Cooperative permeability-increasing extraction method for coal mine gas

Abstract

The invention discloses a coal mine gas collaborative anti-reflection extraction method, which belongs to the field of coal mine gas extraction, and comprises the following steps: S1, drilling a plurality of vertical drilling wells and a plurality of horizontal drilling wells in a coal seam area to form a three-dimensional drilling network; s2, composite electric field fracturing is conducted, specifically, transient impact is conducted through a high-voltage pulse electric field, and then low-frequency electromagnetic waves are introduced for continuous action; s3, geothermal water in the underground abandoned mine is pumped through a high-pressure pump, the geothermal water is heated to the set temperature through a heat pump and then mixed with high-pressure nitrogen, the mixture is introduced into a wellhead of the three-dimensional well drilling network in a pulse mode, and water is pumped out after the set time and returned and conveyed into the underground abandoned mine; and S4, gas is extracted from the wellhead position through negative pressure adsorption equipment. By the adoption of the coal mine gas collaborative anti-reflection extraction method, advanced technologies such as a three-dimensional well drilling network, composite electric field fracturing and pulse type geothermal water and nitrogen mixed injection are combined, and the extraction rate is greatly increased.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine gas extraction, and in particular to a coal mine gas collaborative permeability enhancement extraction method. Background Art

[0002] Gas, also known as coal-bed methane, refers to hydrocarbon gas stored in coal seams with methane as the main component, mainly adsorbed on the surface of coal matrix particles, and partially free in coal pores or dissolved in coal seam water. It is a mineral resource associated with coal and an unconventional natural gas. It is a clean, high-quality energy and chemical raw material that has emerged internationally in the past 10 to 20 years. When the gas-air concentration reaches 5%-16%, it will explode when exposed to open flames, resulting in explosion accidents in coal mines. In order to solve the above problem, gas is extracted before coal mining, thereby reducing the coal mine gas explosion rate to 70% to 85%.

[0003] The existing gas extraction methods mainly include:

[0004] 1. Ground drilling extraction: (1) Vertical and horizontal well drilling: Drilling into the coal seam through the surface with a drilling rig to build a wellbore directly reaching the coal seam. This method is suitable for deep coal seams or situations where it is difficult to extract gas directly from the inside of the mine. In this way, gas in the coal seam can be pre-extracted in advance, reducing safety risks during mining.

[0005] (2) Hydraulic fracturing and permeability enhancement technology: Similar to shale gas development, high-pressure liquid (usually water mixed with proppant) is injected into the coal seam to create cracks in the coal seam, increase permeability, and thereby enhance gas fluidity and extraction efficiency.

[0006] The drilling extraction method requires a large amount of capital investment to establish and maintain a ground drilling system, including the purchase, installation and daily operating expenses of drilling equipment. In addition, drilling activities may damage the surface ecological environment, especially when constructing in nature reserves or sensitive areas, special attention should be paid to environmental protection issues. At the same time, the application effect of ground drilling technology may be limited for shallow coal seams or areas with complex geological structures.

[0007] 2. Underground drilling and extraction: (1) Along-seam drilling: Drill holes are arranged along the direction of the coal seam. These holes are usually located in the preparation area before the working face to release gas pressure in advance and prevent the occurrence of coal outburst accidents.

[0008] Cross-layer drilling: that is, drilling through non-coal rock layers to reach the target coal seam, forming a cross-connected channel network, so that the originally isolated small-scale high-concentration gas areas can be gathered and extracted centrally.

[0009] The underground drilling extraction method requires drilling operations inside the mine, which is dangerous. Accident hazards such as gas outbursts and roof collapse are difficult to completely avoid. In addition, due to the small underground space and limited ventilation conditions, the drilling speed is slow, resulting in a long overall extraction cycle. At the same time, as the mining progresses, the original boreholes gradually become ineffective, and new boreholes need to be constantly re-arranged, which increases the difficulty and cost of management.

[0010] 3. Protective layer mining method: By first mining the relatively safe rock layer above or below as a "protective layer", its pressure relief effect is used to reduce the stress state in the adjacent coal seam, causing the gas to escape naturally into the goaf and then be collected. This method can not only effectively control the amount of gas outburst, but also improve the working environment and reduce the risk of coal dust explosion.

[0011] When using the protective layer mining method, a portion of high-quality coal resources will be occupied, which causes a waste of resources to a certain extent. Moreover, not all mining areas have the conditions suitable for protective layer mining, especially when there is no suitable rock layer above the target coal seam. Although the gas emission can be significantly reduced in the short term, in the long run, as the mining depth increases, the pressure relief effect gradually weakens, and the pressure of later governance is still relatively large.

