Coal microbial gasification method for simulating in-situ coal seam environment in laboratory

Abstract

The invention relates to the field of coal fluidized mining, in particular to a coal microbial gasification method for simulating an in-situ coal seam environment in a laboratory, which sequentially comprises the following steps: (1) preparing a coal measure rock sample; (2) forming an injection channel; (3) culturing microorganisms; (4) loading stress and temperature; (5) nutrient solution injection; (6) effect inspection; according to the coal microorganism gasification method for simulating the in-situ coal seam environment in the laboratory, by simulating the rock stratum where the coal seam is located and the ground stress environment, the influence of mineral substances separated out of the rock stratum on microorganism growth and the influence of ground stress on gas-liquid transmission are studied, laboratory tests are closer to the in-situ environment, and the laboratory data accuracy is improved; and the technology is promoted to be transferred to the site.

Description

Technical Field

[0001] The invention relates to the field of fluidized coal mining, in particular to a coal microbial gasification method for simulating an in-situ coal seam environment in a laboratory. Background Art

[0002] my country's coal industry faces the technical challenge of how to efficiently recover legacy coal resources that are difficult to mine economically and develop new mining methods for deep coal resources. Studies have shown that using in-situ microbial communities or artificially domesticated composite microorganisms, coal can be gradually degraded and converted into methane, thereby realizing in-situ mining of coalbed methane. The core principle of microbial gasification of coal is to inject specific nutrient solutions and microorganisms into coal seams, and convert coal into methane through fermentation under anaerobic conditions for mining. This technology is particularly suitable for unmined residual coal and in-situ coal seams, providing an innovative solution for the efficient utilization of coal resources.

[0003] The generation process of coalbed methane occurs in a coal seam environment with complex physical and chemical properties and multiphase interactions, mainly including factors such as high pressure, different temperatures, the distribution of different mineral components, and the structure of coal seam microcracks. The existing microbial gasification method injects specific nutrient solutions and microorganisms into the coal seam, and utilizes the anaerobic degradation of coal to convert it into methane, thereby realizing the extraction of coalbed methane. However, the existing experimental equipment has significant limitations in simulating the complex environment deep in the coal seam, resulting in a gap between the experimental results and the actual coalbed methane generation process, affecting the generation efficiency and recovery rate of coalbed methane. Specifically, the existing technology faces the following three main problems: First, the type and distribution of rock minerals in the coal seam have an important influence on the interaction between the coal-microorganism reaction solution. Some dissolved substances or precipitates in the mineral components (such as sulfides, carbonates, etc.) may change the chemical properties of the reaction solution, thereby affecting the metabolic pathways of microorganisms and the rate of methane production. Existing equipment is difficult to reproduce this complex mineral-reaction solution interaction, resulting in low efficiency of the microbial gasification process; secondly, the high-pressure environment deep in the coal seam has an important impact on the physical structure of the coal and its interaction with microorganisms. Under high-pressure conditions, the pore structure of the coal may be compressed, affecting the permeability of the gas and the contact efficiency with microorganisms. However, the existing experimental equipment has failed to effectively simulate the impact of high pressure on the structure of the coal seam, resulting in difficulty for the gas to fully contact the coal body, which in turn affects the generation of methane; finally, the generation of coalbed methane not only depends on the reaction between coal and microorganisms, but is also affected by the effective transmission between the gas and liquid phases. Under high pressure conditions, the solubility, transmission rate and contact efficiency of the gas-liquid interface will be significantly reduced. Especially in the process of coalbed methane generation, methane must be fully dissolved in the liquid phase and migrate to the recoverable area through microcracks. However, existing equipment is difficult to simulate this complex gas-liquid transmission process, resulting in low efficiency of gas dissolution and migration in the liquid phase, which ultimately affects the release and recovery of methane. Therefore, it is urgent to develop experimental equipment that can accurately simulate the rock minerals, high pressure conditions, temperature changes and gas-liquid transmission effects in the coalbed environment, so as to optimize the microbial gasification process and improve the generation rate and recovery efficiency of coalbed methane. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of unrealistic simulation and inaccurate test data in coalbed methane generation experiments in the prior art, and to propose a coal microbial gasification method that simulates the in-situ coal seam environment in the laboratory. This method reproduces the complex environment in the coal-bearing strata through systematic operating steps, thereby enhancing the coalbed methane generation and gas-liquid transmission effects under laboratory conditions.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment, characterized in that it comprises the following steps:

[0007] Step 1: Preparation of coal series rock samples:

[0008] A coal-bearing sedimentary rock sample is selected and processed into a core specimen with a shape suitable for the inner cavity of a microbial reactor. The core specimen is cut into two sub-core specimens of the same size, and a coaxial blind hole is processed at the center position of the cut surface of the sub-core specimen. The coal sample is filled into the coaxial blind hole and compacted;

[0009] Step 2: Forming the injection channel:

[0010] A diversion hole is drilled in the center of the other side of one of the sub-core specimens, the diversion hole is connected to the coaxial blind hole of the sub-core specimen, and then the two sub-core specimens are re-bonded to form a composite core body, and the two coaxial blind holes are connected;

[0011] Step 3: Microbial culture:

[0012] Select and cultivate microbial strains suitable for anaerobic conditions and capable of effectively degrading coal samples to ensure the survival and metabolic activity of the microbial strains in subsequent high pressure and high temperature environments;

[0013] Step 4: Stress and temperature loading:

[0014] The composite rock core body is placed in the inner cavity of the microbial reactor for experiment, and the diversion hole is kept at the liquid inlet of the microbial reactor. During the experiment, the composite rock core body is subjected to axial pressure and confining pressure by a testing machine, and the temperature is precisely controlled to simulate the actual multi-directional stress state and temperature environment of the coal seam;

[0015] Step 5: Injection of culture medium and microbial solution:

[0016] At the liquid inlet of the microbial reactor, culture medium and microbial liquid are regularly injected to ensure that the microorganisms can continuously obtain nutrients and promote methane production;

[0017] Step 6: Effect test:

[0018] The generated gas samples are collected from the gas outlet of the microbial reactor at set time intervals and their components are analyzed. Through a control experiment, a control sample that does not adopt the method of the present invention but has the same conditions is used as a reference to compare the differences in daily gas production, total gas production and other coalbed methane generation indicators between the two, so as to study the gas generation and diffusion laws of coal-bearing rock formations under a high-pressure and temperature-controlled environment.

[0019] As a further preferred solution, in step one, the composition and size of coal-bearing rock samples can be selected according to demand, and the size of the through cavity can be freely adjusted according to the research focus.

[0020] As a further preferred solution, in step 2, the material used to bond the two sub-core specimens is epoxy resin glue.

[0021] As a further preferred solution, in step three, the microbial strain can be selected from fermentation bacteria or methanogens, and the coal sample can be used as its metabolic raw material, that is, the coal is converted into methane and other soluble small molecular organic matter through microbial activity to achieve an efficient gasification process.

[0022] As a further preferred solution, in step four, the range of loading pressure is controlled within the compressive strength range of the selected coal-bearing rock (within the uniaxial compressive strength range of the selected coal-bearing rock, the maximum generally does not exceed 30 MPa) so as to truly simulate the multi-directional stress environment of the coal seam.

[0023] As a further preferred embodiment, the microbial reactor comprises a high temperature and high pressure resistant stainless steel cavity wall, an upper pressure head, and a lower pressure head; the high temperature and high pressure resistant stainless steel cavity wall is a cylindrical structure with upper and lower ends opening, and the interior is hollow, the upper pressure head and the lower pressure head are partially inserted into the upper and lower ends opening of the high temperature and high pressure resistant stainless steel cavity wall, respectively, the upper pressure head and the lower pressure head are respectively provided with sealing rings with the high temperature and high pressure resistant stainless steel cavity wall, and the upper pressure head and the lower pressure head are both provided with a channel connected to the high temperature and high pressure resistant stainless steel cavity wall;

[0024] The inner wall of the high temperature and high pressure resistant stainless steel cavity wall is provided with a confining pressure cavity and an elastic film, the outer wall is provided with a temperature-controlled electric heating sleeve, and the outer wall is also provided with a confining pressure pipe connected to the internal space;

[0025] The lower pressure head has a liquid inlet pipe connected to its internal channel on the outside, and a lower switch is provided on the liquid inlet pipe; the upper pressure head has an air outlet pipe connected to its internal channel on the outside, and an upper switch is provided on the air outlet pipe;

[0026] The microbial reactor is placed between the upper platform and the lower platform of the test machine.

[0027] As a further preferred embodiment, the elastic film is a fluororubber or PTFE composite film.

