CN107313716B - Drilling method for coal-bed gas well crossing goaf by composite plugging broken rock at hole bottom - Google Patents

Abstract

The invention belongs to the technical field of coal bed gas resource exploitation, and provides a drilling method for a coal bed gas well through a goaf by using a hole bottom composite plugging broken rock mass, which aims at solving the problems that drilling is difficult and potential safety hazards exist during drilling when a coal bed gas well is constructed through the goaf; the surrounding rock breaking rock mass of the drilling hole is constructed in three stages, wherein auxiliary measures of injecting foam liquid into the hole bottom are implemented in the middle breaking rock mass section, auxiliary measures of grouting the hole bottom are implemented in the remarkable breaking rock mass section, and casing drilling measures are implemented in the caving zone cavity section. The broken rock mass section and the caving zone cavity are safely and efficiently penetrated; meanwhile, the comprehensive stabilization technology of the surface casing, the technical casing and the production casing is utilized, so that the overall rigidity and stability of the well drilling are greatly enhanced.

Description

Drilling method for coalbed methane wells crossing gobs with composite plugging of broken rock mass at the bottom of the hole

technical field

The invention belongs to the technical field of mining of coalbed methane resources, and in particular relates to a drilling method for coalbed methane wells passing through goafs through composite plugging of broken rock mass at the bottom of holes, mainly adopting pneumatic down-the-hole hammers and auxiliary technologies to excavate and drill wells to form coalbed methane wells, and for drainage and mining. CBM in underground coal seams or gobs.

Background technique

To drill coalbed methane wells in goafs, it is necessary to overcome the problem of drilling broken rock masses in goafs. Usually, the drilling methods for coalbed methane wells mainly include mud circulation drilling and pneumatic down-the-hole hammer drilling. The surface casing is used in the upper part, and the technical casing wall can also be used in the broken rock mass section to prevent the hole from collapsing. The gap between the casing and the borehole wall is filled with cement slurry.

The technical staff of the State Key Laboratory of Coal and Coalbed Methane Co-mining in Shanxi Jincheng Anthracite Mining Group Co., Ltd. combined with the analysis of the construction site found that the main problems existing in the existing technology are: (1) For mud circulation drilling, when crossing the goaf There will be mud leakage in the fissure zone or the caving zone, and it will be impossible to drill; (2) For the drilling of the pneumatic down-the-hole hammer, when passing through the fissure zone or caving zone in the goaf, there will also be high-pressure gas leakage, and there will be no return wind Or a large amount of gas gushes out of the wellhead, which makes it impossible to continue drilling safely to the design depth; (3) In the broken rock mass section, there are drill sticking and pinching phenomena, and drill drop occurs in the cavity area of the caving zone, which may lead to production safety problems.

Contents of the invention

The invention aims at the problems of drilling difficulties and potential safety hazards in the construction of coalbed methane wells passing through goafs, and further provides a drilling method for coalbed methane wells passing through goafs in which the bottom of a hole is compounded to seal broken rock mass.

The present invention adopts following technical scheme:

A drilling method for a coalbed methane well crossing a goaf with composite plugging of the broken rock mass at the bottom of the hole, using a triple casing structure and a three-split drilling construction process. Drilling hole and technical casing, three-drilling drilling and production casing, the second drilling stage passes through the goaf, and during the construction of the second drilling through the goaf, the broken rock mass of the surrounding rock of the coalbed methane well drilling is carried out. Composite plugging in sections; the broken rock mass of the surrounding rock of the drilling hole is divided into three stages of construction in turn. The first stage is to implement the auxiliary measures of injecting foam liquid at the bottom of the hole in the moderately broken rock mass section, and the second stage is to implement the auxiliary measures of injecting foam liquid at the bottom of the hole, and the second stage is to significantly break the rock mass. The auxiliary measures of hole bottom grouting are implemented in the body section, and the third stage is the implementation of follow-up drilling measures in the cavity section of the caving zone.

The top openings of the surface casing, the technical casing and the production casing are connected and coupled to form a stable pipe well structure system.

