Coal seam anti-reflection method for electric pulse-assisted staged hydraulic fracturing

Abstract

The invention discloses an electric pulse assisted segmented hydraulic fracturing coal seam anti-reflection method, which comprises the following steps of: constructing by taking two adjacent directional long drill holes as a group, synchronously dividing a plurality of packing intervals in the two directional long drill holes, and synchronously performing hydraulic fracturing on the packing intervals corresponding to the two directional long drill holes, cracks are generated in the surrounding coal seams of the two packing intervals with the closest distance; then the packing intervals are continuously filled with water, the fracture closing possibility is reduced through pore pressure, meanwhile, water serves as a dielectric medium to fill all fractures, and when a follow-up electric pulse transceiver excites electric pulses with set power, the electric pulses can enter all the fractures generated in one packing interval along the dielectric medium; at the moment, two adjacent coal seams filled with dielectric medium fractures are broken down under the action of electric pulses to form through connection, so that the space distribution volume of the multi-scale hole fractures of the coal body is increased; and finally, global fracturing of the thick coal seam is achieved. And the construction process is simple, and application and popularization are convenient.

Description

Technical Field

[0001] The invention relates to a coal seam permeability enhancement method for electric pulse assisted segmented hydraulic fracturing, belonging to the technical field of coal seam gas extraction. Background Art

[0002] China's coal seams generally have the characteristics of "high gas pressure, high gas content, high ground stress, and low porosity and permeability", which seriously restricts the safe mining of coal mines. In order to reduce the impact of gas disasters in the coal mining process, it is usually necessary to strengthen the fracturing and permeability of low-permeability coal seams, and transform the coal seam structure with the help of external medium energy, thereby generating a large number of fracture networks and improving the porosity and permeability characteristics of the coal body.

[0003] Hydraulic fracturing technology is one of the commonly used coal seam fracturing technologies. This technology mainly pumps high-pressure water into the coal seam and fractures it. Affected by ground stress, the induced fractures are usually single long fractures that penetrate the coal seam area, which can be connected with the original pore fracture structure of the coal seam to form fractures in a certain area; at the same time, high-pressure water will be lost as the fracture space expands, and the continuous reduction of pore pressure may cause the fracture fracture to close, and the impact range has certain limitations. Hydraulic fracturing technology acts on coal rock mass and usually forms a stress shadow in a certain area in the reservoir, causing the stress concentration phenomenon in the unfractured area of ​​the coal rock mass to be prominent, resulting in the inability to improve the porosity and permeability characteristics of the coal seam in this area, which makes it difficult for coal seam gas to migrate out by pressure relief, seriously restricting the safe mining of coal seams.

[0004] Therefore, how to provide a new coal seam permeability enhancement method that can expand the distribution of fractures in the coal seam in the hydraulic fracturing affected area, make it spatially connected, form a complex fracture network, and ultimately effectively improve the permeability enhancement and porosity and permeability characteristics of thick coal seams is the research direction required by the present invention. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a coal seam permeability enhancement method using electric pulse assisted staged hydraulic fracturing, which can expand the distribution of cracks in the coal seam in the hydraulic fracturing affected area, make them spatially connected, form a complex fracture network, and ultimately effectively improve the permeability enhancement and porosity and permeability characteristics of thick coal seams.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a coal seam permeability enhancement method by electric pulse assisted staged hydraulic fracturing, the specific steps are:

[0007] A. Use a directional drill bit to construct two directional long boreholes from the side wall of the tunnel to the target coal seam to the designed length, and the two directional long boreholes are parallel to each other in the target coal seam. Fix the electric pulse receiver on the first section of the drill pipe close to the directional drill bit, so that the two electric pulse receivers are drilled into the bottom of the two directional long boreholes along with the directional drill bit.

[0008] B. After the construction is completed, the first high-pressure packer is placed in each of the two directional long boreholes for sealing, so that the first isolation interval is formed between the bottom of each of the two directional long boreholes and the first high-pressure packer, and the electric pulse receiver is in the first isolation interval.

