A cementing technology method suitable for casing removal in oil layer

Abstract

The present invention provides a cementing technology method suitable for casing removal in oil-bearing layers, which relates to the technical field of oil extraction. The cementing technology method suitable for casing removal in oil-bearing layers comprises the following steps: Step 1: weighting and maintaining the well repair fluid in the oil-bearing layer, using SPNH-1 and NPAN glue for long-term maintenance before weighting, and using 1.8g / cm 3 The workover fluid is circulated and weighted, and SPNH-1 and NPAN glue are used for maintenance after weighting. During the drilling of the whole well, DJ-C is used to adjust the viscosity and cutting force to maintain the performance of the workover fluid. Step 2: Wellbore cleaning and cementing preparation, oil layer casing is installed with plugs, casing milling barrel is lifted 1.5m, and 1.7m is used. 3 Circulate the workover fluid at a rate of more than 100 / min for 2 to 3 weeks to flush the wellbore wall and mud cake for cementing. This method of replacing casing in the oil layer provides a technical means to effectively achieve interlayer separation, support casing, protect casing, and protect the oil layer, thereby overcoming problems such as substandard cementing quality and interlayer channeling, which can lead to oil layer and environmental pollution.

Description

Technical Field

[0001] The invention relates to the technical field of oil extraction, in particular to a well cementing method suitable for casing removal in oil layers. Background Art

[0002] Oil extraction involves the excavation of deeply buried fluid minerals for use in industrial production and daily life, providing energy and convenience for people. Oil and gas drive is a common method of oil extraction, encompassing five key components: water-driven reservoir flooding, dissolved gas drive, elastic water drive, gas cap drive, and gravity drive. Through advanced technology and manual intervention, underground oil is lifted and, through a series of filtration and separation processes, ultimately converted into a valuable energy source.

[0003] At present, as the Daqing Oilfield enters the late stage of development, the number of casing damage in oil and water wells is increasing, accounting for more than 50% of all casing damage wells. However, in cementing wells after casing removal from the oil layer, there are problems of low displacement efficiency and poor cementing quality. When cementing conventional wells into the oil layer, they are limited by conventional cementing technology, and their displacement is small and cannot form flocculence, resulting in small gap annulus, low cement slurry displacement efficiency, and poor cementing quality. When cementing inclined wells, they are limited by the well inclination rate. On the one hand, conventional tubing is difficult to reach the effective cementing depth. On the other hand, they are limited by the process, with low displacement efficiency and poor cementing quality. When cementing shallow formations, due to sparse formation porosity, large wellbore and small displacement, cement slurry is highly fluid, with low effective occupancy and poor cementing quality. When cementing any well section, previous technical methods made it difficult to achieve arbitrary position occupancy due to the cement slurry's gravity drop. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a cementing technology method suitable for entering the oil layer and removing the casing, which solves the problems of unqualified cementing quality and interlayer channeling, which in turn lead to oil layer pollution and environmental pollution.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A cementing technology method suitable for casing removal in an oil layer, comprising the following steps:

[0006] Step 1: Add weight to the workover fluid before entering the oil layer. Before adding weight, use SPNH-1 and NPAN glue for long-term maintenance. By using 1.8g / cm 3 The workover fluid is circulated and weighted, and then maintained with SPNH-1 and NPAN glue. During the whole well drilling, DJ-C is used to adjust the viscosity and cutting force to maintain the performance of the workover fluid.

[0007] Step 2: Borehole cleaning and cementing preparation, oil layer casing installation plug sleeve milling barrel lift 1.5m, to 1.7m 3 Circulate the workover fluid at a rate of more than / min for 2 to 3 weeks to flush the well wall and mud cake for cementing;

[0008] Step 3: When the well type is an inclined well with an inclination of ≥10°, the cementing method of replacing the lead seal connector is adopted. Specifically, the following steps are taken: check the downhole tool, lower it into the well after it passes the inspection, and when it reaches the top of the drop fish, slowly rotate it forward while slowly lowering it so that the drop fish enters the tool and hits the O-ring. Observe the weight gauge and make the tool withstand a pressure of 7 to 9 tons. Slightly lift the downhole string to make the tool at the neutral point to eliminate the elastic resistance of the downhole string. Lift the downhole string again, compress the lead seal, start the pump for pressure test, and reduce the set load to one-fourth of the original load. The test pressure is 35×10 4 Pa~70×10 4 After the pressure test is passed, the pipe string is slowly lowered to make the joint withstand a pressure of 7 to 9 tons. Cement slurry is injected to reach the required return height. The drilling and milling pipe string is lowered to drill out excess cement and bridge plugs. The casing scraper is then lowered to remove cement residue stuck on the casing. The reverse circulation salvage basket is lowered to pick up small debris that has fallen on the bottom of the well.