The specific drilling construction process is as follows:

1) Orifice positioning of coalbed methane wells, preparation of construction materials;

2) First drill hole construction, through the Quaternary series to about 5m below the bedrock surface, and once drill hole is completed;

3) Run into the surface casing, inject the outer casing material into the gap between the first drill hole and the surface casing, and wait for solidification;

4) After the initial setting of the casing material in the outer layer, use the pneumatic down-the-hole hammer to carry out the second drilling construction, pass through the weakly broken rock mass, enter the moderately broken rock mass, inject foam liquid, reduce the air leakage of the broken rock mass, and reduce the High pressure gas leakage;

5) Continue to drill until the rock mass is significantly broken. If there is a large amount of air leakage and drill stuck, a pneumatic down-the-hole hammer is proposed, and a segmented high-pressure grouter is used to inject grout at the bottom of the hole to form a grout with a diameter twice the diameter of the drill hole. body, and then use the pneumatic down-the-hole hammer to drill; repeat step 5) until drilling to the cave in the caving zone;

6) Run into the technical casing, drill with the pneumatic down-the-hole hammer with the pipe, directly pass through the cavity in the caving zone, lift the drill when drilling to the extremely broken rock area below the cavity in the caving zone, and then run into the segmented high-pressure grouting device again. Bottom grouting, waiting for solidification;

7) After the initial setting of the grout at the bottom of the hole, use the pneumatic down-the-hole hammer to follow the pipe to drill to about 20m in the bottom of the coal seam, and the second drilling is completed;

8) High-pressure grouting at the bottom of the second drill hole, so that the cement slurry returns to the cavity in the caving zone; inject the inner casing material between the technical casing and the surface casing, and wait for solidification, so that the top of the technical casing, firm bottom;

9) Drilling construction of three-hole drilling, drilling to the bottom of the lower coal seam, and completion of three-hole drilling;

10) Run into the production casing, and inject cement slurry at the bottom of the third drill hole under high pressure, so that the slurry returns to the hole along the gap between the production casing and the technical casing;

11) At the orifice, use locking steel fasteners to lock the surface casing, technical casing and production casing to complete the drilling construction.

The outer shell material and the inner shell material are respectively prepared by mixing cement, soil and water at a ratio of 1:1.5:1.8.

The grouting at the bottom of the hole is also pure cement slurry with a water-cement ratio of 0.5-1.0.

Step 10) When running the production casing, the nozzle of the production casing should be at least 0.5m above the surface.

The segmental high-pressure grouting device is used for grouting at the bottom of the hole. The segmental high-pressure grouting device includes a pipe body. The pipe body is a three-section integrated structure. The middle part of the pipe body is a flower tube with several grouting grooves , the upper and lower parts of the pipe body are respectively threaded, and the upper and lower threaded parts are respectively equipped with a grout stopper combination, and the section between the upper and lower grout stopper combinations is the grouting section, wherein the upper grout stopper combination It can move up and down along the screw thread on the upper part of the grouting device; the top end of the screw thread on the upper part of the grouting device is equipped with a locking joint for cooperating with the drill pipe and the grouting pipe.

The stopper assembly includes clamping bolts, rubber sealing rings and elastic soft rubber rings, the clamping bolts are connected with threads, and the rubber sealing rings and elastic soft rubber rings are parallel to each other and coaxially tightly sleeved on the clamping bolts Between the casing and the casing, a double-layer sealed slurry structure is formed. The rubber sealing ring is arranged outside the elastic soft rubber ring. That is, for the upper grout stopper combination, the elastic soft rubber ring is installed under the rubber sealing ring, while for the lower grout stopper combination, the elastic soft rubber ring is installed above the rubber seal ring, so the inner side is described relative to the grouting fluid, The elastic soft rubber ring constitutes the first layer of sealing that is in direct contact with the grouting fluid, and the rubber sealing ring constitutes the second layer of sealing.

The length of the grouting section is 0.5-1m.

The grouting groove is a rectangular notch parallel to the axial direction of the pipe body, and there are no less than three layers along the axial direction of the pipe body, each layer has no less than 3 notches, and the notches of adjacent layers are arranged in dislocation. Ensure uniform grouting in the grouting section.

