A method for detecting water-conducting fracture zones and separation spaces in steeply inclined coal seams using a ground three-pronged hole

Abstract

This invention discloses a method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged surface borehole. The method involves deploying a three-pronged surface borehole; geological casing is installed in the directional sections of both the main borehole and the S-shaped branch directional boreholes. The detection section of the S-shaped branch directional borehole is an open borehole, drilling into the fracture zone or roof of the steeply dipping coal seam. During drilling, a real-time surface monitoring system for borehole flushing fluid consumption and a well leakage meter are used to determine the location and amount of leakage. This method obtains the maximum height of the water-conducting fracture zone in the horizontally segmented fully mechanized longwall mining area of ​​the steeply dipping, extra-thick coal seam. The development characteristics of the water-conducting fracture zone and delamination space are determined using in-hole acoustic logging and borehole inspection techniques, and the development range and connectivity of the mining-induced fracture zone are assessed. This method accurately detects the development status and degree of the water-conducting fracture zone and delamination space in the overlying coal seam, reducing drilling rig relocation, saving engineering costs, and achieving efficient detection of the water-conducting fracture zone in the overlying coal seam.

Description

Technical Field

[0001] This invention relates to the field of overburden water-conducting fracture zone detection technology. Specifically, it is a method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole. Background Technology

[0002] Western my country possesses abundant coal reserves, with large areas of steeply dipping, extra-thick coal seams existing in western mining regions such as Xinjiang and Gansu. However, these western mining areas are largely arid and semi-arid, ecologically fragile regions facing severe water shortages. Currently, steeply dipping, extra-thick coal seams are often mined using horizontal segmented fully mechanized longwall mining methods. Due to the unique geological and mining conditions, the overlying strata are severely deformed and damaged, resulting in extremely complex development characteristics of water-conducting fracture zones and delamination spaces. If the development of water-conducting fracture zones in the overlying strata exceeds the limit caused by mining of steeply dipping coal seams, it will lead to water loss and the risk of mine water hazards. On the one hand, mining-induced water-conducting fractures will drain groundwater from the weakly cemented sandstone aquifer and loose porous aquifers in the roof of the coal seam, causing a significant drop in groundwater levels, resulting in surface subsidence and exacerbating desertification. On the other hand, the weakly cemented sandstone aquifer and loose porous aquifers in the roof are prone to collapse into the mine along mining-induced fractures, posing a threat of water and sand collapse. Meanwhile, with the westward shift of my country's precipitation line in recent years, there is a risk that surface water could overflow into the mine along subsidence pits if extreme weather occurs during the rainy season. In summary, mine water hazards and water resource protection have become bottlenecks restricting the safe and efficient development of steeply inclined, extra-thick coal seams in western mining areas. Accurately determining the development of water-conducting fracture zones and delamination spaces in the overlying strata during fully mechanized longwall mining of steeply inclined, extra-thick coal seams is extremely important.

[0003] The height of the overburden water-conducting fracture zone is closely related to factors such as coal seam thickness, mining method, coal seam dip angle, and overburden lithology. Currently, techniques for measuring the height of the overburden water-conducting fracture zone include surface borehole observation, underground borehole observation, and geophysical exploration methods. Surface borehole observation involves drilling to the coal seam roof and observing the development of mining-induced fractures by monitoring fluid leakage. This technique is intuitive and reliable, but requires a large amount of drilling work and is expensive. Underground borehole observation involves drilling inclined boreholes underground and using double-capsule water injection to observe the development of fractures in the roof strata. Its advantage is a relatively small drilling workload, but it has certain observation errors and a limited observation range, making it unsuitable for mining extremely thick coal seams. Geophysical exploration methods include electrical resistivity tomography, electromagnetic methods, and seismic wave methods. Their advantages are ease of implementation and controllable cost, but their accuracy is greatly affected by inversion interpretation.

[0004] In recent years, some mature detection methods and techniques have been developed for the height of water-conducting fracture zones in the overburden of near-horizontal coal seams. The migration and destruction characteristics of overburden in steeply dipping coal seam mining faces differ significantly from those in near-horizontal coal seam mining. In steeply dipping coal seam mining faces, the deformation and destruction of the overburden on the uphill side is severe; however, due to the backfilling effect of caving rock, the deformation and destruction of the overburden on the downhill side is suppressed. Simultaneously, borehole stability in steeply dipping strata is extremely poor, and conventional drilling methods are prone to borehole collapse and drill bit burial, severely affecting the efficient implementation of water-conducting fracture zone observation. Therefore, the destruction range of the overburden in steeply dipping coal seams exhibits asymmetric characteristics. Conventional methods suffer from problems such as large drilling workload, frequent drilling site relocation, high coordination difficulty, and the susceptibility of borehole collapse in steeply dipping strata, making them unsuitable for the detection needs of water-conducting fractures and delamination spaces in the overburden of steeply dipping, extra-thick coal seams. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for detecting water-conducting fracture zones and delamination spaces in steeply inclined coal seams using a three-pronged borehole, so as to solve problems such as large drilling workload, frequent relocation of drilling sites, difficulty in coordination, and easy collapse of boreholes in steeply inclined strata.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for detecting water-conducting fracture zones and delamination spaces in the overlying strata of steeply dipping coal seams using a three-pronged borehole surface method includes the following steps:

[0008] (A) Arrangement of exploratory boreholes: Use ground three-way drilling; that is, determine the opening position on the ground, and drill one main hole and three S-shaped branch directional boreholes.