[0009] C. The tail ends of the drill pipes in the two directional long boreholes are respectively connected to hydraulic fracturing devices. The hydraulic fracturing devices inject high-pressure water into the first isolation intervals of the two directional long boreholes along the drill pipes, and continue to inject water into the first isolation intervals until the injection pressure value reaches the set value. The injection of high-pressure water is stopped and the high pressure is maintained for a period of time. When the pressure value drops significantly, it indicates that the coal seams around the first isolation interval are fractured to produce cracks, allowing high-pressure water to enter the cracks. At this time, the cracks produced in the two first isolation intervals are close to each other, completing the hydraulic fracturing process of the first isolation interval.

[0010] D. After the hydraulic fracturing of the first isolation intervals of the two directional long boreholes is completed, the first isolation intervals are refilled with high-pressure water through the hydraulic fracturing device, and then the electric pulse transceiver in one of the directional long boreholes is used as an electric pulse generating device, and the electric pulse transceiver in the other directional long borehole is used as an electric pulse receiving device. At the same time, the water in the first isolation interval is used as the dielectric medium, and the electric pulse generating device is started with the set electric pulse excitation power. The generated electric pulse reaches the crack along the dielectric medium in the current first isolation interval, and because the crack in the other first isolation interval is also full of dielectric medium, the coal seam between the two adjacent cracks filled with dielectric medium is broken down by the electric pulse to form a through connection; after the current electric pulse transceiver has been working for a period of time, the electric pulse is stopped. At this time, a complex fracture network is formed in the coal seams around the two first isolation intervals and the connectivity is increased, completing the electric pulse permeability enhancement work of the first isolation interval.

[0011] E. Use the existing microseismic monitoring system in the well to monitor the fracture development of the hydraulic fracturing process in step C and the electric pulse permeability enhancement process in step D. If the required requirements are met, proceed to step F. Otherwise, repeat steps C and D until the required requirements are met and proceed to step F.

[0012] F. Place a second high-pressure packer into each of the two directional long boreholes for sealing, so that a second isolation interval is formed between the second high-pressure packer and the first high-pressure packer, and the electric pulse transmitter and receiver is placed in the second isolation interval by retracting the drill; after completion, repeat steps C to E to achieve hydraulic fracturing and electric pulse permeability enhancement process for the second isolation interval; repeat this process to achieve hydraulic fracturing and electric pulse permeability enhancement process for the coal seams around the two directional long boreholes in stages.

[0013] G. Re-determine the drilling positions of multiple directional long boreholes constructed towards the target coal seam, and form a group of two adjacent directional long boreholes. Repeat steps A to F for each group, thereby completing the hydraulic fracturing and electric pulse permeability enhancement process for the entire target coal seam.

[0014] Furthermore, in step C, the high voltage is maintained for 60 minutes; and in step D, the electric pulse transceiver continues to work for 30 minutes.

[0015] Furthermore, the diameter of the directional long drill hole is 90-110 mm, the drilling depth is 500-550 m, and the distance between two adjacent directional long drill holes is 50-60 m.

[0016] Furthermore, the pulse receiver is fixed inside the first section of the drill pipe, and the pulse receiver and the drill pipe are fixed with high-pressure resistant fixing glue. The pulse receiver leads a data transmission line to the hole mouth and is connected to the electric pulse control device.

[0017] Furthermore, the pulse receivers in each group of two directional long boreholes work and retreat synchronously to ensure that they are always within the two isolation intervals with the shortest distance.

[0018] Furthermore, the length of each isolation interval is controlled within a range of 50 to 80 m, and the specific length can be adjusted according to the trajectory of the directional long borehole; this can ensure the hydraulic fracturing and electric pulse permeability enhancement effects of each isolation interval.