The present invention mainly solves the following technical problems:

(1) Drilling technology for safe and efficient crossing of broken rock mass sections. That is, in the moderately broken rock mass section (middle and upper part of the fracture zone), the combined drilling measures of pneumatic down-the-hole hammer combined with injection of foam liquid at the bottom of the hole are adopted; Combined drilling measures for bottom grouting.

(2) Drilling technology for safely and efficiently crossing the cavity in the caving zone. That is to use pneumatic down-the-hole hammer combined with pipe drilling in the cavity of the caving zone, and inject an appropriate amount of grouting at the bottom of the cavity in the caving zone to reinforce the broken rock mass and make the technical casing take root.

(3) Comprehensive stabilization technology for surface casing, technical casing and production casing. That is, the outer casing material is filled in the gap between the surface casing and the first drilling; the inner casing material is filled in the gap between the technical casing and the surface casing at the upper part of the orifice, and the technical casing and the surface casing at the bottom of the second drilling are filled. The gap between the hole walls is filled with cement slurry to stabilize the upper and lower ends of the technical casing; the gap between the production casing and the technical casing and the three-hole drilling is filled with cement slurry to the hole opening, which will greatly enhance the overall rigidity and stability of the drilling.

At the same time, the following technical problems can be solved by using the segmented high-pressure grouting device:

(a) Realize segmental grouting between the casing and the well wall in the casing, and the length of the grouting section can be selected;

(b) Set up double-layer stop grout valves to realize high-pressure grouting;

(c) An independent high-pressure grouting pipe is set up, which can be connected with the grouting device by common exploration drill pipe, which simplifies the grouting equipment.

Therefore, the use of this grouting device for external casing grouting reinforcement of coalbed methane wells can realize high-pressure grouting with a variable section length in the specified drilling section or position, and the outer wall of the casing in the specified area. The rock is reinforced, and the casing is closely attached to the well wall, which greatly enhances the stability of the coalbed methane well.

Description of drawings

Fig. 1 is a sectional view of drilling stage;

Fig. 2 is a section view of the second drilling stage;

Fig. 3 section view of drilling stage three;

Fig. 4 is a structural schematic diagram of a segmented high-pressure grouting device.

1. Quaternary; 2. Weakly broken rock mass (bedrock deflection zone); 3. Moderately broken rock mass (middle and upper part of the fissure zone); 4. Significantly broken rock mass (lower part of the fissure zone); 5. Caving zone Hollow; 6. Upper coal seam; 7. Coal seam floor; 8. Lower coal seam; 9. Orifice; 10. First drilling; 11. Surface casing; .Inner layer casing material; 15. Second drilling; 16. Bottom grouting body; 17. Outer grouting body of technical casing; 18. Third drilling; 19. Production casing; 20. Production casing External grouting body; 21. Locking steel fasteners;

31. Drill pipe; 32. Grouting pipe; 33. Casing; 34. Locking joint; 35. Screw thread on the upper part of the grouting device; 36. Clamping bolt; 37. Rubber sealing ring; 38. Elastic soft rubber ring; 39 . Grouting groove; 40. Bottom screw thread of the grouting device; 41. Pipe body.

Detailed ways

Aiming at the unfavorable geological conditions of coalbed methane well drilling with a large number of broken rock masses or cavities in the goaf, the present invention is based on the pneumatic down-the-hole hammer drilling method, combined with injection of foam liquid at the bottom of the hole, grouting at the bottom of the key broken rock mass, and casing Auxiliary technologies such as follow-up and technical casing end grouting stabilization have solved the drilling technical problems that it is difficult for coalbed methane wells to penetrate the broken rock mass or hollow section of the goaf. The key point of the technique is that the coalbed methane wells are drilled in stages with three opening diameters in sequence, and the second drilling stage passes through the goaf. Among them, in the section of moderately broken rock mass (the middle and upper part of the fracture zone), the auxiliary measures of injecting foam liquid at the bottom of the hole are implemented; in the section of significantly broken rock mass (the lower part of the fracture zone), the auxiliary measures of grouting at the bottom of the hole are implemented; Implement follow-up drilling measures; grout the top and bottom of the technical casing to stabilize the casing, and finally weld the surface casing, technical casing, and production casing at the orifice to complete the drilling construction.