[0028] Beneficial Effects

[0029] The present invention proposes a method for coal microbial gasification that simulates the in-situ coal seam environment in the laboratory, aiming to accurately reproduce the stress and gas-liquid transmission conditions of the coal seam. The core of this method is to place the coal sample in a liquid environment containing microorganisms and wrap it in sedimentary rocks to simulate the potential influence of rock minerals on the coal-microorganism system, so as to obtain experimental results that are closer to the actual coalbed methane generation; at the same time, axial pressure and confining pressure are applied by the equipment to dynamically reproduce the multi-directional stress state of the underground coal seam, so that the experimental environment is closer to the actual coal seam; in addition, the device is equipped with a precise temperature control system to maintain high-pressure temperature conditions suitable for microbial metabolism. By fully simulating the physical environment of the coal seam, this method significantly improves the reliability of the experiment and the accuracy of the results, providing effective experimental support for coalbed methane mining technology.

[0030] The present invention aims to improve the generation efficiency and recovery rate of coal-bed methane by accurately simulating the complex environment of the ground stress of coal-bearing strata, deeply studying the influence of mineral precipitation under stress on microbial metabolism, and the diffusion law of coal-bed methane under in-situ stress conditions. By controlling the pressure, temperature, mineral composition and gas-liquid transmission conditions, the contact between gas and coal rock mass is effectively enhanced, thereby accelerating the generation of methane and improving its release efficiency. This method not only improves the efficiency of the microbial gasification process, but also provides a more efficient and controllable technical solution for coal-bed methane extraction. This method provides a scientific basis for the development of coal-bed methane resources and is of great significance to improving the efficiency of coal-bed methane extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flow chart of coal series rock sample preparation;

[0032] Figure 2 It is a schematic diagram of the cross-section of the microbial reactor structure;

[0033] Figure 3 It is the overall schematic diagram of the microbial reactor system;

[0034] Figure 4 This is a schematic diagram of the sealing ring installation details;

[0035] In the accompanying drawings: 1: core specimen; 2: sub-core specimen; 3: coaxial blind hole; 4: diversion hole; 5: composite core body; 6: high temperature and high pressure resistant stainless steel cavity wall; 7: upper pressure head; 8: lower pressure head; 9: sealing ring; 10: confining pressure cavity; 11: elastic film; 12: confining pressure tube 13: temperature-controlled electric heating sleeve; 14: upper switch; 15: lower switch; 16: upper platform of the testing machine; 17: lower platform of the testing machine. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0037] The present invention provides a method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment, comprising the following steps:

[0038] Step 1: Preparation of coal series rock samples:

[0039] After selecting coal-bearing sedimentary rock samples, detailed physical and chemical property analyses are performed on them, including porosity, permeability, mineral composition, etc.;

[0040] A coal-series sedimentary rock sample is selected and processed into a core specimen 1 with a shape suitable for the inner cavity of a microbial reactor. The core specimen 1 is cut into two sub-core specimens 2 of the same size. A coaxial blind hole 3 is processed at the center position of the cut surface of the sub-core specimen 2. The coal sample is filled into the coaxial blind hole 3 and compacted to facilitate subsequent fluid transmission and stress loading.

[0041] Further optimize the processing technology of core specimens according to the characteristics of coal-bearing sedimentary rock samples. For example, for rock samples with low porosity, use micro-drilling technology to create tiny pores on the surface of core specimens to increase the contact area between coal samples and microorganisms and improve gasification efficiency.

[0042] Step 2: Forming the injection channel:

[0043] A guide hole 4 is drilled in the center of the other side of one of the sub-core specimens 2, and the guide hole 4 is connected to the coaxial blind hole 3 of the sub-core specimen 2. Then, the two sub-core specimens 2 are re-bonded to form a composite core body 5, and the two coaxial blind holes 3 are connected to ensure effective penetration and distribution of the culture medium and the nutrient solution;

[0044] When processing coaxial blind holes and guide holes, high-precision CNC processing technology is used to ensure the dimensional accuracy and surface finish of the holes, and reduce fluid transmission resistance and microbial attachment obstacles;

[0045] Step 3: Microbial culture:

[0046] Select and cultivate microbial strains suitable for anaerobic conditions and capable of effectively degrading coal samples to ensure the survival and metabolic activity of the microbial strains in subsequent high pressure and high temperature environments;

[0047] Step 4: Stress and temperature loading:

[0048] The composite rock core body 5 is placed in the inner cavity of the microbial reactor for experiment, and the diversion hole 4 is kept at the liquid inlet of the microbial reactor. During the experiment, the composite rock core body 5 is subjected to axial pressure and confining pressure by a testing machine, and the temperature is precisely controlled to simulate the actual multi-directional stress state and temperature environment of the coal seam;

[0049] Step 5: Injection of culture medium and microbial solution:

[0050] At the liquid inlet of the microbial reactor, culture medium and microbial liquid are regularly injected to ensure that the microorganisms can continuously obtain nutrients and promote methane production;

[0051] Optimized injection strategy for culture medium and microbial culture liquid: Add an appropriate amount of bicarbonate as a buffer to the culture medium to maintain a stable pH environment required for microbial growth, and add specific growth-promoting factors, such as vitamins such as vitamin B (including B1, B2, B6, B12, etc.), biotin, folic acid, etc., which are components of coenzymes or cofactors necessary for the growth of many microorganisms, participate in the metabolism of microorganisms, and promote their growth and reproduction. Metal ions such as iron, manganese, zinc, and copper can also be added. They are components or activators of the active centers of many enzymes and play an important role in the growth and metabolism of microorganisms. For example, iron ions are components of cytochromes, catalase, etc., and participate in the respiration and electron transfer processes of microorganisms. Enhance the activity of microorganisms and their dispersibility in the pores of coal samples. For the injection of microbial culture liquid, pulse injection technology is used. According to the growth cycle and metabolic rate of microorganisms, high-concentration culture liquid is injected intermittently to improve the colonization efficiency of microorganisms in coal samples and the degradation effect on coal, and promote methane generation.

[0052] Step 6: Effect test:

[0053] The generated gas samples are collected from the gas outlet of the microbial reactor at set time intervals and their components are analyzed. Through a control experiment, a control sample that does not adopt the method of the present invention but has the same conditions is used as a reference to compare the differences in daily gas production, total gas production and other coalbed methane generation indicators between the two, so as to study the gas generation and diffusion laws of coal-bearing rock formations under a high-pressure and temperature-controlled environment.

[0054] Improvement measures for gas collection and analysis: The collected gas is transported to a gas chromatography-mass spectrometry analyzer (GC-MS) for component analysis. Using real-time online monitoring technology, gas samples are automatically collected and analyzed at short intervals (such as 1 hour), which can not only accurately determine the content of major gases such as methane, but also detect trace amounts of other organic and inorganic gas components, and fully understand the laws of gas generation and diffusion.

[0055] Structural improvement and performance enhancement of the microbial reactor: The high temperature and high pressure resistant stainless steel cavity wall of the microbial reactor is surface treated, and special coating technology (such as ceramic coating) is used to enhance its corrosion resistance and high temperature and high pressure resistance, and reduce the erosion and chemical reaction of minerals on the cavity wall.

[0056] In step 1 of the present invention, coal-bearing rock samples of different components and sizes can be selected according to needs, and the size of the through cavity can be freely adjusted according to the research focus.

[0057] Adjustment method:

[0058] 1. Adjust according to the properties of the coal sample: If the permeability of the coal sample is low, the size of the through cavity can be appropriately increased to increase the channel area for fluid transmission and reduce the fluid flow resistance; if the pore structure of the coal sample is complex and small, a larger cavity is also required to ensure the effective penetration of the culture medium and nutrient solution.

[0059] 2. Adjust according to the purpose of the experiment: If the focus is on studying the diffusion and distribution of microorganisms in coal samples, through cavities of different sizes can be designed, such as setting up a series of gradually increasing cavities to observe the diffusion of microorganisms at different spatial scales. If the focus is on the impact of changes in the mechanical properties of coal samples under high pressure on microbial gasification, the cavity size can be appropriately reduced to increase the effective force-bearing area of ​​the coal sample while ensuring a certain fluid transmission capacity.

[0060] 3. Adjustment in combination with the simulated environment: When simulating the deep coal seam environment, due to the high pressure on the deep coal seam, the cavity size can be appropriately reduced to be closer to the dense structure of the actual coal seam; when simulating the shallow coal seam environment, the pressure is relatively small, and the cavity size can be appropriately increased to make the fluid transmission closer to the actual situation.

