Method for pre-draining gas by staged fracturing of horizontal wells in a strip of combined shaft and ground tunneling passing through a roadway

Abstract

The invention discloses a method for rapidly pre-draining gas by staged fracturing of a horizontal well in a combined wellbore and ground tunneling strip passing through a roadway: Step 1, construct the first open hole section of the L-shaped long horizontal well, which is a vertical well section; Step 2, construct the second open hole section of the L-shaped long horizontal well, and the second open hole section consists of three well sections: vertical, deviated, and horizontal; Step 3, fabricate the third open artificial wellbore and construct the third open hole section of the L-shaped long horizontal well, and the third open hole section is an upwardly inclined well section; Step 4, perform staged perforating and fracturing on the upwardly inclined well section of the third open hole and install a gas drainage head. The invention changes the original gas drainage method for the tunneling strip, adopts a relatively safe ground construction method, and at the same time, can save the construction costs of the underground floor rock roadway and the floor cross-cut holes.

Description

Technical Field

[0001] The present invention relates to the technical field of gas pre-drainage in coal mining areas, and particularly to a method for pre-draining gas by staged fracturing of a horizontal well passing through a roadway in a combined well-ground tunneling strip. Background Art

[0002] As one of the factors affecting the safe excavation of coal mines, especially for high-gas mines, before the excavation of coal seams, it is necessary to conduct advanced gas pre-treatment to prevent gas outbursts or explosions during the excavation of coal seams, which may cause serious losses of life and property. Before the normal excavation of the coal seam mining face, it is necessary to form auxiliary roadways such as intake air, return air, and transportation roadways. Before the construction of the coal seam roadway driving strip, it is also necessary to conduct advanced treatment of the gas in the driving strip. The speed and effect of gas treatment in the driving strip are crucial for the normal construction of the coal seam roadway according to the plan. Therefore, it is particularly important to efficiently and quickly achieve gas treatment in the driving strip. The existing coal mine gas pre-drainage technologies can be mainly divided into two categories: gas drainage technologies combining surface horizontal wells and staged fracturing technologies, and gas drainage technologies combining underground long boreholes and staged fracturing technologies.

[0003] Gas drainage technology combining surface horizontal wells and staged fracturing technologies: First, a horizontal well with a long horizontal section passing through the coal seam or roof to be mined is drilled on the surface, and then large-scale staged fracturing construction is carried out on the surface to increase the desorption amount of gas rich in the coal seam, the permeability enhancement range, and the number of channels for gas to diffuse into the horizontal well section. Finally, gas drainage equipment is installed on the surface to carry out gas drainage. The main advantages of this method are that the surface operation space is large, large-scale staged fracturing construction can be carried out, the permeability enhancement range is large in all directions along the coal mining face, and the number of boreholes arranged on the coal mining face or roof can be effectively reduced. However, gas drainage by this technology requires a long time of drainage work before gas drainage work can be carried out.

[0004] Gas drainage technology combining underground long boreholes and staged fracturing technologies: First, a long borehole along the coal seam or roof is drilled underground, and then staged fracturing construction is carried out underground to increase the desorption amount of gas rich in the coal seam, the permeability enhancement range, and the number of channels for gas to diffuse into the long borehole. Finally, gas drainage equipment is installed underground to carry out gas drainage. The main advantages of this method are that negative pressure drainage conditions can be formed underground after the fracturing construction, and gas drainage work can be carried out without waiting for a long time of drainage work. However, this technology is restricted by the small underground operation space, and it is difficult to implement large-scale staged fracturing technology. The permeability enhancement range is small in all directions along the coal mining face. Therefore, it is necessary to appropriately increase the number of boreholes arranged on the coal mining face or roof.

[0005] Based on the deficiencies of the above two existing advanced treatment methods for coal mine gas disasters, it is urgent to study a method that can efficiently and rapidly achieve gas drainage in the driving strip to effectively ensure the normal construction of the coal seam roadway according to the plan. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for staged fracturing and pre-draining gas in a horizontal well for driving a strip through a roadway by combining well and ground, so as to solve the problems existing in the existing gas drainage technology, such as the need for long-term drainage work and the small range of permeability enhancement in all directions of the working face, resulting in the need to increase the number of borehole layouts.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions to solve:

[0008] A method for staged fracturing and pre-draining gas in a horizontal well for driving a strip through a roadway by combining well and ground, the specific steps are as follows:

[0009] Step 1, construct the first open hole section of the L-shaped long horizontal well, and the first open hole section is a vertical well section;

