Automatic pressure supplementing device and method for carbon dioxide flooding injection well casing

Abstract

The application discloses a kind of carbon dioxide drive injection well casing automatic pressure supplement device and automatic pressure supplement method, comprising: carbon dioxide storage tank;High-pressure injection pump, inlet is connected with the outlet of carbon dioxide storage tank, outlet is connected with the inlet of first tubing valve;Casing protection liquid storage tank;Reciprocating piston cylinder, one side of piston is A cavity, the other side of piston is B cavity;The end of reciprocating piston cylinder A cavity upper port is connected with the outlet of second tubing valve by first switch valve, the end of reciprocating piston cylinder A cavity lower port is connected with carbon dioxide absorption tank by second switch valve;The outlet of casing protection liquid storage tank is connected with the end of reciprocating piston cylinder B cavity upper port by third switch valve, the end of reciprocating piston cylinder B cavity lower port is connected with protection liquid injection pipeline by fourth switch valve, and the outlet of protection liquid injection pipeline is connected with the inlet of casing valve. Including gas injection, casing pressure supplement, piston reversing, circulating pressure increasing and the like steps. The application can accurately control casing differential pressure, reduce gas seal pipe column and packer leakage risk.

Description

Technical Field

[0001] This invention relates to an automatic pressure replenishment device for the casing of a carbon dioxide flooding injection well, and also to an automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well, belonging to the field of carbon dioxide flooding and storage technology. Background Technology

[0002] Carbon dioxide enhanced oil recovery (CO2) and its storage technology is becoming increasingly important for oilfield recovery and environmental remediation, but the safety issues of CO2 injection wells are also becoming more prominent. CO2 injection wells protect the casing by using gas-tight tubing and packers to prevent CO2 from entering the annulus. However, if the injection pressure is too high, or the pressure difference between the tubing and casing becomes too large, exceeding the tolerance range of the gas-tight tubing and packers, CO2 can leak into the annulus, causing accelerated casing corrosion and stress damage.

[0003] Chinese invention patent CN107420091B discloses an annular pressure monitoring and control device for deepwater oil and gas wellheads. The device includes an upper piston in an upper hydraulic cylinder connected to a lower piston in a lower hydraulic cylinder via a piston rod; the upper hydraulic cylinder is connected to the lower hydraulic cylinder via a connector; a pressure relief port is provided on the side wall of the lower hydraulic cylinder; multiple annular pressure pipes are installed around the casing via a bottom connection device for the lower hydraulic cylinder; a pressure sensor is installed at the annular fluid inlet of the casing; the output of the pressure sensor is connected to a logic control system, the output of the logic control system is connected to a hydraulic pump, and the outlet of the hydraulic pump is connected to the inlet of the upper hydraulic cylinder; in use, the logic control system receives the pressure signal from the pressure sensor, and when the annular pressure signal is lower than a preset lower limit pressure value, it pressurizes the fluid into the casing annulus.

[0004] The drawbacks of this technical solution are as follows: 1. It uses a hydraulic cylinder piston container and an external hydraulic pump. When pressure replenishment is needed, the hydraulic pump is started to drive the upper piston of the upper hydraulic cylinder downwards, which in turn drives the lower piston downwards via the piston rod. The lower piston forces the fluid in the cylinder into the casing annulus, thereby achieving pressure replenishment. This device is only suitable for laboratory testing. Real oil wells are thousands of meters deep, and the volume of the casing space is enormous. The pressure replenishment of a real oil well cannot be achieved by a single piston stroke of the hydraulic cylinder piston container unless an infinitely large capacity hydraulic cylinder piston container is used.

[0005] 2. The purpose of this technical solution is to prevent oxygen from being drawn in due to excessively low annular pressure, which could cause oxygen corrosion of the casing. However, it does not monitor the risk of seal failure caused by excessive pressure difference between the tubing and the casing.

[0006] 3. It cannot be used in carbon dioxide flooding wells because the tubing injected with carbon dioxide flooding is filled with carbon dioxide gas. Once carbon dioxide leaks into the casing annulus, it will cause carbon dioxide corrosion of the casing. Since the gas is compressible, its volume can expand hundreds of times, which is not something that a single liquid cylinder can contain or balance. If the volume is slightly larger, it will be classified as special equipment and fall under the jurisdiction of pressure vessels, posing a great safety risk.

[0007] 4. When the casing pressure is too high, this technical solution releases pressure through the pressure relief port on the hydraulic cylinder, which is not only detrimental to environmental protection, but also prevents the hydraulic cylinder from working repeatedly.

