A combined protection method for oil and gas wells above and below the ground near goafs

Abstract

The present invention discloses a combined protection method for oil and gas wells above and below ground near a goaf, belonging to the technical field of coal mining. It conducts an investigation and prediction on the goaf formed after the coal seam working face is mined to determine the construction positions below and above ground, and then conducts combined protection below and above ground respectively. The present invention weakens the integrity of the roof to the greatest extent by constructing vertical boreholes underground, changes the stress distribution of the roof, cuts off the caving range of the working face roof towards the direction of the oil and gas well, and forms a "protective wall" on one side above the oil and gas well on the ground, effectively reducing the shear and tensile effects on the oil and gas well assembly caused by surface movement during the coal face mining process; through the combined protection above and below ground, the range of goaf collapse settlement is effectively reduced, and the stress propagation of the loose layer is cut off to achieve the purpose of reducing the impact on the oil and gas well, so as to meet the protection and treatment requirements of the oil and gas well.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mining, and in particular to a combined protection method for oil and gas wells above and below the ground near a goaf. Background Art

[0002] Coal seam mining in the overlapping area of gas resources causes overlying strata to collapse and deform, forming a dynamic moving and subsiding basin on the ground, resulting in deformation and damage of oil and gas wells within the affected range of the subsidence basin, leading to casualties and work safety accidents. Therefore, it is very important to develop a protection and treatment technology suitable for protecting oil and gas wells in the overlapping area.

[0003] Currently, the conventional treatment method is to leave a coal pillar of a certain size to protect the oil and gas wells to maintain their stability. However, the setting of the coal pillar will cause a large amount of resource waste. In the design process of this method, the determined parameter is the movement angle of the loose layer and the bedrock. The determination of this parameter often relies on experience. Given the complexity of the underground geological conditions, the finally determined movement angle is quite different from the actual situation. In the actual treatment process, for safety reasons, the parameter determination is relatively conservative. Therefore, the finally determined size of the coal pillar is relatively large, resulting in relatively serious resource waste. At the same time, the method of leaving a coal pillar also belongs to a passive protection method, and this conventional protection method cannot reduce the area of ground subsidence and cannot balance the requirements of full resource exploitation and the safety of oil and gas wells. Summary of the Invention

[0004] The purpose of the present invention is to provide a combined protection method for oil and gas wells above and below the ground near a goaf to solve the problems in the background art.

[0005] To achieve the above purpose, the present invention provides a combined protection method for oil and gas wells above and below the ground near a goaf, including the following steps:

[0006] S1. Conduct an investigation and prediction on the goaf formed after the coal seam working face is mined, and determine the construction positions above and below the ground;

[0007] S2. In the underground protection, reserve a safety distance between the oil and gas wells and the boreholes in the working face, determine the borehole positions, ensure that the axis of the completed borehole is an approximate straight line, and then perform hydraulic fracturing;

[0008] S3. In the above-ground protection, within the tensile range of the ground loose soil mass position, construct a ground protection line borehole, insert a casing, and perform split grouting with cement slurry, and arrange a protection wall parallel to the oil well.

[0009] Preferably, in S1, determine the ground position and underground position of the working face, and according to the exploration boreholes near the working face, determine the formation composition of the coal seam working face, and obtain the rock thickness and lithology characteristics of the roof and floor of the coal seam working face.

[0010] Preferably, the specific steps of S2 are as follows:

[0011] S21. Determine the advanced influence angle and advanced influence distance according to the construction position obtained in S1, then reserve a safety distance, and determine the construction sequence;

[0012] S22. Determine the drilling spacing, drilling depth and drilling angle according to the specific composition of the working face;

[0013] S23. Conduct drilling. During the drilling process, try to reduce the drilling speed, reduce the feeding force of the drill rig, and ensure the straightness of the drill hole; after drilling and forming the hole, use the drill rig to gradually send the packer to the bottom of the hole through the water injection drill pipe to implement fracturing.

[0014] Preferably, in S23, a composite drill bit with artificial diamond bits and diamond composite bits is used to complete the drilling, and the flushing fluid is clear water;

[0015] Among them, for hard rock formations, artificial diamond bits are used for drilling, with a rotation speed of 150 - 200 rpm, a pressure of 900 - 1000 kg, and a flushing fluid volume of 50 L / min;

[0016] For other rock formations, diamond composite bits are used for drilling, with a rotation speed of 150 - 200 rpm, a pressure of 500 - 550 kg, and a flushing fluid volume of 50 L / min.

