CN112983418A - Method for hydraulic fracturing pressure relief of coal mine underground coal face withdrawal channel - Google Patents
Method for hydraulic fracturing pressure relief of coal mine underground coal face withdrawal channel Download PDFInfo
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- CN112983418A CN112983418A CN202110399901.2A CN202110399901A CN112983418A CN 112983418 A CN112983418 A CN 112983418A CN 202110399901 A CN202110399901 A CN 202110399901A CN 112983418 A CN112983418 A CN 112983418A
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21C—MINING OR QUARRYING
- E21C37/00—Other methods or devices for dislodging with or without loading
- E21C37/06—Other methods or devices for dislodging with or without loading by making use of hydraulic or pneumatic pressure in a borehole
- E21C37/12—Other methods or devices for dislodging with or without loading by making use of hydraulic or pneumatic pressure in a borehole by injecting into the borehole a liquid, either initially at high pressure or subsequently subjected to high pressure, e.g. by pulses, by explosive cartridges acting on the liquid
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B33/00—Sealing or packing boreholes or wells
- E21B33/10—Sealing or packing boreholes or wells in the borehole
- E21B33/13—Methods or devices for cementing, for plugging holes, crevices, or the like
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21C—MINING OR QUARRYING
- E21C35/00—Details of, or accessories for, machines for slitting or completely freeing the mineral from the seam, not provided for in groups E21C25/00 - E21C33/00, E21C37/00 or E21C39/00
Abstract
The invention relates to the technical field of underground coal mine mining, and discloses a method for hydraulic fracturing pressure relief of a withdrawal channel of an underground coal mining working face of a coal mine, which comprises the following steps: step 1) determining roof strata structure parameters, and acquiring the influence range and the influence strength of the advanced support pressure of a coal face; step 2): performing primary fracturing when a rock body to be fractured is outside the influence range of the advanced bearing pressure of the coal face to form a plurality of hydraulic cracks in the horizontal direction; and 3) performing secondary fracturing when the rock mass to be fractured is in the influence range of the advanced bearing pressure of the coal face, forming a series of hydraulic cracks in the vertical direction, and cutting off the roof rock stratum. The method for hydraulic fracturing pressure relief of the coal face retraction channel in the coal mine can efficiently and safely crush the top plate above the coal face retraction channel in the coal mine, weaken the disturbance of the advanced bearing pressure on surrounding rocks of the retraction channel, and ensure normal retraction during the end mining period of the coal face.
Description
Technical Field
The invention relates to the technical field of underground coal mine mining, in particular to a method for hydraulic fracturing pressure relief of a withdrawal channel of an underground coal face of a coal mine.
Background
The coal face and the withdrawal channel of the fully mechanized caving coal face are under the action of the pressure of the front support, so that a strong mine pressure phenomenon can occur, a roof can be suspended due to large-area concentrated caving, the support quality during the tunneling of the withdrawal channel of the coal face and the withdrawal speed of the support after the withdrawal are seriously influenced, the support of the coal face is seriously damaged, even a conveyor is pressed down, and the coal face is forced to stop production.
In the prior art, a drilling blasting technology is usually adopted to pre-crack a hard top plate in front of a coal face, so that the stress concentration degree of a coal rock mass in front is reduced, and the deformation of the top plate and surrounding rocks of the coal face and a withdrawal channel is reduced, wherein the patent publication number is CN108661643A, the patent named as a roof cutting, pressure relief and lane protection method for the withdrawal channel at the end of coal face and the patent publication number is CN107060760A, and the patent named as a method for pre-cracking blasting, roof caving and pressure relief of a coal mine withdrawal roadway propose a method for arranging rows of drill holes in the withdrawal channel, and a through crack is formed between the drill holes after explosive charging blasting to realize the advanced breakage of the top plate, and the method has the following defects: 1) the method relates to initiating explosive devices such as detonators, explosives and the like, and special transportation and storage are needed underground, so that the method is not beneficial to economical and efficient production of mines; 2) potential safety hazards exist when blasting is carried out on a high-gas coal seam; 3) the shock wave generated by blasting can bring impact load to the support in the retraction channel, and is not beneficial to roadway maintenance.
