Gas extraction method based on advanced fracturing and directional bedding drilling

Abstract

The invention relates to a gas extraction method based on advanced fracturing and directional bedding drilling, and belongs to the technical field of coal mine gas treatment. The method comprises the following steps: constructing an advanced fracturing drill hole extending to a transportation gate road at the head-on of an air return gate road, and performing hydraulic fracturing on a coal seam through the advanced fracturing drill hole to form an anti-reflection crack; directional bedding drill holes extending along the transportation crossheading are constructed at the head-on of the transportation crossheading, and the directional bedding drill holes cover a certain range of the upper side and the lower side of the roadway; and the advanced fracturing and the directional bedding drilling are cooperatively constructed in a segmented manner. According to the method, advanced fracturing drilling and directional bedding drilling are cooperatively constructed in the coal seam, so that the gas permeability coefficient of the coal seam is increased by 3-5 times, the single-hole gas extraction pure quantity is increased by 2-4 times, the construction period is shortened by 30%-40%, the problems that gas extraction of the low-gas-permeability coal seam cannot be carried out and extraction is not fast are effectively solved, construction safety and extraction efficiency are considered, and the method is suitable for large-scale popularization and application. The method is suitable for gas control of coal seams with high gas content, low gas permeability and rock burst.

Description

Technical Field

[0001] This invention belongs to the field of coal mine gas control technology, and relates to a gas extraction method based on advanced fracturing and directional in-seam drilling. Background Technology

[0002] In the coal mining sector, as mining depths increase, coal seam gas occurrence conditions become increasingly complex, and safety issues in mining high-gas-content, high-gas-pressure coal seams are becoming increasingly prominent. In the mining of high-gas, low-permeability, and difficult-to-extract coal seams, gas outbursts during roadway excavation and face mining are particularly significant. Roadway gas problems directly affect the efficient excavation of roadways; if roadway excavation cannot be completed efficiently, it will inevitably severely impact the continuity of mining operations, thereby affecting the mine's efficient production. On the one hand, gas emission from the tunneling face mainly includes gas emission from the coal wall and gas emission from coal falling in front of the tunneling face. Among them, gas emission from the coal wall is the main source of gas emission from the tunneling roadway. Gas emission from the coal wall of the tunneling face can easily lead to excessive gas concentration at the tunneling face, causing power outages and affecting the efficiency of roadway tunneling. In severe cases, it can even threaten the personal safety of workers. On the other hand, as production capacity increases, gas emission from the mining face shows a significant upward trend. Relying solely on conventional ventilation and dilution methods, the air volume required for mining faces in high-gas mines far exceeds the actual ventilation capacity of the mine, which seriously restricts the efficient mining of the face.

[0003] Hydraulic fracturing, as an effective coal seam permeability enhancement technology, creates a fracture network within the coal seam using high-pressure water, significantly improving its permeability. However, traditional hydraulic fracturing often employs conventional borehole segmentation, which suffers from problems such as unreasonable intervals between fracturing segments, difficulty in precisely controlling the fracturing range, and a lack of coordination with directional boreholes after fracturing. This leads to inefficient gas extraction in the enhanced permeability area, and some fracturing fractures may reclose due to untimely gas extraction, reducing the effectiveness of permeability enhancement and extraction. Furthermore, in gas control of ultra-long working faces (such as the 2906 working face in a certain mine with a dip length of 300-340m), conventional borehole construction cannot achieve complete coverage of the roadway strips and mining areas. Improper control of adjacent borehole overlap can easily create gas control gaps, increasing the gas safety risks during mining. In addition, in mines prone to rockbursts, coal seam mining must also consider rockburst prevention. Traditional gas control technologies, during borehole construction and fracturing operations, can easily induce stress concentration in the coal seam, further exacerbating the risk of rockbursts.

[0004] Chinese patent document CN 121088365 A discloses a method for strip-based pre-fracturing and gas extraction in coal seam groups with steep inclination angles. This method involves creating permeability-enhancing fractures by arranging cross-layer hydraulic fracturing boreholes in the overlying first-mining coal seam roadway; and then arranging directional long boreholes in the underlying coal seam at the location of the roadway to be excavated, forming strip-based pre-fracturing based on the fracture extension direction. A closed-loop operation achieves the orderly connection between borehole construction, gas pre-extraction, roadway excavation, and simultaneous excavation and gas extraction. This scheme solves the problem of rapid pre-extraction before excavation of adjacent coal seam roadways in steep inclination coal seam groups. It is suitable for situations where the distance between adjacent coal seam roadways and the roadway to be excavated is small, or where there are rock roadways near the roadway to be excavated. Pre-fracturing before gas extraction is implemented by arranging pre-fracturing boreholes in adjacent rock roadways and adjacent coal seam mining roadways. However, it is difficult to implement pre-fracturing when there are no rock roadways or adjacent coal seam mining roadways.

