Efficient presplitting carbon dioxide and calcium hydroxide combined displacement gas control method

Abstract

The invention relates to the technical field of gas control, and discloses an efficient presplitting carbon dioxide and calcium hydroxide combined displacement gas control method which comprises the following steps: selecting a presplitting point and a drill hole arrangement mode in a coal seam in combination with physical structure parameter data; the pre-splitting point is cracked in a hydraulic splitting mode; injecting carbon dioxide into the cracked carbon dioxide injection presplitting point by using an optimal carbon dioxide gas injection strategy; and calcium hydroxide is injected into the cracked calcium hydroxide injection pre-splitting point, and gas extraction is conducted through the arranged drill holes. The pre-cracking point is efficiently cracked in combination with drill hole arrangement, the injection efficiency of carbon dioxide and calcium hydroxide is improved, carbon dioxide and gas on the surface of the coal seam compete for an adsorption position to replace gas, and the crack structure is further stabilized through chemical reaction of calcium hydroxide and water in the coal seam; gas can be rapidly displaced and extracted, the coal seam gas concentration can be remarkably reduced, and the gas explosion risk is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of gas control, and in particular to a method for controlling gas by combining pre-cracking carbon dioxide and calcium hydroxide to displace gas. Background Art

[0002] As energy demand continues to grow, coal, as one of the world's major energy sources, still occupies an important position in many countries and regions. However, during coal mining, the outburst of coal seam gas (mainly methane) has always been an important problem restricting coal mine safety production and energy development. Gas not only poses a threat to coal mine safety, but also seriously pollutes the environment, especially methane that reacts with oxygen in the atmosphere to produce a greenhouse effect, becoming one of the main factors in global climate change. Therefore, how to effectively control and manage gas problems in coal mines and ensure the safety of coal mining has become an important issue that needs to be solved urgently. Summary of the invention

[0003] In view of this, the present invention proposes a highly efficient pre-cracking carbon dioxide and calcium hydroxide combined displacement gas control method, which forms a more complex fracture network by artificially pre-cracking the coal seam or gas reservoir, thereby improving the permeability of carbon dioxide and calcium hydroxide and enhancing the displacement effect of gas. The combined use of carbon dioxide and calcium hydroxide can effectively improve the gas recovery rate through the dual effects of chemical reaction and physical penetration, while reducing environmental pollution, providing a sustainable solution for coal mine gas management.

[0004] To achieve the above object, the present invention provides a method for controlling the combined displacement of gas by carbon dioxide and calcium hydroxide with high efficiency pre-cracking, comprising the following steps: S1: obtaining physical structure parameter data of the coal seam, and selecting pre-splitting points and drilling arrangement of the pre-splitting points in the coal seam based on the physical structure parameter data, wherein the pre-splitting points include carbon dioxide injection pre-splitting points and calcium hydroxide injection pre-splitting points; S2: Arrange drilling holes at the pre-crack point based on the drilling arrangement method, and crack the pre-crack point by hydraulic fracturing to obtain the pre-crack point after cracking; S3: using the optimal carbon dioxide gas injection strategy to inject carbon dioxide into the carbon dioxide injection pre-cracking point after cracking, the carbon dioxide has a stronger adsorption capacity than gas, competes with the gas on the surface of the coal seam for adsorption positions, and replaces the gas. The optimal carbon dioxide gas injection strategy uses a feedback-based fuzzy control method to adjust the carbon dioxide injection speed and pressure parameters; S4: Inject calcium hydroxide into the pre-cracking point after cracking to expand and stabilize the coal seam cracks, and monitor the stability of the coal seam cracks. When the stability reaches the preset stability range, stop injecting calcium hydroxide and use the arranged boreholes to extract gas.

[0005] As a further improvement method of the present invention: Optionally, the coal seam surface is divided into a number of non-overlapping coal seam surface areas, the physical structure parameters of each coal seam surface area are extracted, and the physical structure parameters of all coal seam surface areas are used as the physical structure parameter data of the coal seam, including: The physical structural parameters of the coal seam surface area include porosity , Permeability , elastic modulus , crack density , Gas content distribution And water content ; The physical structural parameters of the coal seam surface area are calculated as follows: Collect coal samples from the surface area of ​​the coal seam as coal samples, infiltrate the pores of the coal samples with high-pressure mercury, measure the volume of the infiltrated mercury to calculate the pore volume, and calculate the ratio of the pore volume of the coal sample to the total volume of the coal sample as the porosity of the surface area of ​​the coal seam. The greater the porosity, the stronger the gas storage capacity of the coal seam surface area, which is conducive to gas extraction; Adjust the pressure environment of the coal sample and calculate the permeability of the coal seam surface area : ; in: Indicates the pressure difference of coal sample The fluid flow rate under represents fluid viscosity, G represents coal sample thickness, and R represents the flow cross-sectional area of ​​the fluid. The fluid is the gas in the coal sample. The higher the permeability, the higher the fluidity of the gas stored in the surface area of ​​the coal seam, and the higher the gas extraction efficiency. Uniaxial compression tests were performed on coal samples, stress-strain curves were measured, and elastic modulus was calculated. , the smaller the elastic modulus, the easier it is for the surface area of ​​the coal seam to improve its permeability through pre-cracking technology; Use a microscope to observe the distribution of cracks in the coal sample, calculate the sum of the lengths of all cracks in the coal sample, and calculate the crack density. , where V is the total volume of the coal sample. The higher the fissure density, the lower the mechanical strength of the coal seam surface area, and the greater the risk of coal mine collapse; Coal samples were selected from the center and four corners of the coal seam surface area, and the gas content of the five coal samples was obtained using a gas content meter as the gas content distribution. ; Weigh and record the initial mass of the coal sample, place the coal sample in a drying oven, heat it at a specified temperature of 105°C for a certain time of 1 hour to evaporate the water in the coal sample, weigh and record the dry mass of the coal sample again, and calculate the moisture content of the coal seam surface area. .