The Hydraulic Fracturing technology is widely applied to the field of oil and gas exploitation, and when the pressure is higher than the ground stress near the well wall and the tensile strength of stratum Rock, cracks are generated in the stratum near the well bottom, so that the increase of oil and gas yield is promoted, the Hydraulic Fracturing technology is gradually applied to the field of coal mines in recent years, and comprises goaf hard roof treatment, coal Rock roadway fast driving, low gas coal seam permeability increasing and the like, the expansion of the Hydraulic cracks is influenced by the ground stress state, the 'simulation direct Hydraulic Fractures in heterogenous Rock slabs' paper published by Hubbert and Willis, the 'model direct Hydraulic Fractures in heterogenous Rock slabs' published by He and the like and the patent publication No. CN106150503A entitled 'method for Hydraulic Fracturing treatment of roof plates' indicate that the Hydraulic cracks expand along a plane perpendicular to the direction of minimum ground stress, and in shallow coal seams, the ground stress condition is generally in a reverse ground stress state, the stress in the vertical direction is the minimum main stress, so that only horizontal hydraulic cracks can be generated in a roof rock stratum under the condition of reverse ground stress, and the patent with the patent publication number of CN106321049A and the name of the method and the device for optimizing the position of a stope by hydraulic fracturing pressure relief proposes that a mining area roadway obliquely drills towards a roof, and a plurality of times of drilling are carried out at intervals of a preset distance along the length direction of the mining area roadway; respectively carrying out hydraulic fracturing pressure relief treatment at a plurality of preset positions on each hydraulic fracturing pressure relief hole to form a plurality of cutting cracks; the method cuts off the roof strata along each cutting fracture of each hydraulic fracture relief hole has the following defects: 1) the mining area roadway prepares a roadway for a coal mine, serves the whole mining area, is responsible for tasks such as coal transportation, material transportation, pedestrians and the like, and is limited in drilling operation in the mining area roadway; 2) drilling holes for multiple times at preset intervals along the length direction of the mining area roadway to influence the normal production task in the mining area roadway; 3) influence of a stress condition on a hydraulic crack expansion track under a field condition is ignored, although a grooving drill bit is adopted to perform grooving treatment at a preset position of a hydraulic fracture drilling hole to orient the initiation process of the hydraulic crack, the hydraulic crack expansion track is influenced by a local stress state, the oriented hydraulic crack is difficult to form, and a plurality of through cracks are difficult to effectively form.
The technology similar to the invention is Chinese patent publication No. CN107313777A, and the patent named as 'fully mechanized coal mining working face main withdrawal channel hydraulic fracturing pressure relief method and device' proposes a fully mechanized coal mining working face main withdrawal channel hydraulic fracturing pressure relief method and device, two kinds of drill holes with different parameters are drilled in a withdrawal channel in an inclined way to a roof rock stratum, hydraulic fracturing pressure relief treatment is carried out at a plurality of preset positions of the drill holes to form a plurality of cutting cracks, and the roof rock stratum is cut off along the cutting cracks, and the method has the following defects: 1) the stress state under the field condition is not considered, although the grooving treatment is carried out on the preset position of the drill hole, the hydraulic crack propagation and initiation process is oriented, the hydraulic crack propagation is influenced by the local stress state (the hydraulic crack propagates along a plane vertical to the direction of the minimum ground stress) along with the propagation of the hydraulic crack, the hydraulic crack in the same direction can be formed, the number of the top plate rock strata can be increased, and the top plate is difficult to cut; 2) two kinds of drill holes are arranged at intervals along the axis of the retraction channel, the number of the drill holes is large, and the labor intensity of workers is high; 3) drilling a drill hole at one end of the withdrawal channel in the withdrawal roadway to fracture the top plate of the end of the coal face, which indicates that the fracturing holes arranged in the withdrawal channel are difficult to fracture the triangular area of the end, and drilling holes to treat the top plate of the triangular area are still required to be arranged in the withdrawal roadway, so that the fracturing operation amount is increased, and the production efficiency is low.
