Method for evaluating rock burst ground fracturing pre-control effect of steeply inclined coal seam

Abstract

The invention provides a steeply inclined coal seam rock burst ground fracturing pre-control effect evaluation method. The method comprises the steps that a micro-seismic monitoring system is arranged according to a preset fracturing control range; a micro-seismic event and an underground micro-seismic energy event are monitored through a micro-seismic monitoring system, and the ground fracturing crack extension range, the total energy ratio of the underground micro-seismic energy event and the ratio of the total number of events are obtained; the working face support average working resistance ratio and the working face periodic weighting average dynamic load coefficient are obtained through the variable quantity of the working face support working resistance before and after the fracturing process; the underground roadway is monitored through a multi-point displacement meter, and the roadway surrounding rock deformation is obtained; and calculating the total score of ground fracturing effect evaluation according to the data, and grading the pre-control effect. According to the method, by analyzing and grading the ground fracturing pre-control effect of the rock burst of the steeply inclined coal seam, it is ensured that the pre-control effect reaches the expected effect, and safe and efficient mining of the working face is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of rock burst ground fracturing in steeply inclined coal seams, and in particular to a method for evaluating the pre-control effect of rock burst ground fracturing in steeply inclined coal seams. Background Art

[0002] As shallow resources are gradually exhausted, coal mining has developed into deep areas. The geostress of the coal rock environment is high, and the coal rock mass is prone to accumulate high elastic properties. Especially under the mining conditions of steeply inclined coal seams, the coal seam environment is complex, making it easy for the mining process to induce mine tremors, with a high risk of impact, posing a serious threat to mine safety production.

[0003] In order to reduce the degree of rock burst hazards under the conditions of steeply inclined coal seam mining and prevent the occurrence of rock burst accidents, ground fracturing technology is usually used to pre-control the rock burst in steeply inclined coal seams. Therefore, it is very necessary to design an evaluation method for the pre-control effect of ground fracturing for rock burst in steeply inclined coal seams. Summary of the invention

[0004] The purpose of the present invention is to provide a method for evaluating the pre-control effect of ground fracturing of rock burst in steeply inclined coal seams, so as to analyze and grade the pre-control effect of ground fracturing of rock burst in steeply inclined coal seams, ensure that the pre-control effect reaches the expected effect, and ensure safe and efficient mining of the working face.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A method for evaluating the effect of ground fracturing pre-control in steeply inclined coal seam rock bursts comprises the following steps:

[0007] A microseismic monitoring system is set up according to the preset fracturing control range; the microseismic monitoring system includes a surface geophone and a downhole geophone;

[0008] The microseismic events during the fracturing process are monitored by ground geophones to obtain the expansion range of the ground fracturing cracks; the expansion range of the ground fracturing cracks includes the horizontal expansion range and the vertical expansion range;

[0009] The downhole microseismic energy events during the fracturing process are monitored by downhole geophones to obtain the total energy ratio and the total number of events of the downhole microseismic energy events;

[0010] The average working resistance ratio of the working face support and the average dynamic load coefficient of the working face cycle are obtained by the change of the working resistance of the working face support before and after the fracturing process;

[0011] The underground tunnel is monitored by multi-point displacement meters to obtain the deformation of the tunnel surrounding rock;

[0012] The total score for the ground fracturing effect evaluation is calculated based on the horizontal expansion range, vertical expansion range, total energy ratio of underground microseismic energy events, total event ratio of underground microseismic energy events, average working resistance ratio of working face supports, average dynamic load coefficient of periodic pressure on the working face and deformation of tunnel surrounding rock. The pre-control effect of ground fracturing for rock burst in steeply inclined coal seams is graded according to the total score for the ground fracturing effect evaluation.

[0013] Optionally, the ground geophones are equidistantly arranged on a circle with the wellhead of the fracturing well as the center; there are 6 ground geophones, and the calculation formula for the radius of the circle with the wellhead of the fracturing well as the center is: Wherein, L is the radius and Z is the length of the fracturing control range.