Construction technique of the present invention mainly relates to following key technology:

(1) Segmented composite plugging technology of broken rock mass in surrounding rock of coalbed methane well drilling. Including: In the first stage, in the moderately broken rock mass (the middle and upper part of the fractured zone) 3, foam liquid is injected into the bottom of the hole (the concentration of foam agent and the pump volume are adjusted according to the working conditions) to reduce the air leakage of the broken rock mass and improve the drilling performance. efficiency. In the second stage, in the significantly broken rock mass (the lower part of the fracture zone) 4, a segmented high-pressure grouter is used to grout at the bottom of the hole to form a grouting body 16 with a diameter twice the diameter of the drilled hole. The grouting fluid is pure cement slurry ( Water-cement ratio 0.5-1.0, quick-setting agent water glass 3%, if necessary, add 1% glass fiber), effectively block and reinforce severely broken rock mass, avoid accidents such as pneumatic down-the-hole hammer sticking, high-pressure gas leakage, etc., and improve construction safety.

(2) Drilling construction of coalbed methane well with triple casing structure and its connection and coupling technology. Including: the surface casing 11 passes through the Quaternary 1 formation and is embedded in the underlying bedrock for about 5m; the technical casing passes through the deflection zone 2, the upper middle part 3 and the lower part 4 of the fracture zone, the caving zone and its cavities from the orifice 9 5. Combined with pipe drilling, it reaches about 20m inside the coal seam floor 7; the production casing 19 is installed at a full hole depth after the three-drilling hole 18 is completed, and its nozzle is 0.5m higher than the hole; the triple casings are connected to each other Coupled to form a rigid tube well structure. Among them, the surface casing 11 is filled with the outer casing material 12 (ratio: cement: soil: water = 1: 1.5: 1.80), and the surface casing 11 and the technical casing 13 are bonded by the inner casing material 14 (Proportion: cement:soil:water=1:1.5:1.80), the bottom of the technical casing 13 is bonded to the wall of the second borehole 15 by the external grouting body 17 of the technical casing; the production casing 19 and the technical casing 13 is bonded by the outer grouting body 20 of the production casing; the surface casing 11, the technical casing 13, and the production casing 19 are welded by locking steel fasteners 21 at the orifice to form a stable pipe well structure system.

Concrete drilling construction process of the present invention is as follows:

1) Positioning of the orifice 9 of the coalbed methane well and preparation of construction materials;

2) Construction of drilling 10 in the first drilling, passing through Quaternary 1 to about 5m below the bedrock surface, and completion of drilling in the first drilling;

3) Run into the surface casing 11, inject the outer casing material 12 into the gap between the first drill hole 10 and the surface casing 11, and wait for solidification;

4) After the initial setting of the shell material 12 of the outer layer, use the pneumatic down-the-hole hammer to carry out the second drilling 15 construction, pass through the weakly broken rock mass (bedrock deflection zone) 2, and enter the moderately broken rock mass (the middle and upper part of the fracture zone) ) 3. Inject foam liquid to reduce air leakage of broken rock mass and reduce high-pressure gas leakage;

5) Continue to drill to the significantly broken rock mass (the lower part of the fracture zone) 4. If a large amount of air leakage, drill sticking, etc. occur, a pneumatic down-the-hole hammer is proposed, and a segmented high-pressure grouter is used to inject grout at the bottom of the hole to form a diameter twice that of the hole. The grouting body 16 of the borehole diameter is drilled with a pneumatic down-the-hole hammer. Repeat step 5) until the hole 5 in the caving zone is drilled.

6) Run into the technical casing 13, the pneumatic down-the-hole hammer drills with the pipe, directly pass through the cavity 5 of the caving zone, lift the drill when drilling to the extremely broken rock area at the lower part of the caving zone, and run into the segmented high-pressure grouting device again Grouting at the bottom of the hole, waiting for setting.

