A method for early prevention and control of rockburst in steeply inclined coal seams based on surface deviated shaft fracturing

Abstract

This invention discloses a method for proactive prevention and control of rockburst in steeply inclined coal seams based on surface inclined well fracturing, relating to the field of advanced prevention and control technology for rockburst disasters in steeply inclined coal mines. The method includes: obtaining the physical and mechanical parameters of each rock stratum based on core drilling and mechanical experiments; determining the target fracturing layer based on the correspondence between rock stratum fracture and migration and the dynamic load coefficient of the support; drilling inclined fracturing wells based on the dip angle of the target fracturing layer; optimizing and determining fracturing parameters based on numerical simulation using random polygon graphs and Cohesive elements; and performing segmented perforation based on the dip angle of the target fracturing layer, followed by sealing and fracturing. This invention can achieve large-scale, efficient, and source-based elimination of rockburst occurrence in steeply inclined coal seams.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of advanced prevention and control of rock burst disasters in steeply inclined coal seams, and more particularly to an advanced prevention and control method for rock burst in steeply inclined coal seams based on ground inclined shaft fracturing. BACKGROUND

[0002] In coal mining, coal seams with a dip angle greater than 45° are generally classified as steeply inclined coal seams. Such coal seams are widely distributed in China, accounting for about 15-20% of the total coal reserves in the country. In the western and southwestern mining areas, more than 50% of the main coal seams in the mines are steeply inclined coal seams. Due to complex geological conditions and stress environments, rock burst dynamic disasters frequently occur during the mining of steeply inclined coal seams, seriously restricting the safe and efficient mining of steeply inclined coal seams.

[0003] At present, the prevention and control technologies for rock burst in steeply inclined coal seams are mainly concentrated in the underground mine, including local concentrated stress relief and stope rock burst prevention and support. Local concentrated stress relief generally uses underground hydraulic fracturing and deep hole blasting to damage the integrity of the surrounding rock, inducing the release of the accumulated elastic energy of the surrounding rock, thereby eliminating local stress concentration and avoiding rock burst. Stope rock burst prevention and support usually uses roadway rock burst prevention and support structure, rock burst prevention hydraulic support, and high-strength anchor rod (cable) to strengthen the ability of the stope to resist rock burst. These two prevention and control technologies can control the occurrence of rock burst in steeply inclined coal seams to a certain extent, but they have certain limitations. With the increase of mining depth and intensity, the impact source is often far from the coal seam. Due to the limitations of the operating environment and equipment, the control effect of underground hydraulic fracturing and deep hole blasting is poor and the control range is limited. Rock burst still occurs after these technologies are applied to deep steeply inclined coal seam mining. In addition, the existing stope rock burst prevention and support equipment is a passive defense, which cannot eliminate rock burst from the source and cannot guarantee the control effect.

[0004] Therefore, it is necessary to invent a new method for preventing and controlling rock burst in steeply inclined coal seams with good control effect and wide control range, which is of great significance to the safe and efficient mining of steeply inclined coal seams.

[0005] Therefore, it is necessary to invent a new method for preventing and controlling rock burst in steeply inclined coal seams with good control effect and wide control range, which is of great significance to the safe and efficient mining of steeply inclined coal seams. SUMMARY

[0006] Therefore, the present application provides an advanced prevention and control method for rock burst in steeply inclined coal seams based on ground inclined shaft fracturing, which can provide an advanced prevention and control method for rock burst in steeply inclined coal seams with wide control range, good control effect, and strong operability.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0008] A method for pre-control of rock burst in steep coal seam based on ground inclined shaft fracturing, comprising the following steps:

[0009] Based on the core obtained by drilling downward to the coal seam from the ground, the lithology and thickness of each rock layer are recorded, and the physical and mechanical parameters of each rock layer are obtained by mechanical experiment on the obtained core;

[0010] Based on the arrangement of the station on the ground, the fracture migration law of the rock layer with strength exceeding σ0 and thickness reaching H is monitored, the pressure sensor is installed on the hydraulic support in the well to monitor the working resistance of the hydraulic support, and the dynamic load coefficient K d of the hydraulic support is calculated;