Disclosure of Invention
Technical problem to be solved
Aiming at the defects of the prior art, the invention provides a hydraulic fracturing pressure relief method for a withdrawal channel of an underground coal face of a coal mine, which realizes efficient and safe crushing of a top plate above the withdrawal channel of the underground coal face of the coal mine, weakens the disturbance of advanced bearing pressure on surrounding rocks of the withdrawal channel and ensures normal withdrawal during the end mining period of the coal face.
(II) technical scheme
In order to achieve the purpose, the invention provides the following technical scheme: a method for hydraulic fracturing pressure relief of a coal mine underground coal face withdrawal channel comprises the following steps:
1) determining roof strata structure parameters and coal face geological conditions, and acquiring the influence range and influence strength of the advance support pressure of the coal face;
2) a drilling machine is used for obliquely drilling a group of drill holes on the top plate rock stratum in the front side of the withdrawal passage to serve as primary hydraulic fracturing drill holes; performing primary fracturing when the roof strata to be fractured is outside the influence range of the advance bearing pressure of the coal face to form a plurality of hydraulic cracks in the horizontal direction, and increasing the layering quantity of the roof strata;
3) and (3) with the advance of the coal face, when the roof rock stratum to be fractured is in the influence range of the advanced bearing pressure of the coal face, obliquely excavating a series of drill holes as secondary hydraulic fracturing drill holes to the roof rock stratum by using a drilling machine in the front side of the withdrawal passage, performing secondary fracturing on the roof rock stratum to be fractured to form a series of hydraulic cracks in the vertical direction, penetrating through the plurality of hydraulic cracks in the horizontal direction in the step one, and cutting off the roof rock stratum.
Preferably, the roof strata structure parameters and coal face geological conditions in the step 1) comprise direct roof and basic roof thickness, lithology, coal-rock body strength, coal face mining height, coal face length and the like.
Preferably, the advance bearing pressure of the coal face in the step 1) is obtained by a numerical calculation method, the distribution condition of the front bearing pressure of the coal face at different positions from the withdrawal passage is obtained, and the minimum principal stress direction of the roof strata near the withdrawal passage is obtained.
Preferably, in the step 2), when a hydraulic fracturing drill hole is dug in the withdrawal passage for one time, the hydraulic fracturing drill hole is arranged according to the arrangement parameters such as a preset diameter, a preset inclination angle, a preset length, a horizontal projection of a preset fracturing hole and an included angle between the horizontal projection of the preset fracturing hole and the axial line of the withdrawal roadway; the primary hydraulic fracturing drill holes are arranged in rows, the distance between every two adjacent hydraulic fracturing drill holes is 20-50 m, the preset diameter is 45-98 mm, the preset inclination angle is 20-65 degrees with the horizontal plane as a reference elevation angle, the preset length is 20-60 m, and the included angle between the horizontal projection of the primary hydraulic fracturing drill holes and the axial line of the withdrawal roadway is 0-5.
Preferably, in the step 3), secondary hydraulic fracturing drill holes are dug in the withdrawal channel and divided into long holes and short holes, and the long holes and the short holes are arranged according to parameters such as preset diameter, preset inclination angle, preset length, and included angle between horizontal projection of the preset fracturing holes and the axial line of the withdrawal roadway; the distance between the long holes is 12-40 m, the preset diameter is 45-98 mm, the preset inclination angle is 5-45 degrees taking the horizontal plane as a reference elevation angle, and the preset length is 20-60 m; the included angle between the horizontal projection of the long hole and the axis of the withdrawal roadway is 0-5 degrees, the distance between the short holes is 12-40 m, the preset diameter is 45-98 mm, the preset inclination angle is 20-65 degrees with the horizontal plane as a reference elevation angle, the preset length is 20-60 m, and the included angle between the horizontal projection of the short holes and the axis of the withdrawal roadway is 0-5 degrees.