[0005] In traditional gas control, drilling and fracturing operations are carried out separately, resulting in lengthy construction periods. Furthermore, high-pressure operations are prone to safety hazards such as gas leaks and rock bursts, making it difficult to meet the continuous mining needs of mines. Therefore, how to achieve coordinated efforts between advanced permeability enhancement and directional precision extraction to effectively reduce coal seam gas content while ensuring construction safety and mining efficiency has become a key technical problem that urgently needs to be solved in the mining of high-gas, low-permeability, and rock burst-prone coal seams. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a gas extraction method based on advanced fracturing and directional in-seam drilling, so as to achieve the synergistic effect of advanced permeability enhancement and directional precise extraction of coal seams, and solve the problem of the long construction period of existing drilling and fracturing operations.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A gas extraction method based on advanced fracturing and directional in-seam drilling, which involves the coordinated construction of advanced fracturing boreholes and directional in-seam drilling within the coal seam, includes the following steps: S1 Pre-construction preparation: Collect geological and gas parameters of the coal seam in the area to be treated. Geological and gas parameters include coal seam thickness, geological structure, dip angle, gas pressure, gas content, permeability coefficient, and flow attenuation coefficient. Determine the construction layers for advanced fracturing boreholes and directional in-seam boreholes. S2 is an advanced fracturing borehole extending from the return air roadway to the transport roadway. Hydraulic fracturing is performed on the coal seam through the advanced fracturing borehole to form permeability-enhancing fractures. S3 involves constructing directional bedding boreholes along the transport roadway face. These directional bedding boreholes cover a certain range of the upper and lower sides of the roadway. The directional bedding boreholes are spatially offset from the advance fracturing boreholes to avoid direct connection. S4 Drilling sites are set up at intervals of 300-400m at the face of the roadway. Steps S2-S3 are repeated to carry out construction work on the next drilling site. During the construction process, the overlap distance between adjacent boreholes shall not be less than 20m. After the directional boreholes in the coal seam are completed, gas drainage shall be carried out. The openings of the pre-fracturing boreholes and the directional boreholes in the coal seam shall be connected to drainage pipes for gas drainage.

[0008] Coal seams are typically mined from top to bottom. With the development of goaf-side roadway technology, the roadways of the previous section are usually excavated 1-2 years ahead of the working face of the next section. Moreover, the advance treatment in the previous area means that even with small coal pillar mining, the amount of gas emitted during roadway excavation near the mining face is relatively small, making gas emission control easier compared to the original coal seam roadway excavation. Therefore, by constructing advanced fracturing boreholes in the original coal seam area through the upper section or return airway, it is possible to solve the problem of roadway excavation in the transport roadway and also to perform fracturing and permeability enhancement in the mining area. Thus, it is feasible to construct advanced fracturing boreholes at the face of the return airway in this invention. Compared with the prior art CN 121088365 A, this invention is applicable to a wider range of conditions, including situations where there are no rock roadways or adjacent coal seam mining roadways. Furthermore, since it is a coal seam construction, the pre-fracturing boreholes no longer need the mesh arrangement of the prior art CN 121088365 A, but only a row of in-seam pre-fracturing boreholes, which significantly reduces the number of fracturing boreholes. Therefore, the construction cost is lower and the efficiency is higher.

[0009] Optionally, directional boreholes can be drilled along the bedding plane to cover an area of ​​20m above the upper side and 15m below the lower side of the transport roadway.

[0010] Optionally, in step S2, a backward segmented fracturing process is adopted, with hydraulic fracturing performed with a fracturing segment length of 10m and a segment interval of 10m.

[0011] Optionally, directional boreholes are arranged in the middle of the interbedded gangue layer in the coal seam, and pressure relief between the upper and lower coal seams is achieved by fracturing through the interbedded gangue layer.

[0012] Optionally, the pre-fracturing boreholes are arranged along the extension direction of the return airway, and the spacing L of the pre-fracturing boreholes is 30±5m.

[0013] Optionally, 7 to 9 directional bedding boreholes are arranged in each directional bedding borehole drilling site.

[0014] Optionally, the pre-fracturing borehole adopts directional drilling technology, using a Φ96mm directional drill bit to open a 15m hole, which is then enlarged to a Φ153mm hole and drilled to the designed length. During the drilling process, the borehole trajectory is measured every 50m to ensure that the borehole layer meets the requirements.

