Gas control technology combining segmented hydraulic fracturing and large-diameter drilling in key layers

Abstract

The present invention discloses a gas control process combining segmented hydraulic slitting, fracturing and large-diameter drilling of a key layer, which belongs to the field of gas control technology and includes the following steps: S1, determining the position of the key layer and selecting the key layer for fracturing; S2, determining the slitting pressure and fracturing pressure required for hydraulic slitting and fracturing of the key layer for fracturing; S3, segmented hydraulic slitting and water injection fracturing of the key layer for fracturing; S4, determining the layout spacing of large-diameter boreholes in the coal seam, and constructing large-diameter boreholes in the coal seam below the fracturing area of ​​the key layer; S5, using the "two blocking and one injection" process to seal the large-diameter boreholes; after the sealing is completed, immediately conduct grid-connected pre-extraction. The present invention combines segmented hydraulic slitting, fracturing and large-diameter drilling of the key layer to fully relieve the pressure of the coal body, improve the permeability of the coal seam, and quickly release the depressurized gas to improve the pre-extraction effect of the coal seam gas, thereby solving the problems of low gas extraction efficiency in the recovery process of soft coal seams.

Description

Technical Field

[0001] The invention relates to the technical field of gas control, and in particular to a gas control process combining segmented hydraulic fracturing of key layers with large-diameter drilling. Background Art

[0002] More than 50% of my country's state-owned mines are high-gas or coal and gas outburst mines. Soft and low-permeability coal seams account for as high as 82%. Such coal seams are soft and broken, have low permeability, and have high gas content. The time and space matching problems of pre-extraction of coal seam gas are very prominent. Moreover, as the mining depth of coal seams continues to increase, the ground stress, gas pressure, and gas content of coal seams gradually increase, and the permeability gradually decreases. The difficulty of pre-extraction of coal seam gas increases, and the extraction efficiency is low, which can easily lead to frequent abnormal gas outbursts during the mining process, and easily lead to excessive gas concentrations in the working face, upper corner, and return air lane, which seriously threatens the safe production of coal mines. Therefore, new technologies and processes for coal seam pressure relief, permeability enhancement, and gas extraction are urgently needed.

[0003] At present, the coal seam permeability and pressure relief methods used in coal mines mainly include hydraulic measures, deep hole blasting, and gas fracturing. Among them, hydraulic measures mainly use hydraulic punching, hydraulic fracturing, high-pressure water jet cutting, hole expansion, and hole making to expand and penetrate the original cracks in the coal seam, continuously generate new cracks, release coal seam stress, and improve coal seam permeability to enhance the gas extraction effect. However, the implementation of hydraulic measures in soft coal seams is not only easy to cause the phenomenon of hole collapse and hole blocking, but also the water lock effect will have a negative impact on the gas migration in the coal seam. The deep hole blasting technology mainly uses the stress wave effect generated by the explosive gas during the explosion of explosives to improve the pore and fracture structure of the coal seam, and then improve the permeability of the coal seam to achieve the purpose of strengthening gas extraction. However, in the process of using deep hole blasting for permeability enhancement, the storage, transportation, and use of explosives are extremely dangerous, and the operation process is cumbersome and complicated; in addition, in the mining of deep coal seams, the use of this technology is also prone to induce other dynamic disasters such as rock burst. Gas fracturing and permeability enhancement technology mainly pressurizes inert gases such as nitrogen and carbon dioxide to form high-energy gases, which are then depressurized in the coal seam to form a physical explosion. In this process, the explosion stress wave and thermal stress improve the pore structure of the coal seam, thereby increasing the permeability and permeability of the coal seam, thereby achieving the purpose of improving the gas extraction effect. However, relevant research in recent years has found that in the process of using carbon dioxide for blasting displacement, due to its unique adsorption characteristics, it is more likely to cause dynamic disasters such as carbon dioxide outbursts, forming new safety hazards.

[0004] Due to the coal quality of the soft coal seams, if the above permeability-enhancing measures are used alone, although the coal seam cracks can develop and form a certain crack network, and can also achieve the relevant effect of enhancing gas extraction; but after a period of time, the cracks close quickly, and the permeability and permeability of the coal seam decrease rapidly, resulting in poor gas extraction effect.

