A method for improving the carbon sequestration capacity of an oil reservoir by microbial electrosynthesis

Abstract

The present application belongs to the field of environmental science and technology, petroleum and natural gas science and technology, and particularly relates to a method for improving the carbon sequestration capacity of an oil reservoir by microbial electrosynthesis. The method comprises the following steps: selection of a target oil reservoir, preparation of a slow-release activation system, construction of a microbial electrolysis cell in the near-well zone of an oil well, injection of the slow-release activation system, loading of an electric voltage on the electrolysis cell, and monitoring of the CO2 content. The present application has the characteristics of wide application range, good treatment effect, high economic efficiency, green environmental protection, etc. by constructing a carbon sequestration microbial electrolysis cell in the near-well zone of an oil well and treating the CO2 flowing to the oil well by microbial electrosynthesis to reduce its production. The present application solves the problems of pipeline corrosion caused by the production of CO2, high cost of 2nd collection of produced CO2, and serious pollution.

Description

Technical Field

[0001] This invention belongs to the fields of environmental science and technology and petroleum and natural gas science and technology, and specifically relates to a method for improving the carbon sequestration capacity of oil reservoirs using microbial electrosynthesis. Technical Background

[0002] CO2 is a major greenhouse gas contributing to global warming, and the international community is increasingly focused on reducing CO2 emissions. To date, 136 countries worldwide have made carbon neutrality commitments. In practice, achieving this goal requires work on two fronts: reducing CO2 production and sequestering the generated CO2. Conventional carbon sequestration involves physically storing CO2 by injecting it into deep underground saline aquifers, depleted oil and gas fields, or basalt aquifers. In recent years, CO2 collection, utilization, and storage (CCUS) technology has developed rapidly. This technology can not only sequester CO2 on a large scale but also improve oil recovery, making it an important technological direction for carbon sequestration. However, regardless of conventional physical sequestration or CCUS, the risk of CO2 escaping from the reservoir to the surface environment is unavoidable. Especially with CCUS technology, during implementation, CO2 enters the production well with the fluid, and when the CO2 partial pressure exceeds 2.1 × 10⁻⁶... -3 Exceeding a certain pressure (MPa) will significantly corrode downhole tubing and surface pipelines, affecting normal oilfield production. In addition, the produced CO2 requires two replenishments, primarily through alkali neutralization, which presents problems such as high cost and large mud production. Therefore, effectively improving reservoir CO2 fixation capacity and reducing its production is crucial for the widespread application of this technology.

[0003] Compared to physical carbon sequestration, biological carbon sequestration technology can convert CO2 into carbohydrates, methane, or organic matter, effectively reducing CO2 levels and showing great promise for application. Currently, microalgae and methanogens are promising candidates for industrial application of carbon sequestration, with methanogens widely distributed in oil reservoir environments. Therefore, effectively activating methanogens in oil reservoirs and enhancing their carbon sequestration capacity will significantly promote the early industrial application of oil reservoir carbon dioxide sequestration and displacement technologies.

[0004] CN110284150A discloses a method for promoting the electrochemical conversion of carbon dioxide to methane by microorganisms. The method involves constructing a microbial electrolysis cell containing a cathode and an anode. A methanogenic culture medium is added to the anode cell, and a redox substance is added to the cathode cell. Under applied voltage, hydrogen gas is generated. Hydrogen bacteria in the electrolysis cell oxidize the hydrogen gas, simultaneously converting carbon dioxide into methane. However, the microorganisms used can only tolerate temperatures up to 37°C; above this temperature, their activity decreases significantly. Since the temperature of most actual oil reservoirs exceeds 50°C, this limits the application of the invention in oil reservoirs.

[0005] CN107152266A discloses a method for improving the biogasification rate of residual oil in an oil reservoir and its application. The method involves constructing electrodes in the reservoir using hydraulic fracturing, injecting an aqueous solution of an anaerobic microbial activator into the reservoir, and applying voltage to the electrodes to create a micro-electric field in the reservoir. This stimulates the proliferation and metabolism of methanogenic bacteria and their symbiotic metabolites. Once the voltage is stopped, water-bearing liquid is injected into the reservoir to displace the methanogenic bacteria and their symbiotic bacteria to deeper formations, leading to well production of methanogens. The key step of this invention lies in constructing the electrodes using hydraulic fracturing. However, hydraulic fracturing technology is mostly used in low-to-medium permeability reservoirs. In high-to-medium permeability reservoirs, due to high porosity, high permeability, and rapid pressure release, it is difficult to create fractures and construct electrodes. Therefore, this invention is not suitable for integrated, high-water-cut, high-permeability reservoirs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for improving the carbon sequestration capacity of oil reservoirs by utilizing microbial electrosynthesis, addressing the shortcomings of existing technologies. This invention constructs a carbon sequestration microbial electrolysis cell in the near-wellbore zone, utilizing microbial electrosynthesis to treat CO2 flowing towards the oil well and reduce its production. It features wide applicability to various oil reservoirs, good treatment effect, high economic efficiency, and environmental friendliness, solving problems such as pipeline corrosion caused by CO2 production and the high cost and pollution of secondary CO2 replenishment.