7) After the initial setting of the grouting body 16 at the bottom of the hole, use a pneumatic down-the-hole hammer to follow the pipe to drill into the coal seam floor 7 for about 20m, and complete the second drilling 15.

8) High-pressure grouting at the bottom of the second drill hole 15, so that the cement slurry returns to the cavity 5 in the caving zone; inject the inner casing material 14 between the technical casing 13 and the surface casing 11, and wait for it to set. The top and bottom of the technical casing are stable.

9) Drilling construction of the third drill hole 18, drilling to the bottom plate of the lower coal seam 8, and the completion of the third drill hole 18.

10) Run into the production casing 19, the nozzle is 0.5m above the ground surface, and inject cement slurry at the bottom of the third drill hole 18 under high pressure, so that the slurry returns to the hole along the gap between the production casing 19 and the technical casing 13.

11) At the orifice 9, lock the surface casing 11, the technical casing 13 and the production casing 19 with locking steel fasteners 21 to complete the drilling construction.

Among them, the construction process mainly involves the connection of the following key parts:

(1) The gap between the surface casing 11 and the wall of a drilled hole 10 is bonded by the outer casing material 12;

(2) The top part of the nozzle of the technical casing 13 is bonded to the surface casing 11 by the inner shell material 14, and the bottom of the casing is bonded to the wall of the second drill hole 15 by the outer grouting body 17 of the technical casing ;

(3) The production casing 19 and the technical casing 13 are bonded by the outer grouting body 20 of the production casing;

(4) The nozzles of the surface casing 11 , the technical casing 13 and the production casing 19 are welded together by locking steel fasteners 21 .

The segmental high-pressure grouting device as shown in Figure 4 is used for grouting. The pipe body of the segmental high-pressure grouting device is divided into upper, middle and lower parts. The upper part is the upper part of the grouting device with a length of 0.1-0.5m. There are 3 pairs of grouting grooves in the flower tube part, the length is about 0.5m, and the lower part is the bottom thread of the grouting device with a length of 0.2m. The grout stopper assembly (including three clamping bolts, rubber sealing ring and elastic soft rubber ring) is installed at the upper threaded thread of the grouter and the bottom threaded thread of the grouter. The upper grout stopper assembly can move along the upper screw thread of the grouter, so as to realize the grouting between the casing and the well wall in sections in the casing, and the length of the grouting section can be selected, and the length range is generally 0.5-1.0m. The rubber sealing ring and elastic soft rubber ring are set in the grout stopper combination, which has the function of double-layer grout stop. Under the action of grouting pressure, the elastic soft rubber ring is squeezed and closely attached to the casing, which significantly improves the grout stop performance. Realized high pressure grouting.

The special lock joint can connect the drill pipe, the grouting pipe and the screw on the upper part of the grouting device. The drill pipe can be an ordinary exploration drill pipe, and the grouting pipe is a high-pressure grouting pipe, which improves the flexibility of equipment material selection and reduces the cost .

The use process of the segmented high-pressure grouting device is as follows:

(1) Select the appropriate diameter of the grouter body, and prepare the corresponding accessories, including drill pipe, grouting pipe, lock joint, clamping bolt, rubber sealing ring, elastic soft rubber ring, etc.

(2) Screw the lower grout stopper assembly (including three clamping bolts, rubber sealing ring and elastic soft rubber ring) to the screw thread at the bottom of the grouter in sequence.

(3) Screw the upper grout stopper combination (including three clamping bolts, rubber sealing ring and elastic soft rubber ring) to the upper threaded thread of the grouting device in sequence, and adjust the length of the grouting section as required, so that The stopper assembly stops at a fixed position.

(4) Connect the first section of drill pipe and the corresponding grouting pipe with the threaded lock joint, and lift the grouting device into the casing.

(5) According to the above method, connect the drill pipe and the grouting pipe in sequence until reaching the part in the casing that needs to be grouted.

(6) At the casing port on the ground, inject clean water under high pressure from the grouting pipe, and the high-pressure water enters the grouting device, which will squeeze the elastic soft rubber ring to make it closely adhere to the pipe wall, and at the same time seal the grouting hole on the casing break open.

