Coal mine gas control and regional outburst elimination method

Abstract

The application discloses a coal mine gas treatment and regional outburst elimination method, which comprises the following steps: arranging and constructing a horizontal long borehole in a target coal seam or a top and bottom plate of a coal seam in a mining face or a coal lane strip area underground; using a fracturing pipeline to establish a pipeline connection channel between the horizontal long borehole in the mining face or the coal lane strip area underground and a ground fracturing equipment, wherein the ground fracturing equipment uses a high-power fracturing equipment for oil and gas fracturing; using fracturing medium from the ground fracturing equipment transported through the pipeline connection channel to perform fracturing on the target coal seam or the top and bottom plate of the coal seam in the mining face or the coal lane strip area, so as to establish a gas migration channel; arranging a short gas extraction borehole along or through the coal seam in a rock lane adjacent to the target coal seam between two lanes of the mining face, wherein the short gas extraction borehole is communicated with an underground gas extraction pipeline, and the underground horizontal long borehole fracturing and the underground short gas extraction borehole extraction are used to realize regional gas extraction and regional outburst elimination in the mining face or the coal lane strip area.

Description

TECHNICAL FIELD

[0001] The present application relates to a gas control and regional outburst elimination method for a coal mining face or a coal roadway strip area in a coal mine, in particular to a gas control and regional outburst elimination method for a coal mining face (hereinafter referred to as a "mining face") or a coal roadway strip area horizontal long borehole fracturing + short borehole extraction in a coal mine. BACKGROUND

[0002] Coal and gas outburst is a strong dynamic process in which a coal rock mass containing gas in a coal mine moves sharply into a mining space and is accompanied by a large amount of gas emission, and is an extremely complex and serious natural disaster in a coal mine, which seriously threatens the safety production in a coal mine. National policies and regulations require that the gas content per ton of coal and the gas pressure should be reduced to below the national standard before mining.

[0003] In order to reduce the gas pressure in a coal seam, a borehole penetrating a coal seam is usually arranged from an adjacent rock roadway of a mining face or a borehole along a coal seam is arranged from a coal roadway (hereinafter referred to as "two roadways") of a mined mining face at present, and gas extraction and regional outburst elimination are performed. However, the coal seam permeability in China is generally low, the pressure conduction is slow, and the gas extraction efficiency of a local borehole is very low, and a large area of depressurization region cannot be quickly formed.

[0004] In order to improve the coal seam permeability (permeability), a majority of coal mines use hydraulic punching, hydraulic slotting, deep hole blasting, carbon dioxide pre-splitting and other coal seam permeability improvement measures to improve the gas extraction efficiency for low permeability coal seams at present. However, the permeability improvement range of these methods is not more than 10 m in diameter; the permeability improvement range of an underground hydraulic fracturing is not more than 30 m in diameter, and both have the disadvantage of small permeability improvement range.

[0005] In order to overcome the disadvantage of small permeability improvement range, a "surface drilling + surface hydraulic fracturing" method is usually used at present. The surface drilling includes a vertical well section, a deviation well section and a horizontal well section extending along a coal seam in a horizontal direction, and then a coal seam is fractured by using a coal seam fracturing medium, a large range of coal seam fractures are obtained, and then gas is separated from the coal seam fractures, and the gas is extracted through a surface extraction well or a short borehole for gas extraction in a coal mine. This method can be referred to as a surface fracturing + surface or underground extraction outburst elimination method.

[0006] Although this method has the advantages of large permeability improvement range, strong fracture conductivity and long maintenance time, it has disadvantages such as many devices (including surface drilling devices and deviation devices), high cost, long construction period of well construction, long time for gas extraction to reach the standard after a long process of drainage and pressure reduction, and cannot meet the requirements of rapid, safe and economic gas extraction and regional outburst elimination for low permeability coal seams in a coal mine.

[0007] Therefore, the prior art has developed a method of drilling a horizontal well in a coal mine and fracturing a coal seam in the mine. The method of drilling a horizontal well in the mine omits the vertical section and the build-up section of the surface well, thereby saving a large amount of well construction cost and shortening the drilling construction period, and the construction period can be shortened to 10-15 days.

[0008] However, the prior art has a problem that the drilling machine is generally arranged in a rock roadway, and a slant hole needs to be drilled through the rock layer from the rock roadway to the coal seam, and the slant hole section through the rock layer needs to be cemented, which also has a certain cost.

[0009] The drilling of the horizontal well in the mine is also limited by the conditions in the mine, such as the influence of the drilling machine, the drilling bit lubricant, the small pressure of the pump in the mine, and the like, so the length of the horizontal well drilled in the mine is generally not long, and cannot meet the requirement of one-time large-area outburst elimination.

[0010] The conventional drilling in the mine uses a common drilling machine in the mine. The drilling is performed from the two roadways of the mining face. The drilling from the two roadways of the mining face is easy to drill into the coal seam, but the common drilling machine in the mine can only extend along a straight line, and when the coal seam undulates or a fault or the like is encountered, the drilling hole is easy to drill through the roof or floor of the coal seam and enter the rock layer, and after the fracturing operation, the middle part of the coal seam in the mining face will have an unfractured blank zone.

[0011] In addition, the drilling bit needs to be cooled and lubricated. The best drilling bit cooling and lubricant is mud, but there is no place to set a mud pool in the mine, and there is no material to prepare mud, so the water easily obtained in the mine can only be used as the drilling bit lubricant. The lubricating effect of water is not as good as that of mud, and in the case of high-speed drilling and high drilling pressure, the temperature of the drilling bit will be very high, and the drilling bit is easy to be damaged.

[0012] The fracturing medium in the mine is also different from that on the ground. The fracturing medium in the mine is generally clean water, while the fracturing medium on the ground is generally a mixture of water and sand. The sand can be left in the cracks in the coal seam after fracturing and drainage, and can be used to support the cracks and prevent the cracks in the coal seam from being closed again, thereby causing the permeability of the coal seam to decrease.

[0013] The power for the fracturing in the mine comes from the pressure pump in the mine, and the displacement of the pressure pump in the mine is very small, generally not more than 0.5 m3 / min. The small displacement results in a small fracturing range. As described above, the fracturing diameter of the water fracturing in the mine is generally not more than 30 m, and cannot meet the requirement of fully fracturing the coal seam area to be treated, and the result is only water injection in the coal seam. The water injection in the coal seam has a certain effect on reducing dust during the mining of the coal seam, but the water injected into the coal seam blocks the cracks formed after the fracturing or the original cracks, and after the drainage, the cracks will be closed again without the support of the sand, thereby being more unfavorable to the desorption and extraction of the gas.

[0014] The effectiveness of coal seam fracturing is closely related to the displacement of the pressure pump. The more medium injected into the coal seam per unit time, the more coal seam fractures are generated. That is, when the pump displacement is constant, the fracture gap and fracturing range are basically determined.