[0007] The present invention aims to provide a method for improving the carbon fixation capacity of oil reservoirs using microbial electrosynthesis, the method comprising the following steps:

[0008] (1) Screening of target reservoirs;

[0009] (2) Preparation of sustained-release activation system;

[0010] (3) Construction of microbial electrolysis cells in the near-wellbore zone of oil wells;

[0011] (4) Injection of the sustained-release activation system;

[0012] (5) Electrolytic cell loading voltage;

[0013] (6) Monitoring CO2 content during well opening.

[0014] In this invention, preferably, the target reservoir screening criteria in step (1) are:

[0015] (11) CO2 flooding or sequestration of the reservoir;

[0016] (12) The CO2 partial pressure at the producing end of the oil well in the reservoir is greater than 2.1 × 10⁻⁶. -3 MPa, reservoir temperature less than 90℃;

[0017] (13) The reservoir contains one or more of the following: Methanococcus marinum, short-lived methanogenic oval bacteria, palm oil methanogenic bag bacteria, thermoautotrophic methanococcus, Martensia malathi, and thermophilic methanogenic bacteria.

[0018] In this invention, preferably, the composition and mass components of the sustained-release activation system described in step (2) are as follows:

[0019] 2-4 parts embedding agent;

[0020] 2-4 parts of crosslinking agent;

[0021] Activator 4-8 parts;

[0022] 2-4 electronic donors;

[0023] 80-90 parts deionized water.

[0024] In a preferred embodiment, the encapsulating agent is one or more of sodium alginate, polyethylene glycol, and activated carbon; more preferably, the encapsulating agent is sodium alginate or polyethylene glycol.

[0025] In a preferred embodiment, the crosslinking agent is one or more of glutaraldehyde and calcium chloride.

[0026] In a preferred embodiment, the activator is one or more of ammonium chloride, ammonium nitrate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; more preferably, the activator is ammonium nitrate or dipotassium hydrogen phosphate.

[0027] In a preferred embodiment, the electron donor is one or more of sodium nitrite, sodium thiosulfate, and sodium sulfide; more preferably, the electron donor is sodium nitrite or sodium thiosulfate.

[0028] In this invention, preferably, the method for preparing the sustained-release activation system in step (2) is as follows:

[0029] (21) Dissolve the embedding agent in deionized water at 65-70℃ and stir until homogeneous;

[0030] (22) Next, add the activator and stir until homogeneous; then add the electron donor and stir until homogeneous to obtain a mixed solution;

[0031] (23) After cooling to room temperature, the above mixed solution is added to the crosslinking agent using a peristaltic pump, cured for 1-3 hours, then the particles are filtered out and washed with physiological saline to obtain the sustained-release activation system.

[0032] As a further improvement of the present invention, the particle size of the sustained-release activation system is controlled by the peristaltic pump flow rate and the needle. Under the conditions of using an 8-gauge needle and a peristaltic pump flow rate of 0.5 to 0.6 ml / min, the particle size of the prepared sustained-release activation system is 50 to 60 μm.

[0033] In this invention, preferably, the microbial electrolysis cell in step (3) consists of a ground-based solar power generation system, wires, a perovskite anode electrode and its conductive material, and a carbon-based cathode electrode and its conductive material.

[0034] In a preferred embodiment, the ground-mounted solar power generation system includes solar panels, batteries, and a controller.

[0035] In a preferred embodiment, the perovskite anode electrode and the carbon-based cathode electrode are fixed on a packer and connected to a ground-based solar power generation system by wires.

[0036] In a preferred embodiment, the conductive materials of the perovskite anode and carbon-based cathode are prepared by coating the surface of quartz sand with one or more of the following polymers: polyacetylene, polyphenylene oxide, polyaniline, etc.

[0037] As a further improvement of the present invention, the size of the quartz sand is determined according to the formation sand size of the specific oil well, and the average particle size of the selected quartz sand is 2 to 5 times the average particle size of the formation sand.

[0038] In this invention, preferably, the method for constructing the near-wellbore microbial electrolysis cell in step (3) is as follows:

[0039] (31) Use a single tubing string to lower all sand control equipment into the well and use a packer to divide the oil well into upper and lower sections.

[0040] (32) A high-pressure pump truck is used on the ground to squeeze the conductive material into the annulus of the oil casing and the formation outside the wellbore, forming a dense, conductive, and highly permeable zone around the wellbore. The electrode is fixed on the packer and connected to the conductive layer.

[0041] (33) Construct the anode and cathode to form an electrolytic cell; use wires to connect the downhole electrodes to the ground-based solar power generation system.

[0042] As a further improvement of the present invention, the depth to which the electrode of the near-wellbore microbial electrolysis cell extends into the formation is based on the concentrations of CO2, H2CO3, and HCO3 in the produced fluid at the wellhead. - The concentration and CO2 partial pressure in the associated gas determine the depth, which is 1.5m to 2m.

