Ground coal-bed gas well high-intensity acoustic electric field composite anti-reflection method suitable for soft coal seam

Abstract

According to the ground coal-bed gas well high-strength acoustic-electric field composite anti-reflection method suitable for the soft coal bed, the extraction area is enlarged through construction of the ground L-shaped horizontal well, the coal bed anti-reflection range is effectively extended through the acoustic-electric composite anti-reflection technology, and therefore the recovery rate of coal bed gas is increased. According to the horizontal well drilling system with the efficient deslagging and drilling functions, the problems of hole spraying, hole collapse, drill jamming, hole forming difficulty and the like are solved. In addition, it can be ensured that the acoustoelectric composite device can be smoothly conveyed to the fracturing point position of the horizontal well, efficient mining of the soft coal seam is facilitated, and a solution is particularly provided for solving the technical and equipment problems in the construction process of the L-shaped horizontal well. Meanwhile, the method belongs to ground operation and is easy to operate and control, and the reliability and the safety are greatly improved in the anti-reflection process.

Description

Technical Field

[0001] The invention belongs to the technical field of coalbed methane exploitation, and in particular relates to a high-intensity acoustic-electric field composite permeability enhancement method for ground coalbed methane wells suitable for soft coal seams. Background Art

[0002] As a clean energy, coalbed methane plays an important role in coal mine safety production and energy structure. Low-permeability coal seams account for a high proportion in my country and are widely distributed. The effect of gas extraction by directly drilling pre-extraction holes in coal seams is generally poor. In order to improve the extraction efficiency, it is necessary to use external means to artificially intervene in the permeability of coal seams, destroy the internal structure of the coal body, and produce a sufficient number of interconnected pore-crack networks to accelerate the desorption and diffusion rate of coal gas, reduce its flow resistance in the channel, and thus improve the permeability of the coal seam.

[0003] When developing coalbed methane in soft coal seams, due to complex geological conditions, poor well wall stability, and easy blockage of gas production channels, the coalbed methane extraction effect is poor. When implementing permeability enhancement for soft coal seams, hydraulic measures are mostly used, such as the permeability enhancement methods disclosed in CN202011549713.5, CN202110829646.0, and CN201911233543.7. However, during the gas extraction process, the pressure relief holes will continue to collapse due to creep and mudification of residual water, blocking the gas migration channels, causing a sharp decrease in gas extraction flow, and a water lock effect will also occur, inhibiting gas desorption in the cracks, resulting in a longer pre-extraction time for gas and an increase in residual content. Summary of the invention

[0004] The present invention aims to solve the technical problems existing in the prior art, and the purpose of the present invention is to provide a high-intensity acoustic-electric field composite permeability enhancement method for ground coalbed methane wells applicable to soft coal seams.

[0005] To achieve the above object, the present invention adopts the following technical solution: a high-intensity acoustic and electric field composite anti-transmission method for ground coalbed methane wells suitable for soft coal seams, characterized in that it includes the following steps:

[0006] Step 1: Once the well is drilled, the drill bit is used to drill a distance below the bedrock layer from the ground, and the surface casing is lowered to seal the loose strata, and the cementing cement is returned to the ground;

[0007] Step 2: Secondary drilling, using a triangular ladder-tooth drill bit with a single-bend spiral drill pipe to drill into the target coal seam, complete the drilling, run the technical casing, and return the cement to the ground;

[0008] Step 3: Three-opening drilling, using special-shaped directional drilling tools and pneumatic spiral drill pipe drilling tools, equipped with electromagnetic wave drilling measurement system to carry out directional drilling to the horizontal section of the target layer;

[0009] Step 4: After the third drilling is completed, the directional drilling tool is pulled out, and the openable and closable pilot drill bit and the integral large-hole spiral drill pipe are re-inserted. The hole protection screen is inserted into the spiral drill pipe, and the drill is pulled out to realize directional horizontal well drilling. The drilling tool is pulled out, and the hole protection screen passes through the openable and closable pilot drill bit and remains in the hole to seal the hole;

