Low-permeability reservoir carbon dioxide drive under-pressure operation tubular column and operation method

Abstract

The invention discloses a low-permeability reservoir carbon dioxide drive under-pressure operation pipe column and an operation method. The pipe column sequentially comprises a high-pressure screwed plug, a tail pipe, a gas injection valve, a tungsten plating and permeating oil pipe, a lower centralizer, a releasing packer, an upper centralizer, a sliding sleeve valve and an air sealing oil pipe from bottom to top. A tubular column enters a well during operation under pressure, and annulus protection fluid is positively injected for fluid replacement; a constant-pressure valve ball is put in, positive pressing is carried out step by step, and the sealing performance of the tubular column is checked; slowly setting a tubing hanger after pressure relief; then positive pressure is applied to enable the releasing packer to be set, then pressure is continuously increased to break the valve seat thin-wall section of the constant-pressure valve seat, and positive injection communication of the tubular column is achieved; and then water is squeezed forwards, after the sealing performance of the packer is verified, the ground process is connected, carbon dioxide is injected forwards, the carbon dioxide enters a shaft annulus and a stratum, and well closing is conducted after the set gas injection amount is achieved. The device can meet the requirement for under-pressure operation, overflow is avoided in the well descending process, after positive replacement, a ball is thrown to press and set a packer, a shaft is protected, dirt deposition is prevented, and the whole operation process is safe and controllable.

Description

Technical Field

[0001] The present invention relates to a downhole operation pipe string, in particular to a carbon dioxide drive pressure operation pipe string; the present invention also relates to a carbon dioxide drive pressure operation method for low permeability oil reservoirs, belonging to the technical field of downhole injection operations. Background Art

[0002] In the late stage of oil reservoir development or low permeability oil reservoir, the weak driving force of the formation leads to slow development speed and low recovery rate. Water or gas is usually injected into the well through the ground to restore the oil layer pressure and increase the driving force of the oil reservoir, so as to increase the development speed and recovery rate of the oil reservoir.

[0003] Oil recovery methods that use gas as the main oil recovery medium are collectively referred to as gas drive. In the oil recovery industry, carbon dioxide is usually used as the gas drive medium. CO2 drive has become an important means to improve the recovery rate of oil wells. CO2 oil recovery has strong expansion, viscosity reduction and extraction effects, thereby effectively improving the flow capacity of crude oil, reducing residual oil saturation, and improving recovery. In response to the problems of difficult water injection, low oil recovery rate and high decline rate in low permeability reservoirs, more and more oil fields have carried out research and application of CO2 oil recovery technology, which has become one of the important means to improve the recovery rate of oil fields, effectively improving the development effect of low permeability reservoirs and meeting the development requirements of "green, low-carbon and environmentally friendly".

[0004] The mechanism of CO2 flooding is that when CO2 dissolves in crude oil, the viscosity of crude oil decreases significantly, and the extent of the decrease depends on the pressure, temperature and crude oil composition. During the CO2 injection process, as the injection pressure increases, the carbon dioxide dissolved in the crude oil also increases, and the saturation pressure also rises. As the pressure rises, the expansion coefficient of the crude oil at the saturation pressure tends to gradually increase, which can expand the formation crude oil and effectively increase the formation energy and movable oil.

[0005] After CO2 enters the oil layer, it occupies a certain amount of pore space, increases the pressure of the oil layer, and increases crude oil production. During the production process, as the pressure drops, the CO2 dissolved in the crude oil escapes, which has the effect of dissolved gas drive; it generates gas driving force in the liquid, improving the oil recovery effect.

[0006] The Chinese invention patent with publication number CN 102536183A discloses a downhole gas injection string, which can prevent the injection gas from spitting back, can be reversely circulated, and does not require a plugging device to be thrown and salvaged. The packer is installed above the oil layer, the packer is connected to a drop-out return tube above, and the packer is connected to an injection valve below. The upper end of the oil pipe string is connected to a wellhead device, and the lower end of the oil pipe string is connected to a casing pressure valve and a sealing plug from top to bottom. The sealing plug is inserted into the drop-out return tube. The casing pressure valve and the gas injection valve are both single-flow valves. The flow direction of the casing pressure valve is from the oil casing annulus to the oil pipe, and the flow direction of the gas injection valve is from the valve inside to the valve outside.

[0007] The gas injection string in the well has the following problems: 1. The construction process is relatively complicated. It is necessary to first lower the hand-release string, the hand-release return tube, and after the downhole string is pulled out, the gas injection string connected with the casing pressure valve and the sealing plug is lowered, and the sealing plug is inserted into the hand-release return tube to complete the gas injection string; 2. In case of unstable injection, alternating injection of gas and water, and changes in temperature and pressure during the injection process, the pipe string will deform by expansion and contraction, creeping, etc. Firstly, the sealing structure of the sealing plug is easily damaged, and secondly, the downward pressure generated acts on the packer, causing the packer to fail, thus leading to failure of the gas injection pipe string; 3. During the operation or gas injection construction of the gas injection valve, foreign matter is easily deposited on the valve seat, affecting the closing and sealing performance of the valve ball; 4. There is gas leakage in the annulus of the oil casing. The bubbles may cause the casing pressure to be greater than the oil pressure during the rising process. The casing pressure valve will open prematurely, which may cause casing damage and increase well control and safety risks.

[0008] The Chinese utility model patent with publication number CN 204899860U discloses a downhole gas injection valve that can meet the needs of sealing the gas injection packer and unidirectional gas injection into the oil layer. The gas injection valve includes an outer tube, a sliding sleeve and a seat sealing ball. The outer circle of the sliding sleeve is provided with a sealing ring and a locking ring. The outer tube is provided with a balancing hole. The seat sealing ball sits in the conical inner circle of the upper part of the sliding sleeve. The outer tube and the sliding sleeve are fixed by shear nails. The lower part of the outer tube is connected to the valve seat. The body of the valve seat is provided with an air inlet and an air outlet. The center counterbore of the valve seat is equipped with a valve ball and a top cap. The top rod installed on the top of the top cap is inserted into the sliding sleeve. The air inlet is connected to the center counterbore of the valve seat.