[0043] In this invention, preferably, the injection method of the slow-release activation system in step (4) is as follows: after mixing the slow-release activation system with the surface-treated quartz sand, it is squeezed into the formation when constructing the near-wellbore zone electrolytic cell of the oil well, and the mass ratio of the slow-release activation system to the quartz sand is 1:20 to 50.

[0044] In this invention, preferably, the electrolytic cell voltage in step (5) is -0.8 to -1V.

[0045] As a further improvement of the present invention, the steps of the present invention can be repeated two or more times in the oil well to ensure the carbon fixation effect.

[0046] This invention utilizes microbial electrosynthesis technology to generate electrons on a constructed cathode. Methanogens directly acquire these electrons and use them to reduce CO2 to produce methanogens, thus solving the problem of slow extracellular electron transfer in methanogens and limiting the reaction rate, significantly improving the carbon fixation capacity of methanogens. The carbon fixation mechanism of microbial electrosynthesis in oil reservoir environments is as follows:

[0047] 1) Anode reaction: H2O → H + +e - +O2

[0048] 2) Cathode reaction: H + +e - +CO2→CH4+H2O

[0049] This invention addresses the challenges of CO2 sequestration and displacement processes, including pipeline corrosion and increased CO2 recovery costs caused by CO2 entering oil wells and their gathering and transportation systems. It provides a microbial electrosynthesis technology for efficient carbon fixation in the reservoir environment. Compared to traditional microbial carbon fixation technologies, coupling microbial and electrochemical technologies solves the key step of slow extracellular electron transfer, which limits the carbon fixation rate, significantly improving microbial carbon fixation efficiency. Using layered sand control technology, conductive materials and a slow-release activation system are used to construct microbial electrolytic cells in the wellbore and near-wellbore zone, forming a near-wellbore carbon fixation biochemical reaction pool. A micro-electric field is created by applying voltage to the electrolytic cells in the reservoir through a surface power supply system. Methanogenic bacteria and their symbiotic microorganisms within this micro-electric field, after releasing nutrients and redox substances through the slow-release activation system, can stably react with CO2 flowing through the reaction pool, converting CO2, H2CO3, and HCO3 into compounds. - Carbon in various forms is converted into microbial cells or methane gas. Through biochemical reactions, the likelihood of CO2 and other gases flowing into the wellbore and entering the surface gathering and transportation system will be significantly reduced. In addition to carbon fixation through the generation of microbial cells, the CH4 produced in the reaction is a clean energy source that can be collected and utilized after entering the gathering and transportation system.

[0050] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0051] (1) This invention constructs a microbial electrolysis cell in the near-wellbore zone of the oil well, and reacts away the CO2 flowing into the oil well through a biochemical reaction, reducing the CO2 partial pressure at the wellhead to 2.1 × 10⁻⁶. -3 Below MPa, CO2 corrosion of downhole tubing and surface gathering pipelines is minimized, while CO2 capture costs are significantly reduced.

[0052] (2) This invention constructs a microbial electrolysis cell in the near-wellbore zone of an oil well using a layered sand control technology. A voltage is applied to the reservoir electrodes via a surface solar reservoir system, providing extracellular electrons for methanogenic bacteria to utilize CO2, thus significantly increasing the carbon fixation reaction rate. The provided electrolysis cell construction method is simple, easy to operate, and applicable to most oil wells.

[0053] (3) The present invention uses an encapsulation method to fix the activator and redox substances, and squeezes them into the reservoir during the construction of the reservoir microbial electrolysis cell. The activator and redox substances are slowly released and utilized by the reservoir methanogens and their symbiotic microorganisms, which can provide nutrients and electron donors for the reservoir carbon-fixing microorganisms for a long time, ensuring the long-term effectiveness of microbial carbon fixation.

[0054] (4) This invention has the advantages of being highly targeted and easy to operate. Compared with traditional methods, it has the advantages of low cost, good effect and green environmental protection. Attached Figure Description

[0055] Figure 1 CO2 partial pressure at the wellhead after on-site measures in Block A;

[0056] Figure 2 CO2 partial pressure at the wellhead after on-site measures in Block B;

[0057] Figure 3 CO2 partial pressure at the wellhead after on-site measures in Block C;

[0058] Figure 4 CO2 partial pressure at the wellhead after on-site measures in Block D;

[0059] Figure 5 A schematic diagram of the carbon fixation principle of a microbial electrolysis cell in the near-wellbore zone of an oil well. Detailed Implementation