[0012] 4. Electric field fracturing mining method: A strong electric field generated by a high-voltage pulse power supply is used to exert transient impact force on the coal body, causing damage to the internal structure of the coal seam in a short period of time and generating a new micro-crack system. This artificially induced crack provides an additional migration path for gas, significantly increasing the permeability of the coal seam, which is beneficial to the subsequent extraction process.

[0013] When using the electric field fracturing mining method, professional high-voltage power supply equipment and supporting instruments are required, and the one-time construction cost is relatively high.

[0014] In summary, the existing coal seam gas permeability enhancement and extraction methods are relatively simple and the permeability enhancement effect is poor. Summary of the invention

[0015] The purpose of the present invention is to provide a coal mine gas collaborative permeability enhancement and extraction method to solve the above-mentioned technical problems.

[0016] To achieve the above object, the present invention provides a method for coal mine gas synergistic permeability enhancement extraction, comprising the following steps:

[0017] S1. Drill multiple vertical wells and multiple horizontal wells in the coal seam area to form a three-dimensional drilling network and form a primary fracture;

[0018] S2, composite electric field cracking: first use high-voltage pulse electric field for transient impact, then introduce low-frequency electromagnetic wave for continuous action to form secondary cracks;

[0019] S3, using a high-pressure pump to extract geothermal water in an abandoned underground mine, the geothermal water is heated to a set temperature by a heat pump and then mixed with high-pressure nitrogen, and then pulsed into the wellhead of a three-dimensional drilling network. After a set time, the water is extracted and returned to the abandoned underground mine to form a three-level fracture;

[0020] S4. Use negative pressure adsorption equipment to extract gas from the wellhead.

[0021] Preferably, step S1 specifically includes the following steps:

[0022] S11. Geological exploration and planning: Use seismic wave method to conduct geological exploration of coal seam area, and determine the best vertical drilling spacing and depth as well as the best horizontal drilling spacing and depth based on the exploration results to ensure that the drilling can cover the entire target coal seam;

[0023] S12. Vertical drilling: Use rotary drilling equipment to drill vertically downward from the surface at a selected location, drill multiple vertical boreholes, and ensure that the vertical boreholes reach the predetermined depth of the coal seam;

[0024] S13. Horizontal drilling: Based on vertical drilling, horizontal directional drilling technology is used to drill multiple horizontal wells along the vertical well from bottom to top to form a three-dimensional drilling network.

[0025] Preferably, step S11 specifically includes the following steps:

[0026] S111. Preliminary investigation: Collect geological maps of the coal seam area, mining history, coal seam distribution data, and conduct field surveys to record the geomorphic features of the coal seam area;

[0027] S112. At the same time, install seismographs and source equipment in the coal seam area and lay out survey lines based on the preliminary survey results;

[0028] S113, using a seismic source device to excite a seismic source on the laid survey line, and recording underground reflected wave signals through a seismograph;

[0029] S114, after pre-processing the reflected wave signal, using inversion calculation to generate an underground structure image and determine the thickness D, inclination and depth H of the coal seam;

[0030] S115. Determine the spacing and depth of vertical drilling, and the spacing and extension length of horizontal drilling based on the determined coal seam thickness, inclination and depth;

[0031] The calculation formula for vertical drilling spacing is as follows:

[0032]

[0033] Where, Lv Indicates the minimum distance between two adjacent vertical drilling wells, in meters; D h represents the extension length of the horizontal drilling, in m; α represents the angle of the horizontal drilling relative to the vertical direction; d represents the diameter of the vertical drilling, in m;

[0034] The vertical drilling depth calculation formula is as follows:

[0035] D v =H+ΔD (2);

[0036] Where D v It indicates the final depth of vertical drilling, in m; H indicates the depth of coal seam, in m; ΔD indicates the reserved extension safety margin, in m;

[0037] The calculation formula for horizontal drilling spacing is as follows:

[0038]

[0039] Where, L h It represents the minimum spacing between two adjacent horizontal wells, in meters; W represents the lateral distance of the coal seam between two adjacent horizontal wells; β represents the inclination angle of the horizontal well;

[0040] The formula for calculating the extension length of horizontal drilling is as follows:

[0041] D h =L min +ΔL (4);

[0042] Where, L min Indicates the minimum effective extension length, in meters; ΔL indicates the safety extension margin, in meters;

[0043] Among them, the minimum effective extension length L min The calculation formula is as follows:

[0044]

[0045] Where Q represents the expected gas flow rate to be extracted, in m 3 / d; k1 represents the permeability of the coal seam, in Darcy; A represents the cross-sectional area of ​​the flat well, in m 2 ; D represents the thickness of the coal seam, in m.

