Lifting type two-stage oil pipe switch valve and pressure control method for dragging fracturing oil pipe under pressure

Abstract

The invention relates to the technical field of oil field fracturing tools, in particular to a lifting type two-stage oil pipe switch valve and a pressure control method for dragging a fracturing oil pipe under pressure. The lifting type two-stage oil pipe switch valve comprises an upper connector, a central pipe, a push cylinder, a cap, an outer cylinder and a lower connector; the inner side of the outer cylinder corresponding to the position between the sealing ring table and the lower connector is sleeved with an upper valve and a lower valve. Each valve comprises a supporting ring, a valve seat, a valve plate and a torsional spring. The lifting and releasing type double-stage oil pipe switch valve is reasonable in structure, the lifting and releasing type double-stage oil pipe switch valve can be switched between the opening position and the closing position by lifting and releasing a fracturing pipe column, the sand passing and liquid passing requirements of fracturing can be met when the lifting and releasing type double-stage oil pipe switch valve is located at the opening position, and the oil pipe pressure can be controlled when the lifting and releasing type double-stage oil pipe switch valve is located at the closing position; and under-pressure dragging layer transfer is realized.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield fracturing tools, in particular to a lifting and releasing two-stage oil pipe switch valve and a pressure control method for a pressure-drag fracturing oil pipe. Background Art

[0002] The dragging tubing fracturing process is a relatively mature horizontal well fracturing transformation process, including continuous tubing with packer dragging fracturing, tubing with packer dragging fracturing, etc. Among them, the dragging tubing with pressure and double seal fracturing formed by combining with the pressure operation machine is a fracturing technology that is currently being tackled. The dragging fracturing technology with pressure includes five parts: a pressure operation machine, a dragging fracturing wellhead with pressure, a tubing blowout prevention tool, a double seal fracturing tool, and a fracturing tubing. During construction, the dragging fracturing wellhead with pressure is installed first, the double seal fracturing string is lowered, the packer is set and the target layer is fractured, the tubing blowout prevention tool is closed after fracturing, the tubing is dragged up with pressure to change layers for fracturing, and the downhole fracturing is pulled out with pressure. The biggest advantage of this technology is that it has the function of preventing blowout of tubing and oil-casing annulus, and can be used for pressure-drag fracturing construction. The core tool for controlling tubing pressure is the tubing switch valve. To achieve pressure-drag fracturing construction, the tubing switch valve is required to be able to effectively isolate the wellhead and formation pressure when lifting and lowering the tubing, so as to control the tubing; the valve can be opened by lowering the tubing string to connect the wellhead tubing with the formation, thereby meeting the demand for pumping fracturing fluid during fracturing construction; at the same time, the valve can be closed again by lifting the tubing string to control the tubing pressure and meet the demand for pressure-drag layer change. However, currently no tubing switch valve on the market can meet the above performance requirements. Summary of the invention

[0003] The present invention provides a lifting and releasing two-stage oil pipe switch valve and a pressure control method for a pressure-drag fracturing oil pipe, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the problem that the existing oil pipe switch valve cannot meet the requirements of pressure-drag fracturing construction.

[0004] One of the technical solutions of the present invention is achieved through the following measures: a lifting and releasing two-stage oil pipe switching valve, including an upper joint, a center tube, a push tube, a cap, an outer tube and a lower joint, the lower inner side of the upper joint and the upper outer side of the center tube are fixedly connected together, the lower outer side of the center tube and the upper inner side of the push tube are fixedly connected together, the outer side of the center tube corresponding to the upper side position of the push tube is sleeved with a cap, and the center tube and the cap are fixedly connected together by shear nails, the outer side of the push tube is sleeved with an outer tube, the lower outer side of the cap and the upper inner side of the outer tube are fixedly connected together, the lower inner side of the outer tube and the upper outer side of the lower joint are fixedly connected together, the upper inner side of the lower joint is provided with an inner ring groove adapted to the push tube, and the middle of the outer tube The inner side is provided with a sealing ring platform which forms a sliding seal with the outer wall of the push cylinder, and the inner side of the outer cylinder corresponding to the position between the sealing ring platform and the lower joint is sleeved with an upper and lower group of valve parts, each group of valve parts includes a support ring, a valve seat, a valve plate and a torsion spring, the support ring and the valve seat are arranged in the outer cylinder from top to bottom in sequence, and the upper part of the valve seat is sleeved on the lower outer side of the support ring, and the interiors of the support ring and the valve seat respectively form a through-cylinder channel for the push cylinder to pass through, and a valve plate is hinged on the valve seat corresponding to the lower side of the support ring through a pin shaft, and a torsion spring for closing the support ring with the valve plate is provided on the pin shaft, the push cylinder is located above the valve plate of the upper group of valve parts, and the push cylinder can push open the valve plates of the two groups of valve parts and insert them into the inner ring groove when it descends relative to the outer cylinder.

