A method for determining a coal cutting track of a coal mining machine in an intelligentized working face of a mine

Abstract

The present application relates to the technical field of intelligent mining of coal mines, in particular to a method for determining a coal cutting track of a coal mining machine in an intelligent working face of a mine. The method comprises the following steps: S100, testing and counting basic parameters of coal and rock bodies and interfaces at a mining working face and its roof and floor; S200, calculating reasonable construction parameters of underground hydraulic fracturing according to the counted basic parameters of the coal and rock bodies and interfaces; S300, adding support sand and a marking pigment to the fracturing fluid and stirring them evenly, performing underground hydraulic fracturing according to the calculated construction parameters, and forming a strong color difference between the formed cracks and the marking pigment at the coal-rock interface as a special element for image recognition; S400, starting mining at the working face after the hydraulic fracturing is completed, accurately capturing the special element artificially formed by an image recognition device installed at the working face, and determining the coal-rock interface of the mining working face and the coal cutting track of the coal mining machine after image analysis and processing.

Description

Technical Field

[0001] This invention relates to the field of intelligent coal mining technology, specifically a method for determining the coal cutting trajectory of an intelligent coal mining machine in a mine working face. Background Technology

[0002] Intelligent coal mining has been a research hotspot in recent years. To achieve intelligent coal mining in underground longwall faces, it is first necessary to accurately determine the coal cutting trajectory of the coal mining machine or accurately identify the interface between the coal seam and its roof and floor during the longwall mining process. This ensures the safety and cutting efficiency of the coal mining machine's cutting teeth and guarantees that the workload of subsequent coal preparation and the recovery rate of the working face are not increased.

[0003] Currently, the methods for determining the coal cutting trajectory of intelligent coal mining machines mainly rely on feature information such as images, sounds, pressure signals, current signals, and torque signals, combined with autonomous learning methods to identify the coal-rock interface, and then determine the coal cutting trajectory based on the identification results. A number of invention patents, including those with publication numbers CN113435294A, CN110424964A, and CN112990169A, all rely on the above methods and principles for coal-rock interface identification. However, the complex and variable underground environment of coal mines, the strong heterogeneity of coal and rock strata, and the harsh environment of the longwall mining face easily lead to difficulties in image recognition, low accuracy in sound transmission, and low signal recognition, resulting in significant challenges and inaccuracies in coal-rock interface identification.

[0004] To address the aforementioned issues, this method proposes a method for determining the coal cutting trajectory of a coal mining machine in an intelligent working face. It primarily utilizes a combination of underground hydraulic fracturing and image recognition techniques to determine the coal cutting trajectory. Specifically, proppant and marker pigments are added to the fracturing fluid, and construction parameters are adjusted to allow the hydraulic fractures to directionally initiate and extend to the coal seam and its roof and floor interfaces, then extend along the interfaces, i.e., hydraulic fracturing opens the coal-rock interface. The proppant prevents the opened coal-rock interface from closing, and the marker pigments create a strong color difference near the coal-rock interface, forming unique image recognition elements. During the working face mining process, image recognition technology accurately identifies these unique elements to confirm the coal-rock interface, thereby determining the coal cutting trajectory of the mining machine. Summary of the Invention

[0005] The purpose of this invention is to determine the coal-rock interface by integrating downhole hydraulic fracturing technology and image recognition technology, overcoming the problems of existing methods being greatly affected by the coal mining environment, having high equipment requirements, and having low interface recognition accuracy, and to provide a method for determining the coal cutting trajectory of a coal mining machine in an intelligent working face of a mine.

[0006] This invention adopts the following technical solution: a method for determining the coal cutting trajectory of a coal mining machine in an intelligent working face, comprising the following steps: S100: conducting basic parameter testing and statistics on the coal-rock mass and interface at the working face and its roof and floor; S200: calculating reasonable construction parameters for underground hydraulic fracturing based on the statistically obtained basic parameters of the coal-rock mass and interface, under which the hydraulic fractures can extend along the interface when they reach it, thereby opening the coal-rock interface; S300: adding support sand and marker pigment to the fracturing fluid and stirring evenly, and carrying out underground hydraulic fracturing operations according to the calculated construction parameters. The supporting effect of the support sand can prevent the opened coal-rock interface from closing, and the strong color difference between the formed fractures and the marker pigment at the coal-rock interface becomes a special element for image recognition; S400: after the hydraulic fracturing is completed, the working face begins to mine, and the artificially formed special element is accurately captured by the image recognition device installed on the working face. After image analysis and processing, the coal-rock interface of the working face and the coal cutting trajectory of the coal mining machine are determined.