Preferably, in the step 3), secondary hydraulic fracturing drill holes are dug in the withdrawal channel and divided into long holes and short holes, and the preset distance between each long hole and each short hole is 0-0.5 m; the elevation angle of the short hole is larger than that of the long hole, and the depth of the short hole is smaller than that of the long hole; the short hole mainly fractures the basic roof, and the long hole mainly fractures the direct roof.
Preferably, in the step 2), when the roof rock stratum to be fractured is located outside the influence range of the advanced bearing pressure of the coal face, a special grooving tool is used for cutting a series of radial grooving inside the fracturing hole along the axial direction of the fracturing hole, and the distance between adjacent grooving positions is 3-6 m; sealing holes by using a double-seal type hole sealing device; and performing multi-stage retreating type hydraulic fracturing at the pre-cut radial cutting groove.
Preferably, in the step 3), when the roof strata to be fractured is within the influence range of the advance bearing pressure of the coal face, a special cutting tool is used for cutting a series of radial cutting grooves in the fracturing hole along the axial direction of the fracturing hole between the vertical direction distances of the adjacent horizontal hydraulic cracks in the step two; sealing holes by using a double-seal type hole sealing device; and performing multi-stage retreating type hydraulic fracturing at the pre-cut radial cutting groove.
(III) advantageous effects
Compared with the prior art, the invention provides a method for hydraulic fracturing pressure relief of a coal face retraction channel in an underground coal mine, which has the following beneficial effects:
1) the whole hydraulic fracturing process does not generate impact load caused by similar blasting operation, and is favorable for maintaining a withdrawal channel;
2) the fracturing drill holes are uniformly distributed in the withdrawal channel, so that normal production in a mining area is not influenced;
3) the internal stress state of a top plate of a coal face is fully utilized, a series of horizontal direction cracks and vertical direction cracks are formed through twice fracturing respectively, the horizontal direction hydraulic cracks increase the layering number of the top plate rock stratum, the vertical direction hydraulic cracks penetrate through the horizontal direction hydraulic cracks, and the top plate rock stratum can be effectively fractured;
4) the number of the arranged drill holes is small, the labor intensity of workers is reduced, and the economical and efficient production of mines is facilitated;
5) the fracturing effect is more comprehensive, and the hydraulic cracks formed in the two fracturing processes are communicated with each other, so that the fracturing cracks which are beneficial to weakening and withdrawing the roadway rock stratum top plate are formed, the completeness of the coal face top plate rock stratum is further reduced, and the top plate rock stratum in front of the withdrawing channel and the end triangular area can be efficiently crushed.
The method can efficiently and safely crush the top plate above the withdrawing channel of the underground coal face of the coal mine, weaken the disturbance of the advanced bearing pressure on the surrounding rock of the withdrawing channel, and ensure the normal withdrawing of the coal face during the final mining period.
Drawings
FIG. 1 is a plan view of a primary fracturing procedure in accordance with an embodiment of the present invention;
FIG. 2 is a cross-sectional view of a primary fracturing procedure in accordance with an embodiment of the present invention;
FIG. 3 is a plan view of a secondary fracturing procedure in accordance with an embodiment of the present invention;
fig. 4 is a cross-sectional view of a secondary fracturing procedure in accordance with an embodiment of the present invention.