[0010] Step 5: Connect the electric detonation control system and the ultrasonic generator on the ground, use the oil pipe to pull the high-voltage electrode of the electric detonation and the ultrasonic transducer to the end of the horizontal well, and then inject clean water into the horizontal well until the clean water reaches the landing point of the coal seam, and stop water injection;

[0011] Step 6: Take a fracturing method that gradually moves from the end of the horizontal well to the landing point of the coal seam, start the electric explosion control system in advance, and use a multi-level energy discharge excitation method to discharge and excite at the fracturing point closest to the end of the horizontal well through a high-voltage electrode. When the microseismic monitoring system observes that the fracturing range remains unchanged, increase the energy of the high-voltage electrode step by step for discharge excitation, and monitor the fracturing effect in real time through the microseismic monitoring system until the fracturing range remains stable;

[0012] Step 7: When the microseismic monitoring system observes that the fracturing range remains unchanged, the ultrasonic generator is started again, and multi-stage ultrasonic excitation is used to perform ultrasonic excitation at the fracturing point closest to the end of the horizontal well through the ultrasonic transducer, and the action is continued for a period of time. When the microseismic monitoring system observes that the fracturing range remains unchanged, the ultrasonic power is increased step by step, and the action is continued for a period of time. The fracturing effect is monitored in real time through the microseismic monitoring system until the fracturing range remains stable;

[0013] Step 8: When the microseismic monitoring system observes that the fracturing range remains unchanged, excitation is performed at the next position, and steps 6 and 7 are repeated until all fracturing points in the horizontal well are excited;

[0014] Step 9: Turn off the electric detonation control system and ultrasonic generator, take out the high-voltage electrode and ultrasonic transducer, lower the extraction drill pipe, and start the extraction equipment to extract the horizontal well.

[0015] The above technical solution expands the extraction area by constructing an L-shaped horizontal well on the ground, and effectively extends the range of coal seam permeability enhancement through the acoustic-electric composite permeability enhancement technology, thereby improving the recovery rate of coalbed methane. The innovation of this invention lies in its special adaptability to soft coal seams, especially in the process of implementing the construction of L-shaped horizontal wells, through the horizontal well drilling system with efficient slag removal and drilling functions, it solves the problems of blowholes, collapsed holes, stuck drills and difficult holes; in addition, the present invention can also ensure that the acoustic-electric composite device (high-voltage electrodes and ultrasonic transducers) can be smoothly transported to the fracturing point of the horizontal well, and is committed to the efficient mining of soft coal seams, especially in solving technical and equipment problems in the construction process of L-shaped horizontal wells. It provides solutions; at the same time, the present invention belongs to ground operations, is easy to operate and control, and can be used in the process of implementing permeability enhancement. The reliability and safety are greatly improved; in addition, for soft coal seams, the present invention pre-adopts electric detonation technology to crack the soft coal seams, adopts a multi-level energy cracking method, gradually increases the high-voltage electrode to set the action energy at the cracking point for discharge excitation, and then adopts a strong sound field to crack the soft coal seams, adopts a multi-level ultrasonic excitation effect, and gradually increases the ultrasonic power for ultrasonic excitation. The present invention gradually increases the number of excitation levels and penetrates into the coal seam to achieve a more uniform and efficient fracturing effect. The method of gradually increasing the number of excitation levels can also avoid the blockage of developed cracks due to excessive crushing after the coal body is impacted.

[0016] In a preferred embodiment of the present invention, in step three, when serious hole collapse occurs during the three-opening drilling process, a grouting device is used to inject grouting liquid into the borehole for grouting reinforcement, and the collapsed hole section is reinforced before drilling.

[0017] The above technical solution, during the third opening stage, during the drilling of the horizontal well, before the lowering of the hole protection screen, utilizes the solidification characteristics of the grouting fluid to enhance the overall stability of the formation structure, reduce the risk of formation collapse caused by drilling operations, ensure the integrity and safety of the horizontal well channel, and facilitate the smooth advancement of subsequent drilling tools.

[0018] In a preferred embodiment of the present invention, the grouting liquid is a slurry or a curing agent at a certain pressure.