[0060] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0061] Example 1

[0062] Overview of Block A, a carbon dioxide flooding test area in a certain oil production plant of Shengli Oilfield: reservoir temperature 57℃, formation pressure 14.2MPa, oil layer thickness 8.3m, permeability 550×10⁻⁶. -3 μm 2 The formation water salinity reached 16,500 mg / L. Carbon dioxide flooding was implemented in this block in 2019, achieving good field application results and increasing the recovery rate by 5.4% in stages. However, the current wellhead CO2 partial pressure has reached 5.1 × 10⁻⁶. -3 MPa, corrosion problems occurred in the gathering and transportation pipeline. Molecular biotechnology analysis revealed methanogenic bacteria in the wellhead produced fluid, including short-lived methanogenic oval bacteria, thermoautotrophic methanococci, *Dystrophus martensii*, and thermophilic methanogens, with concentrations reaching 5.6 × 10⁻⁶. 3 cells / mL, 1.8 × 10 3 cells / mL, 3.5×10 3 cells / mL, 9.2×10 2 The method of this invention enhances the carbon sequestration capacity of CO2-enhanced oil reservoirs and reduces their recovery rate. The specific steps are as follows:

[0063] (1) Screening of target reservoirs

[0064] The selection criteria for the target reservoirs are as follows: reservoirs undergoing CO2 flooding or sequestration have a CO2 partial pressure at the well production end greater than 2.1 × 10⁻⁶. -3 MPa, reservoir temperature less than 90℃, presence of one or more of the following: marine methanococci, short methanoid oval bacteria, palm oil methanoid sac bacteria, thermoautotrophic methanococci, Martensii octopus, and thermophilic methanogens.

[0065] The reservoir temperature in test area A was 57℃, and the CO2 partial pressure at the well production end reached 5.1×10⁻⁶. -3 The pressure is MPa, and the pipeline has shown signs of corrosion. The reservoir in the test area contains methanogenic microorganisms such as short, oval-shaped methanogenic bacteria, thermoautotrophic methanococci, *Dystrophus martensii*, and thermophilic methanogenic bacilli. Test area A meets the reservoir screening criteria of this invention and can be used to implement this invention.

[0066] (2) Preparation of sustained-release activation system

[0067] A 2% sodium alginate / polyethylene glycol (1:1 mass ratio) solution was dissolved in deionized water at 65°C. Then, 0.15% activated carbon was added and stirred until homogeneous. Next, 4% ammonium chloride and dipotassium hydrogen phosphate were added and stirred until homogeneous. Finally, 3% electron donor was added and stirred until homogeneous, yielding a mixed solution. After cooling to room temperature, the mixed solution was dripped into a 2% crosslinking agent solution using a peristaltic pump at a rate of 0.6 ml / min. The mass ratio of CaCl2 to glutaraldehyde in the crosslinking agent was 1:1. After curing for 1 hour, the particles were filtered out and washed with physiological saline to obtain sustained-release activation system particles with a particle size of 60 μm.

[0068] (3) Constructing a microbial electrolysis cell and injecting a slow-release activation system

[0069] Quartz sand was heated to 120°C and then mixed with a polymer, with the polymer accounting for 2% of the quartz sand volume. During thorough mixing, the polymer melted and coated the surface of the quartz sand. Subsequently, hexamethylenetetramine and calcium stearate were added to solidify the polymer and disperse the quartz sand particles, with each accounting for 0.2% of the quartz sand volume. After cooling to room temperature, the mixture was sieved to obtain a polymer-coated conductive quartz sand material.

[0070] A single tubing string is used to lower all sand control equipment into the well. A specialized packer divides the well into upper and lower sections. At the surface, a high-pressure pump truck injects surface-treated quartz sand and a slow-release activation system (mass ratio 50:1) into the annulus and outer formation of the wellbore, forming a dense, conductive, high-permeability zone within a certain radius around the wellbore. Electrodes are fixed to the packer and connected to the conductive layer, forming the anode and cathode of the reservoir electrolysis cell. A wire is used to connect the downhole electrodes to the surface power supply system. The treatment depth is generally 1.5m, determined by the CO2 partial pressure at the wellhead.

[0071] (4) Applying voltage to stimulate the proliferation and metabolism of methanogens and their symbiotic microorganisms

[0072] A micro-electric field is created by applying a -0.8V voltage to the electrolytic cell in the oil reservoir through the ground power supply system. Within this micro-electric field, methanogenic bacteria and their symbiotic microorganisms release nutrients and redox substances through a slow-release activation system. These substances then react with CO2 flowing through the reaction tank, producing CO2, H2CO3, and HCO3-. - Carbon in various forms is converted into microbial cells or methane gas.

[0073] (5) Monitoring CO2 content during well opening

[0074] The CO2 partial pressure at the wellhead was tested continuously for one month after well opening. The test results are shown below. Figure 1 During the one-month trial run, the CO2 partial pressure remained stable below 0.001 MPa.

[0075] Corrosion evaluation experiments were conducted using Class D rods and N80 pipes, and the results are shown in Table 1 below. The test results show that the corrosion rate of the pipeline was significantly reduced after the treatment measures were implemented, achieving the desired experimental results.

[0076] Table 1. Corrosion rates of Class D rods and N80 rods after 72 hours of corrosion at 57℃.

