Method and apparatus for treating fouled wells
Disclosed herein is a method and apparatus for treating biofouled wells with azide compounds, and/or for preventing biofouling in a well. The well is contacted with an amount of an azide compound effective for treating or preventing biofouling in the well.
This application claims the benefit of U.S. Application No. 60/644,402, filed Jan. 14, 2005, which is incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION1. Field of the Invention
The disclosure provided herein is generally directed to the field of extraction and injection wells, and more particularly, to controlling fouling in wells using azide as a biocide.
2. Description of the Related Art
Wells, for example, extraction and injection wells, are susceptible to fouling. Fouling is a phenomenon in which the throughput of a well, for example, the output rate of an extraction well and/or the injection rate of an injection well, decreases over time. A type of fouling, referred to herein as “biofouling” or “bioclogging,” is believed to arise from the proliferation of microorganisms on and around well components, for example, screens, pumps, and the like, as well as in pores in the soil around the well. These microorganisms are commonly bacteria and/or fungi, which are naturally present in the subterranean environment. The microorganisms are believed to form “biofilms” and/or microcolonies in the soil. R. W. Harvey et al., Appl. Environ. Microbiol., 1984, 48(6), 1197-1202. The microorganisms are believed to reduce the permeability of the soil by at least two mechanisms. First, the microorganisms clog the pores in the soil. Second, the microorganisms produce gases, which occlude the pore necks in the soil. Reynolds et al., Soil Science, 1992, 153, 397-408. Microorganisms also produce other by-products believed to fill the pores in the soil, for example, waste products, glycocalyx, ferrous iron, and even dead microorganisms. Costerton et al., Ann. Rev. Microbiol., 1981, 35, 299-324; Motomura, Bull. Natl. Inst. Agric. Sci. Ser. B 1969, 21, 1-114. The microorganisms also form colonies and/or biofilms on the well components, for example on grates and/or screens, thereby reducing the throughput of these components, which can lead to component failure.
SUMMARY OF THE INVENTIONDisclosed herein is a method and apparatus for treating biofouled wells with azide compounds, and/or for preventing biofouling in a well. The well is contacted with an amount of an azide compound effective for treating or preventing biofouling in the well.
Some embodiments disclosed herein provide a method for treating a well comprising at least the step of contacting the well with an effective amount of azide.
Other embodiments provide a method for in situ remediation of a contaminant comprising at least the steps of injecting an electron donor into an injection well, wherein the injection well is in fluid communication with a water zone comprising a contaminant; and injecting an azide into the injection well, wherein the amount of azide is effective to prevent and/or remedy fouling in the injection well.
Other embodiments provide an apparatus for treating a well comprising a reservoir of azide and a pump fluidly connecting the reservoir and a well to be treated.
In some embodiments, the well is fouled and the amount of azide is effective for improving the hydraulic conductivity thereof. In other embodiments, the well is not fouled and the amount of azide is effective for preventing the fouling thereof. In some embodiments, the well is selected from the group consisting of an injection well, an extraction well, and a monitoring well. In some embodiments, the well is used in an in situ remediation system. In some embodiments, the in situ remediation system is used to remediate a contaminant selected from the group consisting of perchlorate, chlorate, and combinations thereof.
In some embodiments, the azide is selected from the group consisting of salts of N3− and hydrazoic acid. In some embodiments, the azide is selected from the group consisting of sodium azide, potassium azide, and ammonium azide. In some embodiments, the azide is in an aqueous solution. In some embodiments, the azide is mixed with water extracted from an extraction well located downgradient of the injection well. In some embodiments, the solution is buffered. In some embodiments, the concentration of the azide is greater than about 75 mM.
In some embodiments, a pulse of azide is injected into the well. In some embodiments, the hydraulic conductivity of the well after treatment is at least about 50% of the original hydraulic conductivity. In some embodiments, the backpressure in the well is reduced by at least about 50%.
In some embodiments, the method is under automated control.
In some embodiments, the electron donor is selected from the group consisting of citric acid and ethanol.
