Coal seam horizontal kerf pressure relief and permeability increase method based on periodic weighting effect

Abstract

The invention belongs to the technical field of coal seam permeability increasing and efficient gas extraction, and provides a coal seam horizontal joint cutting pressure relief permeability increasing method based on the periodic weighting effect. Comprising the steps of coal mine production background data collection, high-gas low-permeability coal roadway driving face selection, real-time roof weighting step measurement and weighting period prediction, coal face selection, bedding long drill hole drilling and hydraulic horizontal slotting. According to the method, the high-pressure water jet is horizontally cut in a fixed-point retreating mode within the range of the extraction drilling coal seam, so that the number and connectivity of flow guide channels in the coal seam are increased, and a sufficient pressure relief space is formed by slots generated in a coal reservoir after slotting; and a crack network is formed by utilizing increased load of a coal face during periodic weighting and inherent stress of the coal body and by means of an unloading moving space created by horizontal slotting, so that the coal body is further broken and expanded, the gas pressure of the coal seam is reduced, and the gas permeability of the coal seam is improved.

Description

Technical Field

[0001] The invention relates to the technical field of coal seam permeability enhancement and gas efficient extraction, and in particular to a coal seam horizontal slit pressure relief and permeability enhancement method based on periodic pressure action. Background Art

[0002] As the shallow coal resources are mined out, the development and mining of mines gradually enters the deep buried areas of coal seams. The gas content of coal seams is directly proportional to the thickness of the overlying bedrock. The gas outburst during mining has gradually changed from low-gas mines to high-gas mines. At the same time, deep mines generally have the technical problem of poor extraction effect due to poor coal seam permeability. The coal mine gas problem will restrict the safe production of coal mines in my country for a long time. The essence of the coal body fracturing and destruction process is to take relevant measures to disrupt the essential structure of the coal body and achieve the fracturing effect. The process is complex and shows dynamic changes. The key to preventing and controlling gas accidents is to take technical methods to decompress the coal seams. The main technical measures include protective layer decompression mining, hydraulic fracturing (hydraulic fracturing, hydraulic cutting, hydraulic punching), deep hole pre-splitting blasting and CO2 blasting fracturing.

[0003] The above methods basically focus on fracturing by expanding from the hole to the surrounding areas, but ignore the inherent stress of the coal body itself, and do not make use of the deadweight of the old roof, the load of the overlying rock strata, and the downward impact load formed by the collapse of the roof within a certain span during the coal mine cycle. In particular, in the coal roadway, the protective layer mining principle is not used, and horizontal space is not created and utilized as a mobile compensation space in a larger range of the coal body to achieve overall fracturing of the coal seam, resulting in poor results. Summary of the invention

[0004] A method for unloading and enhancing permeability of coal seam horizontal slits under periodic pressure, comprising:

[0005] Collecting coal mine production background information, and selecting a high-gas and low-permeability coal tunnel excavation working face based on the coal mine production background information;

[0006] Determine the real-time roof pressure step distance of the high-gas and low-permeability coal roadway excavation working face, calculate the pressure data according to the real-time roof pressure step distance collected historically, and predict the pressure cycle according to the pressure data;

[0007] In the pressure cycle, a coal mining face on one side of the advanced stress concentration zone is selected;

[0008] Drilling to a pre-designed position using a drill rod on the coal mining face to obtain a long borehole along the layer;

[0009] After the drill is withdrawn, the drill rod is replaced with a horizontal slotting device, and the drill is advanced to the starting slotting position set in the long borehole in the bed, and the high-pressure water jet of the horizontal slotting device is used to perform fixed-point backward horizontal cutting within the range of the drilled coal seam to obtain a moving compensation space;

[0010] According to the increased load of the coal mining face during periodic pressure, the inherent stress of the coal body and the movement compensation space, a fracture network is obtained;

[0011] Based on the fracture network, the coal body is controlled to be over-pressurized and expand, so as to obtain the target coal seam with pressure relief and permeability enhancement.

[0012] Preferably, the coal mine production background data includes: distribution characteristics of the geostress field, coal seam density and thickness, gas content and pressure, and coal seam permeability.

[0013] Preferably, the pressure data include: the mine pressure time in the first period, the pressure cycle during historical mining, the pressure step distance and the cycle pressure peak value.

