Sand flushing method with pressure and anti-circulation

Abstract

The application discloses a kind of with pressure anti-circulation sand washing method, adopt coiled tubing operation drill and grind the drillable bridge plug in the well of well to be operated;With pressure operation equipment is installed at wellhead;With pressure goes into well pipe column in the well to be operated and implements well-through;Oil sleeve annulus pressure control uses pressure operation equipment;The control of pipe string downhole force uses pressure operation equipment;Sand washing pipe column is connected with the pressure pipeline and pressure equipment under pressure in the well to be operated;Pressure, anti-sand valve reversing, open sand washing passage;Sand washing pipeline and equipment are connected;Start pump truck, anti-circulation sand washing operation;Oil sleeve annulus pressure control uses pressure operation equipment;The first single is connected;Start sand washing pump truck, continue sand washing;Second single is connected.The application has the advantages of protecting formation energy, reducing oil and water treatment capacity, stabilizing oil well production and realizing comprehensive benefit maximization.

Description

Technical Field

[0001] This invention relates to the field of well workover technology in oil production engineering in the petroleum industry, and in particular to a pressurized blowout prevention reverse circulation sand flushing method. Background Technology

[0002] Sand production in oil and water wells is a common wellbore problem. In oil wells, sand production often leads to sand burial of the oil layer, affecting production. It also erodes valves and pump casings, causing pump leakage and affecting the lifespan of the pump. In water wells, sand production often causes blockage of the water injection channel, preventing water injection. It also leads to unsuccessful testing and commissioning, affecting normal injection. Therefore, sand flushing is one of the most common minor workover operations. The book "Well Workover Operations," edited by Ma Jizhen and published by the Petroleum Industry Press, introduces two main sand flushing methods: direct circulation sand flushing and reverse circulation sand flushing. Direct circulation sand flushing is characterized by low displacement, high flushing force, slow return speed, and a high risk of sand jamming, and is commonly used for vertical well sand flushing operations. Reverse circulation sand flushing is characterized by high displacement, low flushing force, fast return speed, and a low risk of sand jamming, and is commonly used for horizontal well sand flushing operations. However, in recent years, due to the development of unconventional reservoir horizontal wells, a number of horizontal wells with high wellhead pressure have emerged. For these horizontal wells, conventional sand flushing techniques are difficult to apply, requiring pressurized blowout preventer reverse circulation sand flushing methods. Therefore, preventing blowouts is the fundamental technical problem to be solved during the lowering and retrieval of sand flushing pipes.

[0003] Before the application of this innovative technology, sand flushing operations in high-pressure horizontal wells were carried out using a depressurization method, reducing the wellhead pressure to below 1 MPa before sand flushing could proceed. However, this method of sand flushing gradually exposes the oil layer, posing a risk of a sudden pressure surge and potentially triggering a blowout. Horizontal well sand flushing technology often employs reverse circulation sand flushing because it features a large sand discharge capacity, rapid return speed, and strong sand-carrying capacity, thus reducing the occurrence of sand jamming accidents.

[0004] The method of pressurized blowout prevention with positive circulation sand flushing is also used in field operations. For example, the book "Live Operation Technology and Equipment" compiled by Wang Feng et al. and published by Petroleum Industry Press describes this method as connecting a check valve between the sand flushing tip and the tubing to prevent blowout during well running and tripping. The principle is that the casing pressure is higher than the tubing pressure, and the check valve is closed. When flushing fluid is injected through the tubing, the tubing pressure is higher than the wellbore pressure, opening the check valve and realizing the sand flushing operation. This sand flushing method has drawbacks: slow return speed of the flushing fluid, sand settling during single-section runs, and a high risk of sand jamming accidents. This is especially true in horizontal wells, where sand jamming accidents are more likely to occur. Therefore, this method is not recommended for sand flushing operations in horizontal wells. Summary of the Invention

[0005] To solve the above problems, this invention provides a pressurized anti-blowout reverse circulation sand flushing method.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a pressurized anti-blowout reverse circulation sand flushing method, comprising the following steps:

[0007] Step 1: Use coiled tubing to drill away the drillable bridge plug inside the well to be drilled;

[0008] Step 2: Install the pressurized work equipment at the wellhead; the pressurized work equipment from bottom to top: safety blowout preventer assembly, semi-sealed gate blowout preventer I, balance pressure relief system, ring blowout preventer, semi-sealed gate blowout preventer II, hydraulic cylinder, fixed slips, movable slips, and work platform.

