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

Abstract

The present application relates to the field of coal fluidized mining, especially to a coal microbial gasification method for simulating in-situ coal seam environment in laboratory, which comprises the following steps in sequence: (1) preparing coal rock sample; (2) forming injection channel; (3) microbial culture; (4) stress and temperature loading; (5) nutrient solution injection; (6) effect test; the present application proposes a coal microbial gasification method for simulating in-situ coal seam environment in laboratory, which simulates the rock stratum and ground stress environment where the coal seam is located, studies the influence of rock stratum mineral matter on microbial growth and ground stress on gas-liquid transmission, and the laboratory test is closer to in-situ environment, improves the accuracy of laboratory data, and promotes the transfer of the technology to the field.

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 efficiently recovering legacy coal resources that are difficult to mine economically and developing new mining methods for deep coal resources. Research has shown that using in situ microbial communities or artificially domesticated composite microorganisms, coal can be gradually degraded and converted into methane, thereby enabling in situ mining of coalbed methane. The core principle of microbial coal gasification is to inject specific nutrient solutions and microorganisms into the coal seam, and then convert the coal into methane through fermentation under an anaerobic environment 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 micro-cracks. 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 major 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 or precipitated substances (such as sulfides and carbonates) in the mineral composition may alter the chemical properties of the reaction solution, thereby affecting the metabolic pathways of the microorganisms and the rate of methane production. Existing equipment has difficulty reproducing 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 a significant impact on the physical structure of the coal and its interaction with the microorganisms. Under high pressure, the pore structure of the coal may be compressed, affecting the permeability of the gas and the contact efficiency with the microorganisms. However, existing experimental equipment fails to effectively simulate the impact of high pressure on the coal seam structure, resulting in insufficient contact between the gas and the coal body, which in turn affects methane production. Finally, the generation of coalbed methane depends not only on the reaction between the coal and the microorganisms but also on the effective transmission between the gas and liquid phases. Under high-pressure conditions, the solubility of gases, the transmission rate, and the contact efficiency of the gas-liquid interface are significantly reduced. This is especially true during coalbed methane generation, where methane must be fully dissolved in the liquid phase and migrate through microcracks to recoverable areas. However, existing equipment struggles to simulate this complex gas-liquid transmission process, resulting in low gas dissolution and migration efficiency in the liquid phase, ultimately impacting methane release and recovery. Therefore, there is an urgent need to develop experimental equipment that can accurately simulate the effects of rock minerals, high-pressure conditions, temperature changes, and gas-liquid transmission in coalbed environments, thereby optimizing the microbial gasification process and improving coalbed methane generation rate and recovery efficiency. 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 existing technology, 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 by comprising the following steps:

[0007] Step 1: Preparation of coal-bearing rock samples:

[0008] Coal-bearing sedimentary rock samples were selected and processed into core specimens with a shape suitable for the inner cavity of the microbial reactor. The core specimens were cut into two sub-core specimens of the same size. A coaxial blind hole was machined in the center of the cut surface of the sub-core specimens. The coal sample was 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, and the diversion hole is connected to the coaxial blind hole of the sub-core specimen. The two sub-core specimens are then bonded together 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 was placed in the inner cavity of the microbial reactor for the experiment, with the diversion hole kept at the liquid inlet of the microbial reactor. During the experiment, the composite rock core was subjected to axial and confining pressures using a testing machine, and the temperature was 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] Culture medium and microbial liquid are regularly injected into the liquid inlet of the microbial reactor 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 is subjected to 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 the coal-bearing rock sample can be selected according to the needs, 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 option, in step three, the microbial strain can be selected from fermentative 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 option, 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 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 includes 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 opened and a hollow interior, and the upper pressure head and the lower pressure head are partially inserted into the upper and lower end openings of the high-temperature and high-pressure resistant stainless steel cavity wall, respectively. There are sealing rings between the upper pressure head and the lower pressure head and 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 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 outside of the lower pressure head is provided with a liquid inlet pipe connected to its internal channel, and the liquid inlet pipe is provided with a lower switch; the outside of the upper pressure head is provided with an air outlet pipe connected to its internal channel, and the air outlet pipe is provided with an upper switch;