[0005] In order to solve the above-mentioned related problems, the present invention proposes a gas control process which combines segmented hydraulic fracturing of key layers with large-diameter drilling of coal seams. Summary of the invention

[0006] The purpose of the present invention is to provide a gas control process that combines segmented hydraulic slitting, fracturing and large-diameter drilling in key layers, so as to fully relieve the pressure of the coal body, improve the permeability of the coal seam, and quickly release the depressurized gas to enhance the effect of coal seam gas pre-extraction, thereby solving the problem of low gas extraction efficiency during the mining of soft coal seams.

[0007] To achieve the above object, the present invention provides a gas control process combining segmented hydraulic fracturing of key layers with large-diameter drilling, comprising the following steps:

[0008] S1. Determine the key layer position and select the key layer for fracturing;

[0009] S2. Determine the cutting pressure and fracturing pressure required for hydraulic cutting and fracturing of the key fracturing layer;

[0010] S3, performing segmented hydraulic fracturing and water injection fracturing on the key fracturing layers;

[0011] S4. Determine the layout spacing of large-diameter boreholes in the coal seam, and construct large-diameter boreholes in the coal seam below the critical layer fracturing area;

[0012] S5. Use the "two plugging and one injection" process to seal large-diameter boreholes; after the sealing is completed, immediately carry out grid-connected pre-pumping.

[0013] Preferably, in S1, the composition and distribution of the overlying rock strata of the coal seam are determined, and based on the cantilever beam theory of materials, the breaking distance of the overlying rock is calculated. By combining the above results and parameters such as the control layer height, the heights of the caving zone, the fracture zone and the curved subsidence zone are theoretically calculated, and a theoretical model of coal seam overlying rock collapse is established. Based on the theoretical collapse model and in combination with the key layer theory, the position of the key layer of the overlying rock is determined. Specifically, an experimental model and a physical model are established, the collapse law, damage state, fracture development and development law of the overlying rock strata are analyzed, the position of the key layer is determined, and the key layer close to the coal seam is selected as the key layer for fracturing.

[0014] Preferably, in S2, rock samples at the critical fracturing layer are collected on site, the physical and mechanical properties of the rock samples at the critical fracturing layer are obtained through tensile and compressive tests, and the cutting pressure and fracturing pressure are determined through theoretical calculations and on-site experiments;

[0015] According to the lithology of the key fracturing layer, different abrasives are selected for the key fracturing layers with different lithologies - quartz sand, garnet, brown corundum, and walnut shell.

[0016] Preferably, in S3, a directional drill is used in the tunnel to arrange long directional boreholes in the key fracturing layer, and drilling is stopped after the holes are drilled to the designed hole depth. A high-pressure abrasive water jet cutting device is used to perform directional rotary cutting in the direction of the coal seam. After all the cutting operations are completed, a sealer is used to perform water injection fracturing.

[0017] Preferably, when the directional rotary slitting is performed in S3, in the slitting area, the pump pressure of the high-pressure abrasive water jet slitting device is increased to the slitting pressure, and a pulse jet is formed through the nozzle to perform directional rotary slitting in the direction of the coal seam. After the slitting in this area is completed, the pump pressure is reduced to the drilling pressure, and water is input into the hole for a period of time to clean the coal dust remaining during the slitting. After the water return of the drilling hole is normal, the drill is withdrawn to the next slitting area until all slitting operations are completed;

[0018] Preferably, when water injection fracturing is performed in S3, the sealer is sent to the deepest cut area of ​​the borehole to start the water injection fracturing process. The water injection fracturing process includes four stages: the natural water pressure rise stage, the manual pressure increase stage, the pressure maintenance stage and the manual pressure relief stage. After the fracturing in this area is completed, move to the next area until all fracturing is completed. The water injection pressure and fracturing time are monitored in real time during the whole process.

[0019] Preferably, in S4, the spacing of large-diameter drill holes in the coal seam is determined based on numerical simulation and measured data of the coal seam, and large-diameter drill holes are constructed in the air intake and return air tunnels of the working face into the coal seam in the decompression coal seam below the key layer fracturing area to complete secondary decompression.