[0015] Due to the above reasons, the length of downhole boreholes is not very long, resulting in low efficiency of downhole fracturing.

[0016] Therefore, efficiently and cost-effectively enhancing coal seam permeability, improving gas extraction efficiency, and achieving rapid and safe large-area outburst elimination are urgent needs for coal mine production. Summary of the Invention

[0017] To solve the technical problems existing in the above-mentioned prior art,

[0018] This invention provides an efficient and low-cost method for enhancing coal seam permeability, improving gas extraction efficiency, and rapidly and safely eliminating gas outbursts over large areas.

[0019] This invention provides a method for drilling horizontal long boreholes in underground coal mines.

[0020] This invention provides a method for drilling horizontal long boreholes in underground coal mine faces.

[0021] This invention provides a method for drilling horizontal long boreholes and performing segmented fracturing at the underground coal mine face.

[0022] The technical solution of this invention is implemented as follows:

[0023] Embodiments of the present invention provide a method for coal mine gas control and regional outburst elimination, the method comprising:

[0024] Drill long horizontal boreholes in underground coal mining faces (mining faces) or coal roadways, complete the horizontal extension section with open holes, and fracture the coal seam; drill short gas extraction boreholes underground to extract gas;

[0025] Use high-power surface fracturing equipment used in the oil and gas industry;

[0026] Use fracturing pipelines to establish pipeline connection channels between the horizontal long boreholes in the underground mining face or coal roadway and the surface fracturing equipment.

[0027] Using fracturing media from the surface fracturing equipment transported via the fracturing pipeline, the target coal seam or the top and bottom plates of the coal seam in the mining face are fracturing;

[0028] A gas extraction channel is established, which consists of underground horizontal long boreholes, gas extraction short boreholes, and underground gas extraction pipelines. Several gas extraction short boreholes along or through coal seams are arranged in the two roadways of the mining face or adjacent rock roadways. Gas is mainly extracted using the underground gas extraction short boreholes.

[0029] In the above scheme, the horizontal long boreholes in the underground coal mine face can be arranged in the coal seam, or in the roof or floor of the coal seam. The borehole openings can be located in coal roadways, high-level coal seam roadways, or low-level coal seam roadways.

[0030] Coal is a type of shale, and the hardness varies depending on the coal quality. The harder and more brittle the coal, the easier it is to form cracks. Some peat or bituminous coal is relatively soft, and it is not easy to generate too many cracks through fracturing. Therefore, under the above-mentioned coal quality conditions, fracturing holes can be drilled in the top or bottom rock strata of the coal seam. Generally, the rock strata are harder than the coal seam, and it is very easy to form abundant cracks.

[0031] When drilling fracturing holes in the roof or floor strata of a coal seam, the distance from the coal seam should not be too far, generally 0-6 meters. When drilling in the roof, this distance is called the first threshold, and when drilling in the floor, this distance is called the second threshold.

[0032] In the above scheme, drilling in the coal seam roof is done along the interface between the coal seam and the coal seam roof, and the distance between the borehole and the coal seam is less than or equal to a first threshold; drilling along the coal seam floor is done at the interface between the coal seam and the floor, and the distance between the borehole and the coal seam is less than or equal to a second threshold.

[0033] In one embodiment of the present invention, depending on the continuous change of the fracturing coefficients of the coal seam and the top and bottom plates of the coal seam, the borehole trajectory of the horizontal long borehole in the underground mining face or coal roadway strip area of ​​the coal mine can be entirely located in the coal seam, or partially located in the coal seam, partially located in the top or bottom plate of the coal seam, in a snake shape.

[0034] In the above scheme, the range of regional fracturing is controlled by controlling the pressure and volume of the fracturing medium injected into the horizontal long borehole in the underground working face. The pressure and volume of the fracturing medium injected into the coal seam are determined based on parameters such as the fracturing range, coal seam thickness, and coal hardness. The injection pressure of the fracturing medium is ≥20MPa and ≤115MPa, and the discharge rate of the fracturing medium is 5-9m³. 3 / min.

[0035] The length of the horizontal long borehole is less than or equal to the pushing length of the coal face to be treated and the coal roadway strip to be treated and the coal outburst eliminated, and the length can reach 200-1000 meters.

[0036] Because high-power fracturing equipment used in the oil and gas industry is large and unsuitable for placement underground, this invention provides a pipeline connection channel for connecting the surface fracturing equipment to the borehole opening of a long horizontal borehole. The pipeline connection channel is a fracturing pipeline connected by tubing. This fracturing pipeline is laid from the surface to the borehole opening using a coal mine roadway; or it can be drilled from the surface or utilize abandoned surface wells, connecting the surface fracturing equipment to the borehole opening through these surface boreholes or abandoned surface wells.

[0037] In the above scheme, the pipeline connection channel between the horizontal long borehole and the surface fracturing equipment is used to transport fracturing media, which includes, but is not limited to, a mixture of water and sand, pure nitrogen, and nitrogen foam liquid. The specific composition and proportion of the fracturing media are selected according to the characteristics of the coal seam or rock strata.

[0038] The diameter design of the fracturing pipeline is determined based on parameters such as the frictional resistance coefficient of the fracturing medium, the fracturing pressure gradient of the local coal seam or its roof and floor, and the coal seam thickness.

[0039] In the above scheme, the drilling site is arranged in the main coal roadway (two roadways of the mining face) of the target coal seam or in the rock roadway adjacent to the target coal seam;

[0040] To avoid the lack of directional flexibility in conventional coal mine drilling rigs, directional drilling rigs are used to construct horizontal long boreholes in the drilling site. This allows the rig to follow the undulations of the coal seam, changing direction and ensuring the borehole always extends forward within the coal seam and the roof and floor adjacent to it.

[0041] In order to drill long horizontal boreholes, or even ultra-long horizontal boreholes, this invention can also use a directional kilometer drilling rig.

[0042] The method for gas control and regional outburst elimination in horizontal long boreholes of underground coal mine faces of the present invention is suitable for fracturing and outburst elimination in coal mining faces as well as fracturing and outburst elimination in coal roadway strips.

[0043] The present invention also includes:

[0044] Short underground gas extraction boreholes are laid in the two roadways or adjacent rock roadways of the mining face to establish gas extraction channels. The gas in the area to be treated is extracted mainly by the short underground gas extraction boreholes, thereby achieving regional gas outburst prevention.

[0045] The underground gas extraction short borehole is a short borehole drilled from the upper and lower rock roadways adjacent to the target coal seam or from the two roadways of the excavated mining face toward the target coal seam;

[0046] The underground gas extraction short boreholes are arranged in several network fracture areas obtained after the horizontal long boreholes fracturing the target coal seam or the top and bottom plates of the coal seam. One or more underground gas extraction short boreholes are drilled in each network fracture area and connected to the gas extraction pipeline to establish a gas extraction channel.