[0009] Step 3: Run the well-clearing string under pressure in the well to be cleaned and perform well cleaning; the well-clearing string consists of a plug, a well gauge, and tubing from bottom to top.

[0010] Step 4: In step 3, pressurized operation equipment is used for annular pressure control of the casing and tubing. When the wellhead pressure is below 10 MPa, an annular blowout preventer is used to achieve an annular seal and run the wellbore string. When the wellhead pressure is in the range of 10 MPa-21 MPa, upper and lower semi-sealed gate blowout preventers are used alternately, and a pressure relief system is used in conjunction to achieve an annular seal and run the wellbore string.

[0011] Step 5: In step 3, the pressure control of the tubing string running-in is carried out using a pressurized operation equipment. When the weight of the tubing is less than the upward force inside the wellbore, the tubing string is run in using a hydraulic cylinder, fixed slips, and moving slips. When the weight of the tubing is greater than the upward force inside the wellbore, the tubing string is run in using the hook of the workover machine. After the well is purged to the sand surface, the tubing string is pulled out after encountering resistance.

[0012] Step 6: Insert the sand flushing string into the well to be constructed under pressure; the sand flushing string consists of a sand flushing pen tip, a backflush valve, and tubing from bottom to top; the backflush valve is threadedly connected to the sand flushing pen tip and tubing.

[0013] Step 7: In step 6, pressurized operation equipment is used for oil casing annular pressure control. When the wellhead pressure is below 10MPa, an annular blowout preventer is used to achieve an oil casing annular seal and sand flushing tubing is installed. When the wellhead pressure is in the range of 10MPa-21MPa, upper and lower semi-sealed gate blowout preventers are used alternately, and a pressure relief system is used in conjunction to achieve an oil casing annular seal and sand flushing tubing is installed.

[0014] Step 8: In step 6, the pressure control of the tubing string running-in is carried out using a pressurized operation equipment. When the weight of the tubing is less than the upward force inside the wellbore, the sand-flushing tubing string is run in using a hydraulic cylinder, fixed slips, and moving slips. When the weight of the tubing is greater than the upward force inside the wellbore, the sand-flushing tubing string is run in using the hook of the workover machine. When the sand-flushing tubing string reaches the sand surface and encounters resistance, one tubing string is lifted up.

[0015] Step 9: Connect the pressurization pipeline and pressurization equipment; connect the pump truck and tanker truck on the ground using high-pressure hose line 2; connect pressure gauge 2, valve 1, pump truck and swivel using high-pressure hose line 1; connect the lower end of the swivel to the stopcock valve; connect the lower end of the stopcock valve to the wellhead tubing.

[0016] Step 10: Pressurize, reverse the backflush valve, and open the flushing channel; the pressurizing valve in the valve seat overcomes the spring preload and pushes the sealing valve downward. The sealing valve is guided by the sliding pin and moves down the slide groove to the lower starting point of the reversing mechanism. Pressurization stops, and under the action of the spring force, the sealing valve reverses to the upper starting point of the short groove, opening the flushing channel; Pump truck pressure (MPa) = wellhead casing pressure (MPa) + wellbore fluid column pressure (MPa) + backflush valve reversing pressure difference (MPa); backflush valve reversing pressure difference 5MPa; After pressurization, close the wellhead plug valve;

[0017] Step 11: Connect the sand flushing pipeline to the equipment; use high-pressure hose line one to connect the wellhead tubing to the sand flushing pump truck; use high-pressure hose line two to connect the pressure gauge one, side valve and valve two of the wellhead four-way valve to the sand flushing pump truck.