[0061] The impact of adjustment methods:

[0062] 1. Fluid transmission and nutrient distribution: Increasing the size can speed up the transmission, expand the penetration range, and facilitate the uniform distribution of nutrients. Otherwise, it may lead to obstructed transmission and uneven distribution, affecting the microorganisms' acquisition of nutrients.

[0063] 2. Microbial growth and metabolism: Appropriate size promotes microbial reproduction, growth and metabolism, enabling them to better contact with coal samples and improve degradation efficiency; too large or too small a size can easily lead to inhibition of growth rate and metabolic activity, uneven distribution of microorganisms, and insufficient contact with coal samples.

[0064] 3. Coal sample mechanics and gas production effect: The size affects the force and internal stress distribution of the coal sample, changes its mechanical properties, and also acts on the internal pressure and temperature distribution. The appropriate size is conducive to stable gas production, while the unreasonable size hinders the stable development of the gas production reaction and affects the gas production effect.

[0065] In step 2, the material used to bond the two sub-core specimens 2 is epoxy resin glue, which has excellent waterproof properties and can also provide high strength and chemical resistance.

[0066] In step three, the microbial strains may be fermentation bacteria or methanogens, and the coal sample may be used as its metabolic raw material, that is, the coal is converted into methane and other soluble small molecular organic matter through microbial activity to achieve an efficient gasification process.

[0067] In step 4, the range of loading pressure is controlled within the compressive strength range of the selected coal-bearing rock so as to truly simulate the multi-directional stress environment of the coal seam.

[0068] With this technical solution, after the sample is pressurized and temperature-controlled, the microbial solution and the in-situ coal seam liquid environment are injected into the coal-bearing rock. Based on the principle of stress-fluid interaction in coal-bearing strata, the present invention accurately reproduces the multi-directional stress and complex temperature underground to ensure that the experimental process is consistent with the actual environment. The gasification process is initiated by injecting microbial solution to make it consistent with the metabolic pathway of anaerobic bacteria, and the in-situ stress conditions are maintained by long-term pressurization to ensure the authenticity and stability of microbial metabolic activities and gas generation processes.

[0069] The present invention can be used in conjunction with a microbial reactor, and the composite rock core body 5 can be placed in the microbial reactor, and the electro-hydraulic servo universal testing machine can be used in conjunction with a temperature-controlled electric heating jacket to perform heating and pressurizing operations. The range of loading pressure is controlled within the compressive strength range of the selected coal-bearing rock, so as to truly simulate the multi-directional stress environment of the coal seam.

[0070] Current microbial reactors have significant deficiencies in simulating the environment of coal-bearing strata. Coal-bearing strata are subject to complex geostress deep underground, and the minerals in the rock formations may be cracked or dissolved due to the stress, gradually releasing minerals such as iron, magnesium, and potassium. These minerals penetrate into the coal seams as water, which not only affects the structure of the coal seams, but may also interfere with the function and stability of the microbial community, thereby significantly affecting the growth and metabolism of microorganisms. However, due to structural limitations, traditional microbial reactors are difficult to restore the multi-directional stress state that coal-bearing strata are subjected to, and are unable to simulate the release and migration process of minerals under high pressure. Therefore, there are deficiencies in the reliability and closeness of the reaction results.

[0071] The microbial reactor of the present invention comprises a high temperature and high pressure resistant stainless steel chamber wall 6, an upper pressure head 7, and a lower pressure head 8; the high temperature and high pressure resistant stainless steel chamber wall 6 is a cylindrical structure with upper and lower ends opened and hollow inside, the upper pressure head 7 and the lower pressure head 8 are partially inserted into the upper and lower ends of the high temperature and high pressure resistant stainless steel chamber wall 6, respectively, and a sealing ring 9 is provided between the upper pressure head 7 and the lower pressure head 8 and the high temperature and high pressure resistant stainless steel chamber wall 6, and a channel communicating with the high temperature and high pressure resistant stainless steel chamber wall 6 is provided in the upper pressure head 7 and the lower pressure head 8;

[0072] The inner wall of the high temperature and high pressure resistant stainless steel cavity wall 6 is provided with a confining pressure cavity 10 and an elastic film 11, the outer wall is provided with a temperature control electric heating sleeve 13, and the outer wall is also provided with a confining pressure pipe 12 connected to the internal space;

[0073] The lower pressure head 8 has a liquid inlet pipe connected to its internal channel on the outside, and a lower switch 15 is provided on the liquid inlet pipe. The upper pressure head 7 has an air outlet pipe connected to its internal channel on the outside, and an upper switch 14 is provided on the air outlet pipe.

