CN113982582A - Method for hydraulic fracturing treatment of end triangular area suspended roof of underground coal mine coal face - Google Patents
Method for hydraulic fracturing treatment of end triangular area suspended roof of underground coal mine coal face Download PDFInfo
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- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
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Abstract
The invention discloses a method for hydraulic fracturing treatment of an end triangular area suspended ceiling of an underground coal face of a coal mine, and relates to the field of underground coal mining. The safe and efficient crushing of the roof rock stratum of the triangular area of the coal face of the underground coal mine is realized, and roof disasters and gas accidents are effectively prevented. The method comprises the following steps: acquiring a roof rock stratum structure and geological conditions of a working face and structural characteristics of roadway protection coal pillars; step two: a drilling machine is used for drilling a row of drill holes above a stoping roadway in the stoping roadway, and the drill holes are divided into fracturing holes and observation holes; step three: performing multi-section backward fracturing on the position of the primary fracturing groove in the fracturing hole drilled in the step two; step four: and C, performing multi-stage backward fracturing on the position of the secondary fracturing cutting groove in the fracturing hole drilled in the step II. The top plate at the end of the coal face of the underground coal mine can be efficiently crushed, so that the occurrence of roof disasters and gas accidents is effectively prevented, and the safe extraction of the face is ensured.
Description
Technical Field
The invention relates to the field of underground coal mine mining, in particular to a method for hydraulically fracturing an end triangular area suspended ceiling of an underground coal face of a coal mine.
Background
Coal seams in northwest areas of China are mostly under shallow buried depth conditions, the roof rock is high in strength, large in thickness, strong in integrity and self-supporting capacity, and the coal seams are difficult to collapse in time after mining; the two lanes of the working face are generally supported by combining anchor nets and cables, so that the distance between the rear suspension tops of the end heads can reach 20 meters. The problem that the suspended roof or the caving of the triangular area at the end of the coal face is not tight mainly causes the following problems to the safe and efficient production of a coal mine: 1) gas accumulation in the goaf is easily caused, and coal left at the upper corner of the goaf can spontaneously combust; 2) sudden collapse of the triangular area top plate easily causes impact mine pressure disasters; 3) when the protective pillars between the working faces are optimized from a 20-25 m wide pillar arrangement to a 5-10 m narrow pillar arrangement, it is often necessary to cut the roof from the working face being mined to drill holes near the face triangle for roof cutting pressure relief, increasing the mining process and economic cost.
The current measures for overcoming the end overhanging of the working face comprise anchor withdrawal, deep hole blasting and static blasting.
A paper published by Wang Lei et al in the prior art and named as 'research on suspended roof treatment in a triangular area at the end of a coal face' discloses a method for promoting the collapse of a hard top plate in the triangular area at the end of the coal face by adopting an anchor withdrawal combined blasting forced roof caving comprehensive treatment scheme technology. The method aims to weaken the shallow roof of the working face by drilling and blasting the goaf and enhance the caving performance of the hard roof of the triangular area of the working face.
However, the use of the drill blasting method for treating a hard roof has the following disadvantages: 1) a gas reservoir is easily formed in a non-caving area, and potential safety hazards exist in blasting; 2) the coal mine in northwest of China strictly controls the initiating explosive devices, and the quantity of explosives which can be stored in the coal mine is extremely limited; 3) before blasting operation, all personnel on the leeward side need to be evacuated, so that normal production organization is influenced; 4) when blasting is performed at the coal face, the generated rock fragments may damage the face equipment under the action of the blast shock wave.
The paper of 'research and application of static directional rock breaking technology in treating roadway suspended ceiling problems' published by Zhanyiwei et al and the paper of 'research on mechanical properties of static breaking agents and application in end suspended ceiling' published by Wuli et al propose a method for manufacturing artificial fractures in hard roof rock layers by a static fracturing technology, and aim to shorten the suspended ceiling distance and reduce the primary caving step distance of a roof by the static fracturing method.