[0018] Step 12: Start the pump truck and perform reverse circulation sand flushing operation; Pump truck pressure (MPa) = wellhead casing pressure (MPa) + wellbore fluid column pressure (MPa) + (3-6MPa); Sand flushing rate: 0.3-0.6 m3 / min;

[0019] Step 13: In step 12, the pressure control of the annulus in the casing and tubing is carried out using pressurized equipment. When the wellhead pressure is below 10 MPa, an annular blowout preventer is used to achieve an annulus seal and sand flushing tubing is installed. When the wellhead pressure is in the range of 10 MPa-21 MPa, upper and lower semi-sealed gate blowout preventers are used alternately, and a pressure relief system is used in conjunction to achieve an annulus seal and sand flushing tubing is installed.

[0020] Step 14: Connect the first single tube; after flushing sand into the tubing, fix the wellhead tubing with fixed slips; shut down the pump truck; close the first stopcock valve; remove the swivel and connect the second tubing; connect the second stopcock valve between the second tubing and the swivel valve.

[0021] Step 15: Start the sand flushing pump truck and continue flushing sand; before starting the sand flushing pump truck, open the first stopcock valve; follow steps 12-13.

[0022] Step 16: Connect the second single pipe; after flushing the sand into the second oil pipe, connect the third oil pipe and the third stopcock valve; follow steps 14-15.

[0023] Step 17: Continue the above operations until the sand flushing operation is completed; when the inlet and outlet liquid properties are consistent, the sand flushing is considered complete.

[0024] Step 18: Close the backflush valve; close the wellhead plug valve, and connect the pump truck to the wellhead plug valve using a high-pressure hose; start the pump truck to pressurize, and the pressurizing valve in the valve seat will overcome the spring preload and push the sealing valve downward. The sealing valve will be guided by the sliding pin to descend along the sliding groove to the lower starting point of the reversing mechanism. Stop pressurizing, and under the action of the spring force, the sealing valve will reverse to the upper starting point of the long groove, and the sand flushing channel will be closed.

[0025] Step 19: Retrieve the sand-flushing tubing under pressure; if the weight of the tubing is greater than the upward force inside the wellbore, use the workover rig's hook to retrieve the sand-flushing tubing; if the weight of the tubing is less than the upward force inside the wellbore, use the hydraulic cylinder, fixed slips, and moving slips in combination to retrieve the sand-flushing tubing.

[0026] This invention employs a backflushing valve, essentially a downhole switch. During the running-in and running-out of the flushing tubing, the backflushing valve is closed, enabling pressurized operation. During the flushing operation itself, the backflushing valve is open, enabling pressurized reverse circulation flushing. This reverse circulation flushing method is more suitable for horizontal well flushing operations, offering advantages such as large displacement, fast return speed, strong sand-carrying capacity, and low sand-stuck accident rate. Pressurized operation protects formation energy, reduces oil and water treatment volume, stabilizes well production, and maximizes overall benefits. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the lowering and lowering of a pressurized anti-blowout reverse circulation sand flushing pipe column;

[0028] Figure 2 This is a schematic diagram of the backwash valve opening operation;

[0029] Figure 3 This is a schematic diagram of a pressurized reverse circulation sand flushing operation;

[0030] Figure 4 This is a schematic diagram illustrating the principle of lowering and retrieving the backwash sand valve;

[0031] Figure 5 This is a schematic diagram illustrating the working principle of a backflushing sand valve;

[0032] Figure 6 This is a schematic diagram of the reversing track.

[0033] Among them, 1. Sandblasting pen tip, 2. Backwashing valve, 3. Oil pipe, 4. Large four-way valve, 5. Safety blowout preventer assembly, 6. Semi-sealed gate blowout preventer I, 7. Balanced pressure relief system; 8. Ring blowout preventer; 9. Semi-sealed gate blowout preventer II; 10. Hydraulic cylinder, 11. Fixed slip, 12. Moving slip, 13. Working platform, 14. Working machine, 15. Large hook, 16. Water tap, 17. Plug valve, 18. Pressure gauge I, 19. Side valve, 20. High-pressure hose line I, 21. Pressure gauge II, 22. Valve I, 23. Pump truck, 24. High-pressure hose line II, 25. Tank truck, 26. Valve II, 27. Sandblasting pump truck, 28. Pressure valve, 29. Valve seat, 30. Sealing valve, 31. Sliding pin, 32. Spring. Detailed Implementation

[0034] The following is in conjunction with the appendix Figure 1-6 The specific embodiments of the present invention will be further described below.