[0017] Preferably, hydraulic fracturing adopts the backward fracturing method, that is, fracturing is carried out successively from the bottom of the drill hole to the hole mouth. During the fracturing process, a high-pressure pump is connected to implement fracturing. Static water continuously enters the packer section through the high-pressure pump via the water injection pipeline. After the fracture is initiated, the water pressure is controlled to drop, and it enters the pressure-holding water injection stage. After the fracturing of the first section is completed, the drill hole is drained through the water injection pipe to release pressure. After all the water in the drill hole is drained, the packer is depressurized, and the packer is gradually withdrawn from the hole for the fracturing of the next section; among them, a 3 - m retreat of the packer is one section of fracturing.

[0018] Preferably, during the fracturing process, the fracturing time for each section is 20 min - 30 min, the pressure is stabilized at 30 Mpa, and the drill hole drainage time is 1.5 - 2 times the fracturing time.

[0019] Preferably, in S3, according to the construction position obtained in S1, determine the final drill hole layer and the number of drill holes. The drilling process is divided into two stages, specifically:

[0020] The first stage: Use a drill bit to drill according to the first hole diameter, lower the casing, and fix the casing with M30 cement;

[0021] The second stage: Drill according to the second hole diameter smaller than the first hole diameter, lower the built-in steel pipe, and inject M30 cement mortar for splitting grouting to reinforce the formation.

[0022] Preferably, during the drilling process, centralizer pieces are welded to the front end before casing is lowered, and a set of crossbeam perforations are cut exactly at a certain distance from the port; a steel cover is additionally welded to the last casing and connected to the cementing equipment.

[0023] Therefore, the method for joint protection of oil and gas wells above and below ground near a goaf of the present invention has the following beneficial effects:

[0024] (1) The present invention can realize the safe operation of oil and gas wells within the subsidence range, is applicable to the overlapping area of coal and oil resources, protects oil and gas wells in the tensile area of the surface subsidence area, avoids the losses caused by the damage of oil and gas wells during coal seam mining, successfully solves the waste caused by leaving coal pillars, can fully mine the coal seam in the overlapping area of coal and oil, brings greater economic benefits to the coal mine; and this method is simple in construction, can quickly achieve the purpose of protecting oil and gas wells, and has important application value and popularization value.

[0025] (2) In the present invention, by constructing vertical boreholes underground, the integrity of the roof is weakened to the greatest extent, the stress distribution of the roof is changed, the caving range of the working face roof towards the direction of the oil and gas well is cut off, and a "protective wall" is formed on one side of the oil and gas well above ground, effectively reducing the shear and tensile effects on the oil and gas well assembly caused by surface movement during the coal face mining process; there is no need to determine the movement angles of the loose layer and the bedrock. Through the joint protection above and below ground, the subsidence range of the mined-out area collapse is effectively reduced, and the stress propagation of the loose layer is blocked to achieve the purpose of reducing the influence on the oil and gas well, so as to meet the protection and treatment requirements of the oil and gas well. Compared with the method of leaving coal pillars, it belongs to an active protection method.

[0026] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0027] Figure 1 is a flowchart of an embodiment of the present invention;

[0028] Figure 2 is a cross-sectional view of the working face borehole of an embodiment of the present invention. Detailed Embodiments

[0029] The technical solution of the present invention will be further described below through the drawings and embodiments.

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0031] Embodiment

[0032] Taking the No. 1 Coal Mine of Shaanxi Xiaobaodang Mining Company as an example, the 132201 working face of the No. 1 Coal Mine of Shaanxi Xiaobaodang Mining Company had been mined to 1920 m by July 12. The 8 natural gas wells in the Shuang 3-24 well field of the Gas Production Plant No. 2 were 1248 m away from the 132201 working face in the strike direction. The 8 natural gas wells in the Shuang 3-24 well field were located within the 132202 working face, 127 m away from the belt conveyor entry of the 132201 working face and 2633 m away from the withdrawal roadway. The protective coal pillar for the oil and gas wells was 200 m.