In the figure: 1, preparing a roadway; 2-coal face; 3-protecting the coal pillars in the roadway; 4-retracting the channel; 5, drilling by primary hydraulic fracturing; 6-hydraulic crack in horizontal direction; 7-mining the roadway; 8, directly ejecting; 9-basic top; 10-coal seam; 11-secondary hydraulic fracturing drilling; 12-vertical direction hydraulic cracking; 13-radial grooving.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, 2, 3 and 4, a method for hydraulic fracturing pressure relief of a withdrawal channel of an underground coal face of a coal mine comprises the following steps:
the method comprises the following steps: determining the structural parameters of the roof strata and the geological conditions of the coal face 2, and acquiring the influence range and the influence strength of the advanced bearing pressure of the coal face 2;
step two: a drilling machine is used for obliquely drilling a group of drill holes towards the top rock layer in the front side of the withdrawal passage 4 to serve as primary hydraulic fracturing drill holes 5; performing primary fracturing when the roof strata to be fractured is outside the influence range of the advance bearing pressure of the coal face 2 to form a plurality of hydraulic cracks 6 in the horizontal direction, and increasing the layering quantity of the roof strata;
step three: with the advance of the coal face 2, when the roof rock stratum to be fractured is in the influence range of the advance bearing pressure of the coal face 2, a drilling machine is used for obliquely drilling a series of drill holes to the roof rock stratum in the front side of the withdrawal passage 4 to serve as secondary hydraulic fracturing drill holes 11, secondary fracturing is carried out on the roof rock stratum to be fractured to form a series of hydraulic cracks 12 in the vertical direction, and the roof rock stratum is cut off after the plurality of hydraulic cracks 6 in the horizontal direction in the step one are penetrated.
In the first step, the structural parameters of the roof strata and the geological conditions of the coal face 2 comprise the thickness of a direct roof 8 and a basic roof 9, lithology, coal rock strength, mining height of the coal face 2, length of the coal face 2 and the like, the advance bearing pressure of the coal face 2 is obtained through a numerical calculation method, the distribution condition of the front support pressure of the coal face 2 at different positions away from the withdrawal channel 4 is obtained, and the direction of the minimum principal stress of the roof strata near the withdrawal channel 4 is obtained.
In the second step, when the withdrawal passage 4 is dug for one time, hydraulic fracturing drill holes 5 are drilled according to the arrangement parameters such as the preset diameter, the preset inclination angle, the preset length, the horizontal projection of the preset fracturing holes and the included angle of the axis of the withdrawal roadway 4; the primary hydraulic fracturing drill holes 5 are arranged in rows, the distance between the primary hydraulic fracturing drill holes 5 is 20-50 m, the preset diameter is 45-98 mm, the preset inclination angle is 20-65 degrees taking the horizontal plane as the reference elevation angle, the preset length is 20-60 m, and the included angle between the horizontal projection of the primary hydraulic fracturing drill holes 5 and the axis of the withdrawal roadway 4 is 0-5 degrees.
In the third step, secondary fracturing holes 11 are drilled in the withdrawal passage 4 and divided into long holes and short holes, and the long holes and the short holes are arranged according to parameters such as preset diameter, preset inclination angle, preset length, horizontal projection of the preset fracturing holes, an included angle between the horizontal projection of the preset fracturing holes and the axis of the withdrawal tunnel 4 and the like; the distance between the long holes is 12-40 m, the preset diameter is 45-98 mm, the preset inclination angle is 5-45 degrees taking the horizontal plane as a reference elevation angle, and the preset length is 20-60 m; the horizontal projection of the long hole and the axis of the withdrawal tunnel 4 form an included angle of 0-5 degrees; the short hole interval is 12-40 m, the preset diameter is 45-98 mm, the preset inclination angle is 20-65 degrees taking the horizontal plane as a reference elevation angle, and the preset length is 20-60 m; the horizontal projection of the short hole and the axis of the withdrawal roadway 4 form an included angle of 0-5 degrees.
In the third step, a secondary hydraulic fracturing drill hole 11 is dug in the withdrawal passage 4 and is divided into a long hole and a short hole, and the distance between the long hole and the short hole is 0-0.5 m; the elevation angle of the short hole is larger than that of the long hole, and the depth of the short hole is smaller than that of the long hole; the short hole fractures the primary roof 9 and the long hole fractures the direct roof 8.