[0015] Optionally, the directional drilling along the coal seam adopts the directional drilling process. A Φ96mm directional drill bit is used to open a 15m hole, which is then enlarged to a Φ133mm hole. After that, a blowout preventer is installed at the hole opening. The directional drilling proceeds along the designed trajectory. During the drilling process, the drilling trajectory is measured every 50m to ensure that the borehole extends along the coal seam.

[0016] Optionally, in step S2, before fracturing, the packer is first set with a pressure of 4 MPa for 15 minutes to ensure that the packer is fully expanded and in close contact with the borehole wall. When the pressure reaches 5 MPa, the differential pressure sleeve is opened and fracturing begins. During fracturing, the gas concentration in the construction area and the operating status of the high-pressure pipeline are monitored in real time. If any abnormality occurs, the machine is immediately stopped and the pressure is released.

[0017] The beneficial effects of this invention are as follows: 1. This invention has a short construction period. It adopts a construction scheme of coordinating the construction of advanced fracturing boreholes at the return air roadway face and directional in-seam boreholes at the transport roadway face. Compared with the cross-seam advanced fracturing boreholes in the existing technology CN 121088365 A, it no longer requires a network arrangement, only a row of advanced fracturing boreholes, which significantly reduces the number of fracturing boreholes. Therefore, the construction cost is lower, the efficiency is higher, and the construction period of gas drainage is significantly shortened. Moreover, it is applicable to a wider range of conditions, and can be used in situations where there are no rock roadways or no adjacent coal seam mining roadways.

[0018] 2. This invention has high construction efficiency. By adopting "centralized drilling site layout + segmented flow operation", the total construction period of a single drilling site can be controlled within 15 to 20 days, which is 30% to 40% shorter than the traditional process; the daily advance of a single directional drilling hole can reach 80m, which is 4 times higher than that of ordinary drilling.

[0019] 3. The present invention has a significant permeability enhancement effect. Through backward segmented fracturing, a continuous and uniform fracture network is formed in the coal seam, increasing the coal seam permeability coefficient to 3 to 5 times the original level, significantly reducing the borehole gas flow attenuation coefficient, and increasing the pure gas extraction volume of a single borehole by 2 to 4 times.

[0020] 4. This invention is safe and reliable. By precisely controlling the fracturing range and directional drilling trajectory, it avoids stress concentration in the coal seam and reduces the risk of rockburst. Real-time monitoring of gas concentration and high-pressure pipeline status during construction ensures operational safety.

[0021] 5. The invention provides comprehensive coverage: By rationally arranging drilling sites and controlling the overlap distance between adjacent boreholes, it achieves comprehensive coverage of roadway strips and mining areas, eliminating gaps in gas control.

[0022] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the gas extraction method based on advanced fracturing and directional in-seam drilling; Figure 2 Plan view of gas extraction construction; Figure 3 for Figure 2 Section II.

[0024] Attached reference numerals: 1. Pre-extraction borehole; 2. Pre-extraction borehole boundary line; 3. Return airway; 4. Transport roadway; 5. Directional layer-by-layer borehole; 6. Transport roadway face; 7. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0026] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0027] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they 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, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0028] Please see Figures 1-3 A gas extraction method based on pre-fracturing and directional bedding boreholes is described in the figure. The figure shows the following locations: pre-extraction borehole 1, pre-fracturing borehole 2, pre-extraction borehole boundary line 3, return airway 4, transport roadway 5, directional bedding borehole 6, and transport roadway face 7. Pre-extraction borehole 1 is the extraction borehole for the coal seam after fracturing. The spacing between pre-extraction boreholes 1 is relatively small, generally 10m; the spacing between pre-fracturing boreholes 2 is larger, generally 30m. This method employs a centralized drilling site layout and segmented continuous operation. Pre-fracturing boreholes 2 are drilled at the return airway face, and directional bedding boreholes 6 are drilled at the transport roadway face 6. Due to the synergistic effect of pre-fracturing boreholes 2 and directional bedding boreholes 6, the spacing between pre-fracturing boreholes 2 can be significantly increased, thereby reducing the number of pre-fracturing boreholes 2. The specific steps include: Step 1, Pre-construction preparation; Collect geological and gas parameters of the coal seam in the area to be treated, including coal seam thickness, geological structure, dip angle, gas pressure, gas content, permeability coefficient, and flow attenuation coefficient; Determine the construction layers for advanced fracturing boreholes and directional boreholes along the bedding plane; Prepare and debug directional drilling equipment. Step 2, advanced fracturing drilling construction; drilling sites are set up every 300~400m at the face of the roadway, and advanced fracturing boreholes are constructed using directional drilling rigs; Step 3: Advanced segmented fracturing operation; Step 4: Fracturing followed by hole cleaning; Step 5: Directional drilling along the bedding plane; Step six: Repeat steps two through five to carry out construction work at the next drilling site. During the construction process, the overlap distance between adjacent boreholes shall not be less than 20m.

