A method for gas pre-extraction in a coal mining face area of a coal mine

Abstract

The present application belongs to the technical field of coal mine gas extraction, and relates to a coal mining face area gas pre-extraction method, which adopts "crossing layer + along layer" regional segmented hydraulic fracturing to carry out coal mining face area gas pre-extraction, and comprises the following steps: S1, determining the position of the coal mining face bottom extraction roadway; S2, determining the position of the segmented hydraulic fracturing, drilling the segmented hydraulic fracturing borehole, and carrying out parameter testing of the coal seam original gas; S3, determining the "crossing layer + along layer" regional segmented hydraulic fracturing parameters along the working face tendency; S4, determining the hydraulic fracturing sequence, and completing the "crossing layer + along layer" hydraulic fracturing permeability improvement; S5, fracturing hole connection extraction, coal seam gas extraction borehole construction and extraction. The present application can effectively improve the gas extraction efficiency, reduce the engineering quantity and cost, shorten the advance time, realize the extraction standard, adapt to the change of complex geological conditions and mining methods, and ensure the safety production and resource utilization.

Description

Technical Field

[0001] This invention belongs to the field of coal mine gas extraction technology, and relates to a method for pre-extraction of gas in the coal mining face area. Background Technology

[0002] Coal mine gas refers to the combustible gas contained in or associated with coal seams, mainly composed of methane, which is a highly efficient and clean energy source. However, coal mine gas is also one of the major threats to coal mine safety. If it is not extracted and utilized in a timely and effective manner, it can cause serious accidents such as gas explosions, asphyxiation, and fires, endangering lives and property, and also polluting the environment. To prevent and reduce coal mine gas accidents and improve the utilization rate of coalbed methane resources, regulations stipulate that mines that should extract gas must do so first; mining operations can only be arranged after the extraction effect meets the standard requirements.

[0003] Currently, the commonly used gas extraction methods in my country include the following:

[0004] Pre-extraction method: Before or during mining, boreholes or roadways are drilled or arranged in unmined areas or near mining boundaries to reduce the absolute and relative outflow of the working face into the area.

[0005] Decompression method: During the mining process, boreholes or roadways are drilled or arranged in the upper or lower or adjacent areas of the working face for drilling or roadway extraction, and the extraction effect of the boreholes or roadways is increased by utilizing the decompression effect of mining.

[0006] Roof method: During the mining process, boreholes are drilled or roadways are arranged on the roof of the working face for drilling or roadway extraction, taking advantage of the development and movement of roof fissures to increase the extraction effect of the boreholes or roadways.

[0007] Goaf method: During the mining process, boreholes or roadways are drilled or arranged in the goaf behind the working face to extract gas by utilizing the large amount of residual and diffused gas resources accumulated in the goaf.

[0008] Each of the above methods has its own advantages and disadvantages, and is suitable for different geological conditions and mining methods. Generally speaking, the pre-drainage method can effectively reduce the absolute and relative outflow of gas in the working face entry area, but it requires a long lead time and a large amount of engineering work; the pressure relief method can effectively improve the drainage effect of boreholes or roadways, but it requires high negative pressure and good sealing conditions; the roof method can effectively utilize the development and movement of roof fractures to increase the drainage effect of boreholes or roadways, but it requires good roof conditions; the goaf method can effectively utilize the large amount of residual and diffused gas resources accumulated in the goaf, but it requires good goaf conditions and high drainage negative pressure.

[0009] In practical applications, the above methods often need to be combined or varied according to specific circumstances to achieve the best extraction effect. For example, hydraulic fracturing or hydraulic perforation can be used in pre-extraction boreholes or roadways to improve coal seam permeability and extraction efficiency; gas injection or gas blasting can be used in depressurization boreholes or roadways to increase coal seam gas desorption and extraction effects; and horizontal drilling or horizontal wells can be used in roof boreholes or roadways to increase the effective length of the boreholes or roadways and the extraction range.

[0010] Although my country has made some progress and achievements in coal mine gas extraction technology, some problems and challenges still exist. In particular, the problem of "extraction and mining" in high-gas and even low-gas mines is becoming increasingly prominent, making regional gas control at coal mining faces especially important. The current method involves drilling through the coal seam using multiple bottom extraction roadways along the coal seam (i.e., cross-seam + in-seam) for preliminary gas extraction. However, this method is costly, inefficient, and time-consuming, making it difficult to meet the safety production needs of high-yield and high-efficiency mines.

[0011] Therefore, there is an urgent need to develop a new method for pre-extraction of gas in coal mining faces, which can effectively improve the efficiency and effectiveness of gas extraction, reduce engineering workload and costs, shorten lead time and cycle, adapt to complex geological conditions and changes in mining methods, and ensure safe production and resource utilization. Summary of the Invention

[0012] In view of this, the purpose of the present invention is to solve the problem of gas extraction in coal mining face areas and to provide a method for pre-extraction of gas in coal mining face areas.