[0046] Preferably, in step S12, a verticality check is performed every 5m-10m of drilling to ensure that the vertical deviation of the borehole is controlled within a set range;

[0047] In step S13, the horizontal drilling trajectory is guided by using the measurement while drilling system MWD.

[0048] Preferably, step S2 specifically includes the following steps:

[0049] S21. High-voltage pulse electric field transient impact: Install a high-voltage pulse generator at the wellhead of the three-dimensional drilling network, connect it to the electrodes in the well, and after setting the initial high-voltage pulse parameters, start the high-voltage pulse generator to apply a transient high-voltage electric field to the coal seam, so that cracks are generated in the coal seam, forming the basis for secondary fractures;

[0050] S22, remove the high voltage pulse generator and electrodes;

[0051] S23. Continuous action of low-frequency electromagnetic waves: A low-frequency electromagnetic wave transmitter is installed at the wellhead of the three-dimensional drilling network, connected to the antenna in the drilling well, and after setting the initial low-frequency electromagnetic wave parameters, the low-frequency electromagnetic wave transmitter is started to continuously act on the cracks that have been formed to form secondary cracks.

[0052] Preferably, in step S21, the initial high voltage pulse parameters include voltage amplitude V, pulse width T p and pulse frequency f, where the voltage amplitude V is calculated as follows:

[0053] V = k2 × R × D (6);

[0054] In the formula, k2 represents the empirical coefficient; R represents the resistivity of the coal seam, in Ω / m;

[0055] Pulse width T p The calculation formula is as follows:

[0056]

[0057] In the formula, q represents the constant term; f represents the pulse frequency, the unit is Hz;

[0058] The pulse frequency f is calculated as follows:

[0059]

[0060] In the formula, C represents the capacitance value of the high-voltage pulse generator;

[0061] In step S23, the initial low-frequency electromagnetic wave parameters transmission power P, operating frequency f LF And action time t, where the transmit power P is calculated as follows:

[0062] P=k×σ×D h (9);

[0063] Where, σ represents the electrical conductivity of the coal seam, in units of S / m;

[0064] Operating frequency f LFThe calculation formula is as follows:

[0065]

[0066] Wherein, c represents the speed of light, in m / s; λ represents the wavelength, in m, and λ=k'×D, k' is the proportionality coefficient;

[0067] The calculation formula of action time t is as follows:

[0068]

[0069] Where v represents the propagation velocity of electromagnetic waves in coal seams, in units of m / s.

[0070] Preferably, in step S21 and step S23, a microseismic monitoring system and an electromagnetic wave reflection detection device are installed at the wellhead of the three-dimensional drilling network, wherein the microseismic monitoring system is used to detect vibrations generated during crack expansion, and the electromagnetic wave reflection detection device is used to collect electromagnetic wave reflection data, and based on the vibration data and the electromagnetic wave reflection data, the energy difference ΔE, the time difference ΔT, the current difference ΔI and the crack length difference ΔL are extracted, and the initial high-voltage pulse parameters and the initial low-frequency electromagnetic wave parameters are adjusted in a cyclic iterative manner;

[0071] Among them, the calculation formula of the adjusted voltage amplitude V' is as follows:

[0072] V′=V+k v ×ΔE (12);

[0073] In the formula, k v represents the voltage regulation coefficient,

[0074] Adjusted voltage amplitude pulse width T′ p The calculation formula is as follows:

[0075] T′ p =T p +k t ×ΔT (13);

[0076] In the formula, k t represents the time adjustment coefficient;

[0077] The calculation formula of the adjusted pulse frequency f′ is as follows:

[0078] f′=f+k f ×ΔL (14);

[0079] In the formula, k f represents the frequency adjustment coefficient;

[0080] After adjustment, the calculation formula of the transmit power P′ is as follows:

[0081] P′=P+k P ×ΔI (15);

[0082] In the formula, k P Indicates the power regulation factor;

[0083] Adjusted operating frequency f′ LF The calculation formula is as follows:

[0084] f′ LF =f LF +k f ×ΔL (16);

[0085] The calculation formula of the adjusted working time t′ is as follows:

[0086] t′=t+k t ×ΔT (17).

