Hydraulic fracturing pretreatment combined with goaf ventilation: a method for mining gas-bearing coal seams

Abstract

This invention belongs to the field of disaster prevention and control in deep coal seam mining, and relates to a method for mining gas-bearing coal seams using hydraulic fracturing pretreatment combined with goaf ventilation. The invention involves constructing a track incline and a cut-in on both sides of the mining area's strike, and then connecting them with a long borehole along the bedding plane. Based on this long borehole, hydraulic fracturing and gas extraction are performed on the coal seam within the mining area, achieving depressurization and pre-extraction of gas throughout the entire mining area. All working faces adopt a four-way layout: the transport roadway and auxiliary roadway are connected to the transport incline and linked by a connecting roadway; the return air roadway and track roadway are connected to the track incline and linked by a connecting roadway, with air curtains installed in the connecting roadway. A mixed ventilation scheme with two intakes and two exhausts is used during coal mining; during maintenance, an independent ventilation scheme with two intakes and two exhausts is used, one for the mining area and the other for the goaf. This invention can improve the pre-extraction of gas and the depressurization effect against rockbursts, improve the quality of gas ventilation during coal mining, and solve the gas safety hazards in the goaf.

Description

Technical Field

[0001] This invention belongs to the field of disaster prevention and control in deep coal seam mining, specifically involving a method for mining gas-bearing coal seams with hydraulic fracturing pretreatment combined with goaf ventilation. Background Technology

[0002] Rockbursts and gas explosions are common hazards in coal mining. As the mining depth increases, the formation pressure rises, making the handling of rockbursts and gas explosions more difficult. Hydraulic fracturing is a key method for depressurizing coal seams and extracting gas. However, existing hydraulic fracturing processes are not centralized. Before each working face's roadway excavation and coal seam mining, hydraulic fracturing is required at the corresponding location of the coal seam. Furthermore, existing hydraulic fracturing methods are limited by the lack of smooth airflow, resulting in low gas pre-extraction efficiency.

[0003] Furthermore, pre-extraction of gas cannot completely remove gas from the coal seam. Gas will still be released during mining, mainly concentrated in the mining area. Therefore, high-quality ventilation is required in the mining area. However, the existing U-shaped ventilation system has low ventilation volume and efficiency, making it difficult to adapt to high-gas mines. In addition, coal remaining in the goaf will also release gas, and some of the gas released from the coal seam during mining will also enter the goaf, posing a gas safety hazard in the goaf.

[0004] Therefore, improving the efficiency of gas pre-extraction and rockburst relief, improving the quality of gas ventilation during coal mining, and solving the gas safety hazards in the goaf are key to high-quality mining of deep coal seams. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention proposes a method for mining gas-bearing coal seams with hydraulic fracturing pretreatment and goaf ventilation, comprising the following steps: S1: Constructing a track incline and all working face cut-outs along the dip on both sides of the strike of the mining area, connecting the cut-outs to the main haulage roadway; constructing long boreholes along the bedding plane from the track incline to the cut-outs, and performing hydraulic fracturing and gas extraction on the coal seam within the mining area based on the long boreholes along the bedding plane; S2: Constructing a haulage incline along the dip; sequentially arranging several working faces advancing along the strike along the dip; excavating the first working face: excavating the haulage roadway and auxiliary roadway along the strike from the haulage incline and connecting them with a connecting roadway; excavating the return air roadway and track roadway along the strike from the track incline and connecting them with a connecting roadway; installing air curtains in the connecting roadways; S3: Mining the first working face, opening only the air curtain closest to the cut-out or mining area during the mining shift, allowing fresh air to flow into the haulage roadway and auxiliary roadway simultaneously, reaching the mining area. The exhaust air becomes non-exhaust air, which simultaneously flows into the return airway and the track roadway. During maintenance, only part or all of the air curtains on the goaf side are opened. Fresh air flows into the transport roadway, becomes non-exhaust air after reaching the mining area, and flows into the track roadway. At the same time, fresh air flows into the auxiliary roadway, becomes non-exhaust air after reaching the goaf, and flows into the return airway. S4: Second working face excavation: Excavate the transport roadway and auxiliary roadway along the strike from the transport incline and connect them with a connecting roadway. Excavate the return airway along the strike in the coal pillar section between the transport roadway and auxiliary roadway of the first working face from the track incline. Use the auxiliary roadway of the first working face as the track roadway of the second working face. Retain the connecting roadway in the coal pillar section between the return airway and the track roadway of the second working face. Air curtains are installed in the connecting roadway. S5: Refer to step S3 to carry out mining and ventilation of the second working face. S6: Refer to steps S4-S5 to carry out excavation, mining, and ventilation of the subsequent working faces in the mining area in sequence.