[0019] In a preferred embodiment of the present invention, in step one, when drilling begins, a high-speed crawler drilling rig is used, equipped with a Φ444.5mm drill bit to drill at least 20m below the bedrock layer, and the surface casing is a steel pipe with a diameter of Φ339.7mm, a wall thickness of 9.65mm, and a steel grade of J55.

[0020] The above technical solution, the high-speed crawler drilling rig is equipped with a large torque, high-speed power head, which can effectively solve the problems of drill sticking, hole collapse, etc. that occur during the drilling process.

[0021] In a preferred embodiment of the present invention, in step 2, during the second drilling, a Φ311.15 mm triangular ladder tooth drill bit is used in combination with a single-bend screw, and the technical casing is a steel pipe with a diameter of Φ244.5 mm, a wall thickness of 8.94 mm, and a steel grade of J55.

[0022] The above technical solution, in which the single-bend spiral drill rod is matched with the triangular ladder tooth drill bit, can realize efficient slag removal and drilling, and can greatly improve the drilling efficiency and drilling depth.

[0023] In another preferred embodiment of the present invention, in step three, during the third drilling, a Φ215.9 mm triangular ladder tooth drill bit is used in conjunction with a pneumatic auger drill rod to drill along the middle of the coal seam, and the pneumatic auger drill rod uses a mining air compressor as a power source.

[0024] In the above technical solution, the triangular ladder tooth drill bit cooperates with the pneumatic spiral drill rod to realize directional drilling in the broken soft coal seam.

[0025] In another preferred embodiment of the present invention, in step 4, the diameter of the openable and closable guide drill bit is Φ139.7 mm.

[0026] In another preferred embodiment of the present invention, for a given coal body, the correlation between the degree of coal body damage and the number of excitation actions, excitation intensity and excitation time is obtained through experimental data analysis, and is represented by a damage function Dtotal(N, Eimpact) or Dtotal(T, Eimpact), where D total (N,E impact ) is a multi-level energy discharge excitation, with the number of excitation actions N or the excitation intensity E of each level impact The increase of the cumulative damage degree of the coal seam; D total (T,E impact ) is a multi-stage ultrasonic excitation, with the excitation time T or each level of excitation intensity E impact The increase in the amount of soil damage will increase the cumulative damage to the coal seam.

[0027] In another preferred embodiment of the present invention, in step six, when a multi-level energy fracturing method is adopted, the action energy and the action times are set to 200 kJ and 20 discharges at the fracturing point by a high-voltage electrode, and discharge excitation is performed. When the microseismic monitoring system observes that the fracturing range remains unchanged, the action energy of the high-voltage electrode is increased to 400 kJ and 600 kJ in turn, and each is discharged 20 times for discharge excitation.

[0028] The above technical scheme, when implementing the electric detonation technology, first uses small-power multiple blasts, and then gradually increases the pulse power to promote the development of micro-cracks inside the coal seam and the expansion of existing cracks through multi-level energy fracturing. By controlling the number of actions between each level of excitation, during the fracturing process of the soft coal seam, the coal seam is prevented from being damaged by excessive impact and causing blockage of the developed cracks.

[0029] In another preferred embodiment of the present invention, in step seven, when multi-stage ultrasonic excitation is adopted, a 20kHz / 100kW sound field is first set through the ultrasonic transducer for excitation, and the excitation is continued for 1 hour. When the microseismic monitoring system observes that the fracture range remains unchanged, the ultrasonic transducer power is increased to 50kW and 100kW in turn, and the excitation is continued for 1 hour respectively.

[0030] In the above technical scheme, when implementing ultrasonic excitation, low-power ultrasonic waves are first applied continuously for a period of time, and then the ultrasonic power is increased and applied continuously for a period of time, so as to increase the porosity of the coal body through multi-level ultrasonic excitation, thereby improving the permeability of the coal seam. Moreover, by controlling the action time between each level of excitation, damage to the internal pore structure of the coal body and blockage of developed cracks can be avoided.