[0009] The downhole gas injection valve has the following problems: 1. Since the gas injection valve is equipped with a balance hole and a circulation channel, it is in a normally open state during the downhole process, which cannot meet the requirements of pressure operation and poses a great environmental risk; during the downhole process of the tubing, the well fluid in the annulus overflows from the tubing to the wellhead, causing serious pollution to the wellhead; 2. When the overflow from the wellhead is too large, well killing operations are required. After the well killing fluid is injected into the well, it will damage the oil layer, reducing the mining value and recovery rate; 3. The outlet of the gas injection valve is a small hole, which has no ability to prevent dirt deposition, and the anti-backspitting valve is not closed tightly, causing CO2 backspitting; 4. The outlet for injecting CO2 is a lateral vertical outlet, which directly impacts the casing and causes casing damage; 5. There is no filtering device at the front end of the anti-backflow valve. During operation or gas injection construction, foreign matter is deposited on the valve seat, affecting the closing and sealing performance of the valve ball.

[0010] 6. There is no filter on the outside of the valve body liquid flow channel, which cannot prevent foreign matter from entering the well and affect the sealing effect. Summary of the invention

[0011] The primary purpose of the present invention is to overcome the problems existing in the prior art and provide a low permeability oil reservoir carbon dioxide flooding pressure operation pipe string that can meet the requirements of pressure operation, has no overflow during the downhole process, can replace the wellbore annulus protection fluid and then drop a ball to pressurize the sealing device and form an effective seal, while protecting the wellbore and preventing dirt deposition.

[0012] In order to solve the above technical problems, the low permeability oil reservoir carbon dioxide drive pressurized operation pipe string of the present invention includes a release packer located above the oil layer, the lower part of the release packer is connected to the lower part of the release packer, the lower part of the lower stabilizer is screwed with a tungsten-plated oil pipe, the lower part of the tungsten-plated oil pipe is screwed with an injection valve, the lower part of the injection valve is screwed with a tail pipe, and the lower end of the tail pipe is screwed with a high-pressure wire plug; the upper part of the release packer is connected to the upper part of the release packer, the upper part of the upper stabilizer is screwed with a sliding sleeve valve, and the upper end of the sliding sleeve valve is screwed below the air-tight sealing oil pipe.

[0013] As an improvement of the present invention, the sliding sleeve valve includes a sliding sleeve body, the lower end of the sliding sleeve body is screwed with a double male joint, an inner sliding sleeve is provided below the inner step at the upper end of the sliding sleeve body, the outer wall of the inner sliding sleeve is fitted with the inner wall of the sliding sleeve body, and the upper end of the center hole of the inner sleeve is provided with an inner sliding sleeve bell mouth for soluble ball sealing; a bypass hole is provided on the upper side wall of the sliding sleeve body, the inner port of the bypass hole is covered by the inner sleeve and the upper and lower ends are sealed with the inner sleeve; a sliding sleeve spring is provided at the lower end of the inner sleeve, the lower end of the sliding sleeve spring is supported on the upper port of the double male joint, the sliding sleeve spring is wound around the outer periphery of the liner, the upper end of the liner is screwed into the female thread at the lower end of the inner sleeve, the lower end of the liner is inserted into the inner cavity of the double male joint, and the upper inner edge of the sliding sleeve spring presses against the lower end surface of the inner sleeve.

[0014] When unclamping the valve body, the valve body is emptied and the valve body is sealed.Attorney Docket: 22222PCT of the present invention is a valve body, and a closure is attached to the valve body, and a valve core is attached to the valve body. The closure is attached to the valve core, and the valve core is emptied and the valve core is sealed.

[0015] As a further improvement of the present invention, a large diameter valve seat section is provided on the upper part of the constant pressure valve seat, the large diameter valve seat section is embedded in the upper port of the outer sleeve and rests against the inner step of the outer sleeve, and the top of the large diameter valve seat section is located below the inner step of the upper joint.

[0016] As a further improvement of the present invention, the lower outer wall of the constant pressure valve seat is symmetrically provided with three limit bosses, a flow channel is provided between adjacent limit bosses, the outer end surface of each limit boss is respectively provided with a limit groove, each limit groove is respectively embedded with a limit pin shaft, the inner end surface of each limit pin shaft is respectively provided with a countersunk hole and a limit spring is respectively embedded therein, and each limit spring is respectively supported between the bottom wall of the countersunk hole and the bottom wall of the limit groove.

[0017] As a further improvement of the present invention, the outer end of each of the limit pins is provided with a spherical surface, and the center of each spherical surface abuts against the inner wall of the center hole of the outer sleeve.

[0018] As a further improvement of the present invention, the lower end of the constant pressure valve seat is symmetrically provided with valve seat supporting claws extending downward, and flow passages are provided between adjacent valve seat supporting claws.

[0019] As a further improvement of the present invention, the lower end of the center hole of the outer sleeve that accommodates the constant pressure valve seat is provided with a first diameter expansion section of the outer sleeve, a second diameter expansion section of the outer sleeve and a third diameter expansion section of the outer sleeve with gradually expanding diameters, the length of the first diameter expansion section of the outer sleeve is greater than the distance between the thin-walled section of the valve seat and the limiting boss, the length of the second diameter expansion section of the outer sleeve is greater than the diameter of the limiting pin shaft, and the length of the third diameter expansion section of the outer sleeve is greater than the length of the valve seat support claw.

[0020] As a further improvement of the present invention, when the thin-walled section of the valve seat is pulled off and the anti-return valve seat falls, the valve seat support claw is supported on the top of the valve body, and each limit spring pushes out the limit pin so that the spherical surface of the outer end of each limit pin symmetrically rests against the inner wall of the second expanded diameter section of the outer sleeve.

[0021] As a further improvement of the present invention, the radius of the third expanded section of the outer sleeve is greater than or equal to the radius of the circumference of the outer edge of the valve body axial hole, and the outer edge radius of the valve seat support claw is smaller than the radius of the circumference of the inner edge of the valve body axial hole.

[0022] As a further improvement of the present invention, the middle outer wall of the valve body is covered with a filter screen, and the filter screen covers the outer ports of each radial hole of the valve body.

[0023] As a further improvement of the present invention, the filter screen is evenly provided with a plurality of strip-shaped filter slits extending along the axial direction.

[0024] As a further improvement of the present invention, an annular groove is provided on the outer periphery of the middle portion of the valve body, and the outer port of each radial hole of the valve body is located on the bottom wall of the annular groove.