[0009] (B) Geological casings are laid in the directional sections of both the main borehole and the S-shaped branch directional borehole. The probe section of the S-shaped branch directional borehole is a bare borehole. The probe section of the S-shaped branch directional borehole is drilled into the fracture zone of the steeply inclined coal seam or the roof of the coal seam.

[0010] (C) During the drilling of the exploration section of the S-shaped branch directional borehole, the specific location and amount of leakage are determined by a real-time ground monitoring system for borehole flushing fluid consumption and a well leakage meter. This allows for the determination of the maximum water-conducting fracture zone height in the horizontally segmented fully mechanized longwall mining area of ​​steeply inclined extra-thick coal seams. The development characteristics of the water-conducting fracture zone and the separation space in the overlying rock are determined by a combination of in-hole acoustic logging and borehole inspection techniques. The development range and connectivity of the mining-induced fracture zone are then assessed.

[0011] The above-mentioned method for detecting the water-conducting fracture zone and delamination space of the overburden in steeply dipping coal seams using a three-pronged ground borehole includes, in step (A), a branch borehole in the mining area, an uphill branch borehole, and a downhill branch borehole. The branch borehole in the mining area enters from the middle of the water-conducting fracture zone in the overburden of the steeply dipping coal seam to detect the maximum height of the water-conducting fracture zone and the height of the cross-fall zone in the middle of the mining area. The uphill branch borehole enters from the uphill side of the water-conducting fracture zone in the overburden of the steeply dipping coal seam to detect the maximum height of the water-conducting fracture zone on the uphill side of the mining area. The downhill branch borehole enters from the downhill side of the water-conducting fracture zone in the overburden of the steeply dipping coal seam to detect the maximum height of the water-conducting fracture zone on the uphill side of the mining area and the overburden delamination situation.

[0012] In the above-mentioned method for detecting the water-conducting fracture zone and delamination space of steeply inclined coal seam overburden using a ground three-pronged borehole, in step (A), when there is no obvious ground subsidence and no obstacles, the ground three-pronged borehole adopts a small S-directional borehole; the opening position of the ground three-pronged borehole is located on the ground directly above the working face of the water-conducting fracture zone of the steeply inclined coal seam overburden, the ground three-pronged borehole lags behind the working face by 100-150m, and the ground three-pronged borehole adopts a three-stage borehole structure.

[0013] In the above-mentioned method for detecting water-conducting fracture zones and delamination spaces in steeply inclined coal seams using a ground three-pronged borehole, in step (A), when there is significant ground subsidence or obstacles, the ground three-pronged borehole adopts a large S-shaped directional borehole; the opening position of the ground three-pronged borehole is arranged on the hanging wall of the steeply inclined stratum and located 5-10m outside the stratum movement boundary, the ground three-pronged borehole lags behind the working face by 100-150m, and the ground three-pronged borehole adopts a four-stage borehole structure.

[0014] In the above-mentioned method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a ground-based three-pronged borehole, in step (B), when the ground-based three-pronged borehole uses a small S-directional borehole:

[0015] Step (S-1): First main hole construction: Vertical main hole construction, enter stable bedrock 10-20m, and lower the first-level geological casing;

[0016] Step (Small S-2): Construction of the directional section of the second-stage S-shaped branch directional drilling: Construction of the directional sections of the small S-shaped branch holes in the mining area, the directional sections of the small S-shaped uphill branch holes, and the directional sections of the small S-shaped downhill branch holes are carried out in the lower part of the first-stage main hole. The drilling enters the bedrock above the mining fracture zone by 60-120m and the second-stage geological casing is lowered.

[0017] Step (S-3): Construction of the detection section of the three-section S-shaped branch directional borehole: Continue drilling the detection section of the three-section S-shaped branch directional borehole from the bottom of the directional section of the two-section S-shaped branch directional borehole. The detection section is an open borehole, and the final depth of the detection section is to enter the fracture zone or the roof of the coal seam.

[0018] The above-mentioned method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole has the following steps: In step (S-1), the diameter of the first borehole is 270–350 mm, and the diameter of the first geological casing is 230–260 mm. A single-component cement slurry with a water-cement ratio of 0.6:1 is used for cementing. In step (S-2), the diameter of the second borehole is 215–225 mm, and the diameter of the second geological casing is 165–190 mm. A special casing material is used to fill the annular space between the first and second borehole sections and the geological casing. In step (S-3), the diameter of the third borehole is 110–150 mm.