[0009] Alternatively, when the shallow strata are sparsely porous and there is a risk of surface water intrusion, the cementing method of replacing the cement surface controller is adopted. The cement is lowered into the well along with the casing string and the buckling construction is carried out. The workover fluid is pumped using a pump truck. The pressure is held at 16 MPa to open the tool circulation hole. 5.0 m3 of positive circulation is injected. 3 Then, water with a density of 1.85-1.95 g / cm 3 Cement slurry, adding retarder to the cement slurry, requiring the initial setting time of cement slurry to be 3 hours, the amount of cement slurry should ensure that the cement slurry returns to the designed depth, several nylon balls are put into the wellhead to replace the spacer fluid 2.0m 3 Clean water, then continue to displace the workover fluid, block the circulation port, hold the pressure to 20MPa, and shut down the tool;

[0010] Alternatively, when there is a gas top layer, a two-stage cementing method with a sleeve-changing support is used. Centralizers are installed on the casing at both ends of the double-stage collar. The connection between the double-stage collar and the casing is tightened with a large tong. The casing is circulated before buckling. The well is washed with workover fluid and the buckling fish head is flushed. After buckling, a Φ140-CSJ special lower rubber plug is used as a first-level isolation plug. The test pressure is 15 MPa, the pressure is stabilized for 5 minutes, and a gravity plug is inserted. The gravity plug falls at a speed of 51 m / min and the drilling fluid density is 1.25 g / cm 3 , viscosity 35, opening pressure 6MPa-7MPa, after opening the secondary cementing hole, circulate the workover fluid, wash the well, and when it is considered that the drilling fluid performance meets the requirements, inject the required cement slurry for cementing construction, and put in Φ140-CSJ special rubber plug as the secondary isolation plug. The closing pressure should be 6+(γ cement-γ workover fluid)h×10 -5 +2MPa, maintain pressure for 5min, then release pressure back to zero, where 6MPa is the closing shear pin pressure, (γ cement-γ workover fluid) h×10 -5It is the pressure generated by the density difference between cement slurry and drilling fluid. 2MPa is the additional pressure required to reliably close the double-stage collar. If there is no backflow of workover fluid, hold the pressure and wait for solidification. If the workover fluid flows back, repeat the pressure pumping to close the casing and reduce the pressure. If there is still backflow, close the casing, hold the pressure and wait for solidification. After the cementing acoustic inspection, drill out the upper rubber plug, gravity plug and plug seat in the Φ140-CSJ and send them to the bottom of the well.

[0011] Preferably, in the step three, the sleeve-changing lead seal patching device includes an upper joint, and a plurality of O-rings are provided on the left and right ends of the inner wall of the upper joint, a control ring is provided on the right side of the inner wall of the upper joint, a card seat is provided on the inner left side of the control ring, a plurality of fixed keys are provided on the left end of the outer wall of the card seat, a plurality of slips are provided on the card seat, a locking sleeve is provided on the right side of the inner side of the card seat, an upper extrusion ring, a middle extrusion ring and a lower extrusion ring are provided on the inner side of the locking sleeve from left to right, and the upper extrusion ring, the middle extrusion ring and the lower extrusion ring are connected by a single lead seal, a plurality of spacers are provided on the outer side of the locking sleeve, a plurality of lead grooves are provided on the right end of the inner side of the upper joint, a combined lead seal is provided on the inner side of the lead groove, and a guide shoe is fixedly connected to the right end of the upper joint.

[0012] Preferably, in step three, the replacement cement surface control tool includes a column, an outer sliding sleeve is provided on the outer wall of the column, a plurality of limit section hoops are provided on the outer right side of the column, short sections are fixedly connected to the left and right sides of the column, and a plurality of shear pins are provided on the right end of the outer sliding sleeve.