[0029] Preferably, step two includes Step 2.1: Gas detection personnel test the gas concentration in the construction area three times consecutively, with a 5-minute interval between each test. The hole can only be opened when the concentration is below 0.5%. The drilling position is calibrated using a hole positioning instrument. Rotary drilling is used, with low pressure and slow rotation to open the hole. The hole is stopped when the drilling depth reaches 15m. A 153mm reaming drill bit is then used to enlarge the hole to 15m. The hole is repeatedly washed to ensure that there is no coal slag inside. Step 2.2: Using directional drilling technology, install the bottom hole motor and measuring probe, apply thread-locking adhesive to the threads, tighten manually, and then reinforce with a special pipe wrench. Drill according to the designed length, and measure the drilling trajectory every 50m during the drilling process to ensure that the drilling layer meets the requirements.

[0030] Preferably, step three includes Step 3.1, Tool string pushing; After drilling is completed, clean the coal slag in the hole, connect the fracturing sealing tubing to the tool string, and push the tool string to the first target fracturing section through the drill rod. Avoid rotating the drill rod during the pushing process to prevent the tool string from getting stuck. Step 3.2, staged fracturing; using the retreating staged fracturing process, with a fracturing section length of 10m and a section interval of 10m, the tool string is gradually dragged towards the borehole for staged fracturing. During each stage of fracturing, the parameters of pump pressure, flow rate, and water injection volume are recorded, and any abnormalities are observed in the coal wall and roof. Step 3.3, fracturing monitoring; During the fracturing process, gas detection personnel monitor the gas concentration in the construction area in real time, and safety supervisors observe the operation status of high-pressure pipelines and tool strings. If pipeline leaks or packer failures occur, the machine is immediately shut down and pressure is released to ensure construction safety.

[0031] Preferably, step four includes Step 4.1: After all fracturing in a single borehole is completed, shut down the fracturing pump unit, open the borehole pressure relief device to release pressure and drain water. After the pressure drops to 0 MPa, wait 30 minutes for the packer sleeve to shrink, and then remove the tool string. Step 4.2: Inject clean water into the pre-fracturing borehole to flush out residual coal slag and fracturing fluid. The flushing time should be no less than 30 minutes until the water returning from the borehole is clear, to ensure that subsequent directional drilling operations are not affected.

[0032] Preferably, step five includes installing a directional drilling rig at the downhole drilling site, drilling a 15m hole with a 96mm directional drill bit, expanding it to a 133mm hole, and then installing a blowout preventer at the hole opening; drilling directionally along the designed trajectory, correcting the borehole trajectory every 50m using a measuring probe to ensure that the borehole extends along the coal seam and reaches the designed depth.

[0033] Preferably, in step 3.1, after the tool string is pushed out, the fracturing pump unit is turned on, and the packer is first set with a pressure of 4 MPa for 15 minutes to ensure that the packer is fully expanded and in close contact with the borehole wall. When the pressure reaches 5 MPa, the differential pressure sleeve is opened and the fracturing operation begins.

[0034] Preferably, in step 3.2, if the pressure or flow of a single pump is insufficient, a second fracturing pump set is started to connect the two pumps in parallel, and the pump set parameters are adjusted to ensure stable fracturing pressure. When the fracturing pressure of a certain section drops suddenly or the water injection volume increases abnormally, it is determined that the coal seam has been fractured, and fracturing continues until the designed water injection volume is reached before stopping the fracturing of that section.

[0035] Preferably, in step five, drilling sites are arranged in a cyclical pattern at design intervals of 300-400 m at the face of the transport roadway. The size of each drilling site is 8m×4m×3m. After cleaning the drilling sites, the orientation of the drilling rig is calibrated to ensure that the boreholes can cover a range of 20m on the upper side and 15m on the lower side of the roadway.

[0036] Example 1 Reference Figure 1-3 This invention provides a gas extraction method based on advanced fracturing and directional in-seam drilling, comprising the following steps: Step 1, Pre-construction preparation: Collect geological and gas parameters of the coal seam in the area to be treated, including coal seam thickness, geological structure, dip angle, gas pressure, gas content, permeability coefficient, and flow attenuation coefficient. Determine the construction strata for advanced fracturing boreholes and directional boreholes along the bedding plane. Prepare directional drilling equipment and conduct debugging.