[0005] The following is a further optimization and / or improvement of one of the above invention solutions: The outer cylinder wall corresponding to the position between the cap and the sealing ring platform may be provided with two groups of upper and lower liquid passages.

[0006] The central tube and the cap can be matched to prevent rotation in the circumferential direction; stop screws are arranged between the cap and the outer tube, and between the outer tube and the lower joint.

[0007] The inner wall of the sealing ring platform may be provided with a first mounting ring groove and a second mounting ring groove at intervals in the upper and lower parts, a retaining ring is installed in the first mounting ring groove, and an O-ring is installed in the second mounting ring groove; a third mounting ring groove is provided on the inner wall of the inner ring groove, and an O-ring is installed in the third mounting ring groove.

[0008] An O-ring may be provided between the outer wall of the support ring and the inner wall of the outer tube; an O-ring may be provided between the lower end surface of the support ring and the upper end surface of the valve plate; an O-ring may be provided between the lower inner side of the upper joint and the upper outer side of the center tube; an O-ring may be provided between the lower outer side of the center tube and the upper inner side of the push tube.

[0009] The lower inner side of the upper joint and the upper outer side of the center tube can be connected together by threaded fixation, the lower outer side of the center tube and the upper inner side of the push tube can be connected together by threaded fixation, the lower outer side of the cap and the upper inner side of the outer tube can be connected together by threaded fixation, and the lower inner side of the outer tube and the upper outer side of the lower joint can be connected together by threaded fixation.

[0010] The second technical solution of the present invention is achieved by the following measures: a method for controlling the pressure of a fracturing oil pipe under pressure dragging, comprising the following steps: S1: Lowering the fracturing string into the target well, the fracturing string includes a safety joint, a hydraulic anchor, a lifting and releasing two-stage tubing switch valve, a top seal packer, a throttle, a sandblaster, a bottom seal packer and a guide head which are connected in series on the tubing from top to bottom; S2: When the fracturing string reaches the target layer, the bottom seal packer is first set, and then the fracturing string is lowered to pressurize so that the shear pins are sheared off, and the push tube moves downward relative to the outer tube to open the lifting and releasing two-stage tubing switch valve, and then the fracturing pumping construction is carried out; S3: After the target layer fracturing pumping construction is completed, the position of the fracturing string is kept unchanged so that the lifting and releasing two-stage tubing switch valve is in the open position, and reverse circulation well washing is performed. After the reverse circulation well washing is completed, the fracturing string is lifted up with pressure, and the push tube moves upward relative to the outer tube, so that the lifting and releasing two-stage tubing switch valve is in the closed position again, and the fracturing string is continuously lifted up with pressure to the next target layer to complete the layer change; S4: Repeat steps S2 to S3 until the multi-layer fracturing is completed.

[0011] The following is a further optimization and / or improvement of the second embodiment of the above invention: When the fracturing string is lifted up under pressure in the above step S3, if the bottom seal packer is found to be stuck, the hydraulic turntable of the pressure working machine can be used to rotate the fracturing string, and the torque is transmitted to the bottom seal packer through the upper joint, central pipe, cap, outer tube and lower joint to achieve rotational release.