[0013] Preferably, in step three, the sleeve-replacing support-type two-stage cementing device includes a main body, a closing seat is provided on the front side of the main body, the closing seat is connected to the first joint through a closing pin, a closing sleeve is provided on the main body, an opening seat is provided on the right side of the closing sleeve, an opening pin is provided on the opening seat, an opening sleeve is provided on the right side of the opening seat, a rubber cylinder is provided on the front side of the opening sleeve, and the right end of the main body is fixedly connected to the second joint.

[0014] Preferably, in step three, when adopting the cementing method of replacing the lead-sealed joint, before the cement slurry solidifies, the lower wellbore string is lifted up to restore the set load and maintain the tension state until the cement slurry solidifies.

[0015] The present invention provides a cementing technology method suitable for casing removal in oil-bearing layers. It has the following beneficial effects:

[0016] The present invention can be used for cementing wells by replacing casings in oil layers, providing a technical means for effectively achieving interlayer separation, supporting casing, protecting casing, and protecting oil layers, so as to overcome the problems of unqualified cementing quality, interlayer channeling, and further oil layer pollution and environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1This is a structural diagram of the lead seal patching tool of the present invention;

[0018] Figure 2 This is a structural diagram of the cement surface control tool for replacing a sleeve of the present invention;

[0019] Figure 3 This is a diagram of a replaceable sleeve supporting two-stage cementing device according to the present invention;

[0020] Figure 4 Parameter diagram of the TBJ-Q140 connector of the present invention.

[0021] Among them, 1. upper joint; 2. O-ring; 3. fixing key; 4. holder; 5. slip; 6. control ring; 7. upper extrusion ring; 8. single lead seal; 9. middle extrusion ring; 10. lead groove; 11. lower extrusion ring; 12. locking sleeve; 13. spacer sleeve; 14. guide shoe; 15. combined lead seal; 16. limit section hoop; 17. short section; 18. outer sliding sleeve; 19. shear pin; 20. main body; 21. closing valve; 22. closing pin; 23. first joint; 24. closing sleeve; 25. opening seat; 26. opening pin; 27. opening sleeve; 28. rubber cylinder; 29. ​​second joint; 30. cylinder. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example

[0023] like Figure 1-4 As shown, an embodiment of the present invention provides a cementing technology method suitable for casing removal in an oil layer, comprising the following steps:

[0024] Step 1: Add weight to the wellbore by adding SPNH-1 and NPAN glue to prevent wellbore collapse. 3 The workover fluid circulation is weighted to increase the density of the workover fluid until it reaches the design requirements. After weighting, SPNH-1 and NPAN glue are used for maintenance to control water loss. During the whole well drilling, DJ-C is used to adjust the viscosity and shear force to maintain the performance of the workover fluid.

[0025] Step 2: Borehole cleaning and cementing preparation, oil layer casing installed with plug, casing milling barrel raised 1.5m, to 1.7m 3 Circulate the workover fluid at a rate of more than / min for 2 to 3 weeks to flush the well wall and mud cake for cementing;

[0026] Step 3: When the well type is an inclined well with an inclination of ≥10°, the cementing method of replacing the lead seal connector is adopted. Specifically, the following steps are taken: check the downhole tool, lower it into the well after it passes the inspection, and when it reaches the top of the drop fish, slowly rotate it forward while slowly lowering it so that the drop fish enters the tool and hits the O-ring. Observe the weight gauge and make the tool withstand a pressure of 7 to 9 tons. Slightly lift the downhole string to make the tool at the neutral point to eliminate the elastic resistance of the downhole string. Lift the downhole string again, compress the lead seal, start the pump for pressure test, and reduce the set load to one-fourth of the original load. The test pressure is 35×10 4 Pa~70×10 4 After the pressure test is passed, the pipe string is slowly lowered to make the joint withstand a pressure of 7 to 9 tons. Cement slurry is injected to reach the required return height. The drilling and milling pipe string is lowered to drill out excess cement and bridge plugs. The casing scraper is then lowered to remove cement residue stuck on the casing. The reverse circulation salvage basket is lowered to pick up small debris that has fallen on the bottom of the well.