Secondly, when the top plate rock stratum to be fractured is located outside the influence range of the advanced bearing pressure of the coal face 2, cutting a series of radial cutting grooves 13 in the fracturing hole along the axial direction of the fracturing hole by using a special cutting groove tool, wherein the distance between the adjacent cutting grooves is 3-6 m; sealing holes by using a double-seal type hole sealing device; multi-stage retreat hydraulic fracturing is performed at the pre-cut radial cutting grooves 13.
Thirdly, when the roof rock stratum to be fractured is in the influence range of the advanced bearing pressure of the coal face 2, a series of radial cutting grooves 13 are cut in the fracturing hole along the axial direction of the fracturing hole by using a special cutting groove tool between the distances in the vertical direction of the adjacent horizontal hydraulic cracks 6 in the second step; sealing holes by using a double-seal type hole sealing device; multi-stage retreat hydraulic fracturing is performed at the pre-cut radial cutting grooves 13.
The embodiment provides a method for hydraulic fracturing pressure relief of a coal face withdrawal channel in an underground coal mine, which comprises the steps of firstly, determining roof strata structure parameters and geological conditions of a coal face 2 by using equipment such as a drilling peering instrument and the like, wherein the parameters comprise the thicknesses of a direct roof 8 and a basic roof 9, lithology, coal rock strength, the mining height of the coal face 2, the length of the coal face 2 and the like; and acquiring the influence range and the influence strength of the advanced bearing pressure of the coal face 2 by a numerical simulation technology according to the determined roof strata structure parameters and the geological conditions of the coal face 2.
When the top plate rock stratum of the withdrawal channel 4 is out of the influence range of the advanced bearing pressure of the coal face 2, when the withdrawal channel 4 excavates a hydraulic fracturing drill hole 5 for one time, the hydraulic fracturing drill hole is drilled according to the arrangement parameters such as the preset diameter, the preset inclination angle, the preset length, the horizontal projection of the preset fracturing hole and the included angle of the axis of the withdrawal roadway 4; preferably, the primary hydraulic fracturing boreholes 5 are arranged in rows; the distance between the primary hydraulic fracturing drill holes 5 is 20-50 m, and the distance between the primary hydraulic fracturing drill holes 5 is preferably 30 m; the preset diameter is 45 mm-98 mm, and the further preferable preset diameter is 56 mm; the preset inclination angle is 20-65 degrees with the horizontal plane as a reference elevation angle, and the angle of the elevation angle of the primary hydraulic fracturing drill hole 5 is preferably 45 degrees; the preset length is 20 m-60 m, the included angle between the horizontal projection of the primary hydraulic fracturing drill hole 5 and the axis of the withdrawal roadway 4 is 0-5 degrees, and the included angle between the horizontal projection of the fracturing hole and the axis of the withdrawal roadway 4 is further preferably 0 degrees.
Cutting a series of radial cutting grooves 13 in the primary hydraulic fracturing drill 5 along the axial direction of the fracturing hole by using a special cutting groove tool, wherein the distance between the adjacent cutting grooves is 3-6 m, and the preferable distance is 4 m; sealing holes by using a double-seal type hole sealing device; performing multi-stage retreating type hydraulic fracturing at the pre-cut radial cutting groove 13; and a plurality of horizontal hydraulic cracks 6 are formed, and the number of the top plate strata is increased.
When the top plate rock stratum of the withdrawal channel 4 is within the influence range of the advanced bearing pressure of the coal face 2, a secondary hydraulic fracturing drill hole 11 is dug in the withdrawal channel 4 and is divided into a long hole and a short hole, and the long hole and the short hole are arranged according to parameters such as a preset diameter, a preset inclination angle, a preset length, a preset fracturing hole horizontal projection and an included angle of the axis of the withdrawal tunnel 4;
preferably, the distance between the long holes is 12-40 m, and further preferably 15 m; the preset diameter is 45 mm-98 mm, and the further preferable preset diameter is 56 mm; the preset inclination angle is an angle taking the horizontal plane as a reference elevation angle and is 5-45 degrees, and the further preferred elevation angle is 20 degrees; the preset length is 20 m-60 m, and the preset length is more preferably 50 m; the included angle between the horizontal projection of the long hole and the axis of the retracting tunnel 4 is 0-5 degrees, and the included angle between the horizontal projection of the long hole and the axis of the retracting tunnel 4 is further preferably 0 degrees.
