Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
  • C09K8/58—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids
  • C09K8/582—Compositions for enhanced recovery methods for obtaining hydrocarbons, i.e. for improving the mobility of the oil, e.g. displacing fluids characterised by the use of bacteria

Definitions

• Subsurface oil reservoirs are promising and important sources for the generation and collection of increasing amounts of hydrocarbons as an energy source.
• methods for the recovery of the remaining oil in the reservoirs either as oil or as methane are of great interest.
• Microbes are responsible for biodegrading conventional crude oil to intermediates that are converted by other microbes (methanogens) into methane leaving behind heavy oil, which can be then further biodegraded.
• methanogens microbes
• methanogenesis methane gas generation
• Pathways include
• Methane from Petroleum in Subterranean Formations techniques are described for injecting one or more agents into a reservoir in which methanogenic microbial consortia are present to modify the reservoir environment to promote in situ microbial degradation of petroleum, promote microbial generation of methane, and to demote in situ microbial degradation of methane.
• This invention is based, in part, on the discovery that significant enhancement in methane generation from oil reservoirs can be achieved.
• very high concentrations of nutrients shown to be effective for microbial conversion of oil to methane are added as a bolus into the reservoir thereby enhancing the total amount of nutrients available to the microbes in a manner such that methane generation is maximized while at the same time ensuring that the concentration of nutrients in the reservoir is non-lethal to the microbes.
• the methane production levels in the reservoir are increased significantly such that methane production in the reservoir is exponentially increased over endogenous rates. Under optimal conditions, methane production can be increased to a level of at least 25 MCF and preferably at least 50 MCF per day.
• this invention is directed to a method for enhancing methanogenesis in an oil reservoir comprising methanogenic microbial consortia and foundation water which method comprises adding a solution comprising methanogenic nutrients which comprise at least nitrogen and phosphate ions wherein the amount of said nutrients in the solution is sufficient to enhance the rate of methanogenesis in said reservoir at its final dilution without being lethal to said methanogenic microbial consortia, and
• the added concentration of said nutrients in said solution facilitates dispersion of the nutrients from the said solution into the foundation water.
• the solution of nutrients is preferably an aqueous solution and can occur in a single injection or in an iterative process where the aqueous solution is divided into several injections wherein each injection contains a known concentration of nutrients.
• concentration of nutrients in the foundation water is determined and adjustments are made to each additional injection to achieve the desired concentration of nutrients in the foundation water.
• the amount of water used to inject the nutrients is minimized such that the injected water does not significantly alter the composition of the foundation water but for the nutrients added. That is to say that the salinity of the foundation water will not vary by more than 1 % and preferably not more than 0.1 % after injection as compared to prior to injection except for changes in concentration of the nutrients added. Examples of characteristics which are not significantly altered include salinity, pH, temperature, non-nutrient ion concentrations, etc. [0009] When higher concentrations of nutrients in the water are injected, the volume of reservoir penetration by nutrient at concentration levels sufficient to provoke the desired rate methanogenesis acceleration is increased.
• concentrations to levels previously believed to be deleterious to methanogenesis actually is beneficial as it increases the distance penetration by the injection water/ nutrient mix before the quantity of nutrient available is too low to provoke the desired rate of methanogenesis acceleration.
• concentration of methane produced from an injection point is increased. This, of course, is an important benefit for provoking sufficient hydrocarbon production to make the process commercially viable.
• the concentration of ammonium ions (NH 4 + ) added is up to the saturation concentration and the concentration of phosphate ions (H 2 P0 4 ⁇ ) added is up to the saturation concentration.
• concentration of ammonium and phosphate ions is selected so as to achieve the ideal concentration to provoke the desired rate of methanogenesis acceleration.
• the concentration of ammonium ions added to the reservoir is sufficient that at least a portion of the foundation water has a concentration of ammonium ions of about 5.4 g/L (typically ammonium chloride) and a concentration of phosphate ions (3 ⁇ 4 ⁇ 0 4 ⁇ ) of about 1.376 g/L (typically a potassium or sodium salt).
• saturated concentration refers to either the concentration of the nutrient itself or as a complex with a sequestering agent as is well known in the art.
• methane concentration produced at the well head can be measured.
