments are not limited to wells are constructed with water discharge piping passing through an air-tight well head seal. Similar designs may be implemented for wells that discharge through pit-less adapters or other, and will be apparent to those familiar with the art.
Results from the pilot study to determine the efficacy of exemplary embodiments will now be described.
Testing the efficacy of inerting gas blanketing as an anti-fouling method in water wells was performed at an environmental remediation site where the extraction wells had a history of severe chemical precipitate and biological fouling. Heat and chemical well-cleaning treatments as well as chlorine tablets were historically used to address the fouling in these wells. The well-cleaning treatments were effective at cleaning out fouling debris, but biologic growth could be observed in the wells only weeks after treatment in some wells. Chlorine was effective at reducing or eliminating biofouling; however, the scaling and precipitation continued and was likely enhanced by the oxidative potential of chlorine. The fouling continued in chlorine treated wells, where it clogged piping, inhibited proper well-functioning, and did not eliminate the need for more costly acid-cleaning treatments. Two of the extraction wells, TEW-09 and TEW-10, were chosen to test the inerting gas anti-fouling system as described herein.
The initial test was conceived to determine the feasibility and utility of maintaining an anoxic in-well environment, thus reducing the possibility for non-biological as well as biological fouling. Two additional nearby extraction wells, KC99-235 and KC99-236 were chosen as controls and treated with chlorine over the pilot study period.
Prior to the implementation of the pilot study, wells TEW-09, TEW-10, KC99-235, and KC99-236 were rehabilitated. The rehabilitation included manual cleaning of pump and motors, air lifting of sediments, and acid treatment of the wells and extraction well parts.
Inerting gas delivery systems, specifically those shown in
To begin the study, wells TEW-09 and TEW-10 were flushed with inerting gas, sealed, and pressurized. During this testing period, gas pressure, pumping rates, and D.O. levels were measured; results are summarized in
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The pilot-testing period lasted for longer than 14 months. This time period, of at least 14 months, was chosen as the timeframe to conduct the experiment as this was historically a typical length of time an extraction well could operate before requiring rehabilitation. The effectiveness of the anti-fouling measures over this period was based on the visual buildup of fouling in the well, long-term well performance, and the needs for well rehabilitation.
To evaluate the buildup of fouling in the well, pre-inerting-gas implementation conditions were compared to pilot-study conditions. Pumps from extraction wells TEW-09 and TEW-10 were both pulled at the end of the pilot testing period and visually inspected (
In addition, strainers, flow meters, and other valves that have historically shown evidence of fouling were checked periodically over the testing period.
Long-term reductions in well performance due to fouling were evaluated. No fouling or reduction in pump performance was observed over the pilot period. Because little to no fouling occurred, additional chemical, physical, and/or heat treatments of the wells was not required.
Effectiveness in Creating Anoxic Environments
On week 3, well surface water conditions reached anoxic conditions (<0.5 mg/L, 5.41% D.O. water) in both wells TEW-09 and TEW-10 (
D.O. measurements in chlorine control wells KC99-235 and KC99-236 indicated no significant change during the same 4-week time period.
In TEW-09, a baseline percent D.O. air of 83% (where 100% equals 20.5% total oxygen content of air) was measured in the air column 15 feet below the top of casing. The D.O. air fell to 42.2% during week two and to 31% during week 3 after gas implementation. In TEW-10, a baseline percent D.O. air of 91.5% was measured in the air column 15 feet below the top of casing. The D.O. air fell to 51.4% during week two and 27.0% during week three after gas implementation. Note that during D.O. measurements, the inerting gas supply was turned off and the airtight seal was broken, likely allowing exchange and mixing of oxygen rich atmospheric air with well column airspace. The % D.O. air prior to breaking the seal was believed to be lower than the measured and reported value.
In summary, by three weeks, TEW-09 and TEW-10 had reached anoxic conditions and continued to maintain anoxic conditions within the full water column during the dissolved oxygen measurement period. Wells KC99-235 and KC99-236 did not have fully anoxic water conditions in the full water column during the dissolved oxygen measurement period.
Effectiveness of Nitrogen Versus Carbon Dioxide
N2 was used in well TEW-09, and CO2 was used in well TEW-10. The N2 well achieved a lower dissolved oxygen content and achieved this level sooner than CO2 during the testing period. Approximately 3 weeks into testing, both wells had become anoxic, and both had eliminated new fouling by the end of the pilot test. Since both gases were effective against biological fouling and chemical precipitate and scaling, and the physical and chemical conditions in each well are different, no conclusion could be definitively drawn if one gas was superior in performance.
The pilot-testing period demonstrated that replacing atmospheric air with inerting gas in the air column reduces dissolved oxygen in the water column, thus inhibiting extraction well biological fouling and chemical precipitate and scaling, which benefits long term well performance, maintenance, and rehabilitation costs. Inspections of pump intake motor assemblages and vault peripheral parts indicated little to no new biological fouling or chemical precipitate or scaling during implementation, and the system required very little maintenance. The majority of inerting gas used by the system was during replacement of atmospheric air with inerting gas in the well column air-space, and aforementioned replacement was only required when the well seal was broken during measurements and inspection. Very little inerting gas was used in the daily operation of the wells.
The foregoing examples show the various embodiments in exemplary configurations; however, it should be appreciated that the various components may be configured in a variety of ways. As will be appreciated by those skilled in the art, the components of the various embodiments may be arranged at any location or locations so long as they do not affect the operation of the respective system.
It will be readily understood by those persons skilled in the art that the various embodiments are susceptible to broad utility and application. Many embodiments and adaptations other than those herein described, as well as many variations, modifications and equivalent arrangements, will be apparent from or reasonably suggested by the various embodiments and foregoing description thereof, without departing from the substance or scope of the various embodiments. For example, although the embodiments have been described herein in the context of a particular implementation in a particular environment for a particular purpose, those skilled in the art will recognize that its usefulness is not limited thereto and that the embodiments can be beneficially implemented in other related environments for similar purposes.
Accordingly, while the various embodiments have been described here in detail in relation to its exemplary embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the various embodiments and is made to provide an enabling disclosure of the various embodiments. Accordingly, the foregoing disclosure is not intended to be construed or to limit the various embodiments or otherwise to exclude any other such embodiments, adaptations, variations, modifications, or equivalent arrangements.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5190108 | Mansuy | Mar 1993 | A |
| 7546901 | Hall et al. | Jun 2009 | B1 |
| 10036509 | Markham et al. | Jul 2018 | B2 |
| 10829298 | Young et al. | Nov 2020 | B2 |
| 20090020286 | Johnson | Jan 2009 | A1 |
| 20140221256 | Holtsclaw | Aug 2014 | A1 |
| Entry |
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| USGS Circular 1292, “Volatile Organic Compounds in the Nation's Ground Water and Drinking-Water Supply Wells”, Glossary, Apr. 2006, pp. 1-112, available at https://pubs.usgs.gov/circ/circ1292/. |