[0006] Preferably, in step S1, fresh air is introduced from the cut-in hole, and the fresh air flows through the longitudinal borehole along the bedding plane and its hydraulic fracturing fracture network, becoming exhaust air before reaching the track and being discharged through the track.

[0007] Preferably, in step S2, the construction and transportation are carried uphill close to the track.

[0008] Preferably, in step S2, a sealing wall is constructed at the boundary between adjacent working faces within the cut-in, disconnecting the cut-in from the transport roadway.

[0009] Preferably, in step S2, a section of coal pillar is left between the transport roadway and the auxiliary roadway, and a section of coal pillar is left between the return air roadway and the track roadway; the connecting roadways are arranged at intervals along the direction; the track roadway and the transport roadway are relatively close to each other.

[0010] Preferably, in step S3, fresh air is introduced from the transport uphill, and stale air is discharged uphill via the track.

[0011] Preferably, in step S4, a return airway is excavated along the strike within the coal pillar section between the first and second working faces from the track incline, connecting the auxiliary roadway of the first working face with the track incline to form the track roadway of the second working face; the connecting roadways are arranged at intervals along the strike; the track roadway and the transport roadway are relatively close to the inside.

[0012] Preferably, in step S4, the connecting roadway between the return airway and the goaf of the first working face is sealed with a sealing wall; in the return airway, track roadway and transport roadway of the first working face, a sealing wall is constructed near the transport uphill or stop line.

[0013] The inventive points and beneficial technical effects of this invention are as follows: 1. This invention involves constructing an uphill track along the dip direction on one side of the mining area's strike, and constructing all working face cut-outs along the dip direction on the other side of the mining area's strike, connecting the cut-outs to the main transport roadway; constructing long boreholes along the bedding plane from the track uphill to the cut-outs, and performing hydraulic fracturing and gas extraction on the coal seams within the mining area based on these long boreholes, thereby achieving depressurization and pre-extraction of gas from the coal seams throughout the entire mining area, thus concentrating and pre-positioning the hydraulic fracturing and gas extraction processes, providing a safety guarantee for subsequent roadway excavation and working face recovery within the entire mining area, eliminating the need to construct depressurization and gas extraction boreholes.

[0014] 2. Furthermore, the working face of this invention adopts a four-lane layout. The transport lane and auxiliary lane are connected to the transport incline and linked through a connecting lane. The return air lane and track lane are connected to the track incline and linked through a connecting lane. Air curtains are installed in the connecting lanes. During coal mining, a mixed ventilation scheme with two intakes and two exhausts is adopted to improve the quality of gas ventilation. During maintenance, an independent ventilation scheme with two intakes and two exhausts is adopted, one for the mining area and the other for the goaf. This invention can improve the efficiency and effect of gas pre-extraction and rockburst relief, improve the quality of gas ventilation during coal mining, and solve the gas safety hazards in the goaf. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the construction of long boreholes along the seam in the coal seam mining method of the present invention.

[0016] Figure 2 This is a schematic diagram of the layout of the first working face in the coal seam mining method of the present invention.

[0017] Figure 3 This is a schematic diagram of the two-in, two-out mixed ventilation in the first working face of the coal seam mining method of the present invention.

[0018] Figure 4 This is a schematic diagram of the independent ventilation system with two inlets and two outlets in the first working face of the coal seam mining method of the present invention.

[0019] Figure 5 This is a schematic diagram of the layout of the second working face in the coal seam mining method of the present invention.