[0007] In step S100, the basic parameters of the longwall face and its roof and floor coal and rock mass include layer thickness, elastic modulus, Poisson's ratio, tensile and compressive strength, fracture toughness, and magnitude and direction of in-situ stress. The in-situ stress should include vertical in-situ stress, maximum horizontal principal stress, and minimum horizontal principal stress. The basic parameters of the interface are the shear strength of the coal-roof interface and the coal-floor interface. When the direct roof or direct floor of the coal seam is too thin to test other basic parameters besides the thickness, the shear strength of the interface is calculated as 1.2 to 1.5 times the basic parameters of the coal seam. The shear strength of the interface is calculated as 0.9 to 1.1 times that of the coal seam.

[0008] In step S200, the construction parameters for downhole hydraulic fracturing include the fracturing initiation location, perforation direction and number, injection rate, and the location and spacing of the fracturing holes.

[0009] The initiation point is set in the middle of the longwall face; the perforation direction is perpendicular to the longwall face and dips upward or downward. When the difference in shear strength between the coal-roof interface and the coal-floor interface is within ±10%, and the difference in tensile strength between the roof and floor of the longwall face is within ±20%, bidirectional symmetrical perforation is used; under other conditions, unidirectional perforation is used. For bidirectional perforation, one perforation operation is required at each initiation point; for unidirectional perforation, two perforation operations are required at each initiation point. First, the upper perforation operation is carried out, and then the lower perforation operation is carried out at an interval of 20cm. The height of both bidirectional and unidirectional perforations is 10cm.

[0010] The fracturing hole is located at the midpoint of the coal seam thickness in the cut, along the strike of the coal seam. The fracturing fluid is water-based. The reasonable range for the injection rate is calculated based on the following inequality:

[0011]

[0012]

[0013]

[0014]

[0015] In the formula, P 0 represents the water pressure inside the well, in MPa; P 1 represents the critical water pressure (MPa) required for the hydraulic fracture to propagate across the layer when it reaches the interface; P 2 represents the critical water pressure required for the hydraulic fracture to propagate along the interface when it reaches the interface, in MPa; q The fracturing fluid discharge rate is m. 3 / s; ρ is the density of the fluid, kg / m³ 3 ; h The crack height is in meters (m). γ The viscosity of the fracturing fluid is expressed in mPa·s. E Let GPa be the elastic modulus of the reservoir. K CC The type I fracture toughness of the coal seam, MPa·m 1 / 2 ; l Let m be the half-length of the crack. K RC The fracture toughness of the top or bottom plate, in MPa·m 1 / 2 ; σ V The vertical ground stress is expressed in MPa. σ h The minimum horizontal ground stress is given in MPa; π / 2- α The dip angle of the coal seam is , in °.

[0016] In step S300, the Mohs hardness of the supporting sand is between that of the coal body and the roof and floor rock mass, the particle diameter is between 1.2 and 3 mm, and the volume ratio of the fracturing fluid carrying the sand is 1 to 3%; the marking pigment is a white water-based fluorescent tracer, and the volume ratio of the fracturing fluid to the marking pigment is 5%.

[0017] In step S300, the downhole hydraulic fracturing operation adopts a double-end sealing and retreating fracturing method. Each retreating distance is less than or equal to the length of the working face cut. The fracturing process is as follows: after perforation operation by high-pressure water cutting, the sealing device and hydraulic pressure gauge are installed and adjusted. After pushing the sealing device to the predetermined fracturing initiation position, the sealing device is pressurized to 10MPa. Then, the water pump is turned on to start fracturing until water seeps or gushes out in the roadway roof and floor, coal face or borehole. Following the above steps, the fracturing operation is completed by retreating along the fracturing hole from the working face stop line to the cut.

[0018] The image recognition device is a camera installed on the coal mining machine. The camera acquires video of the coal-rock interface, processes the video data of the coal-rock interface into high-definition images in chronological order, and then inputs them into the vision processing module. The vision processing module identifies special elements formed by fracturing and further identifies the areas by black-and-white or black-and-gray binarization, processing the coal-rock body as black, the marker pigment as white, and the cracks as gray. Then, the position coordinate calculation module calculates the position coordinates of the white and gray areas to determine the trajectory coordinates of the coal-rock boundary line.

