A method for improving gas extraction effect of working face and stability of surrounding rock of adjacent roadway by kilometer horizontal drilling and fracturing

Abstract

The application discloses a method for improving gas extraction effect of a working face and stability of surrounding rock of a neighboring roadway by kilometer horizontal drilling and fracturing, and belongs to the field of coal mining, and the technical points are as follows: first, according to the engineering geological conditions of the working face, the height of the caving zone and the fractured zone, the distribution range of the O-shaped ring, and the horizon and thickness of the hard rock layer which plays a key role in the pressure of the working face, the key parameters of the kilometer horizontal drilling and the hydraulic fracturing are determined; second, the kilometer horizontal drilling is constructed in the drilling field of the recovery working face and the hydraulic fracturing is carried out.

Description

Technical Field

[0001] This invention relates to the field of coal mining, and more specifically, to a method for improving the gas extraction effect and the stability of the surrounding rock in adjacent roadways by using kilometer-level horizontal drilling and fracturing. Background Technology

[0002] As the depth and intensity of underground coal mining increase, geological conditions become more complex, and frequent gas disasters seriously affect the safety of mine workers.

[0003] Currently, some coal mines experience high gas emissions. Traditional kilometer-deep borehole extraction methods have long lead times, resulting in a mismatch between gas control efficiency and the progress of face mining, leading to unsatisfactory extraction effects and impacting efficient coal mine production. Furthermore, after the face mining is completed, the lateral roof above the goaf may not completely collapse, with thick, hard rock strata exhibiting long exposed spans and large exposed areas. This causes adjacent face mining roadways to be affected not only by the support pressure of the adjacent face but also by the combined effects of the preceding and lateral support pressures during adjacent face mining. The roadways and support structures are in a state of high stress and high disturbance for extended periods, compromising the stability of the surrounding rock and causing severe deformation. This significantly increases the difficulty of roadway support and subsequent maintenance costs, and even poses a threat to miners' lives, hindering the safe and efficient development of the mine.

[0004] Therefore, finding a method to improve the gas extraction efficiency of this working face and the stability of the surrounding rock in adjacent roadways is of great significance.

[0005] Therefore, it is necessary to consider both the enhanced gas extraction and the roof cutting and pressure relief protection of the roadway.

[0006] Firstly, the design method for kilometer-long boreholes used to solve gas drainage problems mainly involves fixing the drilling site spacing and calculating or experimentally measuring the height of the caving zone and fracture zone in the overlying strata of the construction area based on empirical formulas. This determines the borehole layout height, generally located in the upper part of the caving zone and the middle to lower part of the fracture zone. The borehole design comprehensively considers factors such as the borehole angle, caving angle, borehole spacing, borehole inclination angle, borehole azimuth angle, and the length of the cantilever beam of the foundation roof. However, currently, the selection of gas drainage parameters for gas drainage boreholes is mostly based on experience, without considering the changes in the gas migration trajectory during working face extraction. This leads to unscientific and unreasonable selection of drainage boreholes, making it difficult to meet gas drainage requirements and resulting in poor drainage effects.

[0007] Secondly, to address the issues of surrounding rock stability and high disturbance and stress in roadway support, various methods exist. One approach involves increasing the width of the coal pillars in the roadway support and using reinforced supports to maintain the stability of the surrounding rock. This involves rationally selecting support structures and parameters to enhance the bearing capacity of the coal pillars themselves. However, field investigations have revealed that under conditions of hard roof strata, high-extraction working faces, and significant burial depth, increasing the width of the coal pillars in the roadway support is not very effective in mitigating the impact of mining. Furthermore, excessive coal pillar provision can lead to a serious waste of coal resources. Reinforced support methods are difficult to implement and have many limitations and time constraints, failing to effectively guarantee the safe and effective use of the roadway throughout its entire lifecycle, including both adjacent and current working face mining activities. Another approach involves roof cutting to relieve stress and maintain stability. Currently, widely used methods include blasting and hydraulic fracturing for roof cutting. However, blasting roof cutting poses significant safety hazards to workers, especially in high-gas mines where it is unsuitable as a conventional pressure relief method. Hydraulic fracturing roof cutting requires drilling multiple sets of pressure relief holes. During on-site construction, gas extraction enhancement and roof cutting pressure relief and roadway protection are considered separately. Often, extraction holes and pressure relief holes need to be drilled separately to solve the corresponding problems, resulting in wasted manpower and increased costs. Summary of the Invention

[0008] This invention provides a method for improving gas extraction efficiency and surrounding rock stability in adjacent roadways through kilometer-level horizontal drilling and fracturing, aiming to solve the problems of existing technologies.

[0009] The specific proposal of this application is as follows:

[0010] A method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling and fracturing includes the following steps:

[0011] First, based on the engineering geological conditions of the mining face, the height of the caving zone and fracture zone, the distribution range of the O-ring, and the stratigraphic position and thickness of the hard rock strata that play a key role in the pressure on the working face, the key parameters for kilometer-level horizontal drilling and hydraulic fracturing are determined.