[0074] The microbial reactor is placed between the upper platform 16 and the lower platform 17 of the test machine.

[0075] The electro-hydraulic servo universal testing machine injects liquid into the confining pressure chamber 10 through an oil pump. The surface of the confining pressure chamber 10 is covered with a high-performance elastic film 11 (such as fluororubber or PTFE composite film). The elastic film 11 transmits the confining pressure to the reactor cavity, thereby ensuring that the stress environment in the reactor is consistent with the multi-directional stress conditions of the in-situ coal seam.

[0076] Embodiment:

[0077] 1. Collect siltstone samples from the roof of the coal seam in the target area and process them into cylindrical core specimens 1 with a diameter of 50 mm and a height of 100 mm.

[0078] Second, the core specimen 1 is cut into two equal-sized sub-core specimens 2 (each with a diameter of 50 mm and a height of 50 mm) along its axis centerline. A coaxial blind hole 3 with a diameter of 10 mm and a depth of 30 mm is machined in the center of the circular end face of each sub-core specimen 2.

[0079] 3. Fill the pores 3 of the two sub-core specimens 2 with coal samples and compact them. A guide hole 4 with a diameter of 2 mm and a depth of 20 mm is machined at the center of the bottom surface of one of the sub-core specimens 2 (the side connected to the coaxial blind hole) to ensure that it is connected to the pore 3 of 10×30 mm.

[0080] Fourth, align the bottom surfaces of the two sub-core specimens 2 and glue them together to form a complete composite core body 5 with a height of 100 mm. At this time, a connected cavity with a diameter of 10 mm and a depth of 60 mm is formed inside.

[0081] 5. Put a set of sealing rings 9 on the upper half of the lower pressure head 8, and clamp the lower opening of the high temperature and high pressure stainless steel cavity wall 6 with the lower pressure head 8. Place the composite core body 5 vertically in the cavity wall 6, fix another set of sealing rings 9 on the upper part of the upper pressure head, clamp the upper pressure head 7 with the stainless steel cavity wall 6, and ensure that the sealing ring 9 completely enters the cavity 6 to ensure the airtightness of the entire system. Next, install the temperature-controlled electric heating sleeve 13 on the outer surface of the cavity wall 6;

[0082] 6. Place the end of the flow guide hole 4 of the composite core body 5 vertically on the lower platform 17 of the test machine along the central axis, start the temperature-controlled electric heating sleeve 13, and set the reaction temperature to 35°C to simulate conditions suitable for microbial metabolism. The liquid is pumped into the hydraulic chamber (not shown) connected to the lower platform 17 of the test machine and the confining pressure chamber 10 connected to the confining pressure pipe 12 by a hydraulic pump (not shown in the figure) to achieve triaxial stress on the composite core body 5. Stop pressurizing when the set pressure is reached to ensure that the composite core body 5 in the experiment is in a simulated in-situ stress environment.

[0083] 7. Open the lower switch 15, and regularly inject the culture medium and microbial liquid into the connected cavity through the diversion hole 4. After the injection is completed, close the lower switch 15 to ensure that the system is airtight and the reaction continues. Then, open the upper switch 14, collect the generated gas samples at the set time interval, and perform component analysis to study the gas generation and diffusion laws of coal-bearing rock formations under high pressure and temperature control environment.

[0084] The present invention develops a method for coal microbial gasification that can accurately simulate the in-situ environment of coal-bearing strata in the laboratory, so as to overcome the limitations of the prior art in terms of pressure simulation and the influence of mineral release. By applying axial pressure and confining pressure to the coal sample during the experiment, the present invention can dynamically reproduce the complex stress state of the coal-bearing strata, and combined with the precise control of temperature and gas-liquid transmission, the microbial reactor is closer to the actual coal seam environment. This method can not only simulate the migration process of elements to the coal seam after the cracking and dissolution of rock minerals, but also ensure that microorganisms efficiently metabolize to generate methane in a high-pressure environment. By optimizing the gas-liquid transmission conditions and the control of multi-directional stress, the present invention provides a reliable experimental basis and technical support for the efficient gasification and mining of deep coal resources and legacy coal seams.