[0010] Step 2, construct the second open hole section of the L-shaped long horizontal well. The second open hole section consists of three well sections: vertical, deviated, and horizontal. Drill until the bottom of the coal seam roof is connected with the already driven roadway at the penetration point to achieve ground and underground connection. Lower the second open hole technical casing and construct the artificial bottom of the second open hole cementing simultaneously. Use pure cement slurry for positive circulation cementing, and the cement slurry returns to the ground;

[0011] Step 3, fabricate the third open hole artificial wellbore and construct the third open hole section of the L-shaped long horizontal well. The third open hole section is an up-dip well section; fabricate the third open hole artificial wellbore in the already driven roadway, establish normal drilling mud circulation between the ground and the bottom of the third open hole, drill an up-dip wellbore with a drill bit, drill to the designed well depth and complete the drilling, remove the third open hole artificial wellbore in the already driven roadway, lower the third open hole production casing and construct the third open hole artificial wellhead in the already driven roadway simultaneously. Use pure cement slurry for positive circulation cementing, and the cement slurry returns to the already driven roadway;

[0012] Step 4, perform staged perforating and fracturing on the third open hole up-dip well section and install a gas drainage head, including the following operations: perform staged perforating and fracturing on the third open hole up-dip well section. Lower a coiled tubing string from the ground through the already driven roadway and into the third open hole up-dip well section, and perform staged perforating and fracturing according to the designed perforation points; install a drainage wellhead at the casing reserved at the orifice of the third open hole up-dip well section in the already driven roadway underground. Connect the drainage wellhead to the negative pressure gas drainage equipment through a drainage pipeline.

[0013] Further, the specific operation of the above Step 1 is as follows:

[0014] For the construction of the first open hole vertical well section, use a Φ346.1mm pneumatic down-the-hole hammer to drill to a depth of 10 - 15m into the bedrock, lower a Φ273.05mm surface casing, and use a cement slurry with a specific gravity of 1.7 - 1.8 g / cm 3The pure cement slurry of Class G oil well is circulated back to the ground for cementing in a direct circulation manner.

[0015] Further, step 2 includes the following sub-steps:

[0016] Step 21: In the construction of the vertical section of the second spudding, a Φ241.3mm pneumatic down-the-hole hammer is used to drill to the designed depth of the vertical section of the second spudding, which is 2 well depths.

[0017] Step 22: In the construction of the inclined section of the second spudding, a Φ241.3mm PDC bit and a water-based mud circulation system are used to drill to the designed landing point at the bottom of the roof of the coal seam driving strip. The well inclination angle of the horizontal well trajectory at the landing point is 90°, and the extension line of the azimuth angle is orthogonal to the excavated roadway.

[0018] Step 23: In the construction of the horizontal section of the second spudding, a Φ241.3mm roller cone bit and a nitrogen circulation system are used to drill to the designed breakthrough point to achieve the connection between the ground and the underground. Then, artificial vertical walls are constructed on both sides of the excavated roadway at the well depth corresponding to the breakthrough point.

[0019] Step 24: A Φ193.7mm technical casing for the second spudding is run in the whole section of the second spudding. A stage collar is connected at a specific position of the technical casing run into the well, and the lateral holes of the stage collar are opened.

[0020] Step 25: Run the casing in the whole section of the second spudding. During this period, an artificial bottom for the second spudding cementing is made in the excavated roadway underground.

[0021] Further, in step 25, the process of making the artificial bottom for the second spudding cementing is as follows:

[0022] A. Run a Φ193.7mm technical casing for the second spudding on the ground. The casing passes through the excavated roadway from the artificial vertical wall on one side of the breakthrough point to the artificial vertical wall on the other side. For the casing section located between the artificial vertical walls, it is designed to be wound with Marisan on the outer wall of this casing section, and the winding thickness does not exceed the size of the second spudding wellbore.

[0023] B. Subsequently, use the hoisting system of the drilling rig on the ground to slowly lift the casing. Synchronously, trigger the Marisan wound on the outer wall of the casing from top to bottom in sequence to achieve the foaming and expansion sealing function, forming a Marisan filling section for the second spudding. Leave a 20cm casing length below the artificial vertical wall at the end of the casing string. Insert 6 thin pipes evenly around the outer wall of the 20cm casing extending from the artificial vertical wall in the excavated roadway underground. The thin pipes pass through the Marisan filling section for the second spudding. Inject pure cement slurry simultaneously through the 6 thin pipes to form a 15m long pure cement filling section for the second spudding by air pump. Then, take out the 6 thin pipes. After the production of the artificial bottom for the second spudding cementing is completed, the pure cement slurry should be left to set for at least 48 hours, and finally, the pure cement slurry is circulated back to the ground for cementing in a direct circulation manner.