• the amount of methane produced is at least 0.7 MCF per day. If the pressure increase is insufficient, additional nutrients can be added as necessary.
• the reservoir can remain closed and the methane produced can increase the pressure in the reservoir in either a localized or a reservoir wide manner.
• a method for increasing the rate of methanogenesis in a petroleum reservoir comprising methanogenic microbial consortia and foundation water comprises: a) injecting through a well head a solution of stimulants comprising ammonium and phosphate ions to the reservoir in an amount such that their concentration in the reservoir is above the critical concentration to effect enhanced methanogenesis but below a lethal dosing to the methanogenic microbial consortia; and
• concentration of the ammonium ions injected into the reservoir is up to about saturation concentration and the concentration of phosphate ions injected into the reservoir is up to about saturation concentration.
• a method for increasing the rate of methanogenesis in a petroleum reservoir comprising methanogenic microbial consortia and foundation water comprises: a) injecting through a well head a solution of stimulants comprising ammonium and phosphate ions to the reservoir in an amount such that their concentration in the reservoir is above the critical concentration to effect enhanced methanogenesis but below a lethal dosing to the methanogenic microbial consortia; and b) maintaining said reservoir under conditions such that the rate of methanogenesis is increased,
• concentration of the ammonium ions injected into the reservoir is from about 1 g/L to its saturation concentration and the concentration of phosphate ions injected into the reservoir is from about 0.4 g/L to its saturation concentration.
• the amount of nutrient enriched solution added to the reservoir is such that the salinity of the reservoir does not change by more than 1% and more preferably by no more than 0.1 % once equilibrium is established.
• the temperature of the nutrient enriched solution is maintained at approximately the temperature of the foundation water in the reservoir to which it is being added.
• the amount of nutrient added is from about 1 g/L to its saturation concentration or about 3 g/L to its saturation concentration of ammonium ions and from about 0.4 g/L to its saturation concentration or about 1.5 g/L to its saturation concentration of phosphate ions.
• the concentration of nutrients added provides for a maximal zone (volume) in the foundation water of an ammonium ion concentration of about 5.400 g/L of a phosphate ion concentration of about 1.376 g/L.
• an ammonium ion concentration of about 5.400 g/L of a phosphate ion concentration of about 1.376 g/L.
• the temperature of the solution of stimulants is maintained at approximately the temperature of the foundation water in the reservoir to which it is being added.
• the solution is an aqueous solution.
• a second solution can be injected into the reservoir through the well head to enhance methanogenesis.
• a second solution comprises an inhibitor or a mixture of inhibitors wherein the amount of the inhibitors in the second solution is sufficient to maintain a rate of methanogenesis in said reservoir in conjunction with the added nutrients and wherein the amount of inhibitors added to said reservoir water is non-lethal to said microbes.
• the inhibitors are included in an aqueous solution and, in another embodiment, the inhibitors are combined with the solution of stimulants. In another embodiment, the inhibitors are included in a separate aqueous solution from that of the stimulants.
• FIG. 1 shows the various microbial mediated pathways that convert hydrocarbons to methane via an acetate intermediate. Also shown are pathways that degrade methane and acetate.
• the term “comprising” is intended to mean that the compositions and methods include the recited elements, but not excluding others.
• the term “about” when used in association with a measurement, or used to modify a value, a unit, a constant, or a range of values refers to variations of +/- 3%. It is to be understood, although not always explicitly stated that all numerical designations are preceded by the term “about”. Accordingly all numerical designations, e.g., pH, temperature, time, concentration, and molecular weight, including ranges, are approximations which are varied (+) or (-) by increments of 3%. It also is to be understood, although not always explicitly stated, that the reagents described herein are merely exemplary and that equivalents of such are known in the art.
• ppm or “parts per million” as used herein refers to the mass ratio of solutes to water multiplied by one million. 1 ppm is equivalent to 1 mg/L.