(7) Prepare the grouting fluid at the surface wellhead, inject the grouting fluid under high pressure from the grouting pipe, and press the grouting fluid into the gap between the casing and the well wall through the grouting hole of the casing, realizing segmental grouting reinforcement.

(8) When the grouting requirements are met, lift the grouting device to the nozzle in time and flush the grouting device.

The connection points and relations of the segmented high-pressure grouting device are as follows:

The drill pipe and the grouting pipe are connected through a lock joint, and the lock joint is connected with the upper grouting device with threads. The grout stopper assembly on the upper part of the grouter includes clamping bolts (3 pieces), rubber sealing rings and elastic soft rubber rings. It has an inner ring, and the inner thread in the inner ring passes through one end of the upper part of the grouter in turn, along the grouting Screw the screw on the upper part of the device to a fixed position. Both the rubber sealing ring and the elastic soft rubber ring are clamped by clamping bolts. Similarly, the grout stopper assembly at the lower part of the grouting device includes clamping bolts (3), rubber sealing rings and elastic soft rubber rings. Screw to secure position. Both the rubber sealing ring and the elastic soft rubber ring are clamped by three clamping bolts. The combination of the upper and lower grout stoppers is closely attached to the casing.

Claims (10)

1. A drilling method for a coal-bed gas well of a hole bottom composite plugging broken rock body to pass through a goaf adopts a triple sleeve structure and a three-opening drilling construction process, wherein the well body of the coal-bed gas well consists of a first-opening drilling hole (10) and a surface sleeve (11), a second-opening drilling hole (15) and a technical sleeve (13), a third-opening drilling hole (18) and a production sleeve (19), and the goaf is passed through at the two-opening drilling stage, and the drilling method is characterized in that: when the secondary drilling construction is carried out through the goaf, sectional composite blocking is carried out on the broken rock mass of the surrounding rock of the coal bed gas well; the drilling surrounding rock breaking rock mass is sequentially divided into three stages for construction, wherein the first stage is to implement auxiliary measures of injecting foam liquid into the hole bottom in the section of the medium breaking rock mass (3), the second stage is to implement auxiliary measures of grouting into the hole bottom in the section of the remarkable breaking rock mass (4), and the third stage is to implement casing drilling measures in the section of the caving zone (5).

2. The method for drilling the coal-bed gas well through the goaf by using the hole bottom composite plugging broken rock mass according to claim 1, wherein the method comprises the following steps: the top end orifices of the surface casing (11), the technical casing (13) and the production casing (19) are connected and coupled to form a stable pipe well structure system.

3. The drilling method for the coal-bed gas well of the hole bottom composite plugging broken rock body to pass through the goaf according to claim 2, which is characterized in that the specific drilling construction process comprises the following steps:

1) Positioning a coal bed gas well orifice (9), and preparing construction materials;

2) Constructing a first drilling hole (10), penetrating through the fourth system (1) to be below the bedrock surface, and finishing the first drilling hole;

3) The surface sleeve (11) is put in, and an outer layer sleeve shell material (12) is injected into a gap between the drill hole (10) and the surface sleeve (11) for waiting to solidify;

4) After the outer shell material (12) is initially set, a pneumatic down-the-hole hammer is adopted to perform two-hole drilling (15) construction, the two-hole drilling penetrates through the weak broken rock mass (2), enters the medium broken rock mass (3), and is injected with foam liquid, so that the air leakage of the broken rock mass is reduced, and the leakage of high-pressure air is reduced;

5) Continuously drilling until the rock mass (4) is obviously broken, if a large amount of air leakage and blocking occur, providing a pneumatic down-the-hole hammer, grouting at the bottom of a hole by using a segmented high-pressure grouting device to form a grouting body (16) with the diameter being 2 times that of the drilled hole, and drilling by using the pneumatic down-the-hole hammer; repeating the step 5) until drilling to the caving zone cavity (5);

6) A technical sleeve (13) is put into, a pneumatic down-the-hole hammer drills with the sleeve, directly penetrates through the caving zone cavity (5), drills up when drilling to a very broken rock area at the lower part of the caving zone cavity (5), and is put into a segmented high-pressure grouting device again to perform grouting at the bottom of the hole, and waiting for solidification;