[0012] Secondly, a kilometer-long horizontal borehole was drilled in the longwall face drilling site and hydraulic fracturing was performed.

[0013] A method for improving gas extraction efficiency and surrounding rock stability in adjacent roadways through kilometer-level horizontal drilling and fracturing includes the following steps:

[0014] S1, Investigate the general engineering geology of the site and collect basic data on the longwall mining face;

[0015] S2, determine the height of the caving zone, the height of the fracture zone, and the stratigraphic position and thickness of the hard rock layer that plays a key role in pressing the working face;

[0016] S3, design parameters for a kilometer-long horizontal borehole and hydraulic fracturing parameters;

[0017] The parameters of the kilometer-long horizontal borehole include: borehole layer, borehole inclination angle, borehole azimuth angle, borehole starting position, borehole ending position, horizontal distance between the first borehole and the mining roadway, vertical and horizontal distances between boreholes, borehole length, and the relationship between the number of horizontal layers of the borehole and the thickness of the hard roof being cut.

[0018] The method for determining the horizontal distance between the first borehole and the mining roadway is as follows:

[0019] First, the horizontal distance between the first borehole and the mining roadway is determined by combining the fracture zone height and the roof rock collapse angle, according to the formula:

[0020] L1=H / tanα

[0021] Where: H - average height of the fracture zone, in meters; α - angle of collapse of the roof rock, in degrees.

[0022] Secondly, the horizontal distance between the first borehole and the recovery roadway is determined by combining the mining height and the rock fragmentation coefficient, according to the formula:

[0023]

[0024] In the formula: ∑h - height of the coal seam being mined, in meters; K p - The rock fragmentation coefficient is usually taken as 1.2 to 1.5.

[0025] Next, compare the results obtained from the two methods above, take the average value, and then apply the formula... L is defined as the horizontal distance between the first borehole and the mining roadway;

[0026] The method for determining the vertical distance between boreholes is as follows:

[0027] When the thickness of the hard roof being cut is less than 5m, the borehole is drilled at 1 / 2 of the rock layer; when the thickness of the hard roof being cut is 5-10m, if gas drainage requires 4 boreholes, all boreholes are drilled at 1 / 4 of the distance from the upper and lower boundaries of the rock layer; if gas drainage requires 6 boreholes, the first two boreholes are drilled at 1 / 4 of the distance from the lower boundary of the rock layer, and the last borehole is drilled at 1 / 4 of the distance from the upper boundary of the rock layer; when the thickness of the hard roof being cut is 10-15m, the boreholes are drilled sequentially at 1 / 6, 1 / 2, and 5 / 6 of the distance from the boundary of the rock layer.

[0028] The method for determining the horizontal distance x between boreholes is as follows:

[0029]

[0030] In the formula: R - the fracturing radius of the top rock layer, in meters, which is usually taken as 3 to 5 meters; h - the vertical distance between boreholes, in meters;

[0031] The relationship between the number of horizontal drilling layers and the thickness of the hard top plate being cut is as follows: when the thickness of the hard top plate being cut is less than 5m, drill 1 horizontal drilling layer; when the thickness of the hard top plate being cut is 5 to 10m, drill 2 different horizontal drilling layers; when the thickness of the hard top plate being cut is 10 to 15m, drill 3 different horizontal drilling layers.

[0032] The hydraulic fracturing parameters include: hydraulic pressure, fracturing direction, and fracturing zone (the hydraulic fracturing parameters need to be determined in conjunction with the geostress test results, uniaxial compressive strength, and thickness of the hard rock layer).

[0033] Determining the water pressure: When the water pressure increases to the point that the tensile stress in the rock mass exceeds the critical tensile strength, hydraulic cracks initiate. The critical water pressure Psc at this point can be obtained by the following formula:

[0034] P sc =2R0+R L

[0035] Where: R0—the stress of the surrounding rock at the crack initiation point, which can be approximated by the self-weight stress, and the unit is MPa; R L —The ultimate tensile strength of rock, expressed in MPa;

[0036] S4, set up the drilling site, conduct on-site construction of a kilometer-long horizontal borehole and perform water pressure fracturing;

[0037] S5, gas extraction is carried out on the overlying strata of the goaf during the mining process and the gas extraction concentration and flow rate of this working face are compared and analyzed.

[0038] S6. Comparative analysis of the surrounding rock deformation of adjacent tunnels before and after hydraulic fracturing.

[0039] Furthermore, the height of the caving zone in S2 is calculated using the following formula:

[0040] H M The scope is:

[0041] Where: H M - Height of the caving zone, m; ∑h - Height of the coal seam being mined, m.

[0042] Furthermore, the fracture zone height in S2 is calculated using the following formula:

[0043] H L The scope is:

[0044] Where: H L- Fracture zone height, m; ∑h - Height of the coal seam being mined, m.