• methanogenic microorganisms or “methanogenic microbes” refer to those microbes or combination of microbes that produce methane from oil in hydrocarbon reservoirs. Such microbes are anaerobic and, accordingly, exogenous oxygen is contra- indicated during any injection. Methanogenic microbes are well known in the art and include, by way of example only, Methanocalculus spp., Methanogenium spp.,
• Methanoculleus spp. members of the Methanosarcinales (all methanogenic archea), and associated syntrophic organisms providing acetate and hydrogen for the methanogens these including Syntrophus spp., Smithella spp. Marinobacter spp., Syntrophobacter spp., Syntrophomonas spp. (all syntrophic bacterial partners that may convert hydrocarbons to substrates for methanogenic archaea) and the like.
• non-lethal means that after addition of the stimulant solution and optionally the inhibitor solution, a viable population of methanogenic microbes remain in the foundation water. Even if some amount of methanogenic microbes may die, as long as there is a viable population of methanogenic microbes in the foundation water, the level of stimulant solution added is considered “non-lethal.”
• the term "nutrient” or “methanogenic nutrient” refers to a component or mixture of components such as gases, inorganic or organic ions including anions, cations and combinations thereof (salts) which stimulate the activity and/or facilitate growth of one or more methanogenic microbes.
• the nutrients can supply one or more key nutritional components to one or more of the microbes comprising the consortium of methanogenic microbes.
• the nutrient can be either an endogenous nutrient already present in the foundation water or an exogenous nutrient - one which is not present in the foundation water.
• the nutrient is an inorganic salt and more preferably is an inorganic salt selected from one or more of NH 4 C1, KH 2 P0 4 , FeS0 4 .7H 2 0, MnCl 2 .4H 2 0, CoCl 2 .6H 2 0, NiCl 2 .6H 2 0, CuCl 2 .2H 2 0, ZnS0 4 .7H 2 0, Na 2 Mo0 .
• inhibitors heretofore considered as nutrients have been found to deleterious to methanogenesis and in a preferred embodiment are excluded from the nutrient composition. Such components include sulfate, nitrate, nitrite, and oxygen.
• the term "inhibitor” refers to a component or mixture of components such as inorganic or organic compounds including anions, cations and combinations thereof (salts) which inhibit one or more microbial reactions which either degrade methane and/or inhibit one or more reactions which divert the petroleum components in the reservoir into products other than methane (“competing reactions"). Such inhibitors can be components that interfere with one or more of these competing reactions or which are selectively toxic to non-methanogenic microbes.
• the inhibitor is an inorganic salt and more preferably is a molybdate salt such as sodium molybdate (Na 2 Mo0 4 ), and hydrates thereof which are inhibitors of sulfate reducers, and sodium chlorate (NaC10 3 ) for inhibiting nitrate reducers.
• a molybdate salt such as sodium molybdate (Na 2 Mo0 4 )
• hydrates thereof which are inhibitors of sulfate reducers, and sodium chlorate (NaC10 3 ) for inhibiting nitrate reducers.
• the inhibitor can be either an endogenous inhibitor - one which is already present in the foundation water or an exogenous inhibitor - one which is not present in the foundation water.
• non-nutrient refers to components which are not nutrients or inhibitors. Such non-nutrients include sodium chloride and other salts which affect the salinity of the water in the reservoir.
• the microbes are adapted to the salinity of the foundation water.
• the injection strategy seeks to maintain essentially the same gross salinity of the foundation water after injection as was present prior to injection.
• petroleum components suitable for methanogenesis refers to liquid, gaseous or solid hydrocarbons (hydrocarbon only) or related petroleum non-hydrocarbons (those containing hydrogen and carbon plus one or more heteroatoms such as sulphur, nitrogen or oxygen) all of which are the major biodegradable components of oil.
• Preferred oils are those rich in n-alkanes in reservoirs in the carbon number range 3 to 30 where natural biodegradation is occurring.
• n-alkanes represent up to a maximum around 10 weight percent of the petroleum components and typically petroleum/oils suitable for methanogenesis will have from 1-5% n-alkanes present.
• oils will also contain an extended suite of homologous alkylbenzenes and alkyltoluenes.
• Oil viscosity can range from very low values (from 5 or 10 centipoise (cP) at 20°C) to values as high as 7000 cP at reservoir conditions. Low values generally mean more reactive oils but higher values favor gas over oil production.
• cP centipoise
• n-alkane rich oils are preferred the inventors have shown that in many reservoirs oils without n- alkanes or alkylbenzenes acceleration of natural methanogenesis is possible as the microorganisms have adapted to consumption of less desirable reactants.