[0019] Furthermore, the high-pressure packer is made of steel with a compressive strength range of 30MPa to 70MPa; the use of this material and parameters can ensure the requirements of hydraulic fracturing and ensure the smooth progress of the fracturing process.

[0020] Compared with the prior art, the present invention constructs two adjacent directional long boreholes as a group. After each group completes the drilling construction, multiple isolation intervals are synchronously divided in the two directional long boreholes, and hydraulic fracturing is synchronously performed on the isolation intervals corresponding to the two directional long boreholes, so that cracks are generated in the coal seams around the two isolation intervals that are closest to each other, and the cracks generated in the two isolation intervals that are synchronously fractured are ensured to be close to each other, in preparation for subsequent electrical breakdown; then the isolation intervals that have completed fracturing continue to be filled with water, which can reduce the possibility of crack closure through pore pressure on the one hand, and at the same time use water as a dielectric medium to fill each crack, so that when the subsequent electric pulse transmitter and receiver excites an electric pulse of set power, the electric pulse can enter the various cracks generated in one of the isolation intervals along the dielectric medium, and And because the cracks generated in the other isolation interval are also filled with dielectric media, the coal seam between the two adjacent cracks filled with dielectric media is broken down by the electric pulse to form a through connection; thereby increasing the spatial distribution volume of the multi-scale pore cracks in the coal body; and through the process of synchronous construction of multiple isolation intervals, the hydraulic fracturing and electric pulse permeability enhancement process of the coal seams around the two directional long boreholes are realized until the hydraulic fracturing and electric pulse permeability enhancement process of the entire target coal seam are completed; this method can make up for the technical defect that multiple main cracks cannot be penetrated after directional long borehole fracturing, and the electric pulse technology can be used to effectively perform secondary breakdown on the fracturing cracks between adjacent directional long boreholes to form through cracks, thereby truly realizing the full-area fracturing of thicker coal seams; and the construction process of the present invention is simple, which is convenient for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a construction schematic diagram of the present invention.

[0022] In the figure: 1-target coal seam; 2-tunnel; 3-directional long drill hole; 4-high pressure packer; 5-data transmission line; 6-electric pulse receiver. DETAILED DESCRIPTION

[0023] The present invention will be further described below.

[0024] like Figure 1 As shown, the specific steps of the present invention are:

[0025] A. Use a directional drill bit to construct two directional long boreholes 3 from the side wall of the tunnel to the target coal seam 1 to the designed length, and the two directional long boreholes 3 are parallel to each other in the target coal seam 1, and fix the pulse receiver 6 inside the first section of the drill pipe close to the directional drill bit. The pulse receiver 6 and the drill pipe are fixed with high-pressure fixing glue. The pulse receiver 6 leads the data transmission line 5 to the hole mouth and is connected to the electric pulse control device, so that the two electric pulse receivers 6 are drilled into the bottom of the two directional long boreholes 3 respectively with the directional drill bit; the aperture of the directional long borehole 3 is 90-110 mm, the drilling depth is 500-550 m, and the distance between two adjacent directional long boreholes 3 is 50-60 m.

[0026] B. After the construction is completed, the first high-pressure packer 4 is placed in each of the two directional long boreholes 3 for sealing, so that a first isolation interval is formed between the bottom of each of the two directional long boreholes 3 and the first high-pressure packer 4, and the electric pulse receiver 6 is in the first isolation interval. The high-pressure packer 4 is made of steel with a compressive strength range of 30MPa to 70MPa.

[0027] C. The tail ends of the drill pipes in the two directional long boreholes 3 are respectively connected to hydraulic fracturing devices. The hydraulic fracturing devices inject high-pressure water into the first isolation intervals of the two directional long boreholes 3 along the drill pipes, and continue to inject water into the first isolation intervals until the injection pressure value reaches the set value. The injection of high-pressure water is stopped and the high pressure is maintained for 60 minutes. When the pressure value drops significantly, it indicates that the coal seams around the first isolation intervals are fractured to produce cracks, allowing high-pressure water to enter the cracks. At this time, the cracks produced in the two first isolation intervals are close to each other, completing the hydraulic fracturing process of the first isolation intervals.

