Simulation Device and Method for Promoting Coal Seam Biogas Production by Migration of Coal Measure Clay Minerals

Abstract

The present application provides a simulation device and method for promoting coalbed biogas production by the migration of coal-series clay minerals. In this device, the simulation box body includes: a box body structure with an open upper end and a box body cover, and the box body cover is rotatably connected to the open end of the box body structure; an electric heating layer is provided inside the box body structure, and a nitrogen inlet and a liquid-phase product outlet are provided on the box body structure; a specimen holder is located inside the simulation box body, and the outlet of the specimen holder is communicated with the liquid-phase product outlet, the confining pressure port is communicated with the confining pressure pump in the hydraulic fracturing module, and the holder inlet is communicated with the fracturing pump in the hydraulic fracturing module; the holder is used to place a specimen simulating the coal-series formation, the confining pressure pump is used to provide a confining pressure simulating the formation stress to the specimen, and the fracturing pump is used to pump a fracturing fluid containing nutrient solution or exogenous bacteria into the holder; the data acquisition module includes: a liquid-phase collection unit and a gas-phase collection unit, the liquid-phase collection unit is communicated with the liquid-phase product outlet, and the gas-phase collection unit is communicated with the gas-phase product outlet.

Description

Technical Field

[0001] This application relates to the technical field of coalbed methane experiments, and particularly to a simulation device and method for promoting coalbed biogas production by the migration of coal-bearing clay minerals. Background Art

[0002] The coal series refers to a set of sedimentary rock series formed during a certain geological historical period, containing coal seams or coal lines and having genetic connections. The coal series usually consists of strata with different lithologies such as coal seams, mudstones, tight sandstones, and limestones. Coalbed gas is various natural gases occurring in the coal series, including coalbed methane, shale gas, and tight sandstone gas. Coalbed gas is an important part of unconventional natural gas. The development of coalbed gas can not only boost the transformation and upgrading of the coal industry, but also has strategic significance for protecting the ecological environment, improving the energy structure, and ensuring national energy security.

[0003] The technology for enhancing coalbed methane production biologically is to inject nutrient solutions or domesticated exogenous bacterial communities into the coal-bearing strata, and use the metabolic activities of methanogens to increase the biological methane production of coal seams.

[0004] During the hydraulic fracturing process, when the fracturing fluid contacts the roof and floor of the coal seam or the parting in the coal seam, on the one hand, the clay minerals in it will enter with the fracturing fluid and undergo hydration swelling and migration, reducing the formation seepage capacity; on the other hand, during the anaerobic fermentation process of methanogens and coal, the addition of a small amount of clay minerals can greatly improve the metabolic activity of the bacterial community, enhance the utilization rate of organic matter in the coal by the bacterial community, thereby increasing the biological gas production of coalbed methane wells; moreover, the increase in the utilization rate of organic matter by the bacterial community increases the permeability of the coal reservoir to a certain extent, further improving the effect of biological enhancement.

[0005] Therefore, during the process of biologically enhancing the coal series, on the one hand, there are the negative effects of clay mineral swelling and migration, and on the other hand, there is the promoting effect of clay minerals on coalbed biogas production. Therefore, how to evaluate the influence of clay mineral migration on the gas production of coalbed methane wells is of great significance. Summary of the Invention

[0006] The purpose of this application is to provide a simulation device and method for promoting coalbed biogas production by the migration of coal-bearing clay minerals to solve or alleviate the problems existing in the above-mentioned prior art.

[0007] To achieve the above purpose, this application provides the following technical solutions:

[0008] This application provides a simulation device for promoting coal seam biogas production by the migration of coal-bearing clay minerals, including: a simulation box body, a sample holder, a hydraulic fracturing module, and a data acquisition module; the simulation box body includes: a box body structure with an open upper end and a box cover, the box cover is rotatably connected to the open end of the box body structure for sealing the open end of the box body structure; an electric heating layer is provided inside the box body structure, and a nitrogen inlet and a liquid-phase product outlet are provided on the box body structure; wherein, the nitrogen inlet and the liquid-phase product outlet are located at the lower end of the side wall of the box body structure; a gas-phase product outlet is provided on the box cover; the sample holder is located inside the simulation box body, and the outlet of the sample holder is communicated with the liquid-phase product outlet, the confining pressure port of the sample holder is communicated with the confining pressure pump in the hydraulic fracturing module, and the inlet of the sample holder is communicated with the fracturing pump in the hydraulic fracturing module; wherein, the sample holder is used to place a coal-bearing simulation sample simulating the coal-bearing stratum, the confining pressure pump is used to provide a confining pressure simulating the stratum stress to the coal-bearing simulation sample, and the fracturing pump is used to pump a fracturing fluid containing nutrient solution or exogenous bacteria into the sample holder; the upper layer of the coal-bearing simulation sample simulating the coal-bearing stratum is a clay mineral layer, and the lower layer is a coal seam; the data acquisition module includes: a liquid-phase collection unit and a gas-phase collection unit, the liquid-phase collection unit is communicated with the liquid-phase product outlet, and the gas-phase collection unit is communicated with the gas-phase product outlet.

