Method for pressure relief and permeability improvement on the basis of horizontal slitting of coal seam under the action of periodic weighting

Abstract

A method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting is provided, which relates to the technical field of permeability improvement and efficient gas extraction of the coal seam. The method comprises the steps: collecting background information of coal mine production, selecting a driving face of a high-gas low-permeability coal roadway, measuring a roof weighting step distance in real time, predicting a weighting cycle, selecting a coalface, drilling a long bedding drill hole, and performing hydraulic horizontal slitting.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application claims the benefit and priority of Chinese Patent Application No. 202411661197.3 filed with the China National Intellectual Property Administration on Nov. 19, 2024, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of permeability improvement and efficient gas extraction of coal seams, and in particular to a method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting.BACKGROUND

[0003] As shallow coal resources are being depleted, mine exploration gradually develops to access to deep reservoir areas of coal seams. The gas content of the coal seam is proportional to the thickness of an overlying bedrock of the coal seam, and therefore an original low-gas mine gradually becomes a high-gas mine depending on the amount of gas emission in the mine excavation process. Meanwhile, deep mines generally have the technical difficulty of a poor extraction effect caused by the poor permeability of the coal seams, and this coal mine gas problem restricts the safe production of China's coal mines in the long term. Essentially, a coal body cracking and destruction process is to take relevant measures to disorder and fracture a basic structure of a coal body, in order to achieve a cracking effect. This process is complex and changes dynamically. The key to preventing and controlling gas accidents lies in pressure relief on the coal seams by means of technical methods. Technical measures mainly include depressurizing exploitation, hydraulic cracking (such as hydraulic fracturing, hydraulic slitting, or hydraulic punching), deep-hole pre-splitting blasting, CO2 blasting and cracking, and the like on a protective layer.

[0004] The above-mentioned methods typically focus on cracking with hole as the center towards the surrounding, but ignore the intrinsic stress of the coal body itself, and do on rely on the self weight of a main roof, the load of an overlaying rock stratum and a downward impact load formed by roof collapse within a certain span range during the periodic weighting of the coal mine. Especially, these methods do not make the use of the principle of protective layer mining in a coal roadway, and do not create and use a horizontal space, which serves as a movement compensation space for the coal body within a larger range, to achieve overall cracking of the coal seam, resulting in a poor effect.SUMMARY

[0005] A method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting includes the steps:

[0006] collecting background information of coal mine production, and selecting a driving face of a high-gas low-permeability coal roadway according to the background information of coal mine production;

[0007] measuring a roof weighting step distance of the driving face of the high-gas low-permeability coal roadway in real time, calculating weighting data according to the roof weighting step distance historically collected in real time, and predicting a weighting cycle according to the weighting data;

[0008] selecting a coalface on one side of an advancing stress concentration zone in the weighting cycle;

[0009] Drilling a drill rod into the coalface to reach a pre-designed position, and then obtaining a long bedding drill hole;

[0010] replacing the drill rod with a horizontal slitting device after reverse drilling, advancing the drilling to reach an initial slitting position set in the long bedding drill hole, using high-pressure water jets of the horizontal slitting device to perform fixed-point retreating horizontal cutting within a range of the drilled coal seam, and then obtaining a movement compensation space;

[0011] obtaining a fracture network according to an increased load of the coalface, an inherent stress of a coal body and the movement compensation space during periodic weighting; and

[0012] controlling excessive stressing and bulking of the coal body on the basis of the fracture network to obtain a target coal seam where the pressure relief and permeability improvement are completed.

[0013] Preferably, the background information of coal mine production includes: distribution characteristics of a ground stress field, the density and thickness of the coal seam, the content and pressure of a gas, and the air permeability of the coal seam.

[0014] Preferably, the weighting data includes: a rock pressure time in a first time period, and the weighting cycle, the weighting step distance and a periodic weighting peak during historical stoping

[0015] Preferably, a cutting water pressure of the horizontal slitting device ranges from 80 to 100 MPa.

[0016] The present disclosure has the following technical effects.

