CN113107450A - Staged fracturing gas advanced extraction method for horizontal well of soft-hard interaction coal seam - Google Patents
Staged fracturing gas advanced extraction method for horizontal well of soft-hard interaction coal seam Download PDFInfo
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Abstract
The invention relates to a staged fracturing gas advanced extraction method for a horizontal well of a soft and hard interaction coal seam. The method comprises the following steps: constructing a vertical well at the structural deep part of the protective coal pillar, wherein the cave position of the vertical well is positioned in the hard coal layering of the soft and hard interaction coal seam; constructing a horizontal well group butted with the vertical well along the direction of a protective coal pillar between planned coal faces, wherein the horizontal section of the horizontal well group is positioned in a hard coal layer of a soft-hard interaction coal bed; performing staged perforating and fracturing construction on the horizontal well in a withdrawing mode, wherein the high-speed jet flow of the staged perforating and fracturing construction induces water flow to puncture hard coal layers and then enters soft coal layers; and after the staged perforation fracturing construction, gas extraction is carried out on the horizontal well, and drainage operation is carried out on the vertical well. The horizontal well planning and deployment of the invention takes the influence of later-stage coal mining activities into consideration, realizes the integrated design of coal mining and gas production, and realizes the purpose of coordinated development of coal and coal bed gas.
Description
Technical Field
The invention relates to a gas advanced extraction method, belongs to the technical field of gas extraction, and particularly relates to a soft-hard interaction coal seam horizontal well staged fracturing gas advanced extraction method.
Background
The soft and hard interaction coal seam refers to a type of coal seam in which soft coal and hard coal exist alternately, the coal seam is very widely distributed in China and has huge gas resource amount, and gas extraction in the coal seam is beneficial to restraining coal mine gas disasters and guaranteeing coal mine safety production. At present, a method for pre-pumping underground drilling gas is generally adopted for treating gas in a mine with a soft and hard interaction coal seam, the method has the problems of large engineering quantity, difficulty in construction, low extraction quantity, unbalanced extraction, long extraction standard reaching time and the like, the contradiction between mining and taking over is very prominent, and the pressure for safe and efficient production is high. If the ground well is used for pre-pumping gas before coal mining, the gas pre-pumping time is greatly shortened, sufficient time and space are provided for roadway tunneling and working face preparation, and the production efficiency of a mine is improved.
At present, the ground vertical well pre-pumping of soft and hard interaction coal seams generally has the characteristics of poor pumping effect and low efficiency, and coal mining and gas production are mutually interfered and influenced, so that the requirements of striping, quick and efficient reduction of gas content in coal mines are difficult to meet. And the horizontal well staged fracturing strengthening extraction of the soft and hard interaction coal seam is a few successful cases. There are several major difficulties: (1) the horizontal well is unreasonable in planning and deployment, and is not consistent with the coal mining and gas production integrated design concept, so that the later coal mining activity is seriously influenced; (2) the horizontal well extraction has the defects of high difficulty in controlling the well track, poor stability of a drilling well wall in a soft coal seam, incapability of forming a hole and high drilling construction risk; (3) the fracturing construction difficulty is high, the soft coal crack extension is difficult, the transformation effect is poor, and the synchronous transformation of soft and hard coal is difficult to realize; (4) the problems of high extraction cost and the like caused by more accidents of drainage and gas production, frequent stop and maintenance of pumps.
In summary, at present, advanced gas extraction and deployment of soft and hard interaction coal seams are unreasonable, drilling track control difficulty of horizontal wells is high, fracturing and drainage effects are poor, coal mining and gas extraction integration is difficult to achieve, and the purposes of rapidly reducing the gas content of the soft and hard interaction coal seams in a large range and achieving the effect of enhanced gas extraction are difficult to achieve.
Therefore, in view of the defects, through careful research and design, the designer researches and designs a soft and hard interaction coal bed horizontal well staged fracturing gas advanced extraction method by combining the experience and the achievement of related industries for many years, so as to overcome the defects.
Disclosure of Invention
The invention aims to provide a soft and hard interaction coal seam horizontal well staged fracturing gas advanced extraction method, and a novel ground gas horizontal well extraction technology which is used for improving the gas yield of a gas horizontal well and realizing a strengthened extraction effect.