[0020] Figure 6This is a schematic diagram of the two-in, two-out mixed ventilation system in the second working face of the coal seam mining method of the present invention.

[0021] Figure 7 This is a schematic diagram of the independent ventilation system with two inlets and two outlets in the second working face of the coal seam mining method of the present invention.

[0022] Figure 8 This is a schematic diagram of the coal seam mining method of the present invention.

[0023] In the diagram: 11-Track uphill; 12-Transport uphill; 13-Long borehole along the bedding plane; 14-Stop mining line; 15-Air curtain; 16-Goaf; 17-Sealing wall; 18-Section coal pillar; 21-Cut-off; 22-Return airway; 23-Track roadway; 24-Connecting roadway; 25-Transport roadway; 26-Auxiliary roadway; 27-Mining area. Detailed Implementation

[0024] The specific embodiments of the present invention will now be described in conjunction with the accompanying drawings.

[0025] like Figures 1-7 As shown, this invention proposes a method for mining gas-bearing coal seams with hydraulic fracturing pretreatment and goaf ventilation, comprising the following steps.

[0026] S1: As Figure 1 As shown, on one side of the mining area's strike, a dipping track 11 is constructed, which connects to the return airway. On the other side of the mining area's strike, cut-outs 21 are constructed along the dip for all working faces, which connect to the haulage roadway. Throughout the mining area, long boreholes 13 are drilled from the dipping track 11 to the cut-outs 21. Based on these long boreholes 13, hydraulic fracturing is performed on the coal seams within the mining area, achieving depressurization of the coal seams throughout the entire mining area. Then, fresh air is introduced through the cut-outs 21. The fresh air flows through the long boreholes 13 and their hydraulic fracturing network, becoming exhaust air before reaching the dipping track 11 and being discharged through it, achieving pre-drainage of gas from the coal seams throughout the mining area. Subsequent roadway excavation and working face recovery within the entire mining area do not require the construction of depressurization and gas drainage boreholes. In this embodiment, the distance between the cut eye 21 and the track uphill 11 is 800-1500m, that is, the length of the bedding-parallel long borehole 13 is 800-1500m; the diameter of the bedding-parallel long borehole 13 is selected as 94mm or 113m, and the spacing of the bedding-parallel long borehole 13 is based on the requirement that the hydraulic fracturing fracture network of adjacent bedding-parallel long boreholes 13 can be connected, and the hydraulic fracturing pressure is 20-40MPa.

[0027] In this invention, dip refers to the dip direction of the coal seam, and strike refers to the strike direction of the coal seam; in the diagram, strike is the left-right direction, and dip is the front-back direction; dip and strike are professional geological terms that express the direction of strata, and will not be elaborated here.

[0028] S2: As Figure 2As shown, a transport uphill section 12 is constructed along the dip of the track uphill section 11, and the transport uphill section 12 is connected to the main transport roadway; several working faces are arranged sequentially along the dip and advancing along the strike; a sealing wall 17 is constructed at the boundary between adjacent working faces within the cut-in 21 to disconnect the cut-in 21 from the main transport roadway. In this embodiment, the width of the working face is between 200-300m.

[0029] First working face excavation: From the transport incline 12, transport roadway 25 and auxiliary roadway 26 are excavated along the strike, with a section coal pillar 18 left between transport roadway 25 and auxiliary roadway 26; several connecting roadways 24 are constructed at intervals along the strike to connect transport roadway 25 and auxiliary roadway 26; From the track incline 11, return air roadway 22 and track roadway 23 are excavated along the strike, with a section coal pillar 18 left between return air roadway 22 and track roadway 23; several connecting roadways 24 are constructed at intervals along the strike to connect return air roadway 22 and track roadway 23; track roadway 23 and transport roadway 25 are relatively close to each other; air curtains 15 are installed in the connecting roadways 24. In this embodiment, the width of the section coal pillar 18 is 20-25m.

[0030] In this invention, transport roadway 25 is mainly used for air intake and coal transportation, auxiliary roadway 26 is mainly used for air intake and pedestrian access; return air roadway 22 is mainly used for return air, and track roadway 23 is mainly used for material transportation and return air.