[0013] To achieve the above objectives, the present invention provides the following technical solution:

[0014] A method for preliminary gas extraction in coal mining faces, employing a "cross-layer + in-layer" regional segmented hydraulic fracturing permeability enhancement approach, includes the following steps:

[0015] S1. Determine the location of the bottom extraction roadway of the coal mining face;

[0016] S2. Determine the location of the segmented hydraulic fracturing, complete the segmented hydraulic fracturing borehole drilling, and conduct parameter testing of the original gas in the coal seam;

[0017] S3. Determine the segmented hydraulic fracturing parameters for the "cross-layer + in-layer" area along the dip of the working face;

[0018] S4. Determine the hydraulic fracturing sequence and complete the "cross-layer + in-layer" hydraulic fracturing permeability enhancement.

[0019] S5. Fracturing hole connection and extraction, coal seam gas extraction drilling construction and extraction.

[0020] Furthermore, in step S1, the location of the bottom drainage roadway is determined based on the length of the coal face, the characteristics of the coal seam, and the drilling capacity. When the length of the coal seam drilled by the underground drilling rig is greater than l1, there is no need to construct a bottom drainage roadway, and the mining area roadway is directly used as a bottom drainage roadway for regional gas control. When the length of the coal seam drilled by the underground drilling rig is less than l1, the length of the bottom drainage roadway is l1-l2. The bottom drainage roadway is required to be located in the middle of the dip of the coal face, and a bottom drainage connecting roadway is constructed at the l2 position of the bottom drainage roadway.

[0021] Wherein, l1 is the strike length of the coal mining face, and l1 is no more than 800m; l2 is the length from the bottom extraction connecting roadway to the cut-off point.

[0022] Furthermore, in step S2, it is required that coal samples be taken every 50m to test the gas content parameters of the coal seam. Since the borehole is long, a closed core sampling device is required to complete the sampling to ensure the accuracy of the gas content test. This gas content is used as the original gas content of the coal seam.

[0023] Furthermore, in step S3, the hydraulic fracturing pressure and the fracturing pump pressure are determined as follows:

[0024] The determination of hydraulic fracturing parameters is based on the geological environment, stress state, and physical and mechanical parameters of the target coal seam. Appropriate fracturing types and pressure parameter limits are selected according to requirements and regulations. The fracturing pressure P of the coal seam is calculated according to formula (1). k ; Under the appropriate fracturing type pressure parameter limit and P calculated according to equation (1) k Among them, the minimum value is taken as P in equation (2). k The pump pressure P of the fracturing pump is calculated according to formula (2). w ;

[0025] P k =3δ h -δ H +δ t -P0 (1)

[0026] In the formula:

[0027] δ h -Minimum principal stress, MPa;

[0028] δ H - Maximum principal stress, MPa;

[0029] δ t - Tensile strength, MPa;

[0030] P0 - Pore pressure, MPa;

[0031] P w =P k +P H +Pr (2)

[0032] In the formula:

[0033] P H -Fracturing pipeline fluid column pressure, P H =ρgH, MPa;

[0034] ρ - density of fracturing fluid, kg / m³ 3 ;

[0035] g - acceleration due to gravity, N / kg;

[0036] H - Elevation difference of fracturing pipeline, which is the final borehole elevation minus the opening elevation, in meters;

[0037] P r -Fracturing fluid friction along the path, P w =Lλ1;

[0038] L - Pipeline length, in meters;

[0039] λ1 - Friction coefficient, MPa / m;

[0040] Furthermore, in step S2, the hydraulic fracturing holes are arranged at equal intervals, running from the bottom pumping connecting roadway through the rock strata and then along the coal seam to the cut-off point; the influence radius of hydraulic fracturing is determined based on the working face dip length, fracturing pump pressure, and coal and rock fracturing pressure, thus obtaining the spacing of the hydraulic fracturing holes.

[0041] Furthermore, in step S4, fracturing is carried out sequentially by alternating adjacent holes, that is, two fracturing holes are not adjacent to each other during the construction process, in order to reduce the impact of fracturing on adjacent holes.

[0042] Furthermore, in step S5, after fracturing is completed, pressure is maintained for 2 to 4 days, and the fracturing holes are connected for extraction; when the fracturing holes are connected for extraction for 15 to 20 days or the extracted gas concentration is less than 3%, a gas extraction hole is constructed between two adjacent fracturing holes.

[0043] The beneficial effects of this invention are as follows:

[0044] 1. This invention adopts a "cross-layer + along-layer" regional segmented hydraulic fracturing permeability enhancement method, which can effectively improve coal seam permeability and extraction efficiency, reduce engineering workload and costs, shorten advance time and cycle, adapt to complex geological conditions and changes in mining methods, and ensure safe production and resource utilization.

