A method for coalbed methane extraction that promotes microbial gasification and enhances efficiency under the action of an electric-magnetic dual field

Abstract

The invention discloses a method for enhancing coalbed methane extraction by promoting microbial gasification under the action of an electric-magnetic dual field, belonging to the technical field of coalbed methane extraction; the steps include: fracturing a coal reservoir through an injection well to form a fracture network; injecting an electrolyte solution and a microbial solution into the fracture network, and the microbial solution contains colony-induced particles; applying an electric field to the coal reservoir to control the migration of the microbial colonies and colony-induced particles in the fracture network in the microbial solution; then applying a low-voltage field to promote further connection of the branch fractures in the fracture network and inducing migration again; applying a magnetic field to the coal reservoir; the invention promotes the proliferation and uniform distribution of microorganisms, accelerates the decomposition of organic matter in the coal seam and the release of methane, and improves the coalbed methane production rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane extraction, and relates to a method for enhancing the efficiency of microbial gasification in coalbed methane extraction under the action of an electric-magnetic dual field. Background Art

[0002] The efficient extraction of coalbed methane (CBM) is of great significance for energy utilization. Traditional coalbed methane extraction methods have problems such as low gasification efficiency and low methane conversion efficiency. In recent years, microbial gasification technology has been studied in coalbed methane extraction, and microorganisms convert coal into methane gas through metabolic processes. However, the existing microbial gasification technology has bottlenecks in microbial diffusion and limited gasification rate. In the in-situ state underground, the microbial flora is unevenly dispersed, resulting in a significant reduction in the efficiency of coalbed methane extraction.

[0003] Patent CN107387044A discloses a method for increasing the production of biogenic coalbed methane by utilizing indigenous fungi in coal seams. This method collects data on the target coalbed methane field, analyzes the in-situ fungal community structure of the coal seam, and further cultivates highly efficient microbial communities, ultimately achieving in-situ biological methane conversion in the coal seam to increase the production of coalbed methane. On this basis, Patent CN110259423A discloses a method for increasing the production of coalbed methane by combining an externally applied direct current electric field and microbial degradation. Based on the exploration of the geological conditions of the coal reservoir and the enrichment of microbial communities and other relevant data, highly efficient microbial communities are enriched, the culture fluid is injected by hydraulic fracturing through a well pattern, a direct current electric field network is established, and then highly efficient microbial communities are injected to activate the electric field network, realizing the combined increase in the production of coalbed methane by the externally applied electric field and microbial degradation.

[0004] Patent CN104031905A discloses a method for enhancing the activity of anaerobic ammonia-oxidizing bacteria by an electric field. The electric field intensity of 1 - 4 V / cm is applied to enhance the activity of anaerobic ammonia-oxidizing bacteria, and the action mode of the electric field is an intermittent action. The intermittent action mode is that the electric field intermittent time is 3 h, 6 h, or 12 h, and the electric field action time is 12 h / 24 h.

[0005] In addition, Patent CN215756658U shows the application of electric field and magnetic field strengthening technology in an anaerobic sludge bed reactor, and improves the treatment efficiency of microorganisms through the synergistic action of the dual fields, indicating the potential of electromagnetic fields in enhancing microorganisms. However, such technologies are mainly applicable to fixed reaction environments and do not solve the cost and efficiency problems in large-scale and open geological applications.