[0035] A pressurized blowout prevention reverse circulation sand flushing method includes the following steps:

[0036] Step 1: Use coiled tubing 3 to drill and grind away the drillable bridge plugs in the well to be drilled; drill and grind 2-3 drillable bridge plugs, and circulate and flush the well to prevent stuck pipe; when the drilling and grinding of the drillable bridge plugs is suspended, coiled tubing 3 must be raised to the vertical well section to prevent stuck pipe.

[0037] Step 2: Install the live-line working equipment at the wellhead; the live-line working equipment, from bottom to top: safety blowout preventer group 5 (semi-sealed gate, full-sealed gate), semi-sealed gate blowout preventer one 6, balanced pressure relief system 7, ring blowout preventer 8, semi-sealed gate blowout preventer two 9, hydraulic cylinder 10, fixed slips 11, moving slips 12, working platform 13; the working pressure of the live-line working equipment is 21 MPa;

[0038] Step 3: Run the well-clearing string under pressure in the well to be cleaned and perform well cleaning; the well-clearing string consists of a plug, a well gauge with an outer diameter of 118 mm, and tubing 3 with an outer diameter of 73 mm from bottom to top; the plug prevents blowout inside tubing 3; the working pressure of the plug is 21 MPa;

[0039] Step 4: In step 3, the pressure control of the annulus in the casing and tubing is carried out using pressurized equipment. When the wellhead pressure is below 10 MPa, an annular blowout preventer 8 is used to achieve an annulus seal and the tubing string is lowered in. When the wellhead pressure is in the range of 10 MPa-21 MPa, upper and lower semi-sealing gate blowout preventers are used alternately, and the pressure relief system 7 is used in conjunction to achieve an annulus seal and the tubing string is lowered in.

[0040] Step 5: In step 3, the pressure control of the tubing string running down the well is carried out using pressurized operation equipment. When the weight of tubing 3 is less than the upward force inside the wellbore, the well-clearing tubing string is run down using the hydraulic cylinder 10, fixed slips 11, and moving slips 12. When the weight of tubing 3 is greater than the upward force inside the wellbore, the well-clearing tubing string is run down using the hook 15 of the workover machine 14. After clearing the well to the sand surface position, the well-clearing tubing string is pulled out after encountering resistance.

[0041] Step 6: Run the sand flushing string under pressure in the well to be drilled; the sand flushing string consists of, from bottom to top, a 73mm outer diameter sand flushing tip 1, a 100mm outer diameter backflushing valve 2, and a 73mm outer diameter tubing 3; the backflushing valve 2 is threadedly connected to the sand flushing tip 1 and the tubing 3; the backflushing valve 3 is in the closed state when it is run into the well (see...). Figure 4 This achieves blowout prevention within oil pipe 3; the backwash sand valve 2 operates at a pressure of 21 MPa.

[0042] Step 7: In step 6, the pressure control of the annulus in the casing and tubing is carried out using pressurized equipment. When the wellhead pressure is below 10 MPa, an annular blowout preventer 8 is used to achieve an annulus seal and sand flushing tubing is installed. When the wellhead pressure is in the range of 10 MPa-21 MPa, upper and lower semi-sealed gate blowout preventers are used alternately, and the pressure relief system 7 is used in conjunction to achieve an annulus seal and sand flushing tubing is installed.

[0043] Step 8: In step 6, the pressure control of the tubing string running downhole is carried out using pressurized operation equipment. When the weight of tubing 3 is less than the upward force inside the wellbore, the sand-flushing tubing string is run down using the hydraulic cylinder 10, fixed slips 11, and moving slips 12. When the weight of tubing 3 is greater than the upward force inside the wellbore, the sand-flushing tubing string is run down using the large hook 15 of the workover machine 14. When the sand-flushing tubing string reaches the sand surface and encounters resistance, one tubing 3 is lifted up.