However, this method has the following disadvantages: 1) the fracturing procedure can be only carried out at a working face with lower supporting pressure, and cannot carry out advanced pre-fracturing under the condition of higher supporting pressure in front of the working face; 2) the drilling process is heavy, and a drilling machine is required to drill a large number of drilled holes; 3) the time (the reaction time of the cracking agent) is about 12 hours for completing one-time cracking, so that the labor cost and the time cost are increased; 4) a large amount of static crushing agents need to be purchased, and the economic cost of rock breaking is increased. In summary, in the field of underground mining of coal mines, a method for processing the suspended roof of the coal face end triangular area with low cost, high efficiency and safety is urgently needed.
In recent years, hydraulic fracturing technology has been widely used in coal seam permeability enhancement and roof management. In the prior art, a patent with the patent publication number of CN108661641A and the name of 'a method for preventing the long-distance suspended ceiling of a gate goaf based on roof cutting pressure relief' discloses a method for treating the suspended ceiling of the gate goaf by hydraulic fracturing, although a transverse or longitudinal grooving drill bit is used for prefabricating cracks, the method ignores the influence of the stress state of a roof rock stratum on the propagation track of the hydraulic crack. A large number of laboratory experiments, numerical simulation and field observation results show that the prefabricated cutting groove can only control the crack initiation direction of the hydraulic crack within a certain range (about twice the diameter of the drilled hole) around the drilled hole, the expansion track after crack initiation cannot be continuously and effectively controlled, and the track far away from the drilled hole expansion after hydraulic crack initiation is influenced by the local stress state in the rock body and expands along the plane perpendicular to the minimum main stress direction. Therefore, hydraulic fracturing requires consideration of local stress conditions at the cut top location.
A paper of 'end suspended roof technology for hydraulic pre-splitting treatment of coal face' published by Yangmai and a paper of 'roof control of suspended roof in triangular area of coal face' published by Dumao propose a method for injecting high-pressure water into suspended roof perforation in triangular area to cause roof collapse due to layered fracturing of rock stratum. The method has the following defects: 1) the drilling depth is limited, and deep rock stratum cannot be fractured; 2) the influence of the ground stress on the hydraulic crack propagation track is not considered; 3) the horizontal hydraulic cracks are generated under the condition of reverse ground stress, only the rock strata can be layered, and the rock strata can be mutually extruded or rotated to form a stable structure under the influence of mine pressure and mining without collapse or tight collapse, so that the caving ability of the rock mass is difficult to improve.
The patent with the patent publication number of CN103541711A and the name of a small-aperture hydraulic fracturing control method for the suspended roof of the end of the coal face provides a hydraulic fracturing method for controlling the suspended roof of the end of the coal face under a coal mine. The anchor cable drilling machine is used for drilling construction, a high-pressure pump is used for carrying out high-pressure hydraulic fracturing on the top plate, the structure of the top plate is improved, the strength of the top plate is weakened, and the roof at the end of the coal face is controlled to fall off in time. The disadvantages of this method are: 1) a large number of drill holes need to be drilled, so that the time and labor cost are increased; 2) the influence of the ground stress on the hydraulic crack propagation track is also ignored; 3) the hydraulic fracturing of small-bore drilling holes must be in a roadway advance support section; 4) similarly, only horizontal hydraulic cracks are generated under the condition of reverse ground stress, the number of old top strata is increased, the strata can be mutually extruded or rotated under the action of mine pressure to form a stable structure, and the stable structure cannot collapse or cannot collapse strictly, so that the purpose of 'top cutting' is difficult to achieve.
The reverse fault ground stress condition is common in shallow coal seams, the minimum ground stress in the reverse ground stress condition is the vertical ground stress, and the hydraulic crack tends to spread along a horizontal plane in the original rock stress state. The existing conventional hydraulic fracturing method for treating the suspended roof of the triangular area can only produce a series of hydraulic cracks in the horizontal direction in the stoping roadway roof, so that the method has limited effect on improving the caving ability of the rock mass.