[0047] The gas extraction channel also includes multiple sets of short gas extraction boreholes. When multiple fracturing zones are formed by segmented fracturing, multiple sets of short gas extraction boreholes along or through the coal seam are drilled for each fracturing zone from the two roadways of the mining face or adjacent rock roadways.

[0048] The length of the short boreholes for gas extraction along the coal seam arranged in the two roadways of the mining face is half the length of the mining face, or slightly shorter or slightly longer than half the length of the mining face.

[0049] The formula for calculating the interval distance of the short boreholes for gas drainage along the coal seam is as follows:

[0050] S=(Q·T) / [L·M·γ(Wy﹣Wd)];where S represents the short borehole spacing, Q represents the single-hole extraction volume of the short borehole, T represents the time for coal seam gas extraction to reach the standard, L represents the short borehole length, M represents the coal seam thickness, γ represents the coal bulk density, Wy represents the original gas content of the coal seam, and Wd represents the gas content of the coal seam that has reached the standard after extraction;

[0051] A blowout preventer is installed at the orifice of the gas extraction short borehole to prevent the sudden ejection of fracturing medium or gas during drilling.

[0052] The above scheme further includes the following method:

[0053] The gas extraction pipeline is used to extract coal seam gas in the fracturing area under positive or negative pressure.

[0054] The above scheme may also include:

[0055] A segmented fracturing tool is lowered into the horizontal long borehole to perform segmented fracturing on the target coal seam or the top and bottom plates of the coal seam.

[0056] The segmented fracturing tools include, but are not limited to, open-hole packers, casing packers, bidirectional anchor packers, hydraulic packers, and track packers.

[0057] In the above scheme, the method may further include: simultaneously drilling the horizontal fracturing borehole in the coal seam and the roof or floor strata of the coal seam, or simultaneously drilling a horizontal long borehole in the roof and floor strata of the coal seam.

[0058] Simultaneously drilling boreholes in the coal seam and its roof or floor strata, or simultaneously drilling boreholes in both the roof and floor strata, allows for sequential depressurization and drainage of the roof or floor strata during fracturing. As the pressure on the upper or lower side of the coal seam decreases, the pressure on the other side will further fracture the roof or floor and the coal seam upwards or downwards, further developing the coal seam fracture system and increasing the coal seam gas release rate.

[0059] The technical solution provided in this application is a highly efficient and low-cost method for enhancing coal seam permeability, improving gas extraction efficiency, and rapidly and safely eliminating large-area outbursts. Compared with existing technologies, drilling fracturing holes in the roof or floor strata of the coal seam, or drilling fracturing holes in sections between the coal seam and its roof or floor, creates an interwoven fracture system between the roof, floor, and coal seam, which improves the gas desorption rate. Due to the use of powerful surface fracturing equipment, the fracturing range of each section during segmented fracturing is larger than the range of single-section fracturing in existing underground technologies. Because the diameter of the single-section fracturing range in this application is large, the interval between each section can be larger. Thus, the fracturing range in the same time period is much wider and longer than the single-section fracturing range of existing technologies, far exceeding the permeability enhancement area, permeability (penetration), and extraction efficiency of existing underground methods in coal mines. The horizontal borehole of this invention can reach lengths of 200-1000 meters, which is several to ten times longer than the existing horizontal borehole technology, which does not exceed 100 meters. Therefore, it can quickly achieve gas extraction from the working face and regional outburst suppression. Attached Figure Description

[0060] To more clearly illustrate the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0061] Figure 1 This is a flowchart illustrating the implementation of a method for controlling gas and eliminating regional outbursts in a horizontal long borehole fracturing operation at an underground coal mine, according to an embodiment of this application.

[0062] Figure 2 This is a flowchart illustrating the implementation of a preferred embodiment of the method for gas control and regional outburst suppression in a coal mine underground face using segmented fracturing of horizontal long boreholes.

[0063] Figure 3 This is a schematic diagram of the cross-section of an underground coal seam and the top and bottom strata of the coal seam according to a preferred embodiment of this application;

[0064] Figure 4 This is a schematic diagram of the horizontal long borehole arrangement and segmented fracturing of a preferred embodiment of this application;

[0065] Figure 5 This is a schematic diagram of a preferred embodiment of the naked-eye packer multi-stage sliding sleeve segmented fracturing string. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some exemplary embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The features of the embodiments in this application can be arbitrarily combined without conflicting with the inventive concept of this invention. The steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of executable instructions. Furthermore, although a logical order is shown in the flowcharts, in some cases, the steps shown or described may be performed in a different order than that shown here.

[0067] Before introducing the technical solutions of the embodiments of this application, let's first explain several technical terms mentioned in this application:

[0068] 1) Long boreholes: Generally speaking, compared to short boreholes, the length of boreholes in underground coal mine drilling depends on geological conditions, drilling rig performance, and actual needs. Short boreholes are constructed using ordinary mining drilling rigs, and their length generally does not exceed 200m, with most around 100m. Boreholes longer than 200m require 1000m directional drilling rigs, and if geological conditions are stable, the length can reach 1000m, with most being 300-500m. Oil and gas extraction drilling rigs have greater drilling capacity, and surface drilling generally results in horizontal wells exceeding 1000m in length.

[0069] In this application, "long borehole" refers to a long horizontal borehole in the well, with a length of ≥200m, or even exceeding 1000m.

[0070] 2) Long horizontal borehole: A long borehole that extends parallel to the coal seam or rock strata. In the context of existing downhole technology, long horizontal boreholes refer to boreholes with a length of ≤200m.

[0071] 3) Drilling site: The location in a coal mine for drilling operations, where drilling rigs are installed. When constructing long horizontal boreholes, the drilling site will be located in either a rock roadway or a coal roadway, depending on the situation. When constructing short underground gas extraction boreholes, the drilling site will be located in the main coal roadway (both roadways of the mining face) or an adjacent rock roadway.

[0072] 4) Coal mining face: also known as the mining face. Before mining, two roadways (one intake airway and one return airway) are excavated parallel to each other along the coal seam. When the design boundary is reached, a coal roadway is excavated to connect the two roadways, forming a U-shape. This connecting roadway is called the cut-in. After installing the coal mining machine, flexible scraper conveyor, and self-propelled hydraulic support in the cut-in, coal can be mined back along the two roadways. Therefore, the coal mining face is also called the return mining face. The length of the cut-in is the length of the mining face. The length of a blasting mining face is 80-150m, and the length of a fully mechanized mining face is over 150m. The length of the mining face push-out is close to the length of the two roadways, ranging from several hundred meters to several thousand meters.

[0073] 5) Two airways in the mining face: These refer to the intake airway and the return airway in the mining face. Generally, the intake airway is equipped with a belt conveyor to transport coal and serves as the main transport; the return airway is laid with tracks to transport equipment and materials and serves as the auxiliary transport. Therefore, the two airways in the mining face are also called the mining face belt conveyor or track conveyor.

[0074] 6) Mining area: The area defined by the two roadways and cut-off points of the mining face in a U-shape.

