A method for extracting gas by coordinated advancement from top to bottom in a particularly thick coal seam well

Abstract

The present invention belongs to the technical field of coal mine gas extraction. It relates to a method for pre-extraction of gas in the coal mining face area of ​​a coal mine, including S1: advance pre-extraction in the hydraulic fracturing area of ​​the ground well, S2: enhanced extraction in the segmented hydraulic fracturing area of ​​the underground directional drilling, and S3: supplementary extraction by drilling through the bottom plate. The present invention is based on the coal seam hydraulic fracturing permeability enhancement technology. Through three-level coordinated progressive extraction such as advance pre-extraction in the ground well area, enhanced extraction by underground directional drilling, and supplementary extraction by drilling through the bottom plate, it effectively solves the problems of high original gas content in extra-thick coal seams, low coal seam permeability, and long extraction period to meet gas extraction standards, thereby achieving efficient extraction of gas from extra-thick and high-gas coal seams, thereby effectively reducing gas control costs, improving coal seam gas utilization, and reducing carbon emissions, providing important guarantees for ensuring safe production in mines.

Description

Technical Field

[0001] This invention belongs to the field of coal mine gas extraction technology, and relates to a method for coordinating and progressively extracting gas from an extra-thick coal seam both above and below ground. Background Technology

[0002] For gas drainage in extra-thick coal seams, the main methods include pre-drainage via bottom-penetrating boreholes, directional drilling, and in-seam drilling. However, due to the large thickness, high initial gas content, high gas pressure, and low permeability of extra-thick, high-gas coal seams, the required drainage period to reach the target is long, and single gas control measures often fail to achieve the desired results. In recent years, hydraulic permeability enhancement measures and surface drilling gas drainage have been widely promoted and applied, providing important approaches and means to solve the gas control problem in extra-thick coal seams. However, problems such as unreasonable gas drainage layout, uncoordinated drainage methods, and defective drainage processes often lead to unsatisfactory gas drainage results and high gas control costs. In view of this, this invention provides a method for coordinated and progressive gas drainage from above-ground and below-ground areas in extra-thick coal seams. By optimizing the drainage layout and gas drainage process design, the gas drainage effect can be effectively improved, achieving efficient regionalized drainage of extra-thick coal seams. Summary of the Invention

[0003] In view of this, the purpose of this invention is to solve the problem of gas extraction from extra-thick coal seams, and to provide a method for gas extraction from extra-thick coal seams through coordinated and progressive extraction both above and below ground. This invention is based on coal seam hydraulic fracturing and permeability enhancement technology, and through a three-stage coordinated and progressive extraction process, namely, pre-extraction in the surface well area, enhanced extraction through directional drilling underground, and supplementary extraction through bottom-layer drilling, it effectively solves the problems of high original gas content, low coal seam permeability, and long extraction period to meet gas extraction standards in extra-thick coal seams. This achieves efficient gas extraction from extra-thick, high-gas coal seams, thereby effectively reducing gas control costs, improving coal seam gas utilization, reducing carbon emissions, and providing an important guarantee for ensuring safe production in mines.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for coordinated, progressive gas extraction from ultra-thick coal seams, comprising the following steps:

[0006] S1: Pre-drainage of coal seam gas in the area by hydraulic fracturing of surface wells: Surface wells are constructed on the surface of the mining area to be drained. After surface hydraulic fracturing to increase permeability, large-scale pre-drainage of coal seam gas in the area is carried out.

[0007] S2: Intensive extraction of coal seam gas in the area by directional drilling and hydraulic fracturing in the underground: After the gas extraction flow rate of the surface well decreases, directional drilling is carried out in the underground boundary roadway to perform sectional hydraulic fracturing and permeability enhancement, and then the gas in the area is extracted intensified.

[0008] S3: Bottom-layer through-hole supplementary extraction: During the excavation of the regional coal seam bottom roadway, bottom-layer through-holes are designed and constructed to supplement the extraction of regional coal seam gas.

[0009] Furthermore, in step S1, the surface wells are arranged parallel to the coal seam strike or dip, with a spacing of 150-200m between them, and the surface wells penetrate the full thickness of the coal seam.

