Method and system for in situ conversion of methane from hydrogen stored in deep aquifers

Abstract

The present application relates to the technical field of underground energy storage and conversion, in particular to a method and system for converting hydrogen stored in deep aquifer into methane in situ, which comprises the following steps: screening a target deep aquifer, drilling and completing the injection well and the production well, and adopting a double-layer completion structure of tubing and casing for the injection well to form an annular channel; injecting hydrogen into the target deep aquifer through the tubing and injecting carbon dioxide through the annular channel at the same time, so that the carbon dioxide forms a physical isolation layer in the annular channel, the volume ratio of hydrogen to carbon dioxide is 4:1, and the injection pressure of carbon dioxide is higher than that of hydrogen; using the natural catalytic conditions of the reservoir to make the mixed hydrogen and carbon dioxide generate in-situ methanation reaction to produce methane; regulating the reservoir environment to guide the migration and accumulation of methane; and extracting the methane through the production well. The present application realizes safe transportation of hydrogen and self-provision of carbon source, solves the problem of hydrogen storage and transportation, and reduces the cost of methanation.

Description

Technical Field

[0001] This invention relates to the field of underground energy storage and conversion technology, specifically a method and system for in-situ conversion of hydrogen storage and methane in deep aquifers. Background Technology

[0002] Against the strategic backdrop of global energy transition and the "dual-carbon" goal, hydrogen, as a zero-carbon, highly efficient clean energy carrier, is regarded as a core medium for optimizing the energy structure and absorbing renewable energy. However, the large-scale commercial application of hydrogen energy faces two major bottlenecks: First, hydrogen has low density, is prone to leakage, and has strong diffusion, and poses a risk of hydrogen embrittlement and corrosion to metal materials. The technical threshold and economic cost of ground high-pressure storage and transportation or liquid storage and transportation remain high, and long-distance transportation is extremely uneconomical. Second, the end-use infrastructure for hydrogen energy is inadequate. The existing energy transmission and distribution system, centered on natural gas pipelines, cannot be directly adapted to the large-scale transportation of hydrogen, and the investment in end-use adaptation and transformation is huge.

[0003] Converting hydrogen into methane via the Sabatier reaction (CO2 + 4H2 → CH4 + 2H2O) is an effective technological approach to solving the aforementioned challenges. Methane, as a core gas source in the existing energy system, can be transported on a large scale, at low cost, and over long distances using existing natural gas pipeline networks. Furthermore, its energy density is far higher than that of hydrogen, and its storage, transportation, and application technologies are fully mature. However, traditional hydrogen methanation processes are all completed in ground-based plants, requiring dedicated fixed-bed catalytic reactors, high-temperature and high-pressure heating equipment, and gas purification and separation devices. This not only results in high equipment investment and operating energy consumption but also faces problems such as high-temperature catalyst deactivation and high regeneration costs, making it difficult to adapt to the distributed, large-scale conversion needs of renewable energy-based hydrogen production.

[0004] Meanwhile, deep aquifers, as natural underground storage sites with wide distribution, huge storage capacity, and excellent caprock sealing, have been widely used globally in the construction of underground natural gas storage facilities and CO2 geological sequestration projects. If deep aquifers can be used as natural underground reactors to convert injected hydrogen and carbon dioxide into methane in situ within the reservoir, the challenges of large-scale hydrogen storage and transportation, as well as the high cost of surface methanation processes, can be solved simultaneously. Furthermore, it can achieve geological sequestration and resource utilization of CO2, resulting in significant economic and environmental benefits.

[0005] However, existing underground in-situ methanation technologies generally employ a single wellbore and a single gas injection method, which has several technical drawbacks: First, when hydrogen is injected directly through the wellbore, prolonged contact with the wellbore casing can easily cause hydrogen embrittlement damage, significantly increasing the risk of wellbore leakage and posing a safety hazard of hydrogen leaking to the surface and causing combustion and explosion. Second, the single injection method cannot achieve a precise and simultaneous ratio of hydrogen and carbon dioxide, easily leading to insufficient carbon source supply and low hydrogen conversion efficiency. Moreover, most technologies rely on naturally occurring dissolved inorganic carbon in the reservoir as a carbon source, and the total amount of carbon source is limited, making it impossible to achieve large-scale continuous conversion. Third, existing technologies have weak control over the underground reaction process, failing to achieve precise control over reaction kinetics and methane migration and enrichment, resulting in low methane accumulation efficiency and recovery rate, making it difficult to achieve industrial application.