[0006] Optionally, the physical structure parameters are standardized, and the first pre-splitting evaluation point and the second pre-splitting evaluation point of the coal seam surface area are calculated using the standardized physical structure parameters, and A coal seam surface areas with the highest first pre-splitting evaluation point are selected as the coal seam surface areas for carbon dioxide injection, and the regional centers of the coal seam surface areas for carbon dioxide injection are used as the carbon dioxide injection pre-splitting points, and B coal seam surface areas with the highest second pre-splitting evaluation point are selected as the coal seam surface areas for calcium hydroxide injection, and the regional centers of the coal seam surface areas for calcium hydroxide injection are used as the calcium hydroxide injection pre-splitting points, wherein A represents the total number of preset carbon dioxide injection pre-splitting points, and B represents the total number of preset calcium hydroxide injection pre-splitting points, including; The standardized processing result of the physical structure parameters is ,in Porosity , Permeability , elastic modulus , crack density , Gas content distribution And water content The standardized processing results; The calculation expression of the first pre-splitting evaluation value is: ; The calculation expression of the second pre-splitting evaluation value is: ; in: Represents the first pre-crack point estimate for the coal seam surface area, An estimate of a second pre-crack point representing a surface area of ​​the coal seam; Represents the weight coefficient of porosity, permeability, elastic modulus, fracture density, gas content distribution and water content.

[0007] Optionally, a drilling arrangement of the pre-splitting point is set based on physical structural parameters of the coal seam surface area where the pre-splitting point is located, and the drilling arrangement includes parallel drilling arrangement, fan-shaped drilling arrangement and grid-shaped drilling arrangement; The standard deviation of the gas content distribution in the coal seam surface area is calculated. If the standard deviation is less than the preset standard deviation threshold, it means that the gas content distribution in the coal seam surface area is uniform; otherwise, it means that the gas content distribution in the coal seam surface area is uneven. If the gas content in the coal seam surface area is evenly distributed, a parallel drilling arrangement is adopted. A group of parallel drilling points are arranged in the coal seam surface area where the pre-cracking point is located as the drilling positions of the pre-cracking point. These drilling points are arranged along the bedding direction or the crack development direction of the coal seam, with even spacing and consistent or close drilling depths. If the gas content distribution in the coal seam surface area is uneven, and the mean value of the gas content distribution is lower than the preset mean threshold, a fan-shaped drilling arrangement is adopted, with the center of the coal seam surface area where the pre-splitting point is located as the starting drilling point, and a number of drilling points are arranged radiating outward in a fan shape within a certain angle range as the drilling positions of the pre-splitting point; If the gas content in the coal seam surface area is unevenly distributed and the mean of the gas content distribution is higher than the preset mean threshold, a grid-shaped drilling arrangement is adopted. According to the grid rule, a number of drilling points are arranged in the coal seam surface area where the pre-cracking point is located as the drilling position of the pre-cracking point. The arranged drilling points form a chessboard arrangement on the coal seam surface area.

[0008] Optionally, the hydraulic fracturing method includes: Use a drill or impact drill to drill holes at the drilling position of the pre-crack point to obtain holes with a hole diameter ranging from 30mm to 45mm. After the drilling is completed, use an air compressor or other tools to clean the debris and dust in the hole; Insert the splitting head of the splitter into the drill hole, and connect the splitter to the hydraulic power station through a high-pressure oil pipe; Open the hydraulic power station, start the hydraulic pump, and the hydraulic oil is transmitted to the splitter through the high-pressure oil pipe, pushing the splitting head to gradually expand and form cracks; Check whether the crack has reached the expected width and depth. If so, shut down the hydraulic power unit.