[0031] Compared with the prior art, the preferred technical solution of the present invention has the following beneficial effects:

[0032] 1) Combined with horizontal well technology, by increasing the length of the horizontal section, the contact area between the coal seam and the well wall is expanded, thereby improving the coverage and extraction efficiency of coalbed methane; at the same time, the application of horizontal well drilling system and hole protection screen ensures the long-term stability and safety of the borehole.

[0033] 2) By integrating high-speed crawler drilling rigs, spiral drill rods, triangular ladder tooth drill bits, pneumatic directional drilling technology, electromagnetic wave measurement while drilling system, hole protection screen technology and grouting reinforcement hole wall technology, a scientific and efficient solution is provided for long drilling construction in soft coal seams.

[0034] 3) First, use electric detonation technology to generate stress waves in the coal seam, causing volume fracturing of the coal seam, forming a new fracture network, and improving the gas seepage channel; then use acoustic field excitation technology to promote the expansion and connectivity of pores through the propagation of sound waves, reduce the flow resistance of gas in coal, and enhance the diffusion and migration capacity of coalbed methane.

[0035] 4) The acoustic-electric composite permeability enhancement technology is used to carry out segmented transformation of coal seam horizontal wells, which greatly improves the connectivity of the pore and fracture structure, provides a high-speed migration channel for gas migration, and realizes the efficient development of coalbed methane.

[0036] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0038] Figure 1 It is a schematic diagram of an anti-reflection operation performed by the anti-reflection method of the embodiment.

[0039] The figure marks in the drawings of the specification include: rock layer 1, coal seam 2, horizontal well 3, oil pipe 4, electric detonation control system 5, high-voltage cable 6, high-voltage electrode 7, ultrasonic generator 8, ultrasonic cable 9, ultrasonic transducer 10. DETAILED DESCRIPTION

[0040] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0041] In the description of the present invention, it is to be understood that the terms “longitudinal”, “lateral”, “vertical”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside” and “outside” etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0042] In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0043] The present invention provides a high-intensity acoustic-electric field composite permeability enhancement method for ground coalbed methane wells applicable to soft coal seams, such as Figure 1 As shown, in a preferred embodiment, the anti-reflection method comprises the following steps:

[0044] Step 1: Once the well is drilled, a high-speed crawler drill rig equipped with a Φ444.5mm drill bit is used to drill from the ground to a distance below the bedrock layer 1, such as at least 20m below the bedrock layer 1, to ensure that the drilled stratum is stable; a surface casing with a diameter of Φ339.7mm, a wall thickness of 9.65mm, and a steel grade of J55 is lowered to seal the loose stratum, and the cementing cement is returned to the ground. The high-speed crawler drill rig is equipped with a high-torque, high-speed power head, which can effectively solve problems such as drill sticking and hole collapse during the drilling process.

[0045] Step 2: Secondary drilling, using Φ311.15mm triangular ladder tooth drill bit with single-bend spiral drill pipe to drill into the target coal seam 2, and then drill into the J55 steel grade casing with a diameter of Φ244.5mm and a wall thickness of 8.94mm, and cementing cement is returned to the ground. The single-bend spiral drill pipe is matched with the triangular ladder tooth drill bit. Through the high-speed rotating spiral blade of the single-bend spiral drill pipe, the coal powder is discharged out of the hole in large quantities and continuously through the conveying channel between the spiral blade and the hole wall, so as to achieve the cleaning of the hole, realize efficient slag removal and drilling, and greatly improve the drilling efficiency and drilling depth.