[0045] 2. This invention determines the segmented hydraulic fracturing parameters of the "through-layer + along-layer" area along the dip of the working face. Based on the coal seam characteristics and gas distribution law, it can rationally design parameters such as fracturing direction, length, spacing, quantity, and pressure to achieve the best fracturing and extraction effects.

[0046] 3. By determining the hydraulic fracturing sequence, this invention can effectively control the impact of fracturing on the coal seam, avoid excessive damage to the coal seam or gas outbursts, and ensure the safety and stability of the fracturing process.

[0047] 4. This invention, through fracturing hole connection, can promptly utilize the high permeability and high extraction efficiency of fracturing holes to achieve rapid extraction and reduction of coal seam gas, providing favorable conditions for subsequent coal seam gas extraction drilling construction and extraction.

[0048] 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

[0049] 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:

[0050] Figure 1 This is a schematic diagram showing the location of the bottom extraction roadway in the coal mining face as determined in this invention.

[0051] Figure 2 This is a schematic diagram of the hydraulic fracturing setup.

[0052] Figure 3 Layout diagram of boreholes for preliminary gas extraction in coal mining faces.

[0053] Figure labels: 1-fracturing hole; 2-extraction hole. Detailed Implementation

[0054] 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.

[0055] 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.

[0056] 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.

[0057] Please see Figures 1-3 This is a method for preliminary gas extraction in coal mining faces. It employs a "cross-layer + in-layer" regional segmented hydraulic fracturing approach to enhance permeability and performs preliminary gas extraction in the coal mining face area. The specific steps include:

[0058] S1. Determine the location of the bottom drainage roadway for the coal mining face. The location of the bottom drainage roadway is determined based on the length of the coal mining face, the characteristics of the coal seam, and the drilling capacity. If the length of the coal seam drilled by the underground drilling rig is greater than l1, there is no need to construct a bottom drainage roadway. The mining area roadway can be directly used as the bottom drainage roadway for regional gas control. If the length of the coal seam drilled by the underground drilling rig is less than l1, the length of the bottom drainage roadway is l1-l2. The bottom drainage roadway is required to be located in the middle of the dip of the coal mining face, and a bottom drainage connecting roadway should be constructed at the l2 position of the bottom drainage roadway.

[0059] Wherein, l1 is the strike length of the coal mining face, and l1 is no more than 800m; l2 is the length from the bottom extraction connecting roadway to the cut-off point.

[0060] S2. Determine the location of the segmented hydraulic fracturing, complete the segmented hydraulic fracturing borehole drilling, and conduct parameter testing of the original gas content of the coal seam. Hydraulic fracturing borehole 1 is arranged at equal intervals, starting from the bottom drainage connecting roadway, penetrating the rock strata, and then along the coal seam to the cut-off point. The influence radius of hydraulic fracturing is determined based on the working face dip length, fracturing pump pressure, and coal-rock fracturing pressure, thus obtaining the spacing of hydraulic fracturing borehole 1. Coal samples are required to be taken every 50m in the coal seam section to test gas content parameters. Due to the long borehole length, a closed coring device must be used to complete the sampling to ensure the accuracy of the gas content test. This gas content is taken as the original gas content of the coal seam.

[0061] S3. Determine the segmented hydraulic fracturing parameters for the "cross-layer + in-layer" area along the dip of the working face;

[0062] S4. Determine the hydraulic fracturing sequence and complete the "through-layer + in-layer" hydraulic fracturing permeability enhancement. Fracturing should be carried out sequentially by alternating adjacent holes, that is, two fracturing holes 1 in succession should not be adjacent during the construction process, in order to reduce the impact of fracturing on adjacent holes. The fracturing sequence is as follows: fracturing hole 1, fracturing hole 3, fracturing hole 5, fracturing hole 7, fracturing hole 2, fracturing hole 4, fracturing hole 6, fracturing hole 8.

[0063] S5. Following the drilling and extraction of coal seam gas from fracturing borehole 1, and after fracturing is completed, pressure is maintained for 2-4 days, and fracturing borehole 1 is then connected for extraction. When fracturing borehole 1 has been connected for extraction for 15-20 days or the extracted gas concentration is below 3%, if... Figure 3 As shown, a gas extraction hole 2 is constructed between two adjacent fracturing holes 1.