Preferably, the distance between the short holes is 12-40 m, and further preferably 15 m; the preset diameter is 45 mm-98 mm, and the further preferable preset diameter is 56 mm; the preset inclination angle is an angle taking the horizontal plane as a reference elevation angle and is 20-65 degrees, and the further preferable elevation angle is 55 degrees; the preset length is 20 m-60 m; further preferably, the preset length is 45 m; the preset distance between the long hole and the short hole is 0-0.5 m; the included angle between the horizontal projection of the short hole and the axis of the withdrawal roadway 4 is 0-5 degrees, and the included angle between the horizontal projection of the short hole and the axis of the withdrawal roadway 4 is further preferably 0 degrees.
The preset distance between the long hole and the short hole is preferably 0-0.5 m, and the preset distance is further preferably 0 m; the elevation angle of the short hole is larger than that of the long hole, and the depth of the short hole is smaller than that of the long hole; the short hole fractures the primary roof 9 and the long hole fractures the direct roof 8.
Cutting a series of radial cutting grooves 13 in the fracturing hole along the axial direction of the fracturing hole by using a special cutting groove tool between the vertical direction distances of the adjacent horizontal hydraulic cracks 6 in the step two; sealing holes by using a double-seal type hole sealing device; and performing multi-stage retreating type hydraulic fracturing at the pre-cut radial cutting groove 13 to form a series of hydraulic cracks 12 in the vertical direction, communicating with the hydraulic cracks 6 in the horizontal direction formed in the step two, cutting each layer of the roof rock stratum, and completing sufficient and efficient crushing of the roof rock stratum. The method can efficiently and safely crush the top plate above the coal face withdrawing channel 4 in the underground coal mine, weaken the disturbance of the advanced bearing pressure to the surrounding rock of the withdrawing channel 4 and ensure the normal withdrawing of the coal face during the end mining period.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (8)
1. A method for hydraulic fracturing pressure relief of a coal mine underground coal face withdrawal channel is characterized by comprising the following steps:
1) determining the structural parameters of the roof strata and the geological conditions of the coal face (2), and acquiring the influence range and the influence strength of the advanced bearing pressure of the coal face (2);
2) a drilling machine is used for obliquely cutting a group of drill holes towards the top plate rock stratum in the front side of the withdrawal passage (4) to be used as primary hydraulic fracturing drill holes (5); performing primary fracturing when the roof strata to be fractured is outside the influence range of the advanced bearing pressure of the coal face (2), forming a plurality of hydraulic cracks (6) in the horizontal direction, and increasing the layering quantity of the roof strata;
3) with the advance of the coal face (2), when the roof rock stratum to be fractured is in the influence range of the advance bearing pressure of the coal face (2), a drilling machine is used for obliquely drilling a series of drill holes to the roof rock stratum in the front side of the withdrawal channel (4) to serve as secondary hydraulic fracturing drill holes (11), secondary fracturing is conducted on the roof rock stratum to be fractured, a series of hydraulic cracks (12) in the vertical direction are formed, the horizontal direction hydraulic cracks (6) in the first step penetrate through, and the roof rock stratum is cut off.
2. The method for hydraulic fracturing pressure relief of a coal face withdrawal channel in an underground coal mine according to claim 1, wherein the structural parameters of the roof strata and the geological conditions of the coal face (2) in the step 1) comprise the thickness of a direct roof (8) and a basic roof (9), lithology, coal-rock body strength, mining height of the coal face (2), length of the coal face (2) and the like.