[0009] Preferably, a holder fixing unit is provided inside the box body structure, and the sample holder fixing unit includes: a connecting part and a clamping part; one end of the connecting part is connected to the inner side wall of the box body structure, and the other end is connected to the clamping part; the sample clamping part is a ring structure, and the inner side wall of the ring structure is adapted to the outer side wall of the sample holder.

[0010] Preferably, the sample clamping part includes a first clamping plate and a second clamping plate symmetrically arranged along its central axis plane, both the first clamping plate and the second clamping plate are arc-shaped plates, and both ends of the arc-shaped plates are provided with connecting ear plates in the radial direction, and the connecting ear plates are detachably connected to the end of the connecting part, wherein, the connecting part is located between the connecting ear plate of the first clamping plate and the connecting ear plate of the second clamping plate.

[0011] Preferably, a temperature sensor is further provided inside the simulation box body, the temperature sensor is located on the inner side wall of the box body structure and is far away from the electric heating layer.

[0012] Preferably, the inner side wall and the inner bottom surface of the box body structure are respectively provided with the electric heating layer.

[0013] Preferably, the box body structure is three-layered, the outer layer is made of metal material, the inner layer is made of stainless steel material, and the electric heating layer is located between the outer layer and the inner layer.

[0014] Preferably, the nitrogen inlet is located at the connection between the inner side wall and the inner bottom surface of the box structure; on the box structure, a liquid-phase product outlet is provided near the bottom surface on the side wall opposite to the nitrogen inlet.

[0015] This application also provides a simulation method for promoting coal seam biogas production by coal-bearing clay mineral migration. The simulation device for promoting coal seam biogas production by coal-bearing clay mineral migration described in any of the above embodiments is used to perform biogas production simulation on a coal-bearing simulation sample with a clay mineral formation on the upper layer and a coal seam on the lower layer. The simulation device for promoting coal seam biogas production by coal-bearing clay mineral migration includes: a simulation box, a sample holder, a hydraulic fracturing module, and a data acquisition module; the method includes: drilling a fracturing hole in the clay mineral formation of the selected coal-bearing simulation sample, and inserting a fracturing pipe into the fracturing hole; wherein, one end of the fracturing pipe extends out of the fracturing hole, and the hole wall of the fracturing hole and the fracturing pipe are sealed; placing the coal-bearing simulation sample provided with the fracturing pipe in the sample holder and closing it; opening the confining pressure pump in the hydraulic fracturing module, after the coal-bearing simulation sample in the sample holder is under a set pressure condition, pumping a fracturing fluid containing nutrient solution or exogenous bacteria into the coal-bearing simulation sample through the fracturing pump in the hydraulic fracturing module, and sequentially performing hydraulic fracturing on the upper clay mineral formation and the coal seam; after the hydraulic fracturing is completed, opening the sample holder, exposing the coal-bearing simulation sample in the simulation box, and closing the box cover of the simulation box; filling nitrogen into the simulation box to displace the air in the simulation box; in response to the environmental temperature in the simulation box rising to a set temperature, collecting the gas-phase products and liquid-phase products of the coal-bearing simulation sample.

[0016] Preferably, pumping the fracturing fluid into the coal-bearing simulation sample through the fracturing pump in the hydraulic fracturing module for hydraulic fracturing includes: the starting pump pressure of the fracturing pump is 20 MPa, and the coal-bearing simulation sample is gradually pressurized by the fracturing pump. The pump pressure of the fracturing pump is a constant value, not less than 28 MPa and not higher than 40 MPa; in response to the pressure of the fracturing pump dropping to the starting pump pressure, the hydraulic fracturing of the coal-bearing simulation sample is completed.

[0017] Preferably, filling nitrogen into the simulation box to displace the air in the simulation box includes: after filling nitrogen into the simulation box for 8 to 10 minutes, continuously measuring the composition of the gas-phase products discharged from the gas-phase product outlet in the simulation box by a gas chromatograph for multiple times; in response to the nitrogen content of the gas-phase products measured continuously for multiple times reaching a preset standard, the displacement of the air in the simulation box is completed.