[0009] Optionally, inject carbon dioxide into the carbon dioxide injection pre-cracking point after cracking, and use a gas content meter to measure the gas content of the carbon dioxide injection pre-cracking point during the injection process, and calculate the difference between the gas content and the gas target content and the difference change rate in real time as carbon dioxide injection feedback; The carbon dioxide injection rate at time t is , the pressure parameter is , gas content is , the target gas content is S, the gas content The difference from the gas target content S is The difference change rate is , the carbon dioxide injection feedback at time t includes , ; Construct three fuzzy sets representing low, medium and high speeds respectively And fuzzy functions, construct three fuzzy sets representing low, medium and high pressure respectively and fuzzy functions; The carbon dioxide injection velocity is calculated by using the fuzzy function in the velocity fuzzy set. In the membership degree of the three speed fuzzy sets, the CO2 injection speed In the speed fuzzy set The membership degrees in are ; Based on the injection feedback of carbon dioxide at time t, the precise value of the membership is calculated. The exact value of is: ; in: Degree of membership The exact value of is the preset segment speed threshold; The degree of membership The exact value of is: ; in: Degree of membership The exact value of is the preset segmented pressure threshold; Based on the membership degree and its exact value, the CO2 injection rate adjustment at time t is calculated. And the pressure parameter adjustment : ; ; Use the carbon dioxide injection rate adjustment at time t And the pressure parameter adjustment Adjust the carbon dioxide injection rate and pressure parameters at time t as the carbon dioxide injection rate at time t+1 And pressure parameters ,in , When the carbon dioxide injection rate is lower than a preset rate threshold, the injection of carbon dioxide into the carbon dioxide injection pre-cracking point after cracking is stopped.

[0010] Optionally, when the injection of carbon dioxide into the carbon dioxide injection pre-cracking point after cracking is stopped, calcium hydroxide is injected into the calcium hydroxide injection pre-cracking point after cracking, and the stability of the coal seam fissure is monitored during the injection process. The stability calculation formula of the coal seam fissure is: ; in: Indicates the stability of coal seam fractures. represents the jth stability index value of coal seam fractures, The stability index weight representing the jth stability index value, wherein the 1st to 4th stability indexes are respectively the crack width, the coal seam permeability, the crack stress state and the crack density, and the stability index value is the change of the 4 stability indexes in a short time after the injection of calcium hydroxide, and the change is used as the stability index value.

[0011] Optionally, the gas extraction process is: A pipeline is installed at the drilling position in the coal seam surface area where the carbon dioxide pre-cracking point is injected. The end of the pipeline is a gas collection device. A negative pressure pump is used to apply negative pressure to the coal seam. The gas displaced by the carbon dioxide is desorbed from the micropores of the coal seam, enters the cracks of the coal seam, flows along the cracks to the drilling position, and the gas is extracted into the gas collection device.

[0012] In order to solve the above problem, the present invention provides an electronic device, the electronic device comprising: A memory storing at least one instruction; Communication interface, enabling electronic equipment to communicate; and The processor executes the instructions stored in the memory to implement the above-mentioned method for controlling the combined displacement of gas by carbon dioxide and calcium hydroxide based on efficient pre-cracking.

[0013] In order to solve the above problems, the present invention also provides a computer-readable storage medium, in which at least one instruction is stored. The at least one instruction is executed by a processor in an electronic device to implement the above-mentioned method for controlling the combined displacement of gas by carbon dioxide and calcium hydroxide based on efficient pre-cracking.

[0014] Compared with the prior art, the present invention proposes a highly efficient pre-cracking carbon dioxide and calcium hydroxide combined displacement gas control method, which has the following advantages: First, this scheme proposes a method for selecting pre-cracking points, collects coal samples from the surface area of ​​the coal seam, calculates multiple indicators of the coal samples, selects the surface area of ​​the coal seam with high gas pressure, developed cracks and good permeability as the pre-cracking point for injecting carbon dioxide, and selects the coal seam with moderate water content, fewer cracks or denser coal body as the pre-cracking point for injecting carbon dioxide and calcium hydroxide. Then, carbon dioxide competes with the gas on the surface of the coal seam for adsorption positions to replace the gas, and calcium hydroxide reacts chemically with the water in the coal seam to produce calcium carbonate, accompanied by volume expansion, generating expansion pressure, which promotes the expansion of coal seam cracks and further stabilizes the crack structure. It can also maintain the permeability of the coal seam for a long time, reduce the gas desorption rate in the coal seam, and achieve the effect of long-term gas control. According to the physical structure parameters of the coal seam surface area, a suitable drilling arrangement is set for the area where the pre-cracking point is located to improve the gas displacement efficiency and hydraulic splitting efficiency.

[0015] At the same time, the present invention proposes a feedback control method for carbon dioxide and calcium hydroxide, which adopts a hydraulic splitting method to expand the drilling position, improve the injection efficiency of carbon dioxide and calcium hydroxide, and in the process of carbon dioxide injection, adopts a fuzzy control method to calculate the difference between the gas content and the gas target content, and performs fuzzy calculation on the difference to form the regulation result of the carbon dioxide injection speed and pressure parameters, realizes feedback control of the carbon dioxide injection efficiency, and monitors the stability of coal seam fissures in real time, controls the injection amount of calcium hydroxide, and adopts a combined displacement method to quickly displace and extract gas, which can significantly reduce the gas concentration in the coal seam and reduce the risk of gas explosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic flow chart of a method for controlling a highly efficient pre-cracking carbon dioxide and calcium hydroxide combined gas displacement according to an embodiment of the present invention.