[0006] In view of the many shortcomings of the existing technologies, there is an urgent need to develop a deep aquifer hydrogen storage in-situ conversion to methane technology that combines safety, efficiency and economy, in order to solve the industry pain points of high safety risks in hydrogen well transportation, insufficient carbon source supply, high cost of surface methanation, and weak underground reaction control capabilities. Summary of the Invention

[0007] The purpose of this invention is to provide a method and system for in-situ conversion of hydrogen storage and methane in deep aquifers, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution.

[0009] A method for in-situ conversion of hydrogen storage in deep aquifers into methane includes the following steps: Step S1: Preliminary reservoir screening and well site preparation.

[0010] Target deep aquifers meeting the reaction conditions were screened, with core screening indicators including: reservoir depth, permeability, porosity, temperature and pressure conditions, caprock sealing, and the presence of catalytic minerals / microorganisms. Drilling and completion of injection and production wells were completed in the target area. Injection wells employed a double-layer completion structure with casing and tubing, forming two independent injection channels: the tubing and the annulus. Two independent injection control systems were constructed on the surface, connected to the tubing and annulus respectively, for independently controlling the injection of hydrogen and carbon dioxide. The surface hydrogen / carbon dioxide storage system, injection pump set, pressure / flow control system, and produced gas processing system were built and commissioned. A sealing pressure test was conducted on the entire pipeline, wellhead, and wellbore to ensure no leakage risk.

[0011] Step S2: Dual-channel collaborative injection.

[0012] First, carbon dioxide is injected into the wellbore annulus through the annulus injection line. After a stable pressure field and a continuous fluid isolation section are formed in the annulus, hydrogen is then injected into the reservoir through the tubing injection line. Both gases are injected synchronously and continuously throughout the process. During injection, hydrogen is injected into the target deep aquifer through the tubing, while carbon dioxide is injected into the target deep aquifer through the annulus. The carbon dioxide forms a continuous physical isolation layer in the annulus, completely isolating hydrogen from direct contact with the wellbore casing, thus fundamentally preventing hydrogen embrittlement damage and wellbore leakage risks. Hydrogen and carbon dioxide only achieve full diffusion and uniform mixing after entering the reservoir pores through the bottom perforation section, avoiding safety risks caused by premature reactions within the wellbore.

[0013] During injection, an independent flow control system strictly controls the injection volume ratio of hydrogen to carbon dioxide to 4:1, precisely matching the stoichiometric ratio of the Sabatier reaction (CO2 + 4H2 → CH4 + 2H2O) to ensure full utilization of the reactants. Two independent closed-loop pressure control systems control the injection pressures of hydrogen and carbon dioxide respectively, always maintaining a carbon dioxide injection pressure 0.5-2 MPa higher than the hydrogen injection pressure. This pressure differential control prevents hydrogen from entering the annulus, ensuring the stability and isolation effect of the annular isolation layer.

[0014] Step S3: In-situ methanation reaction.

[0015] Utilizing the inherent natural catalytic conditions of the target deep aquifer reservoir, under the reservoir's native temperature and pressure environment, the mixed hydrogen and carbon dioxide fully contact the catalytically active sites within the reservoir pores, resulting in an in-situ methanation reaction that continuously generates methane and water as a byproduct. Depending on the reservoir conditions, an appropriate catalytic pathway can be selected, or a dual pathway can be used synergistically to maximize the methanation reaction efficiency.

[0016] (1) Chemical catalysis pathway: For aquifers with a depth of 1000-2000m and a reservoir temperature of 60-120℃, iron, nickel and cobalt-based transition metal sulfides or oxides naturally occurring in the reservoir rocks are used as heterogeneous catalysts to catalyze the Sabatil reaction efficiently without the need for additional chemical catalysts.