[0006] In practical applications, injecting microorganisms into underground coal reservoirs to increase coalbed methane production still faces many challenges. The complex geological conditions make it difficult for the microbial community to achieve uniform diffusion, resulting in low gasification efficiency. Although the introduction of electric and magnetic fields can improve the microbial gasification efficiency to a certain extent, some obvious deficiencies have also emerged. On the one hand, it is difficult to precisely control the movement of microorganisms solely relying on electric or magnetic fields. At the same time, if the fracture channels are not supported in time, leading to fracture shrinkage, it is easy for the microbial community to form blind hole aggregations in the pores, with poor distribution uniformity. In this case, only partial areas with dense colonies can form local gasification efficiency enhancement zones, and the overall gasification area is limited, thereby affecting the improvement of gasification efficiency. On the other hand, even though the gasification effect can be enhanced by applying electric and magnetic fields simultaneously, this method significantly increases the cost. In addition, long-term use of the electric field may also cause excessive consumption of the electrolyte solution. When the electrolyte solution cannot effectively fill the pore fractures of the reservoir, it is difficult for microorganisms to diffuse through the solution to the entire reservoir and adsorb smoothly on the coal seam surface, resulting in a significant decrease in methane conversion efficiency. Therefore, there are still insurmountable bottlenecks in improving the overall gasification efficiency in the existing technology, and further innovation and optimization are needed. Summary of the Invention

[0007] The present invention overcomes the deficiencies of the prior art and provides a coalbed methane extraction method for promoting microbial gasification efficiency enhancement under the action of an electric-magnetic dual field, which further improves the methane conversion efficiency and coalbed methane recovery efficiency, and reduces energy consumption at the same time.

[0008] To achieve the above object, the present invention is realized through the following technical solutions:

[0009] A coalbed methane extraction method for promoting microbial gasification efficiency enhancement under the action of an electric-magnetic dual field, comprising the following steps:

[0010] S1. Fracture the coal reservoir through an injection well to form a fracture network; inject an electrolyte solution and a microbial solution into the fracture network, and the microbial solution contains microbial community-induced particles.

[0011] S2. Apply an electric field to the coal reservoir, with the intensity of the electric field being 0.1 - 1 V / cm, control the movement of the microbial community and the microbial community-induced particles in the fracture network, and monitor the movement situation simultaneously to make the microbial community and the microbial community-induced particles distributed in the fracture network.

[0012] S3. Adjust the voltage of the electric field in the coal reservoir to 1.5 - 5 V and the current to 10 - 50 mA to promote the electrolysis of the electrolyte solution in the coal reservoir and further connect the branch fractures in the fracture network; then adjust the intensity of the electric field to 0.1 - 1 V / cm again to make the microbial community-induced particles move again, and the movement time is 0.5 - 2 h.

[0013] S4. Apply a magnetic field to the coal reservoir. The working frequency range of the magnetic field is 1 Hz to 100 kHz, the magnetic field intensity is 5 to 50 mT, and the time is 1.5 to 2.5 h.

[0014] S5. Repeat steps S3 and S4. During this process, synchronously monitor the pressure of the extraction well. When the pressure in the extraction well increases to a predetermined value, open the extraction well to extract coalbed methane.

[0015] Furthermore, the electrolyte is dissolved in the fracturing fluid to form an electrolyte solution, which is injected into the fracture network together with the fracturing fluid. The concentration of the electrolyte in the fracturing fluid is 0.1 to 5 mol / L.

[0016] Furthermore, at least two rows of boreholes are arranged on the ground as injection wells, and extraction wells are arranged between adjacent two rows of injection wells. The extraction well enters the coal reservoir in a single horizontal comb-shaped well layout. An electro-magnetic field generator is provided at the bottom of the injection well. An electric field and a magnetic field are applied to the coal reservoir through the electro-magnetic field generator.

[0017] Furthermore, the electro-magnetic field generator includes a particle migration control device, an auxiliary electrolysis reaction device, an electro-chemical sensor, and a magnetic field generation device. The particle migration control device controls the migration of the microbial community and the microbially induced particles by applying an electric field. The auxiliary electrolysis reaction device promotes the electrolysis of the electrolyte and forms pores in the coal reservoir by applying a low-voltage field. The magnetic field generation device provides a magnetic field.

[0018] Even further, the particle migration control device, the auxiliary electrolysis reaction device, the electro-chemical sensor, and the magnetic field generation device are respectively electrically connected to the ground control center.