[0087] Preferably, step S3 specifically includes the following steps:

[0088] S31. Use a high-pressure pump to extract geothermal water from an abandoned underground mine;

[0089] S32, sending the extracted geothermal water to a heat pump, heating it to a set temperature by the heat pump, and then outputting it to a geothermal water pipeline;

[0090] S33, using dual channels to connect the geothermal water pipeline and the high-pressure nitrogen pipeline respectively, and setting the input ratio of the geothermal water and the high-pressure nitrogen;

[0091] S34, passing the mixed fluid into the wellhead of the three-dimensional drilling network in a pulse manner;

[0092] S35. After the set time, the water in the borehole is pumped out by a water pump and returned to the underground abandoned mine through a pipeline to form a closed circulation system.

[0093] Preferably, in step S32, the temperature is set to 200°C-350°C;

[0094] In step S33, the input ratio of geothermal water and high-pressure nitrogen is 3:2.5;

[0095] In step S34, each pulse lasts for 10s-15s, and the interval is 20s-35s.

[0096] Therefore, the present invention adopts the above, and has the beneficial effects of:

[0097] 1. Improve gas extraction efficiency: Through the gradual formation of primary, secondary and tertiary cracks, the fracture network of the coal seam is greatly increased, the permeability of the coal seam is improved, and thus the fluidity and extraction efficiency of gas are significantly improved;

[0098] 2. Enhanced safety performance: During the action of high-voltage pulse electric field and low-frequency electromagnetic wave, the crack expansion is monitored in real time and parameters are adjusted in time to ensure the safety and controllability of the operation.

[0099] 3. Environmental protection: The geothermal water in the abandoned underground mine is heated up by heat pumps and then injected into the drilling network again, which not only makes full use of geothermal resources but also reduces energy consumption;

[0100] The geothermal water and high-pressure nitrogen extracted after fracturing are returned to the abandoned underground mine, avoiding environmental pollution and reducing resource waste.

[0101] 4. Dual effect: The combination of hot water and nitrogen utilizes the dual mechanism of thermal stress and gas expansion, which significantly improves the fracturing effect of coal seams.

[0102] 5. Optimize drilling layout: Through detailed geological exploration (seismic wave method, inversion calculation, etc.), accurately determine the optimal drilling spacing and depth to ensure that the drilling can cover the entire target coal seam, thereby improving the success rate of drilling and resource utilization;

[0103] 6. Intelligent parameter adjustment: According to the microseismic monitoring system and electromagnetic wave reflection data, the initial high-voltage pulse parameters and low-frequency electromagnetic wave parameters are adjusted iteratively to make the crack propagation process more efficient and stable;

[0104] To sum up, the coal mine gas collaborative permeability enhancement method of the present invention not only significantly improves the gas extraction efficiency, but also enhances the safety and environmental protection of the operation. Through intelligent parameter adjustment and optimization of drilling layout, it achieves the goal of efficient, safe and environmentally friendly gas extraction, and has broad application prospects and promotion value.

[0105] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 The present invention is a flow chart of a method for coal mine gas coordinated permeability enhancement and extraction. DETAILED DESCRIPTION

[0107] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not used to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0108] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0109] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0110] like Figure 1 As shown, a method for coal mine gas synergistic permeability enhancement extraction comprises the following steps:

[0111] S1. Drill multiple vertical wells and multiple horizontal wells in the coal seam area to form a three-dimensional drilling network and form a primary fracture;

[0112] Step S1 specifically includes the following steps:

[0113] S11. Geological exploration and planning: Use seismic wave method to conduct geological exploration of coal seam area, and determine the best vertical drilling spacing and depth as well as the best horizontal drilling spacing and depth based on the exploration results to ensure that the drilling can cover the entire target coal seam;

[0114] Step S11 specifically includes the following steps:

[0115] S111. Preliminary investigation: Collect geological maps of the coal seam area, mining history, coal seam distribution data, and conduct field surveys to record the geomorphic features of the coal seam area;

[0116] S112. At the same time, install seismographs and source equipment in the coal seam area and lay out survey lines based on the preliminary survey results;

[0117] S113, using a seismic source device to excite a seismic source on the laid survey line, and recording underground reflected wave signals through a seismograph;

[0118] S114, after pre-processing the reflected wave signal, using inversion calculation to generate an underground structure image and determine the thickness D, inclination and depth H of the coal seam;

