A three-dimensional pre-extraction method for gas extraction in panel area based on T-type hole group

Abstract

The present invention discloses a three-dimensional pre-extraction method for gas mining in a panel area based on a T-type hole group: setting up a panel area; constructing multiple ground L-shaped directional holes on the panel area along the center line of the panel area in the width direction; the ground L-shaped directional holes are located on the center line of the panel area in the width direction; constructing multiple pairs of underground near-horizontal directional holes along the length direction for each ground L-shaped directional hole; performing segmented and zoned fracturing on each ground drilling site; utilizing each ground L-shaped directional hole in the panel area and its corresponding underground near-horizontal directional hole to simultaneously extract gas; and recovering the coal seam in the panel area. The present invention solves the problems of precise docking and penetration of ground and underground boreholes, safe and efficient drilling and fracturing, large-scale coverage and balanced extraction, significantly reduces the number of boreholes, and more than doubles the panel area width, thus achieving three-dimensional pre-extraction of gas in the panel area before mining, improving the efficiency and effectiveness of coal mine gas control, and ensuring safe and efficient mining in the mine.

Description

Technical Field

[0001] The present invention relates to a coal mine gas control method, in particular to a three-dimensional pre-extraction control method for panel area gas before mining based on a T-shaped hole group. Background Art

[0002] Pre-extraction gas is a key method for preventing and controlling coal mine gas hazards. Currently, pre-extraction gas is primarily achieved through surface and underground drilling. When underground construction is not possible, surface drilling is used for advanced extraction. Once underground construction is possible, intensive, enhanced extraction is performed through underground drilling. However, gas extraction efficiency is low due to high surface drilling costs, poor underground drilling pressure, and poor extraction equipment.

[0003] Chinese patent application number 201110026899.0 proposes a combined above-and-below extraction method, combining surface and underground drilling for gas extraction and management. The specific principle is: constructing and fracturing vertical boreholes on the surface, then constructing a cluster of directional boreholes underground in the coal mine to connect with the surface vertical boreholes. Water is released from the cluster of directional boreholes underground, and gas extraction is performed using the surface vertical boreholes. However, this method has the following problems: ① The surface vertical boreholes have a short extension distance within the coal seam, resulting in a small impact area, requiring a large number of constructions and high costs; ② After fracturing the surface vertical wells, the coal body in the fracture-affected area is damaged, making the underground cluster directional drilling connection prone to safety accidents and having a low success rate; ③ The underground cluster directional drilling has a small extraction radius, a small coverage area per borehole, and requires a large number of drillings.

[0004] To address the above issues, Chinese patent application number 201810543751.6 proposes a ground-assisted underground drilling gas enhanced extraction method. The specific principle is: constructing a straight hole or directional hole on the ground to enter the underground tunnel of the coal mine, and transporting the ground fracturing pipeline to the underground tunnel of the coal mine through the straight hole or directional hole; at the same time, constructing a large number of boreholes in the coal mine, using ground fracturing equipment to perform high-pressure fracturing on the underground boreholes, and then pre-extracting gas. Although this method increases the gas extraction radius of underground cluster directional drilling and reduces the number of underground directional drilling construction, it has the following problems: ① The ground vertical well is only used to transport fracturing pipelines and no gas extraction is carried out, which is wasteful; ② Gas extraction entirely relies on underground drilling, and the underground gas extraction equipment, extraction pressure and other conditions in coal mines are limited, affecting the extraction effect of underground drilling; ③ Although the ground high-pressure fracturing equipment does not need to be installed underground in the coal mine, part of the underground drilling and fracturing operation still needs to be carried out underground in the coal mine, and the safety risk of high-pressure construction in a restricted environment is relatively high. Summary of the Invention

[0005] In response to the current joint upper and lower gas well management model in underground coal mine pans, which has technical problems such as small effective drilling coverage and high risk of underground fracturing, the designers of this invention have conducted intensive research and design, and integrated the experience and achievements of many years of engagement in related industries to provide a three-dimensional pre-extraction management method for pan gas based on T-type hole groups before mining.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A three-dimensional pre-extraction and treatment method for panel gas before extraction based on a T-shaped hole group comprises the following steps:

[0008] Step 1: Set a panel area, where the panel area length is parallel to the strike direction of the coal seam and the panel area width is perpendicular to the strike direction of the coal seam. The panel area length is equal to the strike range of the coal seam and the panel area width is equal to the dip range of the coal seam.