[0017] (2) Biocatalytic pathway: For aquifers with a depth of 500-1500m and a reservoir temperature of 30-60℃, the naturally occurring hydrogen-producing methanogens in the reservoir are utilized. The microbial community is activated by injecting activators, and efficient methanation under low temperature conditions is achieved through microbial metabolic reactions.

[0018] Step S4: Controlled methane migration and enrichment into reservoirs.

[0019] By coordinating and regulating the reservoir's physicochemical environment with multiple parameters, a stable and controllable pressure gradient is established between the injection well and the production well, creating a directional pressure field within the reservoir. The generated methane has a density far lower than that of formation water. Driven by both buoyancy and the pressure field, it migrates directionally from the reaction zone around the injection well to the trap area at the structural high point of the reservoir, ultimately accumulating within the trap to form a high-purity methane gas reservoir, thus avoiding resource losses caused by the disorderly diffusion of methane.

[0020] The core operations of parameter control include: synergistically adjusting the injection pressure, injection rate, and injection volume ratio of hydrogen and carbon dioxide to control the rate and process of the methanation reaction; adjusting the bottom hole flowing pressure and production rate of the production well to control the distribution of the reservoir pressure field, thereby precisely controlling the migration direction and enrichment area of ​​methane.

[0021] Step S5: Methane extraction and surface processing.

[0022] Once the methane concentration in the enriched area reaches the extraction standard, the enriched methane is extracted to the surface through production wells. The extracted methane-containing gas mixture first enters the surface gas purification system, where it undergoes dehydration, decarbonization, and removal of heavy hydrocarbons and impurities in sequence. After the methane purity of the product gas meets the pipeline transportation standard, it is directly integrated into the existing natural gas pipeline network for storage, transportation, and end-use.

[0023] Step S6: Real-time monitoring and dynamic closed-loop control throughout the entire process.

[0024] A real-time monitoring system is deployed throughout the wellbore of both injection and production wells and within the reservoir, constructing a closed-loop control system encompassing data acquisition, inversion analysis, command issuance, parameter adjustment, and effect verification. Distributed fiber optic sensors and permanent downhole pressure gauges monitor reservoir temperature, pressure, and formation strain in real time. Regular fluid sampling and analysis detect the concentration ratios of H2, CO2, and CH4 in the formation. Additional monitoring of microbial community structure and activity is conducted for the biocatalytic pathway. All monitoring data is transmitted back to the ground control center in real time. Numerical simulation models are used to invert the fluid transport patterns, reactant consumption status, methane enrichment, and reaction progress within the reservoir. Based on the inversion results, hydrogen and carbon dioxide injection parameters and production well production parameters are dynamically adjusted to ensure continuous and stable reaction, maximizing methane accumulation efficiency and resource utilization.

[0025] The present invention also provides a system for in-situ conversion of hydrogen into methane in deep aquifers, used to implement the above-mentioned method, comprising: a dual-channel injection unit, including a hydrogen storage module, a carbon dioxide storage module, a tubing injection pipeline connected to the injection well tubing, an annulus injection pipeline connected to the injection well annulus, two independent injection control systems, and independent pressure control module and flow control module; the two independent injection control systems are respectively connected to the tubing and the annulus, and are used to independently control the injection pressure, injection rate and injection ratio of hydrogen and carbon dioxide.

[0026] The reaction unit is naturally formed by the reservoir space of the target deep aquifer. The natural catalytic minerals and hydrogen-loving methanogens in the reservoir provide the catalytic conditions for the reaction, and the pore space of the reservoir provides the reaction site.

[0027] The production unit includes a production wellbore, surface production pipelines, extraction control module, and gas purification module, which are used to extract methane enriched in the reservoir to the surface and complete the purification process.