[0024] Further, step 3 includes the following sub-steps:

[0025] Step 31: Fabricate a three-way artificial wellbore in the excavated roadway. The three-way artificial wellbore is hermetically connected by multiple high-pressure separating pipes through the flanges with self-tapping holes, fastening screws and fastening bolts on them. Both ends of the artificial wellbore connection string are hermetically anchored to the artificial vertical wall by anchor bolts, and blowout preventer valves are installed on the high-pressure separating pipes connected to both ends of the artificial wellbore.

[0026] Step 32: Use a Ф171.4mm PDC bit and a water-based mud circulation system to drill in the roof of the coal seam driving strip until the designed well depth is reached and the drilling is completed. The horizontal well trajectory of the three-way upward-inclined section is at a distance of 2 - 3m from the interface between the coal seam driving strip and the roof of the coal seam driving strip. After the three-way drilling and pipe pulling are completed, open the blowout preventer valve at the three-way artificial wellbore to release the mud stored in the wellbore annulus on both sides of the artificial wellbore, and then remove the artificial wellbore.

[0027] Step 33: Run a Ф139.7mm three-way production casing through the entire three-way section. An anti-back-off device is installed at a specific position of the casing run into the well. The casing is run to 5m above the completed well depth, leaving a 5m pocket at the bottom of the three-way section. A 50cm extended casing is reserved at the orifice of the three-way upward-inclined section in the excavated roadway for installing wellhead sealers, blowout preventers, etc. for subsequent fracturing and the drainage wellhead. During the process of running the three-way production casing through the entire section, fabricate a three-way artificial wellhead in the excavated roadway.

[0028] Step 34: Cement the three-way upward-inclined section with G-class oil well neat cement slurry with a specific gravity of 1.7 - 1.8g / cm 3 in a positive circulation manner. Wait until the neat cement slurry for cementing returns to the excavated roadway through 6 thin pipes, seal the outlets of the 6 thin pipes. After the pumped neat cement slurry is pressure bumped, the cementing is completed. Close the wellhead on the ground and wait for at least 72 hours for setting, and then reverse the three-way casing and pull out the uncemented casing.

[0029] Further, in step 33, the process of fabricating the three-way artificial wellhead is as follows:

[0030] When the three-opening casing reaches 15 m remaining from the total well depth, in the already excavated roadway, for the 10 m casing at the bottom of the upward-inclined section of the three-opening that has not been lowered yet, it is designed to wrap the outer wall of this casing section with Marisan, and the wrapping thickness shall not exceed the size of the three-opening wellbore. Subsequently, use the drilling rig hoisting system on the ground to slowly lower the casing. Synchronously, trigger the Marisan wrapped on the outer wall of the casing from bottom to top in sequence to form the three-opening Marisan filling section. Then, with the help of an air pump, insert 6 thin pipes evenly around the outer wall of the casing passing through the artificial vertical wall in the already excavated roadway underground. The thin pipes pass through the three-opening Marisan filling section, and pure cement slurry is injected into the 6 thin pipes simultaneously to form a 15 m long three-opening air pump pure cement filling section. After the injection of pure cement slurry by the three-opening air pump is completed, the 6 inserted thin pipes serve as the exhaust holes during the positive circulation cementing process of the pure cement slurry in the upward-inclined section of the three-opening.

[0031] Compared with the prior art, the present invention has the following technical effects:

[0032] (1) By using staged fracturing of horizontal wells on the ground, the fracturing scale is large, the fracturing crack propagation range is wide, and the extraction effect is guaranteed.

[0033] (2) It can effectively reduce the number of boreholes arranged in the coal mining face or roof.

[0034] (3) With the help of the underground negative pressure extraction system for extraction, the extraction cycle is short and the extraction efficiency is high.

[0035] (4) An artificial shaft is made in the already excavated roadway to establish a normal ground drilling circulation system.

[0036] (5) An artificial bottom hole and an artificial wellhead are made in the already excavated roadway to establish the positive circulation flow of pure cement slurry for cementing.

[0037] (6) Underground roadway is used for drainage and gas production, saving the cost of ground extraction equipment and having high underground drainage efficiency.

[0038] (7) For workover operations (well flushing), the underground roadway can be fully utilized, and no workover machine is required on the ground.