[0033] According to the monitoring situation, the maximum surface movement displacement at the center of the 132201 working face was 902.24 mm in absolute displacement, and the maximum subsidence was 2613.38 mm. The maximum subsidence at the simulated gas well position was 43.68 mm, and the absolute displacement was 94.47 mm. The deformation and movement of the overlying strata caused by coal seam mining led to the interaction between the surrounding rock and the concrete composite structure of the gas well shaft, resulting in changes in the stress on the concrete composite structure of the gas well shaft, and thus causing shear, tensile, compressive, and torsional deformations under the combined action of shear, tensile, or compressive deformations in the concrete composite structure of the gas well shaft.

[0034] According to the above situation, the combined surface and underground protection method protected by the present invention was adopted to reduce the damage of the overlying strata movement after coal seam mining to the oil and gas well complex, so as to ensure the safe mining of the working face and the safety of the oil and gas wells. As Figure 1 shown, the specific process is as follows:

[0035] S1. Investigate and predict the goaf formed after the coal seam working face is mined to determine the construction positions underground and on the surface;

[0036] Surface position: Located in the southeast direction of the No. 1 air shaft site. After ground investigation, there were 2 village access cement roads and 3 high-voltage lines near the corresponding surface of the 132201 working face. There were 8 oil and gas wells about 2560 m away from the auxiliary withdrawal roadway, and the other main landforms were fixed sand dunes and semi-fixed sand dunes.

[0037] Underground position: The 112208 working face that has been mined was in the west, the 132202 working face that has not been driven was in the east, the 13th panel development main roadway was in the north, and there were three oil and gas wells in the south. The protective coal pillar for the oil and gas wells was 200 m. The designed driving azimuth angle of the entry was 136°4'21".

[0038] Stratum:

[0039] The belt conveyor entry of the 132201 fully mechanized coal mining working face was designed in 2 -2In the coal seam, according to the nearby exploration boreholes, this coal seam occurs at the top of the fourth member of the Yan'an Formation, with a buried depth of 272 - 340 m, a coal thickness of 4.3 - 5.86 m, and an average coal thickness of 5.1 m. The strata of the working face from old to new are successively: Middle Jurassic Yan'an Formation (J2y), Middle Jurassic Zhiluo Formation (J2z), Middle Jurassic Anding Formation (J2a), Neogene Pliocene Baode Formation (N2b). The borehole cross-sectional view of the 132201 working face is as Figure 2 shown.

[0040] Coal seam:

[0041] The gateway of the 132201 working face is designed in the 2 -2 coal seam. This coal seam occurs at the top of the fourth member of the Yan'an Formation and is the thickest main workable coal seam in the well area. The buried depth is 272 - 340 m, and the elevation of the coal seam floor is 950 - 988 m; the coal thickness is 4.3 - 5.86 m, with an average coal thickness of 5.08 m, mainly thick coal seams; the coal seam gradually thickens from north to south.

[0042] The conditions of the roof and floor of the coal seam are shown in Table 1 below:

[0043] Table 1 Statistics of the roof and floor conditions of the coal seam

[0044]

[0045]

[0046] S2. Underground protection:

[0047] The hydraulic fracturing technology can effectively control the caving of the working face roof, weaken the integrity of the roof to the greatest extent, and make the working face roof collapse in layers in a timely manner. By using the fracturing technology, the disturbance of the surrounding rock layers of the oil and gas wells in the well field of the Shuang 3 - 24 gas well during the coal mining of the working face is cut off, ensuring the safety of the oil and gas wells, and thus ensuring the safety of the coal mining of the working face.

[0048] According to the analysis of surface movement and deformation monitoring, the caving rock movement angle of the working face is 75 - 68°. By constructing vertical boreholes, the integrity of the roof is weakened to the greatest extent, the stress distribution of the roof is changed, and the caving range of the working face roof towards the direction of the oil and gas wells is cut off.