[0075] 7) Coal roadway strip: A roadway that runs along a coal seam is called a coal roadway. A coal roadway strip refers to the strip area formed by the coal roadway and the coal seam within a certain range on both sides. For inclined and steeply inclined coal seams, the strip should extend at least 20m beyond the outline of the upper side and at least 10m beyond the outline of the lower side (both distances are along the coal seam bedding plane); for gently inclined coal seams, the strip should extend at least 15m beyond the outlines of both sides of the roadway.

[0076] Minimum width of coal roadway strip = 20m + roadway width + 10m = 15m + roadway width + 15m = 30m + roadway width ≈

[0077] 35m.

[0078] In coal seams with outbursts, the width of the coal roadway strip controlled by the regional outburst prevention measures adopted in the excavation of coal roadways (including uphill, downhill, face roadways and cut-off points, etc.) shall not be less than 35m.

[0079] 8) Coal Seam Hydraulic Fracturing: This is a technical measure borrowed from the oil and gas extraction field and applied to coal mine outburst mitigation. Coal seam hydraulic fracturing methods are divided into surface fracturing and downhole fracturing. Regardless of the method, a high-viscosity fracturing medium is injected into the coal seam through a high-pressure pipeline using a pressure pump unit. When the injection rate of the fracturing medium exceeds the absorption capacity of the coal seam or its roof or floor, and the pressure exceeds the fracturing pressure value of the coal seam or its roof or floor, the coal seam or its roof or floor will be fractured, creating cracks. To keep the fractures open and prevent them from closing again, proppant, usually silica sand, is injected into the coal seam along with the water.

[0080] The surface fracturing pump set has a large discharge capacity, reaching 5-9m³ / h. 3 / min, which can support the fracturing of horizontal wells hundreds of meters long or even thousands of meters long, with fracturing effect reaching a range of hundreds of meters wide or even thousands of meters long.

[0081] Current underground fracturing technology in coal mines uses very small fracturing pump sets with a displacement generally not exceeding 0.5m³. 3 / min, the area of ​​permeability enhancement after fracturing is less than 30 meters wide and less than 60 meters long, and the fracturing range is small.

[0082] This application involves downhole fracturing using oil and gas fracturing equipment to carry out fracturing on the surface. The fracturing pump set has a large displacement and a large permeability enhancement range. In actual engineering, the permeability enhancement range can reach more than 200 meters wide, 500 meters or even more than 1,000 meters long.

[0083] 9) Gas control and outburst suppression: This includes local gas control and outburst suppression and regional gas control and outburst suppression, with regional gas outburst suppression covering a much larger area than local gas outburst suppression. Compared to local gas control and outburst suppression, regional gas control and outburst suppression methods involve a larger area of ​​single-hole fracturing permeability enhancement and extraction, which can accelerate gas extraction speed. The gas control and outburst suppression in this application refers to the latter, namely regional gas control and outburst suppression. Existing downhole drilling and fracturing gas control and outburst suppression schemes are mainly the former, namely local outburst suppression.

[0084] The aforementioned technical terms are not uncommon in existing technical documents, but in the context of this application, they differ to varying degrees, even qualitatively.

[0085] like Figure 1 As shown, an embodiment of the present invention describes a regional gas outburst mitigation method for horizontal long-bore fracturing and short-bore gas drainage in underground coal mine faces, comprising:

[0086] S(Step)101: Arrange the openings of horizontal long boreholes at the mining face of the target coal seam or in the rock strata close to the top and bottom of the target coal seam in the underground coal mine, and carry out horizontal long borehole construction at the arranged openings.

[0087] In this step, the coal seam located at the mining face can be considered the target coal seam. In practice, a drilling site is set up at the target coal seam or adjacent strata; horizontal long boreholes are drilled at the drilling site. Before drilling, the borehole locations are planned, such as the positions of the borehole openings and bottoms, and the borehole trajectory. Then, a directional drilling rig is used to drill horizontal long boreholes at the mining face according to the designed trajectory. These horizontal long boreholes are then used to fracturing the target coal seam at the mining face to obtain a regional network of fractures.

[0088] S102: Use fracturing pipelines to establish pipeline connection channels between horizontal long boreholes in underground coal mine faces and surface fracturing equipment.

[0089] In this step, before establishing the pipeline connection channel, the model and laying method of the fracturing pipeline steel pipe are determined. Using the determined model of pipeline steel pipe, the fracturing pipeline is laid according to the preset laying method, establishing the pipeline connection channel between the underground working face horizontal long borehole and the surface fracturing equipment. The design of the fracturing pipeline is based on the friction coefficient of the fracturing medium, the fracturing pressure gradient of the coal seam or its roof or floor in this area, and the coal seam thickness. This is equivalent to determining the design parameters of the fracturing pipeline based on the actual operating conditions of the target coal seam and the inherent properties of the fracturing pipeline, such as friction, to achieve safety, reliability, and economy in engineering use.

[0090] S103: Using fracturing medium from the ground fracturing equipment transported via the pipeline connection channel, the target coal seam or the top and bottom plates of the coal seam are fracturing.

[0091] In this step, the fracturing equipment is surface fracturing equipment, such as a fracturing unit, which supplies fracturing media to the downhole for fracturing. Compared to downhole pump fracturing in related technologies, the fracturing technology used in this embodiment expands the fracturing range. It can be understood that during the fracturing process, the flow rate and pressure of the fracturing media can be controlled according to actual conditions, thereby controlling the fracturing range to achieve the desired fracturing extent.

[0092] S104: Establish a gas drainage channel, which mainly consists of underground gas drainage short boreholes and underground gas drainage pipelines. The underground gas drainage channel is used to realize gas drainage and gas outburst suppression in the mining face.

[0093] The gas extraction short borehole is drilled from the upper and lower rock roadways adjacent to the target coal seam or the already excavated main coal roadway (both roadways of the mining face) to the target coal seam of the mining face.

[0094] Because the coal seam has undergone fracturing and contains a large amount of water and fracturing sand, resulting in high pressure, a special gas blowout preventer (BOP) must be installed at the borehole opening during the construction of short boreholes for gas drainage to prevent the sudden ejection of fracturing media or gas. The biggest difference between this BOP and conventional downhole BOPs is its strong pressure-bearing capacity and rapid slip locking during blowouts.

[0095] like Figure 2 As shown, another preferred embodiment of the present invention describes a method for gas control and regional outburst suppression via segmented fracturing of horizontal long boreholes in underground coal mine faces, comprising:

[0096] S(Step)101: Arrange the openings of horizontal long boreholes at the mining face of the target coal seam or in the rock strata close to the top and bottom of the target coal seam in the underground coal mine, and carry out horizontal long borehole construction at the arranged openings.