[0045] Furthermore, in S2, it is necessary to determine the strata of hard rock layers that play a critical role in the working face. There are two conditions for a rock layer to be considered a critical layer: ① Rock stiffness judgment: In the order from bottom to top, the load on the m-th rock layer is greater than the load on the (m+1)-th rock layer. ② Rock fracture distance judgment: In the order from bottom to top, the fracture distance of the n-th rock layer is less than the fracture distance of the (n+1)-th rock layer. ③ A rock layer that simultaneously meets both conditions can be considered a critical layer.

[0046] ① By determining whether each rock layer in the overburden satisfies q1| m+1 <q1| m This strength condition, where q1| m The load exerted by the m-th rock layer on the 1-th layer can be expressed as:

[0047]

[0048] in:

[0049] h i The thickness of the i-th layer is expressed in meters (m).

[0050] γ i The density of the i-th layer is expressed in kN / m³. 3 ;

[0051] E i Let be the elastic modulus of the i-th layer, in GPa.

[0052] ② By determining whether each rock layer in the overburden satisfies L k <L k+1 This strength condition, where L k Let the fracture distance of the k-th layer be expressed as:

[0053]

[0054] in:

[0055] h k Let m be the thickness of the k-th layer;

[0056] σ k Let be the tensile strength of the k-th layer, in MPa;

[0057] q k Let be the load borne by the k-th layer, in MPa.

[0058] Furthermore, step S4 includes: setting up the first drilling site in the return airway starting from 350-550m of the advance cut, and setting up the next drilling site every 350-500m, until the last drilling site exceeds the stop line by 50m; the number of boreholes arranged in each drilling site is 4-6, the number of borehole rows is 1-2, and the borehole length is 520m-620m (through theoretical analysis combined with mine production practice, in the vertical direction of the overlying strata, the final position of the directional high-level drilling is set in the lower part of the fracture zone. When actually arranging boreholes on site, the lithology of the roof strata should also be considered, and geological structural zones and water-rich strata should be avoided as much as possible).

[0059] High-pressure water pumps are installed in the drilling site, and water pressure fracturing is started in the drilling site after drilling is completed.

[0060] The boreholes are arranged in hard rock strata. Each borehole is subjected to multiple fracturing operations using a retreating method. Fracturing is performed every 10 to 30 meters in the borehole, and each fracturing operation lasts for no less than 30 minutes. During fracturing, the direction of the water head must be perpendicular to the roof of the tunnel. Fracturing is stopped when the water pressure suddenly drops significantly. This process is repeated until the hard rock strata in the horizontal borehole are completely fractured.

[0061] Furthermore, step S5 includes: drilling and enlarging the hole with a reamer; removing the reamer and sealing the hole; starting gas extraction and real-time monitoring when the working face begins to advance, and comparing and analyzing the changes in gas extraction flow rate and concentration before and after drilling and fracturing to determine the extraction effect after fracturing.

[0062] Furthermore, step S6 includes: setting up cross-shaped surrounding rock displacement monitoring points in adjacent roadways to monitor the roadway deformation during the entire mining process of the adjacent working face, and comparing and analyzing the deformation of the roof, floor and sidewalls of the adjacent roadways before and after drilling and fracturing.

[0063] Furthermore, the basic data in step S1 includes: gas characteristics after the working face is mined back, and geomechanical information of the surrounding rock of the roadway to be protected;

[0064] Among them, the gas characteristics after the working face is mined include: the geological structure of the mine field, the gas level, the gas situation of the working face, the prediction of the gas emission of the working face, and the current gas extraction effect.

[0065] The geomechanical information of the surrounding rock of the roadway to be protected includes: rock strata structure and thickness, mining technology, lithology of the roof and floor, hydrogeological conditions, structural conditions, impact of mining, and geostress information of the roadway measured by hydraulic fracturing method; geostress information of the roadway measured by hydraulic fracturing method includes: the magnitude and direction of the maximum principal stress and the minimum principal stress.

[0066] The beneficial effects of this application are as follows:

[0067] First, the basic concept of this application is as follows: on the one hand, high-level gas extraction is carried out in the overlying strata during the mining process of this working face, and the changes in gas extraction concentration and flow rate are compared and analyzed; on the other hand, the borehole, in conjunction with hydraulic fracturing, achieves the effect of roof cutting and pressure relief, thereby reducing the deformation and damage of adjacent roadways. The borehole simultaneously considers both gas extraction and pressure relief for roadway protection. Merging two sets of boreholes into one can solve both problems. By using kilometer-long hydraulic fracturing, the gas extraction effect of this working face and the stability of the surrounding rock of adjacent roadways are improved, while the amount of construction work and costs are significantly reduced, effectively improving work efficiency.

[0068] Secondly, the inventive concept of this application lies in combining gas extraction with the promotion of surrounding rock stability, forming a dual-purpose borehole. Specifically, a set of boreholes is drilled and fracturing is applied to enhance the stability of the surrounding rock; and because the fractures created by fracturing can promote high-level gas extraction, a good gas extraction effect is achieved. Merging two sets of boreholes into one solves two problems, improving work efficiency and reducing production costs.