[0019] The special casing material is made of clay powder, fly ash, cement, water and additives. The additive is water glass. The ratio of clay powder, fly ash, cement and water is 0.5:0.3:0.2:1, and the content of additives is 0.3% to 1% of the cement mass.

[0020] In the above-mentioned method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a ground-based three-pronged borehole, in step (B), when the ground-based three-pronged borehole uses a large S-shaped directional borehole:

[0021] Step (Big S-1), Construction of the vertical section of the main borehole: Construction of the vertical main borehole, entering the stable bedrock 10-20m, and lowering the first-level geological casing;

[0022] Step (Big S-2), Construction of the S-shaped extension section of the second main borehole: Construct the S-shaped extension section of the second main borehole towards the steeply inclined coal seam at the lower part of the vertical section of the first main borehole, enter the position 150-200m above the coal seam, and be 30-80m away from the working face to be explored, and lower the second geological casing.

[0023] Step (Big S-3): Construction of the directional section of the three-section big S-shaped branch directional borehole: Construction of the directional sections of the big S-shaped branch boreholes in the mining area, the directional sections of the big S-shaped uphill branch boreholes, and the directional sections of the big S-shaped downhill branch boreholes are carried out separately in the lower part of the S-shaped extension section of the second-section main borehole. The target is entered 30-60m above the bedrock above the water-conducting fracture zone, and the S-shaped directional borehole is transformed into a vertical borehole. The three-section geological casing is then lowered.

[0024] Step (Big S-4): Construction of the detection section of the four-section large S-shaped branch directional borehole: Continue drilling the detection section of the four-section large S-shaped branch directional borehole from the bottom of the directional section of the three-section large S-shaped branch directional borehole. The detection section is an open borehole, and the final depth of the detection section is to enter the fracture zone or the roof of the coal seam.

[0025] The above-mentioned method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole has the following steps: In step (S-1), the diameter of the first borehole is 270–390 mm, and the diameter of the first geological casing is 250–280 mm. A single-component cement slurry with a water-cement ratio of 0.6:1 is used for cementing. In step (S-2), the diameter of the second borehole is 215–225 mm, and the diameter of the second geological casing is 165–195 mm. A special casing material is used to fill the annular space between the first and second borehole sections and the geological casing. In step (S-3), the diameter of the third borehole is 155–175 mm, and the diameter of the third geological casing is 125–150 mm. A special casing material is used to fill the annular space between the third borehole and the geological casing. In step (S-4), the diameter of the fourth borehole is 98–130 mm.

[0026] The above-mentioned method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole, in step (C),

[0027] Step (C-1), during drilling of some branch holes, uphill branch holes, and downhill branch holes in the stope: A real-time surface monitoring system is used to observe the leakage of drilling flushing fluid. The system dynamically and continuously monitors the amount of fluid leakage and automatically calculates the leakage per unit borehole and per unit time per footage. A well leakage tester is used to test the specific location and amount of leakage of drilling flushing fluid throughout the entire depth range of the borehole, thereby comprehensively determining the height of the maximum water-conducting fracture zone in the middle of the stope. Sonic logging is used to analyze the formation fracture rate of the fracture zone. Based on the in-hole sonic logging borehole inspection technology, the development characteristics of the overlying water-conducting fracture zone and the separation space are comprehensively determined, and the development range and connectivity of the mining-induced fracture zone are assessed.

[0028] Step (C-2): After the construction of some branch holes, uphill branch holes and downhill branch holes in the mining area is completed, cut off the casing of the directional section of the S-shaped branch directional drilling hole and pull it out. Use 0.6:1 single liquid cement grout to seal the branch hole.

[0029] In the above-mentioned method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole, step (C-1) involves:

[0030] The theoretical equation was obtained by fitting a logarithmic spiral equation to determine the extent of the water-conducting fracture zone in the overlying strata of steeply dipping coal seams. The six data points used were three points determined by ground exploration, P... 上山 P 中部 and P 下山 , and the three points inherent to the coal seam: P0, P1, and P2;

[0031] Where: P 上山 P represents the location of water-conducting fractures obtained from the exploration of the branch borehole on the uphill slope. 中部P represents the location of water-conducting fractures obtained from partial borehole detection in the mining area. 下山 The locations of water-conducting fractures obtained from the downhill branch borehole detection are: P0 is the intersection of the upper horizontal section and the coal seam roof, P1 is the intersection of the upper horizontal section and the floor, and P2 is the intersection of the lower horizontal section and the coal seam roof.

[0032] Let the polar equation of the logarithmic spiral be:

[0033] r = a·exp(b·θ) (1);

[0034] Where r represents the radial distance, θ represents the rotation angle, and a and b are constants;

[0035] Transform equation (1) into:

[0036] lnr=bθ+lna (2);

[0037] Equation (2) satisfies the form of a linear equation, and thus the coefficients b and lna of equation (2) that best approximate it are fitted.