[0010] After the hydraulic fracturing process of the surface well is completed, it is connected to the surface high negative pressure gas extraction system for gas extraction. The gas extraction monitoring system is used to monitor parameters such as gas extraction flow rate, concentration, and negative pressure in the surface well in real time, and to dynamically grasp the changes in extraction flow rate.

[0011] Furthermore, during surface drilling and hydraulic fracturing, surface fracture monitoring is used to determine the impact range of surface well hydraulic fracturing, providing a basis for the design of downhole directional drilling and bottom plate cross-layer drilling.

[0012] Furthermore, in step S2, the underground directional boreholes are arranged parallel to the coal seam strike or dip, and are divided into directional fracturing boreholes and directional extraction boreholes. During the drilling construction, the directional fracturing boreholes are constructed first, and the directional extraction boreholes are constructed after the directional fracturing boreholes are completed. After the directional boreholes are completed, they are promptly connected to the high negative pressure gas extraction system for gas extraction.

[0013] Furthermore, the directional fracturing boreholes are arranged in the middle of the coal seam, with a designed spacing of 30-50m, and the spacing is optimized based on the actual fracturing influence radius investigation results; the directional extraction boreholes are arranged in the lower middle part of the coal seam, with a designed spacing of 15-20m. Every 50-100m along the construction direction, a top-exploration branch borehole is designed for the directional extraction boreholes, and the top-exploration branch boreholes must penetrate 0.5m above the coal seam roof.

[0014] Furthermore, the layout of directional fracturing boreholes is designed based on the fracturing influence range determined by ground fracture monitoring, and the distance between the fracturing boreholes and the ground boreholes is maintained at more than 50m.

[0015] Furthermore, in step S3, when designing the bottom plate cross-layer drilling, the design is optimized by comprehensively considering the influence range of surface well fracturing and the control range of downhole directional drilling extraction; the drilling is arranged between directional drilling to avoid mutual communication between extraction drillings and affecting the supplementary extraction effect.

[0016] Furthermore, the bottom plate through-layer boreholes are arranged in a fan shape or in parallel, with a spacing of 15 to 20 meters along the coal seam strike, and must penetrate the full thickness of the coal seam to 0.5 meters to the roadway roof.

[0017] Furthermore, after the working face is mined out, the surface wells are repaired and modified to extract gas from the goaf of the working face and to be used for fire prevention and extinguishing observation, grouting or nitrogen injection to prevent spontaneous combustion of residual coal in the goaf. When layered mining is adopted, underground directional drilling and bottom plate through-layer drilling are further used to extract and depressurize gas, realizing the multi-purpose function of one hole.

[0018] The beneficial effects of this invention are as follows:

[0019] (1) This invention is based on the hydraulic fracturing technology for enhancing permeability of coal seams. It uses surface drilling hydraulic fracturing extraction, combined with secondary hydraulic fracturing extraction through underground directional long boreholes and supplementary extraction through bottom plate cross-layer boreholes, to form a coordinated and progressive extraction pattern between the surface and underground. This greatly improves the gas extraction flow rate, extraction concentration and extraction effect, and shortens the gas pre-extraction standard period. It can effectively alleviate the problem of tight extraction, tunneling and mining in extra-thick high-gas coal seam mines.

[0020] (2) This invention fully considers the spatial and temporal layout of gas extraction, overcomes the problems of poor extraction effect of single measures and mutual interference of comprehensive measures, can effectively reduce the cost of gas control, improve the utilization of coal seam gas, reduce carbon emissions, and provide an important guarantee for ensuring safe production in mines.

[0021] (3) This invention uses surface drilling to perform large-area pre-extraction, which can realize the extraction of regional coal seam gas in advance when drilling conditions are not available underground, adapting to the industry development trend of large-area gas extraction in coal mines.

[0022] (4) Using the method in this invention, the surface well can be repaired and modified in the later stage, and the gas can be extracted from the goaf of the working face and used for fire prevention and extinguishing observation, grouting or nitrogen injection to prevent spontaneous combustion of coal residue in the goaf. When layered mining is adopted, underground directional drilling and bottom plate through-layer drilling can be used to extract and depressurize gas, thereby solving the gas control problem during mining, extending the drilling service cycle, and realizing the multi-purpose function of one hole.