[0008] 5. During the pressurization process, the casing space was not protected, which could not prevent carbon dioxide corrosion. Summary of the Invention

[0009] The primary objective of this invention is to overcome the problems existing in the prior art and provide an automatic pressure replenishment device for the casing of a carbon dioxide injection well, which can accurately control the pressure difference between the oil casing and the casing, and reduce the risk of leakage of the gas-tight tubing and packer.

[0010] To solve the above technical problems, the present invention provides an automatic pressure replenishment device for the casing of a carbon dioxide flooding injection well, comprising:

[0011] A carbon dioxide storage tank, containing carbon dioxide;

[0012] The high-pressure injection pump has its inlet connected to the outlet of the carbon dioxide storage tank and its outlet connected to the inlet of the first oil pipe valve.

[0013] A casing protection fluid storage tank, containing casing protection fluid;

[0014] A reciprocating piston cylinder is provided with a piston, with chamber A on one side of the piston and chamber B on the other side of the piston;

[0015] The upper port of the A chamber of the reciprocating piston cylinder is connected to the outlet of the second oil pipe valve through the first switching valve, and the lower port of the A chamber of the reciprocating piston cylinder is connected to the carbon dioxide absorption tank through the second switching valve; the outlet of the casing protection fluid storage tank is connected to the upper port of the B chamber of the reciprocating piston cylinder through the third switching valve, and the lower port of the B chamber of the reciprocating piston cylinder is connected to the protection fluid injection pipeline through the fourth switching valve, and the outlet of the protection fluid injection pipeline is connected to the inlet of the casing valve.

[0016] Furthermore, a damper is installed in the pipeline between the outlet of the second oil pipe valve and the inlet of the first switching valve.

[0017] Furthermore, the bypass port of the protective fluid injection pipeline is connected to a pressure relief valve, and the outlet pipeline of the pressure relief valve is connected to the return port of the casing protective fluid storage tank.

[0018] Furthermore, a tubing pressure transmitter for monitoring tubing pressure is installed at the inlet of the first switching valve or the outlet of the second switching valve, and a casing pressure transmitter for monitoring casing pressure is installed at the inlet of the casing valve. The signal lines of the tubing pressure transmitter and the casing pressure transmitter are respectively connected to the pressure signal input terminal of the control system.

[0019] Furthermore, the first switching valve, the second switching valve, the third switching valve, the fourth switching valve, and the pressure relief valve are all electric valves or pneumatic valves, and their opening and closing are controlled by the control signals of the control system.

[0020] Furthermore, a first Hall proximity switch is provided on the outer side of the end of chamber A of the reciprocating piston cylinder to detect when the piston arrives at the end of chamber A, and a second Hall proximity switch is provided on the outer side of the end of chamber B of the reciprocating piston cylinder to detect when the piston arrives at the end of chamber B.

[0021] Furthermore, the control system is equipped with an MCU, which uses an STM32F103RET6 chip. The signal line output of the oil pipe pressure transmitter E1 outputs an oil pipe pressure current signal proportional to the oil pipe pressure. The negative terminal of the oil pipe pressure transmitter E1 is grounded, and the positive terminal is connected to one end of resistor R6. The other end of resistor R6 is grounded, converting the oil pipe pressure current signal into a voltage sampling signal. This voltage sampling signal is current-limited by resistor R5 and then enters the non-inverting input of AD8552 operational amplifier U2. The output of AD8552 operational amplifier U2 provides the oil pipe pressure voltage signal to the PC1 port of the MCU. The MCU calculates the actual oil pipe pressure value and provides it to the storage unit for storage.

[0022] Furthermore, the signal line output of the bushing pressure transmitter E2 is a bushing pressure current signal proportional to the bushing pressure. The negative terminal of the bushing pressure transmitter E2 is grounded, and the positive terminal is connected to one end of resistor R8. The other end of resistor R8 is grounded, converting the bushing pressure current signal into a voltage sampling signal. This voltage sampling signal is current-limited by resistor R7 and then enters the non-inverting input of AD8552 operational amplifier U3. The output of AD8552 operational amplifier U3 provides the bushing pressure voltage signal to the PC2 port of the MCU. The MCU calculates the actual bushing pressure value and provides it to the storage unit for storage.

[0023] Furthermore, the first switching valve control circuit includes an optocoupler U4 and a transistor Q1. Pin 1 of the optocoupler U4 is connected to a +5V power supply, pin 2 of the optocoupler U4 is connected to the DCF1 port of the MCU, pin 3 of the optocoupler U4 is connected to the base of the transistor Q1, the collector of the transistor Q1 is grounded, pin 4 of the optocoupler U4 is connected to a +24V power supply, and the emitter of the transistor Q1 is connected to the +24V power supply and the control coil interface JV5 of the first switching valve V5; the control circuits for the second to fourth switching valves and the pressure relief valve follow the same pattern.