[0046] Step 3: Three-opening drilling, using special-shaped directional drilling tools and pneumatic spiral drill rods, equipped with electromagnetic wave measurement while drilling system for directional drilling, directional drilling to the horizontal section of the target layer of coal seam 2. Among them, the electromagnetic wave measurement while drilling system is an existing technology, which can realize accurate measurement and control of the trajectory, ensure that the drilling trajectory extends along the coal seam 2, increase the proportion of the drilled coal seam hole section, and enhance the gas extraction effect. The special-shaped directional drilling tool is a Φ215.9mm triangular ladder tooth drill bit. The Φ215.9mm triangular ladder tooth drill bit cooperates with the spiral drill rod to effectively drill along the middle range of coal seam 2. The pneumatic spiral drill rod uses a mining air compressor as the power source. The mining air compressor and the special-shaped directional drilling tool work together to realize directional drilling of the broken soft coal seam 2. Preferably, when serious hole collapse occurs during the drilling process, a grouting device is used to inject grouting liquid (the grouting liquid is a slurry or a curing agent at a certain pressure) into the borehole for grouting reinforcement. The collapsed hole section is reinforced before drilling. After the grouting liquid is injected into the borehole, it can use its own pressure to penetrate into the cracks around the borehole, artificially increasing the mechanical strength of the borehole surrounding pressure. Grouting reinforcement can improve the stability of the hole wall and prevent the borehole from deviating from the center or the hole wall from being damaged.

[0047] Step 4: After the third drilling is completed, the directional drilling tool is pulled out, and the Φ139.7mm openable and closable guide drill bit (a guide drill bit that can be opened and closed) and the integral large-hole spiral drill pipe are re-inserted, and the hole protection screen pipe is sent through the inside of the spiral drill pipe to start drilling to achieve directional horizontal well 3 drilling; open the guide drill bit, pull out the drilling tool, and the hole protection screen pipe passes through the opened guide drill bit and remains in the hole to improve the stability of the borehole, seal the hole, and ensure the long-term stability and safety of the borehole.

[0048] Step 5: If Figure 1 As shown, the high-voltage cable 6 of the electric detonation control system 5 and the ultrasonic cable of the ultrasonic generator 8 are connected on the ground, and the high-voltage electrode 7 of the electric detonation and the ultrasonic transducer 10 are pulled to the end of the horizontal well 3 by the oil pipe 4, and then clean water is injected into the horizontal well 3 until the clean water height reaches the landing point of the coal seam 2, and the water injection is stopped.

[0049] Step 6: Take a fracturing method that gradually moves from the end of the horizontal well 3 to the landing point of the coal seam 2, pre-start the electric detonation control system 5, and adopt a multi-level energy discharge excitation method. First, discharge excitation is performed at the fracturing point closest to the end of the horizontal well 3 (for example, the fracturing point is 50m away from the end of the horizontal section) through the high-voltage electrode 7. The high-voltage electrode 7 generates a high-voltage electric pulse, which is used to generate a high-intensity shock wave in the coal seam 2 for blasting to expand the cracks in the coal seam 2; when the microseismic monitoring system observes that the fracturing range remains unchanged, the energy of the high-voltage electrode 7 of the electric detonation is increased step by step for blasting. The fracturing effect is monitored in real time by the microseismic monitoring system for each blasting until the fracturing range remains stable.

[0050] Step 7: When the microseismic monitoring system observes that the fracturing range remains unchanged, the ultrasonic generator 8 is started again, and a multi-stage ultrasonic excitation is adopted. First, the ultrasonic transducer 10 is set at the fracturing point closest to the end of the horizontal well 3 to generate sound waves, and the coal seam 2 is ultrasonically excited to further promote the expansion and connectivity of the pores and cracks. The ultrasonic excitation continues for a period of time. When the microseismic monitoring system observes that the fracturing range remains unchanged, the ultrasonic power is increased step by step. The ultrasonic excitation continues for a period of time, and the fracturing effect is monitored in real time through the microseismic monitoring system until the fracturing range remains stable.

[0051] Step 8: When the microseismic monitoring system observes that the fracture range remains unchanged, excitation is performed at the next position, and steps 6 and 7 are repeated to perform segmented transformation on the horizontal well 3 of the coal seam 2 until all fracture points in the horizontal well 3 are excited, so that a fracture network is formed in the coal seam 2.

[0052] Step nine: turn off the electric detonation control system 5 and the ultrasonic generator 8, take out the high-voltage electrode 7 and the ultrasonic transducer 10, lower the extraction drill pipe, and start the extraction equipment to extract the horizontal well 3.