[0009] Step 2: Construct multiple L-shaped directional holes on the ground along the center line of the panel in the width direction; the L-shaped directional holes are located on the center line of the panel in the width direction;

[0010] Step 3: For each surface L-shaped directional hole, construct multiple pairs of sub-horizontal directional holes along its length. The sub-horizontal directional holes are perpendicular to the surface L-shaped directional hole. Each pair of sub-horizontal directional holes is symmetrically arranged with respect to the center line of the panel width.

[0011] Step 4: Use fracturing equipment to perform segmented and zoned fracturing of the T-hole group at each surface drilling site one by one;

[0012] Step 5: Use each L-shaped directional hole on the ground and its corresponding sub-horizontal directional hole in the panel area to extract gas simultaneously; after the gas extraction meets the standards, the coal seam in the panel area is mined.

[0013] Furthermore, the step 2 is specifically as follows: along the center line of the panel width direction, a plurality of ground drilling sites are set at equal intervals on the ground above it, and a ground L-shaped directional hole is constructed corresponding to each ground drilling site. The ground L-shaped directional hole enters the coal seam from the rock layer and extends in a direction perpendicular to the direction of the coal seam. The coal seam hole sections of adjacent ground L-shaped directional holes are overlapped in sequence.

[0014] Furthermore, the spacing between the ground drilling sites is the same as the length of the coal seam hole section of the ground L-shaped directional hole; and the coal seam hole sections of all the ground L-shaped directional holes extend along the center line in the width direction of the coal seam.

[0015] Furthermore, the specific operations of step 4 are as follows: two main tunnels are excavated at the edges of both sides of the panel in a direction parallel to the length of the panel, and multiple downhole drilling sites are set at equal intervals in each of the main tunnels; in each of the downhole drilling sites, an downhole nearly horizontal directional hole is constructed toward the corresponding L-shaped directional hole on the ground, and the downhole nearly horizontal directional hole is parallel to the width direction of the panel; a pair of the downhole nearly horizontal directional holes that are opposite to each other and located on the same vertical plane in the width direction of the panel are overlapped with each other.

[0016] Furthermore, the downhole drilling site spacing is smaller than the width of the fracturing affected zone.

[0017] In step 3, when constructing a nearly horizontal directional hole underground, a casing is run into the hole mouth of the nearly horizontal directional hole underground and grouting is performed to fix the casing.

[0018] Furthermore, the fracturing equipment described in step 4 includes a ground fracturing pump and a fracturing tool string, wherein the fracturing tool string includes a guide head, a front end packer, a front connecting pipe, a jet fracturing device, a rear connecting pipe, a rear end packer and a fluid delivery string connected in sequence; the total length of the front end packer, the front connecting pipe, the jet fracturing device, the rear connecting pipe and the rear end packer after being connected is the same as the length of the fracturing segment, the length of the front end packer and the rear end packer are the same, and the length of the front connecting pipe and the rear connecting pipe are the same.

[0019] Furthermore, the diameter of the guide head is 10 to 20 mm smaller than the diameter of the drill hole, and the front end thereof adopts an arc-shaped guide structure.

