Over-well and under-well combined protection method for oil and gas well near goaf

Abstract

The invention discloses a ground and underground combined protection method for an oil and gas well near a goaf, belongs to the technical field of coal mining, and aims to investigate and predict the goaf formed after mining of a coal seam working face, determine underground and ground construction positions, and then respectively perform underground and ground combined protection. According to the method, vertical drill holes are constructed underground, the integrity of a top plate is weakened to the maximum extent, the stress distribution of the top plate is changed, the caving range of the working face top plate in the oil-gas well direction is cut off, a'protective wall 'is formed on one side above the oil-gas well, and the shearing and stretching effects of earth surface movement on an oil-gas well assembly in the working face recovery process are effectively reduced; through the combined protection above and below the well, the collapse and settlement range of the goaf is effectively reduced, the stress propagation of the unconsolidated formation is cut off to achieve the purpose of reducing the influence on the oil-gas well, and the protection and treatment requirements of the oil-gas well are met.

Description

Technical Field

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

[0002] Coal seam mining in the overlapping area of ​​coal gas resources causes the overlying rock to collapse and deform, forming a dynamic moving subsidence basin on the surface, which leads to deformation and damage of oil and gas wells within the influence range of the subsidence basin, causing casualties and production safety accidents. Therefore, it is very important to develop protective management technologies suitable for protecting oil and gas wells in overlapping areas.

[0003] At present, the conventional treatment method is to leave a coal pillar of a certain size for oil and gas wells to protect them, so as to maintain the stability of oil and gas wells. However, the leaving of coal pillars will cause a large waste of resources. In the design process of this method, the parameters determined are the movement angles of the loose layer and the bedrock. The determination of this parameter is often based on experience. In view of the complexity of underground geological conditions, the final movement angle is quite different from the actual situation. In the actual treatment process, the parameters are determined conservatively for safety reasons. Therefore, the size of the coal pillars finally determined is relatively large, which will cause serious waste of resources. At the same time, the method of leaving coal pillars is also a passive protection method. This conventional protection method cannot reduce the area of ​​ground subsidence, and cannot take into account the requirements of full resource exploitation and oil and gas well safety. Summary of the invention

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

[0005] To achieve the above object, the present invention provides a method for combined protection of oil and gas wells above and below the wellbore near the goaf, comprising the following steps:

[0006] S1. Investigate and predict the goaf area formed after the coal seam working face is mined, and determine the construction locations underground and above the well;

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

[0008] S3. In the well protection, within the tensile range of the loose soil on the ground, drilling is carried out through the ground protection line, casing is lowered, splitting and cement slurry is injected, and a protection wall is arranged parallel to the oil well.

[0009] Preferably, in S1, the ground position and underground position of the working face are determined, and the stratigraphic composition of the coal seam working face is determined based on the exploration holes near the working face, and the rock thickness and lithology characteristics of the roof and floor of the coal seam working face are obtained.

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

[0011] S21, according to the construction position obtained in S1, determine the leading influence angle and the leading influence distance, 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 surface;

[0013] S23, drilling is performed, during which the drilling speed is reduced as much as possible, the feed force of the drilling rig is reduced, and the linearity of the borehole is ensured; after the hole is drilled, the sealing device is gradually sent to the bottom of the hole through the water injection drill pipe by the drilling rig to implement fracturing.

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

[0015] Among them, the hard rock layer is drilled with an artificial diamond drill bit, with a rotation speed of 150-200rpm, a pressure of 900-1000kg, and a flushing fluid volume of 50L / min;

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

[0017] Preferably, hydraulic fracturing adopts the reverse fracturing method, that is, fracturing is performed successively from the bottom of the borehole to the hole mouth. During the fracturing process, a high-pressure pump is connected to implement fracturing, and static water continuously enters the isolation section through the high-pressure pump through the water injection pipeline. After the fracture is initiated, the water pressure is controlled to drop and the pressure-maintaining water injection stage is entered. After the first stage of fracturing is completed, water is drained from the borehole through the water injection pipe to relieve the pressure. After all the water in the borehole is drained, the sealer is depressurized and the sealer is gradually withdrawn from the hole to carry out the next stage of fracturing; wherein the sealer is retreated 3m for one stage of fracturing.

[0018] Preferably, during the fracturing process, each fracturing time is 20 min to 30 min, the pressure is stabilized at 30 MPa, and the drilling water release time is 1.5 to 2 times the fracturing time.

[0019] Preferably, in S3, the final hole layer and the number of holes to be drilled are determined according to the construction position obtained in S1, and the drilling process is divided into two stages, specifically:

[0020] Phase 1: Use a drill bit to drill a hole according to the first hole diameter, insert the casing, and fix the casing with M30 cement;

[0021] The second stage: drill a second hole with a smaller diameter than the first hole, lower an internal steel pipe, and inject M30 cement mortar for splitting grouting to reinforce the stratum.