[0020] Preferably, when large-diameter drilling construction is carried out in S4, the large-diameter drilling is completed by replacing the large-diameter drill bit. After the drilling is completed, the coal slag in the hole is drained, and after the drill rod is completely withdrawn, the guide head is installed on the hole opening side, and the hole protection tubes are pushed in one by one by plug-in method until the hole protection tubes are installed throughout the drilling process.

[0021] Therefore, the gas control process of the present invention combining segmented hydraulic slitting and fracturing of key layers with large-diameter drilling has the following beneficial effects:

[0022] (1) Directional rotating hydraulic cutting is carried out in the key layer to pre-determine oriented cracks, and then hydraulic fracturing is carried out in the cutting area to cause damage and destruction. Compared with not pre-determining oriented cracks, the initiation pressure in the next hydraulic fracturing process can be reduced, the crack expansion path can be optimized, and the formation of disordered cracks during hydraulic fracturing can be avoided; an effective and continuous fracture network is formed during the fracturing of the key layer, thereby effectively cutting off the stress transfer path of the overlying rock strata of the coal seam, changing the stress distribution of the overlying rock strata of the coal seam, and causing the coal body to be decompressed.

[0023] (2) By constructing large-diameter boreholes in the decompressed coal seam below the critical layer fracturing, irregular macro cracks are formed in the coal body around the boreholes, resulting in secondary decompression of the coal body and the generation of a large number of new cracks. Compared with ordinary boreholes in the critical layer coal seam without fracturing, the permeability of the coal seam can be significantly improved, and the desorption and emission rates of gas can be increased. Large-diameter boreholes can provide larger gas flow channels, which effectively improves the permeability of the coal seam and increases the efficiency of gas extraction. They can also replace multiple ordinary boreholes, reduce the total number of boreholes, and reduce the cost of drilling construction and maintenance.

[0024] (3) This process is suitable for gas control in soft coal seams with high ground stress, high gas pressure, high gas content and low permeability.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of segmented hydraulic fracturing and hydraulic cutting of key layers in an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of a large-diameter drilling hole in a coal seam according to an embodiment of the present invention;

[0028] Figure 3 A top view of a large-diameter drilling arrangement for a coal seam according to an embodiment of the present invention;

[0029] Figure 4 It is a front view of a large-diameter drilling arrangement of a coal seam according to an embodiment of the present invention;

[0030] Reference numerals:

[0031] 1. Ground; 2. Surface rock and soil layer; 3. Key layer; 4. Intermediate rock layer; 5. Key layer for fracturing; 6. Pseudo roof - direct roof; 7. Return air lane; 8. Large diameter borehole; 9. Coal seam; 10. Inlet air lane; 11. Directional long borehole. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0034] Example

[0035] This embodiment aims to solve the problems of hole collapse and low gas extraction concentration that often occur during the mining of soft coal seams with high ground stress and high gas stress. It adopts segmented hydraulic slitting and fracturing of key layers to relieve the pressure of the coal body and combines large-diameter drilling technology and processes in coal seams to improve the permeability and gas extraction efficiency of coal seams, which can effectively ensure the safe mining of the working face.

[0036] Combine the following Figure 1-4 Describe in detail:

[0037] S1. Using basic drilling geological data, logging data and other data, the ground stress, gas, geology and other profiles at the location are studied to determine the lithology composition and distribution of the overlying strata of the coal seam. From top to bottom, the distribution is as follows: ground 1, surface rock and soil layer 2, intermediate rock layer 4, pseudo-roof-direct roof 6, coal seam 9. Coal seam 9 is equipped with air intake channel 10 and return air channel 7. Based on the cantilever beam theory of material mechanics, the breaking distance of the overlying strata is calculated.

[0038] Combining the above results and the parameters of the control layer height, the height of the caving zone, fracture zone and curved subsidence zone was calculated theoretically, and the theoretical collapse model of the overburden stratum was established. Based on the theoretical collapse model of the overburden stratum, the experimental model and the physical model were established to analyze the collapse law, damage state, fracture development and development law of the overburden stratum, determine the position of the key layer 3, and select the key layer 3 close to the coal seam 9 as the key layer 5 for fracturing.

[0039] S2. Collect rock samples from the 5th layer of the critical fracturing layer on site, obtain the physical and mechanical properties of the rock samples from the 5th layer of the critical fracturing layer through tensile and compressive tests in the laboratory, and determine the cutting pressure and fracturing pressure.