[0069] Third, the third inventive concept of this application lies in the fact that, in previous gas drainage methods, the directional drilling layout could not match the gas migration patterns, resulting in low concentrations and contents of extracted gas, which could not fully solve the problem of high gas levels in coal mines. Based on the characteristics of gas migration, this application designs 1-2 sets of boreholes at different distances from the coal seam roof in a single drilling site. This optimizes the original directional drilling, which could only extract gas from a single horizontal level, into directional drilling at different levels and layers for gas drainage. In other words, it optimizes from one-dimensional "line extraction" to three-dimensional, highly efficient extraction, increasing the concentration and content of extracted gas. Furthermore, the fracturing of the boreholes increases the number of fractures, enhancing gas migration and thus achieving excellent gas drainage results.

[0070] Fourth, the fourth inventive concept of this application is: This application breaks through the conventional surrounding rock control methods that mainly rely on strong support. Considering that the traditional fracturing method for strong support is difficult to construct and has many limitations and timeliness, this application proposes "to carry out water pressure fracturing in the gas drainage hole, cut off the stress transmission path of the roof, and reduce the roof pressure and load on the coal pillar of the next working face roadway", which can effectively improve the stability of the surrounding rock of the next working face and achieve a good roadway protection effect.

[0071] Fifth, the fifth inventive concept of this application is: This application proposes the first method for calculating the horizontal distance between the borehole and the mining roadway. The specific method is as follows: (1) The average height of the fracture zone and the collapse angle of the roof rock are combined to calculate the horizontal distance suitable for enhanced gas extraction; (2) The mining height is combined with the rock fragmentation coefficient to calculate the horizontal distance suitable for protecting the stability of the surrounding rock of the adjacent roadway; (3) The calculated results are compared and the average value is taken.

[0072] Sixth, the sixth inventive concept of this application lies in: this application proposes a method for calculating the horizontal spacing between boreholes. The specific method is based on the formula: Perform the calculation. Attached Figure Description

[0073] Figure 1 This is a design schematic diagram of Example 1.

[0074] Figure 2 yes Figure 1 Section I-I in the diagram.

[0075] Figure 3 yes Figure 1 Section II-II in the diagram.

[0076] Figure 4 This is a design schematic diagram of Example 2.

[0077] Figure 5 yes Figure 4 AA section view.

[0078] Figure 6 yes Figure 4 BB cross-section diagram. Detailed Implementation

[0079] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0080] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0081] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and specific examples.

[0082] Example 1: Fujiayan Mine

[0083] The method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling fracturing, as provided by this invention, is carried out according to the following steps:

[0084] Step I: Conduct on-site investigation of the mine's engineering geological conditions and test and analyze the geomechanical characteristics of the surrounding rock of the proposed protected roadway, such as rock strata structure and thickness, physical and mechanical properties of the surrounding rock, hydrogeological conditions, structural features, and the impact of mining activities. Based on the mine's borehole columnar section, the initial pressure step distance of the previous longwall face was 29.4m, the coal thickness was 5.8m (using fully mechanized longwall mining, with a mining height of 3.2m and a coal release height of 2.6m), and the maximum relative gas emission rate of the mine was 40.60m³. 3 / t, maximum absolute gas emission rate is 107.65m³ 3 The rate is 0.5 m³ / min, which indicates a high-gas mine, with a gas drainage rate of approximately 48.7%.

[0085] Step II: Determine the theoretical height of the collapse zone as 10.3m to 14.7m according to the formula, and determine the theoretical height of the fracture zone as 39.4m to 50.6m according to the formula.

[0086] Based on the following two formulas:

[0087]

[0088]

[0089] Where m represents a rock stratum currently being calculated;

[0090] q1(x)| m This represents the load exerted by the m-th rock layer on the 1st layer, in MPa.

[0091] E1 represents the elastic modulus of the first rock layer from bottom to top, in GPa.

[0092] h1 represents the thickness of the first rock layer, in meters (m).

[0093] h i The thickness of the i-th rock layer is expressed in meters.

[0094] γ i The unit weight of the i-th rock layer is expressed in kN / m³. 3 ;

[0095] E i Let be the elastic modulus of the i-th rock layer, in GPa.

[0096] L k This represents the fracture distance of the k-th rock layer, in meters.

[0097] h k This represents the thickness of the k-th rock layer, in meters (m).

[0098] q k This represents the load borne by the k-th rock layer, in MPa.

[0099] σ k This represents the tensile strength of the k-th rock layer, expressed in MPa.

[0100] The hard rock stratum that plays a key role in compressing the working face was identified as limestone 28.8m from the top of the roadway, with a thickness of 7.0m.

[0101] Step III: Design the parameters for the kilometer-level horizontal borehole and the parameters for hydraulic fracturing. Specifically, the parameters for the kilometer-level horizontal borehole include: the borehole is located in limestone at a distance of 28.8m from the top of the tunnel and in limestone at a distance of 43.3m from the top of the tunnel.