[0077]

[0078] Example 2

[0079] Overview of Block B, a carbon dioxide flooding test area in a certain oil production plant of Shengli Oilfield: reservoir temperature 65℃, formation pressure 11.8MPa, oil layer thickness 13.7m, permeability 259×10⁻⁶. -3 μm 2 The formation water salinity reached 23,000 mg / L. Carbon dioxide flooding was implemented in this block in 2020, achieving good field application results. However, the current wellhead CO2 partial pressure has reached 2.0 × 10⁻⁶. -2 The wellhead production fluid showed signs of corrosion and perforation at a pressure of MPa. Molecular biotechnology analysis revealed the presence of methanogenic microorganisms such as *Methanococcus marinei*, *Methanococcus thermoautotrophus*, *Micrococcus martensii*, and *Methanobacterium thermophilum*, with concentrations reaching 2.0 × 10⁻⁶. 3 cells / mL, 5.8 × 10 3 cells / mL, 8.9×10 3 cells / mL, 4.7×10 2 The method of this invention enhances the carbon sequestration capacity of CO2-enhanced oil reservoirs and reduces their recovery rate. The specific steps are as follows:

[0080] (1) Screening of target reservoirs

[0081] The selection criteria for the target reservoirs are as follows: reservoirs undergoing CO2 flooding or sequestration have a CO2 partial pressure at the well production end greater than 2.1 × 10⁻⁶. -3 MPa, reservoir temperature less than 90℃, presence of one or more of the following: marine methanococci, short methanoid oval bacteria, palm oil methanoid sac bacteria, thermoautotrophic methanococci, Martensii octopus, and thermophilic methanogens.

[0082] The reservoir temperature in test area B was 65℃, and the CO2 partial pressure at the well production end reached 2.1×10⁻⁶. -2 The pressure is MPa, and the pipeline has shown signs of perforation. The reservoir in the test area contains methanogenic microorganisms such as *Methanococcus marinei*, *Methanococcus thermoautotrophus*, *Micrococcus martensii*, and *Methanobacterium thermophilum*. Test area B meets the reservoir screening criteria of this invention and can be used to implement this invention.

[0083] (2) Preparation of sustained-release activation system

[0084] A 4% sodium alginate / polyethylene glycol (1:1 mass ratio) solution was dissolved in deionized water at 65°C. Then, 0.2% activated carbon was added and stirred until homogeneous. Next, 8% ammonium chloride and dipotassium hydrogen phosphate were added and stirred until homogeneous. Finally, 4% electron donor was added and stirred until homogeneous, yielding a mixed solution. After cooling to room temperature, the mixed solution was dripped into a 2% crosslinking agent solution using a peristaltic pump at a rate of 0.5 ml / min. The mass ratio of CaCl2 to glutaraldehyde in the crosslinking agent was 1:1. After curing for 1 hour, the particles were filtered out and washed with physiological saline to obtain sustained-release activation system particles with an average particle size of 50 μm.

[0085] (3) Constructing a microbial electrolysis cell and injecting a slow-release activation system

[0086] Quartz sand was heated to 100°C and then mixed with a polymer, with the polymer accounting for 5% of the quartz sand volume. During thorough mixing, the polymer melted and coated the surface of the quartz sand. Subsequently, hexamethylenetetramine and calcium stearate were added to solidify the polymer and disperse the quartz sand particles, with each accounting for 0.5% of the quartz sand volume. After cooling to room temperature, the mixture was sieved to obtain a polymer-coated conductive quartz sand material.

[0087] A single tubing string is used to lower all sand control equipment into the well. A specialized packer divides the well into upper and lower sections. At the surface, a high-pressure pump truck injects surface-treated quartz sand and a slow-release activation system (mass ratio 20:1) into the annulus and outer formation of the wellbore, forming a dense, conductive, high-permeability zone within a certain radius around the wellbore. Electrodes are fixed to the packer and connected to the conductive layer, forming the anode and cathode of the reservoir electrolysis cell. A wire is used to connect the downhole electrodes to the surface power supply system. The treatment depth is generally 2.0m, determined by the CO2 partial pressure at the wellhead.

[0088] (4) Applying voltage to stimulate the proliferation and metabolism of methanogens and their symbiotic microorganisms

[0089] A micro-electric field is created by applying a -1.0V voltage to the electrolytic cell in the oil reservoir through the ground power supply system. Within this micro-electric field, methanogenic bacteria and their symbiotic microorganisms release nutrients and redox substances through a slow-release activation system. These substances then react with CO2 flowing through the reaction cell, producing CO2, H2CO3, and HCO3-. - Carbon in various forms is converted into microbial cells or methane gas.

[0090] (5) Monitoring CO2 content during well opening

[0091] The CO2 partial pressure at the wellhead was tested continuously for 6 months after well opening. The test results are shown in [link to test results]. Figure 2During the six months of trial operation, the CO2 partial pressure remained stable below 0.0021 MPa.

[0092] Corrosion evaluation experiments were conducted using Class D rods and N80 pipes, and the results are shown in Table 2 below. The test results show that the corrosion rate of the pipeline was significantly reduced after the treatment measures were implemented, achieving the desired experimental results.

[0093] Table 2. Corrosion rates of Class D rods and N80 rods after 72 hours of corrosion at 65℃.