[0020] Furthermore, step 4 includes the following steps:

[0021] Step 41: Lowering the fracturing equipment to the bottom of the hole. Specifically, under the guidance of the guide head, the fracturing tool string of the fracturing equipment is lowered from the L-shaped directional hole on the ground to the bottom of the hole;

[0022] Step 42, positioning and setting the packers, specifically, placing the front packer and the rear packer in the middle of two adjacent parallel, nearly horizontal directional boreholes in the same horizontal plane, and setting the packers in the L-shaped directional borehole on the surface, thereby effectively isolating the fracturing section from other borehole sections;

[0023] Step 42: Staged fracturing, specifically, the surface fracturing pump continuously injects the fracturing fluid along the fluid delivery string, and the fracturing fluid is ejected by the jet fracturing device to fracture the coal seam section of the surface L-shaped directional hole between the front packer and the rear packer, thereby achieving staged fracturing of the current coal seam section;

[0024] Step 43: Zoned fracturing, specifically, the surface fracturing pump continuously injects fracturing fluid. As the fracturing crack expands, the surface L-shaped directional hole is connected to the downhole near-horizontal directional hole of the current coal seam section, and the fracturing fluid enters the downhole near-horizontal directional hole. The coal seam within the fracturing influence zone around the downhole near-horizontal directional hole is fully fractured until the predetermined fracturing pressure is reached and the fracturing is stopped, thus achieving zoned fracturing in the current fracturing influence zone.

[0025] Step 44: fracturing the entire panel area, specifically, releasing the front-end packer and the rear-end packer, lifting the staged fracturing tool string, and the length of each lifting is equal to the length of the fracturing segment. After each lifting, steps 42 to 43 are repeated to realize staged and zoned fracturing from the bottom of the L-shaped directional hole on the ground to the hole mouth, until all the coal seam sections of the L-shaped directional hole on the ground are fractured; the fracturing influence areas of each coal seam section are overlapped in sequence, realizing the overall fracturing of the panel area.

[0026] Furthermore, the length of the fracturing segments is the same as the spacing between the nearly horizontal directional holes underground, and the number of segments is equal to the length of the coal seam hole section of the L-shaped directional hole on the ground divided by the length of the fracturing segments.

[0027] Compared with the prior art, the method of the present invention has the following technical effects:

[0028] This invention utilizes a T-shaped hole group consisting of L-shaped directional holes on the ground and nearly horizontal directional holes underground. By constructing first and then fracturing, performing high-pressure segmented and zoned fracturing on the ground, and combining extraction from above and below the well, it solves the problems of precise connection between ground and underground boreholes, safe and efficient drilling and fracturing, and large-scale coverage and balanced extraction. The number of drill holes is significantly reduced, the width of the panel is more than doubled, and three-dimensional pre-extraction of gas from the panel is achieved before extraction. This improves the efficiency and effectiveness of coal mine gas control and ensures safe and efficient mining in the mine. The specific analysis is as follows:

[0029] 1. First, L-shaped directional holes on the ground and sub-horizontal directional holes are constructed in the well. Then, staged and zoned fracturing is carried out according to the designed intervals of the sub-horizontal directional holes in the well, thus avoiding the safety risks of constructing sub-horizontal directional holes in the fracturing area.

[0030] 2. The nearly horizontal directional holes in the well and the L-shaped directional holes on the ground are arranged vertically and intersect in the coal seam. Taking advantage of the fact that the range of the fracturing influence zone is much larger than the thickness of the coal seam, the nearly horizontal directional holes in the well and the L-shaped directional holes on the ground are connected through the fracturing cracks, solving the problem of high-precision and accurate docking.

[0031] 3. Surface fracturing equipment is used to perform segmented and zoned fracturing on the surface L-shaped directional holes and the downhole near-horizontal directional holes, ultimately achieving overall fracturing of the disk area. All fracturing operations are carried out on the surface, which improves the safety of fracturing operations. At the same time, the effective extraction radius of the downhole near-horizontal directional holes is increased, significantly reducing the number of downhole directional drilling holes.

[0032] 4. Two groups of nearly horizontal directional holes in the well are symmetrically arranged perpendicular to the L-shaped directional holes on the ground. This solves the problem of limited drilling depth of single holes in the nearly horizontal directional holes in the well, which restricts the width of the panel. The panel width can be more than doubled compared with the existing technology.