[0102] The design of the first borehole should take into account the efficient extraction of gas after the mining of this working face, as well as the stress reduction achieved by fracturing the borehole to protect the adjacent working face roadways.

[0103] Therefore, an innovative method for calculating the horizontal distance between the first borehole and the mining roadway is proposed, specifically:

[0104] (1) The horizontal distance suitable for enhanced gas extraction was calculated by combining the average height of the fracture zone and the collapse angle of the roof rock.

[0105] (2) Combine the mining height with the rock fragmentation coefficient to calculate the horizontal distance suitable for protecting the stability of the surrounding rock of adjacent roadways;

[0106] (3) Compare the calculated results and take the average value.

[0107] Based on an innovative method for calculating the horizontal distance between the first borehole and the mining roadway, the calculation process is as follows: The result is determined based on the roof rock collapse angle and fracture zone height; the distance is then calculated using the following formula:

[0108] L1=H / tanα

[0109] Where H is the average height of the fracture zone, and α is the roof rock collapse angle. Specifically, the collapse angle for a moderately stable roof is 60°, and for a stable roof, it is 45°; in this example, the collapse angle is 60°. Based on the above formula, the fracture zone height is determined to be 39.4m to 50.6m, and the average height H is 45m. L1 is calculated to be 25.8m using the formula. The horizontal projection distance between the directional high-level borehole and the return airway should be greater than H / tanα to ensure that the directional borehole is within the fracture zone after sufficient pressure relief. Based on the formula, the horizontal distance between the first borehole and the return airway in this method is 26m.

[0110] Based on the mining height and rock fragmentation coefficient, the distance is calculated using the following formula:

[0111]

[0112] Where ∑h is the mining height, K p The coefficient of rock fragmentation is 1.3. In this example, the mining height is 5.8m and the coefficient of fragmentation is 1.3. According to the formula, the horizontal distance between the first borehole and the mining roadway in this method is 19.7m, which is taken as 20m.

[0113] Compare the results obtained from the two methods above, take the average value, and then apply the formula... The final horizontal distance between the first borehole and the mining roadway was determined to be 23m.

[0114] The horizontal spacing between boreholes is calculated using the following formula:

[0115]

[0116] Where R is the fracturing radius of the top rock layer, and h is the vertical spacing between boreholes.

[0117] Based on the relationship between the number of horizontal drilling layers and the thickness of the rigid top slab being cut, the lower layer thickness is 7m, requiring two horizontal drilling holes, with h taken as 3.5m. According to the formula, the horizontal spacing between the drilling holes is determined to be 4.9m to 9.4m, with an average value of 7.15m, so we take 7.2m. The higher layer thickness is 3.5m, requiring only one horizontal drilling hole, also taken as 7.2m.

[0118] The water pressure can be calculated using the following formula:

[0119] P sc =2R0+R L

[0120] Where: R0 is the surrounding rock stress at the crack initiation point, R L The tensile strength limit of the rock is given by the formula, and the pressure is determined to be 22 MPa.

[0121] Step IV: After determining the borehole layout stratum height and the horizontal distance between the first borehole and the coal pillar, set up the first drilling site 350m from the opening, and set up the next drilling site every 350m until the last drilling site exceeds the stop line by 50m. Install a kilometer-long directional drilling rig in the drilling site, and then start drilling from the first drilling site, drilling 4 boreholes in each drilling site, with a borehole length of 520m to 580m. The initial part of the borehole trajectory is curved, and the main part is an approximately horizontal straight line. Considering the protection of the mining roadway, drilling is carried out on the side close to the solid coal in the mining roadway.

[0122] Hydraulic fracturing was conducted on-site, involving the deployment of high-pressure water pumps within the drilling area. Hydraulic fracturing began at each drilling site after drilling was completed. The boreholes were located in hard rock strata, and each borehole underwent multiple fracturing operations using a retreating method. Fracturing was performed every 20 meters within the borehole, with each fracturing session lasting at least 30 minutes. During fracturing, the water head had to be perpendicular to the roadway roof. Fracturing was stopped when the water pressure suddenly dropped significantly. This process was repeated until the hard rock strata within the horizontal borehole were completely fractured. Then, the working face was mined. When the working face had been mined to approximately 50 meters before the next horizontal borehole, segmented fracturing began on the next horizontal borehole. This cycle continued until the working face was completely mined.

[0123] Step V: Using a 165mm diameter drill bit, drill to a depth of 3m after encountering rock. Then, use a 250mm diameter drill bit to enlarge the hole to the bottom. Lower a 193mm iron pipe to the bottom and connect it to the borehole opening device. Use a 98mm diameter drill bit to drill according to the design, taking measurements every 3m and adjusting the drilling direction based on the design trajectory to ensure drilling quality. After completing the construction according to the design requirements, save the data, remove the drill bit, seal the borehole, and start negative pressure extraction. After drilling is completed, gas extraction begins. In addition to measuring borehole gas parameters on the day the borehole is sealed, all borehole gas parameters are measured weekly and the data is recorded for future research. After the entire working face is mined out, following the hydraulic fracturing effect of the kilometer-long directional horizontal borehole, the number of fractures in the overlying strata of the working face goaf increases, and the gas extraction rate of this working face increases from an average of 0.037 to 0.088 m³ / h. 3 The speed increased to an average of 0.212–0.40 m / min. 3 / min, increasing gas extraction rate.