[0019] Compared with existing technologies, this invention accurately sets the construction parameters for downhole fracturing, causing the hydraulic fractures, after initiation, to extend along the interface between the coal seam and the roof and floor plates in their height direction, thereby opening the coal-rock interface. Relying on the opened coal-rock interface and the marker pigments in the fracturing fluid, special image recognition elements are formed. Combined with image recognition technology, these special elements are accurately identified to determine the coal-rock interface and the coal cutting trajectory of the mining machine. This solves the problems of existing methods being greatly affected by the coal mining environment, having high equipment requirements, and low interface recognition accuracy. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method for determining the coal cutting trajectory of an intelligent coal mining machine in a mine working face according to the present invention;

[0021] Figure 2 This is a schematic diagram of the location of the fracturing borehole and the fracturing initiation point in the method for determining the coal cutting trajectory of the intelligent coal mining face of the present invention;

[0022] Figure 3 for Figure 2 Cross-sectional view;

[0023] Figure 4 This is a schematic diagram showing the position and height of the perforation hole in the bidirectional perforation of the present invention;

[0024] Figure 5 This is a cross-sectional view of the perforation during bidirectional perforation according to the present invention;

[0025] Figure 6 This is a schematic diagram showing the position and height of the perforation hole in the unidirectional perforation of the present invention;

[0026] Figure 7 This is a cross-sectional view of the unidirectional perforation of the present invention;

[0027] Figure 8 This is a flowchart of the image recognition process in the method for determining the coal cutting trajectory of a coal mining machine in an intelligent working face as described in this invention;

[0028] In the diagram, 1-conveyor roadway in the mining area, 2-fracture initiation point, 3-fracturing borehole, 4-return airway, 5-auxiliary haulage roadway, 6-cut hole, 7-cut hole coal wall, 8-coal-roof interface, 9-coal-floor interface, 10-bidirectional perforation location, 11-upper perforation location, 12-lower perforation location, L is the cut hole length in the working face; h is the coal seam thickness; L1 is the distance between fracture initiation points, and h1 is the perforation height. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] like Figure 1 As shown, a method for determining the coal cutting trajectory of a coal mining machine in an intelligent working face of a mine includes the following steps.

[0031] S100: Conduct basic parameter testing and statistics on the coal and rock mass and interfaces at the longwall face, its roof and floor.

[0032] The basic parameters of the longwall face and its roof and floor coal and rock mass should include layer thickness, elastic modulus, Poisson's ratio, tensile and compressive strength, fracture toughness, and magnitude and direction of in-situ stress. In-situ stress should include vertical in-situ stress, maximum horizontal principal stress, and minimum horizontal principal stress. The basic parameters of the interfaces are mainly the shear strength of the coal-roof interface and the coal-floor interface. When the immediate roof or floor of the coal seam is too thin to test other basic parameters besides thickness, they can be statistically calculated at 1.2 to 1.5 times the basic parameters of the coal seam. The shear strength of the interfaces can be statistically calculated at 0.9 to 1.1 times the shear strength of the coal seam.

[0033] S200: Calculate reasonable construction parameters for downhole hydraulic fracturing based on the statistical basic parameters of the coal-rock mass and interface. These construction parameters enable the hydraulic fractures to extend along the interface when they reach it, thereby breaking up the coal-rock interface.

[0034] like Figure 2 , 3 As shown, the initiation point is set in the middle of the longwall face; the perforation direction is perpendicular to the longwall face, dipping upwards or downwards. When the difference in shear strength between the coal-roof interface and the coal-floor interface is within ±10%, and the difference in tensile strength between the roof and floor of the longwall face is within ±20%, bidirectional symmetrical perforation is used (e.g., Figure 4 , 5 Under other conditions, unidirectional perforation is used (e.g.) Figure 6 , 7For bidirectional perforation, one perforation operation is required at each fracture initiation point. For unidirectional perforation, two perforation operations are required at each fracture initiation point. First, perform the upper perforation operation, and then perform the lower perforation operation at a 20cm interval. The height of both bidirectional and unidirectional perforations is 10cm.