[0024] Furthermore, the first Hall proximity switch K1 is connected in series between the +24VDC and the input terminal of the optocoupler U9, and the output terminal of the optocoupler U9 is connected to the PC6 port of the MCU; the second Hall proximity switch K2 is connected in series between the +24VDC and the input terminal of the optocoupler U10, and the output terminal of the optocoupler U10 is connected to the PC6 port of the MCU; when the MCU receives the signal from the first Hall proximity switch K1 or the second Hall proximity switch K2, it controls the opening and closing of the first to fourth switching valves and the pressure relief valve through the DCF1 port to the DCF5 port.

[0025] Another objective of this invention is to overcome the problems existing in the prior art and provide an automatic pressure replenishment method for the casing of a carbon dioxide injection well, which can accurately control the pressure difference between the oil casing and the casing and reduce the risk of leakage of the gas-tight tubing and packer.

[0026] To solve the above technical problems, the present invention provides an automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well, which employs the aforementioned automatic pressure replenishment device for the casing of a carbon dioxide flooding injection well, and includes the following steps in sequence:

[0027] S1. Initial state: Before carbon dioxide injection, the piston in the reciprocating piston cylinder is located at the end of chamber A, and chamber B is filled with sleeve protection fluid; the first switching valve, the second switching valve, the third switching valve, the fourth switching valve and the pressure relief valve are all in the closed state.

[0028] S2, Gas Injection: The high-pressure injection pump starts and injects carbon dioxide downhole, increasing the tubing pressure. When the pressure difference between the tubing and the annulus exceeds the start-up pressure setting value, the first and fourth switching valves open, and the second and third switching valves close.

[0029] S3, Casing Pressure Replenishment: The high-pressure carbon dioxide in the tubing is first depressurized by the damper and then enters the A chamber of the reciprocating piston cylinder, pushing the piston to move to the opposite side, which in turn pushes the casing protection pressure in the B chamber of the reciprocating piston cylinder into the annulus, increasing the casing pressure.

[0030] S4, Piston Reversal: When the piston moves to the end of chamber B, the first switching valve and the fourth switching valve are closed, and the second switching valve V6 and the third switching valve V7 are opened; the casing protection fluid in the casing protection fluid storage tank flows automatically into chamber B of the reciprocating piston cylinder by gravity difference, pushing the piston to the end of chamber A, and the carbon dioxide in chamber A is discharged into the carbon dioxide absorption tank.

[0031] S5. Cyclic pressurization: When the piston moves to the end of chamber A of the reciprocating piston cylinder, the first switching valve and the fourth switching valve open, and the second switching valve V6 and the third switching valve V7 close. The high-pressure carbon dioxide in the oil pipe pushes the piston from chamber A to chamber B again, and presses the casing protection fluid in chamber B back into the casing annulus. Then, return to step S4 to cyclically increase the casing pressure.

[0032] Furthermore, the automatic pressure replenishment method for the casing of carbon dioxide injection wells also includes the following steps:

[0033] S6. Stop pressure replenishment: When the pressure difference between the oil pipe and the casing is less than the stop pressure replenishment setting value, the first switching valve and the fourth switching valve are closed, and the pressure replenishment device stops working.

[0034] Furthermore, the automatic pressure replenishment method for the casing of carbon dioxide injection wells also includes the following steps:

[0035] S7. When the pressure difference between the tubing and the casing exceeds the starting pressure replenishment setting value again, the first switching valve and the fourth switching valve open, and the second switching valve and the third switching valve close; then return to step S3 and start the next round of casing pressure replenishment.

[0036] Furthermore, after the well stops injecting gas, the tubing pressure gradually decreases. When it falls below the casing pressure, the pressure relief valve is opened, the casing is depressurized, and the casing protection fluid in the annulus flows back to the casing protection fluid storage tank. When the casing pressure drops below the tubing pressure and reaches the stop pressure relief set value, the pressure relief valve is closed to stop pressure relief.