BRIEF DESCRIPTION OF THE DRAWINGSThe drawings provided herein are illustrative of certain embodiments only and do not limit the disclosure to the illustrated embodiments.
The term “saturated hydraulic conductivity” refers to the rate at which water percolates through saturated soil under constant pressure. See, for example, K. Seki et al., Eur. J. Soil Sci., 1998, 49, 231-36.
We have discovered a treatment of fouled wells using azide (N3−). It is believed that the azide acts as a biocide in the treatment disclosed herein. An apparatus 100 for treating a well 102 with azide, illustrated in
The azide is any azide compound that is effective in the treatment of a fouled well, for example, salts comprising azide ion (N3−) and hydrazoic acid (HN3). Examples of suitable salts include lithium azide, sodium azide, potassium azide, and ammonium azide. Also suitable are azide salts of organic ammonium cations comprising, for example, one or more groups independently selected from alkyl groups, aryl groups, aralkyl groups, and combinations thereof. Examples include alkylammonium, dialkylammonium, and benzalkylammonium cations. In some embodiments, the ammonium cation is derived from a cyclic amine, for example, piperidine, pyrrolidine, morpholine, and quinuclidine. Also suitable are azide salts of cations derived from aromatic amines, for example, pyridinium cations. Mixtures are also suitable. Without being bound by any theory, it is believed that the biocidal activity of azide arises from the binding of free iron, thereby disrupting the regulation of osmotic pressure by the microorganism.
In some embodiments, the azide is stored in the reservoir 104 as a solution. Examples of suitable solvents include water, organic solvents, ethanol, acetonitrile, N-methylpyrrolidinone, dimethylformamide, and combinations thereof. Concentrated aqueous solutions of azide salts are stable, and easily and safely storable. In some embodiments, the azide is stored in the reservoir 104 is a solid. In some embodiments, a solid azide in the reservoir 104 is dissolved prior to dispensing. In some embodiments, the azide is mixed with another biocide, for example, a tetraalkylammonium compound. In some embodiments, the azide is mixed with an electron donor and/or an electron acceptor. Electron donors and electron acceptors are discussed in greater detail below. In some embodiments, the azide is mixed with another compound, for example, a detergent, soap, or surfactant.
The pump 106 is any pump known in the art that is suitable for dispensing the azide from reservoir 104. Those skilled in the art will understand that the particular pump 106 used in an application will depend on a variety of factors, for example, whether the azide is dispensed as a solid or as a solution. Other factors affecting pump 106 selection include the properties of an azide solution, for example, reactivity, viscosity, corrosiveness, etc. For example, azides are typically not used with certain metals, including copper and brass. Another factor in selecting an appropriate pump 106 is whether the pump injects the azide directly into the well 102, or whether the pump 106 dispenses the azide into a fluid that is then injected into the well 102. Another consideration is whether metering of the azide is desired. Suitable pumps for azide solutions include peristaltic pumps, diaphragm pumps, impeller pumps, piston pumps, vane pumps, screw pumps, and the like. In some embodiments, the pump 106 is a peristaltic pump. In some embodiments, the pump 106 is a metering pump, which permits the user to control the rate at which the azide is dispensed.
In some embodiments, the pump is under automated control, for example, using a microprocessor, computer, and/or programmable logic controller. In some embodiments, the control device also collects data that initiates, terminates, and/or controls the operation of the pump 106. Examples of such data include the pressure and/or flow rate at the well 102. As is discussed in greater detail below, the apparatus illustrated in
Well fouling is often observed in in situ groundwater contamination remediation situations in which microorganism proliferation is stimulated. Remediation of groundwater contamination is broadly divided into two categories: ex situ and in situ. The ex situ method is also referred to as “pump and treat.” The contaminated groundwater is extracted, treated, then re-injected or directed elsewhere. Ex situ remediation often in requires the installation of appropriate infrastructure for decontaminating the extracted water.