7) After the primary setting of the hole bottom grouting body (16), drilling into the coal seam bottom plate (7) by adopting a pneumatic down-the-hole hammer and a pipe, and finishing the two-hole drilling (15);

8) Grouting the bottom of the two holes (15) under high pressure to enable cement paste to return to the caving zone cavity (5); injecting an inner layer sleeve shell material (14) between the technical sleeve (13) and the surface sleeve (11) for curing, so that the top end and the bottom end of the technical sleeve (13) are stable;

9) Drilling construction of a three-way drilling hole (18), wherein the three-way drilling hole (18) is drilled to the bottom plate of the lower coal seam (8);

10 A production casing (19) is put in, cement slurry is injected into the bottom of a three-hole drill (18) at high pressure, and the slurry is returned to the orifice along the gap between the production casing (19) and the technical casing (13);

11 The surface sleeve (11), the technical sleeve (13) and the production sleeve (19) are locked at the orifice (9) by using a locking steel fastener (21), so that the drilling construction is completed.

4. The method for drilling a coal-bed gas well through a goaf by using the hole bottom composite plugging broken rock mass according to claim 3, wherein the method comprises the following steps: the outer shell material (12) and the inner shell material (14) are respectively prepared by mixing cement, soil and water according to the ratio of 1:1.5:1.80.

5. The method for drilling the coal-bed gas well through the goaf by using the hole bottom composite plugging broken rock mass according to claim 4, wherein the method comprises the following steps: the grouting at the bottom of the hole is also pure cement slurry with the water cement ratio of 0.5-1.0.

6. The method for drilling the coal-bed gas well through the goaf by using the hole bottom composite plugging broken rock mass according to claim 5, wherein the method comprises the following steps: step 10) when the production casing (19) is lowered, the pipe orifice of the production casing (19) is at least 0.5m higher than the surface of the earth.

7. The method for drilling the coal-bed gas well through the goaf by using the hole bottom composite plugging broken rock mass according to claim 6, wherein the method comprises the following steps: the method comprises the steps that a sectional high-pressure grouting device is adopted during hole bottom grouting, the sectional high-pressure grouting device comprises a pipe body (41), the pipe body (41) is of a three-section integrated structure, the middle part of the pipe body (41) is a flower pipe provided with a plurality of grouting grooves (39), the upper part and the lower part of the pipe body (41) are respectively provided with screw threads, a grouting plug combination is respectively arranged at the upper screw threads and the lower screw threads, a grouting section is arranged at a section between the upper grouting plug combination and the lower grouting plug combination, and the upper grouting plug combination can move up and down along the screw threads at the upper part of the grouting device; the top end of the screw thread at the upper part of the grouting device is provided with a locking joint (34) which is used for being matched and connected with a drill rod (31) and a grouting pipe (32).

8. The method for drilling the coal-bed gas well through the goaf by using the hole bottom composite plugging broken rock mass according to claim 7, wherein the method comprises the following steps: the slurry stop plug assembly comprises a clamping bolt (36), a rubber sealing ring (37) and an elastic soft rubber ring (38), wherein the clamping bolt (36) is connected with a screw thread in a matched manner, and the rubber sealing ring (37) and the elastic soft rubber ring (38) are mutually parallel and coaxially tightly sleeved between the clamping bolt (36) and the sleeve (33) to form a double-layer sealing slurry stop structure; in the axial direction, the rubber sealing ring (37) is farther from the grouting section than the elastic soft rubber ring (38).

9. The method for drilling the coal-bed gas well through the goaf by using the hole bottom composite plugging broken rock mass according to claim 8, wherein the method comprises the following steps: the length of the grouting section is 0.5-1m.

10. The method for drilling the coal-bed gas well through the goaf by using the hole bottom composite plugging broken rock mass according to claim 9, wherein the method comprises the following steps: the grouting grooves (39) are rectangular notches parallel to the axis direction of the pipe body (41), at least three layers of notches are arranged along the axis direction of the pipe body (41), each layer of notches is at least 3, and notches of adjacent layers of notches are arranged in a staggered mode.

Images