[0018] Beneficial effects:

[0019] In the simulation device for promoting coal seam biogas production by the migration of coal measure clay minerals provided by the embodiments of the present application, the simulation box body includes a box body structure with an open upper end and a box cover. The box cover is rotatably connected to the open end of the box body decoupling stock to seal the open end of the box body structure. An electric heating layer is provided inside the box body structure, and a nitrogen inlet and a liquid-phase product outlet are provided on the box body structure. Both the nitrogen inlet and the liquid-phase product outlet are located at the lower end of the side wall of the box body structure. A gas-phase product outlet is provided on the box cover. Inside the simulation box body, a sample holder is provided. The outlet of the sample holder is communicated with the liquid-phase product outlet, the confining pressure port of the sample holder is communicated with the confining pressure pump in the hydraulic fracturing module, and the inlet of the holder is communicated with the fracturing pump in the hydraulic fracturing module. A coal measure simulation sample simulating the coal measure formation is placed in the sample holder. The confining pressure pump provides a confining pressure simulating the formation stress for the coal measure simulation sample, and the fracturing pump pumps a fracturing fluid containing nutrient solution or exogenous bacteria into the sample holder. The liquid-phase product is collected by the liquid-phase collection unit connected to the liquid-phase product outlet, and the gas-phase product is collected by the gas-phase collection unit connected to the gas-phase product outlet.

[0020] Therefore, during the process of simulating hydraulic fracturing of the coal measure simulation sample, the confining pressure pump provides a confining pressure simulating the formation stress for the coal measure simulation sample; the fracturing pump pumps the fracturing fluid into the sample holder, and hydraulic fracturing is successively carried out on the clay mineral formation and the coal seam of the coal measure simulation sample in the sample holder. Due to the swelling of the clay minerals, they migrate to the coal seam together with the fracturing fluid, causing changes in coal seam biogas production, more truly and effectively simulating the influence of the contact between the bacteria group and the clay minerals in the overlying rock stratum of the coal seam on the gas production effect, and truly reflecting the biological stimulation effect of the swelling and migration of clay minerals on the coal measure formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The schematic diagrams in the specification that form a part of the present application are used to provide a further understanding of the present application. The schematic embodiments and descriptions thereof of the present application are used to explain the present application and do not constitute an improper limitation to the present application. Among them:

[0022] Figure 1 FIG. 1 is a schematic structural diagram of a simulation device for promoting coal seam biogas production by the migration of coal measure clay minerals according to some embodiments of the present application;

[0023] Figure 2 FIG. 2 is a schematic structural diagram of a holder fixing device according to some embodiments of the present application;

[0024] Figure 3 FIG. 3 is a schematic multi-layer structural diagram of a simulation box body according to some embodiments of the present application;

[0025] Figure 4 FIG. 4 is a schematic cross-sectional diagram of a simulation box body according to some embodiments of the present application;

[0026] Figure 5 Schematic diagram of the installation of the electric heating layer provided according to some embodiments of the present application;

[0027] Figure 6 Schematic flow chart of a method for simulating the promotion of coal seam biogas production by the migration of coal-bearing clay minerals provided according to some embodiments of the present application.

[0028] Explanation of reference numerals:

[0029] 1. Nitrogen cylinder; 2. Box structure; 3. Clamp fixing unit; 4. Specimen clamp; 5. Pressure sensor; 6. Temperature sensor; 7. Box cover; 8. Fracturing pump; 9. First regulating valve; 10. Gas-phase product outlet; 11. Second regulating valve; 12. Confining pressure pump; 13. Confining pressure port; 14. Vent port; 15. Liquid chromatograph; 16. Liquid-phase collection unit; 17. Clamp outlet; 18. Nitrogen inlet; 19. Clamp inlet; 20. Electric heating layer; 211. Resistance wire; 212. Crystalline magnesium oxide powder; 201. Outer layer; 202. Inner layer; 301. Connection part; 302. First clamping plate; 303. Bolt fastener; 304. Second clamping plate. Detailed implementation manners

[0030] The present application will be described in detail below with reference to the drawings and in conjunction with embodiments. Each example is provided by way of explanation of the present application rather than limitation of the present application. In fact, those skilled in the art will clearly understand that modifications and variations can be made to the present application without departing from the scope or spirit of the present application. For example, features shown or described as part of one embodiment can be used in another embodiment to yield yet another embodiment. Therefore, it is desirable that the present application include such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0031] The applicant's research found that in the process of evaluating the biological enhancement of coal seams, in the prior art, only physical means were used to increase the permeability of the overlying strata, while ignoring the types of rock minerals contained in the formation itself, and not paying attention to the positive and negative effects of clay mineral swelling and migration on the coal seam biogas production process, making it difficult to truly and effectively reflect the impact of the contact between the microbial community and the clay minerals in the coal seam overlying strata on the biological enhancement effect.