[0044] Step 9: Connect the pressurization pipeline and pressurization equipment; use high-pressure hose line 24 to connect the pump truck 23 and tank truck 25 on the ground; use high-pressure hose line 20 to connect pressure gauge 21, valve 22, pump truck 23 and swivel 16; connect the lower end of swivel 16 to stopcock valve 17; connect the lower end of stopcock valve 17 to wellhead tubing 3;

[0045] Step 10: Pressure test, reverse the backwash valve 2 to open the backwash channel; the pressure valve 28 inside the valve seat 29 overcomes the preload force of the spring 32 to push the sealing valve 30 (initial position is the starting point on the long groove, see...). Figure 6 As the reversing mechanism descends, the sealing valve 30 is guided by the sliding pin 31 down the slide groove to the starting point of the reversing mechanism (see...). Figure 6 Stop pressurizing, and under the action of spring 32, the sealing valve 30 reverses to the starting point on the short slot (see...). Figure 6 The sand flushing channel is opened (see...). Figure 5Pump truck pressure (MPa) = wellhead casing pressure (MPa) + wellbore fluid column pressure (MPa) + backflushing sand valve reversing pressure difference (MPa); backflushing sand valve reversing pressure difference 5MPa; close wellhead plug valve 17 after pressurization;

[0046] Step 11: Connect the sand flushing pipeline to the equipment; connect the wellhead tubing to the sand flushing pump truck 27 via high-pressure hose line 1 20; connect the pressure gauge 1 18, side valve 19, valve 2 26, and sand flushing pump truck 27 via high-pressure hose line 2 24 at the wellhead;

[0047] Step 12: Start the sand flushing pump truck 27 to perform reverse circulation sand flushing operation; pump truck pressure (MPa) = wellhead casing pressure (MPa) + wellbore fluid column pressure (MPa) + (3-6MPa); sand flushing displacement 0.3-0.6m³. 3 / min;

[0048] Step 13: In step 12, the annular pressure control of the casing and tubing is carried out using pressurized equipment. When the wellhead pressure is below 10 MPa, an annular blowout preventer 8 is used to achieve an annular seal and sand flushing string is installed. When the wellhead pressure is in the range of 10 MPa-21 MPa, upper and lower semi-sealed gate blowout preventers are used alternately, and the pressure relief system 7 is used in conjunction to achieve an annular seal and sand flushing string is installed.

[0049] Step 14: Connect the first single pipe; after the sand flushing enters the oil pipe 3, fix the oil pipe 3 with the fixing slip 11; shut off the sand flushing pump truck 27; close the first stopcock valve 17; remove the faucet 16 and connect the second oil pipe 3; connect the second stopcock valve 17 between the second oil pipe 3 and the faucet 16.

[0050] Step 15: Start the sand flushing pump truck 27 and continue flushing sand; before starting the sand flushing pump truck 27, open the first plug valve 17; follow steps 12-13.

[0051] Step 16: Connect the second single pipe; after flushing the sand into the second oil pipe 3, connect the third oil pipe 3 and the third plug valve 17; operate according to steps 14-15;

[0052] Step 17: Continue the above operations until the sand flushing operation is completed; when the inlet and outlet liquid properties are consistent, the sand flushing is considered complete.

[0053] Step 18: Close the backflushing sand valve 2; close the wellhead plug valve 17; connect the pump truck 23 to the wellhead plug valve 17 using high-pressure hose line 20; start the pump truck 23 to pressurize; the pressure valve 28 in the valve seat 29 overcomes the preload force of the spring 32 and pushes the sealing valve 30 (located at the starting point of the short groove, see...) Figure 6 As the reversing mechanism descends, the sealing valve 30 is guided by the sliding pin 31 down the slide groove to the starting point of the reversing mechanism (see...). Figure 6), stop pressurizing, and under the action of spring 32, the sealing valve 30 reverses to the starting point on the long slot (see Figure 6 The sand flushing channel is closed (see...). Figure 4 );

[0054] Step 19: Retrieve the sand-flushing tubing under pressure; when the weight of tubing 3 is greater than the upward force inside the wellbore, use the large hook 15 of the work machine 14 to retrieve the sand-flushing tubing; when the weight of tubing 3 is less than the upward force inside the wellbore, use the hydraulic cylinder 10, fixed slips 11, and moving slips 12 in conjunction to retrieve the sand-flushing tubing.