In order to solve the problems, the invention discloses a staged fracturing gas advanced extraction method for a horizontal well of a soft and hard interaction coal seam, which is characterized by comprising the following steps of:
step 1: arranging a U-shaped remote end butt-joint horizontal well group along the direction of a protective coal pillar between planned coal mining working faces, wherein the longitudinal position of a horizontal section is positioned in a hard coal layer with stable distribution and relatively thicker soft and hard interaction coal layers;
step 2: constructing a butt-joint straight well in the structural deep part of the protective coal pillar, cementing and completing the well by adopting a lower casing, and simultaneously acquiring the buried depth, the coal core structure and the logging parameters of the coal bed with the target point A;
and step 3: constructing a horizontal well pilot hole at the shallow part of the protective coal pillar structure to obtain the buried depth and the coal core structure information of the target point B coal bed;
and 4, step 4: accurately drilling a horizontal borehole in the hard coal stratification and successfully butting the horizontal borehole with a vertical well;
and 5: a horizontal well is put into the anti-channeling well cementation pipe column to perform well cementation and completion in the whole well section;
step 6: performing staged perforating fracturing construction on the horizontal well, and completing synchronous fracturing transformation of soft and hard coal of the whole well section of the horizontal well section by adopting a withdrawing method;
and 7: putting a grinding and washing tool to grind and wash the blocking objects in the casing, and realizing the communication between the horizontal well and the butt-jointed vertical well again;
and 8: and performing high-efficiency gas extraction on the horizontal well.
In the step 1, the horizontal well is deployed, a protective coal pillar with a relatively deep coal seam burial depth is preferably selected for the horizontal well, the vertical stress is larger than the horizontal stress in the three-dimensional ground stress of the coal pillar, the difference between the vertical stress and the horizontal stress of the coal pillar is larger than 4MPa, and the difference between the maximum horizontal stress and the minimum horizontal stress is larger than 4MPa
The stress difference coefficient is more than 0.2 and is more than 2MPa, and a vertical crack is favorably formed during fracturing to synchronously reform the soft and hard interaction coal seam.
And 3, performing pilot hole well construction on the horizontal well in the step 3, drilling through a coal bed when the horizontal well inclination angle reaches about 70-75 degrees and the horizontal well is inclined steadily to drill the pilot hole well before the second-opening landing of the horizontal well, so that the horizontal well can be ensured to drill downwards smoothly to reveal coal bed information, the drilled coal bed position can be ensured to be close to the landing point position of the horizontal well, and the landing position is ensured to be more accurate and reliable.
Constructing the horizontal section in the step 4, and establishing an expected geological profile of target hard coal layered distribution according to A, B target point parameters and by combining the peripheral drilling information of the horizontal well; the method adopts a while-drilling geosteering logging technology, monitors parameters such as the upper and lower resistivity and natural gamma of a horizontal borehole in real time, combines rock strata, rock debris of hard coal and soft coal and logging information during drilling to adjust in real time, controls the horizontal borehole to accurately drill in hard coal layering, and improves the drilling rate of the hard coal layering.
The anti-channeling well cementation tubular column in the step 5 comprises a guide device, a drillable blind plugging device, a packer, a long sleeve, a slotted sleeve, a check valve, a sleeve short section, a shut-in valve and a sleeve string which are sequentially connected. The well cementation pipe column is put into a horizontal well, and the tail end of a guide device at the foremost end of the pipe column is put into a position 0-0.5m away from the butt joint position of the horizontal well and the straight well.
And (5) designing a drillable blind plugging device in the well cementation tubular column to mainly seal a channel between the sleeve and the butt-joint straight well so as to prevent well cementation cement slurry from entering a straight well cave from the sleeve. An external casing packer is designed in the well cementation tubular column and is lowered to a position close to the butt joint position to pack the external annular space of the casing pipe, so that the well cementation cement slurry in the external annular space of the casing pipe is prevented from communicating with the butt joint well. Two ends of a casing pipe nipple in the well cementation pipe column are respectively connected with a drillable check valve and a well shut-in valve, well cementation liquid can be effectively prevented from flowing backwards through the check valve and the well shut-in valve, and a double-safety function is played. The length of a slotted casing connected with the lower end of a check valve of the well cementation tubular column is not less than 2m, the slotted hole density is 20 holes/m, the slotted hole length is 40mm, the width is 10mm, and well cementation cement slurry circulates to a wellhead of a horizontal well through the slotted casing to serve as a cement slurry channel between an inner annulus and an outer annulus of the casing.
