Permeability-increasing and extraction-promoting method for downward drilling coal seam

Abstract

The invention provides a downward drilling coal seam permeability increasing and extraction promoting method, and relates to the technical field of coal mine gas extraction. The downward drilling coal seam permeability increasing and extraction promoting method comprises the following steps that S1, downward drilling is conducted; s2, pipeline plugging arrangement is carried out; s3, primary water injection; s4, high-pressure gas is injected; s5, secondary water injection; s6, lowering an ultrasonic transmitting head; and S7, periodic ultrasonic emission and gas extraction are carried out. According to the method, a synergistic effect mechanism of hydraulic presplitting, gas displacement, hydraulic saturation and ultrasonic enhancement is constructed by actively utilizing the inherent water-rich characteristic of the downward drill hole, and remarkable permeability increasing and efficient gas extraction promoting of the low-permeability coal seam are achieved. According to the method, the defects that in the prior art, the permeability increasing means is single, cost is high, efficiency is limited or the actual working condition of drilling is neglected are effectively overcome, the water-rich characteristic of downward drilling is creatively combined with the multi-physical-field synergistic effect, and a low-permeability coal seam gas permeability increasing and pumping promoting technical scheme which is efficient, low in cost, environmentally friendly and high in pertinence is formed.

Description

Technical Field

[0001] This invention relates to the field of coal mine gas extraction technology, specifically to a method for enhancing permeability and promoting gas extraction in downward-drilled coal seams. Background Technology

[0002] Coal seam gas is a major hazard in coal mining, but it is also a valuable clean energy source. Efficient coal seam gas extraction is crucial for ensuring safe coal mine production and promoting resource recovery. Currently, coal seam gas extraction generally faces technical bottlenecks such as low coal permeability and difficulties in gas desorption and migration, resulting in low extraction efficiency and long extraction cycles.

[0003] To improve coal seam permeability and gas drainage efficiency, various permeability enhancement and drainage-promoting methods have been proposed in existing technologies. For example, hydraulic fracturing technology creates a fracture network in the coal seam through high-pressure water fracturing, but it suffers from problems such as complex equipment, high cost, and potential damage to the coal structure. Chemical grouting uses chemical reagents to dissolve the coal seam, but it also faces the challenge of high cost and potential environmental pollution. Gas injection methods (such as injecting carbon dioxide or nitrogen) aim to promote gas desorption through displacement or pressure-driven processes, but their drainage-promoting efficiency is limited. In addition, some studies have attempted to apply ultrasonic technology to assist gas drainage, utilizing its cavitation and vibration effects to improve coal seam permeability. However, existing ultrasonic applications are mostly for upward drilling and dry coal seam conditions, failing to fully consider the higher transmission efficiency and slower energy attenuation of ultrasound in water, and also failing to effectively integrate with the actual working conditions of the borehole. It is worth noting that downward drainage boreholes constructed in underground coal mines commonly exhibit water accumulation, i.e., "water-rich characteristics." This characteristic is usually considered an unfavorable factor or something that needs to be eliminated in traditional technologies, and existing permeability enhancement technologies have not actively and effectively utilized this condition.

[0004] Therefore, how to develop an efficient, low-cost, and environmentally friendly method to enhance permeability and promote pumping, specifically targeting the water-rich characteristics of downhole drilling, has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] This invention provides a method for enhancing permeability and promoting pumping in coal seams through downward drilling. By utilizing the water-rich characteristics of downward drilling, it achieves efficient, low-cost, and environmentally friendly enhancement of permeability and pumping in low-permeability coal seams.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for enhancing permeability and promoting pumping in downward-drilled coal seams, the method comprising the following steps: S1, Downward drilling; Drill holes in the roadway at a downward angle toward the target coal seam; S2, Pipeline sealing and installation; Extraction and injection pipelines are laid inside the borehole, and the gap between the pipelines and the borehole is sealed using a plugging device. S3, One-time water injection; High-pressure water is injected into the borehole through the injection pipeline to hydraulically fracturing the target coal seam. S4. Inject high-pressure gas; High-pressure gas is injected into the borehole through the injection pipeline to drive the desorption of gas in the target coal body. S5, Secondary water injection; High-pressure water is injected into the borehole through the injection pipeline to saturate the target coal body with water. S6. Lower the ultrasonic transmitter head; Lower the ultrasonic transmitter along the extraction pipeline to the set position and aim it at the target coal section; S7, Periodic ultrasonic emission and gas extraction; The ultrasonic transmitter is periodically activated to generate ultrasonic waves, while gas is extracted through the extraction pipeline.