[0012] The invention has a reasonable structure. By lifting and lowering the fracturing string, the lifting and releasing type two-stage oil pipe switch valve can be switched between the open position and the closed position. When the lifting and releasing type two-stage oil pipe switch valve is in the open position, it can meet the fracturing sand and liquid requirements. When the lifting and releasing type two-stage oil pipe switch valve is in the closed position, it can control the oil pipe pressure to realize pressure-drag layer transfer. The opening and closing of the lifting and releasing type two-stage oil pipe switch valve is only realized by the mechanical action of lifting and lowering the fracturing string, which is not affected by factors such as flow rate and pressure difference, and the working performance is stable and reliable. By setting two sets of valve components, the closing and closing of the two-stage oil pipe switch valve can be realized. Double sealing when closed, good sealing reliability. In addition, when the fracturing pipe is lifted, the valve plate rebounds under the torsion of the torsion spring to close the valve again. At this time, the valve plate is tightly pressed against the support ring under the upward force of the bottom hole pressure, realizing the well pressure-assisted sealing function, further improving the sealing reliability. When the lifting and releasing two-stage tubing switch valve is in the open position, the two groups of valve parts are located in the closed annular cavity formed by the push tube, the outer tube and the lower joint, which are not affected by the fracturing sand and liquid, avoiding the wear of the valve parts by the fracturing sand and liquid, and extending the service life of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Attached Figure 1 It is a schematic diagram of the main cross-sectional structure of the lifting and releasing two-stage oil pipe switching valve in embodiments 1 and 2 of the present invention when it is in the closed position.

[0014] Attached Figure 2 It is a schematic diagram of the main cross-sectional structure of the lifting and releasing two-stage oil pipe switching valve in embodiments 1 and 2 of the present invention when it is in the open position.

[0015] Attached Figure 3 It is a schematic diagram of the front cross-sectional structure of the valve component in embodiments 1 and 2 of the present invention.

[0016] Attached Figure 4 It is a schematic diagram of the structure of the fracturing string in Embodiments 1 and 2 of the present invention.

[0017] The codes in the accompanying drawings are: 1 is an upper joint, 2 is a center tube, 3 is a push tube, 4 is a parallel cap, 5 is an outer tube, 6 is a lower joint, 7 is a shear nail, 8 is an inner ring groove, 9 is a sealing ring platform, 10 is a support ring, 11 is a valve seat, 12 is a valve plate, 13 is a torsion spring, 14 is a pin, 15 is a liquid passage, 16 is a stop screw, 17 is a retaining ring, 18 is an O-ring, 19 is an upper oil pipe, 20 is a safety joint, 21 is a hydraulic anchor, 22 is a lifting and releasing two-stage oil pipe switching valve, 23 is a top seal packer, 24 is a throttle, 25 is a sandblaster, 26 is a bottom seal packer, and 27 is a guide head. DETAILED DESCRIPTION

[0018] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0019] In the present invention, for the convenience of description, the relative position relationship of each component is described according to the attached Figure 1 The positional relationships such as front, back, top, bottom, left, and right are described according to the layout directions of the drawings in the specification.

[0020] The present invention will be further described below in conjunction with embodiments and drawings: Embodiment 1: As shown in the attached Figure 1-4 As shown, the lifting and releasing two-stage oil pipe switching valve includes an upper joint 1, a center tube 2, a push tube 3, a cap 4, an outer tube 5 and a lower joint 6. The lower inner side of the upper joint 1 and the upper outer side of the center tube 2 are fixedly connected together, the lower outer side of the center tube 2 and the upper inner side of the push tube 3 are fixedly connected together, the outer side of the center tube 2 corresponding to the upper side position of the push tube 3 is sleeved with a cap 4, and the center tube 2 and the cap 4 are fixedly connected together by shear nails 7, the outer side of the push tube 3 is sleeved with an outer tube 5, the lower outer side of the cap 4 and the upper inner side of the outer tube 5 are fixedly connected together, the lower inner side of the outer tube 5 and the upper outer side of the lower joint 6 are fixedly connected together, the upper inner side of the lower joint 6 is provided with an inner ring groove 8 adapted to the push tube 3, and the middle inner side of the outer tube 5 is provided with a sealing ring that forms a sliding seal with the outer wall of the push tube 3 Platform 9, the inner side of the outer tube 5 corresponding to the position between the sealing ring platform 9 and the lower joint 6 is sleeved with an upper and lower group of valve parts, each group of valve parts includes a support ring 10, a valve seat 11, a valve plate 12 and a torsion spring 13, the support ring 10 and the valve seat 11 are arranged in the outer tube 5 from top to bottom, and the upper part of the valve seat 11 is sleeved on the outer side of the lower part of the support ring 10, and the interior of the support ring 10 and the valve seat 11 respectively form a tube passage for the push tube 3 to pass through, and the valve seat 11 corresponding to the lower side of the support ring 10 is hinged with a valve plate 12 through a pin shaft 14, and the pin shaft 14 is provided with a torsion spring 13 for the valve plate 12 to close the support ring 10, the push tube 3 is located above the valve plate 12 of the upper group of valve parts, and the push tube 3 can push open the valve plates 12 of the two groups of valve parts when it moves downward relative to the outer tube 5 and insert into the inner ring groove 8.