And 6, carrying out perforation construction on the horizontal well in the step 6, wherein the perforation direction is adjusted according to the position relation of the soft and hard coal, the upper hard-lower soft coal layer is subjected to directional perforation in the vertical downward direction and the direction forming an angle of 45 degrees with the downward direction, the upper soft-lower hard coal layer is subjected to directional perforation in the vertical upward direction and the direction forming an angle of 45 degrees with the upward direction, and the upper soft-middle hard-lower soft coal layer is subjected to perforation in a spiral hole distribution mode with a phase angle of 60 degrees.
And 6, performing staged perforating and fracturing construction on the horizontal well in the step 6, wherein a fracturing method of inducing water flow by high-speed jet flow is adopted, the high-speed jet flow speed is more than 240m/s, the jet flow breakdown stratum depth is more than 1m, the high-speed jet flow can breakdown hard coal layering, the induced fracturing fluid can smoothly enter soft coal layering, the fracturing and reforming effect of the soft coal layering is improved, and the soft and hard coal is synchronously reformed. Simultaneously the jet flow induced water flow fracturing discharge capacity is more than 7m3The sand adding strength is more than 8m and is more than min (determined according to the thickness of the coal bed and the permeability of the coal bed comprehensively3And performing large-displacement and high-strength fracturing construction (specifically, comprehensively determining according to the thickness of a coal seam, the achieved yield increase target and the support effect) to realize the aim of synchronously and efficiently transforming soft and hard coal.
The horizontal well is efficiently extracted in the step 8, the drainage and extraction mode is adjusted according to different gas production stages of the horizontal well, water is drained in a vertical well at the initial stage of gas production, and gas production is carried out in the horizontal well; along with the continuous propulsion of the gas production section to the vertical well, water is drained in the vertical well in the middle and later periods of drainage and production, and gas production is carried out in the vertical well and the horizontal well simultaneously; the intelligent control system is adopted to monitor the dynamic drainage and production parameters such as bottom hole flow pressure, casing pressure, water yield, gas yield and coal powder output concentration in real time, the drainage and production parameters are automatically adjusted in stages, fine drainage and production management is realized, and the aim of 'continuous, slow and stable' pressure reduction and gas production is achieved.
According to the steps, the soft and hard interaction coal seam horizontal well staged fracturing gas advanced extraction method has the following effects:
1. the planning and deployment of the horizontal well take the influence of later-stage coal mining activities into consideration, so that the coal mining and gas production integrated design is realized, and the purpose of coordinated development of coal and coal bed gas is realized;
2. the problems of poor stability of the well wall, incapability of forming holes, high drilling construction risk and the like in soft coal stratification can be solved, the drilling rate of the horizontal well in hard coal stratification is improved, and the drilling construction success rate and the drilling construction effect of the soft and hard interaction coal seam horizontal well are improved;
3. the problems of difficult crack extension of soft coal, poor transformation effect and the like can be solved, synchronous fracturing transformation of soft and hard coal is realized, the yield-increasing transformation effect of a soft and hard interaction coal seam horizontal well is improved, and the purpose of horizontal well enhanced extraction is achieved;
4. the horizontal well has the characteristics of good drainage and gas production effects, high single well yield and extraction efficiency, low production and operation cost and the like, and can realize large-range and rapid reduction of the gas content of the soft and hard interaction coal seam and guarantee the safe production of a coal mine.
The details of the present invention can be obtained from the following description and the attached drawings.
Drawings
Fig. 1-1, 1-2 show a schematic diagram of the horizontal well group planning deployment of the present invention.
FIG. 2 shows a structural schematic diagram of the horizontal well channeling-preventing well-cementing pipe column.
FIG. 3 shows a schematic of a horizontal well completion in hard coal stratification according to the present invention.
FIG. 4 shows a schematic representation of the horizontal well perforation orientation in hard coal layering of the present invention.
FIG. 5 shows a horizontal well synchronous fracturing reconstruction effect diagram in the hard coal stratification of the invention.