Disclosure of Invention
Aiming at the problems, the invention provides a method for processing the suspended roof of the triangular area at the end of the hydraulic fracturing treatment of the underground coal face of the coal mine, which realizes the safe and efficient crushing of the roof rock stratum of the triangular area of the underground coal face of the coal mine and effectively prevents the occurrence of roof disasters and gas accidents.
The technical scheme of the invention is as follows:
the method comprises the following steps: acquiring a roof rock stratum structure and geological conditions of a working face 1 and structural characteristics of a roadway protection coal pillar 2, and determining the advanced bearing pressure strength and the influence range of the working face 1 by using a numerical calculation technology;
step two: as shown in fig. 6, a row of drill holes obliquely upward is excavated in the recovery roadway 3 above the recovery roadway 3 using a drilling machine, the drill hole is divided into fracturing holes 5 and observation holes 6, the observation holes 6 are positioned between two adjacent fracturing holes 5, cutting grooves at preset fracturing positions in each fracturing hole 5 by using a special mining cutter, cutting a plurality of radial cutting grooves suitable for hydraulic crack initiation, wherein the advance supporting pressure of a working face 1 moves along with the forward pushing of the working face 1, the plurality of radial cutting grooves are divided into a primary fracturing cutting groove 9 and a secondary fracturing cutting groove 10 according to the influence range of the advance supporting pressure of the working face 1, the primary fracturing cutting groove 9 is positioned outside the influence range of the advance supporting pressure of the working face 1, the direction of the minimum principal stress at the moment is vertical to the horizontal direction, the secondary fracturing cutting groove 10 is positioned in the influence range of the advance supporting pressure of the working face 1, and the direction of the minimum principal stress at the moment is parallel to the horizontal direction;
step three: as shown in fig. 7-9, a double-seal type hole packer is used to perform multi-stage backward fracturing at the position of the primary fracturing slot 9 in the fracturing hole 5 drilled in the second step, i.e. fracturing one by one from top to bottom, so as to pre-fracture the hard rock stratum at the deep part of the old top 12, generate a series of horizontal disc-shaped hydraulic cracks 7 and increase the number of deep rock stratum layers;
step four: as shown in fig. 10 to 12, a double-seal type hole packer is used to perform multi-stage backward fracturing, i.e., fracturing one by one from top to bottom, at the position of the secondary fracture cut 10 in the fracture hole 5 drilled in the second step, thereby pre-fracturing a shallow hard rock formation to generate a series of vertically disc-shaped hydraulic cracks 8, and the vertically hydraulic cracks 8 penetrate the horizontally hydraulic cracks 7 generated in the third step.
Further, when the roof rock above the mining roadway 3 is hard, the secondary fracturing slot 10 cut by using a special cutter in the second step cannot generate an ideal hydraulic crack 8 in the vertical direction, after the series of primary fracturing slots 9 are cut in the second step, a series of axial cracks are cut in the shallow part of the fracturing hole 5 by using a water jet technology, and the axial distance between the cracks is about 3 m;
and after the primary fracturing groove 9 is subjected to multi-section retreating type fracturing, a double-seal type hole packer is used for carrying out multi-section retreating type fracturing on a series of axial cracks in the fracturing hole 5 to generate a series of axial cracks penetrating through the horizontal hydraulic cracks 7, so that a hard top plate above the stoping roadway 3 is fully crushed, and a goaf top plate of the stoping roadway 3 of the working face 1 is made to collapse in time.
Further, the roof rock structure and the geological conditions of the working face 1 in the step one are obtained by using equipment such as a drilling peeping instrument and the like, the roof rock structure and the geological conditions comprise the thickness, the lithology and the rock strength of the direct roof 11, the thickness, the lithology and the rock strength of the old roof 12 and the mining height of the coal working face 1, and the obtained structural characteristics of the roadway protection coal pillar 2 comprise the width of the roadway protection coal pillar 2 and the coal rock strength, so that the reasonable fracturing height of the roof above the stoping roadway 3 is determined.