[0039] In summary, this method can not only increase the gas permeability range in all directions along the driving face, reduce the number of boreholes arranged in the driving face or roof, but also achieve the condition of negative pressure gas extraction, efficiently and quickly realize the gas control in the driving strip, and effectively ensure the normal construction of the coal seam roadway driving according to the plan. Description of the Drawings

[0040] Figure 1 It is the layout diagram of the horizontal well trajectory in the roof of the driving strip;

[0041] Figure 2 It is the construction schematic diagram of the horizontal well drilling and staged fracturing in the roof of the driving strip;

[0042] Figure 3 Schematic diagram of the enlarged artificial bottom of the well for the second casing

[0043] Figure 4 Schematic diagram of the enlarged artificial wellbore for the third casing

[0044] Figure 5 Schematic diagram of the high-pressure isolation pipe for installing the blowout preventer valve

[0045] Figure 6 Schematic diagram of the high-pressure isolation pipe without installing the blowout preventer valve

[0046] Figure 7 Schematic diagram of the enlarged artificial wellhead for the third casing in the excavated roadway

[0047] Figure 8 Schematic diagram of the negative pressure gas drainage after the drilling and fracturing operations

[0048] The meanings of the various labels in the figure are as follows:

[0049] 1. First casing vertical section, 2. Second casing vertical section, 3. Second casing deviated section, 4. Coal seam excavation strip, 5. Landing point, 6. Stage collar, 7. Second casing Marlex filling section, 8. Second casing horizontal section, 9. Second casing air pump pure cement filling section, 10. Anchor bolt, 11. Excavated roadway, 12. Fastening screw, 13. Fastening bolt, 14. Roof, 15. Third casing Marlex filling section, 16. Artificial vertical wall, 17. Third casing air pump pure cement filling section, 18. Third casing up-dip section, 19. Fracture of the roof during fracturing, 20. Perforation point, 21. Cross-layer fracture, 22. High-pressure isolation pipe, 23. Reverse-thread device, 24. Blowout preventer valve, 25. Penetration point, 26. Flange, 27. Screw hole, 28. Pressure-bearing cap, 29. Drainage pipeline, 30. Negative pressure drainage equipment, 31. Drainage wellhead, 32. Roof of the coal seam excavation strip, 33. Roof of the coal seam pre-excavation working face, 34. Horizontal well position, 35. Horizontal well trajectory. Specific implementation mode

[0050] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0051] This embodiment provides a method for pre-draining gas by staged fracturing of a horizontal well in a combined wellbore and surface operation for tunneling through a roadway. The general idea of this method is as follows: Drill an L-shaped long horizontal well on the ground. The ground L-shaped long horizontal well is designed with a three-opening wellbore structure. The trajectory of this horizontal well is drilled within the roof of the coal seam tunneling strip, horizontally through the mined roadway in the mine, and after passing through the mined roadway, drill an upward-inclined well section until reaching the designed well depth and completing the drilling. Then, conduct staged perforating and fracturing construction on the upward-inclined well section on the ground. After the staged perforating and fracturing construction is completed, create conditions for rapid gas extraction with negative pressure by depressurizing and flushing in the mined roadway in the mine. Finally, install gas extraction equipment at the wellhead of the upward-inclined well section in the mine to achieve the method of rapid pre-draining gas by staged fracturing of a horizontal well in a combined wellbore and surface operation for tunneling through the roof of a roadway. According to the designed coal seam tunneling strip 4 and the coal seam pre-tunneling working face in the coal mine exploitation plan deployment, determine the regional scope deployment of the corresponding coal seam tunneling strip roof 32, the coal seam pre-tunneling working face roof 33, and the horizontal well well position 34, and then design and construct the horizontal well trajectory 35 along the coal seam tunneling strip roof 32, as specifically shown in the appendix Figure 1 shown. A method for rapid pre-draining gas by staged fracturing of a horizontal well in a combined wellbore and surface operation for tunneling through a roadway provided by the present invention is specifically implemented as follows:

[0052] Step 1, construct the first-opening well section of the L-shaped long horizontal well. The first-opening well section is a vertical well section. The specific operation is as follows:

[0053] For the construction of the first-opening vertical well section 1, use a Φ346.1mm pneumatic down-the-hole hammer for fast and straight drilling to 10 - 15m into the bedrock, lower a Φ273.05mm surface casing, and use G-class oil well pure cement slurry with a specific gravity of 1.7 - 1.8g / cm 3 to conduct positive circulation back to the ground for cementing.

[0054] Step 2, construct the second-opening well section of the L-shaped long horizontal well. The second-opening well section consists of a vertical, a deviated, and a horizontal well section. Use a Φ241.3mm bit to drill to the bottom of the coal seam roof and connect the ground and the underground at the penetration point with the mined roadway. Lower a Φ193.7mm second-opening technical casing and construct the artificial bottom of the second-opening cementing in coordination, and use pure cement slurry for positive circulation cementing, with the cement slurry returning to the ground. It specifically includes the following sub-steps:

[0055] Step 21, for the construction of the second-opening vertical well section 2, use a Φ241.3mm pneumatic down-the-hole hammer for fast and straight drilling to the designed depth of the second-opening vertical well section 2;

[0056] Step 22, for the construction of the second-opening deviated well section 3, use a Φ241.3mm PDC bit and a water-based mud circulation system to drill to the designed landing point 5 at the bottom of the coal seam tunneling strip roof 32. The well inclination angle of the horizontal well trajectory 35 at the landing point 5 is 90°, and the extension line of the azimuth angle is orthogonal to the mined roadway 11;

[0057] Step 23: During the construction of the second-opening horizontal well section 8, a Φ241.3 mm roller cone bit is used and the nitrogen circulation system is utilized to drill to the designed breakthrough point 25 to achieve the connection between the ground and the underground. Then, at the well depth corresponding to the breakthrough point 25 of the already excavated roadway 11, artificial vertical walls 16 on both sides of the already excavated roadway 11 are constructed.