[0049] The scope of this hydraulic fracturing is as follows: According to the determination of the advanced influence angle in the Research Report on the Surface Movement Law of the 112201 Working Face in No. 1 Coal Mine of Shaanxi Xiaobaodang Mining Co., Ltd., the advanced influence angle is 60.1°. For safety reasons, the advanced influence angle is determined to be 45° this time. Therefore, the advanced influence distance is determined to be 300 m. After the working face passes through the 3-24 gas well site, a safety distance of 100 m is reserved. The fracturing distance this time is 475 m, and the construction sequence is to construct successively from the cutting-eye direction to the mining direction. Starting position: 120 m in front of the JS16 measuring point in the belt conveyor gateway of the 132201 working face (mining direction), ending position: 74 m behind the JS13 measuring point in the belt conveyor gateway of the 132201 working face (cutting-eye direction).

[0050] Table 2 Advanced influence angle

[0051]

[0052] Determination of the borehole spacing: According to the construction experience of hydraulic fracturing in No. 1 Coal Mine, when the borehole spacing is 10 m, the fracturing effect can reach the best. Therefore, the borehole spacing is determined to be 10 m this time.

[0053] Determination of the borehole depth: To ensure the fracturing effect and the safe mining of the working face, the final position of the borehole this time is the floor of the 1-1 coal seam.

[0054] Engineering quantity: Borehole footage: 75 m × 47 = 3525 m.

[0055] During the drilling process, the opening position of the borehole should be selected as far as possible in the relatively intact section of the coal and rock mass, and the borehole is drilled to the final hole with a bare hole.

[0056] Drill rig setting and angle adjustment (giving the construction borehole angle): Given according to the designed azimuth angle and dip angle. Use a slope gauge to adjust the dip angle, and use the trigonometric function calculation distance method to adjust the azimuth angle and verify it with a compass.

[0057] Then use a composite bit to drill. When encountering hard rock strata, use an artificial diamond-impregnated bit to drill, and use clear water as the flushing fluid. The process parameters are as follows: When using an artificial diamond-impregnated bit to drill in hard rock strata, the rotation speed is 150 - 200 rpm, the pressure is 900 - 1000 kg, and the flushing fluid volume is 50 L / min;

[0058] For other rock strata, use a diamond composite bit to drill, the rotation speed is 150 - 200 rpm, the pressure is 500 - 550 kg, and the flushing fluid volume is 50 L / min.

[0059] Ensure that the axis of the drilled hole is approximately a straight line. It is required to minimize the drilling speed during drilling, reduce the feeding force of the drilling rig, and ensure the straightness of the drilled hole. Then connect the high-pressure pump to implement fracturing. The static water continuously enters the packer section through the high-pressure pump via the water injection pipeline. After the fracture is initiated, control the water pressure drop and enter the pressure-maintaining water injection stage. After completing the fracturing of the first section, drain the water in the drilled hole through the water injection pipe to relieve the pressure. After all the water in the drilled hole is drained, relieve the pressure of the packer and gradually withdraw the packer from the hole for the fracturing of the next section. Among them, a 3m retreat of the packer is one section of fracturing. After the fracturing is completed, first drain the water in the drilled hole through the water injection pipe. The water drainage time in the drilled hole is 1.5 - 2 times the fracturing time. Do not relieve the pressure of the packer until the water drainage is complete. It is strictly prohibited to relieve the pressure of the packer before the water drainage is complete.

[0060] Before fracturing, check the gas concentration and toxic and harmful gases around the operation point to ensure safety before construction. Before fracturing, set up a warning line and check the sealing condition of the joint part to ensure that there is no mistake before starting fracturing. During fracturing, it is strictly prohibited for personnel to pass in front of the high-pressure fracturing pipe to prevent injury in case of high-pressure pipe rupture.

[0061] After fracturing is completed, when the working face is near the fractured section, assign special personnel to monitor the deformation of the roadway. If there are any abnormalities in the roadway, immediately report to the mine and take temporary support measures.

[0062] S3. Above-ground protection: In the tension range of the loose soil mass on the ground, construct ground protection line drill holes, insert casing, and carry out split grouting with cement slurry, and arrange a protection wall parallel to the oil well. Specifically:

[0063] For the positioning measurement of this drill hole, the 2000 National Geodetic Coordinate System is adopted. The elevation measurement accuracy should reach above the fourth-class leveling accuracy and be implemented in accordance with the relevant requirements in the "National Leveling Survey Specifications for the Third and Fourth Classes" (GB / T 12898 - 2009).