[0019] Even further, in step S2, the electro-chemical sensor is used to monitor the migration of the microbial community and the microbially induced particles until the microbial density points are uniform, and the intersection area range of the microbial communities around adjacent two injection wells gradually replaces the blank area without microbial communities until the blank area completely disappears.

[0020] Furthermore, an injection well valve and an injection pump are connected to the top of the injection well. The injection pump is connected to a fracturing fluid storage tank. Open the fracturing pipeline valve provided at the outlet end of the fracturing fluid storage tank. The fracturing fluid in the fracturing fluid storage tank enters the coal reservoir through the injection well to perform fracturing until a fracture network appears in the coal reservoir, and then close the fracturing pipeline valve.

[0021] Furthermore, the microbial solution is methanogenic bacteria, and the microbially induced particles are graphene oxide.

[0022] Further, in step S5, the extraction well valve on the extraction well is opened to extract coalbed methane. The extraction well is connected to an extraction pump and a pressure and gas component monitor. When the CO2 gas concentration in the coalbed methane rises to 20% and the methane concentration drops to 30%, the extraction is stopped. The extraction well is shut in, and then the extraction well is opened again until the coalbed methane production is reduced by 60%, and the coalbed methane extraction work ends.

[0023] The beneficial effects of the present invention compared with the prior art are as follows:

[0024] 1. The present invention realizes the uniform distribution of the microbial community by synergistically regulating the distribution of induced particles by electricity and magnetic fields. The metabolic activity of the microbial community is monitored by the change of the electrical signal, so as to flexibly regulate the diffusion range of the microbial community, and then realize the visual regulation of its diffusion process. The existing magnetic and electric fields are difficult to accurately control the flow of colonies, and the pore fissures will shrink under the action of in-situ stress; the present invention uses induced particles to induce the colonies and also acts as a proppant, and is effectively transported visually under the control of the electricity and magnetic fields, and finally controls the uniform dispersion of the colonies in the fracture network.

[0025] 2. "Multiple wells - multiple groups of electrodes" assist electrolysis to achieve large-area assisted electrolysis of the mixed medium of coal and electrolyte. The CO2 and H2 generated by the assisted electrolysis react with the organic carbon on the pore surface to carry out methanation reaction, promote the development of the pore structure and expand the distribution area of the microbial community, thereby improving the gasification efficiency. At the same time, CO2 and H2 provide additional metabolic substrates for microorganisms to support their growth in the coal seam.

[0026] 3. Under the mutual promotion of the magnetic field and the electric field, the transport of nutrients in the fissures is enhanced, the proliferation of microorganisms is promoted, the excessive consumption of the electrolyte is avoided, and additional metabolic substrates are provided for the microorganisms, accelerating the decomposition of organic matter and methane release in the coal seam, and increasing the coalbed methane production rate and methane concentration.

[0027] 4. The intermittent electric field application method of alternately applying the electric and magnetic fields and alternately cycling the positive and negative electrodes is adopted to avoid the inhibition of microorganisms by the long-term strong electric field and improve their metabolic efficiency. Applying the electric field during the intermittent period further promotes the efficient metabolism of the microbial community during the recovery period, prevents electrode corrosion or excessive consumption of the electrolyte. The polarity reversal technology improves the multi-directional migration of charged particles, optimizes the particle distribution, eliminates the gasification blind area, improves the methane conversion efficiency, and realizes the green and efficient extraction of coalbed methane.