[0033] 5. The combined extraction of gas from ground L-shaped directional holes and underground near-horizontal directional holes not only fully utilizes the capabilities of ground gas extraction equipment, but also solves the problem of uneven gas extraction in the panel area, significantly improving the efficiency and effectiveness of gas extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a three-dimensional schematic diagram of the three-dimensional pre-extraction and treatment method for panel gas before extraction based on T-shaped hole groups of the present invention;

[0035] Figure 2 It is a cross-sectional schematic diagram of the three-dimensional pre-extraction and treatment method for panel gas extraction based on T-shaped hole groups of the present invention;

[0036] Figure 3 It is a schematic plan view of the three-dimensional pre-extraction and treatment method for panel gas extraction based on T-shaped hole groups of the present invention;

[0037] Figure 4 It is a component connection diagram of high-pressure fracturing equipment;

[0038] Figure 5 This is a schematic diagram of the T-hole group staged and zoned fracturing;

[0039] Figure 6 It is a schematic diagram of the overall fracturing of the T-hole group disk area.

[0040] The meanings of the numbers in the figure are: ground L-shaped directional hole 1, underground near-horizontal directional hole 2, coal seam 3, panel length 4, panel width 5, surface drilling site 6, main tunnel 7, underground drilling site 8, fracturing affected area 9, surface fracturing pump 10, guide head 11, front end packer 12, front connecting pipe 13, jet fracturing device 14, rear connecting pipe 15, rear end packer 16, and fluid delivery string 17.

[0041] The present invention will be further described below with reference to the accompanying drawings and examples. DETAILED DESCRIPTION

[0042] The terms involved in this invention are explained as follows:

[0043] Ground L-shaped directional hole: an L-shaped hole formed by entering the coal seam 3 from the ground rock layer and then extending along the direction of the coal seam 3.

[0044] T-type hole: The horizontal projection of the hole section in the coal seam composed of two nearly horizontal directional holes 2 underground and the L-shaped directional hole 1 at the corresponding position on the ground is T-shaped. Multiple T-type holes constitute a T-type hole group.

[0045] See also Figures 1 to 3 The present invention provides a three-dimensional pre-extraction method for gas extraction in a panel area based on a T-shaped hole group, comprising the following steps:

[0046] Step 1: Panel setup. In the coal mine, the panels are designed based on the strike of the coal seam 3. The panel length 4 is parallel to the strike of the coal seam 3, and the panel width 5 is perpendicular to the strike of the coal seam 3. The panel length 4 is equal to the strike range of the coal seam 3, i.e., the length range of the coal seam 3; the panel width 5 is equal to the dip range of the coal seam 3, i.e., the width range of the coal seam 3.

[0047] Step 2: Construction of L-shaped directional holes 1 on the ground. Multiple ground drill sites 6 are set up at equal intervals above the centerline of the panel width 5. One L-shaped directional hole 1 is constructed for each drill site 6. The L-shaped directional holes 1 extend from the rock layer into the coal seam 3 and in a direction perpendicular to the direction of the coal seam 3. The coal seam sections of adjacent L-shaped directional holes 1 are sequentially overlapped.

[0048] The spacing between the ground drilling sites 6 is the same as the length of the coal seam hole section of the ground L-shaped directional hole 1 ; and all the coal seam hole sections of the ground L-shaped directional hole 1 extend along the center line of the coal seam 3 in the width direction.

[0049] Step 3: Construction of sub-horizontal directional boreholes 2 underground. Two main tunnels 7 are excavated parallel to the panel length 4 at the edges of the panel. Multiple sub-horizontal drill sites 8 are set up at equal intervals within the main tunnels 7. A sub-horizontal directional borehole 2 is drilled in each drill site 8 toward the corresponding L-shaped directional borehole 1 on the surface. The sub-horizontal directional boreholes 2 are parallel to the panel width 5. A pair of sub-horizontal directional boreholes 2 that are opposite and located on the same vertical plane along the panel width 5 overlap each other. With this solution, all sub-horizontal directional boreholes 2 located on the same horizontal plane can cover the entire panel.

