A method for efficiently extracting gas from coal seams with increased permeability in coal tunnel top cut

Abstract

The present invention discloses a method for increasing the permeability of coal seams in coal tunnels. The present invention proposes a method for increasing the permeability of coal seams in coal tunnels. After artificial cutting and seaming, the elastic energy stored in the rock layer of the coal seam roof is released, the horizontal stress is activated, and a large difference is produced between the horizontal stress of the coal seam and the rock layer at the coal-rock interface, and the near-field stress of the coal-rock system is transformed. The coal seam is damaged by the high shear stress, cracks develop, and are connected with the drilled cracks, and the gas flow rate increases, ultimately achieving the purpose of improving the gas extraction efficiency. By monitoring the rock layer stress before and after cutting, the gas extraction efficiency and the degree of coal seam damage, the cutting effect and the scope of influence are evaluated.

Description

Technical Field

[0001] The invention relates to the field of coal seam permeability enhancement and gas extraction, and in particular to a method for efficiently extracting gas from a coal seam with a top cut of a coal roadway. Background Art

[0002] Efficient extraction of coal seam gas is an important guarantee for safe production and mining balance in coal mines. At the current stage when mine mining is rapidly shifting to deep areas, further improving the efficiency of coal seam gas extraction has become an important task to ensure the safe and efficient mining of deep coal resources in my country. Most coal seams in my country have the characteristics of high gas content and low permeability. With the increase in coal mining depth, the permeability of coal seams decreases, coal seam gas extraction becomes more difficult, and coal mine safety production is also under greater threat. Therefore, low-permeability coal seam permeability enhancement technology has always been a research hotspot.

[0003] At present, the methods for improving gas extraction efficiency by drilling holes in the layer mainly include hydraulic fracturing, hydraulic perforation, hydraulic cutting, deep hole directional blasting and mechanical coal cutting. The treatment and recovery of water will increase the operating cost. The blasting method has high requirements for safety management and will have an impact on the surrounding environment. The core idea of ​​the above methods is to introduce external energy to destroy the coal seam. The scope of the destruction and permeability of the coal seam is limited. It is necessary to repeat the operation many times to improve the permeability of the coal seam, which has a higher corresponding cost.

[0004] The method of increasing the permeability of coal seams by cutting the top of coal roadways to improve gas extraction efficiency is adopted. The transformation is carried out without affecting the normal mining of the working face. The elastic energy of the roof rock stratum is released by cutting the top, and the horizontal stress of the rock stratum is activated. The difference between the horizontal stress of the rock stratum and the horizontal stress of the coal seam at the coal-rock interface increases, the shear stress on the coal seam increases, the coal body is damaged, and the gas flow rate is increased after the cracks are connected with the drilled cracks, thereby improving the gas extraction efficiency of the boreholes along the layer. At present, the research and application of coal roadway cutting are all aimed at the safety and stability of the roadway. There are few studies on increasing the permeability of coal seams and improving the gas extraction efficiency of coal seams in the working face of coal roadway cutting. At present, there are problems such as low efficiency, long cycle, and insufficient extraction in the working face gas extraction in the coal mining process. Summary of the invention

[0005] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a method for high-efficiency gas extraction by increasing the permeability of coal seams by cutting the top of a coal roadway. In view of the problems of difficult gas extraction and low efficiency, it proposes forced cutting of the top of a coal roadway to release the elastic energy of the top rock layer, transform the near-field stress system of coal rock, increase the shear stress on the coal seam, and increase the crack rate of the coal seam, thereby increasing the gas extraction rate. After cutting the top, the elastic energy of the rock layer is released, the horizontal stress is activated, and a large difference is generated between the horizontal stress of the coal seam and the rock layer at the coal-rock interface. The shear stress on the coal seam is increased, the coal body is damaged, the cracks develop, and are connected to the drilled cracks. The gas flow rate increases, and the purpose of improving the gas extraction efficiency is finally achieved.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for efficiently extracting gas by increasing the permeability of coal seams by cutting the top of a coal roadway, comprising increasing the shear stress damage of coal seams by cutting the top of the roadway and continuously extracting gas by drilling holes along the seams until the target is reached, characterized in that increasing the shear stress damage of coal seams by cutting the top of the roadway comprises the following steps:

[0008] S1: Based on the existing information of the mining area and the analysis of coal samples taken multiple times and at different depths, a three-dimensional geometric model of coal rock geological structure is drawn;

[0009] S2: Conduct basic mechanical tests using on-site coal and rock samples to obtain the basic mechanical properties of the coal and rock mass in the stratum; at the same time, use the strain recovery method to test the vertical and horizontal ground stress distribution of the roof and floor strata on-site, and the test locations are distributed at the boundary of the working face and the tunnel area between the working faces;

[0010] S3: Based on the numerical model of coal-rock tunnel top cutting, the numerical model of coal-rock tunnel top cutting is established in combination with the three-dimensional geometric model of coal-rock geological structure, the basic mechanical properties of coal-rock mass and the vertical and horizontal ground stress distribution of rock strata. The reliability of the model is verified by comparing it with the field measured stress data; the top cutting process is simulated based on the above model to obtain the optimal top cutting width and depth;

[0011] S4: Design and construct through-layer and along-layer drilling holes to initially damage the coal body near the drilling holes in the working face and reduce the shear strength of the coal body in the local area; then use imaging while drilling technology to observe the damage characteristics of the coal body in the borehole, and use images to quantify the degree of coal body damage. After the drilling construction is completed, start gas extraction and record data;

[0012] S5: The top cutting operation is gradually carried out according to the optimal width and depth obtained by numerical simulation. After the top cutting, the horizontal stress of the rock formation is activated, the coal seam at the working face is damaged by the horizontal shear stress at the coal-rock interface, the coal seam cracks are interconnected with the damaged area of ​​the borehole along the layer, and the flow and desorption of gas in the coal seam are accelerated;

[0013] S6: After top cutting, the rock formation stress is measured again, and the imaging while drilling technology is used again to photograph the coal body in the borehole, quantify the crack and damage data in the image, obtain the borehole gas extraction data, compare the horizontal stress of the rock formation, the quantitative characteristics of coal body damage and the change of gas extraction rate before and after top cutting, analyze the changes in borehole gas extraction and coal body damage evolution at different locations, evaluate the effect of increasing the permeability of the top cut coal seam to improve gas extraction, and the impact range of top cutting.

[0014] Preferably, in step S1, previous exploration reports, drilling data, production data, mine stress field, geological maps and geological report information of the mining area are obtained, and geological drilling methods are used to further drill and sample, obtain stratigraphic structure, coal rock type, coal seam distribution, geological structure, coal rock layer inclination information, and draw a three-dimensional geometric model of the coal rock geological structure.

[0015] Preferably, in step S2, the rock samples obtained by drilling are brought back to the laboratory for uniaxial compressive strength testing and triaxial pressure testing, and the basic mechanical properties of the coal rock mass are determined using Mohr's Coulomb's law, including Young's modulus, Poisson's ratio, tangential stiffness, friction angle, cohesion, tensile strength, tensile fracture energy and shear fracture energy.

[0016] Preferably, in step S3, based on the numerical calculation model, a mechanical cutting method is used to study the cutting depth and width, respectively, to analyze the evolution of the differential stress at the coal-rock interface after cutting and the changes in coal body damage and cracks, and to quantify the coal body damage and crack development as key optimization indicators to obtain the optimal cutting depth and width.

[0017] Preferably, in step S4, the design parameters of the in-layer drilling and through-layer drilling are determined according to the anisotropic stress of the coal stratum, the thickness of the coal stratum, the basic mechanical properties of the coal body and the gas pressure.