[0028] In the prior art, the long-term electric field causes electrolyte consumption, making the electrolyte in the pore structure unable to fill the pore space, resulting in ineffective migration of the migrating particles, and further causing the colonies to be unable to quickly diffuse and adsorb on the coal seam surface through the solution. The regulation method of the present invention is divided into two stages, with the electric field and the magnetic field alternating intermittently to ensure the effective migration and diffusion of the induced particles and the colonies. Both the electric and magnetic fields have a promoting effect on the induced particles. During the electric field action stage, a certain amount of H2 and CO2 are generated by the electrolysis of water and organic matter in coal as the source supplement of the colony reactants, which can reduce the injection of hydrogen on the ground and promote the methanation reaction at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the surface well pattern arrangement in Embodiment 1;

[0030] Figure 2 It is a schematic diagram of the surface well pattern arrangement in Embodiment 2;

[0031] Figure 3 It is a schematic diagram of the coalbed methane extraction device for promoting the synergistic effect of microbial gasification under the action of the electric-magnetic dual field in Embodiments 1 and 2;

[0032] Figure 4 It is a schematic diagram of the horizontal slice of the uniform diffusion of the microbial injection in Embodiments 1 and 2;

[0033] Figure 5 It is a schematic diagram of injecting the microbial solution into the fracture network in Embodiments 1 and 2;

[0034] Figure 6 It is a schematic diagram of the stage for assisting the further migration of the colony-induced particles under the action of the electric field in Embodiments 1 and 2;

[0035] Figure 7 It is a schematic diagram of the stage for accelerating the growth of the microbial colonies under the action of the electric-magnetic dual field in Embodiments 1 and 2;

[0036] Figure 8 It is a schematic diagram of the stage for the efficient gasification of the microbial colonies under the action of the magnetic field in Embodiments 1 and 2.

[0037] Reference numerals in the figure: 1 - injection well; 2 - production well; 3 - injection well valve; 4 - injection pump; 5 - fracturing fluid storage tank; 6 - fracturing pipeline valve; 7 - microorganism storage tank; 8 - microorganism pipeline valve; 9 - production well valve; 10 - pressure and gas component monitoring table; 11 - production pump; 12 - ground control center; 13 - electro - magnetic field generator; 1301 - particle migration control device; 1302 - auxiliary electrolytic reaction device; 1303 - electrochemical sensor; 1304 - current; 1305 - magnetic field generating device; 1306 - electromagnetic wave; 14 - fracture network; 15 - floor; 16 - bacteria - induced particles; 17 - roof; 18 - bacteria group; 19 - intersection area; 20 - blank area; 21 - coal reservoir; 22 - fracturing fluid. Detailed implementation manners

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail in combination with embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The technical solutions of the present invention will be described in detail below in combination with embodiments and drawings, but the protection scope is not limited by this.

[0039] Embodiment 1

[0040] Refer to Figure 1 、 Figures 3 to 8 , this embodiment proposes a method for extracting coal - bed methane to promote microbial gasification and efficiency enhancement under the action of an electro - magnetic dual - field. For a coal reservoir 21 with a depth of 200 m and a thickness of 15 m, the specific implementation steps for extracting coal - bed methane are as follows:

[0041] S1. Arrange two rows of boreholes on the ground as injection wells 1, and the spacing between the two rows of injection wells 1 is 50 m; an electro - magnetic field generator 13 is provided at the bottom of the injection well 1; the spacing between the bottom of the injection well 1 and the floor 15 is 1 m. The production well 2 is arranged in the middle of the two rows of injection wells 1 and enters the coal reservoir 21 in a single - horizontal comb - shaped well layout mode, and the horizontal comb - shaped well is 7 m away from the roof 17;

[0042] The electro-magnetic field generator 13 includes a particle migration control device 1301, an auxiliary electrolysis reaction device 1302, an electro-chemical sensor 1303, and a magnetic field generation device 1305; the particle migration control device 1301, the auxiliary electrolysis reaction device 1302, the electro-chemical sensor 1303, and the magnetic field generation device 1305 are all existing devices, and the relevant product names and models are respectively a particle flow control system - Fritsch Analysette 22, an electrolysis reactor - Waldmann Electrolysis Cells, an electro-chemical sensor - Metrohm 6.0555.000, and a magnetic field generation device - Bruker Superconducting Magnet.