[0035] The fracturing hole is located at the midpoint of the coal seam thickness within the cut, along the strike of the coal seam. The fracturing fluid can be water-based, and the appropriate injection rate range is calculated using the following inequality:

[0036]

[0037]

[0038]

[0039]

[0040] In the formula, P 0 represents the water pressure inside the well, in MPa; P 1 represents the critical water pressure (MPa) required for the hydraulic fracture to propagate across the layer when it reaches the interface; P 2 represents the critical water pressure required for the hydraulic fracture to propagate along the interface when it reaches the interface, in MPa; q The fracturing fluid discharge rate is m. 3 / s; ρ is the density of the fluid, kg / m³ 3 ; h The crack height is in meters (m). γ The viscosity of the fracturing fluid is expressed in mPa·s. E Let GPa be the elastic modulus of the reservoir. K CC The type I fracture toughness of the coal seam, MPa·m 1 / 2 ; l Let m be the half-length of the crack. K RC The fracture toughness of the top or bottom plate, in MPa·m 1 / 2 ; σ V The vertical ground stress is expressed in MPa. σ h The minimum horizontal ground stress is given in MPa; π / 2- α The dip angle of the coal seam is , in °.

[0041] S300: Add proppant and marker pigment to the fracturing fluid and stir evenly. Perform downhole hydraulic fracturing operation according to the calculated construction parameters. The proppant's supporting effect prevents the fractured coal-rock interface from closing. The strong color difference between the resulting cracks and the marker pigment at the coal-rock interface becomes a special element for image recognition.

[0042] The Mohs hardness of the proppant sand is between that of the coal body and the roof and floor rock mass, and the particle diameter is between 1.2 and 3 mm. The volume ratio of proppant carried by the fracturing fluid is 1 to 3%. The marking pigment is a white water-based fluorescent tracer, and the volume ratio of fracturing fluid to marking pigment is about 5%.

[0043] Downhole hydraulic fracturing employs a double-end sealing and retreating fracturing method. Each retreating distance is less than or equal to the length of the working face cut. The fracturing process is as follows: after perforation using high-pressure water cutting, a sealing device and a hydraulic pressure gauge are installed and adjusted. The sealing device is pushed to the predetermined fracturing initiation position and pressurized to 10 MPa. Then, water and electricity are supplied to the water pump to begin fracturing until water seeps or gushes out from the roadway roof, floor, coal seam, or borehole. Following these steps, the fracturing operation is completed sequentially along the fracturing borehole from the working face stop line back to the cut.

[0044] S400: After hydraulic fracturing, the working face begins to be mined. The special elements that have been artificially formed are accurately captured by the image recognition device installed on the working face. After image analysis and processing, the coal-rock interface of the mining face and the coal cutting trajectory of the coal mining machine are determined.

[0045] like Figure 8 As shown, the coal-rock interface video is acquired by a camera installed on the coal mining machine. The video data is processed into high-definition images in chronological order and then input into the vision processing module. The vision processing module identifies special elements formed by fracturing and further identifies the area by black-and-white or black-and-gray binarization, processing the coal-rock body as black, the marker pigment as white, and the cracks as gray. Then, the position coordinate calculation module calculates the position coordinates of the white and gray areas to determine the trajectory coordinates of the coal-rock boundary line.

[0046] Coordinate calculation process: The camera's built-in precision gyroscope positioner uses the camera's position coordinates as reference coordinates and the distance from the camera to the coal wall as the relative displacement in the z-axis direction. After determining the shooting focal length, the x-axis and y-axis coordinates of each point in the captured image are inverted through the coordinate transformation matrix.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining a coal cutting trajectory of a coal mining machine in an intelligentized coal face of a mine, characterized in that: Includes the following steps, S100: Conduct basic parameter testing and statistics on the coal and rock mass and interfaces at the longwall face, its roof and floor; S200: Calculate reasonable construction parameters for downhole hydraulic fracturing based on the statistical basic parameters of coal-rock mass and interface. These construction parameters enable hydraulic fractures to extend along the interface when they reach the coal-rock interface, thereby breaking open the coal-rock interface. S300: Add proppant and marker pigment to the fracturing fluid and stir evenly. Perform downhole hydraulic fracturing operation according to the calculated construction parameters. The proppant's supporting effect can prevent the opened coal-rock interface from closing. The strong color difference between the crack and the marker pigment at the coal-rock interface becomes a special element for image recognition. S400: After hydraulic fracturing, the working face begins to be mined. The special elements that have been artificially formed are accurately captured by the image recognition device installed on the working face. After image analysis and processing, the coal-rock interface of the mining face and the coal cutting trajectory of the coal mining machine are determined.