[0031] S3: As Figures 3-4 As shown, the first working face is mined from the cut-in 21 towards the stop line 14. During the mining shift, only the air curtain 15 closest to the cut-in 21 or the mining area 27 is opened. A mixed ventilation scheme with two intakes and two exhausts is adopted to improve the gas ventilation quality during mining. Specifically: fresh air is introduced from the transport incline 12, and the fresh air simultaneously flows into the transport roadway 25 and the auxiliary roadway 26. After reaching the mining area 27, it becomes exhaust air, which simultaneously flows into the return air roadway 22 and the track roadway 23, and then is discharged through the track incline 11. During the maintenance shift (when no mining is carried out), (For maintenance and repair of equipment, etc.) Only open part or all of the air curtain 15 on the side of the goaf 16, and adopt a two-in and two-out independent ventilation scheme. One way is: fresh air is introduced from the transport uphill 12, the fresh air flows into the transport roadway 25, and becomes exhaust air after reaching the stope 27. The exhaust air flows into the track roadway 23 and then is discharged through the track uphill 11. The other way is: fresh air is introduced from the transport uphill 12, the fresh air flows into the auxiliary roadway 26, and becomes exhaust air after reaching the goaf 16. The exhaust air flows into the return air roadway 22 and then is discharged through the track uphill 11.

[0032] S4: As Figure 5As shown, the second working face is excavated as follows: Transport roadway 25 and auxiliary roadway 26 are excavated along the strike from the transport incline 12, with a section coal pillar 18 left between transport roadway 25 and auxiliary roadway 26; several connecting roadways 24 are constructed at intervals along the strike to connect transport roadway 25 and auxiliary roadway 26; a return air roadway 22 is excavated along the strike within the section coal pillar 18 between the first and second working faces from the track incline 11, connecting the auxiliary roadway 26 of the first working face with the track incline 11 to form the track roadway 23 of the second working face; a connecting roadway 24 is retained within the section coal pillar 18 between the return air roadway 22 and the track roadway 23; the track roadway 23 and transport roadway 25 are relatively close to each other; an air curtain 15 is installed in the connecting roadway 24.

[0033] The connecting roadway 24 between the return airway 22 and the goaf 16 of the first working face is sealed with a sealing wall 17; in the return airway 22, track roadway 23 and transport roadway 25 of the first working face, a sealing wall 17 is constructed near the transport uphill 12 or the stop mining line 14.

[0034] S5: As Figures 6-7 As shown, referring to step S3, the second working face is mined and ventilated; specifically, the second working face is mined back from the cut-in 21 towards the stop line 14. During the coal mining shift, only the air curtain 15 closest to the cut-in 21 or the mining area 27 is opened, adopting a two-in, two-out mixed ventilation scheme to improve the gas ventilation quality during coal mining. Specifically, fresh air is introduced from the transport incline 12, and the fresh air simultaneously flows into the transport roadway 25 and the auxiliary roadway 26. After reaching the mining area 27, it becomes exhaust air, which simultaneously flows into the return air roadway 22 and the track roadway 23, and then is discharged through the track incline 11; during maintenance... During shift maintenance (when no coal mining is carried out, only equipment maintenance and repair are performed), only part or all of the air curtains 15 on the side of the goaf 16 are opened, and a two-in, two-out independent ventilation scheme is adopted. One way is: fresh air is introduced from the transport incline 12, the fresh air flows into the transport roadway 25, and becomes exhaust air after reaching the mining area 27. The exhaust air flows into the track roadway 23 and then is discharged through the track incline 11. The other way is: fresh air is introduced from the transport incline 12, the fresh air flows into the auxiliary roadway 26, and becomes exhaust air after reaching the goaf 16. The exhaust air flows into the return air roadway 22 and then is discharged through the track incline 11.

[0035] S6: Refer to steps S4-S5 to sequentially excavate, mine, and ventilate the subsequent working faces within the mining area.