[0017] The present disclosure provides a method for pressure relief and permeability improvement on the basis of the horizontal slitting of the coal seam under the action of periodic weighting, uses a huge stress effect on the coal seam and a hydraulic slitting technique by means of the increased load of the coalface and the inherent stress of the coal body itself during periodic weighting, overcomes the shortcomings of conventional coal seam permeability improvement techniques, and achieves a function of permeability improvement on the coal seam by using the inherent stress of the coal body itself; a tensile shear force is formed inside a coal and rock mass by a high-energy water body from the horizontal slitting device in horizontal and vertical directions, the problems of high gas pressure and low air permeability of the coal seam are solved, and the development of fractures inside the coal and rock mass is achieved.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic flow chart of pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting according to an embodiment of the present disclosure;

[0019] FIG. 2 is a schematic diagram of a periodically fractured rock stratum structure and load distribution of a main roof according to an embodiment of the present disclosure;

[0020] FIG. 3 is an effect view of a compensation space created by means of hydraulic horizontal slitting of the coal seam according to an embodiment of the present disclosure; and

[0021] FIG. 4 is an effect view of pressure relief and permeability improvement on the basis of horizontal slitting of the coal seam under the action of periodic weighting according to an embodiment of the present disclosure.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] FIG. 1 is a schematic diagram of pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting according to an embodiment of the present disclosure. As shown in FIG. 1, and the present disclosure provides a method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting. The method includes:

[0023] step 100, collecting background information of coal mine production, and selecting a driving face of a high-gas low-permeability coal roadway according to the background information of coal mine production;

[0024] step 200, measuring a roof weighting step distance of the driving face of the high-gas low-permeability coal roadway in real time, calculating weighting data according to the roof weighting step distance historically collected in real time, and predicting a weighting cycle according to the weighting data;

[0025] step 300, selecting a coalface on one side of an advancing stress concentration zone during the weighting cycle;

[0026] step 400, drilling a drill rod into the coalface to reach a pre-designed position, and then obtaining a long bedding drill hole;

[0027] step 500, replacing the drill rod with a horizontal slitting device after reverse drilling, advancing the drilling to reach an initial slitting position set in the long bedding drill hole, using high-pressure water jets of the horizontal slitting device to perform fixed-point retreating horizontal cutting within a range of the drilled coal seam, and then obtaining a movement compensation space;

[0028] step 600, obtaining a fracture network according to an increased load of the coalface, an inherent stress of a coal body and the movement compensation space during periodic weighting; and

[0029] step 700, controlling excessive stressing and bulking of the coal body on the basis of the fracture network to obtain a target coal seam where the pressure relief and permeability improvement are completed.

[0030] Further, the background information of coal mine production includes: distribution characteristics of a ground stress field, the density and thickness of the coal seam, the content and pressure of a gas, and the air permeability of the coal seam.

[0031] Specifically, the weighting data includes: a rock pressure time in a first time period, and the weighting cycle, the weighting step distance and a periodic weighting peak during historical stoping.

[0032] Optionally, a cutting water pressure of the horizontal slitting device ranges from 80 to 100 MPa.

[0033] Specifically, the steps of implementing the pressure relief and permeability improvement on the basis of the horizontal slitting of the coal seam under the action of periodic weighting are as follows:

[0034] S1, obtaining the background information of coal mine production, including the distribution characteristics of the ground stress field, the density and thickness of the coal seam, the content and pressure of the gas and the air permeability of the coal seam, and selecting the driving face of the high-gas low-permeability coal roadway on the basis of geological survey of a coal mine;

[0035] S2, measuring the roof weighting step distance of the coalface at a mine site in real time, measuring a time of periodic weighting according to a theoretical equation, and obtaining data such as the rock pressure time of the coalface in the first time period and the weighting cycle, the weighting step distance and the periodic weighting peak during historical stoping, to prejudge next weighting;

[0036] S3, during the periodic weighting, a main roof rock beam breaking and collapsing along a coal wall or even in the coal wall under the self weight of the main roof rock beam and the load of an overlaying rock stratum, causing a general increase in the load of the coalface and a periodical increase in a roof pressure, and using the increased load of the coalface and the inherent stress of the coal body itself during the periodic weighting;