[0037] Step 2, advanced fracturing drilling construction: Drilling sites are set up every 300~400m at the face of the roadway, and advanced fracturing boreholes are constructed using directional drilling rigs; the directional drilling rig selected is the ZYWL-6000DS integrated directional drilling rig. Before use, check whether the drilling depth, torque, speed and other parameters of the drilling rig meet the construction requirements, and ensure that the drilling rig's anchoring device, hydraulic system and power supply system are in good condition.

[0038] Step 3, advanced segmented fracturing operation: The fracturing equipment selected is the BYW220 / 50 coal mine underground fracturing pump set. Before use, check the pressure and flow performance of the pump set. The matching high-pressure pipeline, packer, differential pressure sleeve, tubing short section and other tool strings must be intact and meet the requirements of pressure resistance and explosion protection.

[0039] Step 4: Fracturing followed by hole cleaning.

[0040] Step 5: Directional drilling along the bedding plane.

[0041] Step six: Repeat steps two through five to carry out construction work at the next drilling site. During the construction process, the overlap distance between adjacent boreholes shall not be less than 20m.

[0042] After each cycle is completed, a quality acceptance inspection is conducted: check the accuracy of the formation location of the pre-fracturing borehole (≥95%), the length of the fracturing section (error ≤±0.5m), and the water injection volume (error ≤±5%); check the trajectory deviation of the directional borehole (≤0.5m / 100m), the sealing quality (sealing ≥95%), and the extraction concentration (initial concentration ≥25%); only after the acceptance inspection is passed can the next cycle of construction begin; any unqualified items must be rectified within a specified period (such as re-fracturing or additional drilling), and a re-inspection is conducted after rectification is completed.

[0043] Further optimization of the plan includes the arrangement of safety facilities, setting up a warning zone 200m before and after the construction area and in the area where high-pressure pipelines are laid, hanging warning lines and "High-pressure operation, no entry" warning signs, equipping fire extinguishers and gas monitors, and ensuring good ventilation and sufficient air volume in the construction area.

[0044] A temporary drainage system was set up near the construction site to divert wastewater generated during drilling and fracturing to a water tank, preventing water accumulation from affecting construction.

[0045] Further optimization of the solution, step two includes: Step 2.1: Gas detection personnel test the gas concentration in the construction area three times consecutively, with a 5-minute interval between each test. The hole can only be opened when the concentration is below 0.5%. The drilling position is calibrated using a hole positioning instrument. Rotary drilling is used, with low pressure and slow rotation to open the hole. The hole is stopped when the drilling depth reaches 15m. The hole is then enlarged to 15m using a Φ153mm reaming drill bit. The hole is repeatedly washed to ensure that there is no coal slag inside.

[0046] Specifically, rotary drilling is used with a Φ96mm alloy drill bit for opening the hole. The drilling parameters are: rotation speed 60-80 r / min, thrust 5-8 kN, water pressure 1.5-2.0 MPa. Low pressure and slow rotation are used to ensure a straight borehole section. When the drilling depth reaches 15m, drilling is stopped, the drill rod is removed, and a Φ153mm reaming drill bit (the cutter head is made of cemented carbide) is used. The reaming parameters are: rotation speed 40-60 r / min, thrust 8-12 kN, water pressure 2.0-2.5 MPa. After reaming to 15m, the borehole is repeatedly flushed (flushing time ≥10min) until the return water is clear (slag content ≤0.1%) to ensure that there is no coal slag accumulation in the hole.

[0047] Install a blowout preventer (pressure resistance ≥50MPa, suitable for Φ96mm boreholes) and a four-way connector (material: 20# steel, pressure resistance ≥60MPa) at the borehole opening: The upper interface of the four-way connector connects to a Φ110mm armored extraction pipe (6mm wall thickness, for subsequent extraction), and the lower interface connects to a Φ110mm armored backflow pipe (6mm wall thickness, for borehole backflow and slag removal). The end of the backflow pipe connects to the primary sedimentation tank. Install two Φ12mm stainless steel clamps (tightening torque ≥50N) at all interfaces. m), and interlocked with the flange using M16 bolts (≥2 interlocks, symmetrically arranged) to prevent high-pressure water leakage.

[0048] Step 2.2: Using directional drilling technology, install the bottom hole motor and measuring probe, apply thread-locking adhesive to the threads, tighten manually, and then reinforce with a special pipe wrench. Drill according to the designed length, and measure the drilling trajectory every 50m during the drilling process to ensure that the drilling layer meets the requirements.

[0049] Motor speed 150~200r / min, torque ≥300N m, the thread-fastening adhesive is Loctite 243 thread-fastening adhesive, and the coating thickness is 1-2mm.