[0014] Optionally, there are three downhole geophones; the downhole geophones are respectively arranged at the center of the fracturing control range and on both sides beyond the fracturing control range; the calculation formula beyond the fracturing control range is: Wherein, M is beyond the fracturing control range.

[0015] Optionally, the calculation formula for the total score of the ground fracturing effect evaluation is: Q=0.2×A+0.2×B+0.1×C+0.1×D+0.15×E+0.15×F+0.1×G; wherein Q is the total score of the ground fracturing effect evaluation, A is the horizontal expansion range score, B is the vertical expansion range score, C is the total energy ratio score of the underground microseismic energy events, D is the total number of events ratio score of the underground microseismic energy events, E is the average working resistance ratio score of the working face support, F is the average dynamic load coefficient score of the working face periodic pressure, and G is the deformation score of the tunnel surrounding rock.

[0016] Optionally, the pre-control effect of ground fracturing for rock burst in steeply inclined coal seams is graded according to the total score of ground fracturing effect evaluation, specifically including:

[0017] When 0≤Q<1, the pre-control effect of ground fracturing in the steeply inclined coal seam rock burst is determined to be the first level;

[0018] When 1≤Q<2, the pre-control effect of ground fracturing of the steeply inclined coal seam rock burst is determined to be the second level;

[0019] When 2≤Q<3, the pre-control effect of ground fracturing in the steeply inclined coal seam rock burst is determined to be the third level;

[0020] When 3≤Q≤4, the pre-control effect of ground fracturing in the steeply inclined coal seam rock burst is determined to be the fourth level.

[0021] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the method for evaluating the pre-control effect of ground fracturing of rock burst in steeply inclined coal seams provided by the present invention comprises: setting a microseismic monitoring system according to a preset fracturing control range; the microseismic monitoring system comprises a ground geophone and a downhole geophone; monitoring microseismic events in the fracturing process by the ground geophone to obtain the expansion range of ground fracturing cracks; the expansion range of ground fracturing cracks comprises a horizontal expansion range and a vertical expansion range; monitoring downhole microseismic energy events in the fracturing process by the downhole geophone to obtain the total energy ratio and the total number of events ratio of the downhole microseismic energy events ; The average working resistance ratio of the working face support and the average dynamic load coefficient of the working face periodic pressure are obtained through the change in the working resistance of the working face support before and after the fracturing process; the underground tunnel is monitored by a multi-point displacement meter to obtain the deformation of the tunnel surrounding rock; the total score of the ground fracturing effect evaluation is calculated based on the horizontal expansion range, vertical expansion range, total energy ratio of underground microseismic energy events, total number of underground microseismic energy events, average working resistance ratio of the working face support, average dynamic load coefficient of the working face periodic pressure and deformation of the tunnel surrounding rock, and the ground fracturing pre-control effect of rock burst in steeply inclined coal seams is graded according to the total score of the ground fracturing effect evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0023] Figure 1 This is a flow chart of a method for evaluating the effect of ground fracturing pre-control of rock burst in steeply inclined coal seams according to an embodiment of the present invention;

[0024] Figure 2 A schematic diagram of the microseismic monitoring system according to an embodiment of the present invention.

[0025] Reference numerals: 1. ground detector; 2. downhole detector. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] like Figure 1 As shown, the present invention takes the rock burst ground fracturing process of a steeply inclined coal seam in a mine in Gansu as an example, and this embodiment provides a method for evaluating the pre-control effect of rock burst ground fracturing of a steeply inclined coal seam, including the following steps:

[0029] Step 100: Setting a microseismic monitoring system according to a preset fracturing control range. The microseismic monitoring system includes a surface geophone 1 and a downhole geophone 2.

[0030] Specifically, the comprehensive index method is used to evaluate and predict the rock burst risk level in the mining area, and the fracturing control range is selected according to the evaluation and prediction results. The length Z of the fracturing control range in this embodiment is 240m.