[0094]

[0095] Example 3

[0096] Overview of Block C, a carbon dioxide flooding test area in a certain oil production plant of Shengli Oilfield: reservoir temperature 79℃, formation pressure 13.7MPa, oil layer thickness 12.4m, permeability 523×10⁻⁶. -3 μm 2 The formation water salinity reached 30157 mg / L. Carbon dioxide flooding was implemented in this block in 2019, achieving good field application results and increasing the recovery rate by 7.7% in stages. However, the current wellhead CO2 partial pressure has reached 2.6 × 10⁻⁶ mg / L. -2 The wellhead production fluid showed signs of corrosion and perforation at a pressure of MPa. Molecular biotechnology analysis revealed the presence of methanogenic microorganisms such as *Methanococcus marinei*, thermoautotrophic methanococci, short-lived methanogenic oval bacteria, *Mammillaria palmiformis*, *Dystrophococcus martensii*, and thermophilic methanogens, with concentrations reaching 3.0 × 10⁻⁶. 3 cells / mL, 6.3×10 3 cells / mL, 5.4 × 10 3 cells / mL, 6.2×10 2 cells / mL, 2.4 × 10 3 cells / mL, 8.7×10 2 The method of this invention enhances the carbon sequestration capacity of CO2-enhanced oil reservoirs and reduces their recovery rate. The specific steps are as follows:

[0097] (1) Screening of target reservoirs

[0098] The selection criteria for the target reservoirs are as follows: reservoirs undergoing CO2 flooding or sequestration have a CO2 partial pressure at the well production end greater than 2.1 × 10⁻⁶. -3 MPa, reservoir temperature less than 90℃, presence of one or more of the following: marine methanococci, short methanoid oval bacteria, palm oil methanoid sac bacteria, thermoautotrophic methanococci, Martensii octopus, and thermophilic methanogens.

[0099] The reservoir temperature in test area C was 79℃, and the CO2 partial pressure at the well production end reached 2.6×10⁻⁶. -2The pressure is MPa, and the pipeline has shown signs of perforation. The reservoir in the test area contains methanogenic microorganisms such as *Methanococcus marinea*, *Methanococcus thermoautotrophicus*, *Small methanogenic oval*, *Morphozoa palmiformis*, *Micrococcus martensii*, and *Methanogenic Bacillus thermophilus*. Test area C meets the reservoir screening criteria of this invention and can be used to implement this invention.

[0100] (2) Preparation of sustained-release activation system

[0101] A 4% sodium alginate / polyethylene glycol (1:1 mass ratio) solution was dissolved in deionized water at 65°C. Then, 0.1% activated carbon was added and stirred until homogeneous. Next, 7% ammonium chloride and dipotassium hydrogen phosphate were added and stirred until homogeneous. Finally, 3% electron donor was added and stirred until homogeneous, yielding a mixed solution. After cooling to room temperature, the mixed solution was dripped into a 2% crosslinking agent solution using a peristaltic pump at a rate of 0.5 ml / min. The crosslinking agent contained CaCl2 and glutaraldehyde in a 1:1 mass ratio. After curing for 1 hour, the particles were filtered out and washed with physiological saline to obtain sustained-release activation system particles with an average particle size of 50 μm.

[0102] (3) Constructing a microbial electrolysis cell and injecting a slow-release activation system

[0103] Quartz sand was heated to 120°C and then mixed with a polymer, with the polymer accounting for 3% of the quartz sand volume. During thorough mixing, the polymer melted and coated the surface of the quartz sand. Subsequently, hexamethylenetetramine and calcium stearate were added to solidify the polymer and disperse the quartz sand particles, with the amounts of hexamethylenetetramine and calcium stearate accounting for 0.4% of the quartz sand volume. After cooling to room temperature, the quartz sand was sieved to obtain a polymer-coated conductive material.

[0104] A single tubing string is used to lower all sand control equipment into the well. A specialized packer divides the well into upper and lower sections. At the surface, a high-pressure pump truck injects surface-treated quartz sand and a slow-release activation system (mass ratio 40:1) into the annulus and outer formation of the wellbore, forming a dense, conductive, high-permeability zone within a certain radius around the wellbore. Electrodes are fixed to the packer and connected to the conductive layer, forming the anode and cathode of the reservoir electrolysis cell. A wire is used to connect the downhole electrodes to the surface power supply system. The treatment depth is generally 2.0m, determined by the CO2 partial pressure at the wellhead.

[0105] (4) Applying voltage to stimulate the proliferation and metabolism of methanogens and their symbiotic microorganisms

[0106] A micro-electric field is created by applying a -1.0V voltage to the electrolytic cell in the oil reservoir through the ground power supply system. Within this micro-electric field, methanogenic bacteria and their symbiotic microorganisms release nutrients and redox substances through a slow-release activation system. These substances then react with CO2 flowing through the reaction cell, producing CO2, H2CO3, and HCO3-. - Carbon in various forms is converted into microbial cells or methane gas.