[0037] S4, selecting the coalface on one side of the advancing stress concentration zone when the periodic weighting is about to occur;

[0038] S5, drilling the drill rod to reach the designed position so as to form the long bedding drill hole, replacing a drill bit with the horizontal slitting device after reverse drilling, and advancing the drilling again to reach the initial slitting position set in the long bedding drill hole;

[0039] S6, the horizontal slitting device beginning to perform an operation after being placed;

[0040] S7, horizontally cutting the coal body on two horizontal sides of a drilled coal section by using the high-pressure water of 80 to 100 MPa;

[0041] S8, using the high-pressure water jets to impact a coal and rock mass, and in addition to the coal and rock mass, also impacting and fracturing an internal weak zone of the mass;

[0042] S9, the internal fragile zone of the coal and rock mass constantly extending after impacted and fractured by the water jets, causing a shear strength to be greatly reduced, and resulting in that a shear stress generated by the water jets also has a fracturing effect on the fragile zone;

[0043] S10, constantly developing the internal fractures of the coal and rock mass after the constant impact and the shearing action of the high-pressure water jets, using a high-energy water body to generate a tensile shear force inside the coal and rock mass in horizontal and vertical directions, and further developing the internal fractures of the coal and rock mass when the tensile shear force exceeds a stress limit value of the coal body;

[0044] S11, the high-energy water entering the coal body through the fractures to constantly extend the internal fractures of the coal body under the action of a wedge force generated by pore pressure water, where the coal body is fractured when the tensile stress force exceeds a tensile fracture limit of the coal body;

[0045] S12, when the high-speed water jets reach the inside of the coal body, first generating a water hammer pressure to crush the coal and rock mass, and thus forming shear cracks; meanwhile, generating a large number of tensile cracks in the coal body with a low tensile strength under the tensile stress. Thereafter, due to the continued action of a stagnation pressure, further crushing and spalling the coal body to form corrosion pits, and then forming a horizontal slit perpendicular to the drill hole;

[0046] S13, withdrawing the drill rod after the slitting, and creating and using the horizontal space formed by the horizontal slitting as the movement compensation space for the coal body within the larger range;

[0047] S14, during the periodic weighting, causing a sudden pressure increase in a coalface pressure by the collapse of a main roof, generating a stress downwardly perpendicular to the coal seam, taking into account a change in a coal seam stress under the action of the inherent stress of the coal seam itself and the previous hydraulic slitting, continuously extending and developing the internal fractures of the coal body under the action of the wedge force generated by the pore pressure water, forming the horizontal slit, thus creating the horizontal space to serve as the movement compensation space for the coal body within the larger range, and ultimately reaching the stress limit of the coal body to produce the effect of overall cracking or even gradual overall collapse of the coal seam;

[0048] S15, while further effectively releasing outstanding potential, mitigating a phenomenon of local stress concentration in the coal seam to the maximum extent, promoting the pressure reduction of a coal reservoir, and completing the pressure relief on the coal seam; and

[0049] S16, when next periodic weighting occurs, repeating the above-described process to change an original stress state of the coal body and the opening degree of the fractures, and thus enhancing the air permeability of the coal seam and improving the efficiency of gas extraction.

[0050] Specifically, FIG. 2 illustrates steps S1-S4, during the periodic weighting, the main roof rock beam fractures and collapses along the coal wall or even in the coal wall under the self weight of the main roof rock beam and the load of the overlaying rock stratum, causing a general increase in the load of the coalface and a periodical increase in a roof pressure, and the increased load of the coalface and the inherent stress of the coal body itself are used at the time of the periodic weighting; Arrows indicate the load of the overlaying rock stratum. FIG. 3 illustrates steps S5-S13, the drill rod is used to drill to the designed position of the coal seam so as to form the long drill hole, the drill bit is replaced with the horizontal slitting device after reverse drilling, and once the high-pressure water jets from two ends of the horizontal slitting device act on the coal body (directions indicated by the arrows in the figure are double slit directions, and a slitting direction is a horizontal direction), the horizontal slitting begins; and after the completion of each slitting, reverse drilling is performed until a next slitting position is reached, and the horizontal slitting operation is repeated until the effective horizontal compensation space is created in the coal seam. FIG. 4 illustrates steps S14-S16, at an earlier stage, the number and connectivity (microscopic fractures) of flow guide channels inside the coal seam are increased by means of fixed-point retreating horizontal cutting of the high-pressure water jets within the drilling and extraction range of the drilled coal seam, and slits generated in the coal reservoir after the slitting form a sufficient pressure relief space, the fracture network is then formed by using the increased load of the coalface and the inherent stress of the coal body itself during periodic weighting and by virtue of an unloading movement space created by the horizontal slitting, the coal body is further bulked, and ultimately the stress limit of the coal body is reached to produce the effect of overall cracking or even gradual overall collapse of the coal seam.