[0032] Based on this, the applicant proposed a simulation device and method for promoting coal seam biogas production by the migration of coal-bearing clay minerals to effectively simulate the impact of hydraulic pressure on the gas production effect of coal-bearing strata under biological means, and more truly and effectively reflect the impact of the contact between the microbial community and the clay minerals in the coal seam overlying strata on the biological enhancement effect.

[0033] As Figures 1 to 5As shown, the simulation device for promoting biogas production in coal seams by the migration of coal-series clay minerals includes: a simulation box body, a sample holder 4, a hydraulic fracturing module, and a data acquisition module.

[0034] The simulation box body includes: a box body structure 2 with an open upper end and a box cover 7. The box cover 7 is rotatably connected to the open end of the box body interface for sealing the open end of the box body structure 2. A gas-phase product outlet 10 is provided on the box cover 7. An electric heating layer 20 is provided inside the box body structure 2. A nitrogen inlet 18 and a liquid-phase product outlet are provided on the box body structure 2, and the nitrogen inlet 18 and the liquid-phase product outlet are located at the lower end of the side wall of the box body structure 2.

[0035] The sample holder 4 is located inside the simulation box body. The holder outlet 17 of the sample holder 4 is communicated with the liquid-phase product outlet. The confining pressure port 13 of the sample holder 4 is communicated with the confining pressure pump 12 in the hydraulic fracturing module. The inlet 19 of the sample holder 4 is communicated with the fracturing pump 8 in the hydraulic fracturing module. A coal-series simulation sample simulating the coal-series stratum is placed in the sample holder 4. Among them, the upper layer of the coal-series simulation sample is a clay mineral stratum, and the lower layer is a coal seam. The confining pressure pump 12 provides the confining pressure simulating the stratum stress for the coal-series simulation sample, and the fracturing pump 8 pumps the fracturing fluid containing nutrient solution or exogenous bacteria into the sample holder 4 of the coal-series simulation sample.

[0036] The data acquisition module includes: a liquid-phase collection unit 16 and a gas-phase collection unit. The liquid-phase collection unit 16 is communicated with the liquid-phase product outlet, and the gas-phase collection unit is communicated with the gas-phase product outlet 10.

[0037] In this application, the simulation box body can be a cylinder or other polyhedral structures, and this application does not limit this. Here, for the convenience of description, the simulation box body adopts a regular tetrahedron structure.

[0038] The simulation box body is of an externally single-opening type. The box cover 7 is rotatably connected to the box body, which is convenient for placing and taking out the sample holder 4 inside the box body structure 2. After the box cover 7 is closed, a sealed environment can be ensured inside the box body structure 2. During the test, in order to make the sample holder 4 in a sealed environment, a sealing ring is also provided between the box cover 7 and the box body structure 2. Among them, the sealing ring is pasted on the box cover 7. After the box cover 7 is covered, the box cover 7 and the box body structure 2 are firmly connected by bolt fasteners.

[0039] In this application, the liquid-phase product is collected by the liquid-phase collection unit 16, and the gas-phase product is collected by the gas-phase collection unit. After the gas-phase product and the liquid-phase product are collected, the gas-phase product and the liquid-phase product are respectively measured and analyzed by a gas chromatograph and a liquid chromatograph 15.

[0040] In this application, the specimen holder 4 adopts a Hassler-type core holder. When conducting a hydraulic fracturing simulation test on a coal series simulated specimen, a coal series simulated specimen simulating the coal series formation is placed in the fermentation chamber of the specimen holder 4. The fracturing fluid is pumped in by the fracturing pump 8, so that the coal series simulated specimen and the fracturing fluid ferment in the fermentation chamber, thereby conducting a biogas production test. During this process, when conducting a hydraulic fracturing simulation on the coal series simulated specimen in the specimen holder 4, the confining pressure pump 12 provides the confining pressure simulating the formation stress for the coal series simulated specimen, and the fracturing pump 8 pumps the fracturing fluid into the specimen holder 4, pumping the fracturing fluid containing nutrient solution or exogenous bacteria into the coal series simulated specimen, and the clay minerals promote the activity of methanogens, improving the biogas production efficiency.