[0021] When in use, the safety joint 20, hydraulic anchor 21, lifting and releasing two-stage oil pipe switch valve 22, top seal packer 23, throttle 24, sandblaster 25, bottom seal packer 26 and guide head 27 are sequentially connected in series on the oil pipe 19 from top to bottom to form a fracturing string. Specifically, the top seal packer 23 is a Y344 packer or a K344 packer, the bottom seal packer 26 is a TDY211 packer, the upper joint 1 is connected to the lower part of the hydraulic anchor 21, and the lower joint 6 is connected to the top of the top seal packer 23. During the lowering of the fracturing string, the pipe string consisting of the upper joint 1, the central pipe 2, and the push tube 3 and the pipe string consisting of the parallel cap 4, the outer tube 5, and the lower joint 6 are in a pulled-apart state. The upper end faces of the valve plates 12 of the two valve components abut against the lower end faces of the corresponding support rings 10 under the torsion of the torsion springs 13, thereby closing the lower end opening of the support rings 10. The lifting and releasing two-stage tubing switch valve is in the closed position. The limiting force provided by the shear nails 7 ensures that the push tube 3 and the outer tube 5 do not move relative to each other during the lowering process. The fracturing string is lowered to the pre- After the position is determined, the bottom sealing packer 26 is first seated, and then the fracturing string is lowered to increase pressure. The pressure value is greater than the shearing force of the shear pin 7, the shear pin 7 is sheared, and the push tube 3 moves downward relative to the outer tube 5, pushing open the valve plates 12 of the two sets of valve components until the lower end of the push tube 3 is inserted into the inner ring groove 8 of the lower joint 6. At this time, the internal channel of the lifting and releasing two-stage oil pipe switch valve is connected, the lifting and releasing two-stage oil pipe switch valve is in the open position, and the upper oil pipe 19 is connected to the formation, thereby meeting the demand for pumping sand liquid for fracturing construction. When the target well is completed without fracturing, After the layer fracturing construction, the fracturing string is lifted up, and the push tube 3 moves upward relative to the outer tube 5. The valve plates 12 of the two sets of valve components rebound under the torsion force of the torsion spring 13 to close the lower end opening of the support ring 10 again, and the lifting and releasing two-stage oil pipe switch valve is in the closed position again, thereby isolating the upper oil pipe 19 and the formation pressure, and then the fracturing string is lifted up with pressure by the pressure operation machine to realize the layer change of the fracturing layer; specifically, in this embodiment, the shear force of the shear nail 7 is 30kN, and the pressure of the fracturing string can be 33kN.

[0022] The lifting and releasing type two-stage tubing switch valve of the present application can be switched between the open position and the closed position by lifting and lowering the fracturing pipe string. When the lifting and releasing type two-stage tubing switch valve is in the open position, it can meet the fracturing sand and liquid requirements. When the lifting and releasing type two-stage tubing switch valve is in the closed position, it can control the tubing pressure to realize pressure-drag layer transfer. The opening and closing of the lifting and releasing type two-stage tubing switch valve is only realized by the mechanical action of lifting and lowering the fracturing pipe string, and is not affected by factors such as flow rate and pressure difference. By setting two sets of valve parts, double sealing is achieved when closed, and the sealing is reliable The invention has good performance. In addition, when the fracturing pipe is lifted, the valve plate 12 rebounds under the torsion force of the torsion spring 13 to close the valve again. At this time, the valve plate 12 is tightly pressed against the support ring 10 under the upward force of the bottom hole pressure, realizing the well pressure-assisted sealing function and further improving the sealing reliability. When the lifting and releasing two-stage oil pipe switching valve is in the open position, the two groups of valve parts are located in the closed annular cavity formed by the push tube 3, the outer tube 5 and the lower joint 6, which are not affected by the fracturing sand and liquid, thus avoiding the wear of the valve parts by the fracturing sand and liquid, and extending the service life of the equipment.