[0011] The corresponding relationship between the fracture migration of the rock layer and the dynamic load coefficient K d of the hydraulic support is analyzed to determine the target fracturing layer;

[0012] An inclined fracturing inclined shaft is drilled downward in the target fracturing layer at an inclination angle α;

[0013] A numerical model is constructed, and the target fracturing layer and the upper and lower rock layers in the numerical model are meshed by using a random polygon diagram to complete the construction of the numerical model;

[0014] The target fracturing layer in the numerical model is simulated and calculated by ground fracturing inclined shaft, and the fracturing parameters are optimized and determined;

[0015] A high-energy directional perforating gun is used to vertically fracture the inclined shaft direction, and the target fracturing layer is segmented perforated at an inclination angle β;

[0016] The perforated section is sealed and fractured until the entire fracturing of the target fracturing layer is completed.

[0017] Optionally, the physical and mechanical parameters include: compressive strength R c , shear strength τ, tensile strength R t , Poisson's ratio μ, internal friction angle and cohesion c.

[0018] Optionally, the mechanical experiment includes: uniaxial and triaxial compression experiment, three-point shear experiment and Brazilian splitting experiment.

[0019] Optionally, the relationship between σ0 and H is:

[0020]

[0021] Optionally, the dynamic load coefficient K d of the hydraulic support is related to the maximum average resistance P1 of the support periodic pressure and the maximum average resistance P2 of the support non-periodic pressure, and the relationship is:

[0022] Optionally, the inclination angle alpha is related to the inclination angle theta1 of the target fracturing layer perpendicular to the working face advancing direction, and the relationship is alpha = theta1.

[0023] Optionally, the random polygon graph is subjected to centroid processing through code written in Python language before being imported into the numerical model.

[0024] Optionally, the specific content of constructing the numerical model is as follows:

[0025] According to the physical and mechanical parameters of each rock stratum, a numerical model is established based on the ABAQUS numerical simulation platform, the target fracturing layer and the upper and lower rock strata in the numerical model are subjected to grid division through the externally imported random polygon graph, and the unit surface set is searched and constructed based on Python language programming, the surface set is inserted into the Cohesive unit, the Cohesive unit parameters are determined according to the physical and mechanical parameters of each rock stratum, and the remaining rock strata are subjected to hexahedral grid division through the platform itself; the boundary state of the numerical model is applied according to the three-dimensional stress state of the target fracturing layer, and the construction of the numerical model is completed.

[0026] Optionally, the inclination angle beta is related to the inclination angle theta2 of the target fracturing layer parallel to the working face advancing direction, and the relationship is beta = theta2.

[0027] Optionally, the fracturing parameters include: fracturing pump station pressure P and pump station displacement V.

[0028] According to the above technical solution, compared with the prior art, the present application provides a kind of based on ground inclined shaft fracturing steeply inclined coal seam rock burst advanced prevention and control method, and the beneficial effects are:

[0029] 1) Ground fracturing is not limited by underground operation environment, and is easy to operate;

[0030] 2) The control range of ground inclined shaft area fracturing is wide, and the fracturing effect can be effectively guaranteed by optimizing construction parameters;

[0031] 3) The target fracturing layer selection method is simple and accurate, and can ensure the reliability of steeply inclined coal seam rock burst prevention and control;

[0032] 4) The target fracturing layer is pre-fractured, which can achieve the purpose of eliminating the source of steeply inclined coal seam rock burst. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0034] Figure 1 A flow chart of an advanced prevention and control method for rock burst in steeply inclined coal seams based on ground inclined well fracturing is provided for the present application.

[0035] Figure 2 A ground advanced prevention and control schematic diagram for rock burst in steeply inclined coal seams is provided for the present application.

[0036] Figure 3 A numerical model schematic diagram is provided for the present application.

[0037] Figure 4 An inclined well and segmented perforation schematic diagram is provided for the present application.