[0041] The Hassler-type core holder seals the side wall of the coal series simulated specimen by applying radial pressure to the cylindrical surface of the coal series simulated specimen. Therefore, when placing and removing the coal series simulated specimen, only part of the device needs to be removed instead of the entire device, which is convenient for the specimen holder 4 to be disassembled and assembled in the simulation box, greatly simplifying the experimental operation steps and improving the efficiency of the experiment.

[0042] In this application, a holder fixing unit 3 is provided inside the box structure 2. The holder fixing unit 3 includes: a connecting part 301 and a clamping part; one end of the connecting part 301 is connected to the inner side wall of the box structure 2, and the other end is connected to the clamping part; the clamping part is an annular structure, and the inner side wall of the annular structure is adapted to the outer side wall of the specimen holder 4. Further, the clamping part includes a first clamping plate 302 and a second clamping plate 304 symmetrically arranged along its central axis plane. Both the first clamping plate 302 and the second clamping plate 304 are arc-shaped plates, and both ends of the arc-shaped plates are provided with connecting ear plates along the radial direction. The connecting ear plates are detachably connected to the end of the connecting part 301, wherein the connecting part 301 is located between the connecting ear plate of the first clamping plate 302 and the connecting ear plate of the second clamping plate 304.

[0043] It can be understood that the connecting ear plate at one end of the first clamping plate 302 and the connecting ear plate at one end of the second clamping plate 304 are connected to the connecting part 301, and the connecting ear plate at the other end of the first clamping plate 302 and the connecting ear plate at the other end of the second clamping plate 304 also adopt a detachable connection method. Specifically, holes are drilled in the connecting ear plates, and after the bolt fasteners 303 pass through the holes in the connecting ear plates, the first clamping plate 302 and the second clamping plate 304 are connected together, and the opposite arc-shaped surfaces of the first clamping plate 302 and the second clamping plate 304 tightly hold the outer side wall of the specimen holder 4. Furthermore, the specimen holder 4 is fixed in the simulation box.

[0044] In this application, a temperature sensor 6 is further provided inside the simulation box. The temperature sensor 6 is located on the inner sidewall of the box structure 2 and is far from the electric heating layer 20. The ambient temperature inside the simulation box is monitored in real time through the temperature sensor 6 to control the electric heating layer 20 and provide an appropriate fermentation temperature (35 degrees Celsius) for the coal series simulation sample. Among them, the fermentation temperature is the actual temperature of the formation where the selected coal series simulation sample is located, or it can be determined according to preset requirements. When the fermentation temperature is the actual temperature of the formation where the selected coal series simulation sample is located, for every 100 meters of descent in the position of the selected coal series simulation sample, the formation temperature rises by 3 degrees Celsius.

[0045] Herein, an appropriate temperature for the fermentation of the coal series simulation sample is provided through the electric heating layer 20. Among them, the electric heating layer 20 is provided on the inner sidewall and the inner bottom surface of the box structure 2 respectively. Further, the box structure 2 has three layers. The outer layer 201 is made of metal, the inner layer 202 is made of stainless steel, and the electric heating layer 20 is located between the outer layer 201 and the inner layer 202. Among them, the inner layer 202 is a heat transfer layer. Grooves are formed on the inner side of the outer layer 201, and resistance wires 211 are placed in the grooves. The resistance wires 211 are insulated from the outer layer 201 and the inner layer 202. Crystalline magnesium oxide powder 212 is filled in the gaps between the grooves and the resistance wires 211 to insulate and conduct heat for the resistance wires.

[0046] In addition, a pressure sensor 5 is also provided on the inner sidewall of the box structure 2 to monitor the pressure of the gas-phase products inside the simulation box. When collecting the gas-phase products, when the pressure inside the simulation box is the standard atmospheric pressure, the collection of the gas-phase products is completed. In addition, by setting the pressure sensor, the airtightness of the simulation box is detected before the test to ensure the accuracy of the test data.

[0047] In this application, the nitrogen inlet 18 is located at the connection of the inner sidewall and the inner bottom surface of the box structure 2. On the box structure 2, a liquid-phase product outlet is provided near the bottom on the sidewall opposite to the nitrogen inlet 18. Thereby, the nitrogen inlet 18 is at the lowest position of the height of the box structure 2, ensuring that during the process of filling nitrogen, the air in the box can be completely displaced.

[0048] Herein, the gripper outlet 17 is connected to the liquid-phase collection unit 16 through a pipeline. The pipeline passes through the liquid-phase product outlet. At the same time, the gap between the pipeline and the liquid-phase product outlet is sealed. Herein, the pipeline is made of corrosion-resistant stainless steel. A sealing ring is provided between the pipeline and the liquid-phase product outlet, and sealant is used for sealing.