• the term "foundation water” refers to the water endogenously present in the reservoir and includes the cations, anions, soluble organics, and other components as well as its temperature, pH, salinity, etc.
• MCF means one thousand (1 ,000) cubic feet.
• increment in methane per day refers to the increase in methane production when the reservoir has been treated under conditions to stimulate methanogenesis. In one embodiment, this can be measured by the rate of methanogenesis (e.g., as determined by the increase in pressure at a well head). In a preferred
• this increase is at least 80% of the maximum rate of methane generated from the reservoir over a 60 day period and preferably over a 120 day period.
• well head refers generically to any well head in the reservoir.
• This invention is predicated on the discovery that prior failed attempts to reach reasonable rates of methane production in a reservoir via enhancing in situ
• methanogenesis were based on the erroneous belief that very high concentrations of nutrients would be toxic to the methanogens.
• This invention is further predicated on the discovery that the injection of a very high concentration of nutrients allows for dispersion across a wider range of the foundation water thereby allowing contact of sufficient quantity of nutrient with a greater number of methanogens.
• the nutrients are added to the reservoir without prior assaying of the reservoir, as most reservoirs retain a viable population of methanogens.
• an analysis of the reservoir is conducted prior to addition of the nutrients. Such an analysis comprises: a) evaluating petroleum components in the reservoir, methanogenic microbial consortia present, stimulants and/or inhibitors already present in the reservoir, pressure and temperature, and salinity of foundation water in the reservoir;
• microbes that comprise a methanogenic consortium selected from the group consisting of members of the Methanomicrobiales (Methanocalculus spp., Methanogenium spp., Methanoculleus spp.), the Methanosarcinales and anaerobic hydrocarbon fermenting bacteria such as Syntrophus spp., Smithella spp., Syntrophobacter spp., Syntrophomonas spp., and Marinobacter spp.;
• stimulants are selected from the group consisting of those that stimulate one or more members of the methanogenic microbial consortium set forth in b) and further wherein said stimulants are either endogenous and/or exogenous stimulants;
• inhibitors are selected from the group consisting of those that inhibit one or more non-methanogenic pathways and further wherein said inhibitors are either endogenous and/or exogenous inhibitors;
• methanogenic petroleum biodegradation in oil reservoirs proceeds primarily through syntrophic fermentation. Such biodegradation first leads to acetate and hydrogen as intermediates that are then utilized by various microorganisms for further biodegradation to methane. Microbes involved in the acetoclastic
• methanogenesis pathway convert acetate directly to methane (CH 4 ) and carbon dioxide (CO 2 ).
• Microbes in the syntrophic acetate oxidation pathway proceed to biodegrade acetate to carbon dioxide and hydrogen.
• the carbon dioxide is then reduced by microbes in the hydrogenotrophic methanogenesis pathway to methane.
• These microbes may coexist with those that are adverse to methanogenesis such as sulfate reducing bacteria that metabolize acetate and hydrogen producing hydrogen sulfide (H 2 S) water and C0 2 and methanotrophs that convert methane to various compounds including water and C0 2 .
• H 2 S hydrogen sulfide
• the present invention relates to methods for promoting microbial growth and activity that result in a substantial enhancement in the rate of production of methane (CH 4 ) in a subsurface oil reservoir.
• such enhancement can be effected by identifying the petroleum components of a reservoir and determining that they are suitable for methanogenesis, selection of nutrients shown to be effective for the particular microbial consortia in the oil reservoir and then enhancing and preferably maximizing the total amount of nutrients available to the microbes such that methane generation is maximized while at the same time employing a concentration of nutrients in the well that is non- lethal to the microbes.
• a major factor in activating adequate subsurface organisms to produce methane over a large volume of subsurface reservoir is to deliver nutrient solutions, at a critical nutrient concentration (ConcA) to activate the microorganisms at a commercial rate, to as large a volume of reservoir as possible.
• ConcA critical nutrient concentration
• the objective then becomes injecting the minimum volume of water containing nutrients at the maximum safe concentration to avoid deactivating any key organisms (ConcH).