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

[0027] As a further preferred solution, 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 encapsulate 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] This invention aims to improve the generation efficiency and recovery rate of coalbed methane by accurately simulating the complex environment of geostress in coal-bearing strata, conducting in-depth research on the effects of mineral precipitation from rock strata under stress on microbial metabolism, and the diffusion patterns of coalbed methane under in-situ stress conditions. By controlling pressure, temperature, mineral composition, and gas-liquid transmission conditions, the contact between gas and coal rock is effectively enhanced, thereby accelerating methane generation 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 coalbed methane extraction. This method provides a scientific basis for the development of coalbed methane resources and is of great significance to improving the efficiency of coalbed methane extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart for coal-bearing 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 testing machine; 17: lower platform of testing machine. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described 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-bearing rock samples:

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

[0040] A coal-bearing sedimentary rock sample is selected and processed into a core specimen 1 with a shape suitable for the inner cavity of the microbial reactor. The core specimen 1 is then cut into two sub-core specimens 2 of equal size. A coaxial blind hole 3 is machined in the center 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 based on 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 the core specimens to increase the contact area between the coal sample and microorganisms, thereby improving gasification efficiency.

[0042] Step 2: Forming the injection channel:

[0043] A diversion hole 4 is drilled in the center of the other side of one of the sub-core specimens 2. The diversion hole 4 is connected to the coaxial blind hole 3 of the sub-core specimen 2. The two sub-core specimens 2 are then bonded together to form a composite core body 5. The two coaxial blind holes 3 are connected to ensure effective penetration and distribution of the culture medium and 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, reducing 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 5 is placed in the inner cavity of the microbial reactor for experimentation, with the diversion hole 4 kept at the liquid inlet of the microbial reactor. During the experiment, the composite rock core 5 is subjected to axial pressure and confining pressure using 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] Culture medium and microbial liquid are regularly injected into the liquid inlet of the microbial reactor to ensure that the microorganisms can continuously obtain nutrients and promote methane production;

[0051] Optimizing the injection strategy for culture medium and microbial culture: An appropriate amount of bicarbonate should be added to the culture medium as a buffer to maintain the stable pH environment required for microbial growth. Specific growth-promoting factors should also be added. These factors, such as vitamins like the B complex (including B1, B2, B6, and B12), biotin, and folic acid, are essential components of coenzymes or prosthetic groups for many microbial growth and participate in microbial metabolism, promoting 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 a vital role in microbial growth and metabolism. For example, iron ions are components of cytochromes and catalase, participating in microbial respiration and electron transfer. This enhances microbial activity and dispersion within the pores of the coal sample. For microbial culture injection, a pulsed injection technique is employed, intermittently injecting high concentrations of culture according to the microbial growth cycle and metabolic rate. This improves microbial colonization efficiency and coal degradation, thereby promoting methane production.

[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 is subjected to 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] Improvements to gas collection and analysis: Collected gas is fed to a gas chromatography-mass spectrometry (GC-MS) analyzer for component analysis. Using real-time online monitoring technology, gas samples are automatically collected and analyzed at short intervals (e.g., once an hour). This not only accurately measures the content of key gases like methane, but also detects trace amounts of other organic and inorganic gas components, providing a comprehensive understanding of gas generation and diffusion patterns.

[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. Adjustments based on experimental objectives: If the focus is on studying the diffusion and distribution of microorganisms in coal samples, through-hole cavities of varying sizes can be designed, such as a series of gradually larger 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 maintaining a certain fluid transmission capacity.

[0060] 3. Adjustment based on the simulated environment: When simulating the deep coal seam environment, the cavity size can be appropriately reduced due to the high pressure on the deep coal seam to make it 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] Impact of the adjustment method:

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

[0063] 2. Microbial growth and metabolism: Appropriate size promotes microbial reproduction, growth and metabolism, enabling better contact with coal samples and improving 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 two sub-core specimens 2 are bonded together using epoxy resin glue, which has excellent waterproof properties and can also provide high strength and chemical resistance.

[0066] In step three, the microbial strains can be fermentative bacteria or methanogens, using the coal sample as their 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] Using this technical solution, after pressurizing and temperature-controlling the sample, the microbial solution and the in-situ coal seam fluid environment are injected into the coal-bearing rock. Based on the principles of stress-fluid interaction in coal-bearing strata, this method accurately reproduces the multi-directional stresses and complex temperatures found underground, ensuring that the experimental process is consistent with the actual environment. The injection of the microbial solution initiates the gasification process, aligning it with the metabolic pathway of anaerobic bacteria. Long-term pressurization maintains the in-situ stress conditions, ensuring the authenticity and stability of the microbial metabolic activity and gas generation process.