[0018] The beneficial effects of the present invention are as follows: the present method can improve the stability and safety of the tunnel, remove potential unstable rocks through the top cutting operation, reduce the risk of roof collapse, and ensure the safety of miners. The permeability of the coal seam after top cutting is increased to improve the efficiency of gas extraction. Top cutting increases the cracks between the coal seam and the rocks around the tunnel, improves the permeability of the coal seam, and helps to release and extract gas. At the same time, it improves the efficiency of gas extraction and reduces the gas concentration, effectively avoids the problem of gas exceeding the limit, and reduces the risk of gas explosion; it improves the efficiency of tunnel excavation. Top cutting can reduce the interruption caused by roof collapse, making the tunnel excavation operation more continuous and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a crack distribution diagram of the coal seam working face tunnel and nearby coal bodies to which the embodiment of the present invention is applicable;

[0021] Figure 2 It is a design drawing of the in-layer drilling provided by an embodiment of the present invention;

[0022] Figure 3 It is a design drawing for drilling holes through rock tunnels in the bottom plate of a high-gas coal seam provided by an embodiment of the present invention;

[0023] Figure 4 Schematic diagram of crack distribution of coal seam permeability enhancement after top cutting provided by an embodiment of the present invention;

[0024] Figure 5 It is a specific implementation flow chart of a method for efficiently extracting gas by increasing the permeability of a coal seam in a coal tunnel provided by the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] like Figure 5 As shown, a method for efficiently extracting gas by increasing the permeability of coal seams by cutting the top of a coal roadway comprises increasing the shear stress damage of the coal seams by cutting the top of the roadway and continuously extracting gas by drilling holes along the seams until the target is reached. The method comprises the following steps:

[0027] 1. Obtain previous exploration reports, drilling data and production data, mine stress field, geological maps and geological reports of the mining area. Combined with the actual situation of the mining area, use geological drilling methods to further drill and sample, drill in the coal-bearing strata, and obtain rock and coal samples from different depths. Combined with the samples, further analyze the structure of the strata, rock types and distribution of coal seams, geological structures and inclination of coal and rock strata, and establish Figure 1 The three-dimensional geometric model of coal rock geological structure is shown.

[0028] 2. Bring the rock samples obtained by drilling back to the laboratory for uniaxial compressive strength test and triaxial pressure test, etc., and use Mohr Coulomb's law to determine Young's modulus, Poisson's ratio, tangential stiffness, friction angle, cohesion, tensile strength, tensile fracture energy and shear fracture energy. Use the strain recovery method to test the three-phase stress of the top and bottom rock layers of the tunnel on site. The test locations are on both sides of the mining working face and the tunnel between the cutting eye and the working face.

[0029] 3. Based on the numerical model of coal-rock tunnel top cutting, the above three-dimensional geometric model of coal-rock geological structure is used to carry out the stress analysis of coal-rock layer caused by top cutting, and the numerical model is corrected by combining the field measured stress. Based on the numerical calculation model, the mechanical top cutting method is used to study the top cutting depth and width, and analyze the evolution of the differential stress of the coal-rock interface after top cutting and the change law of coal body damage and cracks, such as Figure 4As shown in the figure, the quantification of coal body damage and crack development is used as the key optimization index to obtain the optimal cutting depth and width.

[0030] 4. Reference Figure 2 and 3 According to the anisotropic stress of coal strata, coal seam thickness, basic mechanical properties of coal body and gas pressure, the design parameters of in-layer drilling and through-layer drilling are determined to initially damage the coal body at the working face and reduce the shear strength of the coal body. The imaging while drilling technology is used to observe the coal body damage imaging at different drilling positions and drilling depths, and the degree of coal body damage is quantified using images. After the drilling construction is completed, gas extraction is carried out and the gas extraction data is recorded.

[0031] 5. Cutting the top gradually according to the designed width and depth. After cutting the top, the horizontal stress of the rock layer is activated, the top rock is damaged, the horizontal shear stress between the coal and rock layers at the working face increases, the coal seam is gradually damaged, and the cracks gradually develop. The final effect is as follows: Figure 4 The coal seam fissures and the damaged areas of the boreholes along the coal seams are interconnected, and the flow and desorption of gas in the coal seams are accelerated, thereby improving the gas extraction efficiency.

[0032] 6. After the top cutting is completed, the rock formation stress is measured again, and the imaging while drilling technology is used again to photograph the coal body in the borehole, quantify the crack data in the image, and extract the borehole gas extraction data. By comparing the horizontal stress of the rock formation, the damage characteristics of the coal body and the changes in the gas extraction rate before and after the top cutting, the changes in the gas extraction of boreholes at different positions and the evolution of coal body damage are analyzed, and the effect of increasing the permeability of the top cut coal seam and improving gas extraction as well as the impact range of the top cutting are evaluated.