[0028] The monitoring and control unit includes a downhole monitoring module, a surface control center, and an execution and control module. The downhole monitoring module is connected to the surface control center via signals. The surface control center is connected to the dual-channel injection unit and the production unit via the execution and control module, respectively, to realize real-time transmission of monitoring data, intelligent analysis and injection of reaction status, and dynamic control of production parameters.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Safety isolation: The present invention adopts a dual-channel coordinated injection method of hydrogen injection in the tubing and carbon dioxide injection in the annulus. The carbon dioxide in the annulus forms a continuous physical isolation layer, completely isolating the direct contact between hydrogen and the well casing, thus avoiding the casing damage problem caused by hydrogen embrittlement from the root. At the same time, through precise pressure differential control of "the carbon dioxide injection pressure is always 0.5-2 MPa higher than the hydrogen injection pressure", the risk of hydrogen entering the annulus is eliminated, which greatly reduces the safety hazards of hydrogen well leakage and explosion, and realizes the full-process safety control of underground hydrogen injection.

[0030] 2. Simultaneous supply and precise ratio of carbon source: In this invention, the carbon dioxide injected into the annulus serves both as a safety protection function for wellbore isolation and as the core carbon source for the methanation reaction. It does not rely on naturally occurring dissolved inorganic carbon in the reservoir, thus overcoming the bottleneck of insufficient carbon source in existing technologies and enabling large-scale continuous conversion. At the same time, through precise control of the injection volume ratio of 4:1, it perfectly matches the stoichiometric ratio of the Sabatil reaction, significantly improving the hydrogen conversion rate and resource utilization rate.

[0031] 3. Controllable reaction: The injection pressure and rate of hydrogen and carbon dioxide are controlled independently, and the mixing ratio can be dynamically adjusted according to the reservoir reaction state to achieve precise front-end control of the methanation reaction.

[0032] 4. Natural catalysis: Utilizing naturally occurring catalytic minerals such as iron, nickel, and cobalt in reservoir rocks, no additional catalysts are required, significantly reducing operating costs.

[0033] 5. Solve the problem of hydrogen storage and transportation: Inject hydrogen directly into deep aquifers to avoid surface storage and transportation; after being converted into methane underground, it can be transported using existing natural gas pipelines, achieving safe and low-cost hydrogen energy transportation.

[0034] 6. Utilizing underground natural reactors: There is no need to build surface catalytic reactors. By utilizing the mineral catalysis and microbial activity of the reservoir itself, hydrogen can be methanated in situ, which greatly reduces investment and operating costs.

[0035] 7. Synergistic effect of CO2 resource utilization and geological storage: This invention injects industrial CO2 as a reaction raw material underground, converts it into methane through methanation to achieve resource utilization, and the unreacted CO2 is geologically stored in deep aquifers for a long time, taking into account both economic and environmental benefits and helping to achieve the "dual carbon" goal. Attached Figure Description

[0036] Figure 1 This is a complete flowchart of the method of the present invention.

[0037] Figure 2 This is a schematic cross-sectional view of the deep aquifer of the present invention.

[0038] Figure 3 This is a schematic diagram of the process flow and equipment layout of the present invention.

[0039] Figure 4 This is a schematic diagram of the wellbore structure and gas injection state of the dual-channel injection method of the present invention.

[0040] Figure 5 This is a schematic diagram of the reaction enrichment of methane according to the present invention.

[0041] Figure 6 This is a schematic diagram of methane enrichment and extraction according to the present invention.

[0042] Figure 7 This is a diagram showing the layout and feedback control logic of the real-time monitoring system of the present invention.

[0043] Figure 8 This is a kinetic curve of the in-situ methanation reaction of the present invention.

[0044] In the diagram: 1. Caprock; 2. Deep aquifer reservoir; 3. H2 gas tank; 4. CO2 gas tank; 5. Injection well; 6. Tubing; 7. Permanent downhole pressure gauge; 8. Fiber optic sensor; 9. Surface control center; 10. Production well; 11. CO2; 12. H2; 13. Enrichment zone; 14. Reaction zone; 15. CH4; 16. H2O. Detailed Implementation

[0045] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0046] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0047] The core inventive concept of this invention is to solve the safety risks of hydrogen wellbore transportation and the problem of simultaneous carbon source supply by using a dual-channel synergistic injection technology of hydrogen injection through tubing and carbon dioxide injection through annulus; to construct an underground natural reactor by utilizing the natural mineral catalysis and microbial catalysis conditions of deep aquifers to achieve in-situ efficient methanation of hydrogen and carbon dioxide; and to achieve precise control of the reaction process and methane enrichment through a closed-loop monitoring and dynamic regulation system, ultimately realizing safe and low-cost storage and transportation of hydrogen and large-scale synthesis of methane.