[0025] As a further improvement of the present invention, the outer port of the radial hole of the valve body is inclined upward.

[0026] As a further improvement of the present invention, the lower end of the valve seat pressure cap is conically contracted to be closed, and a plurality of pressure cap slit channels are evenly distributed on the lower circumference of the valve seat pressure cap.

[0027] As a further improvement of the present invention, each of the pressure cap strip slit channels extends from the cylindrical end to the tapered section.

[0028] As a further improvement of the present invention, an upper joint light hole section is provided above the female thread at the lower end of the upper joint, and an upper joint sealing ring is embedded in the inner wall of the upper joint light hole section to achieve sealing with the outer wall of the upper port of the outer sleeve.

[0029] As a further improvement of the present invention, at least one constant-pressure valve seat sealing ring is embedded in the outer wall of the large-diameter section of the valve seat to achieve sealing with the inner wall of the upper port of the outer sleeve.

[0030] As a further improvement of the present invention, a sleeve smooth hole sealing section is provided above the female thread at the lower end of the sleeve, a sleeve sealing ring is embedded in the inner wall of the sleeve smooth hole sealing section, and the sleeve sealing ring is sealed with the upper cylindrical section of the valve body.

[0031] As a further improvement of the present invention, a lower joint smooth hole sealing section is provided below the upper female thread of the lower joint, and a lower joint sealing ring is embedded in the inner wall of the lower joint smooth hole sealing section to achieve sealing with the lower cylindrical section of the valve body.

[0032] As a further improvement of the present invention, a pressure cap sealing ring is embedded in the upper outer wall of the valve seat pressure cap to achieve sealing with the lower inner wall of the valve body.

[0033] Another object of the present invention is to overcome the problems existing in the prior art and provide a method for pressurized carbon dioxide flooding in low permeability reservoirs, which can meet the requirements of pressurized operations, has no overflow during the process of going down the well, can replace the wellbore annulus protection fluid, and then drop a ball to pressurize the sealing device and form an effective seal, while protecting the wellbore and preventing dirt deposition.

[0034] In order to solve the above technical problems, the low permeability reservoir carbon dioxide flooding pressure operation method of the present invention comprises the following steps in sequence: S1. Prepare the wellbore and install the wellhead equipment; S2. Assemble the pressure operation string as claimed in claim 1 and run it into the well section by section, and remove the soluble ball and the constant pressure valve ball before assembly; S3. The pressure-operated pipe string is lowered to the designed depth, and the anti-return valve ball is seated on the anti-return valve seat to prevent the well fluid in the annulus from entering the gas-sealed oil pipe; S4. Inject annular protection fluid from the surface until the wellbore annulus fluid is completely replaced; S5. Throw the pressure regulating valve ball into the wellhead, and the pressure regulating valve ball rolls down and is seated on the upper part of the pressure regulating valve seat; S6. Pressurize step by step to 16MPa and check the tightness of the pipe string; then reduce the pressure to 8MPa and slowly place the tubing hanger to support the upper end of the pipe string on the wellhead; S7. Pressurize to 18 MPa to set the hand-free packer, then continue to increase the pressure to break the thin-walled section of the constant pressure valve seat, and the lower part of the constant pressure valve seat falls off, so that the string can be connected with positive injection; S8. Squeeze water to verify and confirm that the seal of the drop packer is good; S9. Connect to the surface process and inject carbon dioxide from the wellhead. The carbon dioxide pushes the anti-return valve ball and enters the wellbore annulus through the radial hole of the valve body, and then enters the formation; after reaching the set gas injection volume, it enters the wellbore.

[0035] As an improvement of the present invention, during the gas injection process in step S9, if the casing pressure rises, the gas injection is stopped and the process goes to step S10: a soluble ball is put in, and after positive pressure is applied to verify the sealing of the tubing string above the sleeve valve, the pressure is continued to be increased to open the bypass hole of the sleeve valve, and the well is washed and degassed by positive circulation, and then the annulus protection fluid is replaced. After the pressure is released, the bypass hole of the sleeve valve is closed, and after the soluble ball is dissolved, the gas injection is continued to observe whether the casing pressure rises.

[0036] As a further improvement of the present invention, in step S10, after the soluble ball is dissolved, if the casing pressure still rises by continuing to inject gas, the following steps are entered: Step S11. Add the soluble ball again and pressurize to open the bypass hole of the sleeve valve; Step S12. Positively circulating well killing fluid to kill the well and degas; Step S13. After the soluble ball is dissolved, a throw-away ball is thrown into the oil pipe, and positive pressure is applied to release the upper part of the throw-away packer, and the pressurized operation string is lifted out of the wellhead; Step S14: salvage the pipe string under pressure to salvage the hand-free packer and the pipe string below it.

[0037] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. The gas injection valve can prevent the well fluid from flowing out through the anti-return valve ball and the anti-return valve seat, can realize pressurized operation, reduce the well occupation period, and reduce the operating cost, which is of great significance to safety, environmental protection and other aspects.

[0038] 2. The constant pressure valve seat adopts a thin-wall pull-off opening structure. By controlling the thickness of the thin wall, the constant pressure opening pressure is more accurate compared to shearing with multiple pins. It also avoids the sharp edge of the pin after shearing to damage the inner wall of the outer sleeve, and can also reduce the downward resistance of the constant pressure valve seat opening and prevent foreign objects from falling into the well.

[0039] 3. A limit mechanism is set in three equal parts of the middle circle of the constant pressure valve seat, and the flow channel between the three equal parts of the limit mechanism can be used as a positive injection channel. The limit mechanism adopts a limit pin and a limit spring structure, which is reliable in limiting. The contact part between the limit pin and the inner wall of the jacket adopts a spherical structure, which effectively protects the inner wall of the jacket from damage, and has low friction resistance, which is convenient for the constant pressure valve seat to open and move downward.

[0040] 4. A filter screen is installed outside the liquid flow channel of the valve body to prevent foreign matter from entering the well, thus preventing the valve ball from being tightly sealed and affecting pressure operation. An annular groove is installed in the flow channel of the valve body to ensure the flow area.