[0049] Using the simulation device for promoting coal seam biogas production by migration of coal measure clay minerals of the present application, during the process of simulating hydraulic fracturing of coal measure simulated specimens, confining pressure simulating formation stress is provided to the coal measure simulated specimens through the confining pressure pump 12; fracturing fluid is pumped into the specimen holder 4 through the fracturing pump 8 to perform hydraulic fracturing on the clay mineral formation and the coal seam in sequence. Due to the swelling and migration of clay minerals, they enter the underlying coal seam together with the fracturing fluid, causing changes in coal seam biogas production. Since clay minerals promote the activity of methanogens and improve the gas production efficiency, it more truly and effectively simulates the influence of the contact between the microbial community and the clay minerals in the overlying strata of the coal seam on the fracturing effect and the gas production effect, and truly reflects the biological production increase effect of clay mineral swelling and migration on the coal measure strata.

[0050] In the simulation method for promoting coal seam biogas production by migration of coal measure clay minerals provided by the present application, the simulation device for promoting coal seam biogas production by migration of coal measure clay minerals in any of the above embodiments is used to perform gas production simulation on a coal measure simulated specimen with a clay mineral layer on the upper layer and a coal seam on the lower layer. As Figure 6 shown, the simulation method for promoting coal seam biogas production by migration of coal measure clay minerals includes:

[0051] Step S101: Drill a fracturing hole in the clay mineral formation on the selected coal measure simulated specimen, and insert a fracturing pipe into the fracturing hole; wherein, one end of the fracturing pipe extends out of the fracturing hole, and the hole wall of the fracturing hole and the fracturing pipe are sealed.

[0052] In the present application, a coal measure simulated specimen with a specification of a diameter of 50 mm and a length of 100 mm is drilled. A fracturing hole is drilled at the end face of the coal measure simulated specimen, the fracturing pipe is inserted into the fracturing hole for a certain length and a certain length is left exposed outside the fracturing hole, and the hole wall of the fracturing hole and the fracturing pipe are sealed with a high-strength resin (7120 sealant).

[0053] Step S102: Place the coal measure simulated specimen provided with the fracturing pipe into the specimen holder 4 and close it.

[0054] During this process, open the box cover 7 of the simulation box, fix the specimen holder 4 with the coal measure simulated specimen through the holder fixing unit 3 in the box structure 2, and connect the holder inlet 19 and the confining pressure port 13 of the coal body specimen holder 4 to the fracturing pump 8 and the confining pressure pump 12 outside the simulation box through pipelines respectively. At the same time, a first regulating valve 9 is provided on the pipeline connecting the holder inlet 19 and the fracturing pump 8, and a second regulating valve 11 is provided on the pipeline connecting the confining pressure pump 12 and the confining pressure port 13, so as to regulate the pressure of the pipeline connecting the holder inlet 19 and the fracturing pump 8 and the pressure of the pipeline connecting the fracturing pump and the confining pressure port 13 through the first regulating valve 9 and the second regulating valve 11.

[0055] Step S103: Turn on the confining pressure pump 12 in the hydraulic fracturing module. After the coal series simulated sample in the sample holder 4 is under the set pressure condition, pump the fracturing fluid containing nutrient solution or exogenous bacteria into the coal series simulated sample through the fracturing pump 8 in the hydraulic fracturing module, and perform hydraulic fracturing on the upper clay mineral formation and the lower coal seam in sequence.

[0056] During this process, an air vent 14 is provided on the connecting pipe between the confining pressure pump 12 and the confining pressure port 13. Before applying confining pressure to the coal series simulated sample, the gas in the sample holder 4 is discharged through the air vent 14, and then the confining pressure pump 12 pressurizes the coal series simulated sample to simulate the formation stress of the taken coal series simulated sample. After the confining pressure is stable, start the fracturing pump 8. The starting pump pressure of the fracturing pump 8 is 20 MPa. The fracturing pump 8 pressurizes the coal series simulated sample step by step. The pump pressure of the fracturing pump 8 is a constant value, not less than 28 MPa and not higher than 40 MPa. When the pressure of the fracturing pump 8 drops to the starting pump pressure, the hydraulic pressure of the coal series simulated sample is completed.

[0057] Step S104: After the hydraulic fracturing is completed, open the sample holder 4 to expose the coal series simulated sample in the simulation box, and close the box cover 7 of the simulation box; fill nitrogen into the simulation box to displace the air in the simulation box.