Reference numerals:
1-horizontal well; 2-butting the vertical well; 3-leading the eye well; 4-layering soft coal; 5-hard coal layering; 6-horizontal wellbore; 7-cementing a well blockage in the casing; 8-perforation orientation; 9-a perforation tool; 10-perforation hole; 11-fracturing the crack; 12-an introducer; 13-blind plugging device; 14-an external tubular packer; 15-long sleeve; 16-slotted sleeves; 17-a check valve; 18-casing nipple; 19-shut-in valve; 20-casing string; 21-coal face; 22-protection of coal pillars.
Detailed Description
The invention is described in detail below with reference to the following figures and detailed description:
referring to the attached drawings, the invention discloses a staged fracturing gas advanced extraction method for a horizontal well of a soft and hard interaction coal seam, which is used for advanced enhanced extraction outburst elimination of ground gas and treatment of regional gas disasters in the soft and hard interaction coal seam.
The soft and hard interaction coal seam horizontal well staged fracturing gas advanced extraction method comprises the following steps:
step 1: a U-shaped remote end butt-joint horizontal well group is arranged along the direction of a protective coal pillar 22 between planned coal faces 21, and the longitudinal position of a horizontal section is positioned in a hard coal layer 5 with stable distribution and relatively thicker soft and hard interaction coal layers;
specifically, the horizontal well 1 is arranged along the direction of the protective coal pillar 22 between the planned coal mining working faces 21, the situation that the arrangement of the horizontal well 1 on the working faces 21 influences later-stage coal mining activities can be avoided, the drainage and mining vertical well 2 is located in the deep portion of the protective coal pillar structure, the horizontal well 1 is located in the shallow portion of the protective coal pillar structure and is in butt joint with the drainage and mining vertical well 2, the depressurization area of the horizontal section of the whole coal seam can be increased during drainage and mining, and the development effect of the horizontal well is improved. The horizontal section well track is deployed in the hard coal layering 5 which is stable in distribution and relatively thick, the horizontal well wall is relatively good in stability, hole collapse and drill burying are not prone to occurring, and the drilling risk is low.
Meanwhile, a protective coal pillar with relatively deep buried depth is preferably selected, the vertical stress is more than the horizontal stress in the three-dimensional ground stress of the coal pillar, the difference between the vertical stress and the horizontal stress of the coal pillar is more than 4MPa, the difference between the maximum horizontal stress and the minimum horizontal stress is more than 2MPa, and the stress difference coefficient is more than 0.2, so that a vertical crack is favorably formed during fracturing to synchronously reform a soft and hard interaction coal bed, and the enhanced gas extraction effect is improved.
Step 2: constructing a butt-joint straight well 2 in the deep part of the coal pillar structure, cementing and completing a well by adopting a lower casing, and simultaneously acquiring the buried depth, the coal core structure and the logging parameters of the coal bed with the target point A;
and step 3: constructing a horizontal well pilot hole well 3 at the shallow part of the protective coal pillar structure to obtain the buried depth and the rock debris information of the target point B coal bed;
specifically, when the horizontal well pilot hole well 3 is constructed, when the horizontal well 1 is drilled for two times until the inclination angle reaches about 70-75 degrees and the pilot hole well 3 is drilled in a stable inclination manner, the coal bed information can be disclosed by ensuring that the horizontal well 1 is drilled downwards safely, the position of the drilled coal bed approaches to the position of the landing point of the horizontal well 1, and the landing position is more accurate and reliable.
And 4, step 4: accurately drilling a horizontal well hole 6 in the hard coal layer 5 and successfully butting with the drainage and mining vertical well 2;
specifically, horizontal segment construction establishes an expected geological profile of target hard coal layered distribution according to A, B target point parameters and by combining peripheral drilling information of a horizontal well 1; the method adopts a while-drilling geosteering logging technology, monitors parameters such as the upper and lower resistivity and natural gamma of a horizontal borehole in real time, combines rock strata, hard coal and rock debris of soft coal and logging information during drilling to adjust in real time, controls the horizontal borehole to accurately drill in a hard coal layer 5 of a soft-hard interaction coal layer, and improves the drilling rate of the hard coal layer 5.