[0028] D. After the hydraulic fracturing of the first isolation intervals of the two directional long boreholes 3 is completed, the first isolation intervals are refilled with high-pressure water through the hydraulic fracturing device, and then the electric pulse receiver 6 in one of the directional long boreholes 3 is used as an electric pulse generating device, and the electric pulse receiver 6 in the other directional long borehole is used as an electric pulse receiving device. At the same time, the water in the first isolation interval is used as the dielectric medium, and the electric pulse generating device is started with the set electric pulse excitation power. The generated electric pulse reaches the crack along the dielectric medium in the current first isolation interval, and because the crack in the other first isolation interval is also full of dielectric medium, the coal seam between the two adjacent cracks filled with dielectric medium is broken down by the action of the electric pulse to form a through connection; after the current electric pulse receiver 6 has been working for 30 minutes, the electric pulse is stopped. At this time, a complex crack network is formed in the coal seams around the two first isolation intervals and the connectivity is increased, completing the electric pulse permeability enhancement work of the first isolation interval.

[0029] E. Use the existing microseismic monitoring system in the well to monitor the fracture development of the hydraulic fracturing process in step C and the electric pulse permeability enhancement process in step D. If the required requirements are met, proceed to step F. Otherwise, repeat steps C and D until the required requirements are met and proceed to step F.

[0030] F. Place a second high-pressure packer 4 into each of the two directional long boreholes 3 for sealing, so that a second isolation interval is formed between the second high-pressure packer and the first high-pressure packer, and the electric pulse transceiver 6 is placed in the second isolation interval by withdrawing the drill; the pulse transceivers 6 in each group of two directional long boreholes 3 work and withdraw synchronously to ensure that they are always in the two isolation intervals with the shortest distance; after completion, repeat steps C to E to realize the hydraulic fracturing and electric pulse permeability enhancement process of the second isolation interval; repeat this process to realize the hydraulic fracturing and electric pulse permeability enhancement process of the coal seams around the two directional long boreholes 3 in stages.

[0031] G. Re-determine the drilling positions of multiple directional long boreholes 3 constructed towards the target coal seam 1, and group two adjacent directional long boreholes 3 into a group, and repeat steps A to F for each group, thereby completing the hydraulic fracturing and electric pulse permeability enhancement process for the entire target coal seam 1.

[0032] As an improvement of the present invention, the length of each isolation interval is controlled within 50 to 80 m, and the specific length can be adjusted according to the trajectory of the directional long borehole 3; this can ensure the hydraulic fracturing and electric pulse permeability enhancement effects of each isolation interval.