[0023] The above embodiment 1 may be further optimized and / or improved according to actual needs: As attached Figure 1-2 As shown, two groups of upper and lower liquid passages 15 are provided through the wall of the outer cylinder 5 corresponding to the position between the cap 4 and the sealing ring platform 9. According to the requirements, each group of liquid passages 15 includes a plurality of liquid passages 15 arranged at intervals along the circumference of the outer cylinder 5. In this embodiment, the liquid passages 15 are slits of 0.2*30mm. The liquid passages 15 are provided to balance the internal and external pressure difference between the annular cavity formed between the push cylinder 3 and the outer cylinder 5 and the outer space of the outer cylinder 5.

[0024] As attached Figure 1-2 As shown, the center tube 2 and the cap 4 are circumferentially anti-rotationally matched; anti-retraction screws 16 are provided between the cap 4 and the outer tube 5, and between the outer tube 5 and the lower joint 6. The center tube 2 and the cap 4 are circumferentially anti-rotationally matched, so that the two can be assembled together to transmit torque. Therefore, when the bottom seal packer 26 is found to be stuck when the fracturing string is lifted, the hydraulic turntable of the pressure operation machine can be used to rotate the fracturing string, and the torque is transmitted to the bottom seal packer 26 through the upper joint 1, the center tube 2, the cap 4, the outer tube 5, and the lower joint 6 to achieve rotational unblocking. Specifically, the outer contour of the cross section of the center tube 2 is a regular hexagon, and the inner contour of the cross section of the cap 4 is a regular hexagon that matches the outer contour of the cross section of the center tube 2. Therefore, when the center tube 2 and the cap 4 are sheathed together inside and outside, they cannot rotate relative to each other, thereby achieving circumferential anti-rotational matching.

[0025] As attached Figure 1-2As shown, the inner wall of the sealing ring platform 9 is provided with a first mounting ring groove and a second mounting ring groove at intervals, a retaining ring 17 is installed in the first mounting ring groove, and an O-type sealing ring 18 is installed in the second mounting ring groove. Thus, the sliding sealing cooperation between the sealing ring platform 9 and the outer wall of the push cylinder 3 is realized.

[0026] As attached Figure 1-2 As shown, a third mounting ring groove is provided on the inner wall of the inner ring groove 8, and an O-ring 18 for sealing with the push tube 3 is installed in the third mounting ring groove. Therefore, when the push tube 3 is inserted into the inner ring groove 8, the push tube 3 and the lower joint 6 are sealed and connected together, which can effectively prevent the sand injection liquid during the fracturing construction from entering the closed annular cavity formed between the push tube 3, the outer tube 5, and the lower joint 6.

[0027] As attached Figure 1-2 As shown, an O-ring 18 is provided between the outer wall of the support ring 10 and the inner wall of the outer tube 5; an O-ring 18 is provided between the lower end surface of the support ring 10 and the upper end surface of the valve plate 12; an O-ring 18 is provided between the lower inner side of the upper joint 1 and the upper outer side of the center tube 2; and an O-ring 18 is provided between the lower outer side of the center tube 2 and the upper inner side of the push tube 3.

[0028] Specifically, the lower inner side of the upper joint 1 and the upper outer side of the center tube 2 are fixed together by threads, the lower outer side of the center tube 2 and the upper inner side of the push tube 3 are fixed together by threads, and the lower outer side of the cap 4 and the upper inner side of the outer tube 5 are fixed together by threads, and the lower inner side of the outer tube 5 and the upper outer side of the lower joint 6 are fixed together by threads.