[0085] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment, characterized in that: The following steps are involved: Step 1: Preparation of coal series rock samples: A coal-bearing sedimentary rock sample is selected and processed into a core specimen (1) having a shape suitable for the inner cavity of a microbial reactor; the core specimen (1) is cut into two sub-core specimens (2) of the same size; a coaxial blind hole (3) is processed at the center position of the cut surface of the sub-core specimen (2); a coal sample is filled into the coaxial blind hole (3) and compacted; Step 2: Forming the injection channel: A flow guide hole (4) is drilled in the center of the other side of one of the sub-core specimens (2), the flow guide hole (4) is connected to the coaxial blind hole (3) of the sub-core specimen (2), and then the two sub-core specimens (2) are re-bonded to form a composite core body (5), and the two coaxial blind holes (3) are connected; Step 3: Microbial culture: Select and cultivate microbial strains suitable for anaerobic conditions and capable of effectively degrading coal samples to ensure the survival and metabolic activity of the microbial strains in subsequent high pressure and high temperature environments; Step 4: Stress and temperature loading: The composite rock core body (5) is placed in the inner cavity of the microbial reactor for experiment, and the diversion hole (4) is kept at the liquid inlet of the microbial reactor. During the experiment, the composite rock core body (5) is subjected to axial pressure and confining pressure by a testing machine, and the temperature is precisely controlled to simulate the actual multi-directional stress state and temperature environment of the coal seam; Step 5: Injection of culture medium and microbial solution: At the liquid inlet of the microbial reactor, culture medium and microbial liquid are regularly injected to ensure that the microorganisms can continuously obtain nutrients and promote methane production; Step 6: Effect test: The generated gas samples are collected from the gas outlet of the microbial reactor at set time intervals and their components are analyzed. Through a control experiment, a control sample that does not adopt the method of the present invention but has the same conditions is used as a reference to compare the differences in daily gas production, total gas production and other coalbed methane generation indicators between the two, so as to study the gas generation and diffusion laws of coal-bearing rock formations under a high-pressure and temperature-controlled environment.

2. The method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment according to claim 1, characterized in that: In the step 1, the composition and size of the coal-bearing rock sample can be selected according to the requirements, and the size of the coaxial blind hole (3) can be freely adjusted according to the research focus.

3. The method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment according to claim 1, characterized in that: In the step 2, the material used to bond the two sub-core specimens (2) is epoxy resin glue.

4. The method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment according to claim 1, characterized in that: In step three, the microbial strains may be fermentation bacteria or methanogens, and the coal sample is used as its metabolic raw material, that is, the coal is converted into methane and other soluble small molecular organic matter through microbial activity to achieve an efficient gasification process.

5. The method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment according to claim 1, characterized in that: In the step 4, the range of the loading pressure is controlled within the compressive strength range of the selected coal-bearing rock, so as to truly simulate the multi-directional stress environment of the coal seam.

6. The method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment according to claim 1, characterized in that: The microbial reactor comprises a high temperature and high pressure resistant stainless steel cavity wall (6), an upper pressure head (7), and a lower pressure head (8); the high temperature and high pressure resistant stainless steel cavity wall (6) is a cylindrical structure with upper and lower ends opened and a hollow interior; the upper pressure head (7) and the lower pressure head (8) are respectively partially inserted into the upper and lower ends of the high temperature and high pressure resistant stainless steel cavity wall (6); a sealing ring (9) is respectively provided between the upper pressure head (7) and the lower pressure head (8) and the high temperature and high pressure resistant stainless steel cavity wall (6); and a channel communicating with the high temperature and high pressure resistant stainless steel cavity wall (6) is provided in the upper pressure head (7) and the lower pressure head (8); The inner wall of the high temperature and high pressure resistant stainless steel cavity wall (6) is provided with a confining pressure cavity (10) and an elastic film (11), the outer wall is provided with a temperature control electric heating sleeve (13), and the outer wall is also provided with a confining pressure pipe (12) communicating with the internal space; The lower pressure head (8) has a liquid inlet pipe connected to its internal channel on the outside, and a lower switch (15) is provided on the liquid inlet pipe; the upper pressure head (7) has an air outlet pipe connected to its internal channel on the outside, and an upper switch (14) is provided on the air outlet pipe; The microbial reactor is placed between the upper platform (16) and the lower platform (17) of the test machine.

7. The method for coal microbial gasification in a laboratory simulating an in-situ coal seam environment according to claim 6, characterized in that: The elastic film (11) is a fluororubber or PTFE composite film.

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