[0053] In practical application, representative coal samples can be collected in the target coal seam first, and the hardness of the coal samples can be tested using special equipment such as hardness testers to determine the hardness distribution characteristics of the coal seam. Then, according to the test results of the coal seam hardness, reasonable acoustic and electric field excitation intensities are designed; lower excitation intensity is used for coal seams with lower hardness to avoid excessive damage to the coal seam; the excitation intensity is appropriately increased for coal seams with higher hardness to ensure the excitation effect. Finally, considering the thickness and hardness of the coal seam, a technical solution of multi-level electric field excitation and multi-level acoustic field is designed. By gradually increasing the number of excitation levels, the internal part of the coal seam can be penetrated to achieve a more uniform and efficient fracturing effect; at the same time, the number of actions or action time between each level of excitation is controlled to avoid excessive impact damage to the coal seam.

[0054] For a given coal body, in the actual fracturing process, when multiple excitations act on the coal seam, the degree of coal body damage will continue to accumulate. For a given coal body, through the analysis of experimental data, the correlation between the degree of coal body damage and the number of excitations, excitation intensity and excitation time is obtained, which is expressed by the damage function Dtotal(N,Eimpact) or Dtotal(T,Eimpact).

[0055] Among them, D total (N,E impact ) is a multi-level energy discharge excitation, with the number of excitation actions N or the excitation intensity E of each level impact The increase in the cumulative damage to the coal seam;

[0056] D total (T,E impact ) is a multi-stage ultrasonic excitation, with the excitation time T or each level of excitation intensity E impact The increase in the amount of soil damage will increase the cumulative damage to the coal seam.

[0057] For coal seams, there is a damage threshold σ, when the cumulative damage D total When this threshold is exceeded, the coal seam will be damaged. Therefore, in the initial stage of the acoustic-electric composite permeability enhancement of the coal seam, the present invention uses a low-energy impact intensity to significantly reduce the crushing area of ​​the coal body and effectively increase the number of cracks inside the coal seam. When the action energy gradually increases in the later stage, the shock wave or ultrasonic cavitation effect generated inside the coal body will be able to propagate to a farther distance, easily forming large and wide cracks, thereby achieving large-scale permeability enhancement of the coal seam, and then promoting the effective migration and output of coalbed methane.

[0058] In a specific implementation, for soft coal seams, due to the low strength of the coal body, the electric field and acoustic field excitation intensity are adjusted and controlled to avoid excessive crushing of the coal body after impact, accelerate the attenuation of the impact force, and make the fracturing effect poor. Electric detonation technology is used to crack soft coal seams in advance, and the high-voltage electrode of the electric detonation equipment is set to 200kJ and 20 times at the fracturing point for discharge excitation. When the microseismic monitoring system observes that the fracturing range remains unchanged, the high-voltage electrode action energy is increased to 400kJ and 600kJ in turn, and each discharges 20 times for discharge excitation. When a strong acoustic field is subsequently used to crack soft coal seams, the ultrasonic transducer is set to 20kHz / 20kW acoustic field for excitation, and the excitation time lasts for 1h. When the microseismic monitoring system observes that the fracturing range remains unchanged, the ultrasonic transducer action power is increased to 50kW and 100kW in turn, and the excitation lasts for 1h respectively.

[0059] In the present invention, the microseismic monitoring system belongs to the ground equipment, which is not lowered into the horizontal well. It is turned on before each implementation of the acoustic and electrical action for real-time monitoring. After the horizontal well position and the fracture point position are determined, the microseismic sensor is arranged at the ground position above the fracture point of the horizontal well by using the height difference, horizontal ring and ray arrangement, buried 10 cm below the surface, arranged vertically on the ground, fixed with gypsum, and each site is numbered so that the microseismic sensor corresponds to the microseismic monitoring system one by one. During the test, the microseismic data of each discharge operation and ultrasonic intense operation are collected in real time and analyzed in real time, and the fracture range during the test is monitored. After the fracture range is observed to no longer change, the next position fracture test is carried out. Before carrying out the next point fracture, the microseismic sensor should also be moved to the ground above the next fracture point. After the microseismic sensor is arranged, the electric explosion control system and the ultrasonic generator are turned on.