Further, in the step one, the numerical calculation technology is applied to calculate the influence range and the influence strength of the advanced bearing pressure of the working face 1, the front stress distribution state of the working face 1 is obtained when the coal face 1 is different from the top plate to be fractured, and the direction of the minimum principal stress in the top plate rock mass near the top plate to be fractured is determined.
Further, a drilling machine is used for drilling a row of drill holes in the direction of the center line of the roadway towards the top plate of the mining roadway 3 in the second step, the drilled row of drill holes comprises two fracturing holes 5 and an observation hole 6, the fracturing holes 5 and the observation hole 6 are arranged at intervals, the preset interval is 4 m-20 m, and the preset row spacing is 10 m-40 m.
Further, the preset diameter of the hydraulic fracturing drill hole dug in the second step is 45 mm-98 mm, the distance between the drill hole and the two sides of the mining roadway 3 is equal, the included angle between the horizontal projection of the preset drill hole and the axis of the mining roadway is 0-5 degrees, the included angle between the preset drill hole and the top plate is 30-70 degrees, and the length of the preset drill hole is 10 m-30 m.
Further, in the second step, a special cutter is used for grooving at the preset position of the fracturing hole 5, the distance between the adjacent grooving positions is 3 m-6 m, according to the structural characteristics of the top plate obtained in the first step, the grooving in the second step is divided into a primary fracturing grooving 9 and a secondary fracturing grooving 10, and a horizontal hydraulic crack 7 and a vertical hydraulic crack 8 are generated at the position of the primary fracturing grooving 9 and the position of the secondary fracturing grooving 10 respectively.
Furthermore, in the second step to the fourth step, the water outlet condition of the adjacent observation holes 6 is observed during each fracturing, and when a large amount of water is discharged from the observation holes 6, the pump is stopped, and the fracturing is completed.
Further, in the second step to the fourth step, an emulsion pump at the working face 1 is used for carrying out double-sealing type hydraulic fracturing on the fracturing holes 5.
Compared with the prior art, the invention has the following advantages: 1) the number of the arranged drill holes is small, so that the labor intensity of workers is reduced; 2) the emulsion pump at the working face is used for replacing a high-pressure water pump with high price, so that economic and efficient production of a mine is facilitated; 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, and the vertical direction hydraulic cracks penetrate through the horizontal direction hydraulic cracks; 4) the advanced pre-splitting is carried out at the position far away from the working face, so that the normal production work at the working face is not influenced; 5) the fracturing effect is more comprehensive, can presplit deep old top hard rock stratum and shallow part rock stratum, and the hydraulic fracture that twice fracturing process formed link up each other, is convenient for form the fracturing fracture that is favorable to weakening the triangular region roof, further reduces coal face triangular region roof rock stratum integrality can high-efficient broken end suspended ceiling. The method can efficiently crush the top plate at the end of the coal face of the underground coal mine, effectively prevent the occurrence of roof disasters and gas accidents, and ensure the safe recovery of the working face.
Drawings
Figure 1 is a reference diagram one of the working conditions of the recovery process,
figure 2 is a working state reference diagram two of the recovery process,
figure 3 is a reference diagram three of the working state of the recovery process,
figure 4 is a working state reference diagram of the recovery process,
figure 5 is a diagram of the operating state of the recovery process with reference to figure five,
figure 6 is a reference diagram of the working state of the device during the hole opening,
figure 7 is a reference diagram of the working state of the hydraulic fracturing device in one time,
figure 8 is a cross-sectional view taken along line a-a of figure 7,
figure 9 is a cross-sectional view taken along line B-B of figure 7,
figure 10 is a reference diagram of the working state of the hydraulic fracturing device in the second hydraulic fracturing,
figure 11 is a cross-sectional view taken along line C-C of figure 10,
fig. 12 is a sectional view taken along line D-D of fig. 10.