[0027] Alternatively, when the shallow strata are sparsely porous and there is a risk of surface water intrusion, the cementing method of replacing the cement surface controller is adopted. The cement is lowered into the well along with the casing string and the buckling construction is carried out. The workover fluid is pumped using a pump truck. The pressure is held at 16 MPa to open the tool circulation hole. 5.0 m3 of positive circulation is injected. 3 Then, water with a density of 1.85-1.95 g / cm 3 Cement slurry, adding retarder to the cement slurry, requiring the initial setting time of cement slurry to be 3 hours, the amount of cement slurry should ensure that the cement slurry returns to the designed depth, several nylon balls are put into the wellhead to replace the spacer fluid 2.0m 3 Clean water, then continue to displace the workover fluid, block the circulation port, hold the pressure to 20MPa, and shut down the tool;

[0028] Alternatively, when there is a gas top layer, a two-stage cementing method with a sleeve-changing support is used. Centralizers are installed on the casing at both ends of the double-stage collar. The connection between the double-stage collar and the casing is tightened with a large tong. The casing is circulated before buckling. The well is washed with workover fluid and the buckling fish head is flushed. After buckling, a Φ140-CSJ special lower rubber plug is used as a first-level isolation plug. The test pressure is 15 MPa, the pressure is stabilized for 5 minutes, and a gravity plug is inserted. The gravity plug falls at a speed of 51 m / min and the drilling fluid density is 1.25 g / cm 3 , viscosity 35, opening pressure 6MPa-7MPa, after opening the secondary cementing hole, circulate the workover fluid, wash the well, and when it is considered that the drilling fluid performance meets the requirements, inject the required cement slurry for cementing construction, and put in Φ140-CSJ special rubber plug as the secondary isolation plug. The closing pressure should be 6+(γ cement-γ workover fluid)h×10 -5 +2MPa, maintain pressure for 5min, then release pressure back to zero, where 6MPa is the closing shear pin pressure, (γ cement-γ workover fluid) h×10 -5It is the pressure generated by the density difference between cement slurry and drilling fluid. 2MPa is the additional pressure required to reliably close the double-stage collar. If there is no backflow of workover fluid, hold the pressure and wait for solidification. If the workover fluid flows back, repeat the pressure pumping to close the casing and reduce the pressure. If there is still backflow, close the casing, hold the pressure and wait for solidification. After the cementing acoustic inspection, drill out the upper rubber plug, gravity plug and plug seat in the Φ140-CSJ and send them to the bottom of the well.

[0029] In the calculation formula of slurry dosage, Vcs is the cement slurry dosage, unit is m 3 , db is the outer diameter of the milling head, the unit is m, k is the hole expansion coefficient of the milling head, the value is 1.2, dco is the outer diameter of the casing, the unit is m, Dt is the sealing section length, the unit is m, 1+20% is the additional amount.

[0030] The sleeve-changing lead seal patching device includes an upper joint 1, and multiple O-rings 2 are provided on the left and right ends of the inner wall of the upper joint 1. A control ring 6 is provided on the right side of the inner wall of the upper joint 1, and a card seat 4 is provided on the inner left side of the control ring 6. A plurality of fixed keys 3 are provided on the left end of the outer wall of the card seat 4, and a plurality of slips 5 are provided on the card seat 4. A locking sleeve 12 is provided on the right side of the inner side of the card seat 4, and an upper extrusion ring 7, a middle extrusion ring 9 and a lower extrusion ring 11 are provided on the inner side of the locking sleeve 12 from left to right. The upper extrusion ring 7, the middle extrusion ring 9 and the lower extrusion ring 11 are all connected by a single lead seal 8. A plurality of spacers 13 are provided on the outer side of the locking sleeve 12, a plurality of lead grooves 10 are provided on the right end of the inner side of the upper joint 1, and a combined lead seal 15 is provided on the inner side of the lead groove 10. The right end of the upper joint 1 is fixedly connected to a guide shoe 14.

[0031] The cement surface control tool for replacing the sleeve includes a column 30, an outer sleeve 18 is provided on the outer wall of the column 30, a plurality of limit hoops 16 are provided on the right side of the outside of the column 30, short sections 17 are fixedly connected to the left and right sides of the column 30, and a plurality of shear pins 19 are provided on the right end of the outer sleeve 18.

[0032] The effective length is 1900mm, the maximum outer diameter is Φ200mm, the tool outer diameter is Φ178mm, the tool inner diameter is Φ124mm, the tool weight is 90Kg, the applicable well diameter is ≥Φ210mm, the opening pressure is 13~20MPa, the closing pressure is 20MPa, the allowed hanging casing length is ≤1000m, and the tool inner diameter after completion is Φ124mm.