[0060] The present invention solves the problems of coal softening, mudification and water lock effect caused by water from the source through the combined effect of ultrasound and electric explosion technology, and makes up for the shortcomings of hydraulic technology to a certain extent. The "fatigue damage" brought by the mechanical vibration effect of electric explosion technology can make the surface of the pore structure of coal smoother, and the "micro jet" brought by the ultrasonic cavitation effect can well clean the impurities in the pore channels inside the coal body, which helps to reduce the flow resistance of gas in coal and enhance the diffusion and migration capacity of coal seam 2 gas. At the same time, the high-intensity shock wave generated by electric explosion based on the liquid-electric effect has a huge impact on the coal body, so that the original cracks in the coal body are expanded and new cracks are developed, which is easy to form a crack network inside the coal seam 2, enhance the connectivity of the coal body pore crack structure, improve the gas extraction efficiency, and reduce environmental pollution and operating costs at the same time. It has broad application prospects and significant economic and social benefits. Using special-shaped directional drilling tools and pneumatic spiral drill pipe drilling tools, effective drilling of horizontal well 3 is achieved, the degree of crack penetration inside the pre-mined coal seam 2 is improved, and the maximum utilization of coal resources and gas resources is fully increased.

[0061] In the description of this specification, the description with reference to the terms "preferred embodiment", "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0062] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A high-intensity acoustic-electric field composite permeability enhancement method for ground coalbed methane wells suitable for soft coal seams, characterized in that: The steps include: Step 1: Once the well is drilled, the drill bit is used to drill a distance below the bedrock layer from the ground, and the surface casing is lowered to seal the loose strata, and the cementing cement is returned to the ground; Step 2: Secondary drilling, using a triangular ladder-tooth drill bit with a single-bend spiral drill pipe to drill into the target coal seam, complete the drilling, run the technical casing, and return the cement to the ground; Step 3: Three-opening drilling, using special-shaped directional drilling tools and pneumatic spiral drill pipe drilling tools, equipped with electromagnetic wave drilling measurement system to carry out directional drilling to the horizontal section of the target layer; Step 4: After the third drilling is completed, the directional drilling tool is pulled out, and the openable and closable pilot drill bit and the integral large-hole spiral drill pipe are re-inserted. The hole protection screen is sent through the spiral drill pipe, and the drill is pulled out to realize the directional horizontal well drilling. The drilling tool is pulled out, and the hole protection screen passes through the openable and closable pilot drill bit and remains in the hole to seal the hole; Step 5: Connect the electric detonation control system and the ultrasonic generator on the ground, use the oil pipe to pull the high-voltage electrode of the electric detonation and the ultrasonic transducer to the end of the horizontal well, and then inject clean water into the horizontal well until the clean water reaches the landing point of the coal seam, and stop water injection; Step 6: Take a fracturing method that gradually moves from the end of the horizontal well to the landing point of the coal seam, start the electric explosion control system in advance, and use a multi-level energy discharge excitation method to discharge and excite at the fracturing point closest to the end of the horizontal well through a high-voltage electrode. When the microseismic monitoring system observes that the fracturing range remains unchanged, increase the energy of the high-voltage electrode step by step for discharge excitation, and monitor the fracturing effect in real time through the microseismic monitoring system until the fracturing range remains stable; Step 7: When the microseismic monitoring system observes that the fracturing range remains unchanged, the ultrasonic generator is started again, and multi-stage ultrasonic excitation is used to perform ultrasonic excitation at the fracturing point closest to the end of the horizontal well through the ultrasonic transducer, and the action is continued for a period of time. When the microseismic monitoring system observes that the fracturing range remains unchanged, the ultrasonic power is increased step by step, and the action is continued for a period of time. The fracturing effect is monitored in real time through the microseismic monitoring system until the fracturing range remains stable; Step 8: When the microseismic monitoring system observes that the fracturing range remains unchanged, excitation is performed at the next position, and steps 6 and 7 are repeated until all fracturing points in the horizontal well are excited; Step 9: Turn off the electric detonation control system and ultrasonic generator, take out the high-voltage electrode and ultrasonic transducer, lower the extraction drill pipe, and start the extraction equipment to extract the horizontal well.