[0055] This invention enables blowout prevention within the tubing and pressurized sealing of the annulus during the running-in and running-out of the sand-flushing tubing string, effectively solving the challenges of sand-flushing operations in high-pressure horizontal wells, further improving sand-flushing efficiency, and ensuring safe operation. This method can be extended to CCUS technology applications; for CO2 injection high-pressure wells, this method can be used for sand-flushing operations, ensuring both high efficiency and safety.

[0056] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pressurized anti-blowout reverse circulation sand flushing method, characterized in that, Includes the following steps: Step 1: Use coiled tubing to drill away the drillable bridge plug inside the well to be drilled; Step 2: Install the pressurized work equipment at the wellhead; the pressurized work equipment from bottom to top: safety blowout preventer assembly, semi-sealed gate blowout preventer I, balance pressure relief system, ring blowout preventer, semi-sealed gate blowout preventer II, hydraulic cylinder, fixed slips, movable slips, and work platform. Step 3: Run the well-clearing string under pressure in the well to be cleaned and perform well cleaning; the well-clearing string consists of a plug, a well gauge, and tubing from bottom to top. Step 4: In step 3, pressurized operation equipment is used for annular pressure control of the casing and tubing. When the wellhead pressure is below 10 MPa, an annular blowout preventer is used to achieve an annular seal and run the wellbore string. When the wellhead pressure is in the range of 10 MPa-21 MPa, upper and lower semi-sealed gate blowout preventers are used alternately, and a pressure relief system is used in conjunction to achieve an annular seal and run the wellbore string. Step 5: In step 3, the pressure control of the tubing string running-in is carried out using a pressurized operation equipment. When the weight of the tubing is less than the upward force inside the wellbore, the tubing string is run in using a hydraulic cylinder, fixed slips, and moving slips. When the weight of the tubing is greater than the upward force inside the wellbore, the tubing string is run in using the hook of the workover machine. After the well is purged to the sand surface, the tubing string is pulled out after encountering resistance. Step 6: Insert the sand flushing string into the well to be constructed under pressure; the sand flushing string consists of a sand flushing pen tip, a backflush valve, and tubing from bottom to top; the backflush valve is threadedly connected to the sand flushing pen tip and tubing. Step 7: In step 6, pressurized operation equipment is used for oil casing annular pressure control. When the wellhead pressure is below 10MPa, an annular blowout preventer is used to achieve an oil casing annular seal and sand flushing tubing is installed. When the wellhead pressure is in the range of 10MPa-21MPa, upper and lower semi-sealed gate blowout preventers are used alternately, and a pressure relief system is used in conjunction to achieve an oil casing annular seal and sand flushing tubing is installed. Step 8: In step 6, the pressure control of the tubing string running-in is carried out using a pressurized operation equipment. When the weight of the tubing is less than the upward force inside the wellbore, the sand-flushing tubing string is run in using a hydraulic cylinder, fixed slips, and moving slips. When the weight of the tubing is greater than the upward force inside the wellbore, the sand-flushing tubing string is run in using the hook of the workover machine. When the sand-flushing tubing string reaches the sand surface and encounters resistance, one tubing string is lifted up. Step 9: Connect the pressurization pipeline and pressurization equipment; connect the pump truck and tanker truck on the ground using high-pressure hose line 2; connect pressure gauge 2, valve 1, pump truck and swivel using high-pressure hose line 1; connect the lower end of the swivel to the stopcock valve; connect the lower end of the stopcock valve to the wellhead tubing. Step 10: Pressurize, reverse the backflush valve, and open the flushing channel; the pressurizing valve in the valve seat overcomes the spring preload and pushes the sealing valve downward. The sealing valve is guided by the sliding pin and moves down the slide groove to the lower starting point of the reversing mechanism. Pressurization stops, and under the action of the spring force, the sealing valve reverses to the upper starting point of the short groove, opening the flushing channel; Pump truck pressure (MPa) = wellhead casing pressure (MPa) + wellbore fluid column pressure (MPa) + backflush valve reversing pressure difference (MPa); backflush valve reversing pressure difference 5MPa; After pressurization, close the wellhead plug valve; Step 11: Connect the sand flushing pipeline to the equipment; use high-pressure hose line one to connect the wellhead tubing to the sand flushing pump truck; use high-pressure hose line two to connect the pressure gauge one, side valve and valve two of the wellhead four-way valve to the sand flushing pump truck. Step 12: Start the pump truck and begin reverse circulation sand flushing; pump truck pressure (MPa) = wellhead casing pressure (MPa) + wellbore fluid column pressure (MPa) + (3-6MPa); sand flushing displacement: 0.3-0.6m³ 3 / min; Step 13: In step 12, the pressure control of the annulus in the casing and tubing is carried out using pressurized equipment. When the wellhead pressure is below 10 MPa, an annular blowout preventer is used to achieve an annulus seal and sand flushing tubing is installed. When the wellhead pressure is in the range of 10 MPa-21 MPa, upper and lower semi-sealed gate blowout preventers are used alternately, and a pressure relief system is used in conjunction to achieve an annulus seal and sand flushing tubing is installed. Step 14: Connect the first single tube; after flushing sand into the tubing, fix the wellhead tubing with fixed slips; shut down the pump truck; close the first stopcock valve; remove the swivel and connect the second tubing; connect the second stopcock valve between the second tubing and the swivel valve. Step 15: Start the sand flushing pump truck and continue flushing sand; before starting the sand flushing pump truck, open the first stopcock valve; follow steps 12-13. Step 16: Connect the second single pipe; after flushing the sand into the second oil pipe, connect the third oil pipe and the third stopcock valve; follow steps 14-15. Step 17: Continue the above operations until the sand flushing operation is completed; when the inlet and outlet liquid properties are consistent, the sand flushing is considered complete. Step 18: Close the backwash sand valve; close the wellhead plug valve, and connect the pump truck to the wellhead plug valve using a high-pressure hose line. When the pump truck is started and pressurized, the pressurizing valve in the valve seat overcomes the spring preload and pushes the sealing valve downward. The sealing valve is guided by the sliding pin and moves down the slide groove to the starting point of the reversing mechanism. Pressurization stops, and under the action of the spring force, the sealing valve reverses to the starting point of the long groove, and the sand flushing channel is closed. Step 19: Retrieve the sand-flushing tubing under pressure; if the weight of the tubing is greater than the upward force inside the wellbore, use the workover rig's hook to retrieve the sand-flushing tubing; if the weight of the tubing is less than the upward force inside the wellbore, use the hydraulic cylinder, fixed slips, and moving slips in combination to retrieve the sand-flushing tubing.