[0023] 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

[0024] 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:

[0025] Figure 1 This is a flowchart of the method for coordinated and progressive extraction of gas from an extra-thick coal seam.

[0026] Figure 2 This is a plan view of the surface drilling and downhole directional drilling.

[0027] Figure 3 This is a cross-sectional layout diagram of surface drilling and downhole directional drilling.

[0028] Figure 4 This is a cross-sectional layout diagram of the drilling holes through the layers of the base plate.

[0029] Attached reference numerals: 1-Area to be extracted; 2-Surface well; 3-Underground area boundary roadway; 4-Directional borehole; 4a-Directional fracturing borehole; 4b-Directional extraction borehole; 5-Top exploration branch borehole; 6-Regional coal seam floor roadway; 7-Floor cross-layer borehole. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Please see Figures 1-4 This is a method for coordinated and progressive gas extraction from ultra-thick coal seams, comprising the following steps:

[0034] S1: Pre-drainage of the hydraulically fractured area of ​​surface well 2: that is, to construct surface well 2 on the surface of the mining area to be drained area 1, and after the surface hydraulic fracturing to increase permeability, large-scale pre-drainage of coal seam gas in the area is carried out.

[0035] Among them, surface well 2 is arranged parallel to the strike or dip of the coal seam, with a spacing of 150-200m between surface wells 2, and surface well 2 penetrates the full thickness of the coal seam; after the hydraulic fracturing process of surface well 2 is completed, it is connected to the surface high negative pressure gas extraction system for gas extraction, and the gas extraction flow rate, concentration, negative pressure and other parameters of surface well 2 are monitored in real time through the gas extraction monitoring system to dynamically grasp the changes in extraction flow rate.

[0036] During surface drilling and hydraulic fracturing, the impact range of surface well 2 hydraulic fracturing is determined by surface fracture monitoring, providing a basis for the design of downhole directional drilling 4 and bottom plate through-layer drilling 7.

[0037] S2: Enhanced extraction of coal seam gas in the area by 4-segment hydraulic fracturing in the underground directional borehole: After the gas extraction flow rate of the surface well 2 decreases, directional borehole 4 is drilled through the boundary roadway 3 in the underground area to carry out segmented hydraulic fracturing and permeability enhancement, thereby enhancing the extraction of coal seam gas in the area.

[0038] Among them, the underground directional borehole 4 is arranged parallel to the coal seam strike or dip, and is divided into directional fracturing borehole 4a and directional extraction borehole 4b. During the drilling construction, directional fracturing borehole 4a is constructed first, and directional extraction borehole 4b is constructed after the directional fracturing borehole 4a is completed. After the directional borehole 4 is completed, it is connected to the high negative pressure gas extraction system in a timely manner for gas extraction.

[0039] The directional fracturing borehole 4a is located in the middle of the coal seam, with a designed spacing of 30-50m, and the design is optimized based on the actual fracturing influence radius investigation results. The directional extraction borehole 4b is located in the lower middle part of the coal seam, with a designed spacing of 15-20m. A top-exploration branch borehole 5 is designed every 50-100m along the construction direction of the directional extraction borehole 4b, and the top-exploration branch borehole 5 must penetrate 0.5m above the coal seam roof.

[0040] The layout of the directional fracturing borehole 4a is designed based on the fracturing influence range determined by ground fracture monitoring, and the distance between the fracturing borehole and the ground borehole is maintained at more than 50m.

[0041] S3: Bottom-layer through-hole 7 supplementary extraction: During the excavation of the regional coal seam bottom roadway 6, bottom-layer through-hole 7 is designed and constructed to supplement the extraction of regional coal seam gas.

[0042] In the design of the bottom plate through-layer borehole 7, the design was optimized by comprehensively considering factors such as the impact range of fracturing of surface well 2 and the extraction control range of underground directional borehole 4. The boreholes were arranged between the directional boreholes 4 to avoid cross-contamination between the extraction boreholes and affecting the supplementary extraction effect. The bottom plate through-layer borehole 7 is arranged in a fan shape or in parallel, with a design spacing of 15-20m along the coal seam strike, and must penetrate the full thickness of the coal seam to 0.5m of the roadway roof.