The in situ or “in place” method relies on microorganisms to decontaminate the groundwater, for example, through oxidation-reduction reactions. A large number of microorganisms have been discovered in the soil that are capable of effectively rendering a variety of contaminants less harmful or harmless. These microorganisms typically occur naturally in the aquifer, although in some cases, particular microorganisms are introduced into an aquifer to treat a particular contaminant or contaminants. Unlike ex situ remediation, in situ remediation typically does not require the construction of a substantial infrastructure for decontaminating the groundwater.
In some environments, a limitation in one or more compounds in the groundwater and/or soil limits the population of microorganisms, and consequently, the decontamination rate. For example, a soil in which the contaminant is an electron acceptor, for example, perchlorate, can be deficient in electron donors. Consequently, a carbon-containing substrate (electron donor) is introduced into the aquifer to promote microorganism growth, thereby accelerating the remediation process. Conversely, injecting an electron acceptor into a soil that is deficient in electron acceptors where the contaminant is an electron donor would also accelerate the remediation.
One type of in situ remediation system uses a closed-loop recirculation system in which impacted groundwater is extracted using a down-gradient well, amended with a suitable electron donor, and recharged into the same water zone using an injection well. In some cases, one or more observation or monitoring wells are provided to monitor the remediation progress. As the system is operated, the increasing population of microorganisms in and around the injection well reduces the hydraulic conductivity, thereby increasing the backpressure in the well. Such a well is referred to herein as “biofouled.” Biofouling both reduces the rate of remediation by reducing the rate at which the electron donor/groundwater mixture is injected into the soil, as well as imposes a strain on the equipment, for example, pumps, screens, casings, valves, and the like. In some cases, the additional strain leads to equipment failure and/or reduced lifetime.
One method for restoring the hydraulic conductivity of the well is to eliminate or reduce the microorganism population in the well and the immediate vicinity of the well by injecting a biocide into the well. This process is also referred to herein as “disinfecting the well.” Typical biocides include, for example, hypochlorite (OCI−), chlorine dioxide gas (ClO2, CDG), chlorine, and/or chloramine (H2NCl) and derivatives thereof.
As a biocide, azide exhibits several advantages over other biocides used in treating biofouled wells, for example, hypochlorite (OCl−), chlorine dioxide gas (ClO2, CDG), chlorine, and/or chloramine (H2NCl) and derivatives thereof. For example, these compounds generate potentially hazardous chlorinated organic compounds through reactions with organic matter in the soil, for example, humic acids and the dead microorganisms themselves. Another drawback is that CDG is itself a hazardous gas that is typically generated on site. CDG is also incompatible with many materials, including steel and stainless steel. In contrast, azides are compatible with a wide range of materials, including steel, stainless steel, polyvinyl chloride (PVC), rubber, and glass. As is known in the art, azides are not compatible with certain materials, including copper, brass, and bronze.
CDG also generates molecular oxygen in the soil. Many of the microorganisms effective in metabolizing electron acceptor contaminants, for example, nitrate, chlorate, and/or perchlorate preferentially use molecular oxygen as the terminal electron acceptor under aerobic conditions. Consequently, the electron acceptor contaminant is metabolized by these microorganisms only under anaerobic conditions. Remediation of the electron acceptor contaminant does not proceed until the oxygen is exhausted from the soil, which slows the overall remediation process.
EXAMPLE 1
The citric acid solution was added using a pulse-addition mode with a one hour pulse of a citric acid solution injected several times weekly. The initial citric acid concentration was set at 579 mg/L based on the concentrations of oxygen, nitrate, perchlorate, and chlorate in the groundwater. The citric acid concentration was adjusted downwards during the experiment according to the demand calculated from the analysis of the water taken from the extraction well.
Over four months of operation, the pressure required to recharge the extracted groundwater increased from less than 1 psig (6.89 kPa) at 10 gal/min (37.9 L/min) to 65 psig (448.2 kPa) at 4 gal/min (15.1 L/min). The increased pressure appeared to be caused by biofouling, which reduced the permeability within the injection well and/or surrounding gravel/sand/silt pack.