[0097] In this step, the coal seam located at the mining face can be considered the target coal seam. In practice, a drilling site is set up at the target coal seam or adjacent strata; horizontal long boreholes are drilled at the drilling site. Before drilling, the borehole locations are planned, such as the positions of the borehole openings and bottoms, and the borehole trajectory. Then, a directional drilling rig is used to drill horizontal long boreholes at the mining face according to the designed trajectory. These horizontal long boreholes are then used to fracturing the target coal seam at the mining face to obtain a regional network of fractures.

[0098] S102: Insert a segmented fracturing tool into a horizontal long borehole in the underground coal mine face;

[0099] In this step, the segmented fracturing tools are sequentially lowered into the horizontal long borehole of the production face using a downhole drilling rig.

[0100] S103: Use fracturing pipelines to establish pipeline connection channels between horizontal long boreholes in underground coal mine faces and surface fracturing equipment.

[0101] In this step, before establishing the pipeline connection channel, the model and laying method of the fracturing pipeline steel pipe are determined. Using the determined model of pipeline steel pipe, the fracturing pipeline is laid according to the preset laying method, establishing the pipeline connection channel between the underground working face horizontal long borehole and the surface fracturing equipment. The design of the fracturing pipeline is based on the friction coefficient of the fracturing medium, the fracturing pressure gradient of the coal seam or its roof or floor in this area, and the coal seam thickness. This is equivalent to determining the design parameters of the fracturing pipeline based on the actual operating conditions of the target coal seam and the inherent properties of the fracturing pipeline, such as friction, to achieve safety, reliability, and economy in engineering use.

[0102] S104: Using fracturing medium from the ground fracturing equipment transported via the pipeline connection channel, the target coal seam or the top and bottom plates of the coal seam are subjected to segmented fracturing.

[0103] In this step, the fracturing equipment is surface fracturing equipment, such as a fracturing unit, which supplies fracturing media to the downhole for fracturing. The staged fracturing technology used in this embodiment expands the fracturing range compared to single-stage fracturing in related technologies. It can be understood that during the fracturing process, the flow rate and pressure of the fracturing media can be controlled according to actual conditions, thereby controlling the fracturing range to achieve the desired fracturing extent.

[0104] S105: Establish a gas drainage channel, which mainly consists of underground gas drainage short boreholes and underground gas drainage pipelines. The underground gas drainage channel is used to realize gas drainage and gas outburst suppression in the mining face.

[0105] The gas extraction short borehole is drilled from the upper and lower rock roadways adjacent to the target coal seam or the already excavated main coal roadway (both roadways of the mining face) to the target coal seam of the mining face.

[0106] Because the coal seam has undergone fracturing and contains a large amount of water and fracturing sand, resulting in high pressure, a special gas blowout preventer (BOP) must be installed at the borehole opening during the construction of short boreholes for gas drainage to prevent the sudden ejection of fracturing media or gas. The biggest difference between this BOP and conventional downhole BOPs is its strong pressure-bearing capacity and rapid slip locking during blowouts.

[0107] The gas extraction short borehole is connected to an extraction wellhead device, which includes a pressure relief nozzle, a gas-water separator, and a gas metering device, and is connected to the gas extraction pipeline, drainage pipeline, and negative pressure extraction pipeline. The extraction wellhead device has at least three interfaces: one end connects to a gas and water ejection prevention device; one end is equipped with a pressure gauge to observe wellhead pressure changes; and the other end connects to the pressure relief nozzle and subsequent gas extraction process devices, such as the gas-water separator, gas metering device, gas extraction pipeline, drainage pipeline, and negative pressure extraction pipeline. After fracturing, the extraction process valves are opened, the wellhead pressure gauge is observed, and pressure relief extraction is performed through the pressure relief nozzle.

[0108] In another embodiment of the invention, the horizontal long borehole for segmented fracturing in the well also serves as a gas production borehole. This borehole also requires the installation of a gas and water ejection prevention device. This device is connected to an orifice device, which includes a pressure relief nozzle, a gas-water separator, and a gas metering device, and is connected to a gas extraction pipeline, a drainage pipeline, and a negative pressure extraction pipeline. The orifice device has at least four interfaces: one end connects to the gas and water ejection prevention device (the other end of which connects to the orifice of the horizontal long borehole used for gas extraction), one end connects to the fracturing pipeline, one end is equipped with a pressure gauge to observe changes in orifice pressure, and the other end connects to the pressure relief nozzle and downstream gas extraction processes. Before coal seam fracturing, the orifice valve connected to the extraction process is closed. After fracturing, the fracturing pipeline valve is closed, the extraction process valve is opened, the orifice pressure gauge is observed, and pressure relief and extraction operations are performed through the pressure relief nozzle.

[0109] The downhole segmented fracturing horizontal long borehole and gas extraction short borehole extraction methods are different from conventional downhole extraction methods. The negative pressure extraction pipeline cannot be directly connected to the borehole to avoid a large amount of fracturing medium flowing into the negative pressure extraction pipeline and causing blockage.

[0110] The entire extraction process is divided into three stages: pressure reduction and drainage, positive pressure extraction, and negative pressure extraction.

[0111] (1) Pressure Reduction and Drainage Stage: Control the drainage rate to drain water from the coal seam, slowly reduce the coal seam pressure, and produce gas. Control the drainage rate and pressure reduction speed by adjusting the pressure relief nozzle of the orifice device. Too fast a speed can easily cause sand in the cracks to be discharged with the water, leading to the cracks closing again. Too slow a speed will result in too long a pumping time, making it impossible to meet the pumping requirements in the shortest time. Therefore, based on the mathematical model of unidirectional water flow, the most suitable pressure reduction speed and drainage rate for this stage should be calculated. Under the premise of protecting the coal seam cracks from premature closure, the orifice pressure should be reduced to below the analytical pressure as soon as possible to achieve positive pressure pumping conditions.

[0112] (2) Positive pressure extraction stage: As the pressure at the orifice decreases, the coal seam analysis area increases, and the gas production will gradually increase. At this time, a reasonable pressure drop rate is an important means to ensure the gas extraction volume. If the pressure drop rate is too fast, the gas analysis volume will be too large, which will cause the fracturing sand in the coal seam to be produced with the gas with too fast flow rate. Once too much sand is produced in the coal seam, it will cause the coal seam cracks to close and the permeability to decrease. Therefore, it is necessary to control the water output at the orifice, slow down the analysis rate of gas in the reservoir, and allow the water at the far end to flow and produce, further increasing the analysis area until the pressure at the orifice drops to 0, the positive pressure extraction ends, and the negative pressure extraction stage begins.

[0113] (3) Negative pressure extraction stage:

[0114] When the orifice pressure drops to 0, it indicates that the coal seam analysis area has expanded to its maximum, and the extraction rate will gradually decrease. At this point, it is necessary to use a negative pressure extraction pipeline in the coal mine for extraction. By adjusting the negative pressure intensity, the residual gas in the coal seam is extracted, and the gas content in the coal seam is reduced to the minimum. The core control at this stage is adjusting the negative pressure intensity to avoid excessive negative pressure intensity causing the fracturing sand and coal dust in the orifice to be extracted, thereby reducing the permeability of the coal seam.