2. The high-intensity acoustic-electric field composite anti-reflection method for ground coalbed methane wells applicable to soft coal seams according to claim 1 is characterized in that: In step three, when serious hole collapse occurs during the third drilling process, a grouting device is used to inject grouting liquid into the borehole for grouting reinforcement, and the collapsed hole section is reinforced before drilling.

3. The high-intensity acoustic-electric field composite anti-reflection method for ground coalbed methane wells applicable to soft coal seams according to claim 2, characterized in that: The grouting liquid is a slurry or a curing agent at a certain pressure.

4. The high-intensity acoustic-electric field composite anti-reflection method for ground coalbed methane wells applicable to soft coal seams according to claim 1, characterized in that: In step 1, when drilling begins, a high-speed crawler drilling rig is used, equipped with a Φ444.5mm drill bit, and drilled at least 20m below the bedrock layer. The surface casing is a steel pipe with a diameter of Φ339.7mm, a wall thickness of 9.65mm, and a steel grade of J55.

5. The high-intensity acoustic-electric field composite anti-reflection method for ground coalbed methane wells applicable to soft coal seams according to claim 4, characterized in that: In step 2, during the second drilling, a Φ311.15 mm triangular ladder tooth drill bit is used in conjunction with a single-bend screw rod for drilling. The technical casing is a steel pipe with a diameter of Φ244.5 mm, a wall thickness of 8.94 mm, and a steel grade of J55.

6. The high-intensity acoustic-electric field composite anti-reflection method for ground coalbed methane wells applicable to soft coal seams according to claim 5, characterized in that: In step three, during the third drilling, a Φ215.9 mm triangular ladder tooth drill bit is used in conjunction with a pneumatic auger drill rod to drill along the middle of the coal seam. The pneumatic auger drill rod uses a mining air compressor as a power source.

7. The high-intensity acoustic-electric field composite anti-reflection method for ground coalbed methane wells applicable to soft coal seams according to claim 6, characterized in that: In step 4, the diameter of the openable and closable guide drill bit is Φ139.7 mm.

8. The high-intensity acoustic-electric field composite permeability enhancement method for ground coalbed methane wells applicable to soft coal seams according to any one of claims 1 to 7, for a given coal body, the correlation between the degree of coal body damage and the number of excitation actions, excitation intensity and excitation time is obtained through experimental data analysis, and is represented by a damage function Dtotal(N,Eimpact) or Dtotal(T,Eimpact), in, D total (N,E impact ) is a multi-level energy discharge excitation, with the number of excitation actions N or the excitation intensity E of each level impact The increase of the cumulative damage to the coal seam; D total (T,E impact ) is a multi-stage ultrasonic excitation, with the excitation time T or each level of excitation intensity E impact The increase in the amount of soil damage will increase the cumulative damage to the coal seam.

9. The high-intensity acoustic-electric field composite anti-reflection method for ground coalbed methane wells applicable to soft coal seams according to claim 8, characterized in that: In step six, when a multi-level energy fracturing method is adopted, the action energy and the number of discharges are set to 200 kJ and 20 times respectively at the fracture point through the high-voltage electrode for discharge excitation. When the microseismic monitoring system observes that the fracture range remains unchanged, the action energy of the high-voltage electrode is increased to 400 kJ and 600 kJ in turn, and each is discharged 20 times for discharge excitation.

10. The high-intensity acoustic and electric field composite anti-reflection method for ground coalbed methane wells applicable to soft coal seams according to claim 9, characterized in that: In step seven, when multi-stage ultrasonic excitation is used, first set the ultrasonic transducer to a 20kHz / 100kW sound field for excitation, and continue the excitation for 1 hour. When the microseismic monitoring system observes that the fracture range remains unchanged, increase the ultrasonic transducer power to 50kW and 100kW in turn, and continue the excitation for 1 hour respectively.

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