[0031] Specifically, Figure 2 As shown, the ground detectors 1 are equidistantly arranged on a circle with the wellhead of the fracturing well as the center and a radius of L. There are 6 ground detectors 1 in total, and the calculation formula for the radius of the circle with the wellhead of the fracturing well as the center is: Wherein, L is the radius, and Z is the length of the fracturing control range. In this embodiment, the radius L is 80m.

[0032] Specifically, there are three downhole geophones 2. The downhole geophones 2 are arranged in the working face slot, one is arranged at the center of the fracturing control range in the slot, and one is arranged on each of the left and right sides beyond the fracturing control range, and the excess length is M. The calculation formula for exceeding the fracturing control range is: The excess length M in this embodiment is 40 m.

[0033] Step 200: Monitor microseismic events during the fracturing process through the ground geophone 1 to obtain the extension range of the ground fracturing cracks.

[0034] Specifically, the expansion range of the ground fracturing crack includes a horizontal expansion range and a vertical expansion range. In this embodiment, the horizontal expansion range is 218m, and the vertical expansion range is 49.6m.

[0035] Step 300: Monitor the downhole microseismic energy events during the fracturing process through the downhole geophone 2 to obtain the total energy ratio and the total number of events ratio of the downhole microseismic energy events.

[0036] Specifically, the time range for monitoring the downhole microseismic energy events during the fracturing process by the downhole geophone 2 is one month before and after the fracturing process. The total energy ratio of the downhole microseismic energy events in this embodiment is 1.17, and the total number of downhole microseismic energy events is 1.26.

[0037] Step 400: Obtain the average working resistance ratio of the working face support and the average dynamic load coefficient of the working face during the periodic fracturing by using the change in the working resistance of the working face support before and after the fracturing process.

[0038] Specifically, the average working resistance ratio of the working surface support in this embodiment is 1.31, and the average dynamic load coefficient of the working surface periodic pressure is 1.24.

[0039] Step 500: Monitor the underground tunnel through a multi-point displacement meter to obtain the deformation of the tunnel surrounding rock.

[0040] Specifically, a multi-point displacement meter is installed in the underground tunnel to monitor the deformation of the tunnel surrounding rock within the fracturing control range after the ground fracturing. The deformation of the tunnel surrounding rock in this embodiment is 356 mm.

[0041] Step 600: The total score of the ground fracturing effect evaluation is calculated based on the horizontal expansion range, the vertical expansion range, the total energy ratio of underground microseismic energy events, the total number of underground microseismic energy events, the average working resistance ratio of the working face support, the average dynamic load coefficient of the working face periodic pressure and the deformation of the tunnel surrounding rock, and the ground fracturing pre-control effect of the rock burst in the steeply inclined coal seam is graded according to the total score of the ground fracturing effect evaluation.

[0042] Specifically, firstly, the respective evaluation index scores are obtained according to the horizontal expansion range a, vertical expansion range b, total energy ratio of underground microseismic energy events c, total number of underground microseismic energy events d, average working resistance ratio of working face support e, average dynamic load coefficient of working face periodic pressure f and deformation of tunnel surrounding rock g. The judgment criteria for different evaluation index scores are as follows:

[0043] When 0≤a<60, the horizontal expansion range score is 1; when 60≤a<120, the horizontal expansion range score is 2; when 120≤a<180, the horizontal expansion range score is 3; when 180≤a, the horizontal expansion range score is 4. The horizontal expansion range score of this embodiment is 4.

[0044] When 0≤b<15, the vertical expansion range score is 1; when 15≤b<30, the vertical expansion range score is 2; when 30≤b<45, the vertical expansion range score is 3; when 45≤b, the vertical expansion range score is 4. The vertical expansion range score of this embodiment is 4.