[0050] Adjust the drilling trajectory and drilling parameters (rotation speed, thrust) to ensure the borehole extends along the coal seam and avoids deviating from the designed stratum. If rock inclusions are encountered during drilling, adjust the drilling pressure and rotation speed appropriately. If the rock inclusions are too thick to pass through, adjust the drilling trajectory to bypass them or stop drilling, analyze the geological conditions, and redesign the drilling parameters.

[0051] After drilling is completed, the drilling trajectory is re-measured, and the integrity of the borehole is checked using a panoramic borehole imaging instrument. If there is a collapsed hole (collapse length > 5m) or a borehole deviation (deviation > 1m / 100m), the drilling must be redone. After the re-measurement is qualified, the coal slag in the hole is cleaned (using high-pressure water flushing, water pressure 3.0~3.5MPa, flushing time ≥15min) to prepare for fracturing operation.

[0052] Further optimization of the solution, step three includes: Step 3.1, Tool string pushing; After drilling is completed, clean the coal slag in the hole, connect the fracturing sealing tubing to the tool string, and push the tool string to the first target fracturing section through the drill rod. Avoid rotating the drill rod during the pushing process to prevent the tool string from getting stuck. Step 3.2, staged fracturing; using the retreating staged fracturing process, with a fracturing section length of 10m and a section interval of 10m, the tool string is gradually dragged towards the borehole for staged fracturing. During each stage of fracturing, the parameters of pump pressure, flow rate, and water injection volume are recorded, and any abnormalities are observed in the coal wall and roof. Step 3.3, fracturing monitoring; During the fracturing process, gas detection personnel monitor the gas concentration in the construction area in real time, and safety supervisors observe the operation status of high-pressure pipelines and tool strings. If pipeline leaks or packer failures occur, the machine is immediately shut down and pressure is released to ensure construction safety.

[0053] Further optimization of the solution, step four includes: Step 4.1: After all fracturing in a single borehole is completed, shut down the fracturing pump unit, open the borehole pressure relief device to release pressure and drain water. After the pressure drops to 0 MPa, wait 30 minutes for the packer sleeve to shrink, and then remove the tool string. Step 4.2: Inject clean water into the pre-fracturing borehole to flush out residual coal slag and fracturing fluid. The flushing time should be no less than 30 minutes until the water returning from the borehole is clear, to ensure that subsequent directional drilling operations are not affected.

[0054] Further optimization of the scheme includes step five: installing a directional drilling rig at the roadway drilling site, drilling a 15m hole with a 96mm directional drill bit, expanding it to a 133mm hole, and then installing a blowout preventer at the hole opening; drilling directionally according to the designed trajectory, correcting the drilling trajectory every 50m using a measuring probe to ensure that the borehole extends along the coal seam and reaches the designed depth.

[0055] Further optimize the scheme. In step 3.1, after the tool string is pushed out, start the fracturing pump group and first set the packer with a pressure of 4MPa for 15 minutes to ensure that the packer is fully expanded and in close contact with the borehole wall. When the pressure reaches 5MPa, the differential pressure sleeve opens and the fracturing operation begins.

[0056] To further optimize the scheme, in step 3.2, if the pressure or flow of a single pump is insufficient, start the second fracturing pump set to connect the two pumps in parallel, adjust the pump set parameters to ensure stable fracturing pressure, and when the fracturing pressure of a certain section drops suddenly or the water injection volume increases abnormally, it is determined that the coal seam has fractured, and fracturing continues until the designed water injection volume is reached before stopping the fracturing of that section.

[0057] Further optimize the plan. In step five, drill sites are arranged at the face of the transport roadway at design intervals of 300~400m / cycle. The size of the drill site is 8m×4m×3m. After cleaning the drill site, the orientation of the drilling rig is calibrated to ensure that the borehole can cover a range of 20m on the upper side and 15m on the lower side of the roadway.

[0058] To further optimize the plan, after the extraction begins, continuously monitor parameters such as extraction concentration, flow rate, and negative pressure in the directional boreholes, record the data once a day, plot the extraction curve, analyze the changing trend of the extracted gas volume, and calculate the gas extraction rate.

[0059] After a period of extraction (e.g., 60 days), test boreholes are drilled in the pre-extraction area to determine the residual gas content of the coal seam. If the residual gas content is reduced to the design target (e.g., below 4.5 m³ / t), the extraction effect is satisfactory. If it is not satisfactory, the extraction time is extended or additional boreholes are drilled until the target is met.

[0060] Example 2 The gas extraction method based on advanced fracturing and directional bedding borehole provided by this invention has been applied in the 2906 project of Changcheng No. 2 Mine of Inner Mongolia Fucheng Mining Co., Ltd., and has achieved excellent results.