[0115] In one embodiment of this application, the underground horizontal long borehole is drilled in the longitudinal face of the main coal roadway, and its borehole trajectory is one or a combination of several of the following: borehole along the coal seam, borehole along the coal seam roof, and borehole along the coal seam floor. From the perspective of the borehole trajectory, the borehole trajectory along the coal seam is parallel to the main coal roadway (both roadways of the face).

[0116] The distance between the borehole along the top of the coal seam and the coal seam should be less than or equal to a first threshold; the distance between the borehole along the bottom of the coal seam and the coal seam should be less than or equal to a second threshold.

[0117] The borehole trajectory of the horizontal long borehole in the mining face adopts one or a combination of borehole trajectories that are drilled along the coal seam or along the top or bottom plate of the coal seam.

[0118] The length of the horizontal long borehole in the mining face is usually less than or equal to the length of the area to be treated to eliminate the outburst.

[0119] The drilling strata for the horizontal long boreholes in the underground coal mine face can be arranged at the coal seam face or in adjacent strata, such as the end faces of the top and bottom strata of the coal seam. Horizontal long boreholes can be drilled regardless of the stratum. This is easy to implement in engineering and has high feasibility.

[0120] In another embodiment of this application, the horizontal fracturing borehole is drilled simultaneously in the coal seam and the roof or floor strata of the coal seam. During fracturing, the pressure of the coal seam or the roof or floor strata is reduced and drainage is carried out sequentially.

[0121] In another embodiment of this application, horizontal long boreholes can be drilled simultaneously in the roof and floor strata of the coal seam, and during fracturing, the roof or floor strata can be depressurized and drained sequentially.

[0122] In one embodiment of this application, the underground horizontal long borehole is also applicable to gas extraction and outburst suppression in coal seam strips of coal roadways. The borehole trajectory of the horizontal long borehole in the coal roadway strip adopts one or a combination of borehole trajectories that are drilled along the coal seam or along the roof and floor of the coal seam, and its borehole trajectory is parallel to the excavated coal roadway (including uphill, downhill, face roadways and cut-off holes, etc.).

[0123] In one embodiment of this application, the target coal seam can be fracturing in stages using an open-hole packer. Stage fracturing with an open-hole packer is easy to implement in engineering and highly feasible.

[0124] like Figure 4 and Figure 5 As shown, the method for gas control and regional outburst suppression via segmented fracturing of horizontal long boreholes in an underground coal mine face according to a certain embodiment of this application can be regarded as a method for gas control and regional outburst suppression via segmented fracturing of horizontal long boreholes in an underground coal mine face. In engineering, it can be implemented according to the following steps:

[0125] 1. Select the area to be treated.

[0126] Based on the actual needs of coal mining and safety production requirements, areas to be treated and areas to eliminate outbursts are selected in the mining face. The coal seam in the area to be treated is the target coal seam.

[0127] 2. Select the borehole type and completion method for horizontal long boreholes in underground coal mine faces.

[0128] 2.1 Selection of horizontal long borehole type and completion method in underground coal mine working face

[0129] Considering that this embodiment requires staged fracturing of long horizontal boreholes in underground coal mine faces, the selection of borehole type and completion method for long horizontal boreholes in underground coal mine faces should follow the following principles:

[0130] (1) The borehole shape meets the requirements of staged fracturing;

[0131] (2) The solid pore quality meets the requirements of the maximum design pressure for fracturing;

[0132] (3) The pressure-splitting process technology can meet the requirements of the coal mine underground orifice to allow the entry of segmented fracturing tools and the implementation of segmented fracturing tools.

[0133] In summary, based on the capabilities of downhole directional drilling rigs and the downhole space environment, the horizontal long borehole type for the mining face adopts either in-seam drilling or cross-seam drilling, with screen completion or open-hole completion selected as the completion method. Cross-seam drilling includes drilling along the coal seam roof or along the coal seam floor.

[0134] 2.2 Design of the borehole structure for horizontal long boreholes in underground coal mine faces

[0135] The borehole structure dimensions of the horizontal long borehole at the production face are derived from the fracturing string. First, the pipeline friction pressure is calculated for different fracturing string diameters under different drilling flows. Based on the actual operating pressure limit, the pipeline friction pressure is determined. Then, the fracturing string dimensions are determined based on the pipeline friction pressure. Finally, the borehole structure dimensions of the horizontal borehole at the production face are determined by the fracturing string dimensions and the corresponding drill bit dimensions. Furthermore, considering that fracturing fluid is generally active water-based, the drilling flow is relatively large, and the friction is relatively high, and that the exposed high-pressure pipelines in the horizontal long borehole at the coal mine production face are long and have many bends, the construction risk is much greater than that of horizontal well fracturing at the surface. The longer the selected high-pressure pipeline, the greater its friction, and the larger the pipe diameter should be. Taking all factors into consideration, the outer diameter of the horizontal long borehole at the production face should not be less than [a certain value]. (mm) technical sleeve + outer diameter not less than Fracturing and completion tubing.

[0136] 3. Arrange the positions of horizontal long boreholes in the downhole production face, and carry out construction and complete the segmented fracturing tools in the boreholes;

[0137] 3.1 Arranging the borehole trajectory of horizontal long boreholes in the downhole working face

[0138] The borehole trajectory of the horizontal long borehole in the underground mining face adopts one or a combination of drilling along the coal seam, drilling along the coal seam roof, and drilling along the coal seam floor.

[0139] The borehole trajectory along the coal seam is arranged parallel to the two roadways of the mining face, and its length is no greater than the length of the mining face roadway.

[0140] Drill holes along the roof of the coal seam, not exceeding the first threshold such as 6m (meters) from the coal seam, or drill holes along the interface between the roof of the coal seam and the coal seam, with the hole trajectory parallel to the coal seam and the hole length less than or equal to the length of two roadways in the mining face;

[0141] Drill holes along the bottom of the coal seam, no more than 6m (meters) from the coal seam, or drill holes along the interface between the bottom of the coal seam and the coal seam, with the hole trajectory basically parallel to the coal seam and the hole length less than or equal to the length of two roadways in the mining face;

[0142] 3.2 Lower Stage Fracturing Tools

[0143] In underground coal mines, for completed production holes, the drill pipe of the downhole drilling rig is used to send the segmented fracturing well string to the predetermined position. The string is lowered to the designed hole depth, and the volume of the well is circulated with clean water at least three times its normal volume. A fracturing ball is dropped, and after it lands on the pressure-regulating ball seat, the pressure is slowly increased to 16-18 MPa. Pressure continues to be increased inside the string, shearing the open-hole packer pin. The open-hole packer begins to set, and the pressure is gradually increased to 20 MPa to secure the unidirectional anchoring slip. The pressure is then increased further to 25 MPa, causing the pressure-regulating ball seat to shear the pin and fall into the guide shoe, thus ensuring unobstructed flow within the tubing. A special fracturing wellhead is installed at the wellhead.