2. The pressurized anti-blowout reverse circulation sand flushing method according to claim 1, characterized in that, In step 1, the drill can drill 2-3 bridge plugs, and the well needs to be circulated and flushed to prevent the drill from getting stuck.

3. The pressurized anti-blowout reverse circulation sand flushing method according to claim 1, characterized in that, In step 1, when the drilling rig is paused, the coiled tubing 3 needs to be raised to the vertical well section to prevent the drill bit from getting stuck.

4. The pressurized anti-blowout reverse circulation sand flushing method according to claim 1, characterized in that, In step 2, the lower part of the safety blowout preventer assembly is a semi-sealed gate, and the upper part is a fully sealed gate.

5. The pressurized anti-blowout reverse circulation sand flushing method according to claim 1, characterized in that, In step 3, the outer diameter of the well gauge is 118 mm.

6. The pressurized anti-blowout reverse circulation sand flushing method according to claim 1, characterized in that, In step 3, the outer diameter of the oil pipe is 73 mm.

7. The pressurized anti-blowout reverse circulation sand flushing method according to claim 1, characterized in that, In step 6, the outer diameter of the sandblasting pen tip is 73mm.

8. The pressurized anti-blowout reverse circulation sand flushing method according to claim 1, characterized in that, In step 6, the outer diameter of the backwash valve is 100mm.

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