[0061] This invention is applied in the gas control of the transport roadway of the 2906 working face of the Changcheng No. 2 Mine of Inner Mongolia Fucheng Mining Co., Ltd.

[0062] Project Background: The 2906 working face mines coal seam No. 9, with a burial depth of 774.6–998.8 m, an average coal seam thickness of 3.5 m (including 0.4 m of interbedded rock), a dip angle of 26°, a gas pressure of 1.20–1.80 MPa, an initial gas content of 4.00–7.64 m³ / t, and a permeability coefficient of 0.337085–0.410452 m² / MPa². d is a high-gas, low-permeability coal seam; the designed length of the transport roadway is 1806.5m, and this method is required to control the gas in the coal roadway strips to ensure that the absolute gas emission during tunneling is ≤3m³ / min.

[0063] Implementation process: Preparations before construction: Collect geological parameters of coal seam No. 9, determine the location of the pre-fracturing borehole in the interbedded rock layer, and directional boreholes along the bedding layer cover the upper side 20m and the lower side 15m; select ZYWL-6000DS directional drilling rig and BYW220 / 50 fracturing pump set, and after commissioning and qualification, set up warning zone, temporary drainage system and gas monitoring instrument.

[0064] Advanced fracturing drilling: One drilling site is set up every 300m, with a hole diameter of 96mm, which is enlarged to 153mm, and directional drilling is carried out for 320m. The drilling trajectory deviation is ≤0.5m / 100m. A total of 4 cycles of advanced fracturing drilling are carried out, with a total drilling footage of 1280m.

[0065] Advanced fracturing operation: adopts retreat-type segmented fracturing, each segment is 10m long, the segment interval is 10m, the water injection volume per segment is 43m³, and the fracturing pressure is 31.2MPa; dual pumps operate in parallel, with a total discharge of 350L / min, fracturing a total of 76 segments, with an effective fracturing length of 760m.

[0066] Post-fracturing hole washing: After depressurization, retrieve the tool string, wash the hole with clean water for 30 minutes, and check the borehole patency after the return water is clear.

[0067] Directional drilling along the bedding plane: Seven directional boreholes were drilled at each drilling site (four on the upper side and three on the lower side), with a depth of 320-400m and a sealing length of 18m. A total of 28 boreholes were drilled, with a total drilling footage of 10,840m. After 60 days of extraction, the residual gas content of the boreholes was tested and found to be 3.8-4.2m³ / t, with an extraction rate of 62%, which met the standard.

[0068] Cyclic construction: Four cycles of construction were completed, with a total treatment length of 1200m. The absolute gas emission during the excavation of the transport roadway was 2.8 to 3.0 m³ / min, and there were no gas exceeding the limit accidents.

[0069] Implementation results: Gas control effect: Coal seam permeability coefficient increased to 1.2–1.5 m² / MPa² d (increased by 3 to 4 times), the initial extraction concentration of directional boreholes is 35% to 45%, and the extraction cycle is shortened by 30%; the tunneling speed of the transport roadway is increased to 205m / month (meeting the design requirements), and the subsequent gas emission of the mining face is reduced to 28.39m³ / min (when the daily production capacity is 3636t / d), meeting the ventilation and dilution requirements.

[0070] Safety and economic benefits: There were no accidents such as gas leaks or high-pressure water injuries during construction; compared with traditional technology, the cost of gas control per ton of coal was reduced by 15%, the working face was put into production 3 months ahead of schedule, and the economic benefits were about 20 million yuan.

[0071] This invention achieves precise permeability enhancement through directional segmented fracturing technology: it adopts a backward segmented fracturing method with a fracturing segment length of 10m and a segment interval of 10m, combined with a pressure control logic of 4MPa setting packer + 5MPa differential pressure sliding sleeve opening, to form a continuous and uniform fracture network in the coal seam. Especially for the interbedded rock layer between coal seam 9 and coal seam 9 above 9, the advanced fracturing boreholes are precisely arranged in the middle of the interbedded rock layer, and the interbedded rock layer is penetrated to achieve coordinated pressure relief between the upper and lower coal seams.

[0072] Verification using both tracer methods and moisture content monitoring showed that the permeability coefficient of the coal seam increased to 3–5 times its original level after fracturing, and the borehole gas flow attenuation coefficient increased from 0.05768 to 0.17085 d. - ¹Decreased to 0.02–0.03 days - ¹ The single-hole gas extraction capacity has increased from 0.1–0.3 m³ / min in traditional boreholes to 0.8–1.2 m³ / min, improving extraction efficiency by 2–4 times, effectively solving the core problems of "not being able to extract gas or extracting it quickly" in low-permeability coal seam gas extraction.