[0050] Specifically, the distance between the downhole drilling sites 8 is smaller than the width of the fracturing affected area 9 .

[0051] Specifically, during construction of the sub-horizontal directional borehole 2, casing should be run through the borehole opening and grouting should be performed to secure the casing. The casing length should be greater than half the width of the fracturing zone 9, and its pressure resistance should be greater than the fracturing pressure. Casing is a component used to seal and protect the borehole opening of a downhole directional drill hole. Casing prevents high-pressure fracturing fluid from the surface from passing through the downhole directional drill hole and connecting to the tunnel, potentially leaking the fracturing fluid and affecting the safety of personnel and equipment within the tunnel.

[0052] Step 4: T-hole group staged and zoned fracturing. Using fracturing equipment, perform staged and zoned fracturing on each surface drill site 6. This staged and zoned fracturing of each surface drill site 6 involves performing staged and zoned fracturing on the surface L-shaped directional borehole 1 and the sub-horizontal directional borehole 2 corresponding to that surface drill site 6. This step effectively improves the permeability of the panel coal seam 3 and increases the effective extraction radius of the borehole.

[0053] See also Figure 4 The fracturing equipment used may be common fracturing equipment in the art, including a ground fracturing pump 10 and a fracturing tool string, wherein the fracturing tool string includes a guide head 11, a front end packer 12, a front connecting pipe 13, a jet fracturing device 14, a rear connecting pipe 15, a rear end packer 16 and a fluid delivery string 17 connected in sequence; the diameter of the guide head 11 is 10 to 20 mm smaller than the borehole diameter, and the front end adopts an arc-shaped guide structure for easy passage; the total length of the front end packer 12, the front connecting pipe 13, the jet fracturing device 14, the rear connecting pipe 15 and the rear end packer 16 after being connected is the same as the length of the fracturing segment, the length of the front end packer 12 and the rear end packer 16 are the same, and the length of the front connecting pipe 13 and the rear connecting pipe 15 are the same.

[0054] See also Figure 5 、 Figure 6 , step 4 specifically includes the following sub-steps:

[0055] Step 41: Lowering the fracturing equipment to the bottom of the hole. Specifically, under the guidance of the guide head 11, the fracturing tool string of the fracturing equipment is lowered from the L-shaped directional hole 1 on the ground to the bottom of the hole.

[0056] Step 42, positioning and setting, specifically, places the front packer 12 and the rear packer 16 in the middle of two adjacent, parallel, downhole, nearly horizontal directional boreholes 2 on the same horizontal plane, and sets the packers in the L-shaped directional borehole 1 on the surface, effectively isolating the fracturing section from other borehole sections.

[0057] Step 42: Staged Fracturing. Specifically, the surface fracturing pump 10 continuously injects fracturing fluid along the fluid delivery string 17, which is ejected by the jet fracturing device 14 to fracture the coal seam section of the surface L-shaped directional hole 1 between the front packer 12 and the rear packer 16, thereby achieving staged fracturing of the current coal seam section.

[0058] Step 43: Zoned fracturing. Specifically, the surface fracturing pump 10 continuously injects fracturing fluid. As the fracturing crack expands, the surface L-shaped directional hole 1 connects to the downhole near-horizontal directional hole 2 in the current coal seam section. The fracturing fluid enters the downhole near-horizontal directional hole 2 and fractur- es the coal seam 3 within the fracturing influence zone 9 surrounding the downhole near-horizontal directional hole 2. Fracturing is stopped until the predetermined fracturing pressure is reached, thus achieving zoned fracturing in the current fracturing influence zone 9.

[0059] Step 44: Complete panel fracturing. Unseat the front-end and rear-end packers 12, 16, and raise the staged fracturing tool string. Each lift is equal to the length of the fracturing segment. Repeat steps 42 and 43 after each lift, achieving staged and zoned fracturing from the bottom of the L-shaped directional borehole 1 to the borehole head, until all coal seam sections of the L-shaped directional borehole 1 are fully fractured. The fracturing affected zones 9 of each coal seam section are sequentially overlapped, achieving complete panel fracturing.