[0064] Determine that the final hole layer of the drill hole is 10m into the bedrock section. For the first stage of the drill hole, drill a hole with a diameter of Φ480mm, insert a casing of Φ377mm×8mm×10m, and use M30 cement to fix the pipe. For the second stage of the drill hole, drill a hole with a diameter of Φ300mm, insert an internal steel pipe of Φ180mm×8mm×70m (inject grouting perforated pipe with a wall thickness of 6mm at the bottom 6m), and inject M30 cement mortar for split grouting to reinforce the formation.

[0065] Attention should be paid to the following during this process:

[0066] 1) Before lowering the casing: weld 3-5 sets of straightening plates at the port, and cut a set of Φ100-150mm round holes at a position 700mm away from the port as the crossbeam perforations for lowering the casing; if the weight of the casing exceeds the load of the derrick, a buoyancy plug must be loaded at a certain position, and the specific position is determined according to the actual situation on site. Before lowering the casing, the hole must be re-marked and the mud performance parameters must be kept within a reasonable range to ensure that the wellbore is stable, leak-free, and does not collapse. And carry out a large cycle of no less than 3 weeks to ensure that the hole is clean and that the casing is smoothly lowered to the predetermined position. The base must be stable and reliable. Check the lifting system, large rope and power machine of the drilling rig. The weight of the working casing is more than 46 tons, and it is necessary to install support hoops and tilting to ensure the safety of the lowering pipe.

[0067] 2) The turntable base must be level when lowering the casing, and the casing seat must be processed if necessary. Gas shielded welding is used for casing welding to ensure welding quality. The welding of the welds must be meticulous and strictly implemented in accordance with the standards when lowering the casing. Ensure that the inner wall is smooth and there is no water leakage. The lowering speed must be controlled to reduce pressure excitement. Prevent objects from falling into the casing, and fill the mud in time to keep the casing lowered smoothly.

[0068] The last casing is welded with a steel cap and connected to the cementing equipment to make the cementing pipeline connection work. Use M30 cement mortar to grout the entire hole, extract the slurry sample, and check and preserve it. When injecting cement, maintain the accuracy of cement slurry measurement and the continuity of cement slurry column to prevent cross-channel. When replacing slurry, accurate measurement is required. It is necessary to ensure that the cement returns to the predetermined height, and to prevent empty replacement. After the replacement of slurry is completed, close the gate and return water. If it is found that the gate is not closed tightly and there is backwater dripping, add a plug to seal it, close the well and wait for solidification. When the cement slurry does not return to the wellhead, use the reinjection method to inject cement slurry.

[0069] After the construction was completed, after observing the displacement and stress monitoring results of the surface and underground of the control line, it was concluded that the overall trend of the strain of the inner and outer casings of the double 3-24 simulated gas well was consistent with the initial monitoring period, and the strain caused by the stress of the inner and outer casings did not undergo abnormal mutations. At the same time, the overall change trend of the strain value gradually stabilized with the mining of the working face. The mining of the 132201 working face of the No. 1 Coal Mine did not have a destructive effect on the double 3-24 simulated gas well, thereby ensuring the safe mining of the working face and the safety of the oil and gas wells. It shows that hydraulic fracturing technology can effectively control the collapse of the working face roof, minimize the integrity of the roof, and make the working face roof collapse in layers in a timely manner. A "protective wall" is formed on one side of the oil and gas well, which effectively reduces the shear and tensile effects of surface movement on the oil and gas well assembly during the mining of the working face.