[0058] Step 24: A Φ193.7 mm second-opening technical casing is run in the entire second-opening well section. A stage collar 6 is connected at a specific position of the second-opening technical casing run into the well. When the pure cement slurry for well cementing is pumped into the casing, the stage collar 6 is triggered and activated, enabling the stage collar 6 to bear pressure and seal the inner annulus of the casing at a specific position within the casing. The lateral holes of the stage collar 6 are opened, thereby effectively establishing a positive circulation flow of the pure cement slurry for well cementing, and thus achieving efficient and high-quality well cementing.

[0059] Step 25: During the running of the second-opening casing in the entire well section, an artificial bottom for the second-opening well cementing is fabricated in the already excavated underground roadway 11. Specifically, the process of fabricating the artificial bottom for the second-opening well cementing is as Figure 3 shown. A. On the ground, a Φ193.7 mm second-opening technical casing is run in. The casing passes through the already excavated roadway 11 from the artificial vertical wall 16 on one side of the breakthrough point 25 to the artificial vertical wall 16 at the other end. For the casing section located between the artificial vertical walls 16, it is designed to be wrapped with Marisan on the outer wall of this casing section, and the wrapped thickness shall not exceed the size of the second-opening wellbore. B. Subsequently, the casing is slowly lifted on the ground using the drilling rig lifting system. Synchronously, the Marisan wrapped on the outer wall of the casing is triggered successively from top to bottom to achieve the foaming and expansion sealing function, so as to seal the annular space between the wellbore wall and the casing in the well section several meters above the breakthrough point 25 of the roadway, forming a second-opening Marisan filling section 7. A 20-cm casing length is reserved at the end of the casing string below the artificial vertical wall for installing a pressure-bearing cap 28. Six thin pipes are evenly inserted around the outer wall of the casing through the 20-cm casing extending from the artificial vertical wall 16 of the already excavated underground roadway 11. The thin pipes pass through the second-opening Marisan filling section 7, and a G-class oil well quick-setting pure cement slurry with a specific gravity of 1.7 - 1.8 g / cm 3 is injected simultaneously through the six thin pipes to form a 15-m long second-opening air pump pure cement filling section 9. Then, the six thin pipes inserted into the second-opening Marisan filling section 7 are removed in the already excavated underground roadway 11. After the fabrication of the artificial bottom for the second-opening well cementing is completed, the pure cement slurry is allowed to set for at least 48 hours. Finally, a G-class oil well pure cement slurry with a specific gravity of 1.7 - 1.8 g / cm 3 is circulated back to the ground for well cementing in a positive circulation manner.

[0060] Step 3: Fabricate a three-opening artificial wellbore and construct the three-opening section of the L-shaped long horizontal well. The three-opening section is an up-dip section. Fabricate a three-opening artificial wellbore in the excavated roadway, establish normal drilling mud circulation between the ground and the bottom of the three-opening well, drill an up-dip wellbore using a Ф171.4 mm bit, complete the drilling when reaching the designed well depth, remove the three-opening artificial wellbore in the excavated roadway, and lower the Ф139.7 mm three-opening production casing to cooperate with the fabrication of the three-opening artificial wellhead in the excavated roadway, and use positive circulation cementing with neat cement slurry. The cement slurry returns to the excavated roadway. It specifically includes the following sub-steps:

[0061] Step 31: Before the construction of the three-opening up-dip section 18, first fabricate a three-opening artificial wellbore in the excavated roadway 11, as Figure 4 shown, so as to establish mud circulation during the normal drilling of the three-opening well. The three-opening artificial wellbore is sealed and connected by flange plates 26 with self-tapping holes 27, fastening screws 12 and fastening bolts 13 between multiple high-pressure separating pipes 22. Both ends of the artificial wellbore connection string are hermetically anchored to the artificial vertical wall 16 through anchor bolts 10. Blowout preventer valves 24 are installed on the high-pressure separating pipes 22 connected to both ends of the artificial wellbore.