3. The method for hydraulic fracturing pressure relief of the coal face retraction channel in the underground coal mine according to claim 1, characterized in that the advanced bearing pressure of the coal face (2) in the step 1) is obtained through a numerical calculation method, the distribution condition of the front support pressure of the coal face (2) at different positions from the retraction channel (4) is obtained, and the minimum principal stress direction of the roof strata near the retraction channel (4) is obtained.
4. The method for hydraulic fracturing pressure relief of the withdrawing channel of the underground coal face of the coal mine according to claim 1, wherein in the step 2), when the withdrawing channel (4) drills a hydraulic fracturing drill hole (5), the hydraulic fracturing drill hole is arranged according to arrangement parameters such as a preset diameter, a preset inclination angle, a preset length, a preset fracturing hole horizontal projection and an axial line included angle of the withdrawing channel (4); the primary hydraulic fracturing drill holes (5) are arranged in rows, the distance between every two adjacent hydraulic fracturing drill holes is 20-50 m, the preset diameter is 45-98 mm, the preset inclination angle is an angle with the horizontal plane as a reference elevation angle and is 20-65 degrees, the preset length is 20-60 m, and the included angle between the horizontal projection of the primary hydraulic fracturing drill holes (5) and the axis of the withdrawal roadway (4) is 0-5.
5. The method for hydraulic fracturing pressure relief of the withdrawal channel of the underground coal mining working face of the coal mine according to claim 1, wherein in the step 3), secondary hydraulic fracturing drill holes (11) are dug in the withdrawal channel (4) and are divided into long holes and short holes, and the long holes and the short holes are arranged according to parameters such as preset diameters, preset inclination angles, preset lengths, horizontal projections of the preset fracturing holes and an included angle between the horizontal projections of the preset fracturing holes and the axial line of the withdrawal roadway (4); the distance between the long holes is 12-40 m, the preset diameter is 45-98 mm, the preset inclination angle is 5-45 degrees taking the horizontal plane as a reference elevation angle, and the preset length is 20-60 m; the included angle between the horizontal projection of the long hole and the axis of the withdrawal roadway (4) is 0-5 degrees, the distance between the short holes is 12-40 m, the preset diameter is 45-98 mm, the preset inclination angle is 20-65 degrees with the horizontal plane as a reference elevation angle, the preset length is 20-60 m, and the included angle between the horizontal projection of the short hole and the axis of the withdrawal roadway (4) is 0-5 degrees.
6. The method for hydraulic fracturing pressure relief of the withdrawing channel of the underground coal face of the coal mine according to claim 1, wherein in the step 3), secondary hydraulic fracturing drill holes (11) are dug in the withdrawing channel (4) and divided into long holes and short holes, and the preset distance between each long hole and each short hole is 0-0.5 m; the elevation angle of the short hole is larger than that of the long hole, and the depth of the short hole is smaller than that of the long hole; the short hole mainly fractures the basic roof (9), and the long hole mainly fractures the direct roof (8).
7. The method for hydraulic fracturing pressure relief of the coal face retraction channel in the underground coal mine according to claim 1, wherein in the step 2), when the roof rock stratum to be fractured is outside the influence range of the advance bearing pressure of the coal face (2), a series of radial cutting grooves (13) are cut in the fracturing hole along the axial direction of the fracturing hole by using a special cutting groove tool, and the distance between the adjacent cutting grooves is 3-6 m; sealing holes by using a double-seal type hole sealing device; and performing multi-stage backward hydraulic fracturing at the pre-cut radial cutting grooves (13).
8. The method for hydraulic fracturing pressure relief of the coal face retraction channel in an underground coal mine according to claim 1, characterized in that in the step 3), when the roof strata to be fractured is within the influence range of the advance bearing pressure of the coal face (2), a series of radial cutting grooves (13) are cut in the fracturing hole along the axial direction of the fracturing hole by using a special cutting groove tool at the vertical direction distance of the adjacent horizontal hydraulic cracks (6) in the step two; sealing holes by using a double-seal type hole sealing device; and performing multi-stage backward hydraulic fracturing at the pre-cut radial cutting grooves (13).
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