[0014] Preferably, the cutting water pressure range of the horizontal slitting device is 80 to 100 MPa.

[0015] The present invention discloses the following technical effects:

[0016] The present invention provides a method for unloading and increasing the permeability of coal seams by horizontal cutting under periodic pressure. The method solves the shortcomings of traditional coal seam permeability increasing technology by combining the increased load on the working face during periodic pressure, the huge stress on the coal seam formed by the inherent stress of the coal body itself, and the hydraulic cutting technology, and realizes the function of increasing the permeability of coal seams by utilizing the inherent stress of the coal body itself. The horizontal and vertical tensile shear forces formed by the high-energy water body of the horizontal cutting device inside the coal rock mass solve the problems of high gas pressure and low permeability of the coal seam, and realizes the development of cracks in the coal rock mass. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a process for unloading and enhancing permeability of coal seam horizontal slits under periodic pressure provided by an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of the basic top periodic fractured rock layer structure and load distribution provided by an embodiment of the present invention;

[0019] Figure 3 The effect diagram of creating compensation space for hydraulic horizontal cutting of coal seams provided in the embodiment of the present invention;

[0020] Figure 4 A diagram showing the pressure relief and permeability enhancement effect of horizontal slits in coal seams under periodic pressure provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0021] Figure 1 A schematic diagram of a process flow of coal seam horizontal cutting pressure relief and permeability enhancement based on periodic pressure provided by an embodiment of the present invention is shown in FIG. Figure 1 As shown, the present invention provides a method for unloading pressure and increasing permeability of coal seam horizontal slits under periodic pressure, comprising:

[0022] Step 100: Collecting coal mine production background data, and selecting a high-gas and low-permeability coal roadway excavation working face according to the coal mine production background data;

[0023] Step 200: determining the real-time roof pressure step distance of the high-gas and low-permeability coal roadway excavation working face, calculating the pressure data according to the real-time roof pressure step distance collected historically, and predicting the pressure cycle according to the pressure data;

[0024] Step 300: selecting a coal mining face on one side of the advanced stress concentration zone within a pressure cycle;

[0025] Step 400: Drilling to a pre-designed position using a drill rod in the coal mining face to obtain a long borehole along the layer;

[0026] Step 500: After the drill is withdrawn, the drill rod is replaced with a horizontal slotting device, and the drill is advanced to the starting slotting position set in the long borehole in the bed. The high-pressure water jet of the horizontal slotting device is used to perform a fixed-point backward horizontal cutting within the range of the drilled coal seam to obtain a movement compensation space;

[0027] Step 600: obtaining a fracture network according to the increased load on the coal mining face during periodic pressure, the inherent stress of the coal body, and the movement compensation space;

[0028] Step 700: Based on the fracture network, control the coal body to be over-pressurized and expand, and obtain the target coal seam with pressure relief and permeability enhancement.

[0029] Furthermore, the coal mine production background data includes: distribution characteristics of the ground stress field, coal seam density and thickness, gas content and pressure, and coal seam permeability.

[0030] Specifically, the pressure data include: the mine pressure time in the first period, the pressure cycle during historical mining, the pressure step distance and the cycle pressure peak value.

[0031] Optionally, the cutting water pressure range of the horizontal cutting device is: 80 to 100 MPa.

[0032] Specifically, the steps for implementing the pressure relief and permeability enhancement of the horizontal seam of the coal seam under the action of periodic pressure are as follows:

[0033] S1: Obtain the background data of coal mine production, including the distribution characteristics of the ground stress field, the density and thickness of the coal seam, the gas content and pressure, and the permeability of the coal seam. According to the geological survey of the coal mine, select the coal tunneling working face with high gas and low permeability;

[0034] S2: Real-time detection of roof pressure step distance at the working face of the mine site, and measurement of periodic pressure time based on theoretical formula, to obtain data such as the mine pressure time of the working face in the first period, the pressure cycle during historical mining, pressure step distance, and periodic pressure peak value, so as to predict the next pressure;

[0035] S3: During the periodic pressure, the old roof rock beams will break and collapse along the coal wall or even in the coal wall under the action of their own weight and the load of the overlying rock strata. The load on the working face will generally increase, and the roof pressure will increase periodically. With the help of the increased load on the working face during the periodic pressure and the inherent stress of the coal body itself;