[0038] Actual measurement: On the profile perpendicular to the mining advance direction, a Cartesian coordinate system is established with the coal seam dip direction as the X-axis and the normal direction as the Y-axis. The origin of the coordinate system is located at the intersection of the upper horizontal plane and the coal seam roof. The coordinates of these 6 points are measured.

[0039] Using the intersection of the roof of the upper left roadway and the roof of the coal seam as the origin, rotate counterclockwise to establish a polar coordinate system, and transform the coordinates of the 6 data points into polar coordinates; use Origin software to fit equation (2) to obtain the coefficients b and lna of equation (2);

[0040] Substituting the coefficients b and lna back into equation (1), we obtain the polar coordinate equation of the logarithmic spiral, give the boundary curve of the fracture zone on the cross section, and predict the development range of the water-conducting fracture zone in the overburden of the horizontal segmented fully mechanized longwall mining face of the steeply inclined extra-thick coal seam.

[0041] The technical solution of the present invention achieves the following beneficial technical effects:

[0042] 1. The ground three-way borehole detection technology of the present invention provides a new field measurement method for detecting the water-conducting fracture zone and delamination space of steeply inclined coal seams. Based on whether there is obvious ground subsidence or obstacles, the ground three-way borehole is divided into small S-shaped ground three-way boreholes and large S-shaped ground three-way boreholes. It can not only accurately detect the development of the water-conducting fracture zone and delamination space of the overlying rock, but also obtain data on the degree of development of overlying rock mining fractures. At the same time, it reduces the relocation of drilling rigs, which can significantly reduce the amount of drilling work, save engineering costs, and reduce the engineering cost of measuring the water-conducting fracture zone and delamination space of the overlying rock, thus achieving efficient exploration of the water-conducting fracture zone of steeply inclined coal seams.

[0043] 2. The height of the maximum water-conducting fracture zone in the central part of the stope is determined by combining a real-time surface monitoring system for flushing fluid and a well leakage meter. Sonic logging is used to analyze the formation fracture rate within the fracture zone. This invention not only accurately determines the location of leakage but also the degree of mining-induced fracture development. The central stope borehole is used to detect the height of the maximum fracture zone and the caving zone in the central stope; the uphill branch borehole is used to detect the height of the water-conducting fracture zone on the uphill side; and the downhill branch borehole is used to detect the height of the water-conducting fracture zone on the downhill side and the overburden separation condition. Furthermore, the spiral equation is used to predict the development range of the overburden water-conducting fracture zone in the horizontally segmented fully mechanized longwall face of a steeply dipping, extra-thick coal seam, and the equation parameters are obtained through linear regression analysis.

[0044] 3. Addressing the asymmetric deformation and failure characteristics of the overburden in steeply dipping coal seams, the surface three-pronged borehole system comprises one main borehole and S-shaped branch boreholes. This allows for direct and reliable measurement of overburden deformation and failure in the middle, uphill, and downhill sides of the working face. Simultaneously, a multi-stage wellbore structure is employed, with geological casing lowered into non-observation sections to ensure the stability of the S-shaped directional borehole and prevent borehole collapse from affecting on-site observation efficiency. The surface three-pronged borehole system eliminates the need for constructing new exploratory boreholes, significantly reducing detection time and engineering costs. Attached Figure Description

[0045] Figure 1 Three-pronged borehole layout on the ground when there is no obvious ground subsidence and no obstacles;

[0046] Figure 2 Three-pronged drilling layout for ground when there is significant ground subsidence or obstacles;

[0047] Figure 3 A schematic diagram of the fitting of the water-conducting fracture zone range of the overburden in a steeply inclined, extra-thick coal seam.

[0048] The reference numerals in the attached diagram are as follows: 1-Surface three-way borehole; 2-Main borehole; 2-1-Vertical section of main borehole; 2-2-S-shaped extension of main borehole; 3-S-shaped branch directional borehole; 3-1-Partial branch borehole in the mining area; 3-2-Uphill branch borehole; 3-3-Downhill branch borehole; 4-Steeply inclined coal seam; 5-Water-conducting fracture zone of overlying strata; 6-Crossing zone; 7-Loose layer; 8-Bedrock; 9-Directional drilling rig. Detailed Implementation

[0049] Example 1: Method and construction technology for detecting water-conducting fracture zones and delamination spaces in the overlying rock of steeply dipping coal seams using a three-pronged borehole in a western mine.

[0050] Step (A): Since the working face is only 70m long, which is relatively small, and there is no obvious ground subsidence and no obstacles, the ground three-way borehole adopts the small S-directional hole. The ground three-way borehole is only set in the middle of the ground directly above the working face of the water-conducting fracture zone of the steeply inclined coal seam overburden. The borehole adopts a three-stage borehole structure.