• each reservoir or oil field contains a unique mixture of petroleum components and microbes. Accordingly, the type of petroleum components and microbes present will dictate the nutrients and/or inhibitors which are to be used for that reservoir. Assays for determining the microbes present are known in the art including laboratory incubations of reservoir samples, culturing and culture independent analysis. Likewise, the mixture of hydrocarbons in the reservoir can be determined by conventional analytical means. In one embodiment, a single sample of hydrocarbons is used to determine the hydrocarbons present. In another, multiple samples are used to provide for a higher degree of certainty regarding the hydrocarbon components.
• Nutrients and/or inhibitors for the microbes again can be determined based on the microbe type or by laboratory incubations under different conditions.
• the selection of the appropriate nutrient(s) and/or inhibitor(s) as well as the total injected amount, rates of injection and injection points is then based on the size of the reservoir, the reservoir properties such as permeability and porosity and the amount and type of petroleum components present as well as the endogenous microbes and the presence of any non-nutrients.
• the size of the reservoir determination of the field size, the water present, the concentration of nutrients and non-nutrients (e.g., salinity) already in the reservoir are well within the skill of the art.
• the amount of nutrient (and/or inhibitors) added (injected) into the reservoir is conducted in an iterative process wherein a first injection of nutrients is conducted and after diffusion and equilibration, the concentration of nutrients is determined. Second and subsequent injections, if necessary, can be included until the desired concentration of nutrients is reached.
• the reservoir can be tested after injection and preferably after equilibration to confirm the concentration of each nutrient and/or inhibitor. Additionally, the reservoir can be retested periodically during methanogenesis to determine if additional nutrient and/inhibitor should be added.
• each of the injections is made through a well head or a plurality of well heads.
• Such well heads are conventional well heads having access to the subsurface reservoir. If recovery of methane is desired, then the well head(s) for injection can be the same well head(s) for such recovery. Alternatively, the well head(s) can be used to measure the increase in pressure within the reservoir which is reflective of the amount of methane production.
• the phosphate ion concentrations for use in combination with the ammonium ions are chosen such that the molar ratio of nitrogen to phosphorus is approximately 4: 1. Higher concentrations of phosphorus may be employed including nitrogen to phosphorus ratios of 3.5: 1, 3:1, and 2.5: 1. The appropriate phosphorus concentration relative to the nitrogen concentration may be dependent on the particular phosphate reagent that is used and on the nature of the subsurface reservoir. In general the type and amount of phosphate chosen will minimize any precipitation of solids that is typically seen at higher phosphate concentrations.
• the nitrogen is provided by NH 4 C1.
• Other sources of nitrogen include ammonium phosphate.
• the phosphate ion is provided by KH 2 P0 4 .
• Other sources of phosphate ions for use in the present methods include NaH 2 P0 4 , either in anhydrous or hydrous form.
• the phosphate ion (KH 2 P0 4 ⁇ ) is preferably added in an amount of from 0.2 to about 1.376 g/L.
• the injected stimulants comprise ammonium, phosphate, nickel, and cobalt ions. It is understood, of course, that type and amount of the injected stimulants will be based on the presence and amount of stimulants already present in the reservoir.
• one or more buffers are injected into the reservoir.
• Suitable buffers include carbonates (such as sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate) and alkali and alkaline earth hydroxides (such as LiOH, NaOH, KOH, Cs 2 OH, Mg(OH) 2 , and Ca(OH) 2 ).
• the buffer is NaHC0 3 .
• the amount of buffer to be added is dependent on the salinity and pH of the reservoir, which can vary from reservoir to reservoir.
• one or more complexing agents are injected into the reservoir. Such agents include nitrilotriacetic acid.
• the complexing agents can be used to bind to the stimulants to prevent precipitation and aid in stabilizing the stimulant mixture, can act as inhibitors by binding to metals detrimental to methanogenesis, or act as a source of carbon or nitrogen for microbes to further facilitate biodegradation of oil and methanogenesis, or act as complexing agents to accelerate natural uptake of key nutrient elements from the host reservoir rock.
• inhibitors that minimize microbial activity that slow or are detrimental to methanogenesis may be used.
• Inhibitors include those that inhibit the activity of iron-reducing, nitrate-reducing, or sulphate-reducing bacteria.