[0036] This invention is not limited to the preferred embodiments described above. Anyone can derive other methods in various forms under the guidance of this invention. Any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A method for mining gas-bearing coal seams with hydraulic fracturing pretreatment combined with goaf ventilation, characterized in that, Includes the following steps: S1: Construct the track incline and all working face cut-outs along the dip on both sides of the strike of the mining area, and connect the cut-outs with the main transport roadway; Construct long boreholes along the bedding from the track incline to the cut-outs, and perform hydraulic fracturing and gas extraction on the coal seams in the mining area based on the long boreholes along the bedding. S2: Construction and transportation uphill along the dip; several working faces advancing along the strike are arranged sequentially along the dip; the first working face excavation: the transportation roadway and auxiliary roadway are excavated along the strike from the transportation uphill and connected by connecting roadways; the return air roadway and track roadway are excavated along the strike from the track uphill and connected by connecting roadways; air curtains are installed in the connecting roadways; S3: The first working face of the longwall mining. During the mining shift, only the air curtain closest to the cut or stope is opened. Fresh air flows into the transport roadway and auxiliary roadway at the same time. After reaching the stope, it becomes exhaust air. The exhaust air flows into the return air roadway and track roadway at the same time. During the maintenance shift, only part or all of the air curtains on the goaf side are opened. Fresh air flows into the transport roadway. After reaching the stope, it becomes exhaust air. The exhaust air flows into the track roadway. At the same time, fresh air flows into the auxiliary roadway. After reaching the goaf, it becomes exhaust air. The exhaust air flows into the return air roadway. S4: Second working face excavation: Excavate the transport roadway and auxiliary roadway along the strike from the transport uphill and connect them with a connecting roadway; excavate the return air roadway along the strike in the coal pillar section between the transport roadway and auxiliary roadway of the first working face from the track uphill, and use the auxiliary roadway of the first working face as the track roadway of the second working face. The connecting roadway is retained in the coal pillar section between the return air roadway and the track roadway of the second working face; air curtains are installed in the connecting roadway; S5: Refer to step S3 to carry out mining and ventilation of the second working face; S6: Refer to steps S4-S5 to sequentially excavate, mine, and ventilate the subsequent working faces within the mining area.

2. The method for mining gas-bearing coal seams according to claim 1, characterized in that, In step S1, fresh air is introduced through the cut-in hole. The fresh air flows through the long borehole along the bedding plane and its hydraulic fracturing fracture network, becomes exhaust air, and then reaches the track for incline and is discharged through the track for incline.

3. The method for mining gas-bearing coal seams according to claim 1, characterized in that, In step S2, the construction and transportation work is carried out on the mountainside near the track.

4. The method for mining gas-bearing coal seams according to claim 1, characterized in that, In step S2, a sealing wall is constructed at the boundary between adjacent working faces within the cut-in, disconnecting the cut-in from the transport roadway.

5. The method for mining gas-bearing coal seams according to claim 1, characterized in that, In step S2, a section of coal pillar is left between the transport roadway and the auxiliary roadway, and a section of coal pillar is left between the return air roadway and the track roadway.

6. The method for mining gas-bearing coal seams according to claim 5, characterized in that, In step S2, the connecting lanes are spaced apart along the direction; the track lanes and transport lanes are relatively close to the inside.

7. The method for mining gas-bearing coal seams according to claim 6, characterized in that, In step S3, fresh air is introduced into the transport system, while stale air is discharged through the track.

8. The method for mining gas-bearing coal seams according to claim 1, characterized in that, In step S4, the return airway is excavated along the strike within the coal pillar section between the first and second working faces from the track incline, connecting the auxiliary roadway of the first working face with the track incline to form the track roadway of the second working face.

9. The method for mining gas-bearing coal seams according to claim 8, characterized in that, In step S4, the connecting lanes are spaced apart along the direction; the track lanes and transport lanes are relatively close to the inside.

10. The method for mining gas-bearing coal seams according to claim 9, characterized in that, In step S4, the connecting roadway between the return airway and the goaf of the first working face is sealed with a sealing wall; in the return airway, track roadway and transport roadway of the first working face, sealing walls are constructed near the transport uphill or stop line.

Images