[0022] Preferably, during the drilling process, a straightening piece is welded at the front end before lowering the casing, and a group of crossbeam holes are cut and perforated at a certain distance from the port; a steel cover is welded to the last casing and connected to the cementing equipment.

[0023] Therefore, the above-ground and underground combined protection method of oil and gas wells near the 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 collapse range, and is suitable for the overlapping areas of coal and oil resources. It can protect the oil and gas wells in the tension zone in the surface collapse area, avoid the losses caused by the damage to the oil and gas wells during the coal seam mining process, and successfully solve the waste caused by leaving coal pillars. It can fully mine the coal seams in the overlapping areas of coal and oil, bringing greater economic benefits to the coal mine. In addition, the method is simple to construct and can quickly achieve the purpose of protecting oil and gas wells. It has important application value and promotion value.

[0025] (2) In the present invention, vertical drilling is carried out underground to weaken the integrity of the roof to the greatest extent, change the stress distribution of the roof, cut off the collapse range of the working face roof toward the oil and gas wells, and form a "protective wall" on the upper side of the oil and gas wells, effectively reducing the shear and tensile effects of surface movement on the oil and gas well assembly during the recovery process of the working face; there is no need to determine the movement angle of the loose layer and the bedrock, and through the combined protection of the well and underground, the scope of the mining 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 wells, so as to meet the protection and management requirements of the oil and gas wells. Compared with the method of leaving coal pillars, this method is a method of active protection.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0028] Figure 2 This is a cross-sectional view of a working surface drilling according to an embodiment of the present invention. DETAILED DESCRIPTION

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

[0030] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0031] Example

[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 has been mined to 1920m as of July 12. The working face is 1248m away from the 8 natural gas wells in the Shuang 3-24 well field of the Gas Production Plant No. 2. The 8 natural gas wells in the Shuang 3-24 well field are located in the 132202 working face, 127m away from the rubber transport chute of the 132201 working face, 2633m away from the withdrawal channel, and the protective coal pillar of the oil and gas wells is 200m.

[0033] According to the monitoring situation, the surface movement displacement at the center of the 132201 working face is the largest, with an absolute displacement of 902.24mm and a maximum settlement of 2613.38mm. The maximum settlement at the simulated gas well position is 43.68mm, with an absolute displacement of 94.47mm. The deformation and movement of the overburden during coal seam mining causes the surrounding rock to interact with the gas well shaft concrete composite structure, and the stress on the gas well shaft concrete composite structure changes, causing the gas well shaft concrete composite structure to experience shear, tension, compression, and distortion deformation under the combined action of shear, tension or compression deformation.

[0034] According to the above situation, the above-ground and underground combined protection method of the present invention is adopted to reduce the damage of the overburden movement to the oil and gas well assembly after coal seam mining, thereby ensuring the safe recovery of the working face and the safety of the oil and gas well. Figure 1 As shown, the specific process is as follows:

[0035] S1. Investigate and predict the goaf area formed after the coal seam working face is mined, and determine the construction locations underground and above the well;

[0036] Ground location: Located southeast of No. 1 wind well site. According to ground survey, the 132201 working face corresponds to the surface, with 2 village cement roads and 3 high-voltage lines. There are 8 oil and gas wells about 2560 meters away from the auxiliary withdrawal channel, and other major landforms are fixed sand dunes and semi-fixed sand dunes.

[0037] Underground location: The west is the mined 112208 working face, the east is the unexplored 132202 working face, the north is the 13th panel development tunnel, the south is three oil and gas wells, and the oil and gas well protection coal pillar is 200m. The designed excavation azimuth of the drift is 136°4'21".

[0038] Strata:

[0039] 132201 Comprehensive Mining Face Tunnel Design in 2 -2According to the nearby exploration holes, the coal seam is located at the top of the fourth section of the Yan'an Formation, with a burial depth of 272 to 340 meters, a coal thickness of 4.3 to 5.86 meters, and an average coal thickness of 5.1 meters. The strata of the working face are from old to new: the Yan'an Formation of the Middle Jurassic (J2y), the Zhiluo Formation of the Middle Jurassic (J2z), the Anding Formation of the Middle Jurassic (J2a), and the Baode Formation of the Upper Pliocene (N2b). The drilling section of the 132201 working face is shown in the figure below. Figure 2 shown.

[0040] Coal seam:

[0041] 132201 working face drift design in 2 -2 Among the coal seams, this coal seam is located at the top of the fourth section of the Yan'an Formation and is the thickest and main exploitable coal seam in the well area. The burial depth is 272-340m, and the elevation of the coal seam floor is 950-988m; the coal thickness is 4.3-5.86m, with an average coal thickness of 5.08m, and the coal seam is mainly thick; the coal seam gradually thickens from north to south.