[0007] Furthermore, the occluder is configured as an inflatable capsule; The specific process of S2 is as follows: An expansion capsule is placed between the pipeline and the borehole, and a high-pressure water pipeline passes through the borehole. The two ends of the high-pressure water pipeline are connected to the expansion capsule and the first high-pressure water injection device, respectively. High-pressure water of a set flow rate and pressure is injected into the expansion capsule through the first high-pressure water injection device and the high-pressure water pipeline.

[0008] Furthermore, the specific process of S3 is as follows: The second high-pressure water injection device is connected to the injection pipeline via a pipeline, and high-pressure water with a set flow rate and pressure is injected into the borehole through the injection pipeline via the second high-pressure water injection device.

[0009] Furthermore, the specific process of S4 is as follows: The high-pressure gas injection device is connected to the injection pipeline via a pipeline, and high-pressure gas with a set flow rate and pressure is injected into the borehole through the injection pipeline via the high-pressure gas injection device.

[0010] Furthermore, the specific process of S5 is as follows: The second high-pressure water injection device is connected to the injection pipeline via a pipeline, and high-pressure water with a set flow rate and pressure is injected into the borehole through the injection pipeline via the second high-pressure water injection device.

[0011] Furthermore, after the S7 has been running for a set time, the ultrasonic transmitter head is moved to another set position to align with another target coal section.

[0012] Furthermore, the ultrasonic generator is connected to the ultrasonic transmitter head via a cable, the cable is wound onto a reel, and the ultrasonic transmitter head is mounted on a trolley equipped with a counterweight. The specific process of S6 is as follows: By rotating the reel, the trolley is moved along the extraction pipeline to the set position.

[0013] Furthermore, the reel is connected to a crank handle, which is manually turned to rotate the reel.

[0014] Furthermore, prior to S7, sealing materials are used to seal the gap between the pipeline and the borehole.

[0015] Furthermore, the middle and lower sections of the extraction pipeline are designed as perforated pipes.

[0016] The method for enhancing permeability and promoting gas extraction in downburst coal seams of this invention actively utilizes the inherent water-rich characteristics of downburst boreholes to construct a synergistic mechanism of "hydraulic pre-fracturing—gas displacement—hydraulic saturation—ultrasonic enhancement," achieving significant permeability enhancement and efficient gas extraction in low-permeability coal seams, and obtaining the following outstanding technical effects: 1. By first injecting water to hydraulically fracturing the target coal body, an initial fracture network is formed, increasing the permeability channels of the coal. Compared with traditional hydraulic fracturing, this method utilizes the water accumulation conditions in the borehole, resulting in more direct hydraulic energy transfer and more targeted fracturing. Furthermore, subsequent steps can effectively compensate for the tendency of single hydraulic fracturing fractures to close easily. While achieving increased permeability, hydraulic fracturing is performed at relatively low pressure, avoiding excessive damage to the coal structure that high-pressure hydraulic fracturing might cause, preventing safety risks such as roadway instability, and improving operational safety.

[0017] 2. After the initial fractures are formed, high-pressure gas is injected. Utilizing the gas pressure drive and gas displacement effect, the desorption of adsorbed methane in the coal matrix is ​​effectively promoted, and free methane is driven into the seepage channels. Compared to the gas injection method alone, this method, based on a hydraulic fracture network, allows gas to penetrate more fully and act on the deeper parts of the coal body, greatly improving the displacement range and replacement efficiency.