[0060] Among them, the length of the fracturing segment is the same as the spacing between the nearly horizontal directional holes 2 underground, and the number of segments is equal to the length of the coal seam hole section of the L-shaped directional hole 1 on the ground divided by the length of the fracturing segment.

[0061] Step 5: Gas extraction in the panel area. Simultaneously extract gas using the L-shaped directional hole 1 on the surface and the nearly horizontal directional hole 2 underground. Once gas extraction meets the required standards, the coal seam 3 in the panel area is mined.

[0062] Although this document frequently uses terms such as surface L-shaped directional hole 1, downhole near-horizontal directional hole 2, coal seam 3, panel length 4, panel width 5, surface drilling site 6, main roadway 7, downhole drilling site 8, fracturing affected area 9, surface high-pressure fracturing pump 10, guide head 11, front packer 12, front connecting pipe 13, jet fracturing device 14, rear connecting pipe 15, rear packer 16, and fluid delivery string 17, the use of other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitations is contrary to the spirit of the present invention.

Claims

1. A three-dimensional pre-extraction method for gas extraction in a panel area based on a T-shaped hole group, characterized in that: The following steps are involved: Step 1: Set a panel area, wherein the panel area length (4) is parallel to the strike direction of the coal seam (3), and the panel area width (5) is perpendicular to the strike direction of the coal seam (3). The panel area length (4) is equal to the strike range of the coal seam (3), and the panel area width (5) is equal to the dip range of the coal seam (3); Step 2: constructing a plurality of ground L-shaped directional holes (1) on the panel along the center line of the panel width (5); the ground L-shaped directional holes (1) are located on the center line of the panel width (5); Step 3: For each ground L-shaped directional hole (1), construct multiple pairs of downhole nearly horizontal directional holes (2) along its length direction, wherein the downhole nearly horizontal directional holes (2) are perpendicular to the ground L-shaped directional hole (1); each pair of downhole nearly horizontal directional holes (2) are symmetrically arranged relative to the center line of the panel width (5); Step 4: Using fracturing equipment, perform segmented and zoned fracturing on each surface drilling site (6) of the T-type hole group one by one; the specific operation is as follows: parallel to the direction of the disk length (4), two main tunnels (7) are excavated at the edges of both sides of the disk, and multiple downhole drilling sites (8) are set at equal intervals in each of the main tunnels (7); in each downhole drilling site (8), a downhole near-horizontal directional hole (2) is constructed toward the corresponding surface L-shaped directional hole (1), and the downhole near-horizontal directional hole (2) is parallel to the disk width (5); a pair of the downhole near-horizontal directional holes (2) that are opposite to each other and located on the same vertical plane in the disk width (5) are overlapped; The steps include: Step 41: lowering the fracturing equipment to the bottom of the hole, specifically, under the guidance of the guide head (11), lowering the fracturing tool string of the fracturing equipment from the L-shaped directional hole (1) on the ground to the bottom of the hole; Step 42, positioning and setting the seal, specifically, placing the front end seal (12) and the rear end seal (16) in the middle of two adjacent parallel downhole nearly horizontal directional holes (2) in the same horizontal plane, and setting the seals in the L-shaped directional hole (1) on the ground, which can effectively isolate the fracturing section from other hole sections; Step 42: Staged fracturing, specifically, the surface fracturing pump (10) continuously injects the fracturing fluid along the fluid delivery string (17), and the fracturing fluid is ejected by the jet fracturing device (14), and the coal seam hole section of the surface L-shaped directional hole (1) between the front end packer (12) and the rear end packer (16) is fractured, thereby achieving staged fracturing of the current coal seam hole section; Step 43: zonal fracturing, specifically, the surface fracturing pump (10) continuously injects fracturing fluid, and as the fracturing crack expands, the surface L-shaped directional hole (1) is connected to the downhole near-horizontal directional hole (2) of the current coal seam hole section, and the fracturing fluid enters the downhole near-horizontal directional hole (2), and fracturing the coal seam (3) within the fracturing influence zone (9) around the downhole near-horizontal directional hole (2) is performed, and fracturing is stopped until a predetermined fracturing pressure is reached, thereby achieving zonal fracturing of the current fracturing influence zone (9); Step 44: fracturing the entire panel area, specifically, releasing the front-end packer (12) and the rear-end packer (16) from setting, lifting the segmented fracturing tool string, and the length of each lifting is equal to the length of the fracturing segment. After each lifting, steps 42 to 43 are repeated to realize segmented and zoned fracturing from the bottom of the L-shaped directional hole (1) on the ground to the hole mouth, until all the coal seam sections of the L-shaped directional hole (1) on the ground are fractured; the fracturing influence areas (9) of each coal seam section are overlapped in sequence, realizing the overall fracturing of the panel area; Step 5: Utilize each surface L-shaped directional hole (1) and its corresponding underground near-horizontal directional hole (2) in the panel area to simultaneously extract gas; after the gas extraction reaches the standard, the coal seam (3) in the panel area is mined.