[0058] In this application, after the hydraulic fracturing is completed, remove the pipes connecting the fracturing pump 8 and the confining pressure pump 12, open the sample holder 4 to expose the fractured coal series simulated sample in the simulation box, fill nitrogen into the simulation box to displace the air in the simulation box, and provide an anaerobic environment for the gas production of the coal series simulated sample.

[0059] During this process, fill nitrogen into the simulation box for 8 to 10 minutes, and continuously measure the components of the gas phase products discharged from the gas phase product outlet 10 in the simulation box by a gas chromatograph; when the nitrogen content of the continuously measured gas phase products reaches the preset standard, the air displacement in the simulation box is completed. Specifically, the gas phase products are measured by the gas chromatograph every 10 minutes, and when the nitrogen contents in the continuously measured gas phase products are the same for 3 times, the air displacement in the simulation box is completed.

[0060] Here, connect a nitrogen cylinder 1 through a pipe at the nitrogen inlet 18 to fill nitrogen into the simulation box. When the nitrogen content of the continuously measured gas phase products reaches the nitrogen concentration in the nitrogen cylinder 1, the air displacement in the simulation box is completed. After the air displacement in the simulation box is completed, close the nitrogen cylinder 1 and the gas phase product outlet 10 to conduct a gas production test, and continuously detect the fermentation temperature of the coal series simulated sample through the temperature sensor 6.

[0061] Step S105: After the environmental temperature in the simulation chamber rises to the set temperature, collect the gas-phase products and liquid-phase products of the coal-series simulation sample.

[0062] After filling nitrogen to displace the air in the simulation chamber, start the electric heating layer 20, adjust the temperature in the simulation chamber, heat the temperature in the simulation chamber to the formation temperature where the coal-series simulation sample is taken, conduct a gas production test, collect the gas-phase products and liquid-phase products at fixed intervals, and analyze the gas production capacity of the coal-series simulation sample through a gas chromatograph and a liquid chromatograph 15.

[0063] It can be understood that the fracturing fluid can be a nutrient solution (the main components include NH 4 Cl, MgCl 2 , KH 2 PO 4 , K 2 HPO 4 , yeast extract, tryptone, cysteine salt, sodium bicarbonate, sodium acetate, sodium formate, etc.), or a liquid added with exogenous bacteria. Specifically, after the fracturing fluid passes through the clay mineral formation, due to the swelling and migration of the clay minerals, the clay minerals enter the coal seam along with the fracturing fluid. Through the biological gas production test and gas-liquid analysis of the coal seam, evaluate and analyze the biological stimulation effect of the swelling and migration of the clay minerals on the coal-series formation. In addition, a clay anti-swelling agent, such as KCl, can be added to the nutrient solution or exogenous bacteria. Thus, conduct hydraulic fracturing on the coal-series simulation sample with fracturing fluids of different formulations, and compare to realize the influence of the migration of clay minerals on gas production.

[0064] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A simulation device for promoting coal seam biogas production by the migration of coal measure clay minerals, characterized in that, it includes a simulation box body, a sample holder, a hydraulic fracturing module and a data acquisition module; The simulation box body includes: a box body structure with an open upper end and a box cover, the box cover is rotatably connected to the open end of the box body structure for closing the open end of the box body structure; an electric heating layer is provided inside the box body structure, and a nitrogen inlet and a liquid phase product outlet are provided on the box body structure; wherein, the nitrogen inlet and the liquid phase product outlet are located at the lower end of the side wall of the box body structure; a gas phase product outlet is provided on the box cover; The sample holder is located inside the simulation box body, and the outlet of the sample holder is communicated with the liquid phase product outlet, the confining pressure port of the sample holder is communicated with the confining pressure pump in the hydraulic fracturing module, and the inlet of the sample holder is communicated with the fracturing pump in the hydraulic fracturing module; wherein, the sample holder is used to place a coal measure simulation sample of the coal measure formation, the confining pressure pump is used to provide a confining pressure simulating the formation stress to the sample, and the fracturing pump is used to pump a fracturing fluid containing nutrient solution or exogenous bacteria into the sample holder; the upper layer of the coal measure simulation sample is a clay mineral layer, and the lower layer is a coal seam, and the fracturing fluid containing nutrient solution or exogenous bacteria enters from the upper layer and flows through the clay mineral layer into the coal seam; The data acquisition module includes: a liquid phase collection unit and a gas phase collection unit, the liquid phase collection unit is communicated with the liquid phase product outlet, and the gas phase collection unit is communicated with the gas phase product outlet; A holder fixing unit is provided inside the box body structure, and the holder fixing unit includes: a connecting part and a clamping part; one end of the connecting part is connected to the inner side wall of the box body structure, and the other end is connected to the clamping part; The clamping part is a ring structure, and the inner side wall of the ring structure is adapted to the outer side wall of the sample holder; The clamping part includes a first clamping plate and a second clamping plate symmetrically arranged along its central axis plane, both the first clamping plate and the second clamping plate are arc-shaped plates, and both ends of the arc-shaped plate are provided with connecting ear plates along the radial direction, and the connecting ear plates are detachably connected to the end of the connecting part, wherein, the connecting part is located between the connecting ear plate of the first clamping plate and the connecting ear plate of the second clamping plate; A temperature sensor is also provided inside the simulation box body, and the temperature sensor is located on the inner side wall of the box body structure and away from the electric heating layer.