[0033] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for increasing coal seam permeability by electric pulse assisted staged hydraulic fracturing, characterized in that: The specific steps are: A. Use a directional drill bit to drill two directional long boreholes from the side wall of the tunnel to the target coal seam to the designed length, and the two directional long boreholes are parallel to each other in the target coal seam, and fix the electric pulse transmitter and receiver on the first section of the drill rod close to the directional drill bit, so that the two electric pulse transmitter and receiver are drilled to the bottom of the two directional long boreholes respectively along with the directional drill bit; B. After the construction is completed, the first high-pressure packer is placed in each of the two directional long boreholes for sealing, so that a first isolation interval is formed between the bottom of each of the two directional long boreholes and the first high-pressure packer, and the electric pulse transmitter and receiver is in the first isolation interval; C. The tail ends of the drill pipes in the two directional long boreholes are respectively connected to hydraulic fracturing devices, which inject high-pressure water into the first isolation intervals of the two directional long boreholes along the drill pipes, and continue to inject water into the first isolation intervals until the injection pressure value reaches the set value, then stop injecting high-pressure water and maintain high pressure for a period of time. When the pressure value drops significantly, it indicates that the coal seams around the first isolation intervals are fractured and cracks are generated, allowing high-pressure water to enter the cracks. At this time, the cracks generated in the two first isolation intervals are close to each other, completing the hydraulic fracturing process of the first isolation intervals; D. After the hydraulic fracturing of the first isolation intervals of the two directional long boreholes is completed, the first isolation intervals are refilled with high-pressure water through the hydraulic fracturing device, and then the electric pulse transceiver in one of the directional long boreholes is used as an electric pulse generating device, and the electric pulse transceiver in the other directional long borehole is used as an electric pulse receiving device. At the same time, the water in the first isolation interval is used as the dielectric medium, and the electric pulse generating device is started with the set electric pulse excitation power. The generated electric pulse reaches the crack along the dielectric medium in the current first isolation interval, and because the crack in the other first isolation interval is also full of dielectric medium, the coal seam between the two adjacent cracks filled with dielectric medium is broken down by the electric pulse to form a through connection; after the current electric pulse transceiver has been working for a period of time, the electric pulse is stopped. At this time, the coal seams around the two first isolation intervals form a complex fracture network and increase the connectivity, completing the electric pulse permeability enhancement work of the first isolation interval; E. Using the existing microseismic monitoring system in the well, the hydraulic fracturing process in step C and the electric pulse permeability enhancement process in step D are monitored for fracture development. If the required requirements are met, step F is entered. Otherwise, steps C and D are repeated until the required requirements are met and step F is entered. F. Place a second high-pressure packer into each of the two directional long boreholes for sealing, so that a second isolation interval is formed between the second high-pressure packer and the first high-pressure packer, and the electric pulse transmitter and receiver is placed in the second isolation interval by withdrawing the drill; after completion, repeat steps C to E to achieve hydraulic fracturing and electric pulse permeability enhancement process for the second isolation interval; repeat in this way, thereby achieving hydraulic fracturing and electric pulse permeability enhancement process for the coal seams around the two directional long boreholes in stages; G. Re-determine the drilling positions of multiple directional long boreholes constructed towards the target coal seam, and form a group of two adjacent directional long boreholes. Repeat steps A to F for each group, thereby completing the hydraulic fracturing and electric pulse permeability enhancement process for the entire target coal seam.

2. The method for increasing coal seam permeability by electric pulse assisted staged hydraulic fracturing according to claim 1, characterized in that: In step C, the high voltage is maintained for 60 minutes; in step D, the electric pulse receiver continues to work for 30 minutes.

3. The method for increasing coal seam permeability by electric pulse assisted staged hydraulic fracturing according to claim 1, characterized in that: The diameter of the directional long drill hole is 90-110 mm, the drilling depth is 500-550 m, and the distance between two adjacent directional long drill holes is 50-60 m.

4. The method for increasing coal seam permeability by electric pulse assisted staged hydraulic fracturing according to claim 1, characterized in that: The pulse transceiver is fixed inside the first section of the drill pipe, and the pulse transceiver and the drill pipe are fixed with high-pressure resistant fixing glue. The pulse transceiver leads a data transmission line to the hole mouth and is connected to the electric pulse control device.

5. The method for increasing coal seam permeability by electric pulse assisted staged hydraulic fracturing according to claim 1, characterized in that: The pulse receivers in each group of two directional long boreholes work synchronously and withdraw synchronously to ensure that they are always within the two isolation intervals with the shortest distance.

6. The method for increasing coal seam permeability by electric pulse assisted staged hydraulic fracturing according to claim 1, characterized in that: The length of each isolation interval is controlled at 50 to 80 m, and the specific length can be adjusted according to the trajectory of the directional long drilling.

7. The method for increasing coal seam permeability by electric pulse assisted staged hydraulic fracturing according to claim 1, characterized in that: The high-pressure packer is made of steel and has a compressive strength ranging from 30 MPa to 70 MPa.

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