[0017] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0018] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0019] The embodiment of the present application provides a method for controlling the combined displacement of gas by carbon dioxide and calcium hydroxide with high efficiency pre-cracking. The execution subject of the method for controlling the combined displacement of gas by carbon dioxide and calcium hydroxide with high efficiency pre-cracking includes but is not limited to at least one of the electronic devices such as a server and a terminal that can be configured to execute the method provided in the embodiment of the present application. In other words, the method for controlling the combined displacement of gas by carbon dioxide and calcium hydroxide with high efficiency pre-cracking can be executed by software or hardware installed on a terminal device or a server device, and the software can be a blockchain platform. The server includes but is not limited to: a single server, a server cluster, a cloud server or a cloud server cluster, etc.

[0020] Reference Figure 1 , Embodiment 1 of the present invention is: A highly efficient pre-cracking carbon dioxide and calcium hydroxide combined displacement gas control method comprises the following steps: S1: Obtain physical structure parameter data of the coal seam, and select pre-splitting points and drilling arrangements of the pre-splitting points in the coal seam based on the physical structure parameter data, wherein the pre-splitting points include carbon dioxide injection pre-splitting points and calcium hydroxide injection pre-splitting points.

[0021] The coal seam surface is divided into several non-overlapping coal seam surface areas, and the physical structure parameters of each coal seam surface area are extracted. The physical structure parameters of all coal seam surface areas are used as the physical structure parameter data of the coal seam, including: The physical structural parameters of the coal seam surface area include porosity , Permeability , elastic modulus , crack density , Gas content distribution And water content ; The physical structural parameters of the coal seam surface area are calculated as follows: Collect coal samples from the surface area of ​​the coal seam as coal samples, infiltrate the pores of the coal samples with high-pressure mercury, measure the volume of the infiltrated mercury to calculate the pore volume, and calculate the ratio of the pore volume of the coal sample to the total volume of the coal sample as the porosity of the surface area of ​​the coal seam. The greater the porosity, the stronger the gas storage capacity of the coal seam surface area, which is conducive to gas extraction; Adjust the pressure environment of the coal sample and calculate the permeability of the coal seam surface area : ; in: Indicates the pressure difference of coal sample The fluid flow rate under represents fluid viscosity, G represents coal sample thickness, and R represents the flow cross-sectional area of ​​the fluid. The fluid is the gas in the coal sample. The higher the permeability, the higher the fluidity of the gas stored in the surface area of ​​the coal seam, and the higher the gas extraction efficiency. Uniaxial compression tests were performed on coal samples, stress-strain curves were measured, and elastic modulus was calculated. , the smaller the elastic modulus, the easier it is for the surface area of ​​the coal seam to improve its permeability through pre-cracking technology; Use a microscope to observe the distribution of cracks in the coal sample, calculate the sum of the lengths of all cracks in the coal sample, and calculate the crack density. , where V is the total volume of the coal sample. The higher the fissure density, the lower the mechanical strength of the coal seam surface area, and the greater the risk of coal mine collapse; Coal samples were selected from the center and four corners of the coal seam surface area, and the gas content of the five coal samples was obtained using a gas content meter as the gas content distribution. ; Specifically, the model of the gas content meter used is the gas content rapid meter WP-1; Weigh and record the initial mass of the coal sample, place the coal sample in a drying oven, heat it at a specified temperature of 105°C for a certain time of 1 hour to evaporate the water in the coal sample, weigh and record the dry mass of the coal sample again, and calculate the moisture content of the coal seam surface area. .

[0022] The physical structure parameters are standardized, and the first pre-splitting evaluation point and the second pre-splitting evaluation point of the coal seam surface area are calculated using the standardized physical structure parameters, and A coal seam surface areas with the highest first pre-splitting evaluation point are selected as the coal seam surface areas for carbon dioxide injection, and the regional centers of the coal seam surface areas for carbon dioxide injection are used as the carbon dioxide injection pre-splitting points, and B coal seam surface areas with the highest second pre-splitting evaluation point are selected as the coal seam surface areas for calcium hydroxide injection, and the regional centers of the coal seam surface areas for calcium hydroxide injection are used as the calcium hydroxide injection pre-splitting points, wherein A represents the total number of preset carbon dioxide injection pre-splitting points, and B represents the total number of preset calcium hydroxide injection pre-splitting points, including; The standardized processing result of the physical structure parameters is ,in Porosity , Permeability , elastic modulus , crack density , Gas content distribution And water content The standardized processing results; specifically: ; ; in: The preset porosity, permeability, elastic modulus, crack density, gas content distribution and maximum water content are listed in order. is the preset minimum elastic modulus, is the preset minimum moisture content. Indicates the preset optimal moisture content. Indicates the calculation of gas content distribution The mean of The calculation expression of the first pre-splitting evaluation value is: ; The calculation expression of the second pre-splitting evaluation value is: ; in: Represents the first pre-crack point estimate for the coal seam surface area, An estimate of a second pre-crack point representing a surface area of ​​the coal seam; Represents the weight coefficients of porosity, permeability, elastic modulus, fracture density, gas content distribution, and water content; The carbon dioxide injection pre-cracking point is used for gas displacement, crack expansion and gas extraction, and is suitable for coal seam surface areas with well-developed cracks, high permeability and high gas content; the calcium hydroxide injection pre-cracking point is used for chemical reaction to generate expansion pressure, further expand the cracks and stabilize the crack structure.