• Specific inhibitors include sodium molybdate (Na 2 Mo0 4 ) and hydrates of sodium molybdate for inhibiting sulfate reducers, and sodium chlorate (NaC10 3 ) for inhibiting nitrate reducers. Concentrations of sodium molybdate and sodium chlorate of about 20 mM are contemplated as suitable for use in this invention.
• the stimulants ammonium and phosphate ions, minerals, etc.
• buffers, and other agents may be combined together in one or more aqueous formulations. In one aspect, the ammonium and phosphate ions are contained in a single formulation. Salts such as NaCl and CaCl 2 may also be included in the formulations.
• the formulations may also be sparged with N 2 that will remove oxygen.
• the water used in the formulations is the natural foundation water from the reservoir.
• an aqueous solution of saturated ammonium and phosphate ions optionally having a salinity between 0.1 to 1.
• the aqueous solution is foundation water, wherein the foundation water contains NaCL or CaC12.
• the total salinity of the injected solutions being added to the reservoir will have a salinity similar to that of the reservoir.
• the salinity of the solutions may be adjusted by modifying the amount of added salts such as NaCl and CaCl 2 or other major ions present in the foundation water naturally.
• the formulation is believed to promote growth of microbes in the syntrophic fermentation, acetoclastic methanogenesis, syntrophic acetate oxidation, and hydro genotrophic pathways shown in Fig. 1.
• Microbes involved in methanogenic hydrocarbon degradation include methanogens from the
• Methanomicrobiales (Methanocalculus spp., Methanogenium spp., Methanoculleus spp.), Methanosarcinales and anaerobic hydrocarbon fermenting bacteria such as Smithella spp., Syntrophus spp., Syntrophobacter spp., Syntrophomonas spp., and Marinobacter spp..
• an optional step of identifying reservoirs having one or more of above features are provided.
• Such an optional analysis of the reservoir's environment can provide information that can be used to determine suitable microbial growth stimulants or in situ
• the analysis can include determining the reservoir's temperature and pressure, which can be obtained in any suitable manner. While many reservoirs contain biodegraded oils, not all reservoirs contain currently active microbial populations. In one implementation, the analysis is to identify a zone in a reservoir that includes relevant active organisms biodegrading reactive petroleum components that can be accelerated to recover economic levels of methane through petroleum biodegradation. [0068] To determine the environment in the reservoir, a geochemical analysis can be made of one or more fluids of the reservoir, such as foundation water and petroleum, and/or one or more solids of the reservoir, which analyses are familiar to those skilled in the art.
• the fluid analysis can include measurement of the state values ⁇ e.g., temperature and pressure) as well as a geochemical analysis of the foundation water, which can include assays for major anions and cations, pH, oxidation potential (Eh), chloride, bicarbonate, sulphate, phosphate, nitrate, ammonium ion, salinity, selenium,
• state values ⁇ e.g., temperature and pressure
• geochemical analysis of the foundation water which can include assays for major anions and cations, pH, oxidation potential (Eh), chloride, bicarbonate, sulphate, phosphate, nitrate, ammonium ion, salinity, selenium,
• the geochemical analysis can identify products that are known to be produced by indigenous microbial activity. For example, the presence of methane, C0 2 , RN A, DNA, and/or specific carboxylic acids can be indicative of microbial activity. Methane relatively depleted in the carbon 13 isotope is frequently found in oilfields where natural methanogenesis has occurred.
• anaerobic hydrocarbon degradation metabolites such as alkyl and aryl substituted succinates or reduced naphthoic acids, are markers of systems in which the anaerobic degradation of hydrocarbons is taking place. The identification of such markers can be used in determining the presence of active anaerobic petroleum degrading microbial consortia. See, for example, International Patent Application
• Injection of methanogenic nutrients into the foundation water of a petroleum reservoir can be accomplished using a variety of methods.
• the nutrients may be injected from a vertical injection well or a horizontal injection well.
• a horizontal injection well can be beneficial for the commercial scaling of the process as a larger area of the methanogen active formation oil/water zone can be accessed with the nutrient containing water injected for a single injection well.
• the commercial impact of the process can also be increased by injecting the nutrients using hydraulic fracturing which can increase the distance penetrated by the nutrient at quantities sufficient to provoke the desired rate of accelerated methanogenesis.