2. The method for determining the coal cutting trajectory of an intelligent coal mining machine in a mine working face according to claim 1, characterized in that: In step S100, the basic parameters of the longwall face and its roof and floor coal and rock mass include layer thickness, elastic modulus, Poisson's ratio, tensile and compressive strength, fracture toughness, and magnitude and direction of in-situ stress. The in-situ stress should include vertical in-situ stress, maximum horizontal principal stress, and minimum horizontal principal stress. The basic parameters of the interface are the shear strength of the coal-roof interface and the coal-floor interface. When the direct roof or direct floor of the coal seam is too thin to test other basic parameters besides the thickness, the shear strength of the interface is calculated as 1.2 to 1.5 times the basic parameters of the coal seam. The shear strength of the interface is calculated as 0.9 to 1.1 times that of the coal seam.

3. The method for determining the coal cutting track of the intelligent coal face mining machine in the mine according to claim 1, characterized in that: In step S200, the construction parameters for downhole hydraulic fracturing include the fracturing initiation location, perforation direction and number, injection rate, and the location and spacing of the fracturing holes.

4. The method for determining the coal cutting track of the intelligent coal face mining machine in the mine according to claim 3, characterized in that: The initiation point (2) is set in the middle of the longwall face; the perforation direction is perpendicular to the longwall face and tends upward or downward. When the difference in shear strength between the coal-roof interface (8) and the coal-floor interface (9) is within ±10%, and the difference in tensile strength between the roof and floor of the longwall face is within ±20%, bidirectional symmetrical perforation is adopted. Under other conditions, unidirectional perforation is adopted. When bidirectional perforation is used, each initiation point can be perforated once. When unidirectional perforation is used, each initiation point can be perforated twice. First, the upper side perforation is performed, and the lower side perforation is performed at an interval of 20cm. The height of both bidirectional and unidirectional perforation is 10cm.

5. The coal cutting track determination method for a mine intelligentized working face coal mining machine according to claim 3, characterized in that: The fracturing hole is located at the midpoint of the coal seam thickness in the cut, along the strike of the coal seam. The fracturing fluid is water-based. The reasonable range for the injection rate is calculated based on the following inequality: In the formula, P 0 represents the water pressure inside the well, in MPa; P 1 represents the critical water pressure (MPa) required for the hydraulic fracture to propagate across the layer when it reaches the interface; P 2 represents the critical water pressure required for the hydraulic fracture to propagate along the interface when it reaches the interface, in MPa; q The fracturing fluid discharge rate is m. 3 / s; ρ is the density of the fluid, kg / m³ 3 ; h The crack height is in meters (m). γ The viscosity of the fracturing fluid is expressed in mPa·s. E Let GPa be the elastic modulus of the reservoir. K CC The type I fracture toughness of the coal seam, MPa·m 1 / 2 ; l Let m be the half-length of the crack. K RC The fracture toughness of the top or bottom plate, in MPa·m 1 / 2 ; σ V The vertical ground stress is expressed in MPa. σ h The minimum horizontal ground stress is given in MPa; π / 2- α The dip angle of the coal seam is , in °.

6. The coal cutting track determination method for a mine intelligentized working face coal mining machine according to claim 1, characterized in that: In step S300, the Mohs hardness of the supporting sand is between that of the coal body and the roof and floor rock mass, the particle diameter is between 1.2 and 3 mm, and the volume ratio of the fracturing fluid carrying the sand is 1 to 3%; the marking pigment is a white water-based fluorescent tracer, and the volume ratio of the fracturing fluid to the marking pigment is 5%.

7. The method for determining the coal cutting trajectory of an intelligent coal mining machine in a mine working face according to claim 1, characterized in that: In step S300, the downhole hydraulic fracturing operation adopts a double-end sealing and retreating fracturing method. Each retreating distance is less than or equal to the length of the working face cut. The fracturing process is as follows: after perforation by water cutting, the sealing device and hydraulic pressure gauge are installed and adjusted. After pushing the sealing device to the predetermined fracturing initiation position, the sealing device is pressurized to 10MPa. Then, the water pump is turned on to start fracturing until water seeps or gushes out in the roadway roof and floor, coal face or borehole. Following the above steps, the fracturing operation is completed by retreating along the fracturing hole from the working face stop line to the cut.

8. The method for determining the coal cutting track of the intelligent coal face mining machine in the mine according to claim 1, characterized in that: The image recognition device is a camera installed on the coal mining machine. The camera acquires video of the coal-rock interface, processes the video data of the coal-rock interface into high-definition images in chronological order, and then inputs them into the vision processing module. The vision processing module identifies special elements formed by fracturing and further identifies the areas by black-and-white or black-and-gray binarization, processing the coal-rock body as black, the marker pigment as white, and the cracks as gray. Then, the position coordinate calculation module calculates the position coordinates of the white and gray areas to determine the trajectory coordinates of the coal-rock boundary line.

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