FIG. 1-working surface; 2-protecting the coal pillar of the roadway; 3, mining a roadway; 4-coal bed; 5-fracturing the hole; 6-observation hole; 7-hydraulic horizontal cracking; 8-vertical hydraulic cracking; 9-primary fracturing and grooving; 10-secondary fracturing of the grooves; 11-immediate roof; 12-old top.
Detailed Description
In order to clearly explain the technical features of the present patent, the following detailed description of the present patent is provided in conjunction with the accompanying drawings.
The extraction process is as shown in fig. 1-5, the extraction roadway 3 needs to be dug first, then the working face 1 is exploited reversely, and as the exploitation progresses, roof rocks should gradually collapse as shown in fig. 5. In the case, in the stoping process, in order to avoid the shallow burial depth condition, the roof rock has high strength, large thickness, strong integrity and strong self-supporting capability, and the coal seam is difficult to collapse in time after being mined, as shown in fig. 6 to 12, the case is carried out according to the following steps:
the method comprises the following steps: acquiring a roof rock stratum structure and geological conditions of a working face 1 and structural characteristics of a roadway protection coal pillar 2, and determining the advanced bearing pressure strength and the influence range of the working face 1 by using a numerical calculation technology;
step two: as shown in fig. 6, a row of drill holes obliquely upward is excavated in the recovery roadway 3 above the recovery roadway 3 using a drilling machine, the drill hole is divided into fracturing holes 5 and observation holes 6, the observation holes 6 are positioned between two adjacent fracturing holes 5, cutting grooves at preset fracturing positions in each fracturing hole 5 by using a special mining cutter, cutting a plurality of radial cutting grooves suitable for hydraulic crack initiation, wherein the advance supporting pressure of a working face moves along with the forward propulsion of the working face, the plurality of radial cutting grooves are divided into a primary fracturing cutting groove 9 and a secondary fracturing cutting groove 10 according to the influence range of the advance supporting pressure of the working face 1, the primary fracturing cutting groove 9 is positioned outside the influence range of the advance supporting pressure of the working face 1, the direction of the minimum principal stress at the moment is vertical to the horizontal direction, the secondary fracturing cutting groove 10 is positioned in the influence range of the advance supporting pressure of the working face 1, and the direction of the minimum principal stress at the moment is parallel to the horizontal direction;
step three: as shown in fig. 7-9, a double-seal type hole packer is used to perform multi-stage backward fracturing at the position of the primary fracturing slot 9 in the fracturing hole 5 drilled in the second step, i.e. fracturing one by one from top to bottom, so as to pre-fracture the hard rock stratum at the deep part of the old top 12, generate a series of horizontal disc-shaped hydraulic cracks 7 and increase the number of deep rock stratum layers;
step four: as shown in fig. 10 to 12, a double-seal type hole packer is used to perform multi-stage backward fracturing, i.e., fracturing one by one from top to bottom, at the position of the secondary fracture cut 10 in the fracture hole 5 drilled in the second step, thereby pre-fracturing a shallow hard rock formation to generate a series of vertically disc-shaped hydraulic cracks 8, and the vertically hydraulic cracks 8 penetrate the horizontally hydraulic cracks 7 generated in the third step.
Further, when the roof rock above the mining roadway 3 is hard, the secondary fracturing slot 10 cut by using a special cutter in the second step cannot generate an ideal hydraulic crack 8 in the vertical direction, after the series of primary fracturing slots 9 are cut in the second step, a series of axial cracks are cut in the shallow part of the fracturing hole 5 by using a water jet technology, and the axial distance between the cracks is about 3 m;
and after the primary fracturing groove 9 is subjected to multi-section retreating type fracturing, a double-seal type hole packer is used for carrying out multi-section retreating type fracturing on a series of axial cracks in the fracturing hole 5 to generate a series of axial cracks penetrating through the horizontal hydraulic cracks 7, so that a hard top plate above the stoping roadway 3 is fully crushed, and a goaf top plate of the stoping roadway 3 of the working face 1 is made to collapse in time.