[0062] Step 32: Then use a Ф171.4 mm PDC bit and a water-based mud circulation system to drill in the roof 32 of the coal seam driving strip until reaching the designed well depth. The horizontal well trajectory 35 of the three-opening up-dip section 18 is strictly controlled within a range of 2 - 3 m from the interface between the coal seam driving strip 4 and the roof 32 of the coal seam driving strip. After the three-opening drilling and pulling out of the drill string are completed, open the blowout preventer valve 24 at the three-opening artificial wellbore to release the mud stored in the wellbore annulus on both sides of the artificial wellbore, and then remove the artificial wellbore.

[0063] Step 33: Lower the Ф139.7 mm three-opening production casing for the entire three-opening section. A reverse-thread device 23 is installed at a specific position of the casing lowered into the well. The casing is lowered to 5 m above the completed well depth, and a 5 m pocket is reserved at the bottom of the three-opening well. An extended casing of 50 cm is reserved at the orifice of the three-opening up-dip section 18 in the excavated roadway 11 for installing subsequent wellhead sealers, blowout preventers, etc. and the drainage wellhead 31. During the lowering of the casing for the entire three-opening section, fabricate a three-opening artificial wellhead in the excavated roadway 11, as Figure 7As shown in the figure, in the production process of the three-opening artificial wellhead, when the three-opening casing reaches 15 m remaining from the total drilled depth, in the already excavated roadway, for the 10 m casing of the 11 pairs that have not yet reached the bottom of the 18 upward-inclined section of the three-opening well, it is designed to wind the outer wall of this casing section with Marisan. The winding thickness shall not exceed the size of the three-opening wellbore. Subsequently, the casing is slowly lowered by the drilling rig lifting system on the ground. Synchronously, the Marisan wound on the outer wall of the casing is triggered sequentially from bottom to top to achieve the foaming and expanding sealing function, so as to seal the annular space between the wellbore wall and the casing within a 10 m range at the orifice of the 18 upward-inclined section of the three-opening well in the already excavated roadway 11, forming the 15 Marisan filling section of the three-opening. Then, with the help of an air pump, 6 thin pipes are evenly inserted around the outer wall of the casing passing through the artificial vertical wall 16 in the already excavated roadway 11 underground. The thin pipes pass through the 15 Marisan filling section of the three-opening. The 6 thin pipes are simultaneously injected with G-class oil well quick-setting pure cement slurry with a specific gravity of 1.7 - 1.8 g / cm 3 to form a 15 m long pure cement filling section 17 of the three-opening air pump. After the injection of the pure cement slurry by the three-opening air pump is completed, the 6 inserted thin pipes do not need to be removed and need to remain unblocked, serving as the exhaust holes during the positive circulation cementing process of the pure cement slurry in the 18 upward-inclined section of the three-opening.

[0064] Step 34, for the 18 upward-inclined section of the three-opening, positive circulation cementing is carried out with G-class oil well pure cement slurry with a specific gravity of 1.7 - 1.8 g / cm 3 . After the cement slurry for cementing returns from the 6 thin pipes to the already excavated roadway 11, the outlets of the 6 thin pipes are blocked. After the pumped pure cement slurry is pressure bumped, the cementing is completed. The wellhead is closed on the ground and left to set for at least 72 hours. Then, the three-opening casing is reversed and the uncemented casing is removed.

[0065] Step 4, the 18 upward-inclined section of the three-opening is segmented perforated and fractured and a gas drainage head is installed. The specific operations are as follows:

[0066] The 18 upward-inclined section of the three-opening is segmented perforated and fractured. A coiled tubing string is lowered on the ground through the already excavated roadway 11 and into the 18 upward-inclined section of the three-opening. At the optimized fracturing section, according to the designed perforation points 20, segmented perforating and fracturing are carried out to generate large-scale complex cross-layer fractures 21 that penetrate the roof and communicate with the coal seam, and at the same time, small-scale fractured roof fractures 19 are also generated. After the segmented perforating and fracturing construction is completed, a drainage wellhead 31 is installed at the 50 cm casing reserved at the orifice of the 18 upward-inclined section of the three-opening in the already excavated roadway 11 underground. The drainage wellhead 31 is connected to the negative-pressure gas drainage equipment 30 through a drainage pipeline 29, as Figure 8 shown in the figure. Finally, the horizontal well in the roof of the combined tunneling strip is segmented fractured and quickly pre-drained of gas, effectively ensuring that the coal seam roadway tunneling can be carried out normally according to the plan.