[0043] S2. Connect the fracturing fluid storage tank 5 to the injection well valve 3 and the injection pump 4 at the top of the injection well 1, and open the fracturing pipeline valve 6 provided at the outlet end of the fracturing fluid storage tank 5; the fracturing fluid 22 in the fracturing fluid storage tank 5 enters the coal reservoir 21 through the injection well 1 to perform fracturing until a fracture network 14 appears in the coal reservoir 21, and then close the fracturing pipeline valve 6. In this embodiment, the fracturing fluid 22 in the fracturing fluid storage tank 5 contains an electrolyte with a concentration of 3.5 mol / L, and the electrolyte is NaCl. While maintaining the electric field environment in the coal reservoir 21, the electrolyte positively promotes the electrolysis reaction and the methanation reaction, and further promotes the connectivity of the pore structure.

[0044] S3. Connect the microbial storage tank 7 to the injection well valve 3 and the injection pump 4 at the top of the injection well 1, and open the microbial pipeline valve 8 at the outlet end of the microbial storage tank 7. The concentration of the microbial community 18 in the microbial solution in the microbial storage tank 7 is 1×10 6 CFU / mL. The microbial solution is mixed with microbial-induced particles 16; the microbial solution enters the fracture network 14 through the injection well 1; at the same time, turn on the particle migration control device 1301 in the electro-magnetic field generator 13 to control the microbial-induced particles 16 in the fracture network 14 so that the microbial-induced particles 16 are evenly distributed in the fracture network 14; the particle migration control device 1301 controls the migration of the microbial community 18 and the microbial-induced particles 16 in the coal seam fractures by applying an electric field, and the electric field strength is set to 0.5 V / cm. The particle migration control device 1301 is connected to the ground control center 12. Synchronously monitor the migration of the microbial community 18 through the electro-chemical sensor 1303 until the density points of the microbial community 18 are relatively uniform, and in the horizontal slice image, the range of the intersection area 19 of the microbial community 18 around two adjacent injection wells 1 gradually replaces the blank area 20 without the microbial community 18 until the blank area 20 completely disappears (see Figure 4 )

[0045] The electrochemistry sensor 1303 is also connected to the ground control center 12. The metabolic activities of the microbial community 18 in the fissures will change the local conductivity. By recording the changes in the electrical signals through the electrochemistry sensor 1303, the metabolic activities and distribution of the microbial community 18 can be monitored, and then the data is transmitted to the ground control center 12.

[0046] It should be noted that: the microbial solution mainly consists of anaerobic fermentative bacteria. In this embodiment, a combined strain of multiple methane-producing bacteria such as Methanobacterium and Methanomonas is used, which is an existing strain purchased; the microbial community-induced particle 16 is graphene oxide. Under the action of an electric field, the uniform distribution and diffusion of the microbial community 18 can be guided through the microbial community-induced particle 16.

[0047] S4. Turn on the auxiliary electrolysis reaction device 1302 in the electro-magnetic field generator 13, set the electric field voltage to 2V, and the current 1304 to a low voltage field of 20 mA to promote the electrolysis of the electrolyte. During the electrolysis of the electrolyte, the coal reservoir 21 will be induced to generate pore fissures, thereby promoting the further connection of the pore fissures; the initial electrolysis is carried out for 5 h. After that, turn on the particle migration control device 1301 in the electro-magnetic field generator 13 again to induce the further migration of the microbial community-induced particle 16 and the microbial community 18. The induction migration time in this step is 1.5 h; after the migration of the microbial community-induced particle 16 is basically stable, the auxiliary electrolysis stage is completed.

[0048] The auxiliary electrolysis reaction device 1302 includes multiple groups of positive and negative electrodes to assist the electrolyte in carrying out a low voltage electrolysis reaction in the coal reservoir 21 rich in electrolyte. Under the electric field condition, through the electrolysis of the electrolyte, water and the coal body, the generation of gas for inducing methanation reaction such as H2 and CO2 is promoted, and further the local fissure pore structure is increased. The relevant reactions that can occur in the coal reservoir 21 rich in electrolyte are:

[0049] ;

[0050] .