2. The simulation device for promoting coal seam biogas production by the migration of coal measure clay minerals according to claim 1, characterized in that, the inner side wall and the inner bottom surface of the box body structure are respectively provided with the electric heating layer.

3. The simulation device for promoting coal seam biogas production by the migration of coal measure clay minerals according to claim 2, characterized in that, the box body structure is three-layer, the outer layer is made of metal material, the inner layer is made of stainless steel material, and the electric heating layer is located between the outer layer and the inner layer.

4. The simulation device for promoting coal seam biogas production by the migration of coal measure clay minerals according to claim 1, characterized in that, The nitrogen inlet is located at the connection of the inner side wall and the inner bottom surface of the box structure; on the box structure, a liquid-phase product outlet is provided near the bottom surface on the side wall opposite to the nitrogen inlet.

5. A method for simulating coalbed methane production promoted by the migration of coal-bearing clay minerals Characterized in that The gas production simulation is carried out on a coal-bearing simulation sample with a clay mineral layer on the upper layer and a coal seam on the lower layer by using the coal-bearing clay mineral migration-promoted coalbed methane production simulation device according to any one of claims 1-4. The coal-bearing clay mineral migration-promoted coalbed methane production simulation device includes: a simulation box, a sample holder, a hydraulic fracturing module, and a data acquisition module; the method includes: Drill a fracturing hole in the clay mineral formation of the selected coal-bearing simulation sample, and insert a fracturing pipe into the fracturing hole; wherein, one end of the fracturing pipe extends out of the fracturing hole, and the hole wall of the fracturing hole and the fracturing pipe are sealed. Place the coal-bearing simulation sample provided with the fracturing pipe in the sample holder and close it. Open the confining pressure pump in the hydraulic fracturing module, and after the coal-bearing simulation sample in the sample holder is under the set pressure condition, pump the fracturing fluid containing nutrient solution or exogenous bacteria into the coal-bearing simulation sample through the fracturing pump in the hydraulic fracturing module, and sequentially carry out hydraulic fracturing on the upper clay mineral formation and the coal seam in the coal-bearing simulation sample. After the hydraulic fracturing is completed, open the sample holder to expose the coal-bearing simulation sample in the simulation box, and close the box cover of the simulation box; fill the simulation box with nitrogen to displace the air in the simulation box. In response to the environmental temperature in the simulation box rising to the set temperature, collect the gas-phase products and liquid-phase products of the coal-bearing simulation sample.

6. The method for simulating coalbed methane production promoted by the migration of coal-bearing clay minerals according to claim 5, Characterized in that The step of pumping the fracturing fluid containing nutrient solution or exogenous bacteria into the coal-bearing simulation sample through the fracturing pump in the hydraulic fracturing module and sequentially carrying out hydraulic fracturing on the upper clay mineral formation and the coal seam in the coal-bearing simulation sample includes: The starting pump pressure of the fracturing pump is 20 MPa, and the coal-bearing simulation sample is gradually pressurized by the fracturing pump. The pump pressure of the fracturing pump is a constant value, and is not less than 28 MPa and not higher than 40 MPa. In response to the pressure of the fracturing pump dropping to the starting pump pressure, the hydraulic fracturing of the coal-bearing simulation sample is completed.

7. The method for simulating coalbed methane production promoted by the migration of coal-bearing clay minerals according to claim 5, Characterized in that The step of filling the simulation box with nitrogen to displace the air in the simulation box includes: After filling the simulation box with nitrogen for 8 to 10 minutes, continuously measure the composition of the gas-phase products discharged from the gas-phase product outlet in the simulation box by a gas chromatograph for multiple times. In response to the nitrogen content of the gas-phase products measured continuously for multiple times reaching the preset standard, the displacement of the air in the simulation box is completed.

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