[0051] Step (B)

[0052] Step (S-1), Construction of the first main hole 2: Construct the vertical main hole, enter the stable bedrock 15m, and lower the first-level geological casing; the diameter of the first borehole is Φ311.1mm, and a Φ244.5mm casing is lowered.

[0053] Step (Small S-2): Construction of the directional section of the second-stage S-shaped branch directional borehole: Construction of the directional sections of the small S-shaped branch boreholes 3-1, 3-2, and 3-3 in the lower part of the first-stage main borehole, respectively, to enter the bedrock above the mining fracture zone by 60m and lower the second-stage geological casing; the second-stage borehole diameter is Φ215.9mm, and a Φ177.8mm casing is lowered. The annular space between the first-stage and second-stage boreholes and the geological casing is filled with special casing material.

[0054] The special casing material is made of clay powder, fly ash, cement, water and additives. The additive is water glass. The ratio of clay powder, fly ash, cement and water is 0.5:0.3:0.2:1, and the content of additives is 0.5% of the cement mass.

[0055] Step (S-3), Construction of the detection section of the three-section S-shaped branch directional borehole: Continue drilling the detection section of the three-section S-shaped branch directional borehole at the bottom of the directional section of the two-section S-shaped branch directional borehole. The detection section is an open hole with a diameter of Φ133mm. The final depth of the detection section is to enter the fracture zone or the roof of the coal seam.

[0056] Step (C): The specific location and amount of leakage are determined by using a real-time ground monitoring system for borehole flushing fluid consumption and a well leakage meter, thereby obtaining the height of the maximum water-conducting fracture zone in the middle of the stope. The development characteristics of the overlying water-conducting fracture zone and the delamination space are determined by using in-hole sonic logging and borehole inspection technology, and the development range and connectivity of the mining-induced fracture zone are assessed.

[0057] During the construction of the exploration section of borehole 3-1 in the mining area, the real-time ground monitoring system reported a borehole flushing fluid consumption of 7.6 m³. 3 / h, the well leakage meter measured a loss of 6.2m at a vertical depth of 288.42m at the bottom of the well. 3 / h, the height of the maximum water-conducting fracture zone in the middle of the mining area is estimated to be 96.32m;

[0058] During the construction of the exploration section of branch borehole 3-2, the ground real-time monitoring system reported a borehole flushing fluid consumption of 6.5 m³. 3 / h, the well leakage meter measured a loss of 4.6m at a vertical depth of 301.63m at the bottom of the well. 3 / h, the estimated maximum water-conducting fracture zone height in the mining area is 57.49m;

[0059] During the construction of the exploration section of branch borehole 3-3, the ground real-time monitoring system reported a borehole flushing fluid consumption of 7.2 m³. 3 / h, the well leakage meter measured a loss of 5.1m at a vertical depth of 303.68m at the bottom of the well. 3 / h, the maximum water-conducting fracture zone height in the downhill mining area is estimated to be 115.72m. During the drilling process, there was no drill bit dropping, and borehole inspection showed that the overlying strata were not well developed.

[0060] In polar coordinates, P0, P1, P2, P 上山 P 中部 P 下山 The coordinates of these 6 points are shown in Table 1 below.

[0061] Table 1. Coordinates of points in polar coordinates in Example 1

[0062] serial number Radial distance (m) Rotation angle θ (°) <![CDATA[p0]]> 2.8 0 <![CDATA[p1]]> 19.23 104 <![CDATA[p 上山 ]]> 50.86 186 <![CDATA[P 中部 ]]> 62.52 215 <![CDATA[P 下山 ]]> 68.42 245 <![CDATA[P2]]> 118.75 360

[0063] Using the Oringin software for phenomenon regression, the coefficient b of equation (2) is 0.594, and lna = 1.59. Therefore, equation (2) is...

[0064] ln(r) = 1.59 + 0.594θ;

[0065] Substituting back into equation (1), we get

[0066] r = 1.59·exp(0.594θ) (1);

[0067] The polar coordinate equation (1) of the logarithmic spiral gives the boundary curve of the fracture zone on the cross section, which can predict the development range of the water-conducting fracture zone in the overburden of the horizontal segmented fully mechanized longwall mining face of steeply inclined extra-thick coal seams.

[0068] Example 2: Method and construction technology for detecting water-conducting fracture zones and delamination spaces in the overlying rock of steeply dipping coal seams using a three-pronged borehole in a western mine.

[0069] Step (A): Due to ground subsidence and water accumulation, the ground three-way borehole adopts a large S-shaped directional borehole, which is arranged 20m outside the ground movement range. The borehole adopts a four-stage borehole structure.

[0070] Step (B)

[0071] In step (Big S-1), the construction of the vertical section 2-1 of the first main borehole is as follows: the vertical main borehole is constructed, entering the stable bedrock for 15m, and the first-level geological casing is lowered; the diameter of the first wellbore borehole is 381mm, the diameter of the first geological casing is 273.05mm, and the well is cemented with single-liquid cement slurry with a water-cement ratio of 0.6:1.