Further, the roof rock structure and the geological conditions of the working face 1 in the step one are obtained by using equipment such as a drilling peeping instrument and the like, the roof rock structure and the geological conditions comprise the thickness, the lithology and the rock strength of the direct roof 11, the thickness, the lithology and the rock strength of the old roof 12 and the mining height of the coal working face 1, and the obtained structural characteristics of the roadway protection coal pillar 2 comprise the width of the roadway protection coal pillar 2 and the coal rock strength, so that the reasonable fracturing height of the roof above the stoping roadway 3 is determined.
Further, in the step one, the numerical calculation technology is applied to calculate the influence range and the influence strength of the advanced bearing pressure of the working face 1, the front stress distribution state of the working face 1 is obtained when the coal face 1 is different from the top plate to be fractured, and the direction of the minimum principal stress in the top plate rock mass near the top plate to be fractured is determined.
Further, a drilling machine is used for drilling a row of drill holes in the direction of the center line of the roadway towards the top plate of the mining roadway 3 in the second step, the drilled row of drill holes comprises two fracturing holes 5 and an observation hole 6, the fracturing holes 5 and the observation hole 6 are arranged at intervals, the preset interval is 4 m-20 m, and the preset row spacing is 10 m-40 m.
Further, the preset diameter of the hydraulic fracturing drill hole dug in the second step is 45 mm-98 mm, the distance between the drill hole and the two sides of the mining roadway 3 is equal, the included angle between the horizontal projection of the preset drill hole and the axis of the mining roadway is 0-5 degrees, the included angle between the preset drill hole and the top plate is 30-70 degrees, and the length of the preset drill hole is 10 m-30 m.
Further, in the second step, a special cutter is used for grooving at the preset position of the fracturing hole 5, the distance between the adjacent grooving positions is 3 m-6 m, according to the structural characteristics of the top plate obtained in the first step, the grooving in the second step is divided into a primary fracturing grooving 9 and a secondary fracturing grooving 10, and a horizontal hydraulic crack 7 and a vertical hydraulic crack 8 are generated at the position of the primary fracturing grooving 9 and the position of the secondary fracturing grooving 10 respectively.
Furthermore, in the second step to the fourth step, the water outlet condition of the adjacent observation holes 6 is observed during each fracturing, and when a large amount of water is discharged from the observation holes 6, the pump is stopped, and the fracturing is completed.
Further, in the second step to the fourth step, an emulsion pump at the working face 1 is used for carrying out double-sealing type hydraulic fracturing on the fracturing holes 5.
The embodiment provides a method for treating an end triangular area suspended ceiling of a coal mine underground coal face by hydraulic fracturing, which comprises the steps of firstly, determining the structure and the geological conditions of a top plate rock stratum of a working face 1 by using equipment such as a drilling peeping instrument and the like, wherein the thickness, the lithology, the rock strength, the mining height of the coal face 1 and the like comprise the thickness of a direct roof 11 and an old roof 12, acquiring the structural characteristics of a roadway protection coal pillar 2, including the width of the roadway protection coal pillar 2 and the coal rock strength, and determining the reasonable cracking height of the top plate above a stoping roadway 3; and determining the strength and the influence range of the advanced bearing pressure of the working face 1 by using a numerical calculation technology according to the obtained geological condition characteristics of the working face 1. When the rock stratum to be fractured is located outside the influence range of the advance supporting pressure of the working face 1, a row of hydraulic fracturing drill holes are drilled on the top plate of the mining roadway 3 in the mining roadway 3 by using a drilling machine, wherein each row of hydraulic fracturing drill holes comprises two fracturing holes 5 and an observation hole 6, the fracturing holes 5 and the observation holes 6 are arranged at intervals of 5m, the row distance is about 10m, the preset diameter of each hydraulic fracturing drill hole is 56mm, the distances between the drill holes and the two sides of the mining roadway 3 are equal, the included angle between the horizontal projection of each drill hole and the axis of the mining roadway 3 is 0, the included angle between each drill hole and the top plate is 45 degrees, and the length of each drill hole is about 15 m; and grooving