[0067] The present invention forms a fracture network in the coal seam tunneling strip range through ground horizontal well segmented fracturing and drainage. The fracturing scale on the ground is large, and the ground fracturing scale is 8 - 14 m3 / min, while the downhole fracturing scale is only 1 - 2 m 3 / min. Therefore, the ground fracturing cracks extend far and the drainage range is large, which is beneficial to the coal seam gas drainage. Using the roadway connected to the horizontal well for drainage, there is no need to drill the butt straight well in the conventional way, and there is no need to install the drainage equipment. Moreover, during the downhole drainage, due to the liquid column pressure in the horizontal wellbore, only the opening of the drainage valve needs to be controlled for operation, which is convenient for implementation. In the later stage, it can be connected to the downhole negative pressure drainage system for drainage, which can reduce the reservoir pressure by 4 - 35 Kpa and further promote the desorption of coal seam gas. The present invention changes the original gas drainage method of driving strips, adopts a relatively safe ground construction method, and at the same time, can save the construction costs of the underground floor rock roadway and the floor cross-cut holes, which conforms to the concept of "people-oriented, life first" in our country.

Claims

1. A method for pre-draining gas by staged fracturing of horizontal wells in a strip of combined underground and surface tunneling passing through a roadway, characterized in that The specific steps are as follows: Step 1, construct the first-opening section of the L-shaped long horizontal well, and the first-opening section is a vertical well section; Step 2, construct the second-opening section of the L-shaped long horizontal well. The second-opening section consists of three well sections: vertical, deflecting, and horizontal. Drill until the bottom of the coal seam roof communicates with the excavated roadway at the penetration point to achieve surface-to-underground connection. Lower the second-opening technical casing and construct the artificial bottom of the second-opening cementing in coordination. Use pure cement slurry for positive circulation cementing, and the cement slurry returns to the surface; Step 3, fabricate the artificial wellbore for the third opening and construct the third-opening section of the L-shaped long horizontal well. The third-opening section is an upward-inclined well section; fabricate the artificial wellbore for the third opening in the excavated roadway, establish normal drilling mud circulation between the surface and the bottom of the third opening, drill an upward-inclined wellbore using a drill bit, drill to the designed well depth to complete the drilling, remove the artificial wellbore for the third opening in the excavated roadway, lower the third-opening production casing and construct the artificial wellhead for the third opening in the excavated roadway in coordination. Use pure cement slurry for positive circulation cementing, and the cement slurry returns to the excavated roadway; Step 4, perform staged perforating and fracturing on the upward-inclined well section of the third opening and install a gas drainage head, including the following operations: Staged perforating and fracturing of the upward-inclined well section of the third opening. Lower a coiled tubing string on the surface through the excavated roadway and into the upward-inclined well section of the third opening, and perform staged perforating and fracturing according to the designed perforation points; Install a drainage wellhead at the casing reserved at the orifice of the upward-inclined well section of the third opening in the excavated roadway underground, and connect the drainage wellhead to the negative-pressure gas drainage equipment through a drainage pipeline.

2. The method for pre-draining gas by staged fracturing of horizontal wells in the well-ground combined tunneling strip passing through the roadway as described in claim 1, characterized in that, The specific operation of Step 1 is as follows: For the construction of a vertical section of an open well, a Φ346.1mm pneumatic down-the-hole hammer is used to drill to a depth of 10 - 15m into the bedrock. Then, a Φ273.05mm surface casing is lowered, and a G-class oil well neat cement slurry with a specific gravity of 1.7 - 1.8g / cm 3 is circulated in a positive direction to the ground for well cementing.

3. The method for pre-draining gas by staged fracturing of horizontal wells in the well-ground combined tunneling strip passing through a roadway as claimed in claim 1, wherein, Step 2 includes the following sub-steps: Step 21, use a Φ241.3mm pneumatic down-the-hole hammer to drill the second-opening vertical well section to the designed well depth of the second-opening vertical well section (2); Step 22, use a Φ241.3mm PDC bit and a water-based mud circulation system to drill the second-opening deflecting well section to the designed landing point at the bottom of the roof of the coal seam driving strip. The well inclination angle of the horizontal well trajectory at the landing point is 90°, and the extension line of the azimuth angle is orthogonal to the excavated roadway; Step 23, use a Φ241.3mm roller cone bit and a nitrogen circulation system to drill the second-opening horizontal well section to the designed penetration point to achieve surface-to-underground connection; then construct artificial vertical walls on both sides of the excavated roadway at the well depth corresponding to the penetration point of the excavated roadway; Step 24, lower a Φ193.7mm second-opening technical casing into the entire second-opening section, and connect a stage collar at a specific position of the second-opening technical casing lowered into the well, and open the lateral holes of the stage collar; Step 25, perform casing running for the entire second-opening section, and during this period, fabricate the artificial bottom of the second-opening cementing in the excavated roadway underground.