[0038] Among them, 1-target fracturing layer, 2-vertical well, 3-inclined well, 4-random polygonal diagram, 5-upper and lower rock strata, 6-Cohesive unit, 7-segment, 8-perforation, 9-working face advancing direction. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] Referring to Figure 1 , the present application discloses an advanced prevention and control method for rock burst in steeply inclined coal seams based on ground inclined well fracturing, comprising the following steps:

[0041] Based on drilling downward to the coal seam from the ground to obtain rock cores, the lithology and thickness of each rock stratum are recorded, and mechanical experiments are carried out on the obtained rock cores to obtain the physical and mechanical parameters of each rock stratum;

[0042] Based on the ground, a station is arranged to monitor the breaking and migration law of the rock stratum with a strength exceeding σ0 and a thickness reaching H, a pressure sensor is installed on the hydraulic support in the well to monitor the working resistance of the hydraulic support, and the dynamic load coefficient K d of the hydraulic support is calculated.

[0043] The corresponding relationship between the breaking and migration of the rock stratum and the dynamic load coefficient K d of the hydraulic support is analyzed to determine the target fracturing layer.

[0044] An inclined well is drilled downward at an inclination angle α in the target fracturing layer.

[0045] Specifically, a vertical well is drilled vertically downward from the surface of a horizontal non-mining working face to a target fracturing layer, stress relief method is used to test the three-dimensional stress state of the target fracturing layer, and casing is used for cementing after the vertical well is cemented.

[0046] A numerical model is constructed, and a random polygon map is used to divide the target fracturing layer and the upper and lower rock layers in the numerical model into grids to complete the construction of the numerical model.

[0047] The target fracturing layer in the numerical model is simulated and calculated by ground fracturing inclined wells, and the fracturing parameters are optimized and determined.

[0048] A high-energy directional perforating gun is used to vertically fracture the inclined well direction, and the target fracturing layer is segmented perforated at an inclination angle β.

[0049] The perforated section is sealed and fractured until the entire fracturing of the target fracturing layer is completed.

[0050] Specifically, the rock layer that breaks and moves when the dynamic load coefficient of the hydraulic support is greater than K0 is determined as the target fracturing layer, K0 is related to the distance h between the target fracturing layer and the coal seam, and the relationship is:

[0051]

[0052] In order to ensure the accuracy of the determination of the target fracturing layer, neither is it selected too much nor is it selected too much, and the fracturing cost is effectively reduced.

[0053] Specifically, the target fracturing layer is segmented perforated at an inclination angle β, and the segmented distance is L.

[0054] Further, the physical and mechanical parameters include: compressive strength R c , shear strength τ, tensile strength R t , Poisson's ratio μ, internal friction angle cohesion c.

[0055] Further, the mechanical experiments include: uniaxial and triaxial compression experiments, three-point shear experiments and Brazilian splitting experiments.

[0056] Further, the relationship between σ0 and H is:

[0057]

[0058] Specifically, in order to ensure that no rock layer that may cause sudden inclined coal seam mining induced rock burst is missed, and too many rock layers are not monitored to break and move, the monitoring cost is reduced.

[0059] Further, the dynamic load coefficient K dThe relationship between the maximum average resistance P1 of the support periodic compression and the maximum average resistance P2 of the support non-periodic compression is as follows:

[0060] Further, the inclination angle a is related to the inclination angle of the target fracturing layer perpendicular to the working face advancing direction, and the relationship is as follows: a = 1.

[0061] Specifically, in order to ensure that the fracturing inclined well can be parallel to the target fracturing layer and always inside the target fracturing layer, the fracturing effect of the target fracturing layer is improved.

[0062] Further, the random polygon graph is subjected to centroid processing by Python language programming before being imported into the numerical model.

[0063] Specifically, in order to ensure the convergence of the numerical model calculation and effectively reduce the calculation time.

[0064] Further, the specific content of constructing the numerical model is as follows:

[0065] According to the physical and mechanical parameters of each rock layer, a numerical model is established based on the ABAQUS numerical simulation platform. The target fracturing layer and the upper and lower rock layers in the numerical model are meshed by an externally imported random polygon graph. Based on Python language programming, the element face set is searched and constructed. The face set is inserted into the Cohesive element. The Cohesive element parameters are determined according to the physical and mechanical parameters of each rock layer. The remaining rock layers are meshed by the platform's own hexahedral mesh. According to the three-dimensional stress state of the target fracturing layer, the boundary state of the numerical model is applied, and the construction of the numerical model is completed.