[0124] Step VI: After the entire working face has been mined out, and following the hydraulic fracturing effect of the kilometer-long directional horizontal borehole, the hard roof above the goaf of the working face has largely collapsed, reducing the impact of mining on adjacent roadways. The low-level heave of the adjacent working face decreased from 1.5m to 0.3m, and the deformation of the sidewalls decreased from 2.0m to 0.4m. The roadways maintained good stability, laying a solid foundation for subsequent coal pillar optimization.

[0125] Example 2: Changcun Mine

[0126] The method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling fracturing, as provided by this invention, is carried out according to the following steps:

[0127] Step I: Conduct on-site investigation of the mine's engineering geological conditions and test and analyze the geomechanical characteristics of the surrounding rock of the roadway to be protected, such as rock strata structure and thickness, physical and mechanical properties of the surrounding rock, hydrogeological conditions, structural features, and the impact of mining activities. Based on the mine's borehole columnar section, the initial pressure step distance of the previous longwall face (21.2m), coal thickness (6.35m, using fully mechanized longwall mining, mining height 3.7m, coal release height 2.65m), and the original gas content of the 2303 working face (7.5-9.5m),... 3 / t, residual gas content is 2.21m 3 The recoverable reserves at the 2303 longwall face are 3,555,900 tons, and the absolute gas emission rate is 148.31 m³. 3 / min, relative outflow rate is 9.95m³ 3 / t, with an initial gas content of 9.5m³. 3 / t, the original gas reserves of the coal seam at the working face are 33.7811 million m³. 3 Changcun Coal Mine is a high-gas mine.

[0128] Step II: Determine the theoretical height of the collapse zone as 10.8m to 15.2m according to the formula, and determine the theoretical height of the fracture zone as 40.6m to 51.8m according to the formula.

[0129] According to the formula

[0130]

[0131]

[0132] The hard rock stratum that plays a key role in the pressure on the working face was identified as fine-grained sandstone located 27.98m from the top of the roadway, with a thickness of 11.05m.

[0133] Step III: Design the parameters for the kilometer-level horizontal borehole and the parameters for hydraulic fracturing. Specifically, the parameters for the kilometer-level horizontal borehole include: the borehole is located in fine-grained sandstone at a distance of 27.98m from the top of the tunnel and at a distance of 41.88m from the top of the tunnel.

[0134] Based on an innovative method for calculating the horizontal distance between the first borehole and the mining roadway, the calculation process is as follows: The result is determined based on the roof rock collapse angle and fracture zone height; the distance is then calculated using the following formula:

[0135] L1=H / tanα

[0136] Where H is the average height of the fracture zone, and α is the roof rock collapse angle. Specifically, the collapse angle for a moderately stable roof is 60°, and for a stable roof, it is 45°; in this example, the collapse angle is 45°. Based on the above formula, the fracture zone height is determined to be 40.6m to 51.8m, and the average height H is 46.2m. L1 is calculated to be 46.2m using the formula. The horizontal projection distance between the directional high-level borehole and the return airway should be greater than H / tanα to ensure that the directional borehole is within the fracture zone after sufficient pressure relief. Based on the formula, the horizontal distance between the first borehole and the return airway in this method is 47m.

[0137] Based on the mining height and rock fragmentation coefficient, the distance is calculated using the following formula:

[0138]

[0139] Where ∑h is the mining height, K p The coefficient of rock fragmentation is given. In this example, the mining height is 6.35m and the coefficient of fragmentation is 1.2. Based on the formula, the horizontal distance between the first borehole and the mining roadway in this method is calculated to be 31.75m, which is taken as 32m.

[0140] Compare the results obtained from the two methods above, take the average value, and then apply the formula... The final horizontal distance between the first borehole and the mining roadway was determined to be 39.5m, but we adopted 40m.

[0141] The horizontal spacing between boreholes is calculated using the following formula:

[0142]

[0143] Where R is the fracturing radius of the top rock layer, and h is the vertical spacing between boreholes.

[0144] Based on the relationship between the number of horizontal drilling layers and the thickness of the rigid top slab being cut, the lower layer thickness is 11.05m, requiring 3 horizontal drillings, with h taken as 3.7m. The horizontal spacing between the drillings, determined by the formula, ranges from 4.7m to 9.3m, with an average of 7.0m. The higher layer thickness is 6.7m, requiring 2 horizontal drillings, with h taken as 3.4m. The horizontal spacing between the drillings, determined by the formula, ranges from 4.9m to 9.4m, with an average of 7.15m, and is therefore selected as 7.2m.