[0036] S4: Select the coal mining face close to the advanced stress concentration area during periodic pressure;

[0037] S5: Use a drill rod to drill to the designed position to form a long borehole in the layer. After the drill is withdrawn, the drill bit is replaced with a horizontal slotting device, and the drill is again drilled to the designed starting slot position in the long borehole in the layer;

[0038] S6: After the horizontal slitting device is placed, the slitting device starts to operate;

[0039] S7: Use 80-100 MPa high pressure water to horizontally cut the coal bodies on both sides of the drilled coal hole section;

[0040] S8: Using high-pressure water jets to impact the coal-rock mass will not only impact the coal-rock mass, but also cause impact damage to the weak areas inside it;

[0041] S9: After the water jet impact damage, the fragile area inside the coal rock body continues to expand, the shear strength is greatly reduced, and the shear stress generated by the water jet will also have a destructive effect on the fragile area;

[0042] S10: After continuous impact and shearing by high-pressure water jets, cracks in the coal and rock mass continue to develop. High-energy water will form horizontal and vertical tensile shear forces inside the coal and rock mass. When the tensile shear forces exceed the stress limit of the coal mass, cracks in the coal and rock mass will further develop.

[0043] S11: High-energy water enters the coal body through cracks. The cracks inside the coal body continue to expand under the action of the wedge force formed by the pore pressure water. When the tensile stress exceeds the tensile failure limit of the coal body, the coal body will be destroyed.

[0044] S12: When the high-speed water jet reaches the inside of the coal body, it first generates water hammer pressure, which breaks the coal rock and generates shear cracks. At the same time, the coal body with low tensile strength generates a large number of tensile cracks under the action of tensile stress. After that, due to the continuous action of stagnation pressure, the coal body further breaks and peels off, forming erosion pits, and then forming a horizontal slot perpendicular to the drill hole;

[0045] S13: After the cutting is completed, the drill rod is pulled out to create and utilize the horizontal space formed by the horizontal cutting as a movement compensation space within a larger range of the coal body;

[0046] S14: When the pressure comes periodically, the collapse of the old roof will cause the pressure of the working face to increase suddenly, forming stress perpendicular to the coal seam. Considering the inherent stress of the coal seam itself and the effect of hydraulic cutting in the early stage, the stress of the coal seam changes. The cracks inside the coal body continue to expand and develop under the wedge force formed by the pore pressure water, forming horizontal seams, creating horizontal space as a movement compensation space in a larger range of the coal body. Finally, the pressure of the coal body reaches the limit, resulting in overall fracturing and even the gradual collapse of the coal seam.

[0047] S15: While further effectively releasing the potential, it also alleviates the phenomenon of local stress concentration in the coal seam to the maximum extent, promotes the reduction of coal reservoir pressure, and completes the decompression of the coal seam.

[0048] S16: When the next cycle of pressure comes, repeat the above process to change the original stress state of the coal body and the opening degree of the cracks, thereby enhancing the permeability of the coal seam and improving the gas extraction efficiency.

[0049] Specifically, Figure 2 Corresponding to S1-S4, during the period of cyclic pressure, the old roof rock beam will break and collapse along the coal wall or even in the coal wall under the action of its own weight and the load of the overlying strata. The load on the working face will generally increase, and the roof pressure will increase periodically, relying on the increased load on the working face during cyclic pressure and the inherent stress of the coal body itself; the arrows represent the load of the overlying strata. Figure 3 Corresponding to S5-S13, a drill rod is used to drill to the designed position of the coal seam to form a long borehole. After the drill is withdrawn, the drill bit is replaced with a horizontal slotter. High-pressure water jets are ejected from both ends of the horizontal slotter to act on the coal body (the arrow in the figure indicates the direction of the double grooves, and the cutting direction is horizontal), and horizontal slotting can begin. After each slotting is completed, the drill is withdrawn to the next slotting position, and the horizontal slotting operation is repeated until an effective horizontal compensation space is created in the coal seam. Figure 4Corresponding to S14-S16, in the early stage, high-pressure water jets were used to perform fixed-point backward horizontal cutting within the range of the coal seam to increase the number and connectivity (micro cracks) of diversion channels inside the coal seam. The seams generated in the coal reservoir after cutting formed sufficient pressure relief space. The increased load on the coal mining face during periodic pressure and the inherent stress of the coal body were then used to form a crack network with the help of the unloading movement space created by the horizontal cutting, which further caused the coal body to break and swell. Finally, the coal body was compressed to the limit, resulting in overall fracturing and even the gradual collapse of the coal seam.