[0041] 5. A slit channel is provided at the lower end of the seat cap to prevent foreign matter from entering the valve body during positive injection operations such as well washing or fluid replacement, thereby affecting the closing performance of the anti-return valve ball.

[0042] 6. When the casing pressure rises, you can perform positive well washing and degassing to protect the wellbore and repair minor faults. If the casing pressure continues to rise after positive well washing, you can also perform positive circulation well pressure and degassing to ensure well control safety during the process of lifting the tubing. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The accompanying drawings are only provided for reference and explanation and are not intended to limit the present invention.

[0044] Figure 1 This is a schematic diagram of the structure of a low permeability reservoir carbon dioxide flooding pressure operation string according to the present invention; Figure 2 It is a structural schematic diagram of the gas injection valve in the present invention; Figure 3 It is an enlarged cross-sectional view of a constant pressure valve seat in a gas injection valve; Figure 4 for Figure 3 Bottom view of Figure 5 is an enlarged cross-sectional view of the jacket in the gas injection valve; Figure 6 This is a state diagram after the constant pressure valve seat in the gas injection valve is pulled off; Figure 7 for Figure 6 Sectional view along AA; Figure 8 It is a structural schematic diagram of the sliding sleeve valve in the present invention; In the figure: A. high-pressure plug; B. tail pipe; C. injection valve; D. tungsten-plated tubing; E. lower centralizer; F. hand-release packer; G. upper centralizer; H. sliding sleeve valve; J. gas-sealed tubing; 1. upper joint; 2. upper joint sealing ring; 3. constant-pressure valve seat; 3a. large-diameter section of valve seat; 3b. thin-wall section of valve seat; 3c. limiting groove; 3d. valve seat support claw; 3e. constant-pressure valve seat sealing ring; 4. constant-pressure valve ball; 5. limiting pin; 6. limiting spring; 7. outer jacket; 7a. first diameter expansion section of outer jacket; 7b. second diameter expansion section of outer jacket; 7 c. The third expanded diameter section of the outer sleeve; 7d. The outer sleeve sealing ring; 8. The valve body; 8a. The axial hole of the valve body; 8b. The valve cavity; 8c. The radial hole of the valve body; 8d. The annular groove; 9. The filter screen; 9a. The strip filter slit; 10. The anti-return valve ball; 11. The anti-return valve seat; 12. The valve seat pressure cap; 12a. The pressure cap slit channel; 12b. The pressure cap sealing ring; 13. The lower joint; 13a. The lower joint sealing ring; 14. The sliding sleeve body; 14a. The bypass hole; 15. The soluble ball; 16. The inner sliding sleeve; 17. The liner; 18. The sliding sleeve spring; 19. The double male joint. Implementation

[0045] In the following description of the present invention, the directions or positional relationships indicated by terms such as "up", "down", "front", "back", "left", "right", "inside" and "outside" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and do not mean that the device must have a specific direction.

[0046] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below with reference to specific diagrams.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0048] like Figure 1 As shown, the low permeability reservoir carbon dioxide flooding pressure operation pipe string of the present invention comprises a Y445J type release packer located above the oil layer, the release packer F is connected with a lower centralizer E below, a tungsten-plated oil pipe D is screwed to the lower part of the lower centralizer E, a gas injection valve C is screwed to the lower part of the tungsten-plated oil pipe D, a tail pipe B is screwed to the lower part of the gas injection valve C, and a high-pressure wire plug A is screwed to the lower end of the tail pipe B; the release packer F is connected with an upper centralizer G above, a sleeve valve H is screwed to the upper part of the upper centralizer G, the upper end of the sleeve valve H is screwed to the lower part of the gas-tight oil pipe J, the upper 1000m adopts 3Cr gas-tight oil pipe, and the rest adopts N80 gas-tight oil pipe.

[0049] like Figures 2 to 7As shown, the gas injection valve C in the present invention is used for pressure working wells, and includes an upper joint 1, a constant pressure valve seat 3, a constant pressure valve ball 4, a jacket 7, a valve body 8, an anti-return valve seat 11, an anti-return valve ball 10, a valve seat pressure cap 12 and a lower joint 13. The female thread at the lower end of the upper joint 1 is screwed with the male thread at the upper part of the jacket 7, and an upper joint light hole section is provided above the female thread at the lower end of the upper joint 1. The inner wall of the upper joint light hole section is embedded with an upper joint sealing ring 2 to achieve sealing with the outer wall of the upper port of the jacket 7.

[0050] The upper inner cavity of the outer sleeve 7 is fixed with a constant pressure valve seat 3, and the upper part of the constant pressure valve seat 3 is provided with a valve seat large diameter section 3a, which is embedded in the upper port of the outer sleeve 7 and abuts against the upper inner step of the outer sleeve 7, and the top of the valve seat large diameter section 3a is located below the inner step of the upper joint 1, so that the constant pressure valve seat 3 is suspended in the upper inner cavity of the outer sleeve 7 while achieving axial positioning. Two constant pressure valve seat sealing rings 3e are embedded in the outer wall of the valve seat large diameter section 3a to achieve sealing with the inner wall of the upper port of the outer sleeve 7.

[0051] A valve seat thin-walled section 3b is provided below the large-diameter section 3a of the valve seat. If the set tensile force is exceeded, the valve seat thin-walled section 3b will be pulled off. A cylindrical section is provided below the valve seat thin-walled section 3b, and a valve seat inner cone surface that is wide at the top and narrow at the bottom is provided at the lower end of the center hole. A constant-pressure valve ball 4 is seated on the valve seat inner cone surface. After the constant-pressure valve ball 4 is seated in the constant-pressure valve seat 3, a pressure is generated, which is used to seat the packer above the gas injection valve C or to pull off the valve seat thin-walled section 3b. After the valve seat thin-walled section 3b is pulled off, no radial sharp edge will be generated, and the fracture will not scratch the inner wall of the outer sleeve 7 during the falling process.

[0052] The female thread at the lower end of the outer sleeve 7 is screwed into the male thread at the upper end of the valve body 8. A outer sleeve light hole sealing section is provided above the female thread at the lower end of the outer sleeve 7. A outer sleeve sealing ring 7d is embedded in the inner wall of the outer sleeve light hole sealing section. The outer sleeve sealing ring 7d is sealed with the upper cylindrical section of the valve body 8.