[0144] 4. Select the size and model of the fracturing pipeline, and use the fracturing pipeline to establish a pipeline connection channel between the downhole horizontal long borehole and the surface fracturing equipment.

[0145] The type and laying method of the fracturing pipeline are determined based on the predicted construction pressure of the target coal seam and the frictional resistance of the fracturing pipeline. The laying process of the fracturing pipeline can be carried out simultaneously with processes such as horizontal long borehole drilling in the mining face. In engineering terms, the type of fracturing pipeline can be determined by the coal seam fracturing pressure, the type of fracturing medium, the frictional resistance under different discharge rates of different fracturing tubing strings, the hydrostatic pressure generated by the coal seam depth, and the construction pressure limit. Determining the type of fracturing pipeline involves determining its diameter and internal pressure resistance. Different sizes and models of fracturing pipelines result in different diameters and internal pressure resistances. In actual operations, there are two laying methods for fracturing pipelines: one is to lay them directly from the surface through the coal mine roadway to the opening of the long borehole in the underground mining face; the other is to drill a fracturing pipeline delivery well on the surface, connecting the underground fracturing pipeline through the surface delivery well and communicating with the horizontal long borehole in the mining face.

[0146] 5. Use ground fracturing equipment to perform segmented fracturing on the target coal seam or the top and bottom of the coal seam to greatly improve the permeability of the coal seam.

[0147] The fracturing method in this embodiment is open-hole packer segmented fracturing. The fracturing medium can be, but is not limited to, water with sand, pure nitrogen, nitrogen foam liquid, etc. Fracturing is carried out segment by segment within the selected coal seam to establish communication between the borehole and the coal seam through the fracturing fractures, thereby creating a gas extraction channel.

[0148] The segmented fracturing technology in this application embodiment includes, but is not limited to, multi-stage sliding sleeve open-hole packer segmented fracturing technology.

[0149] Open-hole segmented fracturing tubing with an outer diameter not less than The structure of the completion tubing for fracturing.

[0150] Figure 5This is a schematic diagram of a multi-stage sliding sleeve open-hole packer segmented fracturing string in an embodiment of this application. The guide shoe guides the fracturing tubing during insertion. The screen connects the pressure inside and outside the tubing. The pressure-regulating ball has two functions: one is to set the open-hole packer and the one-way anchor slips, and the other is to connect the tubing cavity to the formation, providing a channel for the next ball deployment. The tubing serves as a connector. The ball-dropping sliding sleeve pressurizes and shears the pins, providing a channel for fluid outflow. The open-hole packer acts as a separator. The one-way anchor slips stabilize the tubing during fracturing. The casing fixes the one-way anchor slips and seals the orifice. The principle of open-hole packer staged fracturing technology: Open-hole sliding sleeve packer staged fracturing uses a multi-stage packer design to mechanically isolate the open-hole section of a horizontal well. Multiple sliding sleeves are distributed according to the fracturing initiation location. Before fracturing, the tubing is pressurized to achieve stable packer setting. During fracturing, balls are dropped sequentially from smallest to largest to open the sliding sleeves. Fracturing fluid enters the formation through the injection port until proppant addition is complete. After fracturing, the fracturing fluid is flowed back into the formation for production. Key tools for open-hole sliding sleeve packer staged fracturing include unidirectional anchoring slips, the open-hole packer, the ball-dropping sliding sleeve, and the pressure-controlled ball sealing mechanism.

[0151] The embodiments of this application employ multi-stage sliding sleeve open-hole packer segmented fracturing technology for coal seam fracturing, which is easy to implement in engineering and has high feasibility.

[0152] In this embodiment, segmented fracturing technology is used to perform segmented fracturing of the target coal seam. Compared with single-segment fracturing in related technologies, segmented fracturing can expand the fracturing range and improve the efficiency of gas control and regional outburst suppression.

[0153] Compared with the surface drilling, directional drilling, and horizontal long borehole construction schemes in related technologies, the method for gas control and regional outburst suppression in the coal mine underground face using the horizontal long borehole segmented fracturing method in this application embodiment does not require surface drilling. It can directly construct horizontal long boreholes in the coal seam of the underground face and perform segmented fracturing on the target coal seam. The fracturing range is expanded, the permeability of the coal seam is enhanced, and the gas extraction efficiency can be greatly improved, realizing regional gas extraction and regional outburst suppression in the face.

[0154] Advantages of the embodiments of this application:

[0155] (1) The technical solution of this application has high construction efficiency. Compared with the surface drilling and gas extraction solution, it does not require surface drilling. It only requires long boreholes in the well construction face for segmented fracturing, which effectively shortens the construction cycle. The construction period is short, about 10-15 days, and the economic cost is low.

[0156] (2) Large permeability enhancement area: Compared with conventional outburst suppression measures used in coal mines in related technologies, where the single permeability enhancement area is only less than 6 meters wide and less than 60 meters long, in this embodiment, the underground horizontal long borehole segmented fracturing utilizes oil and gas fracturing equipment to carry out fracturing on the surface. The fracturing pump has a large displacement, resulting in a large permeability enhancement area. In actual engineering, the permeability enhancement area can be increased to more than 200 meters wide, and 300 meters, 500 meters, or even more than 800-1000 meters in length. The permeability enhancement area of ​​the technical solution in this embodiment is expanded, and it can be used as a gas control and outburst suppression measure in the mining area.

[0157] (3) Economic costs are reduced. In this embodiment, horizontal long boreholes are used for fracturing, which can make full use of existing coal mining roadways or rock roadways for drilling construction. No additional roadways are needed, and no release layer is needed to achieve large-scale gas extraction and outburst elimination at the mining face, which can greatly reduce workload and investment.

[0158] (4) Excellent extraction effect: In the embodiments of this application, after the horizontal long boreholes are segmented for fracturing, short holes along the coal seam (i.e., boreholes along the seam, which must be equipped with blowout preventers at the borehole openings during construction to prevent sudden ejection of fracturing fluid or gas) are evenly arranged in both roadways of the mining face. Due to the segmented fracturing of the horizontal long boreholes in the mining face, the fracturing range and permeability enhancement area are significantly increased. Using underground gas extraction pipelines to perform positive or negative pressure extraction on the horizontal long boreholes and the short holes along the coal seam in the mining face results in high extraction efficiency, which can be increased by several times or even tens of times, and can quickly achieve the target for gas extraction in the mining face area and regional outburst elimination.

[0159] (5) Under normal circumstances, boreholes are drilled along the coal seam from the two roadways of the working face for gas drainage and regional outburst suppression. Ordinary drilling rigs are used for drilling. However, in the two roadways adjacent to the working face, the borehole openings are prone to hitting the coal seam. In the middle of the working face, due to geological structures such as coal seam undulations and faults, boreholes are more likely to hit the roof or floor, resulting in a blank zone in the coal seam. By arranging long horizontal boreholes in the middle of the working face and using directional drilling rigs for segmented fracturing, blank zones can be eliminated, coal seam permeability can be enhanced, drainage efficiency can be improved, and the reliability of drainage compliance assessment can be ensured.