[0070] Therefore, for the joint protection method of oil and gas wells above and below ground near the gob area of the present invention, by constructing vertical boreholes underground, the integrity of the roof is weakened to the greatest extent, the stress distribution of the roof is changed, the caving range of the working face roof towards the oil and gas wells is cut off, and a "protection wall" is formed on one side above the oil and gas wells on the ground, effectively reducing the shear and tensile effects on the oil and gas well assembly caused by surface movement during the coal mining process of the working face; through the joint protection above and below ground, the gob collapse settlement range is effectively reduced, and the stress propagation of the loose layer is blocked to achieve the purpose of reducing the impact on the oil and gas wells, so as to meet the protection and treatment requirements of the oil and gas wells. Compared with the method of leaving coal pillars, it belongs to an active protection method.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A combined protection method for oil and gas wells above and below ground near a goaf, characterized in that, It includes the following steps: S1. Conduct an investigation and prediction on the gob area formed after the coal seam working face is mined, determine the ground position and underground position of the working face, determine the stratigraphic composition of the coal seam working face based on the exploration holes near the working face, obtain the rock thickness and lithological characteristics of the roof and floor of the coal seam working face, and determine the construction positions underground and above ground; S2. In underground protection, reserve the safety distance for oil and gas wells and boreholes in the working face, determine the borehole positions, ensure that the axis of the completed borehole is an approximate straight line, and then carry out hydraulic fracturing. The specific steps are as follows: S21. According to the construction positions obtained in S1, determine the advanced influence angle and advanced influence distance, then reserve the safety distance, and determine the construction sequence; S22. According to the specific composition of the working face, determine the borehole spacing, borehole depth and borehole angle. During the borehole drilling process, select the relatively intact section of the coal and rock mass to open the borehole. Given the borehole angle according to the designed azimuth angle and dip angle, adjust the dip angle with a slope gauge, adjust the azimuth angle by the trigonometric function calculation distance method and verify it with a compass; S23. Carry out borehole drilling, ensure that the axis of the completed borehole is an approximate straight line, reduce the drilling speed during the drilling process, reduce the feed force of the drill rig, and ensure the straightness of the borehole; after drilling and forming the hole, use the drill rig to gradually send the packer to the bottom of the hole through the water injection drill pipe to implement fracturing. During the fracturing process, connect the high-pressure pump to implement fracturing. The static water continuously enters the packer section through the high-pressure pump via the water injection pipeline. After the fracture starts to form, control the water pressure to drop and enter the pressure-holding water injection stage. After completing the fracturing of the first section, drain the water in the borehole through the water injection pipe to relieve the pressure. After all the water in the borehole is drained, relieve the pressure of the packer and gradually withdraw the packer from the hole to carry out the fracturing of the next section; among them, the packer retreats 3m for one section of fracturing; the fracturing time for each section is 20min - 30min, and the pressure is stable at 30Mpa; After the fracturing is completed, first drain the water in the borehole through the water injection pipe. The borehole drainage time is 1.5 - 2 times the fracturing time. After the drainage is complete, relieve the pressure of the packer; S3. In above-ground protection, within the tensile range of the loose soil mass on the ground, construct boreholes along the ground protection line, insert casing, and carry out split grouting with cement slurry, and arrange a protection wall parallel to the oil well. Specifically: According to the construction positions obtained in S1, determine the final borehole layer and the number of boreholes. The borehole drilling process is divided into two stages. Specifically: The first stage: Use a drill bit to drill a hole according to the first hole diameter, insert the casing, and fix the casing with M30 cement. Weld a centralizer at the front end before inserting the casing, and cut a set of crossbeam perforations in alignment near the port position; if the weight of the casing exceeds the load of the derrick, load a float collar, and the specific position is determined according to the actual situation on site; before inserting the casing, it is necessary to ream the hole to explore the hole; The second stage: Drill a hole according to a second hole diameter smaller than the first hole diameter, lower an inner steel pipe, inject M30 cement mortar for splitting grouting to reinforce the formation. When injecting cement, ensure the accuracy of the cement slurry measurement and the continuity of the cement slurry column to prevent channeling. When displacing the slurry, require accurate measurement. After the displacement of the slurry is completed, close the gate valve, release the water. If it is found that the gate valve cannot be closed tightly and there is water dripping back, add a plug for sealing, close the well and wait for setting. When the cement slurry does not return to the wellhead, use the re-injection method to inject the cement slurry; During the drilling process described above, weld a steel cover to the last casing and connect it to the cementing equipment.

2. The joint protection method for oil and gas wells above and below the ground near a gob area according to claim 1, characterized in that: In S23 described above, use a composite bit of a synthetic diamond-impregnated bit and a polycrystalline diamond compact bit to complete the drilling, and the flushing fluid is clean water; Among them, for hard rock formations, use a synthetic diamond-impregnated bit for drilling, with a rotational speed of 150 - 200 rpm, a pressure of 900 - 1000 kg, and a flushing fluid volume of 50 L / min; For other rock formations, use a polycrystalline diamond compact bit for drilling, with a rotational speed of 150 - 200 rpm, a pressure of 500 - 550 kg, and a flushing fluid volume of 50 L / min.

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