[0023] Based on the physical structural parameters of the coal seam surface area where the pre-splitting point is located, setting a drilling arrangement of the pre-splitting point, wherein the drilling arrangement includes parallel drilling arrangement, fan-shaped drilling arrangement and grid-shaped drilling arrangement; The standard deviation of the gas content distribution in the coal seam surface area is calculated. If the standard deviation is less than the preset standard deviation threshold, it means that the gas content distribution in the coal seam surface area is uniform; otherwise, it means that the gas content distribution in the coal seam surface area is uneven. If the gas content in the coal seam surface area is evenly distributed, a parallel drilling arrangement is adopted. A group of parallel drilling points are arranged in the coal seam surface area where the pre-cracking point is located as the drilling positions of the pre-cracking point. These drilling points are arranged along the bedding direction or the crack development direction of the coal seam, with even spacing and consistent or close drilling depths. If the gas content distribution in the coal seam surface area is uneven, and the mean value of the gas content distribution is lower than the preset mean threshold, a fan-shaped drilling arrangement is adopted, with the center of the coal seam surface area where the pre-splitting point is located as the starting drilling point, and a number of drilling points are arranged radiating outward in a fan shape within a certain angle range as the drilling positions of the pre-splitting point; If the gas content in the coal seam surface area is unevenly distributed and the mean of the gas content distribution is higher than the preset mean threshold, a grid-shaped drilling arrangement is adopted. According to the grid rule, a number of drilling points are arranged in the coal seam surface area where the pre-cracking point is located as the drilling position of the pre-cracking point. The arranged drilling points form a chessboard arrangement on the coal seam surface area.

[0024] S2: Arrange drilling holes at the pre-crack points based on the drilling arrangement method, and crack the pre-crack points by hydraulic fracturing to obtain the pre-crack points after cracking.

[0025] The hydraulic fracturing method includes: Use a drill or impact drill to drill holes at the drilling position of the pre-crack point to obtain holes with a hole diameter ranging from 30mm to 45mm. After the drilling is completed, use an air compressor or other tools to clean the debris and dust in the hole; Insert the splitting head of the splitter into the drill hole, and connect the splitter to the hydraulic power station through a high-pressure oil pipe; Open the hydraulic power station, start the hydraulic pump, and the hydraulic oil is transmitted to the splitter through the high-pressure oil pipe, pushing the splitting head to gradually expand and form cracks; Check whether the crack has reached the expected width and depth. If so, shut down the hydraulic power unit.

[0026] S3: Injecting carbon dioxide into the carbon dioxide injection pre-cracking point after cracking using the optimal carbon dioxide gas injection strategy.

[0027] Injecting carbon dioxide into the carbon dioxide injection pre-cracking point after cracking, and measuring the gas content of the carbon dioxide injection pre-cracking point with a gas content meter during the injection process, and calculating the difference between the gas content and the gas target content and the difference change rate in real time as carbon dioxide injection feedback; The carbon dioxide injection rate at time t is , the pressure parameter is , gas content is , the target gas content is S, the gas content The difference from the gas target content S is The difference change rate is , the carbon dioxide injection feedback at time t includes , ; Construct three fuzzy sets representing low, medium and high speeds respectively And fuzzy functions, construct three fuzzy sets representing low, medium and high pressure respectively and fuzzy functions; specifically, the three speed fuzzy sets correspond to low speed, medium speed and high speed in turn, and the three pressure fuzzy sets correspond to low pressure, medium pressure and high pressure in turn; The carbon dioxide injection velocity is calculated by using the fuzzy function in the velocity fuzzy set. In the membership degree of the three speed fuzzy sets, the CO2 injection speed In the speed fuzzy set The membership degrees in are Specifically, the membership calculation formula based on the fuzzy function in the speed fuzzy set is: ; ; ; in: is the preset segment speed threshold, ; The pressure parameter is calculated by using the fuzzy function in the pressure fuzzy set. In the membership degree of the three pressure fuzzy sets, the pressure parameter In the pressure fuzzy set The membership degrees in are Specifically, the membership calculation formula based on the fuzzy function in the pressure fuzzy set is: ; ; ; in: is the preset segment pressure threshold, ; Based on the injection feedback of carbon dioxide at time t, the precise value of the membership is calculated. The exact value of is: ; in: Degree of membership The exact value of is the preset segment speed threshold; The degree of membership The exact value of is: ; in: Degree of membership The exact value of is the preset segmented pressure threshold; Based on the membership degree and its exact value, the CO2 injection rate adjustment at time t is calculated. And the pressure parameter adjustment : ; ; Use the carbon dioxide injection rate adjustment at time t And the pressure parameter adjustment Adjust the carbon dioxide injection rate and pressure parameters at time t as the carbon dioxide injection rate at time t+1 And pressure parameters ,in , When the carbon dioxide injection rate is lower than a preset rate threshold, the injection of carbon dioxide into the carbon dioxide injection pre-cracking point after cracking is stopped.