[0045] When 1.00 ≤ c < 1.05, the total energy ratio score of the downhole microseismic energy events is 1; when 1.05 ≤ c < 1.15, the total energy ratio score of the downhole microseismic energy events is 2; when 1.15 ≤ c < 1.20, the total energy ratio score of the downhole microseismic energy events is 3; when 1.20 ≤ c, the total energy ratio score of the downhole microseismic energy events is 4. The total energy ratio score of the downhole microseismic energy events in this embodiment is 3.

[0046] When 1.00 ≤ d < 1.15, the total number ratio score of the downhole microseismic energy events is 1; when 1.15 ≤ d < 1.30, the total number ratio score of the downhole microseismic energy events is 2; when 1.30 ≤ d < 1.40, the total number ratio score of the downhole microseismic energy events is 3; when 1.40 ≤ d, the total number ratio score of the downhole microseismic energy events is 4. The total number ratio score of the downhole microseismic energy events in this embodiment is 2.

[0047] When 1.00 ≤ e < 1.10, the average working resistance ratio score of the face supports is 1; when 1.10 ≤ e < 1.20, the average working resistance ratio score of the face supports is 2; when 1.20 ≤ e < 1.30, the average working resistance ratio score of the face supports is 3; when 1.30 ≤ e, the average working resistance ratio score of the face supports is 4. The average working resistance ratio score of the face supports in this embodiment is 4.

[0048] When 1.50 < f, the average dynamic load coefficient score of the periodic weighting of the face is 1; when 1.35 ≤ f < 1.50, the average dynamic load coefficient score of the periodic weighting of the face is 2; when 1.20 ≤ f < 1.35, the average dynamic load coefficient score of the periodic weighting of the face is 3; when f < 1.20, the average dynamic load coefficient score of the periodic weighting of the face is 4. The average dynamic load coefficient score of the periodic weighting of the face in this embodiment is 3.

[0049] When 1500 < g, the score of the roadway surrounding rock deformation is 1; when 900 ≤ g < 1500, the score of the roadway surrounding rock deformation is 2; when 300 ≤ g < 900, the score of the roadway surrounding rock deformation is 3; when g < 300, the score of the roadway surrounding rock deformation is 4. The score of the roadway surrounding rock deformation in this embodiment is 3.

[0050] Specifically, the calculation formula for the total score of the ground fracturing effect evaluation is: Q = 0.2 × A + 0.2 × B + 0.1 × C + 0.1 × D + 0.15 × E + 0.15 × F + 0.1 × G; wherein Q is the total score of the ground fracturing effect evaluation, A is the horizontal expansion range score, B is the vertical expansion range score, C is the total energy ratio score of the underground microseismic energy event, D is the total number of underground microseismic energy events, E is the average working resistance ratio score of the working face support, F is the average dynamic load coefficient score of the working face periodic pressure, and G is the deformation score of the surrounding rock of the tunnel. The total score Q of the ground fracturing effect evaluation in this embodiment is 3.45.

[0051] More specifically, the specific steps of grading the pre-control effect of ground fracturing of steeply inclined coal seams according to the total score of ground fracturing effect evaluation include:

[0052] When 0≤O<1, the pre-control effect of ground fracturing in the steeply inclined coal seam rock burst is determined to be of poor grade;

[0053] When 1≤Q<2, the pre-control effect of ground fracturing in the steeply inclined coal seam rock burst is determined to be medium level;

[0054] When 2≤Q<3, the pre-control effect of ground fracturing in the steeply inclined coal seam rock burst is determined to be good;

[0055] When 3≤O≤4, the pre-control effect of rock burst ground fracturing in steeply inclined coal seams is determined to be excellent. The pre-control effect of rock burst ground fracturing in steeply inclined coal seams in this embodiment is excellent, indicating that the surface fracturing project has achieved the expected effect, and the mine pressure intensity is significantly reduced during the subsequent mining process of the working face, and no strong mine pressure and rock burst phenomena occur, which verifies the feasibility and correctness of the evaluation method for pre-control effect of rock burst ground fracturing in steeply inclined coal seams.