Wherein, the detritus has obvious difference in the soft or hard coal drilling, hard coal layering 5 indicates the coal seam section that the well hard coal that gives first place to with primary structure and cracked structure is main distributes, soft coal layering 4 indicates the coal seam section that the garrulous soft coal that gives first place to with crumb structure and millet arris structure is main distributes, hard coal layering 5 bores the in-process and forms the coal scurf and gives first place to with graininess, fragmental and piece, soft coal layering 4 bores the in-process and forms the coal scurf and gives first place to with crumbling granule, powdered, can discern the position of meeting of drilling of horizontal well 1 through the detritus of soft or hard coal.
The soft and hard coal has obvious logging response characteristics, the hard coal layer 5 has high resistivity and low natural gamma characteristics, the soft coal layer 4 has low resistivity and low natural gamma characteristics, the top and bottom plate rocks have low resistivity and high natural gamma characteristics, and the drilling-while-drilling geosteering logging technology is adopted to monitor parameters such as the upper and lower resistivity and the natural gamma of a borehole in real time during drilling so as to judge the position of a borehole track in real time.
And 5: the horizontal well 1 is put into a channeling-preventing well cementation pipe column to perform well cementation and completion in the whole well section;
specifically, the anti-channeling well cementation tubular column comprises a guide device 12, a drillable blind plug device 13, a packer 14, a long casing 15, a slotted casing 16, a check valve 17, a casing nipple 18, a shut-in valve 19 and a casing string 20 which are connected in sequence. The well cementation pipe column is put into the horizontal well 1, and the tail end of the guide 12 at the foremost end of the pipe column is put into the range of 0-0.5m away from the butt joint position of the horizontal well 1 and the vertical well.
Wherein, the anti-channeling well cementation tubular column is provided with a drillable blind plugging device 13 which mainly seals a channel between the sleeve and the butt-joint straight well 2 to prevent well cementation cement slurry from entering a straight well cave from the sleeve. An external casing packer 14 is designed in the well cementation tubular column, and is lowered to the position close to the butt joint point to pack the external annular space of the casing pipe, so that well cementation cement slurry in the external annular space of the casing pipe is prevented from communicating with the butt joint straight well 2. Two ends of a casing nipple 18 in the well cementation pipe column are respectively connected with a drillable check valve 17 and a well closing valve 19, so that well cementation liquid can be effectively prevented from flowing backwards through the check valve 17 and the well closing valve 19, and a double-safety function is played. The lower end of a check valve 17 of the well cementation tubular column is connected with a slotted casing 16, the length of the casing is not less than 2m, the density of slotted holes is 20 holes/m, the length of the slotted holes is 40mm, the width of the slotted holes is 10mm, well cementation cement slurry circulates to the wellhead of the horizontal well 1 through the slotted casing 16 and serves as a cement slurry channel between the inner annulus and the outer annulus of the casing. Meanwhile, a rigid roller centralizer is connected in the casing string 20, and the design interval of the centralizer is 30 m. The purpose is to reduce the frictional resistance between the casing and the well wall and reduce the casing running difficulty; meanwhile, the centering degree of the casing of the horizontal well section is improved, and the cementing quality of the horizontal well section is improved.
Step 6: performing segmented perforation fracturing construction on the horizontal well 1, and completing synchronous fracturing transformation of soft and hard coal of the whole well segment of the horizontal well segment by adopting a withdrawing method;
specifically, the perforation azimuth 8 of the horizontal well is adjusted according to the position relation of soft and hard coal, the upper hard coal layer and the lower hard coal layer are subjected to directional perforation in the vertical downward direction and the direction forming an angle of 45 degrees with the downward direction, the upper soft coal layer and the lower hard coal layer are subjected to directional perforation in the vertical upward direction and the direction forming an angle of 45 degrees with the upward direction, and the upper soft coal layer, the middle hard coal layer and the lower soft coal layer are subjected to perforation in a spiral hole distribution mode with a phase angle of 60 degrees.