[0033] The replaceable sleeve supporting two-stage cementer includes a main body 20, a closing seat 21 is provided on the front side of the main body 20, the closing seat 21 is connected to the first joint 23 through a closing pin 22, a closing sleeve 24 is provided on the main body 20, an opening seat 25 is provided on the right side of the closing sleeve 24, an opening pin 26 is provided on the opening seat 25, an opening sleeve 27 is provided on the right side of the opening seat 25, a rubber cylinder 28 is provided on the front side of the opening sleeve 27, and the right end of the main body 20 is fixedly connected to the second joint 29.

[0034] The tool has a total length of 1100mm and a maximum outer diameter of 203mm. After drilling and removing the rubber plug, the tool has a diameter of 122mm. It is suitable for wellbore diameters of 215 to 250mm. The total length of the opening plug is 500mm, and the total length of the closing plug is 230mm. The opening pressure is 6 to 8MPa, and the closing pressure is 6 to 8MPa + ΔMPa, where Δ is the pressure difference caused by the liquid density difference inside and outside the casing at the tool. The tool adapts to an ambient temperature of -35 to 80°C and a downhole temperature of less than 150°C.

[0035] When using the lead seal replacement joint cementing method, before the cement slurry solidifies, lift the lower wellbore string to restore the set load and maintain the tension state until the cement slurry solidifies.

[0036] Case 1

[0037] On April 24, 2019, the Nan 1-20-P31 well was constructed by casing through the oil layer. By using the casing milling barrel cementing method, there was no oil layer pollution or environmental pollution after the construction. It has now been put into production normally, with a cumulative water injection of 1.30×10 4 m 3 .

[0038] Case 2

[0039] On September 15, 2001, the North 2-6-444 well was constructed by removing the casing through the oil layer. By using the cementing method of lead-sealed joint, there was no oil layer pollution or environmental pollution after the construction. It has now been put into production normally, with a cumulative water injection of 34.7×10 4 m 3 .

[0040] Case 3

[0041] On June 24, 2001, Gao 101-30 well was constructed by removing the casing through the oil layer. By using the cementing method of lead-sealed joint, there was no oil layer pollution or environmental pollution after the construction. It has now been put into normal production. 4 m 3 .