An embodiment of a method 300 for in situ remediation is illustrated as a flowchart in
In step 302, an injection well 202 is provided. In some embodiments, the injection well 202 is an existing well. In other embodiments, a new injection well 202 is provided in step 302. Some embodiments comprise a plurality of injection wells 202. Some embodiments also include an optional extraction well(s) 212, and/or observation or monitoring well(s) 214. Those skilled in the art will understand that the configuration of the injection well 202, extraction well 212, and monitoring wells 214 will depend on the hydrology of the particular site, for example, the particular water-bearing zone or zones that are contaminated, the concentration of the contaminant(s), the composition of the groundwater, the flow rate of the groundwater, the pressure of the groundwater, and the like. Typically, the injection well 202 is upgradient of the extraction well 212. Monitoring wells 214 are typically disposed between the injection well 202 and the extraction well 212, and are situated to sample the plume between the two. As such, the monitoring wells 214 are not necessarily disposed on the line between the injection well 202 and the extraction well 212.
In some embodiments, the injection well 202 is an infiltration trench. Infiltration trenches are used, for example, where the soil permeability is low. In some embodiments, the length of the infiltration trench is 1000′ (300 m) or greater. The depth of the infiltration trench is suitable for treating the impacted water zone(s).
In step 304, an electron donor is injected into the soil. The electron donor is any suitable electron donor known in the art for use in in situ remediation. The choice of the electron donor depends on factors known in the art, including the characteristics of the groundwater, the contaminant to be remediated, the particular microorganism for which growth is desired, other microorganisms present in the soil and the like. In some embodiments, the contaminant to be remediated is a contaminant for which remediation is facilitated through the addition of an electron donor, for example, nitrate, nitrite, chlorate, and/or perchlorate. Suitable electron donors are known in the art and include, for example, citric acid, lactic acid, acetic acid, benzoic acid, fatty acids, edible oils, amino acids, ethanol, glucose, sugars, sugar acids, sugar alcohols, corn syrup, molasses, hydrogen, propane, and mixtures thereof. Some of these compounds are readily converted into salts, which are also suitable.
In some embodiments, in step 304, an electron acceptor is used rather than an electron donor. Those skilled in the art will understand that the in situ remediation of certain contaminants is facilitated through the addition of an electron acceptor, for example, gasoline, benzene, hydrocarbons, organic compounds, and the like. Suitable electron acceptors are known in the art, for example, dissolved oxygen.
As used herein, the term “injected” is used to mean that the electron donor and/or electron acceptor is caused to enter the desired water-containing zone, with or without the aid of pressure. In some embodiments, the electron donor and/or electron acceptor is mixed with groundwater removed from the extraction well 212, and the mixture is injected into the well 202. In some embodiments, the electron donor and/or electron acceptor is mixed with water from another source, and the mixture injected into the well 202. In some embodiments, other compounds are mixed with the electron donor and resulting mixture coinjected into the soil. Examples of such compounds include tracers; which are useful, for example, for monitoring groundwater movement; standards, which are useful, for example, for monitoring the concentration of the contaminant(s); and particular microorganisms. Some embodiments use a mixture of electron donors and electron acceptors, for example, to encourage the proliferation of particular microorganisms.
In some embodiments, the electron donor and/or electron acceptor is injected continuously. In other embodiments, the electron donor and/or electron acceptor is injected using a predetermined sequence. In other embodiments, the electron donor and/or electron acceptor is injected based on the progress of the remediation process.
In some embodiments, the injection of the electron donor and/or electron acceptor is under automated control, for example, based on data taken from samples from the monitoring wells 214 and/or the extraction well 212. In some embodiments, the data acquisition is also under automated control. Suitable controllers are known in the art.
In embodiments in which an electron donor is injected, for example, to remediate an electron acceptor in a soil that also contains sulfate, those skilled in the art will understand that certain microorganisms will also reduce sulfate to sulfide, which may be an undesirable outcome. Consequently, the amount of electron donor injected into the soil is controlled to reduce the reduction of sulfate.
In step 306, the injection well 202 is treated with an amount of azide effective to treat the well. In some embodiments, the azide is used prophylactically, before the well 202 is fouled. In other embodiments, the azide is used to treat a fouled well 202. When used prophylactically, an effective treatment prevents the well 202 from fouling. When used remedially, an effective treatment improves the hydraulic conductivity at the well 202.