[0028] S4: Inject calcium hydroxide into the pre-cracking point after cracking to expand and stabilize the coal seam cracks, and monitor the stability of the coal seam cracks. When the stability reaches the preset stability range, stop injecting calcium hydroxide and use the arranged boreholes to extract gas.

[0029] When the injection of carbon dioxide into the pre-cracking point for carbon dioxide injection after cracking is stopped, calcium hydroxide is injected into the pre-cracking point for calcium hydroxide injection after cracking, and the stability of the coal seam fissure is monitored during the injection process. The calculation formula for the stability of the coal seam fissure is: ; in: Indicates the stability of coal seam fractures. represents the jth stability index value of coal seam fractures, The stability index weight representing the jth stability index value, wherein the 1st to 4th stability indexes are respectively the crack width, the coal seam permeability, the crack stress state and the crack density, and the stability index value is the change of the 4 stability indexes in a short time after the injection of calcium hydroxide, and the change is used as the stability index value.

[0030] As an embodiment of the present invention, a laser rangefinder or a crack width sensor is used to monitor the change of the crack width in real time, and a stress sensor or seismic wave monitoring equipment is used to measure the stress change around the coal seam cracks as the change in the stress state of the cracks.

[0031] The gas extraction process is as follows: A pipeline is installed at the drilling position in the coal seam surface area where the carbon dioxide pre-cracking point is injected. The end of the pipeline is a gas collection device. A negative pressure pump is used to apply negative pressure to the coal seam. The gas displaced by the carbon dioxide is desorbed from the micropores of the coal seam, enters the cracks of the coal seam, flows along the cracks to the drilling position, and the gas is extracted into the gas collection device.

[0032] Embodiment 2: This scheme conducts comparative experiments on the gas control method based on efficient pre-cracking of carbon dioxide and calcium hydroxide combined displacement, carbon dioxide injection displacement method, sodium hydroxide injection displacement method and traditional gas extraction method. The traditional gas extraction method directly extracts gas through drilling. The comparative experimental environment is: coal seam thickness: 4 meters, gas content: 25 , gas pressure: 1.5 MPa, fracture permeability: 6 mD, comparative experimental results are shown in Table 1: Table 1 ; As shown in Table 1, the method for controlling the combined displacement of gas by carbon dioxide and calcium hydroxide based on efficient pre-cracking is significantly higher than other methods in terms of gas displacement efficiency and extraction efficiency. Carbon dioxide can effectively improve the gas displacement efficiency and extraction efficiency, and sodium hydroxide can effectively improve the range and stability of fracture expansion.

[0033] It should be understood that the embodiment is for illustration only and the scope of the patent application is not limited to this structure.

[0034] It should be noted that the serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages and disadvantages of the embodiments. And the terms "including", "comprising" or any other variants thereof in this article are intended to cover non-exclusive inclusion, so that a process, device, article or method including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, device, article or method. In the absence of further restrictions, an element defined by the sentence "including a ..." does not exclude the presence of other identical elements in the process, device, article or method including the element.

[0035] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes a number of instructions for a terminal device (which can be a mobile phone, a computer, a server, or a network device, etc.) to execute the methods described in each embodiment of the present invention.

[0036] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for controlling gas displacement by combining carbon dioxide and calcium hydroxide with high efficiency pre-cracking, characterized in that: The method comprises: S1: obtaining physical structure parameter data of the coal seam, and selecting a pre-splitting point in the coal seam and a drilling arrangement of the pre-splitting point in combination with the physical structure parameter data, wherein the pre-splitting point includes a carbon dioxide injection pre-splitting point and a calcium hydroxide injection pre-splitting point, the carbon dioxide injection pre-splitting point is a carbon dioxide injection pre-splitting point, and the calcium hydroxide injection pre-splitting point is a calcium hydroxide injection pre-splitting point; S2: Arrange drilling holes at the pre-crack point based on the drilling arrangement method, and crack the pre-crack point by hydraulic fracturing to obtain the pre-crack point after cracking; S3: using the optimal carbon dioxide gas injection strategy to inject carbon dioxide into the carbon dioxide injection pre-cracking point after cracking, the carbon dioxide has a stronger adsorption capacity than gas, competes with the gas on the surface of the coal seam for adsorption positions, and replaces the gas. The optimal carbon dioxide gas injection strategy uses a feedback-based fuzzy control method to adjust the carbon dioxide injection speed and pressure parameters; S4: Inject calcium hydroxide into the pre-cracking point after cracking to expand and stabilize the coal seam cracks, and monitor the stability of the coal seam cracks. When the stability reaches the preset stability range, stop injecting calcium hydroxide and use the arranged boreholes to extract gas.