[0051] The present disclosure has the following beneficial effects.

[0052] On the basis of the principle of protective layer mining, this method produces a huge stress effect on the coal seam by using the increased load of the coalface and the inherent stress of the coal body itself during the periodic weighting, then creates the effective horizontal compensation space by using a hydraulic slitting technique to perform space compensation, so that the shortcomings (blasting and cracking, hydraulic cracking and the like that spread towards the surrounding with the coal seam hole as the center, but ignore the intrinsic stress of the coal body itself) of conventional coal seam permeability improvement techniques are overcome; and after using the constant impact and shearing action of the high-pressure water jets, a horizontal compensation space is formed by means of slitting, the coal seam is displaced above the horizontal slit, the coal seam loses the effect of a vertical stress below the slit, and the coal seam stress still exists on the left and right sides of the slit, causing the expansion of the lower seam to generate an upward displacement, so that the internal fractures of the coal and rock mass constantly develop; the high-energy water body generates the tensile shear force inside the coal and rock mass in the horizontal and vertical directions, and the internal fractures of the coal and rock mass further develop when the tensile shear force exceeds the stress limit value of the coal body, so that the gas pressure of the coal seam is reduced, the air permeability of the coal seam is improved, meanwhile, it is also possible to reduce the gas content of an adjacent protected high-gas or outburst-risk coal seam, an outburst risk thereof is eliminated, and subsequent coal seam mining is facilitated. The method is safe, easy to control and high in repeatability. This method has the advantages that the roof weighting is periodical, the water jets are efficient, clean, low in heat and low in vibration in the process of impacting and crushing a coal rock material, etc. The method has great theoretical and practical significance for further improving a extraction technology, perfecting two theories of prevention and control, promoting the development of dynamic disaster science in mines, improving the advancing speed of the coal roadway, perfecting a fracturing mechanism of the coal seam in coal roadway, reducing the production costs of the coal mine and decreasing safety accidents.

Examples

Embodiment Construction

[0022]FIG. 1 is a schematic diagram of pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting according to an embodiment of the present disclosure. As shown in FIG. 1, and the present disclosure provides a method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting. The method includes:[0023]step 100, collecting background information of coal mine production, and selecting a driving face of a high-gas low-permeability coal roadway according to the background information of coal mine production;[0024]step 200, measuring a roof weighting step distance of the driving face of the high-gas low-permeability coal roadway in real time, calculating weighting data according to the roof weighting step distance historically collected in real time, and predicting a weighting cycle according to the weighting data;[0025]step 300, sele...

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application claims the benefit and priority of Chinese Patent Application No. 202411661197.3 filed with the China National Intellectual Property Administration on Nov. 19, 2024, the disclosure of which is incorporated by reference herein in its entirety as part of the present application.TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of permeability improvement and efficient gas extraction of coal seams, and in particular to a method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting.BACKGROUND

[0003] As shallow coal resources are being depleted, mine exploration gradually develops to access to deep reservoir areas of coal seams. The gas content of the coal seam is proportional to the thickness of an overlying bedrock of the coal seam, and therefore an original low-gas mine gradually becomes a high-gas mine depending on the amount of gas emission in the mine excavation process. Meanwhile, deep mines generally have the technical difficulty of a poor extraction effect caused by the poor permeability of the coal seams, and this coal mine gas problem restricts the safe production of China's coal mines in the long term. Essentially, a coal body cracking and destruction process is to take relevant measures to disorder and fracture a basic structure of a coal body, in order to achieve a cracking effect. This process is complex and changes dynamically. The key to preventing and controlling gas accidents lies in pressure relief on the coal seams by means of technical methods. Technical measures mainly include depressurizing exploitation, hydraulic cracking (such as hydraulic fracturing, hydraulic slitting, or hydraulic punching), deep-hole pre-splitting blasting, CO2 blasting and cracking, and the like on a protective layer.