The effectiveness of the treatment at any point in or around the well 202 will depend, for example, on both the concentration of azide and duration of contact at that point. Under some conditions, the azide completely disinfects a zone in and around the well, for example, the gravel pack 206 and/or filter pack 208; however, it is believed that effective treatment does not require complete disinfection. Those skilled in the art will understand that the amount of azide and duration of contact will depend on a variety of factors, for example, whether the treatment is prophylactic or remedial. The characteristics of the well 202 will also affect the treatment, for example, the depth of the well, the design of the well, the presence or absence of a gravel pack 206, the hydraulic conductivity of the soil, and the particular microorganism(s) contributing to the fouling.
In some embodiments, the hydraulic conductivity of the well is monitored. In some embodiments, the hydraulic conductivity of the well during or after treatment is compared to the original hydraulic conductivity of the well. In some embodiments, the comparative hydraulic conductivity is at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90%. In some embodiments, the backpressure in the well—i.e., the pressure required to inject a fluid into the well—is monitored. In some embodiments, the backpressure is reduced by at least about 50%, at least about 60%, at least about 70%, at least about 80%, or at least about 90%.
Without being bound by any theory, it is believed that the interfaces between different parts of the well 202 are prone to biofouling. For example, for a well with a gravel pack 206, examples of interfaces are between the well casing 204 and the gravel pack 206, and between the gravel pack 206 and the filter pack 208. For a well without a gravel pack, an interface exists between the well casing 204 and the filter pack 208. Accordingly, in some embodiments, the treatment is designed to contact these interfaces with an effective concentration and contact time of azide. In some embodiments, the void volume of the well 202 including the casing 204, gravel pack 206 (if applicable), and filter pack 208 is determined, either empirically and/or theoretically to determine the concentration and contact time of the azide to be used in treating the interfaces.
In some embodiments, the azide is mixed with water extracted from the extraction well 212 to provide a solution with a predetermined concentration of azide and the solution is injected into the injection well 202. In some embodiments, another compound is also mixed with the azide solution, for example, another biocidal compound, a surfactant, a detergent, a soap, or a combination thereof. In some embodiments, a buffering agent is mixed with the azide solution, for example, to prevent the formation of hydrazoic acid from azide anion. In some embodiments, an electron donor and/or electron acceptor is mixed with the azide solution.
Some embodiments use a treatment profile that specifies, for example the concentration of the azide solution, and flow rate and/or pressure at each time point of step 306. In some embodiments, the concentration of azide varies with time over the course of the treatment, for example, as a gradient. In some embodiments, the treatment comprises of a single pulse of azide injected into the well 202. In other embodiments, the treatment comprises a plurality of pulses of azide injected into the well 202. In some embodiments, the pulses of azide are interspersed with the injection of another fluid, for example, water or a solution of a surfactant. In other embodiments, no other fluid is injected between pulses of azide. In other embodiments, a combination of fluid injection and no fluid injection is used between pulses of azide. In some embodiments, the treatment in step 306 is automated, for example, using a computer, microprocessor, or programmable logic controller.
For example, in some embodiments, water taken from extraction well 212 is recharged substantially continuously into the water zone through injection well 202. A pulse of azide is added to the water that is injected, for example, for one hour. After a predetermined time, for example, two days, a characteristic of the well 202 is determined, for example, the back pressure or throughput. If additional treatment is desired, the procedure is repeated. Those skilled in the art will understand that other treatment schedules are possible, and will depend on factors including the degree of fouling in the well, the nature of the soil, and the like. As discussed above, in some embodiments, the procedure is automated.