[0037] Compared with existing technologies, this invention achieves the following beneficial effects: 1. In carbon dioxide injection wells, as carbon dioxide is continuously injected into the tubing, the pressure inside the tubing gradually increases, and the pressure difference with the casing gradually increases. The greater the pressure difference borne by the downhole gas-tight tubing string and packer, the greater the operational risk. Once the packer's rubber sleeve seal fails, it not only leads to intercalation but also causes carbon dioxide to enter the annulus, accelerating casing corrosion. When the pressure difference between the tubing and the casing is too large, this device first reduces the pressure of the high-pressure carbon dioxide in the tubing through a damper via a pipeline before it enters the A chamber of the reciprocating piston cylinder to push the piston. This pushes the casing protection fluid in the B chamber of the reciprocating piston cylinder into the annulus through a pipeline, reducing the pressure difference between the tubing and the casing.

[0038] 2. When the piston reaches the end of chamber B, the piston is triggered to reverse direction by the Hall proximity switch. The liquid in the casing protection fluid tank flows into chamber B by gravity difference, pushing the piston to the end of chamber A. The carbon dioxide in chamber A is discharged into the absorption tank. Through the reciprocating motion of the reciprocating piston cylinder, a large amount of liquid and pressure is replenished until the oil-casing pressure difference meets the requirements, reducing the risk of leakage of the gas-tight tubing and packer. This is of great significance for the safe injection of carbon dioxide and ensuring the smooth implementation of the carbon dioxide flooding project.

[0039] 3. During casing pressure replenishment, no external power is required. The oil medium and oil pressure in the tubing are used as the injection power for the reciprocating piston cylinder. The carbon dioxide absorption tank is used to depressurize chamber A and enable chamber B to be automatically replenished with casing protective fluid without power. The casing can be injected with fluid indefinitely by switching valves. No external power is required for long-term operation.

[0040] 4. As the casing is injected with fluid and pressurized, the pressure difference between the tubing and the casing gradually decreases. The power in chamber A of the reciprocating piston cylinder automatically decreases. Without interference, the injection endpoint will be reached automatically, preventing reverse pressure difference between the casing and the tubing due to excessive fluid injection. Even if the pressure transmitter fails, this device remains safe and reliable.

[0041] 5. Because reciprocating piston cylinders can automatically cycle and reciprocate, and can replenish fluid and pressure indefinitely, the volume of reciprocating piston cylinders can be very small, eliminating the need for large-capacity pressure vessels. Therefore, they do not fall under the category of special equipment, reducing operational safety risks.

[0042] 6. During the operation of reducing the oil-casing pressure difference, injecting casing protection fluid into the casing helps to protect the inner wall of the casing from acid corrosion by carbon dioxide.

[0043] 7. During the casing pressurization process, the high-pressure injection pump does not affect the gas injection operation into the oil pipe, resulting in high production efficiency;

[0044] 8. This device can operate unattended and automatically in a cyclical manner, meeting the requirements of oilfield automation and low energy consumption; the injection volume can be calculated by the number of reciprocating piston cylinder strokes, and no matter how many cycles are worked, there is no medium discharge during operation, which meets the environmental protection requirements of oilfields. Attached Figure Description

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The drawings are provided for reference and illustration only and are not intended to limit the present invention.

[0046] Figure 1 This is a flowchart of the automatic pressure replenishment device for the casing of a carbon dioxide flooding injection well according to the present invention;

[0047] Figure 2 This is an enlarged view of the wellhead device in this invention;

[0048] Figure 3 This is a diagram showing the state during gas injection in this invention;

[0049] Figure 4 This is a diagram showing the state of the bushing during pressurization according to the present invention;

[0050] Figure 5 This is a state diagram of the piston during reversal in this invention;

[0051] Figure 6 This is a state diagram of the cyclic pressurization process of the present invention;

[0052] Figure 7 The principle of the control system in this invention Figure 1 ;

[0053] Figure 8The principle of the control system in this invention Figure 2 ;

[0054] In the diagram: 1. Carbon dioxide storage tank; 2. High-pressure injection pump; 3. Damper; 4. Reciprocating piston cylinder; 5. Casing protection fluid storage tank; 6. Carbon dioxide absorption tank; 7. Casing; 8. Oil pipe; 9. Control system;

[0055] V1. First tubing valve; V2. Second tubing valve; V3. First casing valve; V4. Second casing valve; V5. First switching valve; V6. Second switching valve; V7. Third switching valve; V8. Fourth switching valve; V9. Pressure relief valve;

[0056] P1. Tubing pressure gauge; P2. Casing pressure gauge; E1. Tubing pressure transmitter; E2. Casing pressure transmitter; K1. First Hall effect proximity switch; K2. Second Hall effect proximity switch. Detailed Implementation

[0057] In the following description of the present invention, the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship 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 orientation.

[0058] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention.