[0051] S5. Turn on the magnetic field generating device 1305 in the electro-magnetic field generator 13 to emit electromagnetic waves 1306, set the working frequency to 75 Hz, the magnetic field intensity to 50 mT, and apply the magnetic field for 2 h to further increase the activity of the microbial community 18. The ground control center 12 is connected to the electrochemistry sensor 1303 to monitor the density change of the microbial community 18 until the density of the microbial community 18 shows a significant increase.

[0052] The electromagnetic waves 1306 generated by the magnetic field generating device 1305 can make up for the shortcomings of the current-dependent medium (rich in electrolyte solution environment), thereby constructing a large-area regional magnetic field, significantly improving the metabolic activity of microorganisms, and enhancing the electron transfer ability of cells.

[0053] S6. Repeat steps S4 and S5 cyclically. The intermittent application of the electric field can prevent the long-term inhibition of the microbial community 18 by the strong electric field, while the application of the magnetic field during the intermittent period further promotes the more efficient metabolism of the microbial community 18 during the recovery period and simultaneously prevents the electrodes from being corroded or the electrolyte solution from being excessively consumed.

[0054] During this process, the pressure of the extraction well 2 is monitored synchronously. When there is an obvious upward trend in the pressure of the extraction well 2, the extraction well valve 9 on the extraction well 2 is opened to extract coalbed methane mainly composed of methane. The extraction well 2 is connected to an extraction pump 11 and a pressure and gas component monitoring table 10; when the CO2 gas concentration in the coalbed methane increases to 20% and the methane concentration decreases to 30%, the extraction is stopped. The well is shut in, and after a period of time, the extraction well 2 is opened again until the coalbed methane production decreases by 60%, and the coalbed methane extraction work ends.

[0055] It should be noted that: under the alternating action of the low-voltage electric field and the magnetic field, the transport efficiency of nutrients in the fractures can be improved, the proliferation of microorganisms can be accelerated, and the distribution density of the microbial community 18 can be increased. By enhancing electron transfer and promoting energy metabolism, the microbial gasification process in the coalbed methane is accelerated. At the same time, the electrolytically generated hydrogen (H2) and carbon dioxide (CO2) can provide additional metabolic substrates for the microorganisms, further promoting the decomposition of organic matter in the coal reservoir 21 and the release of methane gas. The relevant reaction relationships are as follows:

[0056] ;

[0057] 。

[0058] Example 2

[0059] Refer to Figures 2 to 8 , this example proposes a coalbed methane extraction method for promoting microbial gasification and enhancing efficiency under the action of an electric-magnetic dual field. For a large-area coal reservoir 21 with a depth of 300 m, a thickness of 8 m, and a working face length of 180 m, the specific implementation steps are as follows:

[0060] S1. Arrange three rows of boreholes on the ground as injection wells 1, and the spacing between adjacent two rows of injection wells 1 is 60 m; an electric-magnetic field generator 13 is provided at the bottom of the injection well 1; the electric-magnetic field generator 13 includes a particle migration control device 1301, an auxiliary electrolytic reaction device 1302, an electrochemistry sensor 1303, and a magnetic field generation device 1305; the electric-magnetic field generator 13 is the same as that in Example 1;

[0061] The distance between the bottom of the injection well 1 and the floor 15 is 0.5 m. A extraction well 2 is provided between adjacent two rows of injection wells 1. The extraction well 2 enters the coal reservoir 21 in a single horizontal comb-shaped well layout mode, and the horizontal comb-shaped well is 4 m away from the roof 17.

[0062] S2. Connect the fracturing fluid storage tank 5 to the injection well valve 3 and the injection pump 4 at the top of the injection well 1, and open the fracturing pipeline valve 6 provided at the outlet end of the fracturing fluid storage tank 5; the concentration of the electrolyte in the fracturing fluid 22 in the fracturing fluid storage tank 5 is 5 mol / L. The fracturing fluid 22 enters the coal reservoir 21 through the injection well 1 to carry out fracturing until a fracture network 14 appears in the coal reservoir 21, and then close the fracturing pipeline valve 6; in this embodiment, the electrolyte is NaHCO3.