[0029] Embodiment 2: As shown in the attached Figure 1-4 As shown, the pressure-controlled fracturing oil pipe pressure control method with pressure dragging comprises the following steps: S1: lowering the fracturing string into the target well, the fracturing string includes a safety joint 20, a hydraulic anchor 21, a lifting and releasing two-stage tubing switch valve 22, a top seal packer 23, a throttle 24, a sandblaster 25, a bottom seal packer 26 and a guide head 27 which are connected in series on the tubing 19 from top to bottom; S2: When the fracturing string reaches the target layer, the bottom seal packer 26 is first set, and then the fracturing string is further lowered to pressurize so that the shear nails 7 are sheared off, and the push tube 3 moves downward relative to the outer tube 5, so that the lifting and releasing two-stage oil pipe switch valve 22 is in the open position, and then the fracturing pumping construction is carried out; S3: After the target layer fracturing pumping construction is completed, the position of the fracturing string is kept unchanged so that the lifting and releasing two-stage tubing switch valve 22 is in the open position, and reverse circulation well washing is performed. After the reverse circulation well washing is completed, the fracturing string is lifted up with pressure, and the push tube 3 moves upward relative to the outer tube 5, so that the lifting and releasing two-stage tubing switch valve 22 is in the closed position again, and the fracturing string is continuously lifted up with pressure to the next target layer to complete the layer change; S4: Repeat steps S2 to S3 until the multi-layer fracturing is completed.

[0030] Specifically, in step S2, when the fracturing string reaches the target layer, the target layer is located between the top seal packer 23 and the bottom seal packer 26. When the fracturing pumping construction is implemented, the throttling pressure difference generated by the sandblaster 25 is used to seal the top seal packer 23, and the fracturing fluid enters the target layer through the sandblaster 25. After the target layer is fracturing, the pump is stopped and the top seal packer 23 is unsealed. During the fracturing pumping process, the hydraulic anchor is anchored to provide a supporting force to ensure that the push tube 3 will not fall out of the lower joint 6 and the valve member due to the creep of the fracturing string. The pressure control method of the pressure-drag fracturing oil pipe in this method can realize the switching of the lifting and releasing two-stage oil pipe switch valve between the open position and the closed position by lifting and lowering the fracturing string. When the lifting and releasing two-stage oil pipe switch valve is in the open position, it can meet the requirements of fracturing sand and liquid. When the lifting and releasing two-stage oil pipe switch valve is in the closed position, it can control the oil pipe pressure, realize the pressure-drag layer transfer, and greatly improve the pressure-drag fracturing construction efficiency.

[0031] The above-mentioned second embodiment may be further optimized and / or improved according to actual needs: Specifically, when the fracturing string is lifted up under pressure in step S3, if the bottom seal packer 26 is found to be stuck, the hydraulic turntable of the pressure-operated machine can be used to rotate the fracturing string, and the torque is transmitted to the bottom seal packer 26 through the upper joint 1, the central pipe 2, the cap 4, the outer tube 5, and the lower joint 6 to achieve rotational release.

[0032] The above technical features constitute the best embodiment of the present invention, which has strong adaptability and best implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

Claims

1. A lifting and releasing two-stage oil pipe switch valve, characterized in that It includes an upper joint, a center tube, a push tube, a cap, an outer tube and a lower joint. The lower inner side of the upper joint and the upper outer side of the center tube are fixedly connected together, the lower outer side of the center tube and the upper inner side of the push tube are fixedly connected together, the outer side of the center tube corresponding to the upper side of the push tube is sleeved with a cap, and the center tube and the cap are fixedly connected together by shear nails, the outer side of the push tube is sleeved with an outer tube, the lower outer side of the cap and the upper inner side of the outer tube are fixedly connected together, the lower inner side of the outer tube and the upper outer side of the lower joint are fixedly connected together, the upper inner side of the lower joint is provided with an inner ring groove adapted to the push tube, and the middle inner side of the outer tube is provided with a sliding seal formed with the outer wall of the push tube The sealing ring platform is a sealing ring platform, and the inner side of the outer cylinder corresponding to the position between the sealing ring platform and the lower joint is sleeved with an upper and lower group of valve parts, each group of valve parts includes a support ring, a valve seat, a valve plate and a torsion spring. The support ring and the valve seat are arranged in the outer cylinder from top to bottom, and the upper part of the valve seat is sleeved on the lower outer side of the support ring. The interiors of the support ring and the valve seat respectively form a through-cylinder channel for the push cylinder to pass through. A valve plate is hinged on the valve seat corresponding to the lower side of the support ring through a pin shaft, and the pin shaft is provided with a torsion spring for closing the support ring with the valve plate. The push cylinder is located above the valve plate of the upper group of valve parts, and the push cylinder can push open the valve plates of the two groups of valve parts and insert into the inner ring groove when it descends relative to the outer cylinder.