2. The method for controlling the efficient pre-cracking of carbon dioxide and calcium hydroxide combined displacement of gas according to claim 1, characterized in that: The coal seam surface is divided into several non-overlapping coal seam surface areas, and the physical structure parameters of each coal seam surface area are extracted. The physical structure parameters of all coal seam surface areas are used as the physical structure parameter data of the coal seam, including: The physical structural parameters of the coal seam surface area include porosity , Permeability , elastic modulus , crack density , Gas content distribution And water content ; The physical structural parameters of the coal seam surface area are calculated as follows: Collect coal samples from the surface area of ​​the coal seam as coal samples, infiltrate the pores of the coal samples with high-pressure mercury, measure the volume of the infiltrated mercury to calculate the pore volume, and calculate the ratio of the pore volume of the coal sample to the total volume of the coal sample as the porosity of the surface area of ​​the coal seam. The greater the porosity, the stronger the gas storage capacity of the coal seam surface area, which is conducive to gas extraction; Adjust the pressure environment of the coal sample and calculate the permeability of the coal seam surface area : ； in: Indicates the pressure difference of coal sample The fluid flow rate under represents fluid viscosity, G represents coal sample thickness, and R represents the flow cross-sectional area of ​​the fluid. The fluid is the gas in the coal sample. The higher the permeability, the higher the fluidity of the gas stored in the surface area of ​​the coal seam, and the higher the gas extraction efficiency. Uniaxial compression tests were performed on coal samples, stress-strain curves were measured, and elastic modulus was calculated. , the smaller the elastic modulus, the easier it is for the surface area of ​​the coal seam to improve its permeability through pre-cracking technology; Use a microscope to observe the distribution of cracks in the coal sample, calculate the sum of the lengths of all cracks in the coal sample, and calculate the crack density. , where V is the total volume of the coal sample. The higher the fissure density, the lower the mechanical strength of the coal seam surface area, and the greater the risk of coal mine collapse; Coal samples were selected from the center and four corners of the coal seam surface area, and the gas content of the five coal samples was obtained using a gas content meter as the gas content distribution. ; Weigh and record the initial mass of the coal sample, place the coal sample in a drying oven, heat it at a specified temperature of 105°C for a certain time of 1 hour to evaporate the water in the coal sample, weigh and record the dry mass of the coal sample again, and calculate the moisture content of the coal seam surface area. .

3. The method for controlling the combined displacement of gas by high-efficiency pre-cracking carbon dioxide and calcium hydroxide as claimed in claim 2, characterized in that: The physical structure parameters are standardized, and the first pre-splitting evaluation point and the second pre-splitting evaluation point of the coal seam surface area are calculated using the standardized physical structure parameters, and A coal seam surface areas with the highest first pre-splitting evaluation point are selected as the coal seam surface areas for carbon dioxide injection, and the regional centers of the coal seam surface areas for carbon dioxide injection are used as the carbon dioxide injection pre-splitting points, and B coal seam surface areas with the highest second pre-splitting evaluation point are selected as the coal seam surface areas for calcium hydroxide injection, and the regional centers of the coal seam surface areas for calcium hydroxide injection are used as the calcium hydroxide injection pre-splitting points, wherein A represents the total number of preset carbon dioxide injection pre-splitting points, and B represents the total number of preset calcium hydroxide injection pre-splitting points, including; The standardized processing result of the physical structure parameters is ,in Porosity , Permeability , elastic modulus , crack density , Gas content distribution And water content The standardized processing results; The calculation expression of the first pre-splitting evaluation value is: ； The calculation expression of the second pre-splitting evaluation value is: ； in: Represents the first pre-crack point estimate for the coal seam surface area, An estimate of a second pre-crack point representing a surface area of ​​the coal seam; Represents the weight coefficient of porosity, permeability, elastic modulus, fracture density, gas content distribution and water content.