[0064] In step S3, the hydraulic fracturing pressure and the fracturing pump pressure are determined as follows:

[0065] The determination of hydraulic fracturing parameters is based on the geological environment, stress state, and physical and mechanical parameters of the target coal seam. Appropriate fracturing types and pressure parameter limits are selected according to requirements and regulations. The fracturing pressure P of the coal seam is calculated according to formula (1). k ; Under the appropriate fracturing type pressure parameter limit and P calculated according to equation (1) k Among them, the minimum value is taken as P in equation (2). k The pump pressure P of the fracturing pump is calculated according to formula (2). w ;

[0066] P k =3δ h -δ H +δ t -P0 (1)

[0067] In the formula:

[0068] δ h -Minimum principal stress, MPa;

[0069] δ H - Maximum principal stress, MPa;

[0070] δ t - Tensile strength, MPa;

[0071] P0 - Pore pressure, MPa;

[0072] P w =P k +P H +P r (2)

[0073] In the formula:

[0074] PH -Fracturing pipeline fluid column pressure, P H =ρgH, MPa;

[0075] ρ - density of fracturing fluid, kg / m³ 3 ;

[0076] g - acceleration due to gravity, N / kg;

[0077] H - Elevation difference of fracturing pipeline, which is the final borehole elevation minus the opening elevation, in meters;

[0078] P r -Fracturing fluid friction along the path, P w =Lλ1;

[0079] L - Pipeline length, in meters;

[0080] λ1 - Friction coefficient, MPa / m.

[0081] 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 pre-extraction of gas in a coal mining face area, characterized in that, The method of "cross-layer + in-layer" regional segmented hydraulic fracturing for pre-extraction of gas in coal mining faces includes the following steps: S1. Determine the location of the bottom drainage roadway for the coal mining face. The location is determined based on the length of the coal mining face, coal seam characteristics, and drilling capacity. When the underground drilling rig has drilled into a coal seam length greater than... In this case, there is no need to construct a bottom drainage roadway; the mining area roadway can be directly used as a bottom drainage roadway for regional gas control. When the length of the coal seam drilled by the underground drilling rig is less than... The length of the bottom extraction tunnel is The bottom drainage roadway is required to be located in the middle of the dip direction of the coal face, and in the bottom drainage roadway Construction is underway at the location via a bottom-extraction connecting tunnel; in, This refers to the length of the coal mining face. No more than 800m; The length from the bottom-extraction connecting roadway to the cut-off point; S2. Determine the location of the segmented hydraulic fracturing, complete the segmented hydraulic fracturing borehole drilling, and conduct parameter testing of the original gas in the coal seam. It is required to take coal samples every 50m to test the gas content parameters. Due to the long borehole, a closed coring device is required to complete the sampling to ensure the accuracy of the gas content test. This gas content is taken as the original gas content of the coal seam. The hydraulic fracturing holes are arranged at equal intervals, starting from the bottom pumping connecting roadway, penetrating the rock strata, and then along the coal seam to the cut-off point. The influence radius of hydraulic fracturing is determined according to the dip length of the working face, the fracturing pump pressure, and the coal and rock fracturing pressure, thus obtaining the spacing of the hydraulic fracturing holes. S3. Determine the segmented hydraulic fracturing parameters for the "cross-layer + in-layer" area along the dip of the working face; determine the hydraulic fracturing fracture pressure and fracturing pump pressure as follows: The determination of hydraulic fracturing parameters is based on the geological environment, stress state, and physical and mechanical parameters of the target coal seam. Appropriate fracturing types and pressure parameter limits are selected according to requirements and regulations, and the fracturing pressure of the coal seam is calculated according to formula (1). ; Under the appropriate fracturing type pressure parameter limit and calculated according to equation (1) Among them, the minimum value is taken as the value of equation (2). The pump pressure of the fracturing pump is calculated according to formula (2). ; （1） In the formula: —Minimum principal stress, MPa; —Maximum principal stress, MPa; —Tensile strength, MPa; —Pore pressure, MPa; （2） In the formula: —Fracturing pipeline fluid column pressure MPa; ρ—Density of fracturing fluid, kg / m³ 3 ; g—acceleration due to gravity, N / kg; H—Elevation difference of fracturing pipeline, which is the final borehole elevation minus the opening elevation, in meters; —Fracturing fluid friction along the path ; L—pipeline length, in meters; λ1—Friction coefficient, MPa / m; S4. Determine the hydraulic fracturing sequence and complete the "penetrating layer + in-layer" hydraulic fracturing permeability enhancement; adopt the method of alternating adjacent holes to carry out fracturing in sequence, that is, the two fracturing holes before and after each other are not adjacent during the construction process, so as to reduce the impact of fracturing on adjacent holes. S5. Fracturing hole connection and extraction, coal seam gas extraction drilling construction and extraction.

2. The method for preliminary gas extraction in coal mining face area according to claim 1, characterized in that: In step S5, after fracturing is completed, pressure is maintained for 2 to 4 days, and the fracturing holes are connected for extraction. When the fracturing holes are connected for extraction for 15 to 20 days or the extracted gas concentration is less than 3%, a gas extraction hole is constructed between two adjacent fracturing holes.

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