[0145] The horizontal spacing between boreholes at lower levels is 7.0m; the horizontal spacing between boreholes at higher levels is 7.2m.

[0146] The water pressure can be calculated using the following formula:

[0147] P sc =2R0+R L

[0148] Where: R0 is the surrounding rock stress at the crack initiation point, R L The ultimate tensile strength of the rock is determined according to the formula.

[0149] The pressure is 11.3 MPa.

[0150] Step IV: After determining the borehole layout strata height and the horizontal distance between the first borehole and the coal pillar, set up the first drilling site 550m from the opening. Set up the next drilling site every 500m, until the last drilling site extends 50m beyond the stop line. Install a kilometer-long directional drilling rig within each drilling site, and then start drilling from the first drilling site, drilling 6 boreholes per site, with a borehole length of 540m to 620m. The initial part of the borehole trajectory is curved, while the main part is an approximately horizontal straight line. Considering the protection of the return roadway, drilling is carried out close to the solid coal side of the return roadway.

[0151] Hydraulic fracturing was conducted on-site, involving the deployment of high-pressure water pumps within the drilling area. Hydraulic fracturing began at each drilling site after drilling was completed. The boreholes were located in hard rock strata, and each borehole underwent multiple fracturing operations using a retreating method. Fracturing was performed every 20 meters within the borehole, with each fracturing session lasting at least 30 minutes. During fracturing, the water head had to be perpendicular to the roadway roof. Fracturing was stopped when the water pressure suddenly dropped significantly. This process was repeated until the hard rock strata within the horizontal borehole were completely fractured. Then, the working face was mined. When the working face had been mined to approximately 50 meters before the next horizontal borehole, segmented fracturing began on the next horizontal borehole. This cycle continued until the working face was completely mined.

[0152] Step V: Using a 165mm diameter drill bit, drill to a depth of 3m after encountering rock. Then, use a 250mm diameter drill bit to enlarge the hole to the bottom. Lower a 193mm iron pipe to the bottom and connect it to the borehole opening device. Use a 98mm diameter drill bit to drill according to the design, taking measurements every 3m and adjusting the drilling direction based on the design trajectory to ensure drilling quality. After completing the construction according to the design requirements, save the data, remove the drill bit, seal the borehole, and start negative pressure extraction. After drilling is completed, gas extraction begins. In addition to measuring borehole gas parameters on the day the borehole is sealed, all borehole gas parameters are measured weekly and the data is recorded for future research. After the entire working face is mined out, after the hydraulic fracturing effect of the kilometer-long directional horizontal borehole, the number of fractures in the overlying strata of the working face goaf increases, and the gas extraction rate of this working face increases from an average of 0.041 to 0.09m³. 3 / min increased to an average of 0.312–0.433m 3 / min, increasing gas extraction rate.

[0153] Step VI: After the entire working face has been mined out, and following the hydraulic fracturing effect of the kilometer-long directional horizontal borehole, the hard roof above the goaf of the working face has largely collapsed, reducing the impact of mining on adjacent roadways. The floor heave of the adjacent working face decreased from 1.6m to 0.4m, and the deformation of the sidewalls decreased from 1.8m to 0.5m. The roadways maintained good stability, laying a solid foundation for subsequent coal pillar optimization.

[0154] The above-described embodiments are preferred embodiments of the present invention and are only used to facilitate the illustration of the present invention. They are not intended to limit the present invention in any way. Any person skilled in the art who makes local modifications or alterations to the technical content disclosed in the present invention without departing from the scope of the technical features of the present invention shall still fall within the scope of the technical features of the present invention.