The hard coal has relatively high elastic modulus and small Poisson ratio, the soft coal has relatively low elastic modulus and high Poisson ratio, the expansion rate and effect of the crack in the hard coal layer 5 are better than those of the soft coal layer 4, and the difficulty of extending the crack to the soft coal layer is increased due to the existence of the interface of the soft and hard coal. Therefore, the horizontal well fracturing construction adopts a fracturing method of inducing water flow by high-speed jet, the high-speed jet speed is more than 240m/s, and the jet breakdown formation depth is more than 1 m. The high-speed jet flow can break down the hard coal layering 5, and the fracturing water flow can smoothly enter the soft coal layering 4 under the induction of the high-speed jet flow, so that the fracturing transformation effect of the soft coal layering 4 is improved, and the soft and hard coal synchronous transformation is realized. Simultaneously the jet flow induced water flow fracturing discharge capacity is more than 7m3The sand adding strength is not less than 8 m/min (determined by coal seam thickness and coal seam permeability) and3and performing high-displacement and high-strength fracturing construction on the coal seam (specifically, comprehensively determining the thickness of the coal seam, the achieved yield increase target and the support effect), and realizing the aim of synchronously and efficiently transforming soft and hard coal. The sand setting risk of the horizontal well is reduced and the sand carrying effect is improved by adopting large discharge; the high-strength fracturing process is adopted to prolong the fracture and improve the supporting effect, the construction success rate and the fracturing transformation effect are improved, and the aim of strengthening transformation is achieved.
And 7: a grinding and washing tool is put in to grind and wash the well cementation obstruction 7 in the sleeve, and communication between the horizontal well and the butt-jointed vertical well is achieved again;
and 8: and performing high-efficiency gas extraction on the horizontal well.
Specifically, the horizontal well track is declined along the coal seam, under the condition of the same desorption pressure, the horizontal well 1 produces gas firstly, and the gas production section is gradually pushed to the vertical well 2, so that the drainage and production mode is adjusted according to different gas production stages of the horizontal well 1, the gas is produced naturally, the water is drained in the vertical well 2 at the initial gas production stage (the gas production stage is just started), and the gas production is carried out in the horizontal well 1; as the gas production section is continuously pushed to the vertical well 2, water is drained in the vertical well 2 at the middle and later periods of drainage and production (the subsequent drainage and production stage that the horizontal well continues to produce gas and the vertical well starts to produce gas), and gas production is simultaneously carried out in the vertical well 2 and the horizontal well 1; the resistance of the gas in the process of moving to the vertical well 2 can be overcome, the influence of the coal powder and the produced gas carried by the gas on the operation of the drainage and production equipment is reduced, and the continuity and the stability of drainage and gas production are improved. Meanwhile, an intelligent control system is adopted to monitor the dynamic discharge and production parameters such as bottom hole flow pressure, casing pressure, water yield, gas yield and coal powder output concentration in real time, the discharge and production parameters are automatically adjusted in stages, fine discharge and production management is realized, and the aim of 'continuous, slow and stable' pressure reduction and gas production is achieved.
According to the steps, the soft and hard interaction coal seam horizontal well staged fracturing gas advanced extraction method has the following effects:
1. the planning and deployment of the horizontal well take the influence of later-stage coal mining activities into consideration, so that the coal mining and gas production integrated design is realized, and the purpose of coordinated development of coal and coal bed gas is realized;
2. the problems of poor stability of the well wall, incapability of forming holes, high drilling construction risk and the like in soft coal stratification can be solved, the drilling rate of the horizontal well in hard coal stratification is improved, and the drilling construction success rate and the drilling construction effect of the soft and hard interaction coal seam horizontal well are improved;
3. the problems of difficult crack extension of soft coal, poor transformation effect and the like can be solved, synchronous fracturing transformation of soft and hard coal is realized, the yield-increasing transformation effect of a soft and hard interaction coal seam horizontal well is improved, and the purpose of horizontal well enhanced extraction is achieved;
4. the horizontal well has the characteristics of good drainage and gas production effects, high single well yield and extraction efficiency, low production and operation cost and the like, and can realize large-range and rapid reduction of the gas content of the soft and hard interaction coal seam and guarantee the safe production of a coal mine.
It should be apparent that the foregoing description and illustrations are by way of example only and are not intended to limit the present disclosure, application or uses. While embodiments have been described in the embodiments and depicted in the drawings, the present invention is not limited to the particular examples illustrated by the drawings and described in the embodiments as the best mode presently contemplated for carrying out the teachings of the present invention, and the scope of the present invention will include any embodiments falling within the foregoing description and the appended claims.