[0018] 3. The water-rich characteristics of the borehole are transformed from an unfavorable factor into a favorable one. Secondary water injection saturates the coal seam fissures, creating ideal "water-acoustic coupling" water-rich conditions for efficient ultrasonic energy transmission. The periodically emitted ultrasonic waves exhibit slow energy attenuation and high transmission efficiency in water. Their cavitation effect generates intense, instantaneous high-pressure micro-jets in the water, continuously scouring, expanding, and clearing coal seam fissures. Simultaneously, the high-frequency mechanical vibration of the ultrasonic waves acts on the coal particles, causing fatigue damage, increasing the specific surface area, and effectively reducing the gas adsorption barrier. This achieves a "dynamic and continuous" enhancement of coal permeability and gas desorption capacity during extraction. By combining periodic ultrasonic action with continuous extraction, the desorbed gas can be efficiently extracted and utilized, achieving a balance between safety, environmental protection, and resource recovery.

[0019] 4. The entire process mainly utilizes the existing water injection, gas injection, and extraction systems in the mine. The ultrasonic equipment has relatively low power, and the overall process combination is ingenious. It eliminates the need for additional expensive and complex fracturing or chemical injection equipment, significantly reducing implementation costs and operational complexity. The enhanced permeability and extraction primarily rely on physical effects (water pressure, gas pressure, and sound waves), without using harmful chemical reagents, thus avoiding environmental pollution risks. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the method for enhancing permeability and promoting extraction in downward drilling coal seams according to an embodiment of the present invention; Figure 2 This is a construction layout diagram for improving the permeability and promoting extraction of coal seams through downward drilling, according to an embodiment of the present invention. Figure 3 for Figure 2 A magnified view of a section at point A in the middle; In the picture, 11. Roadway, 12. Target coal seam, 13. Borehole, 21. Drainage pipeline, 22. Injection pipeline, 23. High-pressure water pipeline, 31. Ultrasonic transmitter, 32. Ultrasonic generator, 33. Coil, 34. Trolley, 35. Handle, 4. Expansion capsule, 51. First high-pressure water injection device, 52. Second high-pressure water injection device, 6. High-pressure gas injection device, 7. Gas drainage system. Detailed Implementation

[0021] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. Certain embodiments of the invention will be described more fully below with reference to the accompanying drawings, and some, but not all, of these embodiments will be shown. In fact, various embodiments of the invention can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to enable the invention to meet applicable legal requirements.

[0022] In the description of this invention, it should be noted that the terms "inner," "outer," "upper," "lower," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] This embodiment is based on the actual situation of a coal mine and refers to... Figures 1 to 3 As shown, a method for improving permeability and promoting pumping in downward drilling coal seams is provided, the method comprising the following steps: S1, Downward drilling; Based on the geological conditions of the coal seam and the gas occurrence parameters, boreholes 13 are drilled downwards in roadway 11 toward the target coal body 12. This step is the basis for subsequent steps. By drilling boreholes 13 downwards, high-pressure water can be injected into the downwardly inclined boreholes 13 to saturate the target coal body 12 with water.

[0024] S2, Pipeline sealing and installation; An extraction pipeline 21 and an injection pipeline 22 are laid inside the borehole 13. The middle and lower parts of the extraction pipeline 21 are made into perforated pipes. The gap between the pipelines (extraction pipeline 21 and injection pipeline 22) and the borehole 13 is sealed using a plug.

[0025] The occluder is configured as an expansion capsule 4, and the specific process of S2 is as follows: The expansion capsule 4 is placed between the pipeline (extraction pipeline 21 and injection pipeline 22) and the borehole 13. The high-pressure water pipeline 23 passes through the borehole 13, and the two ends of the high-pressure water pipeline 23 are connected to the expansion capsule 4 and the first high-pressure water injection device 51, respectively. High-pressure water of a set flow rate and pressure is injected into the expansion capsule 4 through the high-pressure water pipeline 23 by the first high-pressure water injection device 51 and pressure is maintained to expand the expansion capsule 4, thereby reliably sealing the pipeline and the borehole 13, effectively preventing gas leakage and ensuring operational safety.

[0026] S3, One-time water injection; High-pressure water is injected into borehole 13 through injection pipeline 22 to hydraulically fracture the target coal body 12, forming an initial fracture network and increasing the permeability channels of the target coal body 12.

[0027] The specific process of S3 is as follows: The second high-pressure water injection device 52 is connected to the injection pipeline 22 via a pipeline, and high-pressure water with a set flow rate and pressure is injected into the borehole 13 through the injection pipeline 22 via the second high-pressure water injection device 52.