[0072] In step (large S-2), the second main borehole S-shaped extension section 2-2 is constructed: the second main borehole S-shaped extension section is constructed at the lower part of the vertical section of the first main borehole towards the steeply inclined coal seam, reaching a position 200m above the coal seam and 50m horizontally from the working face to be explored, and the second geological casing is lowered; the diameter of the second borehole is 215mm, and the diameter of the second geological casing is 193mm. Special casing material is used to fill the annular space between the first and second borehole sections and the geological casing;

[0073] The special casing material is made of clay powder, fly ash, cement, water and additives. The additive is water glass. The ratio of clay powder, fly ash, cement and water is 0.5:0.3:0.2:1, and the content of additives is 0.5% of the cement mass.

[0074] In step (Big S-3), the directional section construction of the three-section large S-shaped branch directional borehole is carried out as follows: the directional sections of the large S-shaped stope branch hole 3-1, the large S-shaped uphill branch hole 3-2, and the large S-shaped downhill branch hole 3-3 are constructed separately in the lower part of the S-shaped extension section of the second-section main hole. The target is entered 50m above the bedrock above the water-conducting fracture zone, and the S-shaped directional hole is transformed into a vertical borehole. The three-section geological casing is then lowered. The diameter of the directional section of the three-section large S-shaped branch directional borehole is 171.45mm, and the diameter of the three-section geological casing is 139.7mm. The annular space between the three-section borehole and the geological casing is filled with special casing material.

[0075] In step (large S-4), the exploration section of the four-section large S-shaped branch directional borehole is constructed: the bottom of the directional section of the three-section large S-shaped branch directional borehole continues to be drilled into the exploration section of the four-section large S-shaped branch directional borehole. The exploration section is an open borehole, and the final depth of the exploration section is to enter the fracture zone or the roof of the coal seam; the diameter of the four-section borehole is Φ114.3mm, and the final depth of the exploration section is to enter the fracture zone or the roof of the coal seam.

[0076] Using the same testing method, we obtained:

[0077] During the construction of the exploration section of borehole 3-1 in the large S-shaped stope, the real-time ground monitoring system reported a borehole flushing fluid consumption of 7.6 m³. 3 / h, the well leakage meter measured a loss of 6.9m at a vertical depth of 473.65m at the bottom of the well. 3 / h, the height of the maximum water-conducting fracture zone in the middle of the mining area is estimated to be 113.38m;

[0078] During the construction of the exploration section of the large S-shaped uphill branch borehole 3-2, the ground real-time monitoring system reported a borehole flushing fluid consumption of 6.2 m³. 3 / h, the well leakage meter measured a loss of 5.5m at a vertical depth of 485.88m at the bottom of the well. 3 / h, the estimated height of the maximum water-conducting fracture zone on the upper slope of the mining area is 77.32m;

[0079] During the construction of the exploration section of the large S-shaped downhill branch borehole 3-3, the ground real-time monitoring system reported a borehole flushing fluid consumption of 7.5 m³. 3 / h, the well leakage meter measured a loss of 5.8m at a vertical depth of 490.17m at the bottom of the well. 3 / h, the estimated maximum water-conducting fracture zone height in the downhill mining area is 165.37m;

[0080] During the drilling process, the drill bit dropped 1.6m at a vertical depth of 502.3m. Drill hole inspection showed that there was some delamination of the overlying rock.

[0081] In polar coordinates, P0, P1, P2, P 上山 P 中部 P 下山 The coordinates of these 6 points are shown in Table 2 below.

[0082] Table 2. Coordinates of points in polar coordinates (Example 2)

[0083] serial number Radial distance (m) Rotation angle θ (°) <![CDATA[p0]]> 3 0 <![CDATA[p1]]> 25.74 104 <![CDATA[p 上山 ]]> 72.73 186 <![CDATA[P 中部 ]]> 83.15 215 <![CDATA[P 下山 ]]> 88.17 245 <![CDATA[P2]]> 137.73 360

[0084] Using the Oringin software for phenomenon regression, the coefficient b of equation (2) is 0.605, and lna = 1.79. Therefore, equation (2) is...

[0085] ln(r) = 1.79 + 0.605θ;

[0086] Substituting back into equation (1), we get

[0087] r = 1.79·exp(0.605θ) (1);

[0088] The polar coordinate equation (1) of the logarithmic spiral gives the boundary curve of the fracture zone on the cross section, which can predict the development range of the water-conducting fracture zone in the overburden of the horizontal segmented fully mechanized longwall mining face of steeply inclined extra-thick coal seams.