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

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

[0044]

[0045]

[0046] S2. Underground protection:

[0047] Hydraulic fracturing technology can effectively control the collapse 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. The fracturing technology is used to cut off the disturbance of the rock formations around the oil and gas wells in the Shuang 3-24 gas well field during the recovery of the working face, ensuring the safety of the oil and gas wells, thereby ensuring the safety of the recovery of the working face.

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

[0049] The scope of this hydraulic fracturing is: According to the "Research Report on the Surface Movement Law of the 112201 Working Face of the No. 1 Coal Mine of Shaanxi Xiaobaodang Mining Co., Ltd.", the leading influence angle is determined to be 60.1°. In order to ensure safety, the leading influence angle is determined to be 45°, so the leading influence distance is determined to be 300m. The working face is left with a safety distance of 100m after passing the 3-24 gas well site. The fracturing distance is 475 meters. The construction sequence is from the cutting direction to the mining direction. Starting position: 120m before the JS16 measuring point of the 132201 working face rubber transport chute (mining direction), and the end position: 74m after the JS13 measuring point of the 132201 working face rubber transport chute (cutting direction).

[0050] Table 2 Leading influence angle

[0051]

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

[0053] Determination of drilling hole depth: In order to ensure the fracturing effect and safe recovery of the working face, the final hole position of this drilling is 1-1 coal bottom plate.

[0054] Project quantity: Drilling footage: 75m×47=3525m.

[0055] During the drilling process, the drilling location should be selected in a relatively complete section of the coal rock mass. The open hole is drilled to the final hole.

[0056] Drilling machine setting and angle adjustment (construction drilling angle setting): according to the designed azimuth and depression angle. Use the slope gauge to adjust the depression angle, use the trigonometric function to calculate the distance method to adjust the azimuth angle and use the compass to check.

[0057] Then use a composite drill bit to drill, and use a man-made diamond drill bit to drill hard rock formations, and use clean water as the flushing fluid. The process parameters are: use a man-made diamond drill bit to drill hard rock formations, the speed is 150-200rpm, the pressure is 900-1000kg, and the flushing fluid volume is 50L / min;

[0058] Diamond composite drill bits are used to drill other rock formations, with a rotation speed of 150-200rpm, a pressure of 500-550kg, and a flushing fluid volume of 50L / min.

[0059] To ensure that the axis of the completed borehole is an approximate straight line, it is required to reduce the drilling speed as much as possible during the drilling process, reduce the feed force of the drilling rig, and ensure the linearity of the borehole; then connect the high-pressure pump to implement fracturing, and the static pressure water will continuously enter the isolation section through the high-pressure pump through the water injection pipeline. After the fracturing is initiated, the water pressure is controlled to drop and the pressure-maintaining water injection stage is entered. After the first stage of fracturing is completed, the borehole is drained through the water injection pipe to release the pressure. After all the water in the borehole is released, the sealer is depressurized and the sealer is gradually withdrawn from the hole to carry out the next stage of fracturing; the sealer retreats 3m for one stage of fracturing. After the fracturing is completed, the borehole is drained through the water injection pipe first. The borehole drainage time is 1.5-2 times the fracturing time. The sealer can be depressurized only after the water is completely drained. It is strictly forbidden to depressurize the sealer before the water is completely drained.

[0060] Before fracturing, check the gas concentration and toxic and harmful gases around the work point to ensure safety before construction; before fracturing, draw a cordon and check the sealing of the joints to ensure that there is no problem before starting fracturing; during the fracturing process, it is strictly forbidden for people to pass in front of the fracturing high-pressure pipe to prevent the high-pressure pipe from rupturing and injuring people.

[0061] After fracturing is completed, a special person is assigned to monitor the deformation of the tunnel when the working face approaches the fracturing section. If there is any abnormality in the tunnel, it will be reported to the mine immediately and temporary support measures will be taken.

[0062] S3. Well protection: within the tensile range of the loose soil on the ground, drill holes through the ground protection line, insert casing, split and inject cement slurry, and arrange a protection wall parallel to the oil well. Specifically:

[0063] The drilling positioning measurement adopts the National Geodetic Coordinate System 2000. The elevation measurement accuracy should reach the fourth-class leveling accuracy or above, and should be carried out in accordance with the relevant requirements of the National Third and Fourth Class Leveling Specifications (GB / T12898-2009).

[0064] The final hole position of the drilling was determined to be 10m into the bedrock section. The first drilling hole was drilled with a Φ480mm diameter, and a Φ377mm×8mm×10m casing was inserted, and the pipe was fixed with M30 cement; the second drilling hole was drilled with a Φ300mm diameter, and a Φ180mm×8mm×70m internal steel pipe (grouting flower pipe 6m below the bottom, with a wall thickness of 6mm) was inserted, and M30 cement mortar was injected for splitting and grouting to reinforce the stratum.