[0004] The above-mentioned methods typically focus on cracking with hole as the center towards the surrounding, but ignore the intrinsic stress of the coal body itself, and do on rely on the self weight of a main roof, the load of an overlaying rock stratum and a downward impact load formed by roof collapse within a certain span range during the periodic weighting of the coal mine. Especially, these methods do not make the use of the principle of protective layer mining in a coal roadway, and do not create and use a horizontal space, which serves as a movement compensation space for the coal body within a larger range, to achieve overall cracking of the coal seam, resulting in a poor effect.SUMMARY

[0005] A method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting includes the steps:

[0006] collecting background information of coal mine production, and selecting a driving face of a high-gas low-permeability coal roadway according to the background information of coal mine production;

[0007] measuring a roof weighting step distance of the driving face of the high-gas low-permeability coal roadway in real time, calculating weighting data according to the roof weighting step distance historically collected in real time, and predicting a weighting cycle according to the weighting data;

[0008] selecting a coalface on one side of an advancing stress concentration zone in the weighting cycle;

[0009] Drilling a drill rod into the coalface to reach a pre-designed position, and then obtaining a long bedding drill hole;

[0010] replacing the drill rod with a horizontal slitting device after reverse drilling, advancing the drilling to reach an initial slitting position set in the long bedding drill hole, using high-pressure water jets of the horizontal slitting device to perform fixed-point retreating horizontal cutting within a range of the drilled coal seam, and then obtaining a movement compensation space;

[0011] obtaining a fracture network according to an increased load of the coalface, an inherent stress of a coal body and the movement compensation space during periodic weighting; and

[0012] controlling excessive stressing and bulking of the coal body on the basis of the fracture network to obtain a target coal seam where the pressure relief and permeability improvement are completed.

[0013] Preferably, the background information of coal mine production includes: distribution characteristics of a ground stress field, the density and thickness of the coal seam, the content and pressure of a gas, and the air permeability of the coal seam.

[0014] Preferably, the weighting data includes: a rock pressure time in a first time period, and the weighting cycle, the weighting step distance and a periodic weighting peak during historical stoping

[0015] Preferably, a cutting water pressure of the horizontal slitting device ranges from 80 to 100 MPa.

[0016] The present disclosure has the following technical effects.

[0017] The present disclosure provides a method for pressure relief and permeability improvement on the basis of the horizontal slitting of the coal seam under the action of periodic weighting, uses a huge stress effect on the coal seam and a hydraulic slitting technique by means of the increased load of the coalface and the inherent stress of the coal body itself during periodic weighting, overcomes the shortcomings of conventional coal seam permeability improvement techniques, and achieves a function of permeability improvement on the coal seam by using the inherent stress of the coal body itself; a tensile shear force is formed inside a coal and rock mass by a high-energy water body from the horizontal slitting device in horizontal and vertical directions, the problems of high gas pressure and low air permeability of the coal seam are solved, and the development of fractures inside the coal and rock mass is achieved.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic flow chart of pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting according to an embodiment of the present disclosure;

[0019] FIG. 2 is a schematic diagram of a periodically fractured rock stratum structure and load distribution of a main roof according to an embodiment of the present disclosure;

[0020] FIG. 3 is an effect view of a compensation space created by means of hydraulic horizontal slitting of the coal seam according to an embodiment of the present disclosure; and

[0021] FIG. 4 is an effect view of pressure relief and permeability improvement on the basis of horizontal slitting of the coal seam under the action of periodic weighting according to an embodiment of the present disclosure.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] FIG. 1 is a schematic diagram of pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting according to an embodiment of the present disclosure. As shown in FIG. 1, and the present disclosure provides a method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting. The method includes:

[0023] step 100, collecting background information of coal mine production, and selecting a driving face of a high-gas low-permeability coal roadway according to the background information of coal mine production;

[0024] step 200, measuring a roof weighting step distance of the driving face of the high-gas low-permeability coal roadway in real time, calculating weighting data according to the roof weighting step distance historically collected in real time, and predicting a weighting cycle according to the weighting data;

[0025] step 300, selecting a coalface on one side of an advancing stress concentration zone during the weighting cycle;

[0026] step 400, drilling a drill rod into the coalface to reach a pre-designed position, and then obtaining a long bedding drill hole;

[0027] step 500, replacing the drill rod with a horizontal slitting device after reverse drilling, advancing the drilling to reach an initial slitting position set in the long bedding drill hole, using high-pressure water jets of the horizontal slitting device to perform fixed-point retreating horizontal cutting within a range of the drilled coal seam, and then obtaining a movement compensation space;

[0028] step 600, obtaining a fracture network according to an increased load of the coalface, an inherent stress of a coal body and the movement compensation space during periodic weighting; and

[0029] step 700, controlling excessive stressing and bulking of the coal body on the basis of the fracture network to obtain a target coal seam where the pressure relief and permeability improvement are completed.

[0030] Further, the background information of coal mine production includes: distribution characteristics of a ground stress field, the density and thickness of the coal seam, the content and pressure of a gas, and the air permeability of the coal seam.

[0031] Specifically, the weighting data includes: a rock pressure time in a first time period, and the weighting cycle, the weighting step distance and a periodic weighting peak during historical stoping.

[0032] Optionally, a cutting water pressure of the horizontal slitting device ranges from 80 to 100 MPa.

[0033] Specifically, the steps of implementing the pressure relief and permeability improvement on the basis of the horizontal slitting of the coal seam under the action of periodic weighting are as follows:

[0034] S1, obtaining the background information of coal mine production, including the distribution characteristics of the ground stress field, the density and thickness of the coal seam, the content and pressure of the gas and the air permeability of the coal seam, and selecting the driving face of the high-gas low-permeability coal roadway on the basis of geological survey of a coal mine;

[0035] S2, measuring the roof weighting step distance of the coalface at a mine site in real time, measuring a time of periodic weighting according to a theoretical equation, and obtaining data such as the rock pressure time of the coalface in the first time period and the weighting cycle, the weighting step distance and the periodic weighting peak during historical stoping, to prejudge next weighting;

[0036] S3, during the periodic weighting, a main roof rock beam breaking and collapsing along a coal wall or even in the coal wall under the self weight of the main roof rock beam and the load of an overlaying rock stratum, causing a general increase in the load of the coalface and a periodical increase in a roof pressure, and using the increased load of the coalface and the inherent stress of the coal body itself during the periodic weighting;

[0037] S4, selecting the coalface on one side of the advancing stress concentration zone when the periodic weighting is about to occur;

[0038] S5, drilling the drill rod to reach the designed position so as to form the long bedding drill hole, replacing a drill bit with the horizontal slitting device after reverse drilling, and advancing the drilling again to reach the initial slitting position set in the long bedding drill hole;

[0039] S6, the horizontal slitting device beginning to perform an operation after being placed;

[0040] S7, horizontally cutting the coal body on two horizontal sides of a drilled coal section by using the high-pressure water of 80 to 100 MPa;

[0041] S8, using the high-pressure water jets to impact a coal and rock mass, and in addition to the coal and rock mass, also impacting and fracturing an internal weak zone of the mass;

[0042] S9, the internal fragile zone of the coal and rock mass constantly extending after impacted and fractured by the water jets, causing a shear strength to be greatly reduced, and resulting in that a shear stress generated by the water jets also has a fracturing effect on the fragile zone;