[0028] S4. Inject high-pressure gas; High-pressure gas is injected into borehole 13 through injection pipeline 22 to drive the desorption of gas in target coal body 12. After one water injection is completed, the high-pressure gas drives the desorption of adsorbed gas in the coal matrix of target coal body 12 along the permeation channel of target coal body 12 by utilizing gas pressure and gas displacement effect, and drives free gas into the permeation channel.

[0029] The specific process of S4 is as follows: The high-pressure gas injection device 6 is connected to the injection pipeline 22 via a pipeline. High-pressure gas (such as carbon dioxide or compressed air) with a set flow rate and pressure is injected into the borehole 13 through the injection pipeline 22. The injection pressure of the high-pressure gas is usually between 1.5 and 3 times the original pressure of the target coal body 12.

[0030] S5, Secondary water injection; High-pressure water is injected into borehole 13 through injection pipeline 22 to make the target coal body 12 water saturated, so as to provide water-rich conditions for subsequent ultrasonic emission "water-acoustic coupling" and at the same time, to displace and replace some of the gas.

[0031] The specific process of S5 is as follows: The second high-pressure water injection device 52 is connected to the injection pipeline 22 via a pipeline, and high-pressure water with a set flow rate and pressure is injected into the borehole 13 through the injection pipeline 22 via the second high-pressure water injection device 52.

[0032] S6. Lower the ultrasonic transmitter head; The ultrasonic transmitter 31 is lowered along the extraction pipeline 21 to the set position and aligned with the target coal section.

[0033] The ultrasonic generator 32 is connected to the ultrasonic transmitter 31 via a cable, which is wound onto a coil 33. The ultrasonic transmitter 31 is mounted on a trolley 34 equipped with a counterweight. A crank 35 is connected to the coil 33, allowing manual rotation of the coil 33 by cranking the crank 35. A pulley 211 is installed at the bend of the extraction pipeline 21, and the cable passes around this pulley 211. A closed coil chamber is located at the outer end of the extraction pipeline 21, connected to the pipeline. The coil 33 is rotatably connected inside the chamber, and its shaft is connected to the crank 35's shaft via a magnetic coupling. This design ensures the sealing of the extraction pipeline 21 while allowing manual rotation of the crank 35 to drive the coil 33.

[0034] The specific process of S6 is as follows: By rotating the reel 33, the cable is wound and unwound, allowing the trolley 34 to travel along the extraction pipeline 21 to the set position.

[0035] S7. Sealing with sealing material; The gap between the pipelines (extraction pipeline 21 and injection pipeline 22) and the borehole 13 is sealed with sealing material to ensure a reliable seal of the borehole 13 during subsequent gas extraction, prevent gas leakage from the borehole 13, and ensure operational safety and mining efficiency.

[0036] S8, Periodic ultrasonic emission and gas extraction; The ultrasonic transmitter 31 is periodically activated to generate ultrasonic waves, and gas is extracted simultaneously through the gas extraction system 7 connected to the extraction pipeline 21.

[0037] For example, the ultrasonic generator 32 is set to operate for 10-30 minutes, with an interval of 30-60 minutes, and this cycle is repeated. The periodically emitted ultrasonic waves have slow energy attenuation and high transmission efficiency in water. Their cavitation effect generates strong, instantaneous high-pressure micro-jets in the fissure water of the target coal section, violently impacting the coal structure and continuously scouring, expanding, and clearing the coal fissures. At the same time, the high-frequency mechanical vibration of the ultrasonic waves acts on the coal particles, causing fatigue damage to the coal particles, increasing the specific surface area, effectively reducing the adsorption barrier of gas, and promoting desorption. This achieves a "dynamic and continuous" enhancement of coal permeability and gas desorption capacity during the extraction process. The entire extraction process continues until the gas concentration in the target coal section drops below the safe threshold.

[0038] Specifically, after the set time of operation in S8, when the gas concentration in the target coal section drops below the safety threshold, the ultrasonic transmitter 31 is moved to another set position to align with another target coal section. This is achieved by rotating the reel 33, causing the trolley 34 to travel along the extraction pipeline 21 to another set position, and continuing the process described in S8.