[0160] (6) Preferred Mining Seam: Since the technical solution of this application embodiment can increase the permeability enhancement range of fracturing, in the field of coal mining technology, the technical solution of this application embodiment can be used as one of the measures for gas control and regional outburst elimination in the mining face area. In engineering, this measure can be used to eliminate outbursts in a fixed area. In practical applications, the technical solution of this application embodiment can select coal seams with higher economic value for priority mining, without having to mine the protective layer with lower economic value first.

[0161] It is understood that the values ​​involved in the above technical solutions, such as 10-15 days, 300 meters, 500 meters, etc., are only examples. Any other reasonable values ​​are within the scope of the embodiments of this application and will not be listed here.

[0162] In the several embodiments provided in this application, it should be understood that the disclosed methods can be implemented in other ways. The embodiments described above are merely illustrative.

[0163] The methods disclosed in the several method embodiments provided in this application can be arbitrarily combined without conflict to obtain new method embodiments.

[0164] The features disclosed in the several method embodiments provided in this application can be arbitrarily combined without conflict to obtain new feature embodiments.

[0165] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for coal mine gas control and regional outburst elimination, characterized in that: Drill long horizontal boreholes in the underground mining face or strip area to fracture the coal seam; drill short gas extraction boreholes underground to extract gas. The horizontal long borehole can be arranged in the coal seam, or the rock strata on the roof of the coal seam, or the rock strata on the floor of the coal seam; The length of the horizontal long borehole is less than or equal to the pushing length of the coal face to be treated and the coal roadway strip to be treated and the coal outburst eliminated; Use high-power surface fracturing equipment used in the oil and gas industry; Use fracturing pipelines to establish pipeline connection channels between the horizontal long boreholes in the underground mining face or coal roadway strip area of ​​the coal mine and the surface fracturing equipment. Using fracturing media from the surface fracturing equipment transported via the fracturing pipeline, the target coal seam or the top and bottom plates of the coal seam in the mining face or strip area are fractured to establish a gas migration channel; A gas drainage channel is established, consisting of underground horizontal long boreholes, short gas drainage boreholes, and underground gas drainage pipelines. Several short gas drainage boreholes along the coal seam are arranged in both roadways of the working face, primarily utilizing these short boreholes for gas extraction. The extraction process is divided into three stages: pressure reduction and drainage, positive pressure extraction, and negative pressure extraction. The formula for calculating the interval distance of the short gas drainage boreholes along the coal seam is: S = (Q·T) / [ [L·M·γ(Wy﹣Wd)]; where S represents the short borehole spacing, Q represents the single-hole extraction volume of the short borehole, T represents the time for coal seam gas extraction to reach the standard, L represents the short borehole length, M represents the coal seam thickness, γ represents the coal bulk density, Wy represents the original coal seam gas content, and Wd represents the extracted coal seam gas content that meets the standard; the length of the short boreholes for coal seam gas extraction arranged in the two roadways of the mining face is half the length of the mining face, or slightly shorter or slightly longer than half the length of the mining face. By controlling the pressure and volume of the fracturing medium injected into the horizontal long borehole in the underground production face, the range of regional fracturing can be controlled. The pressure and volume of the fracturing medium injected into the coal seam are determined according to the fracturing range, coal seam thickness, and coal hardness. The injection pressure of the fracturing medium is ≥20MPa and ≤115MPa, and the discharge rate of the fracturing medium is 5-9m³ / min.

2. The method according to claim 1, characterized in that: A segmented fracturing tool is lowered into the horizontal long borehole to perform segmented fracturing on the target coal seam or the top and bottom plates of the coal seam.

3. The method according to claim 2, characterized in that: The segmented fracturing tools include open-hole packers, casing packers, bidirectional anchored packers, hydraulic packers, or track packers.

4. The method according to claim 1 or 2, characterized in that: The borehole trajectory of the horizontal long borehole in the underground mining face or coal roadway strip area of ​​a coal mine can be entirely located in the coal seam, or partially located in the coal seam, partly in the coal seam roof layer or partly in the coal seam floor layer.

5. The method according to claim 4, characterized in that: Drilling in the roof of a coal seam means drilling along the interface between the coal seam and the roof, with the distance between the borehole and the coal seam being less than or equal to a first threshold; drilling along the floor of a coal seam means drilling at the interface between the coal seam and the floor, with the distance between the borehole and the coal seam being less than or equal to a second threshold.

6. The method according to claim 1, characterized in that, The gas extraction short borehole is a short borehole drilled from the upper and lower rock roadways adjacent to the target coal seam or from the two roadways of the excavated mining face toward the target coal seam; The gas extraction short boreholes are arranged in several network fracture areas obtained after the horizontal long boreholes fracturing the target coal seam or the top and bottom plates of the coal seam. One or more underground gas extraction short boreholes are drilled in each network fracture area and connected to the gas extraction pipeline to establish a gas extraction channel. The gas extraction channel also includes multiple sets of short gas extraction boreholes. When multiple fracturing zones are formed by segmented fracturing, multiple sets of short gas extraction boreholes along or through the coal seam are drilled for each fracturing zone from the two roadways of the mining face or adjacent rock roadways. A blowout preventer is installed at the orifice of the gas extraction short borehole to prevent the sudden ejection of fracturing medium or gas during drilling.

7. The method according to claim 1, characterized in that: Drilling sites are arranged in the two roadways of the target coal seam or in the rock roadways adjacent to the target coal seam; Horizontal long boreholes were constructed using directional drilling rigs within the drilling site.

8. The method according to claim 1, characterized in that: The fracturing pipeline connection channel between the horizontal long borehole and the ground fracturing equipment is used to transport fracturing media. The fracturing media includes a mixture of water and sand, pure nitrogen or nitrogen foam liquid. The specific composition and proportion of the fracturing media are selected according to the characteristics of the coal seam or rock strata.

9. The method according to claim 1, characterized in that: The fracturing pipeline is laid from the surface to the opening of the underground horizontal long borehole using the mine roadway; or it is drilled from the surface or uses an abandoned surface well, and the surface fracturing equipment is connected to the opening of the underground horizontal long borehole through the surface borehole or the abandoned surface well. The diameter design of the fracturing pipeline is determined based on the frictional resistance coefficient of the fracturing medium, the fracturing pressure gradient of the local coal seam or the top and bottom plates, and the thickness of the coal seam.

10. The method according to claim 1, characterized in that: The length of the horizontal long borehole is ≥200m.

11. The method according to claim 1, characterized in that: The length of the horizontal long borehole is ≥1000m.

12. The method according to claim 1, characterized in that: The borehole trajectory of the horizontal long borehole extends partly in the coal seam and partly in the roof or floor strata of the coal seam.

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