[0053] A plurality of through valve body axial holes 8a are evenly arranged along the circumference of the valve body 8 for passing the liquid flow from top to bottom. A valve cavity 8b with a closed upper end is arranged in the center of the valve body 8, and a throat is arranged at the lower part of the valve cavity 8b. An anti-return valve seat 11 is abutted below the throat. An anti-return valve ball 10 is seated in the upper port of the anti-return valve seat 11. A valve seat pressing cap 12 is supported below the anti-return valve seat 11. The middle part of the valve seat pressing cap 12 is screwed into the lower port of the valve body 8. Valve body radial holes 8c are symmetrically arranged on the outer peripheral wall of the valve body 8 to communicate with the middle part of the valve cavity 8b, and a lower joint 13 is screwed on the outer lower end of the valve body 8. The valve body radial holes 8c are usually symmetrically arranged in two, and each valve body axial hole 8a is distributed on the outer side of the valve cavity 8b, and is staggered in phase with the valve body radial hole 8c and is not connected to each other.

[0054] The lower outer wall of the constant pressure valve seat 3 is symmetrically provided with three limit bosses, and a flow channel is provided between adjacent limit bosses. The outer end face of each limit boss is respectively provided with a limit groove 3c extending radially along the constant pressure valve seat, and a limit pin 5 is respectively inserted in each limit groove 3c. The inner end face of each limit pin 5 is respectively provided with a countersunk hole and a limit spring 6 is respectively embedded. Each limit spring 6 is respectively supported between the bottom wall of the countersunk hole and the bottom wall of the limit groove 3c, and an outward thrust is applied to the limit pin 5, so that the outer end of the limit pin 5 is reliably abutted against the inner wall of the outer sleeve 7, and can adapt to the change of the inner diameter of the outer sleeve, so that after the thin-walled section 3b of the valve seat is pulled off, the falling constant pressure valve seat 3 is kept centered in the inner cavity of the outer sleeve 7, thereby ensuring that the annular liquid flow channel between adjacent limit bosses is evenly distributed, and as a positive injection channel, the injection of anti-corrosion liquid or carbon dioxide or water into the well is more uniform.

[0055] The outer end of each limit pin 5 is provided with a spherical surface, and the center of each spherical surface abuts against the inner wall of the center hole of the outer sleeve 7. While keeping the constant pressure valve seat 3 centered, the friction resistance of the limit pin 5 when sliding down is reduced, effectively protecting the inner wall of the outer sleeve from damage, and ensuring that after the thin wall section 3b of the valve seat is broken, the constant pressure valve seat 3 can fall reliably to achieve constant pressure opening.

[0056] The lower end of the constant pressure valve seat 3 is symmetrically provided with valve seat support claws 3d extending downward. After the valve seat thin wall section 3b is pulled off, the lower part of the constant pressure valve seat 3 falls down. When the valve seat support claws 3d fall on the top of the valve body 8, the constant pressure valve seat 3 falls into place. There are also flow passages between adjacent valve seat support claws 3d. When the valve seat thin wall section 3b is pulled off, the constant pressure valve ball 4 is in a floating state, and the valve seat center hole can also be used as an auxiliary liquid flow channel to reduce injection resistance.

[0057] The central hole of the outer sleeve that accommodates the constant pressure valve seat 3 is the section with the smallest inner diameter of the outer sleeve. The lower end of the central hole of the outer sleeve is provided with an expanded first diameter expansion section 7a of the outer sleeve. The length of the first diameter expansion section 7a of the outer sleeve is greater than the distance between the thin wall section 3b of the valve seat and the limiting boss, so that the first diameter expansion section 7a of the outer sleeve can accommodate the main body of the constant pressure valve seat 3 after being pulled apart.

[0058] A second enlarged diameter section 7b of the outer sleeve is provided below the first enlarged diameter section 7a of the outer sleeve, and the length of the second enlarged diameter section 7b of the outer sleeve is greater than the diameter of the limit pin 5, so as to facilitate the abutment of the outer end of the limit pin 5. When the valve seat thin wall section 3b is pulled off to make the anti-return valve seat 11 fall, the valve seat support claw 3d is supported on the top of the valve body 8, and each limit spring 6 pushes the limit pin 5 out so that the spherical surface of the outer end of each limit pin symmetrically abuts against the inner wall of the second enlarged diameter section 7b of the outer sleeve.

[0059] A third expansion section 7c of the outer sleeve is provided below the second expansion section 7b of the outer sleeve for further expansion. The length of the third expansion section 7c of the outer sleeve is greater than the length of the valve seat support claw 3d, so that when the valve seat support claw 3d falls on the top of the valve body 8, the limit pin 5 cooperates with the inner wall of the second expansion section 7b of the outer sleeve.

[0060] The radius of the third expanded diameter section 7c of the outer sleeve is greater than or equal to the radius of the circumference of the outer edge of the valve body axial hole 8a, and the outer edge radius of the valve seat support claw 3d is smaller than the radius of the circumference of the inner edge of the valve body axial hole 8a, so that both the inner and outer sides avoid obstruction to the liquid flow in and out of the valve body axial hole 8a.

[0061] The middle outer wall of the valve body 8 is covered with a filter screen 9, which covers the outer ports of the radial holes 8c of each valve body. The filter screen 9 is evenly provided with multiple strip-shaped filter slits 9a extending along the axial direction to prevent debris and other foreign matter in the wellbore annulus from entering the radial holes 8c of the valve body, so as to avoid the anti-return valve ball 10 from being loosely sealed and causing wellhead backflow pollution during pressure operation.

[0062] An annular groove 8d is provided on the outer periphery of the middle part of the valve body 8, and the upper and lower ends of the annular groove 8d are close to the upper and lower edges of the filter screen 9 to expand the volume of the annular space inside the filter screen 9 and make the liquid flow in and out more unobstructed; the outer port of each valve body radial hole 8c is located on the bottom wall of the annular groove 8d.

[0063] The outer port of the radial hole 8c of the valve body is inclined upward to prevent the fluid flowing out of the radial hole 8c of the valve body from directly scouring the inner wall of the wellbore when the anti-corrosion liquid or carbon dioxide is injected, thereby reducing damage to the wellbore.