Claims

1. A method for improving gas extraction efficiency and surrounding rock stability in adjacent roadways through kilometer-level horizontal drilling and fracturing, characterized in that, Includes the following steps: S1, Investigate the general engineering geology of the site and collect basic data on the longwall mining face; S2, determine the height of the caving zone, the height of the fracture zone, and the stratigraphic position and thickness of the hard rock layer that plays a key role in pressing the working face; S3, design parameters for a kilometer-long horizontal borehole and hydraulic fracturing parameters; The parameters of the kilometer-level horizontal borehole include: borehole layer, borehole start position, borehole end position, horizontal distance between the first borehole and the mining roadway, vertical and horizontal distances between boreholes, borehole length, and the relationship between the number of horizontal layers of the borehole and the thickness of the hard roof being cut. The hydraulic fracturing parameters include: hydraulic pressure, fracturing direction, and fracturing zone; The method for determining the horizontal distance L between the first borehole and the mining roadway is as follows: First, the horizontal distance L1 between the first borehole and the mining roadway is determined by combining the height of the fracture zone and the caving angle of the roof rock: L1=H / tanα Where: H - average height of the fracture zone, in meters; α - angle of collapse of the roof rock, in degrees. Secondly, the horizontal distance L2 between the first borehole and the recovery roadway is determined by combining the mining height and the rock fragmentation coefficient: L2=∑h / (K p -1); In the formula: ∑h - height of the coal seam being mined, in meters; K p - Rock fragmentation coefficient; Next, the horizontal distance L from the first borehole to the mining roadway is calculated using the following formula: L = (L1 + L2) / 2; The method for determining the horizontal spacing x of the boreholes is as follows: x=(4R 2 -h 2 ) 0.5 ; In the formula: R - the fracturing radius of the top rock layer, in meters; h - Vertical spacing between boreholes, in meters; Wherein, the water pressure P satisfies the following formula: P>2R0+R L ; Where: R0—the surrounding rock stress at the crack initiation point, in MPa; R L —The ultimate tensile strength of rock, expressed in MPa; S4. Set up drilling sites and conduct horizontal drilling of 1,000 meters on-site, followed by hydraulic fracturing. Starting 350-550m from the pre-cut hole, set up the first drilling site in the return airway, with subsequent sites every 350-500m, until the last site extends 50m beyond the stop line. Each drilling site contains 4-6 boreholes in 1-2 rows, with a borehole length of 520-620m. High-pressure water pumps are installed within the drilling sites. Hydraulic fracturing begins at each site after drilling is completed. The boreholes are located in hard rock formations. Each borehole employs a retreating, multiple-fracturing method, fracturing every 10-30m, with each fracturing session lasting at least 30 minutes. During fracturing, the water head must be perpendicular to the roadway roof. Stop fracturing at that section when the water pressure suddenly drops significantly. Repeat this process until the hard rock formation within the horizontal borehole is completely fractured. S5, gas extraction is carried out on the overlying strata of the goaf during the mining process and the gas extraction concentration and flow rate of this working face are compared and analyzed. S6. Comparative analysis of the surrounding rock deformation of adjacent tunnels before and after hydraulic fracturing.

2. The method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling fracturing as described in claim 1, characterized in that, In S2, it is necessary to identify the stratigraphic layers of hard rock that play a critical role in the pressure on the working face. Any rock layer that meets the following two conditions is identified as a critical layer: ① Rock stiffness judgment: The rock strata are arranged in order from bottom to top. The load exerted by the m-th rock stratum on the 1st rock stratum is greater than the load exerted by the (m+1)-th rock stratum on the 1st rock stratum. ② Determination of rock fracture distance: The rock strata are arranged in order from bottom to top, and the fracture distance of the nth rock stratum is less than that of the (n+1)th rock stratum.

3. The method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling fracturing according to claim 2, characterized in that: The load q1 exerted by the m-th rock layer on the 1st layer m Calculate using the following formula: The load q1 exerted by the (m+1)th rock layer on the first layer m+1 Calculate using the following formula: in: h1 is the thickness of the first layer, in meters (m). h i The thickness of the i-th layer is expressed in meters (m). γ i The density of the i-th layer is expressed in kN / m³. 3 ; E i Let be the elastic modulus of the i-th layer, in GPa.

4. The method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling fracturing according to claim 2, characterized in that: The fracture distance L of the kth layer k The fracture distance L of the (k+1)th layer k+1 Calculate using the following formula: L k =h k ·(2σ k / q k ) 0.5 ; L k+1 =h k+1 ·(2σ k+1 / q k+1 ) 0.5 ; in: h k h k+1 The thicknesses of the k-th and k+1-th layers are in meters. σ k σ k+1 represents the tensile strength of the k-th and k+1-th layers, in MPa; q k q k+1 This represents the load borne by the k-th and k+1-th layers, in MPa.

5. The method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling fracturing as described in claim 3, characterized in that... Step S5 includes: drilling and enlarging the hole with a reamer; removing the reamer and sealing the hole; starting gas extraction and monitoring it in real time when the working face begins to advance, and comparing and analyzing the changes in gas extraction flow rate and concentration before and after drilling and fracturing to determine the extraction effect after fracturing.

6. The method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling fracturing according to claim 5, characterized in that, Step S6 includes: setting up cross-shaped surrounding rock displacement monitoring points in adjacent roadways to monitor the roadway deformation during the entire mining process of the adjacent working face, and comparing and analyzing the deformation of the roof, floor and sidewalls of the adjacent roadways before and after drilling and fracturing.

7. The method for improving gas extraction efficiency and surrounding rock stability of adjacent roadways through kilometer-level horizontal drilling fracturing according to claim 1, characterized in that, The basic data in step S1 includes: gas characteristics after the working face is mined back, and geomechanical information of the surrounding rock of the roadway to be protected; Among them, the gas characteristics after the working face is mined include: the geological structure of the mine field, the gas level, the gas situation of the working face, the prediction of the gas emission of the working face, and the current gas extraction effect. The geomechanical information of the surrounding rock of the roadway to be protected includes: rock strata structure and thickness, mining technology, lithology of the roof and floor, hydrogeological conditions, structural conditions, impact of mining, and geostress information of the roadway measured by hydraulic fracturing method; geostress information of the roadway measured by hydraulic fracturing method includes: the magnitude and direction of the maximum principal stress and the minimum principal stress.

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