[0040] Minimum horizontal stress σ of the critical fracturing layer 5 h =7MPa, maximum horizontal stress σ H =14MPa, combined with the mechanical properties test of the key fracturing layer 5, the rock tensile strength σ t =13.3MPa;

[0041] According to the calculation formula of hydraulic fracturing pressure of rock formation:

[0042] p b =3σ h -σ H +σ t

[0043] The calculation shows that the fracture initiation pressure of the key fracturing layer 5 is 20.3 MPa; the cutting pressure is 1.5 times of the fracture initiation pressure.

[0044] According to the above calculation, the single hydraulic cutting pressure of the key fracturing layer 5 is about 30MPa. After field experimental analysis, it is found that the abrasive 0.03m 3 The average single cutting time is about 15 minutes; the hydraulic fracturing pressure is about 20MPa, and the continuous pumping of high-pressure water is about 20 minutes.

[0045] S3, the key layer 3 is fine-grained sandstone, and quartz sand can be used as abrasive for hydraulic cutting. The directional drilling rig is arranged in the return air lane 7 of the working face, with a hole height of 1.8m, an azimuth angle of 90°, and an inclination angle of 15°. A directional long drill hole 11 is constructed for the key fracturing layer 5, with a hole diameter of 98mm and a hole depth of 140m.

[0046] According to numerical simulation and measured data of coal mines, the hydraulic fracturing radius is 15-20 m, and the spacing between two adjacent directional long boreholes 11 is 30-40 m.

[0047] According to the above results, a high-pressure abrasive water jet cutting device is used to perform segmented hydraulic cutting and fracturing on the critical fracturing layer 5. A directional drill is used in the return air lane 7 of the working face to drill a directional long borehole 11 on the critical fracturing layer 5. After drilling to the designed hole depth, the drilling is stopped. A high-pressure abrasive water jet cutting device is used to increase the pump pressure to a cutting pressure of 30 MPa. The high-pressure water and abrasive are fully mixed in the drill pipe, and a pulse jet is formed through the nozzle to perform directional rotary cutting on the coal seam 9. The average single cutting time is 15 minutes.

[0048] After the slitting is completed, reduce the pump pressure to the drilling pressure, and pump water into the hole for a period of time to remove the coal dust remaining during the slitting. After the water return to the borehole is normal, withdraw the drill to the next slitting area and repeat the above operation until all slitting is completed.

[0049] After all the slits are completed, the assembled sealer is connected to the drill pipe and sent into the deepest slit area of ​​the borehole to start water injection. The water injection process is manually operated on site to monitor the water injection pressure and fracturing time in real time. The water injection fracturing process is divided into four stages: 1) The natural rise of water pressure stage, the natural pressure increase and slow water injection ensure that the two ends of the capsule sealer bulge and effectively seal the borehole; 2) The manual pressure increase stage, the water injection pressure is slowly increased after the sealer achieves effective sealing, and the fracture pressure is maintained at 20MPa and water is continuously injected after the rock fracture pressure is reduced; 3) The pressure maintenance stage, the high-pressure water injection power is maintained for 20 minutes to allow the rock to fully fracture and repeatedly fracture; 4) The manual pressure relief stage, the pressure is manually relieved and the water injection equipment is shut down to complete the fracturing. After the first fracturing point is completed, the capsule sealer is fully drained and depressurized, and then withdrawn to the next slit area and the above steps are repeated.

[0050] S4. Through numerical simulation and coal seam measured data, it is determined that the arrangement spacing of large-diameter boreholes 8 in the coal seam is about 8m. In the decompression coal seam below the fracturing area of ​​the key fracturing layer, a drilling rig is used to construct large-diameter boreholes 8 in the coal seam in the return air tunnel of the working face. The designed borehole depth is 110m, the hole diameter is 220mm, the borehole opening is 1.5m away from the tunnel bottom plate, and the borehole arrangement spacing is 8m.