[0064] The upper outer wall of the valve seat cap 12 is embedded with a cap seal ring 12b to seal with the lower inner wall of the valve body 8. The lower end of the valve seat cap 12 is conically contracted to be closed, and multiple cap slit channels 12a are evenly distributed on the lower circumference of the valve seat cap 12. Each cap slit channel 12a extends from the cylindrical end to the conical section to ensure sufficient flow area. When the well washing fluid is positively injected downward along the axial hole 8a of the valve body, each cap slit channel 12a can prevent foreign matter from entering the inner cavity of the valve seat cap 12, and avoid the mating surface of the anti-return valve seat 11 and the anti-return valve ball 10 from affecting the closing performance of the anti-return valve ball 10 due to foreign matter.

[0065] A lower joint light hole sealing section is provided below the upper female thread of the lower joint 13 , and a lower joint sealing ring 13 a is embedded in the inner wall of the lower joint light hole sealing section to achieve sealing with the lower cylindrical section of the valve body 8 .

[0066] like Figure 8As shown, the sliding sleeve valve H includes a sliding sleeve body 14 , the lower end of which is screwed with a double male connector 19 , and the upper end of the double male connector 19 is embedded with two sealing rings to achieve sealing with the inner wall of the lower end of the sliding sleeve body 14 . An inner sleeve 16 is provided below the inner step at the upper end of the sliding sleeve body 14, and the outer wall of the inner sleeve 16 fits with the inner wall of the sliding sleeve body 14, and the upper end of the center hole of the inner sleeve 16 is provided with an inner sleeve trumpet for the soluble ball 15 to be sealed; a bypass hole 14a is provided on the upper side wall of the sliding sleeve body 14, and the inner port of the bypass hole 14a is covered by the inner sleeve 16, and the upper and lower sides of the inner port of the bypass hole 14a are sealed with the inner sleeve 16 through the inner sleeve sealing ring; a sliding sleeve spring 18 is provided at the lower end of the inner sleeve 16, and the sliding sleeve spring 18 is wound around the outer periphery of the liner 17, and the upper end of the liner 17 is screwed into the female thread at the lower end of the inner sleeve 16, and the lower end of the liner 17 is inserted into the inner cavity of the double male joint 19, which plays a guiding role and can slide up and down, and the lower end of the sliding sleeve spring 18 is supported on the upper port of the double male joint 19.

[0067] The low permeability reservoir carbon dioxide flooding pressure operation method of the present invention comprises the following steps in sequence: S1. Prepare the wellbore, including completing wellbore clearance, scraping and casing inspection, and then install the CC-level KQ35 / 65 wellhead device.

[0068] S2. Assemble the pressure operation string and run it into the well section by section. From bottom to top, it includes high-pressure wire plug A, tail pipe B, gas injection valve C, Φ73mm tungsten-plated tubing D, lower centralizer E, drop packer F, upper centralizer G, and sleeve valve H. Tail pipe B can also use Φ73mm tungsten-plated tubing D. The upper end of the sleeve valve H is screwed under the Φ73mm gas-sealed tubing J. Before assembly, remove the soluble ball 15 of the sleeve valve H and the pressure-regulating valve ball of the gas injection valve C.

[0069] S3. The pressure-carrying operation string is lowered to the designed depth, and the drop-out packer F is located above the oil layer. During the lowering process, the well fluid in the wellbore annulus passes through the filter screen 9, and is pressed on the anti-return valve ball 10 through the radial hole 8c of the valve body. The anti-return valve ball 10 is seated on the anti-return valve seat 11, closing the downward passage. The well fluid in the annulus cannot enter the valve seat pressure cap 12, and will not pass through the axial hole 8a of the valve body into the oil pipe above, which can prevent the well fluid from flowing out of the ground and polluting the environment.

[0070] S4. Prepare 1% carbon dioxide corrosion inhibitor + 300ppm bactericide as annulus protection liquid, inject annulus protection liquid through the surface, the annulus protection liquid passes through the center hole of the constant pressure valve seat 3, and then goes down along the axial holes 8a of each valve body into the lower joint 13, and then enters the inner cavity of the valve seat cap 12 from the slit channels 12a of each cap, and then pushes the anti-return valve ball 10 upward into the valve cavity 8b, and then enters the wellbore annulus through the radial holes 8c of the valve body, completely replacing the wellbore annulus well fluid, delaying the corrosion of the wellbore and oil pipe. The valve cavity 8b is provided with a conical top to accommodate the anti-return valve ball 10 after floating.

[0071] S5. A Φ45 mm constant pressure valve ball 4 is dropped from the wellhead. The constant pressure valve ball 4 rolls down along the oil pipe and lands on the inner conical surface of the constant pressure valve seat 3 to seal.

[0072] S6. Pressurize in steps according to the design requirements and check the tightness of the pipe string. First pressurize to 8MPa; after stabilizing the pressure for 3 minutes, continue to increase the pressure to 12MPa; after stabilizing the pressure for 3 minutes, continue to increase the pressure to 14MPa; after stabilizing the pressure for 3 minutes, continue to increase the pressure to 16MPa. Then reduce the pressure to 8MPa, slowly install the oil pipe hanger, so that the upper end of the pipe string is supported on the wellhead; S7. Pressurize to 18 MPa to make the rubber tube of the drop packer F set on the inner wall of the wellbore to protect the wellbore above; then Figure 6 , Figure 7 As shown, the pressure is continuously increased to break the thin-walled section 3b of the constant-pressure valve seat 3, and the lower part of the constant-pressure valve seat 3 falls downward until the lower end of the valve seat support claw 3d abuts against the top of the valve body 8. At this time, the limiting boss of the constant-pressure valve seat 3 reaches a position aligned with the second expanded diameter section 7b of the outer sleeve. Under the tension of the limiting spring 6, each limiting pin 5 extends outward, and the spherical surface of the outer end of each limiting pin abuts against the inner wall of the second expanded diameter section 7b of the outer sleeve, so that the constant-pressure valve seat 3 is in a centered state, and the flow channels between the three limiting bosses are evenly distributed. At this time, the pipe column realizes positive injection connection.

[0073] S8. Water is being squeezed out to verify and confirm that the rubber sleeve of the drop-out packer F is well sealed with the inner wall of the wellbore.