[0048] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0049] Figure 1 This is a complete flowchart of the present invention, which is described below in conjunction with... Figure 1 Each step is described in detail.

[0050] Example 1 (Chemical Catalysis Pathway)

[0051] This embodiment provides a method for in-situ conversion of hydrogen storage in deep aquifers into methane using a chemical catalytic pathway and dual-channel synergistic injection technology.

[0052] 1) Preliminary reservoir screening and well site preparation.

[0053] First, target deep aquifers that meet the reaction conditions are selected. For example... Figure 2As shown, the deep aquifer structure involved in this invention includes a caprock 1 at the top, a bottom layer at the bottom, and a deep aquifer reservoir 2 located between the caprock 1 and the bottom layer. A deep aquifer with a depth of 1000-2000 meters, good permeability, a temperature range of 60-120℃, and a pressure range of 10-25 MPa is selected as the target reservoir. The reservoir rocks contain natural catalytic minerals, such as nickel pyrite ((Ni,Fe)9S8), pyrite (FeS2), or cobalt-containing sulfides, which can provide catalytically active sites for the Sabatil reaction.

[0054] like Figure 2 and Figure 3 As shown, injection well 5 and production well 10 are drilled in the target area, forming a certain well network layout. Injection well 5 adopts a double-layer structure of casing and tubing 6, with an annulus formed between the casing and tubing 6. Two independent injection control systems are built on the surface, connected to tubing 6 and the annulus respectively, to independently control the injection pressure and flow rate of hydrogen and carbon dioxide.

[0055] like Figure 3 As shown, H2 storage tank 3 and CO2 storage tank 4 are installed on the ground to store hydrogen and carbon dioxide, respectively. Pressure tests are conducted on the ground pipelines and wellheads to ensure that the pipelines, joints, and wellheads are leak-free and puncture-free.

[0056] 2) Dual-channel collaborative injection stage.

[0057] like Figure 4 As shown, this step employs a dual-channel coordinated injection method. Industrial by-product hydrogen (H212) with a purity of approximately 95% is injected into the target reservoir through tubing 6. The injection pressure is maintained 3-8 MPa higher than the original reservoir pressure, and the injection rate is dynamically adjusted based on reservoir permeability and pressure response (e.g., an initial injection rate of 5 tons / hour). Simultaneously, supercritical carbon dioxide (CO211) with a purity of approximately 95% is injected into the target reservoir through the annulus. The injection pressure is controlled to be 0.5-2 MPa higher than the hydrogen injection pressure. The carbon dioxide forms a continuous physical isolation layer in the annulus, completely isolating hydrogen from direct contact with the well casing, thus fundamentally preventing hydrogen embrittlement damage and wellbore leakage risks. Hydrogen and carbon dioxide only achieve full diffusion and uniform mixing after entering the reservoir pores through the bottom perforated section, avoiding safety risks caused by premature reactions within the wellbore.

[0058] The injection volume ratio of H212 and CO211 is strictly controlled at 4:1 to precisely match the stoichiometry of the Sabatier reaction (CO2 + 4H2 → CH4 + 2H2O). After entering the reservoir at the bottom of the well, the two mix to form a uniform reaction gas mass.

[0059] 3) In-situ methanation reaction stage.

[0060] Under reservoir temperature (approximately 90°C) and pressure (approximately 15 MPa), the mixed hydrogen (H212) and carbon dioxide (CO211) diffuse in the reservoir and come into contact with the reservoir rocks. Natural nickel pyrite in the reservoir rocks acts as a catalyst, catalyzing the Sabatil reaction (Equation 1): CO2 + 4H2 → CH4 + 2H2O (Equation 1).

[0061] As the reaction proceeds, hydrogen and CO2 are gradually consumed, methane (CH4) is gradually generated, and water (H2O) is generated as a byproduct. Figure 8 The graph shows the reactant consumption and methane generation kinetics of the in-situ methanation reaction in the method of this invention, illustrating the consumption trends of H212 and CO211 and the generation trend of CH4 during the reaction.