• Injecting fluid through a well head into the zone of maximum microbial populations can include injecting fluid into the zone through a first set of one or more well heads, and producing gas from the zone can include producing gas from the zone through a second set of one or more wells. Injecting fluid into the zone can be concurrent with producing gas from the zone or can cease while producing gas from the zone.
• Injecting fluid into the zone can include injecting fluid into the zone through a first set of one or more wells and producing gas from the zone can include producing gas from the zone through a second set of one or more wells.
• a soak cycle can be allowed to endure in a region of the zone situated beneath a third set of one or more wells, while injection and production occur from the first and second set of one or more wells.
• the first set of one or more wells can be allowed to endure a soak cycle, fluid can be injected into the zone through the second set of one or more wells and gas can be produced from the zone from the third set of one or more wells.
• production parameters can be monitored including the pressure in the reservoir and composition of the generated gas. Based on the monitored production parameters, injection into and/or production from the zone are controlled to enhance generation of biogenerated methane within the zone.
• Controlling injection into and/or production from the zone to enhance generation of biogenerated methane from the zone can include controlling one or more of the following: an injector well flow rate; a composition of the one or more injectants injected into the reservoir; a quantity of the one or more injectants injected into the reservoir; a composition of the gas injected into the reservoir; a quantity of the gas injected into the reservoir; or a duration of injection, soak and production cycles for the reservoir.
• an increase in reservoir pressure in the zone in response to an increase in biogenerated methane and the injected fluid can be monitored. Based on the reservoir pressure, the zone's gas saturation can be determined. Production of hydrocarbons (oil, methane, and the like) from the zone can be commenced when the zone's gas saturation reaches a threshold gas saturation.
• the injectants can be added to the reservoir together or in separate injection steps. For example, a slug or bank of water carrying one injectant can be followed by a second slug or bank of water carrying a second injectant. Another example may include alternately injecting one water bank followed by a gas injection step. In some
• injectants operating as stimulants may be injected at one location to enhance methanogenesis, and injectants operating as inhibitors may be injected at a different location, to prevent or minimize detrimental processes, such as methane oxidation.
• Injection of gas below a degrading oil column may facilitate circulation of water and nutrients to the microorganisms present.
• layered reservoir bioreactors can be used for methane production and to facilitate methane removal.
• the biodegrading oil column and/or residual oil zones are vertically segmented and the environment can be controlled, for example, in the following manner: (a) a lower zone of degradation of oil or injected reactive organic substrates can be environmentally modified to produce abundant free gas (e.g., methane and/ or carbon dioxide); (b) an upper zone of degradation of oil or injected reactive organic substrates is environmentally modified to produce abundant free methane; and (c) free gas from the lower layer buoyantly moves up through the layered bioreactor and any free methane or methane in aqueous or oil solution partitions into the moving gas phase and is carried to a gas-rich zone for production.
• abundant free gas e.g., methane and/ or carbon dioxide
• an upper zone of degradation of oil or injected reactive organic substrates is environmentally modified to produce abundant free methane
• microorganism activity in a reservoir may be increased by increasing the area where these conditions prevail.
• One method for increasing the area with suitable conditions is to modify the water flood injection rates.
• Yet another method involves forming small-scale environmental interfaces by forming petroleum- water emulsions in the reservoir, or by changing the clay chemistry.
• endogenous methane production refers to the amount of methane produced over a given period of time without any intervention in the reservoir which is low being typically on the order of 10 "4 kg/m 2 of oil water contact area/ year.
• a IL aqueous solution of nutrients for reservoir injection was prepared using the following compounds:
• 2.5 mM Na 2 S can be added as a reducing agent/oxygen scavenger if the solution is stored over a prolonged period of time.
• the Selenite-tungstate Solution is prepared as a 1 liter aqueous solution using the following compounds:
• the Trace Element Solution is prepared as a 1 liter aqueous solution containing the following compounds:
• the nutrients are added to a mixture of foundation water and heavy oil such that the final concentration of the ammonium ions is 5.4 g/L and the final concentration of the phosphate ions is 1.376 g/L. the mixture is incubated under conditions in which methanogenesis is significantly enhanced.

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