[0119] S115. Determine the spacing and depth of vertical drilling, and the spacing and extension length of horizontal drilling based on the determined coal seam thickness, inclination and depth;

[0120] The calculation formula for vertical drilling spacing is as follows:

[0121]

[0122] Where, Lv Indicates the minimum distance between two adjacent vertical drilling wells, in meters; D h represents the extension length of the horizontal drilling, in m; α represents the angle of the horizontal drilling relative to the vertical direction; d represents the diameter of the vertical drilling, in m;

[0123] The vertical drilling depth calculation formula is as follows:

[0124] D v =H+ΔD (2);

[0125] Where D v It indicates the final depth of vertical drilling, in m; H indicates the depth of coal seam, in m; ΔD indicates the reserved extension safety margin, in m;

[0126] The calculation formula for horizontal drilling spacing is as follows:

[0127]

[0128] Where, L h It represents the minimum spacing between two adjacent horizontal drilling wells, in meters; W represents the lateral distance of the coal seam between two adjacent horizontal drilling wells; β represents the inclination angle of the horizontal drilling well;

[0129] The formula for calculating the extension length of horizontal drilling is as follows:

[0130] D h =L min +ΔL (4);

[0131] Where, L min Indicates the minimum effective extension length, in meters; ΔL indicates the safety extension margin, in meters;

[0132] Among them, the minimum effective extension length L min The calculation formula is as follows:

[0133]

[0134] Where Q represents the expected gas flow rate to be extracted, in m 3 / d; k1 represents the permeability of the coal seam, in Darcy; A represents the cross-sectional area of ​​the flat well, in m 2 ; D represents the thickness of the coal seam, in m.

[0135] S12. Vertical drilling: Use rotary drilling equipment to drill vertically downward from the surface at a selected location, drill multiple vertical boreholes, and ensure that the vertical boreholes reach the predetermined depth of the coal seam;

[0136] In step S12, a verticality check is performed every 5m-10m of drilling to ensure that the vertical deviation of the borehole is controlled within the set range;

[0137] S13. Horizontal drilling: Based on vertical drilling, horizontal directional drilling technology is used to drill multiple horizontal wells along the vertical well from bottom to top to form a three-dimensional drilling network.

[0138] In step S13, the horizontal drilling trajectory is guided by using the measurement while drilling system MWD.

[0139] S2, composite electric field cracking: first use high-voltage pulse electric field for transient impact, then introduce low-frequency electromagnetic wave for continuous action to form secondary cracks;

[0140] Step S2 specifically includes the following steps:

[0141] S21. High-voltage pulse electric field transient impact: Install a high-voltage pulse generator at the wellhead of the three-dimensional drilling network, connect it to the electrodes in the well, and after setting the initial high-voltage pulse parameters, start the high-voltage pulse generator to apply a transient high-voltage electric field to the coal seam, so that cracks are generated in the coal seam, forming the basis for secondary fractures;

[0142] In step S21, the initial high voltage pulse parameters include voltage amplitude V, pulse width T p and pulse frequency f, where the voltage amplitude V is calculated as follows:

[0143] V = k2 × R × D (6);

[0144] In the formula, k2 represents the empirical coefficient; R represents the resistivity of the coal seam, in Ω / m;

[0145] Pulse width T p The calculation formula is as follows:

[0146]

[0147] In the formula, q represents the constant term; f represents the pulse frequency, the unit is Hz;

[0148] The pulse frequency f is calculated as follows:

[0149]

[0150] In the formula, C represents the capacitance value of the high-voltage pulse generator;

[0151] S22, remove the high voltage pulse generator and electrodes;

[0152] S23. Continuous action of low-frequency electromagnetic waves: A low-frequency electromagnetic wave transmitter is installed at the wellhead of the three-dimensional drilling network, connected to the antenna in the drilling well, and after setting the initial low-frequency electromagnetic wave parameters, the low-frequency electromagnetic wave transmitter is started to continuously act on the cracks that have been formed to form secondary cracks.

[0153] In step S23, the initial low-frequency electromagnetic wave parameters transmission power P, operating frequency f LF And action time t, where the transmit power P is calculated as follows:

[0154] P=k×σ×D h (9);

[0155] Where, σ represents the electrical conductivity of the coal seam, in units of S / m;

[0156] Operating frequency f LF The calculation formula is as follows:

[0157]

[0158] Wherein, c represents the speed of light, in m / s; λ represents the wavelength, in m, and λ=k'×D, k' is the proportionality coefficient;

[0159] The calculation formula of action time t is as follows:

[0160]

[0161] Where v represents the propagation velocity of electromagnetic waves in coal seams, in units of m / s.