treatment is carried out at a preset fracturing position in each fracturing hole 5 by using a special cutter, a series of radial grooving suitable for hydraulic crack initiation is cut into a primary fracturing grooving 9 and a secondary fracturing grooving 10, the distance between the adjacent grooving positions is about 3m, and the horizontal hydraulic crack 7 and the vertical hydraulic crack 8 are respectively generated at the primary fracturing grooving position 9 and the secondary fracturing grooving position 10. And then, performing retreating type fracturing on the position of a preset primary fracturing groove 9 in the excavated fracturing hole 5 by using an emulsion pump at the working face 1, performing presplitting on a deep old top 12 hard rock stratum, generating a series of horizontal hydraulic cracks 7 to increase the number of deep rock stratum layers, and stopping the pump when a large amount of water flows out of the observation hole 6 to finish the fracturing. And when the rock stratum to be fractured is in the influence range of the advanced bearing pressure of the working face 1, performing retreating fracturing on the position of a preset secondary fracturing groove 10 in the excavated fracturing hole by using an emulsion pump at the working face 1, performing pre-fracturing on the shallow hard rock stratum, generating a series of vertical hydraulic cracks 8 to be communicated with the horizontal hydraulic cracks 7 generated in the step two, and fully crushing the hard top plate above the stoping roadway 3 so that the goaf top plate of the stoping roadway 3 of the working face 1 is timely collapsed. When the roof rock stratum above the stope roadway 3 is hard, when the ideal vertical hydraulic cracks 8 cannot be generated in the preset secondary fracturing groove 10, after a series of primary fracturing grooves are cut, a series of axial cracks are cut in the shallow part of the fracturing hole 5 by using a water jet technology, the axial distance of the cracks is about 3m, when the fracturing rock stratum is in the influence range of the advance bearing pressure of the working face 1, a double-seal type hole packer is used for multi-section retreating type fracturing in the fracturing hole 5 to generate a series of vertical hydraulic cracks 8, and the roof is cut off.
The embodiment completes the sufficient crushing of the hard roof above the stoping roadway through two fracturing processes, effectively prevents roof disasters and gas accidents, and ensures the safe stoping of the working face.
While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (9)
1. A method for processing an end triangular region suspended ceiling of a coal mine underground coal face by hydraulic fracturing is characterized by comprising the following steps:
the method comprises the following steps: acquiring a roof rock stratum structure and geological conditions of the working face (1), structural characteristics of the roadway protection coal pillars (2), and determining the advanced bearing pressure strength and the influence range of the working face (1) by using a numerical calculation technology;
step two: a drilling machine is used for drilling a row of drill holes above a recovery roadway (3) in the recovery roadway (3), the drill holes are divided into fracturing holes (5) and observation holes (6), the observation holes (6) are located between every two adjacent fracturing holes (5), a special mining cutter is used for grooving at preset fracturing positions in each fracturing hole (5), a plurality of radial cutting grooves are cut, the advance supporting pressure of a working face (1) moves along with the forward pushing of the working face (1), the plurality of radial cutting grooves are divided into primary fracturing cutting grooves (9) and secondary fracturing cutting grooves (10) according to the advance supporting pressure influence range of the working face (1), the primary fracturing cutting grooves (9) are located outside the advance supporting pressure influence range of the working face (1), and the secondary fracturing cutting grooves (10) are located in the advance supporting pressure influence range of the working face (1);
step three: performing multi-section backward fracturing on the position of a primary fracturing cutting groove (9) in the fracturing hole (5) drilled in the step two by using a double-seal type hole packer, so as to perform pre-fracturing on the deep hard rock stratum of the old top (12), generate a series of horizontal hydraulic cracks (7) and increase the layering quantity of the deep rock stratum;
step four: and (3) performing multi-stage backward fracturing at the position of the secondary fracturing cutting groove (10) in the fracturing hole (5) drilled in the second step by using a double-seal type hole packer, so as to pre-fracture the shallow hard rock stratum, generate a series of vertical hydraulic cracks (8), and penetrate the horizontal hydraulic cracks (7) generated in the third step by the vertical hydraulic cracks (8).