[0043] S10, constantly developing the internal fractures of the coal and rock mass after the constant impact and the shearing action of the high-pressure water jets, using a high-energy water body to generate a tensile shear force inside the coal and rock mass in horizontal and vertical directions, and further developing the internal fractures of the coal and rock mass when the tensile shear force exceeds a stress limit value of the coal body;

[0044] S11, the high-energy water entering the coal body through the fractures to constantly extend the internal fractures of the coal body under the action of a wedge force generated by pore pressure water, where the coal body is fractured when the tensile stress force exceeds a tensile fracture limit of the coal body;

[0045] S12, when the high-speed water jets reach the inside of the coal body, first generating a water hammer pressure to crush the coal and rock mass, and thus forming shear cracks; meanwhile, generating a large number of tensile cracks in the coal body with a low tensile strength under the tensile stress. Thereafter, due to the continued action of a stagnation pressure, further crushing and spalling the coal body to form corrosion pits, and then forming a horizontal slit perpendicular to the drill hole;

[0046] S13, withdrawing the drill rod after the slitting, and creating and using the horizontal space formed by the horizontal slitting as the movement compensation space for the coal body within the larger range;

[0047] S14, during the periodic weighting, causing a sudden pressure increase in a coalface pressure by the collapse of a main roof, generating a stress downwardly perpendicular to the coal seam, taking into account a change in a coal seam stress under the action of the inherent stress of the coal seam itself and the previous hydraulic slitting, continuously extending and developing the internal fractures of the coal body under the action of the wedge force generated by the pore pressure water, forming the horizontal slit, thus creating the horizontal space to serve as the movement compensation space for the coal body within the larger range, and ultimately reaching the stress limit of the coal body to produce the effect of overall cracking or even gradual overall collapse of the coal seam;

[0048] S15, while further effectively releasing outstanding potential, mitigating a phenomenon of local stress concentration in the coal seam to the maximum extent, promoting the pressure reduction of a coal reservoir, and completing the pressure relief on the coal seam; and

[0049] S16, when next periodic weighting occurs, repeating the above-described process to change an original stress state of the coal body and the opening degree of the fractures, and thus enhancing the air permeability of the coal seam and improving the efficiency of gas extraction.

[0050] Specifically, FIG. 2 illustrates steps S1-S4, during the periodic weighting, the main roof rock beam fractures and collapses along the coal wall or even in the coal wall under the self weight of the main roof rock beam and the load of the overlaying rock stratum, causing a general increase in the load of the coalface and a periodical increase in a roof pressure, and the increased load of the coalface and the inherent stress of the coal body itself are used at the time of the periodic weighting; Arrows indicate the load of the overlaying rock stratum. FIG. 3 illustrates steps S5-S13, the drill rod is used to drill to the designed position of the coal seam so as to form the long drill hole, the drill bit is replaced with the horizontal slitting device after reverse drilling, and once the high-pressure water jets from two ends of the horizontal slitting device act on the coal body (directions indicated by the arrows in the figure are double slit directions, and a slitting direction is a horizontal direction), the horizontal slitting begins; and after the completion of each slitting, reverse drilling is performed until a next slitting position is reached, and the horizontal slitting operation is repeated until the effective horizontal compensation space is created in the coal seam. FIG. 4 illustrates steps S14-S16, at an earlier stage, the number and connectivity (microscopic fractures) of flow guide channels inside the coal seam are increased by means of fixed-point retreating horizontal cutting of the high-pressure water jets within the drilling and extraction range of the drilled coal seam, and slits generated in the coal reservoir after the slitting form a sufficient pressure relief space, the fracture network is then formed by using the increased load of the coalface and the inherent stress of the coal body itself during periodic weighting and by virtue of an unloading movement space created by the horizontal slitting, the coal body is further bulked, and ultimately the stress limit of the coal body is reached to produce the effect of overall cracking or even gradual overall collapse of the coal seam.

[0051] The present disclosure has the following beneficial effects.