[0039] By integrating the ultrasonic transmitter 31 onto the movable trolley 34 and flexibly lowering and positioning it along the extraction pipeline 21, it is possible to precisely process target coal sections at different depths in sequence, achieving precise control and full-section coverage of the permeability enhancement and extraction operation.

[0040] The present invention has been described in detail above with reference to the accompanying drawings. Based on the above description, those skilled in the art should have a clear understanding of the method for enhancing permeability and promoting extraction in downward drilling coal seams according to the present invention. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for enhancing permeability and promoting extraction in downward drilling coal seams, characterized in that, The method includes the following steps: S1, downward drilling; Drill holes in the roadway at a downward angle toward the target coal seam; S2, Pipeline sealing and installation; Extraction and injection pipelines are laid inside the borehole, and the gap between the pipelines and the borehole is sealed using a plugging device. S3, One-time water injection; High-pressure water is injected into the borehole through the injection pipeline to hydraulically fracturing the target coal seam. S4. Inject high-pressure gas; High-pressure gas is injected into the borehole through the injection pipeline to drive the desorption of gas in the target coal body. S5, Secondary water injection; High-pressure water is injected into the borehole through the injection pipeline to saturate the target coal body with water. S6. Lower the ultrasonic transmitter head; Lower the ultrasonic transmitter along the extraction pipeline to the set position and aim it at the target coal section; S7, Periodic ultrasonic emission and gas extraction; The ultrasonic transmitter is periodically activated to generate ultrasonic waves, while gas is extracted through the extraction pipeline.

2. The method for enhancing permeability and promoting extraction in downward drilling coal seams according to claim 1, characterized in that, The occluder is configured as an inflatable capsule; The specific process of S2 is as follows: An expansion capsule is placed between the pipeline and the borehole, and a high-pressure water pipeline passes through the borehole. The two ends of the high-pressure water pipeline are connected to the expansion capsule and the first high-pressure water injection device, respectively. High-pressure water of a set flow rate and pressure is injected into the expansion capsule through the first high-pressure water injection device and the high-pressure water pipeline.

3. The method for enhancing permeability and promoting extraction in downward drilling coal seams according to claim 1, characterized in that, The specific process of S3 is as follows: The second high-pressure water injection device is connected to the injection pipeline via a pipeline, and high-pressure water with a set flow rate and pressure is injected into the borehole through the injection pipeline via the second high-pressure water injection device.

4. The method for enhancing permeability and promoting extraction in downward drilling coal seams according to claim 1, characterized in that, The specific process of S4 is as follows: The high-pressure gas injection device is connected to the injection pipeline via a pipeline, and high-pressure gas with a set flow rate and pressure is injected into the borehole through the injection pipeline via the high-pressure gas injection device.

5. The method for enhancing permeability and promoting extraction in downward drilling coal seams according to claim 1, characterized in that, The specific process of S5 is as follows: The second high-pressure water injection device is connected to the injection pipeline via a pipeline, and high-pressure water with a set flow rate and pressure is injected into the borehole through the injection pipeline via the second high-pressure water injection device.

6. The method for enhancing permeability and promoting extraction in downward drilling coal seams according to claim 1, characterized in that, After the S7 has been running for a set time, the ultrasonic transmitter head is moved to another set position to align with another target coal section.

7. A method for enhancing permeability and promoting extraction in downward-drilled coal seams according to claim 1 or 6, characterized in that, The ultrasonic generator is connected to the ultrasonic transmitter head via a cable, which is wound onto a reel. The ultrasonic transmitter head is mounted on a trolley equipped with a counterweight. The specific process of S6 is as follows: By rotating the reel, the trolley is moved along the extraction pipeline to the set position.

8. A method for enhancing permeability and promoting extraction in downward drilling coal seams according to claim 7, characterized in that, The reel is connected to a crank handle, which is manually turned to rotate the reel.

9. The method for enhancing permeability and promoting extraction in downward drilling coal seams according to claim 1, characterized in that, Prior to S7, sealing materials were used to seal the gap between the pipeline and the borehole.

10. A method for enhancing permeability and promoting extraction in downward drilling coal seams according to claim 1, characterized in that, The middle and lower sections of the extraction pipeline are designed as perforated pipes.

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