[0089] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for detecting water-conducting fracture zones and delamination spaces in the overlying strata of steeply dipping coal seams using a three-pronged borehole, characterized in that... Includes the following steps: Step A, Arrange exploratory boreholes: Use a ground three-way drilling method (1); that is, determine the opening position on the ground, drill a main hole (2) and three S-shaped branch directional boreholes (3); Step B: Geological casing is lowered into the directional sections of the main hole (2) and the S-shaped branch directional borehole. The probe section of the S-shaped branch directional borehole is a bare hole. The probe section of the S-shaped branch directional borehole is drilled into the fracture zone of the steeply inclined coal seam or the roof of the coal seam. In step C, during the drilling of the exploration section of the S-shaped branch directional borehole, the specific location and amount of leakage are determined by a real-time ground monitoring system for borehole flushing fluid consumption and a well leakage meter. This allows the maximum water-conducting fracture zone height of the overburden in the horizontally segmented fully mechanized longwall mining area of ​​the steeply inclined extra-thick coal seam to be obtained. The development characteristics of the overburden water-conducting fracture zone and the separation space are determined by a combination of in-hole sonic logging and borehole inspection techniques. The development range and connectivity of the mining-induced fracture zone are then assessed. The extent of the water-conducting fracture zone in the overlying strata of steeply dipping coal seams was obtained by fitting a logarithmic spiral equation. The six data points used were three points determined by ground exploration, P... 上山 P 中部 and P 下山 , and the three points inherent to the coal seam: P0, P1, and P2; Where: P 上山 P represents the location of water-conducting fractures detected by the uphill branch borehole (3-2). 中部 P represents the location of water-conducting fractures detected by some of the branch boreholes (3-1) in the stope. 下山 The locations of water-conducting fractures detected by the downhill branch borehole (3-3) are: P0 is the intersection of the upper horizontal section with the coal seam roof, P1 is the intersection of the upper horizontal section with the floor, and P2 is the intersection of the lower horizontal section with the coal seam roof. Let the polar equation of the logarithmic spiral be: r = a·exp(b·θ) (1; Where r represents the radial distance, θ This represents the rotation angle, where a and b are constants; Transform equation (1) into: lnr = bθ + lna (2); Equation (2) satisfies the form of a linear equation, and thus the coefficients b and lna of equation (2) that best approximate it are obtained; Actual measurement: On the profile perpendicular to the mining advance direction, a Cartesian coordinate system is established with the coal seam dip direction as the X-axis and the normal direction as the Y-axis. The origin of the coordinate system is located at the intersection of the upper horizontal plane and the coal seam roof. The coordinates of these 6 points are measured. Using the intersection of the roof of the upper left roadway and the roof of the coal seam as the origin, rotate counterclockwise to establish a polar coordinate system, and transform the coordinates of the 6 data points into polar coordinates; use Origin software to fit equation (2) to obtain the coefficients b and lna of equation (2); Substituting the coefficients b and lna back into equation (1), we obtain the polar coordinate equation of the logarithmic spiral, give the boundary curve of the fracture zone on the cross section, and predict the development range of the water-conducting fracture zone in the overburden of the horizontal segmented fully mechanized longwall mining face of the steeply inclined extra-thick coal seam.

2. The method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole as described in claim 1, characterized in that... In step A, the S-shaped branch directional borehole includes a partial branch borehole in the mining area (3-1), an uphill branch borehole (3-2), and a downhill branch borehole (3-3). The partial branch borehole in the mining area enters from the middle of the overlying water-conducting fracture zone (5) of the steeply inclined coal seam (4) to detect the height of the maximum water-conducting fracture zone and the height of the cross-fall zone (6) in the middle of the mining area. The uphill branch borehole (3-2) enters from the uphill side of the overlying water-conducting fracture zone of the steeply inclined coal seam to detect the height of the maximum water-conducting fracture zone on the uphill side of the mining area. The downhill branch borehole (3-3) enters from the downhill side of the overlying water-conducting fracture zone of the steeply inclined coal seam to detect the height of the maximum water-conducting fracture zone on the uphill side of the mining area and the overlying delamination situation.

3. The method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole as described in claim 1, characterized in that... In step A, when there is no obvious ground subsidence and no obstacles, the ground three-way borehole adopts a small S-directional hole; the opening position of the ground three-way borehole is located on the ground directly above the working face of the steeply inclined coal seam overburden water-conducting fracture zone, the ground three-way borehole lags behind the working face by 100-150m, and the ground three-way borehole adopts a three-stage borehole structure.

4. The method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole as described in claim 3, characterized in that... In step A, when there is a significant ground subsidence or obstacles, the ground three-way borehole adopts a large S-shaped directional borehole; the opening position of the ground three-way borehole is arranged on the hanging wall of the steeply inclined stratum and located 5 to 10 m outside the stratum movement boundary, the ground three-way borehole lags behind the working face by 100 to 150 m, and the ground three-way borehole adopts a four-stage borehole structure.