[0062] 4) Controlled methane migration and enrichment into reservoirs.

[0063] like Figure 5 As shown, by coordinating the injection pressure and rate of hydrogen and CO211 in injection well 5, and the bottomhole flowing pressure of production well 10, a stable pressure gradient is established between injection well 5 and production well 10, forming a directional pressure field within the reservoir. The generated methane (CH415) has a density much lower than formation water. Driven by both buoyancy and the pressure gradient, it migrates directionally from the reaction zone 14 near injection well 5 to the enrichment zone 13 at the higher part of the reservoir structure, eventually accumulating in the trap structure at the top of the reservoir to form a high-purity methane gas reservoir. The byproduct water (H2O16) remains in the reservoir pores.

[0064] 5) Methane extraction and surface treatment.

[0065] like Figure 6 As shown, when the methane concentration in enrichment zone 13 reaches ≥90%, production well 10 is opened for methane extraction. The extraction rate is controlled by adjusting the valves of production well 10, and the enriched methane (CH415) is extracted to the surface. The extracted methane-containing gas mixture enters the surface gas purification system, where it undergoes molecular sieve dehydration, amine decarbonization, and low-temperature separation to remove impurities. The final product gas has a methane purity of ≥95%, and after meeting pipeline transportation standards, it is directly connected to the natural gas pipeline network.

[0066] 6) Real-time monitoring and dynamic closed-loop control.

[0067] like Figure 7As shown, distributed fiber optic sensors 8 are deployed throughout the wellbore of injection well 5 and production well 10, and permanent downhole pressure gauges 7 are installed at the bottom of both wells to construct a real-time downhole monitoring system. The distributed fiber optic sensors 8 monitor the reservoir temperature field distribution and formation strain data in real time, while the permanent downhole pressure gauges 7 monitor the pressure changes in the wellbore and reservoir in real time. The monitoring data is transmitted back to the ground control center 9 in real time via wired transmission.

[0068] Meanwhile, formation fluid samples are collected every 7 days using downhole sampling devices and sent to the laboratory for gas chromatography analysis to detect the concentration ratios of H212, CO211, and CH415, assessing the reaction progress and methanation efficiency. Ground control center 9 uses numerical simulation models to invert the fluid migration patterns, reactant consumption status, and methane enrichment within the reservoir based on monitoring data, diagnosing the sustainability of the reservoir reaction and abnormal operating conditions.

[0069] like Figure 7 As shown, the dynamic control rules are as follows: If an abnormal increase in H212 concentration or an H2 / CH4 volume ratio > 0.5 is detected in the reservoir, indicating a lag in the methanation reaction or excessive hydrogen injection, the ground control center 9 automatically issues a control command to increase the injection amount of CO211 through the annular injection pipeline or reduce the hydrogen injection rate to restore the 4:1 stoichiometric ratio and promote the full conversion of the remaining hydrogen. If H212 or CO211 is detected to prematurely exceed the production well 10, the injection rate is immediately reduced or the production well 10 is shut down to maintain pressure until the reactants have fully reacted before resuming production. If an abnormal increase in reservoir pressure is detected, the injection rates of hydrogen and CO211 are simultaneously reduced to avoid damage to the integrity of the caprock 1. Through this closed-loop control system, injection and production parameters are dynamically optimized to ensure the continuous and stable progress of the reaction and maximize the efficiency of methane accumulation.

[0070] Example 2 (Biocatalytic Pathway)

[0071] This embodiment is basically the same as Example 1, with the core difference being that the in-situ methanation reaction adopts a biocatalytic pathway, which is suitable for medium- and low-temperature reservoir conditions. The following only describes the differences from Example 1; the similarities will not be repeated.

[0072] 1) Preliminary reservoir screening and microbial activation.

[0073] A medium-deep aquifer with a depth of 500-1500 meters and a temperature range of 30-60℃ was selected as the target reservoir. Hydrogen-loving methanogenic bacteria (such as Methanobacterium and Methanococcus) naturally exist in the water of this reservoir.