[0033] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for efficiently extracting gas from coal seams by cutting the top of a coal roadway, comprising: increasing the shear stress damage of the coal seam by cutting the top of the roadway and continuously extracting gas by drilling holes along the seam until the target is reached, characterized in that: The tunnel top cutting method to increase the shear stress damage and permeability of the coal seam includes the following steps: S1: Based on the existing information of the mining area and the analysis of coal samples taken multiple times and at different depths, a three-dimensional geometric model of coal rock geological structure is drawn; S2: Conduct basic mechanical tests using on-site coal and rock samples to obtain the basic mechanical properties of the coal and rock mass in the stratum; at the same time, use the strain recovery method to test the vertical and horizontal ground stress distribution of the roof and floor strata on-site, and the test locations are distributed at the boundary of the working face and the tunnel area between the working faces; S3: Based on the numerical model of coal-rock tunnel top cutting, the numerical model of coal-rock tunnel top cutting is established in combination with the three-dimensional geometric model of coal-rock geological structure, the basic mechanical properties of coal-rock mass and the vertical and horizontal ground stress distribution of rock strata. The reliability of the model is verified by comparing it with the field measured stress data; the top cutting process is simulated based on the above model to obtain the optimal top cutting width and depth; S4: Design and construct through-layer and along-layer drilling holes to initially damage the coal body near the drilling holes in the working face and reduce the shear strength of the coal body in the local area; then use imaging while drilling technology to observe the damage characteristics of the coal body in the borehole, and use images to quantify the degree of coal body damage. After the drilling construction is completed, start gas extraction and record data; S5: The top cutting operation is gradually carried out according to the optimal width and depth obtained by numerical simulation. After the top cutting, the horizontal stress of the rock formation is activated, the coal seam at the working face is damaged by the horizontal shear stress at the coal-rock interface, the coal seam cracks are interconnected with the damaged area of ​​the borehole along the layer, and the flow and desorption of gas in the coal seam are accelerated; S6: After top cutting, the rock formation stress is measured again, and the imaging while drilling technology is used again to photograph the coal body in the borehole, quantify the crack and damage data in the image, obtain the borehole gas extraction data, compare the horizontal stress of the rock formation, the quantitative characteristics of coal body damage and the change of gas extraction rate before and after top cutting, analyze the changes in borehole gas extraction and coal body damage evolution at different locations, evaluate the effect of increasing the permeability of the top cut coal seam to improve gas extraction, and the impact range of top cutting.

2. A method for efficiently extracting gas from a coal roadway top-cut coal seam by increasing permeability as claimed in claim 1, characterized in that: In step S1, previous exploration reports, drilling data, production data, mine stress field, geological maps and geological report information of the mining area are obtained, and geological drilling methods are used to further drill and sample, obtain stratigraphic structure, coal rock type, coal seam distribution, geological structure, coal rock layer inclination information, and draw a three-dimensional geometric model of coal rock geological structure.

3. A method for efficiently extracting gas from a coal roadway top-cut coal seam by increasing permeability as claimed in claim 1, characterized in that: In step S2, the rock samples obtained by drilling are brought back to the laboratory for uniaxial compressive strength test and triaxial pressure test, and the basic mechanical properties of the coal rock mass are determined using Mohr's Coulomb's law, including Young's modulus, Poisson's ratio, tangential stiffness, friction angle, cohesion, tensile strength, tensile fracture energy and shear fracture energy.

4. A method for efficiently extracting gas from a coal roadway top-cut coal seam by increasing permeability as claimed in claim 1, characterized in that: In step S3, based on the numerical calculation model, the mechanical cutting method is used to study the cutting depth and width, analyze the evolution of the differential stress at the coal-rock interface after cutting, and the change law of coal body damage and cracks, and quantify the coal body damage and crack development as key optimization indicators to obtain the optimal cutting depth and width.

5. A method for efficiently extracting gas from a coal roadway top-cut coal seam by increasing permeability as claimed in claim 1, characterized in that: In step S4, the design parameters of the in-layer drilling and through-layer drilling are determined according to the anisotropic stress of the coal rock layer, the thickness of the coal seam, the basic mechanical properties of the coal body and the gas pressure.

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