[0050] The beneficial effects of the present invention are as follows:

[0051] This method uses the principle of protective layer mining, with the help of the increased load on the working face during periodic pressure, combined with the inherent stress of the coal body itself, to form a huge stress effect on the coal seam, and then uses hydraulic cutting technology to create an effective horizontal compensation space for spatial compensation, overcoming the shortcomings of traditional coal seam permeability enhancement technology (blasting fracturing, hydraulic fracturing, etc. are based on the coal seam with the hole as the center to spread to the surrounding area for fracturing, while ignoring the inherent stress of the coal body itself); after the continuous impact and shearing of high-pressure water jets, a horizontal compensation space is cut out, and the coal seam above the horizontal seam produces a displacement , the coal seam below loses the effect of vertical stress, and the stress of the coal seams on the left and right sides of the seam still exists, causing the expansion of the lower coal seam to produce an upward displacement, so that the internal cracks of the coal rock mass continue to develop, and the high-energy water body will form horizontal and vertical tensile shear forces inside the coal rock mass. When the tensile shear force exceeds the force limit of the coal body, the internal cracks of the coal rock mass will further develop, greatly reducing the gas pressure of the coal seam and improving the permeability of the coal seam. At the same time, it can also reduce the gas content of the adjacent protected high-gas or dangerous coal seams, eliminate their danger of outbursts, and facilitate subsequent coal seam mining. This method is safe, easy to control, and highly repeatable. It has the characteristics of periodicity of roof pressure and high efficiency, cleanliness, low heat and low vibration of water jets in the process of impacting and crushing coal and rock materials. It has important theoretical and practical significance for further improving the extraction process, improving the two prevention and control theoretical systems, promoting the development of mine dynamic disasters, increasing the speed of coal roadway excavation, improving the cracking mechanism of coal roadway coal seams, reducing coal mine production costs and reducing the occurrence of safety accidents.

Claims

1. A method for unloading pressure and increasing permeability of coal seam horizontal slits under periodic pressure, characterized in that: include: Collecting coal mine production background data, and selecting a high-gas and low-permeability coal tunnel excavation working face based on the coal mine production background data; Determine the real-time roof pressure step distance of the high-gas and low-permeability coal roadway excavation working face, calculate the pressure data according to the real-time roof pressure step distance collected historically, and predict the pressure cycle according to the pressure data; In the pressure cycle, a coal mining face on one side of the advanced stress concentration zone is selected; Drilling to a pre-designed position using a drill rod on the coal mining face to obtain a long borehole along the layer; After the drill is withdrawn, the drill rod is replaced with a horizontal slotting device, and the drill is advanced to the starting slotting position set in the long borehole in the bed, and the high-pressure water jet of the horizontal slotting device is used to perform fixed-point backward horizontal cutting within the range of the drilled coal seam to obtain a moving compensation space; According to the increased load of the coal mining face during periodic pressure, the inherent stress of the coal body and the movement compensation space, a fracture network is obtained; Based on the fracture network, the coal body is controlled to be over-pressurized and expand, so as to obtain the target coal seam with pressure relief and permeability enhancement.

2. The method for unloading pressure and increasing permeability of coal seam horizontal slits under periodic pressure according to claim 1 is characterized in that: The coal mine production background data include: distribution characteristics of ground stress field, coal seam density and thickness, gas content and pressure, and coal seam permeability.

3. The method for unloading pressure and increasing permeability of coal seam horizontal slits under periodic pressure according to claim 1 is characterized in that: The pressure data include: the mine pressure time in the first period, the pressure cycle during historical mining, the pressure step distance and the cycle pressure peak value.

4. The method for unloading pressure and increasing permeability of coal seam horizontal slits under periodic pressure according to claim 1 is characterized in that: The cutting water pressure range of the horizontal slitting device is 80 to 100 MPa.

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