2. The lifting and releasing two-stage oil pipe switch valve according to claim 1 is characterized in that Two groups of upper and lower liquid passages are arranged through the wall of the outer cylinder corresponding to the position between the cap and the sealing ring platform.

3. The lifting and releasing two-stage oil pipe switching valve according to claim 1 or 2, characterized in that The center tube and the cap are circumferentially anti-rotationally matched; anti-retraction screws are provided between the cap and the outer tube, and between the outer tube and the lower joint.

4. The lifting and releasing two-stage oil pipe switching valve according to claim 1 or 2, characterized in that A first mounting ring groove and a second mounting ring groove are arranged on the inner wall of the sealing ring platform at intervals, a retaining ring is installed in the first mounting ring groove, and an O-type sealing ring is installed in the second mounting ring groove; a third mounting ring groove is arranged on the inner wall of the inner ring groove, and an O-type sealing ring is installed in the third mounting ring groove.

5. The lifting and releasing two-stage oil pipe switch valve according to claim 3 is characterized in that A first mounting ring groove and a second mounting ring groove are arranged on the inner wall of the sealing ring platform at intervals, a retaining ring is installed in the first mounting ring groove, and an O-type sealing ring is installed in the second mounting ring groove; a third mounting ring groove is arranged on the inner wall of the inner ring groove, and an O-type sealing ring is installed in the third mounting ring groove.

6. The lifting and releasing two-stage oil pipe switching valve according to claim 1, 2 or 5, characterized in that An O-ring is provided between the outer wall of the support ring and the inner wall of the outer tube; an O-ring is provided between the lower end surface of the support ring and the upper end surface of the valve plate; an O-ring is provided between the lower inner side of the upper joint and the upper outer side of the center tube; an O-ring is provided between the lower outer side of the center tube and the upper inner side of the push tube.

7. The lifting and releasing two-stage oil pipe switching valve according to claim 1, 2 or 5, characterized in that The lower inner side of the upper joint and the upper outer side of the center tube are connected together by threaded fixing, the lower outer side of the center tube and the upper inner side of the push tube are connected together by threaded fixing, the lower outer side of the cap and the upper inner side of the outer tube are connected together by threaded fixing, and the lower inner side of the outer tube and the upper outer side of the lower joint are connected together by threaded fixing.

8. A method for controlling the pressure of oil pipes in a pressure-drag fracturing process using a lifting and releasing two-stage oil pipe switch valve according to any one of claims 1 to 7, characterized in that The following steps are involved: S1: Lowering the fracturing string into the target well, the fracturing string includes a safety joint, a hydraulic anchor, a lifting and releasing two-stage tubing switch valve, a top seal packer, a throttle, a sandblaster, a bottom seal packer and a guide head which are connected in series on the tubing from top to bottom; S2: When the fracturing string reaches the target layer, the bottom seal packer is first set, and then the fracturing string is lowered to pressurize so that the shear pins are sheared off, and the push tube moves downward relative to the outer tube to open the lifting and releasing two-stage tubing switch valve, and then the fracturing pumping construction is carried out; S3: After the target layer fracturing pumping construction is completed, the position of the fracturing string is kept unchanged so that the lifting and releasing two-stage tubing switch valve is in the open position, and reverse circulation well washing is performed. After the reverse circulation well washing is completed, the fracturing string is lifted up with pressure, and the push tube moves upward relative to the outer tube, so that the lifting and releasing two-stage tubing switch valve is in the closed position again, and the fracturing string is continuously lifted up with pressure to the next target layer to complete the layer change; S4: Repeat steps S2 to S3 until the multi-layer fracturing is completed.

9. The method for controlling the pressure of the oil pipe under pressure by dragging the fracturing oil pipe under pressure according to claim 8, characterized in that In step S3, when the fracturing string is lifted up under pressure, if the bottom seal packer is found to be stuck, the hydraulic turntable of the pressure-operated machine can be used to rotate the fracturing string, and the torque is transmitted to the bottom seal packer through the upper joint, the center pipe, the cap, the outer tube, and the lower joint to achieve rotational release.

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