[0162] In step S21 and step S23, a microseismic monitoring system and an electromagnetic wave reflection detection device are installed at the wellhead of the three-dimensional drilling network, wherein the microseismic monitoring system is used to detect vibrations generated during crack expansion, and the electromagnetic wave reflection detection device is used to collect electromagnetic wave reflection data, and based on the vibration data and the electromagnetic wave reflection data, the energy difference ΔE, the time difference ΔT, the current difference ΔI and the crack length difference ΔL are extracted, and the initial high-voltage pulse parameters and the initial low-frequency electromagnetic wave parameters are adjusted in a cyclic iterative manner;

[0163] Among them, the calculation formula of the adjusted voltage amplitude V′ is as follows;

[0164] V′=V+k v ×ΔE (12);

[0165] In the formula, k v represents the voltage regulation coefficient,

[0166] Adjusted voltage amplitude pulse width T′ p The calculation formula is as follows:

[0167] T′p =T p +k t ×ΔT (13);

[0168] In the formula, k t represents the time adjustment coefficient;

[0169] The calculation formula of the adjusted pulse frequency f′ is as follows:

[0170] f′=f+k f ×ΔL (14);

[0171] In the formula, k f represents the frequency adjustment coefficient;

[0172] After adjustment, the calculation formula of the transmit power P′ is as follows:

[0173] P′=P+k P ×ΔI (15);

[0174] In the formula, k P Indicates the power regulation factor;

[0175] Adjusted operating frequency f′ LF The calculation formula is as follows:

[0176] f′ LF =f LF +k f ×ΔL (16);

[0177] The calculation formula of the adjusted working time t′ is as follows:

[0178] t'=t+k t ×ΔT (17).

[0179] S3, using a high-pressure pump to extract geothermal water in an abandoned underground mine, the geothermal water is heated to a set temperature by a heat pump and then mixed with high-pressure nitrogen, and then pulsed into the wellhead of a three-dimensional drilling network. After a set time, the water is extracted and returned to the abandoned underground mine to form a three-level fracture;

[0180] Geothermal water and nitrogen fracturing principle: High-temperature hot water expands the rocks in the coal seam, generating thermal stress, leading to the expansion of micro-cracks and the formation of new cracks, thereby increasing the permeability of the coal seam. At the same time, hot water heats the adsorbed gas (such as gas) in the coal seam, accelerates its desorption process, increases gas pressure, and helps to form new cracks or expand existing cracks.

[0181] After high-pressure nitrogen enters the coal seam, it expands during the cooling process, further expanding the cracks and preventing them from closing. At the same time, nitrogen can drive the gas in the coal seam to the vicinity of the production well, improving the fluidity and recovery rate of the gas. At the same time, the continuous injection of nitrogen can maintain a high formation pressure, prevent the pressure drop caused by steam condensation, and ensure long-term stable gas output.

[0182] Step S3 specifically includes the following steps:

[0183] S31. Use a high-pressure pump to extract geothermal water from an abandoned underground mine;

[0184] S32, sending the extracted geothermal water to a heat pump, heating it to a set temperature by the heat pump, and then outputting it to a geothermal water pipeline;

[0185] In step S32, the temperature is set to 200°C-350°C;

[0186] S33, using dual channels to connect the geothermal water pipeline and the high-pressure nitrogen pipeline respectively, and setting the input ratio of the geothermal water and the high-pressure nitrogen;

[0187] In step S33, the input ratio of geothermal water and high-pressure nitrogen is 3:2.5;

[0188] S34, passing the mixed fluid into the wellhead of the three-dimensional drilling network in a pulse manner;

[0189] In step S34, each pulse lasts for 10s-15s, and the interval is 20s-35s.

[0190] S35. After setting the time, which is 1h-1.5h in this embodiment, the water in the borehole is pumped out by a water pump and returned to the underground abandoned mine through a pipeline to form a closed circulation system.

[0191] S4. Use negative pressure adsorption equipment to extract gas from the wellhead.

[0192] In step S4, after being filtered by activated carbon, the adsorbed pure gas is stored in a gas storage tank.

[0193] Example

[0194] The present invention is used to extract gas from a coal seam area, and the extraction data shown in Table 1 are recorded.