[0074] Before injecting hydrogen and CO2, a microbial activator is first injected into the reservoir through the tubing 6 or annulus of injection well 5. The activator formulation includes: phosphate (0.1-0.5 g / L), trace elements (such as Ni) 2+ Co 2+ MoO4 2- The total concentration of the activator should be ≤0.01 g / L, and the nitrogen source should be 0.1-0.3 g / L (e.g., NH4Cl). After the activator is injected, the well should be shut in and cultured for 2-4 weeks to allow the hydrophilic methanogen population to proliferate.

[0075] 2) Dual-channel synergistic injection and in-situ methanation.

[0076] After activation, the same dual-channel injection method as in Example 1 (e.g.) is used. Figure 4 As shown), hydrogen is injected through oil pipe 6 and CO211 is injected through the annulus, with the injection volume ratio strictly controlled at 4:1. Hydrogen-producing methanogens use hydrogen as an electron donor to reduce CO211 to methane (as shown in Formula 1).

[0077] The reaction can be carried out efficiently under lower temperature (e.g., 40°C) and pressure conditions with lower energy consumption under microbial catalysis.

[0078] 3) Real-time monitoring and dynamic control.

[0079] The controlled migration, enrichment, and purification processes for methane are basically the same as in Example 1. Additional microbial activity monitoring is added, with formation fluid samples collected every 15 days. Microbial community structure and abundance are analyzed using 16S rRNA high-throughput sequencing technology to dynamically assess biocatalytic activity. If a decrease in the abundance of hydrogen-producing methanogens or a reduction in methanation efficiency is detected, microbial activators are promptly injected through injection well 5 to maintain the metabolic activity and reaction efficiency of the microorganisms.

[0080] Example 3 (Dynamic Proportional Adjustment)

[0081] This embodiment is basically the same as Embodiment 1, except that the injection ratio of hydrogen and CO2 is dynamically adjusted around a stoichiometric ratio of 4:1 based on real-time monitoring results.

[0082] like Figure 7As shown, when a high H2 concentration is detected in the reservoir (e.g., an H2 / CH4 volume ratio greater than 0.5), the ground control center automatically instructs an increase in the annular injection rate of CO211, raising the CO211 injection volume to 1.2 times the stoichiometric ratio (i.e., adjusting the volume ratio to approximately 3.3:1) to promote the conversion of remaining hydrogen. Conversely, when a high CO211 concentration is detected, the hydrogen injection rate is appropriately increased or the CO211 injection rate is decreased to restore and maintain the optimal 4:1 ratio. Through this dynamic adjustment, the optimal ratio of reactants in the reservoir is always maintained, improving methanation efficiency and resource utilization.

[0083] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for in situ conversion of methane to hydrogen in deep aquifer storage, characterized by, Includes the following steps: S1. Select target deep aquifers that meet the reaction conditions, complete the drilling and completion of injection wells and production wells, and build the surface injection and production systems. The injection well adopts a double-layer completion structure of tubing and casing to form an annulus channel between the tubing and casing. Two independent injection control systems are built on the surface and connected to the tubing and annulus respectively. S2. Hydrogen is injected into the target deep aquifer through the tubing, and carbon dioxide is injected into the target deep aquifer simultaneously through the annulus, so that the carbon dioxide forms a continuous physical isolation layer in the annulus to prevent direct contact between the hydrogen and the well casing; the injection volume ratio of hydrogen to carbon dioxide is 4:1, and the injection pressure of carbon dioxide is always higher than that of hydrogen. S3. Utilizing the natural catalytic conditions inherent in the target deep aquifer reservoir, under the original temperature and pressure environment of the reservoir, the mixed hydrogen and carbon dioxide undergo an in-situ methanation reaction to generate methane and water as a byproduct. S4. Regulate the reservoir physicochemical environment, establish a pressure gradient field between the injection well and the production well, guide the generated methane to migrate directionally to the structural high and enrich it in the trapped area; S5. Methane from the enriched area is extracted to the surface through production wells, purified, and then connected to the natural gas pipeline network.