[0073] The advanced fracturing and directional drilling operations employ a "centralized drilling site layout + segmented continuous operation" approach. The total construction period for fracturing (16 sections / hole) and drilling (8 holes / cycle) at a single drilling site is controlled within 15-20 days, shortening the time by 30%-40% compared to the traditional decentralized process of "fracturing first and then drilling." Simultaneously, the daily advance per directional borehole reaches 80m, four times that of ordinary drilling (20m / day), meeting the monthly tunneling progress requirement of 205m at the working face. This improves extraction efficiency.

[0074] This invention addresses the complex coal seam conditions characterized by high gas content, low permeability, difficult extraction, and low risk of rockburst. Through a synergistic design of advanced fracturing for enhanced permeability and directional in-seam drilling for extraction, it solves key problems in traditional gas control technologies, such as poor permeability enhancement, low extraction efficiency, high construction safety risks, and incomplete coverage.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A gas extraction method based on advanced fracturing and directional in-seam drilling, characterized in that: The coordinated construction of advanced fracturing boreholes and directional in-seam boreholes in this coal seam includes the following steps: S1 Pre-construction preparation: Collect geological and gas parameters of the coal seam in the area to be treated. Geological and gas parameters include coal seam thickness, geological structure, dip angle, gas pressure, gas content, permeability coefficient, and flow attenuation coefficient. Determine the construction layers for advanced fracturing boreholes and directional in-seam boreholes. S2 is an advanced fracturing borehole extending from the return air roadway to the transport roadway. Hydraulic fracturing is performed on the coal seam through the advanced fracturing borehole to form permeability-enhancing fractures. S3 involves constructing directional bedding boreholes along the transport roadway face. These directional bedding boreholes cover a certain range of the upper and lower sides of the roadway. The directional bedding boreholes are spatially offset from the advance fracturing boreholes to avoid direct connection. S4 Drilling sites are set up every 300-400m at the face of the roadway. Steps S2-S3 are repeated to carry out construction work on the next drilling site. During the construction process, the overlap distance between adjacent boreholes shall not be less than 20m. After the directional drilling of the coal seam is completed, gas drainage shall be carried out.

2. The gas extraction method based on advanced fracturing and directional bedding borehole as described in claim 1, characterized in that: Directional boreholes were drilled along the bedding plane, covering an area of ​​20m on the upper side and 15m on the lower side of the transport roadway.

3. The gas extraction method based on advanced fracturing and directional in-seam drilling according to claim 1, characterized in that: In step S2, a backward segmented fracturing process is adopted, with hydraulic fracturing performed with a fracturing segment length of 10m and a segment interval of 10m.

4. The gas extraction method based on advanced fracturing and directional in-seam drilling according to claim 1, characterized in that: Directional boreholes are arranged in the middle of the interbedded gangue layer in the coal seam, and pressure relief between the upper and lower coal seams is achieved by fracturing through the interbedded gangue layer.

5. The gas extraction method based on advanced fracturing and directional in-seam drilling according to claim 1, characterized in that: The pre-fracturing boreholes are arranged along the extension direction of the return airway, and the spacing L between the pre-fracturing boreholes is 30±5m.

6. The gas extraction method based on advanced fracturing and directional bedding borehole as described in claim 1, characterized in that: Each directional bedding borehole site is equipped with 7 to 9 directional bedding boreholes.

7. The gas extraction method based on advanced fracturing and directional bedding borehole as described in claim 1, characterized in that: The advanced fracturing borehole adopts directional drilling technology. A Φ96mm directional drill bit is used to open a 15m hole, which is then enlarged to a Φ153mm hole and drilled to the designed length. The borehole trajectory is measured every 50m during the drilling process to ensure that the borehole layer meets the requirements.

8. The gas extraction method based on advanced fracturing and directional bedding borehole as described in claim 1, characterized in that: Directional drilling along the coal seam is carried out using directional drilling technology. A Φ96mm directional drill bit is used to open a 15m hole, which is then enlarged to a Φ133mm hole. After that, a blowout preventer is installed at the hole opening. The borehole is then drilled directionally according to the designed trajectory. During the drilling process, the borehole trajectory is measured every 50m to ensure that the borehole extends along the coal seam.

9. The gas extraction method based on advanced fracturing and directional in-seam drilling according to claim 1, characterized in that: In step S2, before fracturing, the packer is first set at a pressure of 4 MPa for 15 minutes to ensure that the packer is fully expanded and in close contact with the borehole wall. When the pressure reaches 5 MPa, the differential pressure sleeve is opened and fracturing begins. During fracturing, the gas concentration in the construction area and the operating status of the high-pressure pipeline are monitored in real time. If any abnormality occurs, the machine is immediately stopped and the pressure is released.

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