[0063] S3. Connect the microbial storage tank 7 to the injection well valve 3 and the injection pump 4 at the top of the injection well 1, and open the microbial pipeline valve 8 at the outlet end of the microbial storage tank 7. The concentration of the flora 18 in the microbial solution in the microbial storage tank 7 is 1×10 8 CFU / mL. At the same time, turn on the particle migration control device 1301 in the electromagnetic field generator 13 to control the flora-induced particles 16 in the fracturing fluid 22, so that the flora-induced particles 16 are evenly distributed in the fracture network 14; the electric field strength is set to 1.5 V / cm, and the migration of the flora 18 is monitored synchronously through the electrochemical sensor 1303 until the density points of the flora 18 are relatively uniform, and in the horizontal slice image, the range of the intersection area 19 of the flora 18 around two adjacent injection wells 1 gradually replaces the blank area 20 without the flora 18 until the blank area 20 completely disappears.

[0064] S4. Turn on the auxiliary electrolysis reaction device 1302 in the electromagnetic field generator 13, set a low voltage field with an electric field voltage of 2 V and a current 1304 of 50 mA, and conduct the primary electrolysis for 3 h. Then turn on the particle migration control device 1301 in the electromagnetic field generator 13 again and induce the further migration of the flora 18, and this process continues for 1 h.

[0065] S5. Turn on the magnetic field generating device 1305 in the electromagnetic field generator 13 to emit electromagnetic waves 1306, set the working frequency to 60 Hz, and the magnetic field strength to 40 mT. Apply the magnetic field for 2 h to further increase the activity of the flora 18. The ground control center 12 is connected to the electrochemical sensor 1303 to monitor the density change of the microbial flora 18.

[0066] S6. Cycle the operations of S4 and S5, and synchronously monitor the pressure of the extraction well 2. When there is an obvious increasing trend in the pressure of the extraction well 2, open the extraction well 2 to extract coalbed methane mainly composed of methane. When the CO2 gas concentration in the coalbed methane increases to 30% and the methane concentration decreases to 30%, stop the extraction. Conduct a shut-in well, and then open the extraction well 2 again after a period of time until the coalbed methane production decreases by 60%, and end the coalbed methane extraction work.

[0067] The working principle of Embodiment 2 is the same as that of Embodiment 1.

[0068] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific embodiments of the present invention are limited to this. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the patent protection scope determined by the claims submitted by the present invention.

Claims

1. A coalbed methane extraction method for promoting microbial gasification efficiency under the action of electric-magnetic dual fields, characterized in that: The following steps are involved: S1. Arranging at least two rows of boreholes on the ground as injection wells (1), fracturing the coal reservoir (21) through the injection wells (1) to form a fracture network (14); injecting an electrolyte solution and a microbial solution into the fracture network (14), wherein the microbial solution contains bacterial colony-inducing particles (16); the microbial solution contains methanogens, and the bacterial colony-inducing particles (16) are graphene oxide; S2, an electro-magnetic field generator (13) is provided at the bottom of the injection well (1); an electric field is applied to the coal reservoir (21) through the electro-magnetic field generator (13), and the intensity of the electric field is 0.1~1V / cm, so as to control the migration of the bacterial colony (18) and the bacterial colony-inducing particles (16) in the microbial solution in the fracture network (14); the electro-magnetic field generator (13) includes an electrochemical sensor (1303), and the migration of the bacterial colony (18) and the bacterial colony-inducing particles (16) is monitored through the electrochemical sensor (1303) until the density of the bacterial colony (18) is uniform, and the intersection area (19) of the bacterial colony (18) around two adjacent injection wells (1) gradually replaces the blank area (20) without the bacterial colony (18), until the blank area (20) completely disappears, so that the bacterial colony (18) and the bacterial colony-inducing particles (16) are distributed in the fracture network (14); S3, adjusting the voltage of the electric field in the coal reservoir (21) to 1.5-5V and the current to 10-50mA, so as to promote electrolysis of the electrolyte solution in the coal reservoir (21) and promote further connectivity of the branch fractures in the fracture network (14); then adjusting the intensity of the electric field to 0.1-1V / cm again, so as to allow the bacterial colony-induced particles (16) to migrate again, and the migration time is 0.5-2h; S4, applying a magnetic field to the coal reservoir (21) through an electro-magnetic field generator (13), wherein the magnetic field operating frequency range is 1 Hz to 100 kHz, and the magnetic field intensity is 5 to 50 mT; and the time is 1.5 to 2.5 hours; S5, looping steps S3 and S4, during which the pressure of the extraction well (2) is synchronously monitored, and when the pressure in the extraction well (2) increases to a predetermined value, the extraction well (2) is opened to extract the coalbed methane.