[0074] S9. Connect the surface process, inject carbon dioxide gas from the wellhead, carbon dioxide flows downward from the annular channel between the constant pressure valve seat 3 and the inner wall of the first expansion section 7a of the jacket, and then passes through the flow channel between the three limit bosses to reach the top of the valve body 8, and flows downward from the axial holes 8a of each valve body to the bottom of the valve body 8; then enter the inner cavity of the valve seat cap 12 from each cap slit channel 12a, and then push the anti-return valve ball 10 upward to enter the valve cavity 8b, and then enter the wellbore annulus through the radial hole 8c of the valve body, and then enter the formation, generate gas driving force in the liquid, and improve the oil displacement effect. After reaching the set gas injection tonnage, enter the well.

[0075] During the gas injection process in step S9, if the casing pressure rises at the wellhead, the gas injection is stopped and the process goes to step S10: a Φ55mm soluble ball 15 is dropped, and the soluble ball 15 falls on the inner sleeve bell mouth of the sleeve valve H to seal it. The positive pressure is applied to verify the sealing of the tubing above the sleeve valve H. If the pressure in the oil pipe does not drop, it is confirmed that the sealing of the upper tubing is reliable.

[0076] The pressure is continuously increased, and the soluble ball 15 pushes the inner sleeve 16 to overcome the tension of the sleeve spring 18 and slide down until the bypass hole 14a is exposed. Then the well washing fluid is positively injected to carry out positive circulation well washing and degassing; the well washing fluid passes through the central hole of the constant pressure valve seat 3, and then goes down along the axial holes 8a of each valve body into the lower joint 13, and the impurities are blocked by the slit channels 12a of each pressure cap, and can fall into the tail pipe B below; the well washing fluid enters the inner cavity of the valve seat pressure cap 12 from each pressure cap slit channel 12a, and then moves upward to push the anti-return valve ball 10 into the valve cavity 8b, and then returns to the wellbore annulus through the radial holes 8c of the valve body.

[0077] Then, the annular protection fluid is injected to replace the fluid in the wellbore annular space. After the fluid replacement is completed, the pressure is released. After the pressure is released, the inner sleeve 16 is reset under the tension of the sleeve spring 18, and the inner sleeve 16 closes the inner port of the bypass hole 14a. After the soluble ball 15 is dissolved, continue to inject gas to observe whether the casing pressure rises. If the casing pressure does not rise, it means that the problem has been solved.

[0078] If the casing pressure still rises, proceed to the following steps: Step S11. The soluble ball 15 is put in again to open the bypass hole 14a of the sleeve valve H by positive pressure; Step S12. Positively circulating well killing fluid to kill the well and degas; Step S13. After the soluble ball 15 is dissolved, a Φ50mm release ball is thrown into the oil pipe, and positive pressure is applied to release the upper part of the release packer F, and the pressurized operation string is lifted out of the wellhead; during the lifting of the string, the rubber cylinder of the release packer F remains in the set state, thereby improving the safety of the operation; Step S14: Use the pressure-relief fishing string to fish out the downhole drop packer F and the string below it.

[0079] The above is only a preferred embodiment of the present invention, which shows and describes the basic principles, main features and advantages of the present invention, but does not limit the scope of patent protection of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. In addition to the above embodiments, the present invention may have other implementation modes without departing from the spirit and scope of the present invention. The present invention may also have various changes and improvements, and all technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection required by the present invention. The scope of protection required by the present invention is defined by the attached claims and their equivalents. The technical features not described in the present invention can be realized by or using existing technologies, which will not be repeated here.

Claims

1. A low permeability reservoir carbon dioxide flooding pressure operation string, including a drop-out packer located above the oil layer, characterized in that: A lower centralizer is connected to the lower part of the release packer, a tungsten-plated oil pipe is screwed to the lower part of the lower centralizer, an injection valve is screwed to the lower part of the tungsten-plated oil pipe, a tail pipe is screwed to the lower part of the injection valve, a high-pressure wire plug is screwed to the lower end of the tail pipe; an upper centralizer is connected to the upper part of the release packer, a sliding sleeve valve is screwed to the upper part of the upper centralizer, and the upper end of the sliding sleeve valve is screwed to the lower part of the airtight sealing oil pipe.

2. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 1, characterized in that: The sliding sleeve valve includes a sliding sleeve body, the lower end of the sliding sleeve body is screwed with a double male joint, an inner sliding sleeve is provided below the inner step at the upper end of the sliding sleeve body, the outer wall of the inner sliding sleeve is fitted with the inner wall of the sliding sleeve body, and the upper end of the center hole of the inner sleeve is provided with an inner sliding sleeve bell mouth for a soluble ball to seal; a bypass hole is provided on the upper side wall of the sliding sleeve body, the inner port of the bypass hole is covered by the inner sliding sleeve and the upper and lower ends are sealed with the inner sliding sleeve; a sliding sleeve spring is provided at the lower end of the inner sleeve, the lower end of the sliding sleeve spring is supported on the upper port of the double male joint, the sliding sleeve spring is wound around the outer periphery of the liner, the upper end of the liner is screwed into the female thread at the lower end of the inner sleeve, and the lower end of the liner is inserted into the inner cavity of the double male joint.

3. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 1, characterized in that: When unclamping the valve body, the valve body is emptied and the valve body is in a state of being pushed and pulled out of the airtight container and the like, and a pressure regulating female is formed on the rim of the valve body, and the regulating female is formed on the pressure regulating female.

4. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 3, characterized in that: A large diameter valve seat section is provided on the upper part of the constant pressure valve seat. The large diameter valve seat section is embedded in the upper port of the outer sleeve and abuts against the upper inner step of the outer sleeve. The top of the large diameter valve seat section is located below the inner step of the upper joint.

5. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 3, characterized in that: The lower outer wall of the constant pressure valve seat is symmetrically provided with three limit bosses, and a flow channel is provided between adjacent limit bosses. The outer end surface of each limit boss is provided with a limit groove, and a limit pin is embedded in each limit groove. The inner end surface of each limit pin is provided with a countersunk hole and a limit spring is embedded therein, and each limit spring is supported between the bottom wall of the countersunk hole and the bottom wall of the limit groove.

6. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 3, characterized in that: The outer end of each of the limit pin shafts is respectively provided with a spherical surface, and the center of each spherical surface is respectively against the inner wall of the center hole of the outer sleeve.

7. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 3, characterized in that: The lower end of the constant pressure valve seat is symmetrically provided with valve seat supporting claws extending downward, and a flow passage is provided between adjacent valve seat supporting claws.

8. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 7, characterized in that: The lower end of the central hole of the outer sleeve accommodating the constant pressure valve seat is provided with a first diameter expansion section of the outer sleeve, a second diameter expansion section of the outer sleeve and a third diameter expansion section of the outer sleeve with gradually expanding diameters in sequence. The length of the first diameter expansion section of the outer sleeve is greater than the distance between the thin-walled section of the valve seat and the limiting boss, the length of the second diameter expansion section of the outer sleeve is greater than the diameter of the limiting pin shaft, and the length of the third diameter expansion section of the outer sleeve is greater than the length of the valve seat support claw.

9. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 8, characterized in that: When the thin-walled section of the valve seat is pulled off and the anti-return valve seat falls, the valve seat support claw is supported on the top of the valve body, and each limit spring pushes out the limit pin so that the spherical surface of the outer end of each limit pin symmetrically rests against the inner wall of the second expanded diameter section of the outer sleeve.

10. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 8, characterized in that: The radius of the third expanded diameter section of the outer sleeve is greater than or equal to the radius of the circumference of the outer edge of the valve body axial hole, and the outer edge radius of the valve seat support claw is smaller than the radius of the circumference of the inner edge of the valve body axial hole.

11. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 5, characterized in that: The middle outer wall of the valve body is covered with a filter screen, and the filter screen covers the outer ports of the radial holes of the valve body.

12. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 11, characterized in that: The filter screen is evenly provided with a plurality of strip-shaped filter slits extending along the axial direction.

13. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 11, characterized in that: An annular groove is arranged on the outer periphery of the middle part of the valve body, and the outer port of each radial hole of the valve body is located on the bottom wall of the annular groove.

14. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 5, characterized in that: The outer end of the radial hole of the valve body is inclined upward.

15. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 5, characterized in that: The lower end of the valve seat pressure cap is conically shrunk to be closed, and a plurality of pressure cap slit channels are evenly distributed on the lower circumference of the valve seat pressure cap.

16. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 5, characterized in that: Each of the cap strip channels extends from the cylindrical end to the tapered section.

17. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 5, characterized in that: An upper joint light hole section is arranged above the female thread at the lower end of the upper joint, and an upper joint sealing ring is embedded in the inner wall of the upper joint light hole section to achieve sealing with the outer wall of the upper port of the outer sleeve.

18. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 2, characterized in that: At least one constant pressure valve seat sealing ring is embedded in the outer wall of the large diameter section of the valve seat to achieve sealing with the inner wall of the upper port of the outer sleeve.

19. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 4, characterized in that: A sleeve light hole sealing section is provided above the female thread at the lower end of the sleeve, and a sleeve sealing ring is embedded in the inner wall of the sleeve light hole sealing section, and the sleeve sealing ring is sealed with the upper cylindrical section of the valve body.

20. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 4, characterized in that: A lower joint light hole sealing section is provided below the upper female thread of the lower joint, and a lower joint sealing ring is embedded in the inner wall of the lower joint light hole sealing section to achieve sealing with the lower cylindrical section of the valve body.

21. The low permeability reservoir carbon dioxide flooding pressure operation pipe string according to claim 5, characterized in that: The upper outer wall of the valve seat pressure cap is embedded with a pressure cap sealing ring to achieve sealing with the lower inner wall of the valve body.

22. A method for carbon dioxide flooding under pressure in low permeability oil reservoirs, characterized in that: The steps are as follows: S1. Prepare the wellbore and install the wellhead equipment; S2. Assemble the pressure operation string as claimed in claim 1 and run it into the well section by section, and remove the soluble ball and the constant pressure valve ball before assembly; S3. The pressure-operated pipe string is lowered to the designed depth, and the anti-return valve ball is seated on the anti-return valve seat to prevent the well fluid in the annulus from entering the gas-sealed oil pipe; S4. Inject annular protection fluid from the surface until the wellbore annulus fluid is completely replaced; S5. Throw the pressure regulating valve ball into the wellhead, and the pressure regulating valve ball rolls down and is seated on the upper part of the pressure regulating valve seat; S6. Pressurize step by step to 16MPa and check the tightness of the pipe string; then reduce the pressure to 8MPa and slowly place the tubing hanger to support the upper end of the pipe string on the wellhead; S7. Pressurize to 18 MPa to set the hand-free packer, then continue to increase the pressure to break the thin-walled section of the constant-pressure valve seat, and the lower part of the constant-pressure valve seat falls off, so that the string can be connected with positive injection; S8. Squeeze water to verify and confirm that the seal of the drop packer is good; S9. Connect to the surface process and inject carbon dioxide from the wellhead. The carbon dioxide pushes the anti-return valve ball and enters the wellbore annulus through the radial hole of the valve body, and then enters the formation; after reaching the set gas injection volume, it enters the wellbore.

23. The low permeability reservoir carbon dioxide flooding pressure operation method according to claim 22, characterized in that: During the gas injection process in step S9, if the casing pressure rises, stop the gas injection and proceed to step S10: put in the soluble ball, and verify the sealing of the tubing string above the sleeve valve by positive pressure testing. Then continue to increase the pressure to open the bypass hole of the sleeve valve, and perform positive circulation to wash the well and degas. Then replace the annulus protection fluid, and after the pressure is released, close the bypass hole of the sleeve valve. After the soluble ball is dissolved, continue to inject gas to observe whether the casing pressure rises.

24. The low permeability reservoir carbon dioxide flooding pressure operation method according to claim 23, characterized in that: In step S10, after the soluble ball is dissolved, if the casing pressure still rises while continuing to inject gas, the following steps are entered: Step S11. Add the soluble ball again and pressurize to open the bypass hole of the sleeve valve; Step S12. Positively circulating the well killing fluid to kill the well and degas; Step S13. After the soluble ball is dissolved, a throw-away ball is thrown into the oil pipe, and positive pressure is applied to release the upper part of the throw-away packer, and the pressurized operation string is lifted out of the wellhead; Step S14: salvage the pipe string under pressure to salvage the hand-free packer and the pipe string below it.

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