5. The method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole as described in claim 3, characterized in that... In step B, when the ground three-way drilling adopts a small S-oriented hole: Construction of the main borehole (2): The main borehole is constructed vertically, and the first-level geological casing is lowered into the stable bedrock 10-20m. Construction of the directional section of the second-stage S-shaped branch directional drilling: Construction of the directional section of the small S-shaped branch hole (3-1), the directional section of the small S-shaped uphill branch hole (3-2), and the directional section of the small S-shaped downhill branch hole (3-3) in the lower part of the first-stage main hole, entering the bedrock above the mining fracture zone by 60-120m, and lowering the second-stage geological casing; Construction of the detection section of the three-section S-shaped branch directional borehole: The bottom of the directional section of the two-section S-shaped branch directional borehole continues to be drilled into the detection section of the three-section S-shaped branch directional borehole. The detection section is an open borehole, and the final depth of the detection section is to enter the fracture zone or the roof of the coal seam.

6. The method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole as described in claim 5, characterized in that... The diameter of the first wellbore borehole is 270–350 mm, and the diameter of the first geological casing is 230–260 mm. Single-component cement slurry with a water-cement ratio of 0.6:1 is used for cementing. The diameter of the second wellbore borehole is 215–225 mm, and the diameter of the second geological casing is 165–190 mm. Special casing material is used to fill the annular space between the first and second wellbore sections and the geological casing. The diameter of the third wellbore borehole is 110–150 mm. The special shell material is made of clay powder, fly ash, cement, water and additives. The additive is water glass. The ratio of clay powder, fly ash, cement and water is 0.5:0.3:0.2:1, and the content of additives is 0.3% to 1% of the cement mass.

7. The method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole as described in claim 4, characterized in that... In step B, when the ground three-way drilling adopts a large S-shaped directional hole: Construction of the vertical section (2-1) of the main borehole: The vertical main borehole is constructed, and the first-level geological casing is lowered into the stable bedrock for 10-20m. Construction of the S-shaped extension section (2-2) of the second main hole: The S-shaped extension section of the second main hole is constructed in the lower part of the vertical section of the first main hole towards the steeply inclined coal seam, reaching a position 150-200m above the coal seam, 30-80m horizontally away from the working face to be explored, and the second geological casing is lowered. Construction of the directional section of the three-section large S-shaped branch directional borehole: In the lower part of the S-shaped extension section of the second-section main borehole, the directional section of the large S-shaped branch borehole in the mining area (3-1), the directional section of the large S-shaped uphill branch borehole (3-2), and the directional section of the large S-shaped downhill branch borehole (3-3) are constructed respectively. The target is entered 30-60m above the bedrock above the water-conducting fracture zone, and the S-shaped directional borehole is transformed into a vertical borehole. The three-section geological casing is then lowered. Construction of the exploration section of the four-section large S-shaped branch directional borehole: The bottom of the directional section of the three-section large S-shaped branch directional borehole continues to be drilled into the exploration section of the four-section large S-shaped branch directional borehole. The exploration section is an open borehole, and the final depth of the exploration section is to enter the fracture zone or the roof of the coal seam.

8. The method for detecting water-conducting fracture zones and delamination spaces in steeply dipping coal seams using a three-pronged borehole as described in claim 7, characterized in that... The first section of the well has a borehole diameter of 270–390 mm and a geological casing diameter of 250–280 mm. A single-component cement slurry with a water-cement ratio of 0.6:1 is used for cementing. The second section has a borehole diameter of 215–225 mm and a geological casing diameter of 165–195 mm. Special casing material is used to fill the annular space between the first and second sections of the borehole and the geological casing. The third section has a borehole diameter of 155–175 mm and a geological casing diameter of 125–150 mm. Special casing material is used to fill the annular space between the third section of the borehole and the geological casing. The diameter of the four-hole drill is 98-130mm.

9. A method for detecting water-conducting fracture zones and delamination spaces in the overlying strata of steeply dipping coal seams using a three-pronged borehole as described in claim 2, characterized in that... In step C, Step C-1: During drilling of some branch holes, uphill branch holes, and downhill branch holes in the stope: A real-time surface monitoring system is used to observe the leakage of drilling flushing fluid. The real-time surface monitoring system dynamically and continuously monitors the amount of flushing fluid leakage and automatically calculates the leakage per unit borehole and the leakage per unit time per unit footage. A well leakage tester is used to test the specific location and amount of leakage of drilling flushing fluid throughout the entire depth range of the borehole, thereby comprehensively determining the height of the maximum water-conducting fracture zone in the middle of the stope; sonic logging is used to analyze the formation fracture rate of the fracture zone, and the development characteristics of the overburden water-conducting fracture zone and the delamination space are comprehensively determined based on the in-hole sonic logging borehole inspection technology, and the development range and connectivity of the mining-induced fracture zone are assessed; Step C-2: After the construction of some branch holes, uphill branch holes, and downhill branch holes in the mining area is completed, cut off the casing of the directional section of the S-shaped branch directional drilling hole and pull it out. Use 0.6:1 single-liquid cement grout to seal the branch hole.

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