[0056] The beneficial effects of the present invention are as follows:

[0057] 1) By analyzing and grading the pre-control effect of ground fracturing on rock burst in steeply inclined coal seams, it is ensured that the pre-control effect achieves the expected effect and ensures safe and efficient mining of the working face;

[0058] 2) The method of the present invention is accurate, reasonable, feasible, correct and universal.

[0059] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0060] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for evaluating the effect of ground fracturing pre-control in steeply inclined coal seam rock burst, characterized in that: The steps include: A microseismic monitoring system is set according to a preset fracturing control range; the microseismic monitoring system includes a ground geophone and a downhole geophone; The microseismic events in the fracturing process are monitored by the ground geophone to obtain the expansion range of the ground fracturing cracks; the expansion range of the ground fracturing cracks includes a horizontal expansion range and a vertical expansion range; The downhole microseismic energy events during the fracturing process are monitored by the downhole geophone to obtain the total energy ratio and the total number of events ratio of the downhole microseismic energy events; The average working resistance ratio of the working face support and the average dynamic load coefficient of the working face cycle are obtained by the change of the working resistance of the working face support before and after the fracturing process; The underground tunnel is monitored by multi-point displacement meters to obtain the deformation of the tunnel surrounding rock; The total score for the ground fracturing effect evaluation is calculated based on the horizontal expansion range, the vertical expansion range, the total energy ratio of the underground microseismic energy events, the total event ratio of the underground microseismic energy events, the average working resistance ratio of the working face supports, the average dynamic load coefficient of the working face periodic pressure and the deformation of the tunnel surrounding rock, and the ground fracturing pre-control effect of the rock burst in the steeply inclined coal seam is graded according to the total score for the ground fracturing effect evaluation.

2. The method for evaluating the effect of ground fracturing pre-control in steeply inclined coal seam rock burst according to claim 1, characterized in that: The ground geophones are equidistantly arranged on a circle with the wellhead of the fracturing well as the center; there are 6 ground geophones, and the calculation formula for the radius of the circle with the wellhead of the fracturing well as the center is: Wherein, L is the radius, and Z is the length of the fracturing control range.

3. The method for evaluating the effect of ground fracturing pre-control in steeply inclined coal seam rock burst according to claim 2, characterized in that: There are three downhole geophones; the downhole geophones are respectively arranged at the center of the fracturing control range and on both sides beyond the fracturing control range; the calculation formula for exceeding the fracturing control range is: Wherein, M is beyond the fracturing control range.

4. The method for evaluating the effect of ground fracturing pre-control in steeply inclined coal seam rock burst according to claim 1, characterized in that: The calculation formula for the total score of the ground fracturing effect evaluation is: Q=0.2×A+0.2×B+0.1×C+0.1×D+0.15×E+0.15×F+0.1×G; wherein Q is the total score of the ground fracturing effect evaluation, A is the horizontal expansion range score, B is the vertical expansion range score, C is the total energy ratio score of the underground microseismic energy event, D is the total number of underground microseismic energy events ratio score, E is the average working resistance ratio score of the working face support, F is the average dynamic load coefficient score of the working face periodic pressure, and G is the deformation score of the tunnel surrounding rock.

5. The method for evaluating the effect of ground fracturing pre-control of rock burst in steeply inclined coal seams according to claim 4, characterized in that: According to the total score of the surface fracturing effect evaluation, the effect of the surface fracturing pre-control of rock burst in steeply inclined coal seams is graded, including: When 0≤O<1, the pre-control effect of ground fracturing of the steeply inclined coal seam rock burst is determined to be the first level; When 1≤Q<2, the pre-control effect of ground fracturing of the steeply inclined coal seam rock burst is determined to be the second level; When 2≤Q<3, the pre-control effect of ground fracturing of the steeply inclined coal seam rock burst is determined to be the third level; When 3≤Q≤4, the ground fracturing pre-control effect of the rock burst in the steeply inclined coal seam is determined to be at the fourth level.

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