[0069] The present invention can be used in conjunction with a microbial reactor. The composite rock core 5 can be placed in the microbial reactor and heated and pressurized using an electro-hydraulic servo universal testing machine in conjunction with a temperature-controlled electric heating jacket. The loading pressure is controlled within the compressive strength range of the selected coal-bearing rock to realistically 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 minerals in the rock formations may crack or dissolve due to the stress, gradually releasing minerals such as iron, magnesium, and potassium. These minerals penetrate into the coal seams along with water, which not only affects the coal seam structure, 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 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, and the upper pressure head 7 and the lower pressure head 8 are partially inserted into the upper and lower end openings of the high-temperature and high-pressure resistant stainless steel cavity wall 6, respectively. 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 cavity wall 6, and a channel is provided in the upper pressure head 7 and the lower pressure head 8 to communicate with the high-temperature and high-pressure resistant stainless steel cavity wall 6;

[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-controlled electric heating jacket 13, and the outer wall is also provided with a confining pressure pipe 12 communicating with the internal space;

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

[0074] The microbial reactor is placed between the upper platform 16 and the lower platform 17 of the testing 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] Example:

[0077] 1. Collect siltstone samples from the coal seam roof 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 center axis. 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. Machine a diversion hole 4 with a diameter of 2 mm and a depth of 20 mm in the center of the bottom surface of one of the sub-core specimens 2 (the side connected to the coaxial blind hole), ensuring that it is connected to the 10×30 mm pore 3.

[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] Fifth, place 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 to the lower pressure head 8. Place the composite core body 5 vertically inside 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 to the stainless steel cavity wall 6, and ensure that the sealing rings 9 are completely inserted into the cavity 6 to ensure the airtightness of the entire system. Next, install the temperature-controlled electric heating jacket 13 on the outer surface of the cavity wall 6;

[0082] 6. Place the composite rock core 5 with its diversion hole 4 vertically along its central axis on the lower platform 17 of the testing machine. Activate the temperature-controlled electric heating jacket 13 and set the reaction temperature to 35°C to simulate conditions suitable for microbial metabolism. A hydraulic pump (not shown) pumps liquid into a hydraulic chamber (not shown) connected to the lower platform 17 of the testing machine and into the confining pressure chamber 10 connected to the confining pressure tube 12 to apply triaxial stress to the composite rock core 5. Pressurization is stopped when the set pressure is reached to ensure that the composite rock core 5 under test is subjected to a simulated in-situ stress environment.

[0083] 7. Open lower switch 15 and regularly inject culture medium and microbial fluid into the connected cavity through diversion hole 4. After injection, close lower switch 15 to ensure the system is airtight and the reaction continues. Then, open upper switch 14 and collect generated gas samples at set intervals for composition analysis to study the gas generation and diffusion patterns in coal-bearing strata under high-pressure and temperature-controlled conditions.

[0084] The present invention develops a coal microbial gasification method that can accurately simulate the in-situ environment of coal-bearing strata in the laboratory, so as to overcome the limitations of existing technologies in pressure simulation and the influence of mineral release. By applying axial pressure and confining pressure to the coal samples 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 produce 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 embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection 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-bearing rock samples: A coal-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 machined 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 guide hole (4) is drilled in the center of the other side of one of the sub-core specimens (2), the guide hole (4) is connected to the coaxial blind hole (3) of the sub-core specimen (2), and the two sub-core specimens (2) are re-bonded to form a composite core body (5), with the two coaxial blind holes (3) 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 experimentation, 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: Culture medium and microbial liquid are regularly injected into the liquid inlet of the microbial reactor to ensure that the microorganisms can continuously obtain nutrients and promote methane production; Step 6: Effect test: The generated gas samples were collected from the gas outlet of the microbial reactor at set time intervals and their components were analyzed. Through control experiments, the coal microbial gasification method that did not simulate the in-situ coal seam environment in this laboratory and the control samples with the same conditions were used as references to compare the differences in daily gas production, total gas production and other coalbed methane generation indicators between the two methods, in order to study the gas generation and diffusion laws of coal-bearing strata under high-pressure and temperature-controlled environments.

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 needs, 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 fermentative 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 partially inserted into the upper and lower end openings of the high-temperature and high-pressure resistant stainless steel cavity 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 cavity wall (6), and a channel is provided in the upper pressure head (7) and the lower pressure head (8) to communicate with the high-temperature and high-pressure resistant stainless steel cavity wall (6); 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-controlled electric heating jacket (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 testing 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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