[0051] The drill rod is connected to a 94mm diameter drill bit and drilled to the designed hole depth with the help of a guide rod; after withdrawing the drill, replace with a 220mm drill bit to drill a large diameter hole 8; after the drilling is completed, drain the coal slag in the hole, and withdraw the drill rods one by one according to the reverse drilling procedure; when all the drill rods are withdrawn, install the guide head on the hole opening side with the pointed head facing forward, and use the drilling rig’s jacking device to push forward, and push the hole guard tubes one by one in a plug-in manner until the hole guard tubes are lowered throughout the drilling process. There are small holes on the hole guard tubes for extracting gas.

[0052] S5. After the drilling tool is completely withdrawn, the large-diameter borehole 8 is sealed using the "two plugging and one injection" process. The sealing length is about 15m and the sealing pressure is 1.5MPa. After the sealing is completed, the grid-connected pre-pumping is immediately carried out.

[0053] Therefore, the gas control process of the present invention, which combines segmented hydraulic slitting and fracturing of key layers with large-diameter drilling, can fully relieve the pressure of the coal body, improve the permeability of the coal seam, and quickly release the depressurized gas to enhance the effect of coal seam gas pre-extraction, thereby solving the problem of low gas extraction efficiency during the mining of soft coal seams.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A gas control process combining segmented hydraulic fracturing and large-diameter drilling in key layers, characterized in that: The following steps are involved: S1. Determine the position of key layers and select key layers for fracturing: Establish a coal seam overburden collapse model, determine the position of key layers of overburden combined with key layer theory, and select the key layers close to the coal seam as the key layers for fracturing; S2. Determine the cutting pressure and fracturing pressure required for hydraulic cutting and fracturing of the key fracturing layer; S3. Perform segmented hydraulic slitting and water injection fracturing on the key fracturing layer: Use a directional drill in the tunnel to set long directional holes in the key fracturing layer, use a high-pressure abrasive water jet slitting device to perform directional rotary slitting in the direction of the coal seam, and after completing all slitting operations, use a sealer to perform water injection fracturing; When performing directional rotary slitting, in the slitting area, the pump pressure of the high-pressure abrasive water jet slitting device is increased to the slitting pressure, and a pulse jet is formed through the nozzle to perform directional rotary slitting in the direction of the coal seam. After the slitting in this area is completed, the pump pressure is reduced to the drilling pressure, and clean water is input into the hole to clean the coal dust remaining during the slitting. After the water return in the drilling hole is normal, the drill is withdrawn to the next slitting area until all slitting operations are completed; S4. Determine the layout spacing of large-diameter boreholes in the coal seam, and construct large-diameter boreholes in the coal seam below the critical layer fracturing area; based on numerical simulation and measured data of the coal seam, determine the layout spacing of large-diameter boreholes in the coal seam, and construct large-diameter boreholes in the coal seam from the air inlet and return air lanes of the working face in the pressure relief coal seam below the critical layer fracturing area to complete secondary pressure relief; S5. Use the "two blocking and one injection" process to seal large-diameter boreholes; after the sealing is completed, immediately carry out grid-connected pre-pumping.

2. The gas control process combining segmented hydraulic fracturing and large-diameter drilling in key layers according to claim 1 is characterized in that: In S2, rock samples at the critical fracturing layer are collected on site, and the physical and mechanical properties of the critical fracturing layer rock samples are obtained through tensile and compressive tests to determine the cutting pressure and fracturing pressure.

3. The gas control process combining segmented hydraulic fracturing and large-diameter drilling in key layers according to claim 1 is characterized in that: When water injection fracturing is performed in S3, the sealer is sent to the deepest cut area of ​​the borehole to start the water injection fracturing process. The water injection fracturing process includes four stages: the natural water pressure rise stage, the manual pressure increase stage, the pressure maintenance stage and the manual pressure relief stage. After the fracturing in this area is completed, it moves to the next area until all fracturing is completed. The water injection pressure and fracturing time are monitored in real time during the whole process.

4. The gas control process combining segmented hydraulic fracturing and large-diameter drilling in key layers according to claim 1 is characterized in that: When large-diameter drilling is carried out in S4, the large-diameter drilling is completed by replacing the large-diameter drill bit. After the drilling is completed, the coal slag in the hole is drained. After the drill rod is completely withdrawn, the guide head is installed on the hole opening side, and the hole protection pipes are pushed in one by one by plugging until the hole protection pipes are installed throughout the drilling process.

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