[0065] Things to note 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, the present invention provides a combined above- and underground protection method for oil and gas wells near the goaf. By constructing vertical drilling holes underground, the integrity of the roof is weakened to the greatest extent, the stress distribution of the roof is changed, and the collapse range of the working face roof toward the oil and gas wells is cut off. A "protective wall" is formed on the upper 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 recovery of the working face. Through combined above- and underground protection, the scope of goaf collapse and settlement is effectively reduced, and the propagation of stress in the loose layer is cut off to achieve the purpose of reducing the impact on the oil and gas wells, so as to meet the protection and management requirements of the oil and gas wells. Compared with the method of leaving coal pillars, this is a method of active protection.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A combined protection method for oil and gas wells above and below the wellbore near the goaf, characterized in that: The following steps are involved: S1. Investigate and predict the goaf area formed after the coal seam working face is mined, and determine the construction locations underground and above the well; S2. In underground protection, reserve a safe distance between the oil and gas wells and the borehole in the working face, determine the location of the borehole, ensure that the axis of the completed borehole is an approximate straight line, and then carry out hydraulic fracturing; S3. In the well protection, within the tensile range of the loose soil on the ground, drilling is carried out through the ground protection line, casing is lowered, splitting and cement slurry is injected, and a protection wall is arranged parallel to the oil well.

2. The method for combined protection of oil and gas wells above and below the wellbore near the goaf according to claim 1, characterized in that: In S1, the ground position and underground position of the working face are determined, and the stratigraphic composition of the coal seam working face is determined based on the exploration holes near the working face, and the rock thickness and lithology characteristics of the roof and floor of the coal seam working face are obtained.

3. The method for combined protection of oil and gas wells above and below the wellbore near the goaf according to claim 1 is characterized by: The specific steps of S2 are: S21, according to the construction position obtained in S1, determine the leading influence angle and the leading influence distance, then reserve a safety distance and determine the construction sequence; S22. Determine the drilling spacing, drilling depth and drilling angle according to the specific composition of the working surface; S23, drilling is performed, and after the hole is formed, a hole sealer is gradually sent into the bottom of the hole through a water-injected drill pipe using a drilling rig to implement fracturing.

4. The method for combined protection of oil and gas wells above and below the wellbore near the goaf according to claim 3 is characterized by: In S23, a composite drill bit of an artificial diamond drill bit and a diamond composite drill bit is used to complete drilling, and the flushing fluid is clean water; Among them, the hard rock layer is drilled with an artificial diamond drill bit, with a rotation speed of 150-200rpm, a pressure of 900-1000kg, and a flushing fluid volume of 50L / min; Diamond composite drill bits are used to drill other rock formations, with a rotation speed of 150-200rpm, a pressure of 500-550kg, and a flushing fluid volume of 50L / min.

5. The method for combined protection of oil and gas wells above and below the wellbore near the goaf according to claim 4 is characterized by: During the fracturing process, a high-pressure pump is connected to carry out fracturing, and static water continuously enters the isolation section through the high-pressure pump via the water injection pipeline. After the fracture is initiated, the water pressure is controlled to drop and the pressure-maintaining water injection stage is entered. After the first stage of fracturing is completed, water is released from the borehole through the water injection pipe to relieve the pressure. After all the water in the borehole is released, the sealer is relieved of pressure and the sealer is gradually withdrawn from the hole to carry out the next stage of fracturing; wherein the sealer is retreated 3m for one stage of fracturing.

6. The method for combined protection of oil and gas wells above and below the wellbore near the goaf according to claim 5 is characterized by: During the fracturing process, each fracturing period lasts for 20 to 30 minutes, the pressure is stabilized at 30 MPa, and the drilling and water release time is 1.5 to 2 times the fracturing time.

7. The method for combined protection of oil and gas wells above and below the wellbore near the goaf according to claim 6, characterized in that: In S3, according to the construction position obtained in S1, the final hole layer and the number of holes to be drilled are determined. The drilling process is divided into two stages, specifically: Phase 1: Use a drill bit to drill a hole according to the first hole diameter, insert the casing, and fix the casing with M30 cement; The second stage: drill a second hole with a smaller diameter than the first hole, lower an internal steel pipe, and inject M30 cement mortar for splitting grouting to reinforce the stratum.

8. The method for combined protection of oil and gas wells above and below the wellbore near the goaf according to claim 7, characterized in that: During the drilling process, a straightening piece is welded at the front end before the casing is lowered, and a group of crossbeam holes are cut to align near the port position; a steel cover is welded to the last casing and connected to the cementing equipment.

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