2. The method for coalbed methane extraction by promoting microbial gasification efficiency under the action of electric-magnetic dual fields according to claim 1 is characterized in that: The electrolyte is dissolved in the fracturing fluid (22) to form an electrolyte solution, which is injected into the fracture network (14) together with the fracturing fluid. The concentration of the electrolyte in the fracturing fluid is 0.1-5 mol / L.

3. The method for coalbed methane extraction by promoting microbial gasification efficiency under the action of electric-magnetic dual fields according to claim 1 is characterized in that: An extraction well (2) is arranged between two adjacent rows of injection wells (1); the extraction well (2) enters the coal reservoir (21) in a single horizontal comb-shaped well arrangement.

4. The method for coalbed methane extraction by promoting microbial gasification efficiency under the action of electric-magnetic dual fields according to claim 3 is characterized in that: The electric-magnetic field generator (13) further comprises a particle migration control device (1301), an auxiliary electrolysis reaction device (1302) and a magnetic field generating device (1305); the particle migration control device (1301) controls the migration of the bacterial colony (18) and the bacterial colony-induced particles (16) by applying an electric field; the auxiliary electrolysis reaction device (1302) promotes the electrolysis of the electrolyte and forms pores in the coal reservoir (21) by applying a low voltage field; and the magnetic field generating device (1305) provides a magnetic field.

5. The method for coalbed methane extraction by promoting microbial gasification efficiency under the action of electric-magnetic dual fields according to claim 4 is characterized in that: The particle migration control device (1301), the auxiliary electrolytic reaction device (1302), the electrochemical sensor (1303) and the magnetic field generating device (1305) are electrically connected to the ground control center (12) respectively.

6. The method for coalbed methane extraction by promoting microbial gasification efficiency under the action of electric-magnetic dual fields according to claim 2 is characterized in that: The top of the injection well (1) is connected to an injection well valve (3) and an injection pump (4); the injection pump (4) is connected to a fracturing fluid storage tank (5); a fracturing pipeline valve (6) provided at the outlet end of the fracturing fluid storage tank (5) is opened; the fracturing fluid (22) in the fracturing fluid storage tank (5) enters the coal reservoir (21) through the injection well (1) to perform fracturing until a fracture network (14) appears in the coal reservoir (21), and the fracturing pipeline valve (6) is closed.

7. The method for coalbed methane extraction by promoting microbial gasification efficiency under the action of electric-magnetic dual fields according to claim 1 is characterized in that: In step S5, the extraction well valve (9) on the extraction well (2) is opened to extract the coalbed methane, and the extraction well (2) is connected to an extraction pump (11) and a pressure and gas composition monitoring meter (10); when the CO2 gas concentration in the coalbed methane increases to 20% and the methane concentration decreases to 30%, the extraction is stopped; the extraction well (2) is shut down, and then the extraction well (2) is opened again until the coalbed methane production decreases by 60%, thereby terminating the coalbed methane extraction work.

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