[0195] Table 1 Gas extraction data

[0196]

[0197] It can be seen from Table 1 that the method of the present invention greatly improves the extraction rate.

[0198] 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 method for coal mine gas synergistic permeability enhancement extraction, characterized in that: The following steps are involved: S1. Drill multiple vertical wells and multiple horizontal wells in the coal seam area to form a three-dimensional drilling network and form a primary fracture; S2, composite electric field cracking: first use high-voltage pulse electric field for transient impact, then introduce low-frequency electromagnetic wave for continuous action to form secondary cracks; S3, using a high-pressure pump to extract geothermal water in an abandoned underground mine, the geothermal water is heated to a set temperature by a heat pump and then mixed with high-pressure nitrogen, and then pulsed into the wellhead of a three-dimensional drilling network. After a set time, the water is extracted and returned to the abandoned underground mine to form a three-level fracture; S4. Use negative pressure adsorption equipment to extract gas from the wellhead.

2. A method for coal mine gas extraction by collaborative permeability enhancement according to claim 1, characterized in that: Step S1 specifically includes the following steps: S11. Geological exploration and planning: Use seismic wave method to conduct geological exploration of coal seam area, and determine the best vertical drilling spacing and depth as well as the best horizontal drilling spacing and depth based on the exploration results to ensure that the drilling can cover the entire target coal seam; S12. Vertical drilling: Use rotary drilling equipment to drill vertically downward from the surface at a selected location, drill multiple vertical boreholes, and ensure that the vertical boreholes reach the predetermined depth of the coal seam; S13. Horizontal drilling: Based on vertical drilling, horizontal directional drilling technology is used to drill multiple horizontal wells along the vertical well from bottom to top to form a three-dimensional drilling network.

3. A method for coal mine gas extraction by collaborative permeability enhancement according to claim 2, characterized in that: Step S11 specifically includes the following steps: S111. Preliminary investigation: Collect geological maps of the coal seam area, mining history, coal seam distribution data, and conduct field surveys to record the geomorphic features of the coal seam area; S112. At the same time, install seismographs and source equipment in the coal seam area and lay out survey lines based on the preliminary survey results; S113, using a seismic source device to excite a seismic source on the laid survey line, and recording underground reflected wave signals through a seismograph; S114, after pre-processing the reflected wave signal, using inversion calculation to generate an underground structure image and determine the thickness D, inclination and depth H of the coal seam; S115. Determine the spacing and depth of vertical drilling, and the spacing and extension length of horizontal drilling based on the determined coal seam thickness, inclination and depth; The calculation formula for vertical drilling spacing is as follows: Where, L v Indicates the minimum distance between two adjacent vertical drilling wells, in meters; D h represents the extension length of the horizontal drilling, in m; α represents the angle of the horizontal drilling relative to the vertical direction; d represents the diameter of the vertical drilling, in m; The vertical drilling depth calculation formula is as follows: D v =H+ΔD (2); Where D v It indicates the final depth of vertical drilling, in m; H indicates the depth of coal seam, in m; ΔD indicates the reserved extension safety margin, in m; The calculation formula for horizontal drilling spacing is as follows: Where, L h It represents the minimum spacing between two adjacent horizontal drilling wells, in meters; W represents the lateral distance of the coal seam between two adjacent horizontal drilling wells; β represents the inclination angle of the horizontal drilling well; The formula for calculating the extension length of horizontal drilling is as follows: D h =L min +ΔL (4); Where, L min Indicates the minimum effective extension length, in meters; ΔL indicates the safety extension margin, in meters; Among them, the minimum effective extension length L min The calculation formula is as follows: Where Q represents the expected gas flow rate to be extracted, in m 3 / d; k1 represents the permeability of the coal seam, in Darcy; A represents the cross-sectional area of ​​the flat well, in m 2 ; D represents the thickness of the coal seam, in m.

4. A method for coal mine gas extraction by coordinated permeability enhancement according to claim 3, characterized in that: In step S12, a verticality check is performed every 5m-10m of drilling to ensure that the vertical deviation of the borehole is controlled within the set range; In step S13, the horizontal drilling trajectory is guided by using the measurement while drilling system MWD.