[0052] On the basis of the principle of protective layer mining, this method produces a huge stress effect on the coal seam by using the increased load of the coalface and the inherent stress of the coal body itself during the periodic weighting, then creates the effective horizontal compensation space by using a hydraulic slitting technique to perform space compensation, so that the shortcomings (blasting and cracking, hydraulic cracking and the like that spread towards the surrounding with the coal seam hole as the center, but ignore the intrinsic stress of the coal body itself) of conventional coal seam permeability improvement techniques are overcome; and after using the constant impact and shearing action of the high-pressure water jets, a horizontal compensation space is formed by means of slitting, the coal seam is displaced above the horizontal slit, the coal seam loses the effect of a vertical stress below the slit, and the coal seam stress still exists on the left and right sides of the slit, causing the expansion of the lower seam to generate an upward displacement, so that the internal fractures of the coal and rock mass constantly develop; the high-energy water body generates the tensile shear force inside the coal and rock mass in the horizontal and vertical directions, and the internal fractures of the coal and rock mass further develop when the tensile shear force exceeds the stress limit value of the coal body, so that the gas pressure of the coal seam is reduced, the air permeability of the coal seam is improved, meanwhile, it is also possible to reduce the gas content of an adjacent protected high-gas or outburst-risk coal seam, an outburst risk thereof is eliminated, and subsequent coal seam mining is facilitated. The method is safe, easy to control and high in repeatability. This method has the advantages that the roof weighting is periodical, the water jets are efficient, clean, low in heat and low in vibration in the process of impacting and crushing a coal rock material, etc. The method has great theoretical and practical significance for further improving a extraction technology, perfecting two theories of prevention and control, promoting the development of dynamic disaster science in mines, improving the advancing speed of the coal roadway, perfecting a fracturing mechanism of the coal seam in coal roadway, reducing the production costs of the coal mine and decreasing safety accidents.

Examples

Embodiment Construction

[0022]FIG. 1 is a schematic diagram of pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting according to an embodiment of the present disclosure. As shown in FIG. 1, and the present disclosure provides a method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting. The method includes:[0023]step 100, collecting background information of coal mine production, and selecting a driving face of a high-gas low-permeability coal roadway according to the background information of coal mine production;[0024]step 200, measuring a roof weighting step distance of the driving face of the high-gas low-permeability coal roadway in real time, calculating weighting data according to the roof weighting step distance historically collected in real time, and predicting a weighting cycle according to the weighting data;[0025]step 300, sele...

Claims

1. A method for pressure relief and permeability improvement on the basis of horizontal slitting of a coal seam under the action of periodic weighting, comprising:collecting background information of coal mine production, and selecting a driving face of a high-gas low-permeability coal roadway according to the background information of coal mine production;measuring a roof weighting step distance of the driving face of the high-gas low-permeability coal roadway in real time, calculating weighting data according to the roof weighting step distance historically collected in real time, and predicting a weighting cycle according to the weighting data; wherein the weighting data comprises: a rock pressure time in a first time period, and the weighting cycle, the weighting step distance and a periodic weighting peak during historical stoping;selecting a coalface on one side of an advancing stress concentration zone during the weighting cycle;drilling a drill rod into the coalface to reach a pre-designed position, and then obtaining a long bedding drill hole;replacing the drill rod with a horizontal slitting device after reverse drilling, advancing the drilling to reach an initial slitting position set in the long bedding drill hole, using high-pressure water jets of the horizontal slitting device to perform fixed-point retreating horizontal cutting within a range of the drilled coal seam, and then obtaining a movement compensation space;obtaining a fracture network according to an increased load of the coalface, an inherent stress of a coal body where the coalface is located, and the movement compensation space during periodic weighting; andcontrolling excessive stressing and bulking of the coal body on the basis of the fracture network to obtain a target coal seam where the pressure relief and permeability improvement are completed.

2. The method for pressure relief and permeability improvement on the basis of horizontal slitting of the coal seam under the action of periodic weighting according to claim 1, wherein the background information of coal mine production comprises: distribution characteristics of a ground stress field, the density and thickness of the coal seam, the content and pressure of a gas, and the air permeability of the coal seam.

3. (canceled)4. The method for pressure relief and permeability improvement on the basis of horizontal slitting of the coal seam under the action of periodic weighting according to claim 1, wherein a cutting water pressure of the horizontal slitting device ranges from 80 to 100 MPa.

Images