Claims (7)
1. A staged fracturing gas advanced extraction method for a horizontal well of a soft-hard interaction coal seam is characterized by comprising the following steps:
constructing a vertical well at the structural deep part of the protective coal pillar, wherein the cave position of the vertical well is positioned in the hard coal layering of the soft and hard interaction coal seam;
constructing a horizontal well group butted with the vertical well along the direction of a protective coal pillar between planned coal faces, wherein the horizontal section of the horizontal well group is positioned in a hard coal layer of a soft-hard interaction coal bed;
performing staged perforating fracturing construction on the horizontal well in a withdrawing mode, wherein high-speed jet flow induced water flow of the staged perforating fracturing construction breaks through hard coal layers and then enters soft coal layers, so that synchronous fracturing transformation of the soft and hard coal is realized;
and after the staged perforation fracturing construction, gas extraction is carried out on the horizontal well, and drainage operation is carried out on the vertical well.
2. The staged fracturing gas advanced extraction method for the horizontal well of the soft and hard interaction coal seam as claimed in claim 1, wherein the vertical stress > the horizontal stress should be satisfied in the three-dimensional ground stress of the protection coal pillar deployed in the horizontal well, the difference between the vertical stress and the horizontal stress of the coal pillar is > 4MPa, the difference between the maximum horizontal stress and the minimum horizontal stress is > 2MPa, and the stress difference coefficient is > 0.2.
3. The staged fracturing gas advanced extraction method for the horizontal well with the soft and hard interaction coal seam according to claim 1, characterized in that during construction of the horizontal well, before the second horizontal well lands, when the inclination angle of the horizontal well reaches 70-75 degrees, a steady drill is carried out to penetrate through the coal seam to carry out pilot hole well drilling.
4. The staged fracturing gas advanced extraction method of the soft-hard interaction coal seam horizontal well as the claim 1 is characterized in that after the horizontal well is constructed, a channeling-prevention well cementation pipe column is put into the horizontal well, wherein the channeling-prevention well cementation pipe column comprises a guide, a drillable blind plug, an external pipe packer, a long sleeve, a slotted sleeve, a check valve, a sleeve short section, a shut-in valve and a sleeve string which are sequentially connected; the tail end of a guide device at the foremost end of the well cementation pipe column is lowered to a position 0-0.5m away from the butt joint position of the horizontal well and the vertical well; the drillable blind plugging device is used for sealing and isolating a channel between the casing and a butted vertical well, and well cementation cement slurry is prevented from entering a vertical well cave from the inside of the casing; the external casing packer is used for sealing and isolating the external casing annulus of the casing after being lowered to a position close to the butt joint position, so as to prevent the well cementing cement slurry of the external casing annulus from communicating with the butt joint well; two ends of the casing pipe nipple are respectively connected with a drillable check valve and a shut-in valve and are used for preventing well cementation liquid from flowing backwards through the check valve and the shut-in valve; the slotted casing is used as a cement slurry channel between the inner and outer annuluses of the casing.
5. The method for staged fracturing gas advanced extraction of the horizontal well in the soft and hard interaction coal seam according to claim 1, wherein in the staged perforation fracturing construction, the perforation direction is adjusted according to the position relation of soft and hard coal, wherein the upper hard and lower soft coal seam is subjected to directional perforation in a vertical downward direction and a direction deviating from the vertical downward direction by 45 degrees; the upper soft-lower hard coal layer is perforated in a direction vertically upward and a direction deviating from the vertical upward by 45 degrees, and the upper soft-medium hard-lower soft coal layer is perforated in a spiral hole distribution mode with a phase angle of 60 degrees.
6. The staged fracturing gas advanced extraction method for the horizontal well of the soft and hard interaction coal seam according to claim 1, which is characterized by comprising the following steps: the horizontal well fracturing construction adopts a fracturing method of high-speed jet flow induced water flow, the high-speed jet flow speed is more than 240m/s, and the jet flow breakdown formation depth is more than 1 m.
7. The staged fracturing gas advanced extraction method for the horizontal well of the soft and hard interaction coal seam according to claim 1, which is characterized by comprising the following steps: adjusting the drainage and production mode according to different gas production stages of the horizontal well, draining water in the vertical well at the initial stage of gas production, and producing gas in the horizontal well; and water is drained in the vertical well in the middle and later periods of drainage and production along with the continuous propulsion of the gas production section to the vertical well, and gas production is carried out in the vertical well and the horizontal well simultaneously.
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