2. The method for pre-extraction gas treatment in a panel area based on a T-shaped hole group according to claim 1, characterized in that: The step 2 specifically comprises: setting a plurality of ground drilling sites (6) at equal intervals on the ground above the center line of the panel width (5), constructing a ground L-shaped directional hole (1) corresponding to each ground drilling site (6), the ground L-shaped directional hole (1) entering the coal seam (3) from the rock layer and extending in a direction perpendicular to the direction of the coal seam (3), and the coal seam hole sections of adjacent ground L-shaped directional holes (1) are overlapped in sequence.

3. The method for pre-extraction gas treatment in a panel area based on a T-shaped hole group according to claim 2, characterized in that: The spacing between the ground drilling sites (6) is the same as the length of the coal seam hole section of the ground L-shaped directional holes (1); the coal seam hole sections of all the ground L-shaped directional holes (1) extend along the center line of the coal seam (3) in the width direction.

4. The method for pre-extraction gas treatment in a panel area based on a T-shaped hole group according to claim 1, characterized in that: In step 3, when constructing the underground nearly horizontal directional hole (2), a casing is run into the hole mouth of the underground nearly horizontal directional hole (2) and grouting is performed to fix the casing.

5. The method for pre-extraction gas treatment in a panel area based on a T-shaped hole group according to claim 4, characterized in that: The spacing between the downhole drilling sites (8) is smaller than the width of the fracturing influence zone (9).

6. The method for pre-extraction gas treatment in a panel area based on a T-shaped hole group according to claim 1, characterized in that: The fracturing equipment described in step 4 includes a ground fracturing pump (10) and a fracturing tool string, wherein the fracturing tool string includes a guide head (11), a front end packer (12), a front connecting pipe (13), a jet fracturing device (14), a rear connecting pipe (15), a rear end packer (16) and a fluid delivery pipe string (17) connected in sequence; the total length of the front end packer (12), the front connecting pipe (13), the jet fracturing device (14), the rear connecting pipe (15) and the rear end packer (16) after being connected is the same as the length of the fracturing segment, the length of the front end packer (12) and the rear end packer (16) are the same, and the length of the front connecting pipe (13) and the rear connecting pipe (15) are the same.

7. The method for pre-extraction gas treatment in a panel area based on a T-shaped hole group according to claim 6, characterized in that: The guide head (11) has a diameter 10-20 mm smaller than the borehole diameter, and its front end adopts an arc-shaped guide structure.

8. The method for pre-extraction gas treatment in a panel area based on a T-shaped hole group according to claim 1, characterized in that: The length of the fracturing segments is the same as the spacing between the nearly horizontal directional holes (2) underground, and the number of segments is equal to the length of the coal seam hole section of the L-shaped directional hole (1) on the ground divided by the length of the fracturing segments.

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