2. The method for in-situ conversion of hydrogen storage and methane in deep aquifers according to claim 1, characterized in that, The in-situ methanation reaction in step S3 includes chemical catalytic pathways and / or biocatalytic pathways; The chemical catalytic pathway is as follows: using iron, nickel, and cobalt-based transition metal sulfides or oxides naturally occurring in reservoir rocks as heterogeneous catalysts, and catalyzing the reaction to produce methane at reservoir temperatures of 60-120℃. The biocatalytic pathway is as follows: using naturally occurring and artificially activated hydrogen-producing methanogens in the reservoir, methane is generated through microbial metabolic reactions at a reservoir temperature of 30-60℃.

3. The method for in-situ conversion of hydrogen storage and methane in deep aquifers according to claim 2, characterized in that, When using the biocatalytic pathway, before step S2, a microbial activator is injected into the target deep aquifer, and the well is shut in for cultivation for 2-4 weeks to activate and proliferate hydrogen-methanogenic bacteria; or during the injection process in step S2, a microbial activator is simultaneously injected into the reservoir. The microbial activator includes at least one of phosphate 0.1-0.5 g / L, nitrogen source 0.1-0.3 g / L, and trace elements ≤0.01 g / L, wherein the trace elements include at least one of nickel ion, cobalt ion, and molybdate ion.

4. The method for in-situ conversion of hydrogen storage and methane in deep aquifers according to claim 1, characterized in that, In step S2, the injection pressure of carbon dioxide is always 0.5-2 MPa higher than that of hydrogen.

5. The method for in-situ conversion of hydrogen storage and methane in deep aquifers according to claim 1, characterized in that, The specific method for regulating the reservoir physicochemical environment in step S4 is to synergistically regulate the injection pressure, injection rate, and injection volume ratio of hydrogen and carbon dioxide, as well as the bottom-hole flowing pressure and production rate of the production well, in order to control the methanation reaction process and form a directional pressure field within the reservoir.

6. The method for in-situ conversion of hydrogen storage and methane in deep aquifers according to claim 1, characterized in that, It also includes step S6: deploying a real-time monitoring system in the wellbore and reservoir of the injection well and production well to monitor reservoir pressure, reservoir temperature, formation strain, fluid composition and microbial activity in real time throughout the entire cycle; the monitoring data is transmitted back to the ground control center in real time, and the reservoir reaction state and fluid migration law are inverted through numerical simulation, and the injection parameters of hydrogen and carbon dioxide and the production parameters of the production well are dynamically adjusted according to the inversion results.

7. The method for in-situ conversion of hydrogen storage and methane in deep aquifers according to claim 6, characterized in that, The real-time monitoring system includes a distributed fiber optic sensing module, a permanent downhole pressure gauge module, and a fluid sampling and analysis module. The distributed fiber optic sensing module is used to monitor reservoir temperature field and formation strain data in real time. The permanent downhole pressure gauge module is used to monitor wellbore and reservoir pressure data in real time. The fluid sampling and analysis module is used to detect formation fluid composition and microbial community structure.

8. A system for in-situ conversion of hydrogen storage and methane in deep aquifers, used to implement the method for in-situ conversion of hydrogen storage and methane in deep aquifers as described in any one of claims 1-7, characterized in that, include: The dual-channel injection unit includes a hydrogen storage module, a carbon dioxide storage module, a tubing injection pipeline connected to the injection well tubing, an annulus injection pipeline connected to the injection well annulus, two independent injection control systems, and independent pressure control modules and flow control modules. The two independent injection control systems are respectively connected to the tubing and the annulus and are used to independently control the injection pressure, injection rate and injection ratio of hydrogen and carbon dioxide. The reaction unit is naturally formed by the reservoir space of the target deep aquifer. The natural catalytic minerals and hydrogen-loving methanogens in the reservoir provide the reaction catalytic conditions, and the reservoir pore space provides the reaction site. The production unit includes a production wellbore, surface production pipelines, extraction control module and gas purification module, which are used to extract methane enriched in the reservoir to the surface and complete the purification process. The monitoring and control unit includes a downhole monitoring module, a surface control center, and an execution and control module. The downhole monitoring module is connected to the surface control center via signals. The surface control center is connected to the dual-channel injection unit and the production unit via the execution and control module, respectively, to realize real-time transmission of monitoring data, intelligent analysis and injection of reaction status, and dynamic control of production parameters.

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