5. A method for coal mine gas extraction by coordinated permeability enhancement according to claim 4, characterized in that: Step S2 specifically includes the following steps: S21. High-voltage pulse electric field transient impact: Install a high-voltage pulse generator at the wellhead of the three-dimensional drilling network, connect it to the electrodes in the well, and after setting the initial high-voltage pulse parameters, start the high-voltage pulse generator to apply a transient high-voltage electric field to the coal seam, so that cracks are generated in the coal seam, forming the basis for secondary fractures; S22, remove the high voltage pulse generator and electrodes; S23. Continuous action of low-frequency electromagnetic waves: A low-frequency electromagnetic wave transmitter is installed at the wellhead of the three-dimensional drilling network, connected to the antenna in the drilling well, and after setting the initial low-frequency electromagnetic wave parameters, the low-frequency electromagnetic wave transmitter is started to continuously act on the cracks that have been formed to form secondary cracks.

6. A method for coal mine gas extraction by coordinated permeability enhancement according to claim 5, characterized in that: In step S21, the initial high voltage pulse parameters include voltage amplitude V, pulse width T p and pulse frequency f, where the voltage amplitude V is calculated as follows: V = k2 × R × D (6); In the formula, k2 represents the empirical coefficient; R represents the resistivity of the coal seam, in Ω / m; Pulse width T p The calculation formula is as follows: In the formula, q represents the constant term; f represents the pulse frequency, the unit is Hz; The pulse frequency f is calculated as follows: In the formula, C represents the capacitance value of the high-voltage pulse generator; In step S23, the initial low-frequency electromagnetic wave parameters transmission power P, operating frequency f LF And action time t, where the transmit power P is calculated as follows: P=k×σ×D h (9); Where, σ represents the electrical conductivity of the coal seam, in S / m; Operating frequency f LF The calculation formula is as follows: Wherein, c represents the speed of light, in m / s; λ represents the wavelength, in m, and λ=k'×D, k' is the proportionality coefficient; The calculation formula of action time t is as follows: Where v represents the propagation velocity of electromagnetic waves in coal seams, in units of m / s.

7. A method for coal mine gas extraction by coordinated permeability enhancement according to claim 6, characterized in that: In step S21 and step S23, a microseismic monitoring system and an electromagnetic wave reflection detection device are installed at the wellhead of the three-dimensional drilling network, wherein the microseismic monitoring system is used to detect vibrations generated during crack expansion, and the electromagnetic wave reflection detection device is used to collect electromagnetic wave reflection data, and based on the vibration data and the electromagnetic wave reflection data, the energy difference ΔE, the time difference ΔT, the current difference ΔI and the crack length difference ΔL are extracted, and the initial high-voltage pulse parameters and the initial low-frequency electromagnetic wave parameters are adjusted in a cyclic iterative manner; Among them, the calculation formula of the adjusted voltage amplitude V' is as follows: V'=V+k v ×ΔE (12); In the formula, k v represents the voltage regulation coefficient, Adjusted voltage amplitude pulse width T' p The calculation formula is as follows: T' p =T p +k t ×ΔT (13); In the formula, k t represents the time adjustment coefficient; The calculation formula of the adjusted pulse frequency f' is as follows: f'=f+k f ×ΔL (14); In the formula, k f represents the frequency adjustment coefficient; After adjustment, the calculation formula of the transmit power P' is as follows: P'=P+k P ×ΔI (15); In the formula, k P Indicates the power regulation factor; Adjusted operating frequency f' LF The calculation formula is as follows: f' LF =f LF +k f ×ΔL (16); The calculation formula of adjusted working time t' is as follows: t'=t+k t ×ΔT (17)。 8. A method for coal mine gas extraction by coordinated permeability enhancement according to claim 7, characterized in that: Step S3 specifically includes the following steps: S31. Use a high-pressure pump to extract geothermal water from an abandoned underground mine; S32, sending the extracted geothermal water to a heat pump, heating it to a set temperature by the heat pump, and then outputting it to a geothermal water pipeline; S33, using dual channels to connect the geothermal water pipeline and the high-pressure nitrogen pipeline respectively, and setting the input ratio of the geothermal water and the high-pressure nitrogen; S34, passing the mixed fluid into the wellhead of the three-dimensional drilling network in a pulse manner; S35. After the set time, the water in the borehole is pumped out by a water pump and returned to the underground abandoned mine through a pipeline to form a closed circulation system.

9. A method for coal mine gas extraction by coordinated permeability enhancement according to claim 8, characterized in that: In step S32, the temperature is set to 200°C-350°C; In step S33, the input ratio of geothermal water and high-pressure nitrogen is 3:2.5; In step S34, each pulse lasts for 10s-15s, and the interval time is 20s-35s.

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