[0066] Further, the inclination angle b is related to the inclination angle of the target fracturing layer parallel to the working face advancing direction, and the relationship is as follows: b = 2.

[0067] Specifically, in order to ensure that the fracturing fracture can be parallel to the working face advancing direction and the target fracturing layer expands, the fracturing effect is effectively improved.

[0068] Further, the fracturing parameters include: fracturing pump station pressure P, pump station displacement V.

[0069] Specifically, the segment distance L and the fracturing pump station pressure P are related to the target fracturing layer's Prowl's coefficient f, and the relationship is as follows: In order to ensure the fracturing effect and reduce the fracturing cost.

[0070] In one specific embodiment:

[0071] Taking the rock burst prevention and control of Wangjiashan Mine as an example, the average inclination of the coal seam vertical working face advancing direction 9 in No. 4 shaft is 55°, which belongs to steeply inclined seam, and the average inclination parallel to the working face advancing direction 9 is 13°. According to the statistics of Wangjiashan Mine, from May 6, 2003 to July 9, 2020, 50 rock bursts occurred in No. 4 shaft, and rock bursts occurred frequently.

[0072] S1: Before mining, drill down to the coal seam based on the ground to obtain rock cores, record the lithology and thickness of each rock layer; carry out uniaxial and triaxial compression experiments, three-point shear experiments and Brazilian splitting experiments on the obtained rock cores to obtain the mechanical parameters of each rock layer: compressive strength R c , shear strength τ, tensile strength R t , Poisson's ratio μ, internal friction angle cohesion c;

[0073] S2: After mining, based on the ground station, the rock layer with strength exceeding 55 MPa and thickness reaching 25 m, strength exceeding 65 MPa and thickness reaching 10 m, and strength exceeding 75 MPa and thickness reaching 6 m in S1 is monitored, a total of two layers, which are fine sandstone 53 m away from the coal seam and fine sandstone 95 m away from the coal seam, pressure sensors are installed on No. 5 and No. 7 hydraulic supports in the underground to monitor the working resistance of No. 5 and No. 7 hydraulic supports, and the dynamic load coefficient K d of No. 5 and No. 7 hydraulic supports is calculated.

[0074] S3: Analyze the corresponding relationship between the rock layer fracture migration and the dynamic load coefficient K d of the hydraulic support, and determine the rock layer with fracture migration when the dynamic load coefficient of the hydraulic support is greater than 1.35 or 1.55 as the target fracturing layer 1, the target fracturing layer 1 is the fine sandstone 53 m away from the coal seam, as shown in Figure 2 .

[0075] S4: Drill a vertical well 2 vertically downward on the same horizontal unsampled working face ground, drill to the target fracturing layer 1 in S3, and test the three-dimensional stress state of the target fracturing layer 1 using stress relief method, then use casing to cement the well, the three-dimensional stress state is σ H = 14.39 MPa, azimuth 58.89°; σ h = 7.79 MPa, azimuth -31.11°; σ H = 12.45 MPa. After the cementing of the vertical well 2 is completed, drill a fracturing inclined well 3 inside the target fracturing layer 1 at an inclination angle of 55°, and use casing to cement the well after the inclined well 3 completely covers the target fracturing area, as shown in Figure 2 .

[0076] S5: According to the physical and mechanical parameters of each rock layer, a numerical model is established based on the ABAQUS numerical simulation platform, and a random polygonFigure 4 The target fracturing layer 1 and the upper and lower rock layers 5 in the numerical model are meshed, and a unit surface set is searched and constructed based on Python language programming. The surface set is inserted into the Cohesive unit 6, the parameters of the Cohesive unit 6 are determined according to the physical and mechanical parameters of each rock layer, and the remaining rock layers are meshed by using the platform's own hexahedral mesh. According to the three-dimensional stress state σ H = 14.39 MPa, azimuth 58.89°, σ h = 7.79 MPa, azimuth -31.11°, σ H = 12.45 MPa, the boundary state of the numerical model is applied, and the construction of the numerical model is completed, as shown in Figure 3 .