4. The method for controlling the efficient pre-cracking carbon dioxide and calcium hydroxide combined displacement of gas according to claim 3, characterized in that: Based on the physical structural parameters of the coal seam surface area where the pre-splitting point is located, setting a drilling arrangement of the pre-splitting point, wherein the drilling arrangement includes parallel drilling arrangement, fan-shaped drilling arrangement and grid-shaped drilling arrangement; The standard deviation of the gas content distribution in the coal seam surface area is calculated. If the standard deviation is less than the preset standard deviation threshold, it means that the gas content distribution in the coal seam surface area is uniform; otherwise, it means that the gas content distribution in the coal seam surface area is uneven. If the gas content in the coal seam surface area is evenly distributed, a parallel drilling arrangement is adopted. A group of parallel drilling points are arranged in the coal seam surface area where the pre-cracking point is located as the drilling positions of the pre-cracking point. These drilling points are arranged along the bedding direction or the crack development direction of the coal seam, with even spacing and consistent or close drilling depths. If the gas content distribution in the coal seam surface area is uneven, and the mean value of the gas content distribution is lower than the preset mean threshold, a fan-shaped drilling arrangement is adopted, with the center of the coal seam surface area where the pre-splitting point is located as the starting drilling point, and a number of drilling points are arranged radiating outward in a fan shape within a certain angle range as the drilling positions of the pre-splitting point; If the gas content in the coal seam surface area is unevenly distributed and the mean of the gas content distribution is higher than the preset mean threshold, a grid-shaped drilling arrangement is adopted. According to the grid rule, a number of drilling points are arranged in the coal seam surface area where the pre-cracking point is located as the drilling position of the pre-cracking point. The arranged drilling points form a chessboard arrangement on the coal seam surface area.

5. The method for controlling the combined displacement of gas by high-efficiency pre-cracking carbon dioxide and calcium hydroxide as claimed in claim 1, characterized in that: The hydraulic fracturing method includes: Use a drill or impact drill to drill holes at the drilling position of the pre-crack point to obtain holes with a hole diameter ranging from 30mm to 45mm. After the drilling is completed, use an air compressor or other tools to clean the debris and dust in the hole; Insert the splitting head of the splitter into the drill hole, and connect the splitter to the hydraulic power station through a high-pressure oil pipe; Open the hydraulic power station, start the hydraulic pump, and the hydraulic oil is transmitted to the splitter through the high-pressure oil pipe, pushing the splitting head to gradually expand and form cracks; Check whether the crack has reached the expected width and depth. If so, shut down the hydraulic power unit.

6. The method for controlling the combined displacement of gas by high-efficiency pre-cracking carbon dioxide and calcium hydroxide according to claim 1, characterized in that: Injecting carbon dioxide into the carbon dioxide injection pre-cracking point after cracking, and measuring the gas content of the carbon dioxide injection pre-cracking point with a gas content meter during the injection process, and calculating the difference between the gas content and the gas target content and the difference change rate in real time as carbon dioxide injection feedback; The carbon dioxide injection rate at time t is , the pressure parameter is , gas content is , the target gas content is S, the gas content The difference from the gas target content S is The difference change rate is , the carbon dioxide injection feedback at time t includes , ; Construct three fuzzy sets representing low, medium and high speeds respectively And fuzzy functions, construct three fuzzy sets representing low, medium and high pressure respectively and fuzzy functions; The carbon dioxide injection velocity is calculated by using the fuzzy function in the velocity fuzzy set. In the membership degree of the three speed fuzzy sets, the CO2 injection speed In the speed fuzzy set The membership degrees in are ; Based on the injection feedback of carbon dioxide at time t, the precise value of the membership is calculated. The exact value of is: ； in: Degree of membership The exact value of is the preset segment speed threshold; The degree of membership The exact value of is: ； in: Degree of membership The exact value of is the preset segmented pressure threshold; Based on the membership degree and its exact value, the CO2 injection rate adjustment at time t is calculated. And the pressure parameter adjustment : ； ； Use the carbon dioxide injection rate adjustment at time t And the pressure parameter adjustment Adjust the carbon dioxide injection rate and pressure parameters at time t as the carbon dioxide injection rate at time t+1 And pressure parameters ,in , When the carbon dioxide injection rate is lower than a preset rate threshold, the injection of carbon dioxide into the carbon dioxide injection pre-cracking point after cracking is stopped.

7. The method for controlling the combined displacement of gas by high-efficiency pre-cracking carbon dioxide and calcium hydroxide as claimed in claim 6, characterized in that: When the injection of carbon dioxide into the pre-cracking point for carbon dioxide injection after cracking is stopped, calcium hydroxide is injected into the pre-cracking point for calcium hydroxide injection after cracking, and the stability of the coal seam fissure is monitored during the injection process. The calculation formula for the stability of the coal seam fissure is: ； in: Indicates the stability of coal seam fractures. represents the jth stability index value of coal seam fractures, The stability index weight representing the jth stability index value, wherein the 1st to 4th stability indexes are respectively the crack width, the coal seam permeability, the crack stress state and the crack density, and the stability index value is the change of the 4 stability indexes in a short time after the injection of calcium hydroxide, and the change is used as the stability index value.

8. The method for controlling the combined displacement of gas by high-efficiency pre-cracking carbon dioxide and calcium hydroxide as claimed in claim 1, characterized in that: The gas extraction process is as follows: A pipeline is installed at the drilling position in the coal seam surface area where the carbon dioxide pre-cracking point is injected. The end of the pipeline is a gas collection device. A negative pressure pump is used to apply negative pressure to the coal seam. The gas displaced by the carbon dioxide is desorbed from the micropores of the coal seam, enters the cracks of the coal seam, flows along the cracks to the drilling position, and the gas is extracted into the gas collection device.

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