[0042] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A cementing technology method suitable for casing removal in oil-bearing layers, characterized in that: The following steps are involved: Step 1: Add weight to the workover fluid before entering the oil layer. Before adding weight, use SPNH-1 and NPAN glue for long-term maintenance. By using 1.8g / cm 3 The workover fluid is circulated and weighted, and then maintained with SPNH-1 and NPAN glue. During the whole well drilling, DJ-C is used to adjust the viscosity and cutting force to maintain the performance of the workover fluid. Step 2: Borehole cleaning and cementing preparation, oil layer casing installed with plug, casing milling barrel raised 1.5m, to 1.7m 3 Circulate the workover fluid at a rate of more than / min for 2 to 3 weeks to flush the well wall and mud cake for cementing; Step 3: When the well type is an inclined well with an inclination of ≥10°, the cementing method of replacing the lead seal connector is adopted. Specifically, the following steps are taken: check the downhole tool, lower it into the well after it passes the inspection, and when it reaches the top of the drop fish, slowly rotate it forward while slowly lowering it so that the drop fish enters the tool and hits the O-ring. Observe the weight gauge and make the tool withstand a pressure of 7 to 9 tons. Slightly lift the downhole string to make the tool at the neutral point to eliminate the elastic resistance of the downhole string. Lift the downhole string again, compress the lead seal, start the pump for pressure test, and reduce the set load to one-fourth of the original load. The test pressure is 35×10 4 Pa~70×10 4 Pa, after the pressure test is passed, the pipe string is slowly lowered to make the joint withstand a pressure of 7 to 9 tons, and cement slurry is injected to reach the required return height. The excess cement and bridge plug are drilled and milled out by the lower drilling and milling pipe string, and then the casing scraper is lowered to remove the cement residue stuck on the casing, and the reverse circulation salvage basket is lowered to fish out the fine debris that falls on the bottom of the well; the sleeve seal joint includes an upper joint (1), and the left and right ends of the inner wall of the upper joint (1) are both provided with a plurality of O-rings (2), the right side of the inner wall of the upper joint (1) is provided with a control ring (6), the left side of the inner wall of the control ring (6) is provided with a holder (4), the left end of the outer wall of the holder (4) is provided with a plurality of fixed keys (3), and the holder ( 4) is provided with a plurality of slips (5), a locking sleeve (12) is provided on the right side of the inner side of the said card seat (4), an upper extrusion ring (7), a middle extrusion ring (9) and a lower extrusion ring (11) are provided on the inner side of the said locking sleeve (12) from left to right, the upper extrusion ring (7), the middle extrusion ring (9) and the lower extrusion ring (11) are connected by a single lead seal (8), a plurality of spacers (13) are provided on the outer side of the said locking sleeve (12), a plurality of lead grooves (10) are provided on the right end of the inner side of the said upper joint (1), a combined lead seal (15) is provided on the inner side of the said lead groove (10), and a guide shoe (14) is fixedly connected to the right end of the said upper joint (1); Alternatively, when the shallow strata are sparsely porous and there is a risk of surface water intrusion, the cementing method of replacing the cement surface controller is adopted. The cement is lowered into the well along with the casing string and the buckling construction is carried out. The workover fluid is pumped using a pump truck. The pressure is held at 16 MPa to open the tool circulation hole. 5.0 m3 of positive circulation is injected. 3 Then, water with a density of 1.85-1.95 g / cm 3 Cement slurry, adding retarder to the cement slurry, requiring the initial setting time of cement slurry to be 3 hours, the amount of cement slurry should ensure that the cement slurry returns to the designed depth, several nylon balls are put into the wellhead to replace the spacer fluid 2.0m 3 Clean water, then continue to displace the workover fluid, block the circulation port, hold the pressure at 20 MPa, and close the tool; the replacement cement surface control tool includes a column (30), the outer wall of the column (30) is provided with an outer sleeve (18), the outer right side of the column (30) is provided with a plurality of limit hoops (16), the left and right sides of the column (30) are fixedly connected with short sections (17), and the right end of the outer sleeve (18) is provided with a plurality of shear pins (19); Alternatively, when there is a gas top layer, a two-stage cementing method with a sleeve-changing support is used. Centralizers are installed on the casing at both ends of the double-stage collar. The connection between the double-stage collar and the casing is tightened with a large tong. The casing is circulated before buckling. The well is washed with workover fluid and the buckling fish head is flushed. After buckling, a Φ140-CSJ special lower rubber plug is used as a first-level isolation plug. The test pressure is 15 MPa, the pressure is stabilized for 5 minutes, and a gravity plug is inserted. The gravity plug falls at a speed of 51 m / min and the drilling fluid density is 1.25 g / cm 3 , viscosity 35, opening pressure 6MPa-7MPa, after opening the secondary cementing hole, circulate the workover fluid, wash the well, and when it is considered that the drilling fluid performance meets the requirements, inject the required cement slurry for cementing construction, and put in Φ140-CSJ special rubber plug as the secondary isolation plug. The closing pressure should be 6+(γ cement-γ workover fluid)h×10 -5 +2MPa, maintain pressure for 5min, then release pressure back to zero, where 6MPa is the closing shear pin pressure, (γ cement-γ workover fluid) h×10 -5 The pressure is generated by the density difference between cement slurry and drilling fluid, and 2MPa is the additional pressure required to reliably close the double-stage collar. If there is no backflow of workover fluid, hold the pressure and wait for solidification. If the workover fluid flows back, repeatedly pressurize the closed casing to reduce the pressure. If there is still backflow, close the casing, hold the pressure and wait for solidification. After the cementing acoustic inspection, drill out the upper rubber plug, gravity plug and plug seat in the Φ140-CSJ and send them to the bottom of the well. The sleeve-replacing support type two-stage cementing device includes a main body (20), and a closing seat (21) is provided on the front side of the main body (20). The closing seat (21) is connected to the first joint (23) via a closing pin (22); a closing sleeve (24) is provided on the main body (20); an opening seat (25) is provided on the right side of the closing sleeve (24); an opening pin (26) is provided on the opening seat (25); an opening sleeve (27) is provided on the right side of the opening seat (25); a rubber cylinder (28) is provided on the front side of the opening sleeve (27); and a second joint (29) is fixedly connected to the right end of the main body (20).

2. A cementing method suitable for casing removal in an oil layer according to claim 1, characterized in that: When the cementing method of replacing the lead-sealed joint is adopted in step 3, before the cement slurry solidifies, the lower wellbore string is lifted up to restore the set load and maintain the tension state until the cement slurry solidifies.

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