[0077] S6: The inclined well 3 fracturing simulation calculation is performed on the target fracturing layer 1 in the numerical model, and the fracturing parameters are optimized and determined, and the fracturing pump station pressure is 25 MPa, and the pump station displacement is 5.5 m 3 / min.

[0078] S7: The high-energy directional perforating gun is perpendicular to the direction of the fracturing inclined well 3, and the segmented 7 perforation 8 is performed on the target fracturing layer 1 at an inclination angle of 13°, and the segmented 7 distance is 35 m, as shown in Figure 4 .

[0079] S8: The perforation section is sealed and fractured from bottom to top in sequence until the entire fracturing of the target fracturing layer is completed.

[0080] Each embodiment in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same and similar parts between each embodiment can be referred to each other.

[0081] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for advanced prevention and control of rock burst in steeply inclined coal seams based on ground-inclined well fracturing, characterized in that, The method comprises the following steps: obtaining cores by drilling downward from the ground to the coal seam, recording the lithology and thickness of each rock layer, and carrying out mechanical experiments on the obtained cores to obtain the physical and mechanical parameters of each rock layer; Based on the ground arrangement of measuring station, the rock breaking migration law of intensity exceeding σ0 and thickness reaching H is monitored, the pressure sensor is installed on the hydraulic support in the well to monitor the working resistance of the hydraulic support, and the dynamic load coefficient K of the hydraulic support is calculated d ; Analyzing the relationship between rock stratum breakage migration and dynamic load coefficient K of hydraulic support d to determine the target fracturing layer; drilling a slant well in the target fracturing layer at an inclination angle α; constructing a numerical model, using a random polygon graph to divide the target fracturing layer and the upper and lower rock layers in the numerical model into grids to complete the construction of the numerical model; simulating and calculating the ground fracturing slant well in the target fracturing layer in the numerical model, and optimizing and determining the fracturing parameters; vertically fracturing the slant well direction with a high-energy directional perforating gun, and performing segmented perforation on the target fracturing layer at an inclination angle β; sealing and fracturing the perforated segments until the entire fracturing of the target fracturing layer is completed; The specific content of constructing the numerical model is: based on the physical and mechanical parameters of each rock layer, a numerical model is established based on the ABAQUS numerical simulation platform, a random polygon graph is used to divide the target fracturing layer and the upper and lower rock layers in the numerical model into grids, and a unit surface set is searched and constructed based on Python language programming, a cohesive unit is inserted using the surface set, the cohesive unit parameters are determined according to the physical and mechanical parameters of each rock layer, the remaining rock layers are divided into hexahedral grids using the platform itself, and the boundary state of the numerical model is applied according to the three-dimensional stress state of the target fracturing layer, thereby completing the construction of the numerical model.

2. The method according to claim 1, wherein, Physical mechanical parameters include: compressive strength R c , shear strength τ, tensile strength R t , Poisson's ratio μ, internal friction angle , cohesion c.

3. The method according to claim 1, wherein, The mechanical experiments include uniaxial and triaxial compression experiments, three-point shear experiments and Brazilian splitting experiments.

4. The method according to claim 1, wherein the method is characterized in that, The relationship between σ0 and H is: 。 5. The method according to claim 1, wherein, Hydraulic support dynamic load coefficient K d The relationship between the maximum average resistance P1 of the support cycle and the maximum average resistance P2 of the support non-cycle is: .

6. The method according to claim 1, wherein the method is characterized in that, The inclination angle a is related to the inclination angle θ1 of the target fracturing layer perpendicular to the working face advancing direction, and the relationship is: .

7. The method according to claim 1, wherein, The random polygon graph is processed by Python language programming before being imported into the numerical model.

8. The method according to claim 1, wherein the method is characterized in that, The inclination angle β is related to the inclination angle θ2 of the target fracturing layer parallel to the working face advancing direction, and the relationship is: .

9. The method according to claim 1, wherein the method is characterized in that, The fracturing parameters include the fracturing pump station pressure P and the pump station displacement V.

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