2. The method for hydraulic fracturing treatment of the end triangular area overhanging roof of the underground coal face of the coal mine according to claim 1, wherein after a series of primary fracturing grooves (9) are cut in the step two, a series of axial cracks are cut in the shallow part of a fracturing hole (5) by using a water jet technology;
and after the primary fracturing cutting groove (9) is subjected to multi-section backward fracturing, a double-seal type hole packer is used for carrying out multi-section backward fracturing on a series of axial cracks in the fracturing hole (5), and a series of axial cracks penetrate through the horizontal hydraulic cracks (7).
3. The method for hydraulic fracturing treatment of the end triangular area suspended roof of the underground coal face of the coal mine according to claim 1, characterized in that a drilling peeking instrument and other equipment are used for acquiring the roof strata structure and the geological conditions of the working face (1) in the step one, wherein the roof strata structure and the geological conditions comprise the thickness, the lithology and the rock mass strength of a direct roof (11), the thickness, the lithology and the rock mass strength of an old roof (12) and the mining height of the coal face (1), and the acquired structural characteristics of the roadway protection coal pillar (2) comprise the width of the roadway protection coal pillar (2) and the coal rock mass strength.
4. The method for hydraulic fracturing treatment of the end triangular area suspended ceiling of the underground coal mine coal face according to claim 1, wherein in the step one, numerical calculation technology is applied to calculate the influence range and the influence strength of the advance bearing pressure of the working face (1), so that when the coal face (1) is different from a top plate to be fractured, the stress distribution state in front of the working face (1) is obtained, and the direction of the minimum principal stress in the top plate rock mass near the top plate to be fractured is determined.
5. The method for hydraulic fracturing treatment of the end triangular area suspended ceiling of the underground coal mining face of the coal mine according to claim 1, wherein a drilling machine is used for drilling a row of drilled holes in the direction of the center line of a roadway in a top plate of a stoping roadway (3) in the second step, the drilled row of drilled holes comprises two fracturing holes (5) and an observation hole (6), the fracturing holes (5) and the observation hole (6) are arranged at intervals, the preset interval is 4 m-20 m, and the preset row spacing is 10 m-40 m.
6. The method for hydraulic fracturing treatment of the end triangular area overhanging roof of the underground coal face of the coal mine according to claim 1, wherein the preset diameter of the hydraulic fracturing drill hole dug in the step two is 45 mm-98 mm, the distance between the drill hole and two sides of the stoping roadway (3) is equal, the included angle between the horizontal projection of the preset drill hole and the axial line of the stoping roadway is 0-5 degrees, the included angle between the preset drill hole and a roof plate is 30-70 degrees, and the length of the preset drill hole is 10-30 m.
7. The method for hydraulic fracturing treatment of the tip triangular area of the underground coal mining face of the coal mine according to claim 1, wherein in the second step, a special cutter is used for grooving at a preset position of a fracturing hole (5), the distance between adjacent grooving positions is 3 m-6 m, according to the structural characteristics of the top plate obtained in the first step, the grooving in the second step is divided into a primary fracturing grooving (9) and a secondary fracturing grooving (10), and a horizontal hydraulic crack (7) and a vertical hydraulic crack (8) are generated at the position of the primary fracturing grooving (9) and the position of the secondary fracturing grooving (10) respectively.
8. The method for hydraulic fracturing treatment of the tip triangular area suspended ceiling of the underground coal mining face of the coal mine according to claim 1, wherein the water outlet condition of the adjacent observation holes (6) is observed during each fracturing in the second step to the fourth step, and when a large amount of water is discharged from the observation holes (6), the pump is stopped to complete the fracturing.
9. The method for hydraulic fracturing treatment of the end triangular area overhanging roof of the underground coal face of the coal mine according to claim 1, wherein in the second step to the fourth step, an emulsion pump at the working face (1) is used for carrying out double-sealing type hydraulic fracturing on the fracturing hole (5).
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