[0107] (5) Monitoring CO2 content during well opening

[0108] The CO2 partial pressure at the wellhead was tested for five consecutive months after well opening. The test results are shown below. Figure 3 During the five-month trial run, the CO2 partial pressure remained stable below 0.0021 MPa.

[0109] Corrosion evaluation experiments were conducted using Class D rods and N80 pipes, and the results are shown in Table 3 below. The test results show that the corrosion rate of the pipeline was significantly reduced after the treatment measures were implemented, achieving the desired experimental results.

[0110] Table 3. Corrosion rates of Class D rods and N80 rods after 72 hours of corrosion at 79℃.

[0111]

[0112]

[0113] Example 4

[0114] Overview of Carbon Dioxide Flooding Test Block D in a Certain Oil Production Plant of Shengli Oilfield: Reservoir temperature 88℃, formation pressure 15.1MPa, oil layer thickness 6.8m, permeability 836×10⁻⁶. -3 μm 2 The formation water salinity reached 18640 mg / L. Carbon dioxide flooding was implemented in this block in 2018, achieving good field application results and increasing the recovery rate by 6.1% in stages. However, the current wellhead CO2 partial pressure has reached 1.3 × 10⁻⁶ mg / L. -2 The wellhead production fluid showed signs of corrosion and perforation at a pressure of MPa. Molecular biotechnology analysis revealed the presence of methanogenic microorganisms such as *Methanococcus marinei*, *Small methanogenic oval*, *Mammillaria palmiformis*, *Thermoautotrophic Methanococcus*, and *Dystrophococcus martensii*, with concentrations reaching 5.6 × 10⁻⁶. 3 cells / mL, 2.7×10 3 cells / mL, 1.5×10 3 cells / mL, 8.0×10 2 cells / mL, 5.9 × 10 2 The method of this invention enhances the carbon sequestration capacity of CO2-enhanced oil reservoirs and reduces their recovery rate. The specific steps are as follows:

[0115] (1) Screening of target reservoirs

[0116] The selection criteria for the target reservoirs are as follows: reservoirs undergoing CO2 flooding or sequestration have a CO2 partial pressure at the well production end greater than 2.1 × 10⁻⁶. -3 MPa, reservoir temperature less than 90℃, presence of one or more of the following: marine methanococci, short methanoid oval bacteria, palm oil methanoid sac bacteria, thermoautotrophic methanococci, Martensii octopus, and thermophilic methanogens.

[0117] The reservoir temperature in test area D was 88℃, and the CO2 partial pressure at the well production end reached 1.3×10⁻⁶. -2 The pressure is MPa, and the pipeline has shown signs of perforation. The reservoir in the test area contains methanogenic microorganisms such as *Methanococcus marinei*, *Small methanogenic oval*, *Malus palmiformis*, *Thermoautotrophic Methanococcus*, and *Dystrophococcus martensii*. Test area D meets the reservoir screening criteria of this invention and can be used to implement this invention.

[0118] (2) Preparation of sustained-release activation system

[0119] Dissolve 3% sodium alginate / polyethylene glycol (mass ratio 1:1) in deionized water at 65℃, then add 0.2% activated carbon and stir until homogeneous. Add 6% ammonium chloride and dipotassium hydrogen phosphate and stir until homogeneous. Add 2% electron donor and stir until homogeneous to obtain a mixed solution. After cooling to room temperature, use a peristaltic pump to dropwise add the above mixed solution into a 2% crosslinking agent solution at a pump rate of 0.5 ml / min. The mass ratio of CaCl2 to glutaraldehyde in the crosslinking agent is 1:1. After curing for 1 hour, filter out the particles, wash with physiological saline, and obtain sustained-release activation system particles with an average particle size of 50 μm.

[0120] (3) Constructing a microbial electrolysis cell and injecting a slow-release activation system

[0121] Quartz sand was heated to 120°C and then mixed with a polymer, with the polymer accounting for 3% of the quartz sand volume. During thorough mixing, the polymer melted and coated the surface of the quartz sand. Subsequently, hexamethylenetetramine and calcium stearate were added to solidify the polymer and disperse the quartz sand particles, with the amounts of hexamethylenetetramine and calcium stearate accounting for 0.4% of the quartz sand volume. After cooling to room temperature, the quartz sand was sieved to obtain a polymer-coated conductive material.

[0122] A single tubing string is used to lower all sand control equipment into the well. A specialized packer divides the well into upper and lower sections. At the surface, a high-pressure pump truck injects surface-treated quartz sand and a slow-release activation system (mass ratio 30:1) into the annulus and outer formation of the wellbore, forming a dense, conductive, high-permeability zone within a certain radius around the wellbore. Electrodes are fixed to the packer and connected to the conductive layer, forming the anode and cathode of the reservoir electrolysis cell. A wire is used to connect the downhole electrodes to the surface power supply system. The treatment depth is generally 1.8m, determined by the CO2 partial pressure at the wellhead.