4. The method for pre-draining gas by staged fracturing of horizontal wells in the strip of combined well and ground tunneling passing through roadways as claimed in claim 3, characterized in that, In Step 25, the process of fabricating the artificial bottom of the second-opening cementing is as follows: A. Lower a Φ193.7mm second-opening technical casing on the surface. The casing passes through the excavated roadway from the artificial vertical wall on one side of the penetration point to the artificial vertical wall on the other end. For the casing section located between the artificial vertical walls, it is designed to wind Marlex around the outer wall of this casing section, and the winding thickness does not exceed the size of the second-opening wellbore; B. Subsequently, use the drill rig lifting system on the ground to slowly lift the casing. Synchronously, trigger the Marisan wrapped around the outer wall of the casing from top to bottom in sequence to achieve the foaming and expansion sealing function, forming the second-opening Marisan filling section. Reserve a 20-cm casing length below the artificial vertical wall at the end of the casing string. Insert 6 thin pipes evenly around the outer wall of the casing at the 20-cm casing extending from the artificial vertical wall of the underground excavated roadway. The thin pipes pass through the second-opening Marisan filling section, and inject pure cement slurry simultaneously through the 6 thin pipes to form a 15-m long second-opening air pump pure cement filling section. Then, remove the 6 thin pipes. After the second-opening cementing artificial bottom is made, the pure cement slurry should wait for setting for at least 48 hours, and finally, use the pure cement slurry to circulate back to the ground for cementing in a positive circulation manner.

5. The method for pre-draining gas by staged fracturing of a horizontal well in a combined well and ground tunneling strip passing through a roadway as described in claim 1, wherein The said step 3 includes the following sub-steps: Step 31, make a third-opening artificial shaft in the excavated roadway. The third-opening artificial shaft is formed by sealing and connecting multiple high-pressure separator pipes through the flange plates, fastening screws and fastening bolts with self-owned screw holes. The two ends of the artificial shaft connection string are sealed and anchored to the artificial vertical wall by anchor bolts, and blowout preventer valves are installed on the high-pressure separator pipes connected to both ends of the artificial shaft. Step 32, use a Ф171.4mm PDC bit and the water-based mud circulation system to drill in the roof of the coal seam tunneling strip to the designed well depth and complete the drilling. The horizontal well trajectory of the third-opening upward-inclined section is at a distance of 2 - 3 m from the interface between the coal seam tunneling strip and the roof of the coal seam tunneling strip. After the third-opening drilling and pipe pulling are completed, open the blowout preventer valve at the third-opening artificial shaft to release the mud stored in the wellbore annulus on both sides of the artificial shaft, and then remove the artificial shaft. Step 33, run in a Ф139.7mm third-opening production casing for the entire third-opening well section. Install a reverse connection device at a specific position of the casing run into the well. The casing is run to 5 m above the completed well depth, and a 5-m pocket is reserved at the bottom of the third-opening. Reserve an extended 50-cm casing at the orifice of the third-opening upward-inclined section in the excavated roadway for installing the wellhead seal, blowout preventer and drainage wellhead for subsequent fracturing. During the process of running in the third-opening production casing for the entire well section, make a third-opening artificial wellhead in the excavated roadway. Step 34, for the three-opening upward-inclined well section, positive circulation cementing is carried out with G-class oil well neat cement slurry with a specific gravity of 1.7~1.8 g / cm 3 . After the neat cement slurry for cementing returns to the excavated roadway through 6 thin pipes, seal the outlets of the 6 thin pipes. After the pumped neat cement slurry is pressure bumped, the cementing is completed. Close the wellhead on the ground and wait for setting for at least 72 hours, and then reverse the three-opening casing and pull out the unsealed casing.

6. The horizontal well sectional fracturing pre-drainage gas extraction method for the combined well and ground tunneling strip passing through the roadway as described in claim 5, characterized in that In the said step 33, the process of making the third-opening artificial wellhead is as follows: When the third-opening casing is run to 15 m remaining from the completed well depth, design to wrap Marisan around the outer wall of the 10-m casing that has not been run into the bottom of the third-opening upward-inclined section in the excavated roadway. The wrapped thickness should not exceed the size of the third-opening wellbore. Subsequently, use the drill rig lifting system on the ground to slowly lower the casing. Synchronously, trigger the Marisan wrapped around the outer wall of the casing from bottom to top in sequence to form the third-opening Marisan filling section. Then, with the help of an air pump, insert 6 thin pipes evenly around the outer wall of the casing passing through the artificial vertical wall in the underground excavated roadway. The thin pipes pass through the third-opening Marisan filling section, and inject pure cement slurry simultaneously through the 6 thin pipes to form a 15-m long third-opening air pump pure cement filling section. After the injection of pure cement slurry by the third-opening air pump is completed, the 6 inserted thin pipes serve as the exhaust holes during the positive circulation cementing process of the pure cement slurry in the third-opening upward-inclined section.

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