In some embodiments, the concentration of the azide solution injected into the well 202 is at least about 75 mM to at least about 7.5 M. In some embodiments, the concentration of the azide solution is at least about 100 mM, at least about 200 mM, at least about 300 mM, at least about 400 mM, at least about 500 mM, at least about 600 mM, at least about 700 mM, at least about 800 mM, at least about 900 mM, at least about 1 M, at least about 1.5 M, at least about 2 M, at least about 2.5 M, at least about 3 M, at least about 3.5 M, at least about 4 M, at least about 4.5 M, at least about 5 M, at least about 5.5 M, at least about 6 M, or at least about 6.5 M. In some embodiments, the azide is sodium azide and the concentration is from at least about 5 mg/L to at least about 500 mg/L.
Those skilled in the art will understand that steps 302 and or 304 are optional for some types of wells. For example, an extraction well may become fouled after prolonged use without carrying out step 304, the addition of an electron donor and/or electron acceptor. The disclosed method is also useful in the prophylactic or remedial treatment of other porous media, for example, injection well screen, infiltration trenches, filter pack, conveyance piping, and cooling towers.
EXAMPLE 2
The soil column 402 was packed with 38″ (1.1 ft3, 31.3 L) of a soil sample taken from a monitor well from a site targeted for perchlorate remediation. The soil sample was a mixture of sand, silt, clay, and gravel. The soil was first purged with nitrogen to displace oxygen from the soil. The soil was than saturated with demineralized water for about 24 hours. A 100 mg/L solution of citric acid was circulated through the soil column 402 for 21 days. The pressure required to circulate the citric acid solution increased from less than 1 psig (7 kPa) to over 20 psig (138 kPa). On the twenty-first day, the solution was changed to a 50 mg/L sodium azide solution. Within two days, the feed pressure dropped to less than 1 psig (7 kPa).
The embodiments illustrated and described above are provided as examples only. Various changes and modifications can be made to the embodiments presented herein by those skilled in the art without departure from the spirit and scope of the teachings herein.
Claims
1. A method for treating a well comprising contacting the well with an effective amount of azide.
2. The method of claim 1, wherein the well is fouled and the amount of azide is effective for improving the hydraulic conductivity thereof.
3. The method of claim 1, wherein the well is not fouled and the amount of azide is effective for preventing the fouling thereof.
4. The method of claim 1, wherein the well is selected from the group consisting of an injection well, an extraction well, and a monitoring well.
5. The method of claim 4, wherein the well is used in an in situ remediation system.
6. The method of claim 5, wherein the in situ remediation system is used to remediate a contaminant selected from the group consisting of perchlorate, chlorate, and mixtures thereof.
7. The method of claim 1, wherein the azide is selected from the group consisting of salts of N3− and hydrazoic acid.
8. The method of claim 7, wherein the azide is selected from the group consisting of sodium azide, potassium azide, and ammonium azide.
9. The method of claim 1, wherein the azide is in an aqueous solution.
10. The method of claim 7, wherein the solution is buffered.
11. The method of claim 7, wherein the concentration of the azide is greater than about 75 mM.
12. The method of claim 1, wherein a pulse of azide is injected into the well.
13. The method of claim 1, wherein the hydraulic conductivity of the well after treatment is at least about 50% of the original hydraulic conductivity.
14. The method of claim 1, wherein the backpressure in the well is reduced by at least about 50%.
15. The method of claim 1, wherein the contacting with azide under automated control.
16. A method for in situ remediation of a contaminant comprising:
- injecting an electron donor into an injection well, wherein the injection well is in fluid communication with a water zone comprising a contaminant; and
- injecting an azide into the injection well, wherein the amount of azide is effective to prevent and/or remedy fouling in the injection well.
17. The method of claim 16, wherein the electron donor is selected from the group consisting of citric acid and ethanol.
18. The method of claim 16, further comprising mixing the azide with water extracted from an extraction well located downgradient of the injection well.
19. The method of claim 16, wherein the contaminant is selected from the group consisting of perchlorate, chlorate, and mixtures thereof.
20. The method of claim 16, wherein the azide is selected from the group consisting of sodium azide, potassium azide, and ammonium azide.
Type: Application
Filed: Jan 13, 2006
Publication Date: Aug 24, 2006
Inventor: Dane Grimshaw (Boulder City, NV)
Application Number: 11/331,825
International Classification: E21B 37/00 (20060101);