[0043] After the working face is mined, the surface well 2 can be repaired and modified to extract gas from the goaf of the working face and to be used for fire prevention and extinguishing observation, grouting or nitrogen injection to prevent spontaneous combustion of residual coal in the goaf. When layered mining is adopted, the underground directional borehole 4 and the bottom plate through-layer borehole 7 can be used to extract depressurized gas, realizing the multi-purpose function of one borehole.

[0044] 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 method for extracting gas from a particularly thick coal seam by coordinated advancement up and down, characterized in that: The following steps are involved: S1: Advance pre-extraction of surface well hydraulic fracturing areas: construct surface wells on the ground in the mining area to be extracted, and after surface hydraulic fracturing to increase permeability, large-scale advance pre-extraction of regional coal seam gas is carried out; the surface wells are arranged parallel to the strike or dip of the coal seam, with a spacing of 150 to 200 meters between them, and the surface wells penetrate the full thickness of the coal seam; after the surface well hydraulic fracturing process is completed, the surface high-negative pressure gas extraction system is connected for gas extraction, and the surface well gas extraction parameters are monitored in real time through the gas extraction monitoring system to dynamically grasp the changes in the extraction flow rate; S2: Underground directional drilling and segmented hydraulic fracturing regional enhanced extraction: After the gas extraction flow rate of the surface well decays, directional drilling is constructed through the boundary tunnels of the underground area, and segmented hydraulic fracturing is carried out to enhance the permeability of the regional coal seam gas. The underground directional drilling holes are arranged parallel to the strike or dip of the coal seam, and are divided into directional fracturing drilling holes and directional extraction drilling holes. During the drilling construction, the directional fracturing drilling holes are constructed first, and the directional extraction drilling holes are constructed after the directional fracturing drilling holes are completed. After the directional drilling holes are completed, they are promptly connected to the high negative pressure gas extraction system for gas extraction; The directional fracturing drilling holes are arranged in the middle of the coal seam, with a design spacing of 30 to 50 m, and the spacing is optimized based on the actual fracturing impact radius survey results; the directional extraction drilling holes are arranged in the middle and lower parts of the coal seam, with a design spacing of 15 to 20 m. A top exploration branch borehole is designed every 50 to 100 m along the construction direction of the directional extraction drilling holes, and the top exploration branch borehole must penetrate 0.5 m above the coal seam roof; the layout of the directional fracturing drilling holes is designed based on the fracturing impact range determined by ground fracture monitoring, and the distance between the fracturing drilling holes and the ground drilling holes is kept at more than 50 m; S3: Bottom plate through-layer drilling for supplementary extraction: During the excavation of the regional coal seam floor tunnel, the bottom plate through-layer drilling is designed and constructed to supplement the extraction of regional coal seam gas; when designing the bottom plate through-layer drilling, the influence range of surface well fracturing and the control range of underground directional drilling extraction are comprehensively considered for optimization design; The boreholes are arranged between directional boreholes to avoid mutual communication between the extraction boreholes and affect the supplementary extraction effect; the bottom plate through-layer boreholes are arranged in a fan shape or in parallel, with a spacing of 15 to 20m along the coal seam strike, and must penetrate the entire thickness of the coal seam to 0.5m on the tunnel roof; after the working face is mined, the ground wells are repaired and renovated to extract gas from the goaf of the working face and used for fire prevention and extinguishing observation, grouting or nitrogen injection to prevent spontaneous combustion of coal left in the goaf. When stratified mining is adopted, underground directional drilling holes and bottom plate through-layer drilling holes are further used to extract and unload pressure gas, realizing the multi-purpose function of one hole.

2. The method for extracting gas from a particularly thick coal seam by coordinated advancement from top to bottom according to claim 1 is characterized in that: During the hydraulic fracturing of surface drilling, the impact range of hydraulic fracturing of the surface well is determined through ground fracture monitoring, providing a basis for the design of downhole directional drilling and bottom plate penetration drilling.

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