[0123] (4) Applying voltage to stimulate the proliferation and metabolism of methanogens and their symbiotic microorganisms

[0124] A micro-electric field is created by applying a -0.9V voltage to the electrolytic cell in the oil reservoir through the ground power supply system. Within this micro-electric field, methanogenic bacteria and their symbiotic microorganisms release nutrients and redox substances through a slow-release activation system. These substances then react with CO2 flowing through the reaction tank, producing CO2, H2CO3, and HCO3-. - Carbon in various forms is converted into microbial cells or methane gas.

[0125] (5) Monitoring CO2 content during well opening

[0126] The CO2 partial pressure at the wellhead was tested continuously for three months after well opening. The test results are shown below. Figure 4 During the three-month trial run, the CO2 partial pressure remained stable below 0.0021 MPa.

[0127] Corrosion evaluation experiments were conducted using Class D rods and N80 pipes, and the results are shown in Table 4 below. The test results show that the corrosion rate of the pipeline was significantly reduced after the treatment measures were implemented, achieving the desired experimental results.

[0128] Table 4. Corrosion rates of Class D rods and N80 rods after 72 hours of corrosion at 88℃.

[0129]

Claims

1. A method for improving the carbon fixation capacity of oil reservoirs using microbial electrosynthesis, characterized in that, Includes the following steps: (1) Screening of target reservoirs; (2) Preparation of the sustained-release activation system; (3) Construction of microbial electrolysis cells in the near-wellbore zone of oil wells; (4) Injection of the sustained-release activation system; (5) Electrolytic cell loading voltage; (6) Monitor CO2 content during well opening; The composition and mass components of the sustained-release activation system described in step (2) are as follows: 2-4 parts embedding agent; 2-4 parts of crosslinking agent; Activator 4-8 parts; 2-4 electronic donors; 80-90 parts deionized water; The encapsulating agent is one or more of sodium alginate, polyethylene glycol, and activated carbon; the crosslinking agent is one or more of glutaraldehyde and calcium chloride; the activator is one or more of ammonium chloride, ammonium nitrate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; the activator is ammonium nitrate or dipotassium hydrogen phosphate. The preparation method of the sustained-release activation system described in step (2) is as follows: (21) Dissolve the embedding agent in deionized water at 65-70℃ and stir until homogeneous; (22) Next, add the activator and stir until homogeneous; then add the electron donor and stir until homogeneous to obtain a mixed solution; (23) After cooling to room temperature, the above mixed solution is added to the crosslinking agent using a peristaltic pump, cured for 1-3 hours, then the particles are filtered out and washed with physiological saline to obtain the sustained-release activation system.

2. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 1, characterized in that, The screening criteria for the target reservoir mentioned in step (1) are as follows: (11) CO2 flooding or sequestration of the reservoir; (12) The CO2 partial pressure at the producing end of the oil well in the reservoir is greater than 2.1 × 10⁻⁶. -3 MPa, reservoir temperature less than 90℃; (13) The reservoir contains one or more of the following: methanococcus marinum, short methanoids, palm oil methanoids, thermoautotrophic methanococcus, Martensia malathiformis, and thermophilic methanogens.

3. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 1, characterized in that, The microbial electrolysis cell described in step (3) consists of a ground-based solar power generation system, wires, a perovskite anode electrode and its conductive material, and a carbon-based cathode electrode and its conductive material.

4. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 3, characterized in that, The ground-mounted solar power generation system includes solar panels, batteries, and a controller.

5. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 3, characterized in that, The perovskite anode electrode and carbon-based cathode electrode are fixed on the packer and connected to the ground-based solar power generation system by wires.

6. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 3, characterized in that, The conductive materials of the perovskite anode and carbon-based cathode are prepared by coating the surface of quartz sand with one or more of the following polymers: polyacetylene, polyphenylene oxide, and polyaniline.

7. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 6, characterized in that, The size of the quartz sand is determined based on the formation sand size of the specific oil well being implemented, and the average particle size of the selected quartz sand is 2 to 5 times the average particle size of the formation sand.

8. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 1, characterized in that, The method for constructing the near-wellbore microbial electrolysis cell in step (3) is as follows: (31) Use a single tubing string to lower all sand control equipment into the well and use a packer to divide the oil well into upper and lower sections; (32) A high-pressure pump truck is used on the ground to squeeze the conductive material into the annulus of the oil casing and the formation outside the wellbore, forming a dense, conductive, and highly permeable zone around the wellbore. The electrode is fixed on the packer and connected to the conductive layer. (33) Construct the anode and cathode to form an electrolytic cell; use wires to connect the downhole electrodes to the ground-based solar power generation system.

9. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 1, characterized in that, The injection method of the slow-release activation system in step (4) is as follows: after mixing the slow-release activation system with the surface-treated quartz sand, it is squeezed into the formation when constructing the near-wellbore zone electrolytic cell of the oil well. The mass ratio of the slow-release activation system to the quartz sand is 1:20~50.

10. The method for improving reservoir carbon fixation capacity using microbial electrosynthesis as described in claim 1, characterized in that, The electrolytic cell voltage in step (5) is -0.8 to -1V.

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