[0060] like Figure 1 , Figure 2 As shown, the automatic pressurization device for carbon dioxide injection well casing of the present invention includes a carbon dioxide storage tank 1, a high-pressure injection pump 2, a damper 3, a reciprocating piston cylinder 4, a casing protection fluid storage tank 5, a carbon dioxide absorption tank 6, and a control system 9. The tubing 8 extends downhole into the casing 7. The upper end of the casing 7 is connected to the lower end of the wellhead cross-connector. A first casing valve V3 and a second casing valve V4 are installed on both sides of the wellhead cross-connector. The upper end of the tubing 8 passes through the wellhead cross-connector and is equipped with a tubing cross-connector. A first tubing valve V1 and a second tubing valve V2 are installed on both sides of the tubing cross-connector.

[0061] The outer port of the first tubing valve V1 is equipped with a tubing pressure gauge P1, and the outer port of the second tubing valve V2 is equipped with a tubing pressure transmitter E1. The tubing pressure gauge P1 and the tubing pressure transmitter E1 can be installed in interchangeable positions.

[0062] The outer port of the first casing valve V3 is equipped with a casing pressure transmitter E2, and the outer port of the second casing valve V4 is equipped with a casing pressure gauge P2. The casing pressure gauge P2 and the casing pressure transmitter E2 can also be installed in interchangeable positions.

[0063] Carbon dioxide is contained in carbon dioxide storage tank 1 and injected into oil pipe 7 via high-pressure injection pump 2. The upper port of chamber A of reciprocating piston cylinder 4 is connected to oil pipe 8 via first switching valve V5, damper 3, and second oil pipe valve V2. The lower port of chamber B of reciprocating piston cylinder 4 is connected to oil sleeve annulus via fourth switching valve V8 and first sleeve valve V3.

[0064] The damper 3 is used to reduce the carbon dioxide pressure in the oil pipe 8 to the reciprocating piston cylinder line and maintain the positive pressure difference between the oil pipe 8 and the casing 7 within a certain range.

[0065] The tubing pressure transmitter E1 is used to monitor the tubing pressure, and the casing pressure transmitter E2 is used to monitor the casing pressure. The control system 9 calculates the pressure difference between the tubing pressure and the casing pressure and controls the first switching valve V5, the second switching valve V6, the third switching valve V7, and the fourth switching valve V8 to switch between them.

[0066] The first switching valve V5, the second switching valve V6, the third switching valve V7, the fourth switching valve V8, and the pressure relief valve V9 are all electric or pneumatic valves, and their opening and closing are controlled by the control signals of the control system.

[0067] In the reciprocating piston cylinder 4, the medium in chamber A is carbon dioxide, and the medium in chamber B is casing protection fluid. The casing protection fluid storage tank 5 is an open container filled with casing protection fluid; the carbon dioxide absorption tank 6 is an open container used to contain the carbon dioxide discharged from chamber A of the reciprocating piston cylinder 4.

[0068] The automatic casing pressure replenishment device reduces the pressure difference between the oil and casing by injecting casing protective fluid into the air gap of the oil and casing annulus, thereby reducing the risk of leakage of the gas-tight tubing and packer.

[0069] S1. Initial state: Before carbon dioxide injection, the piston in the reciprocating piston cylinder 4 is located at the end of chamber A, and chamber B is filled with sleeve protection fluid. The first switching valve V5, the second switching valve V6, the third switching valve V7, the fourth switching valve V8, and the pressure relief valve V9 are all in the closed state.

[0070] S2, Injection: such as Figure 2As shown, during carbon dioxide injection, it is injected downhole via high-pressure injection pump 2, increasing the tubing pressure. When the pressure difference between the tubing and casing exceeds the starting pressure compensation setting value of 3 MPa, the first switching valve V5 and the fourth switching valve V8 open, while the second switching valve V6 and the third switching valve V7 close.

[0071] S3, casing pressure compensation: such as Figure 3 As shown, the high-pressure carbon dioxide in the oil pipe first passes through the damper 3 for appropriate pressure reduction before entering one end of the reciprocating piston cylinder 4, namely chamber A, pushing the piston to move to the left. This pushes the casing protection pressure in the other end of the reciprocating piston cylinder, namely chamber B, into the annulus, increasing the casing pressure.

[0072] S4, Piston reversal: such as Figure 4 As shown, when the piston in the reciprocating piston cylinder 4 moves to the end of chamber B, the first switching valve V5 and the fourth switching valve V8 close, while the second switching valve V6 and the third switching valve V7 open. The casing protection fluid in the casing protection fluid storage tank 5 automatically flows into chamber B using gravity difference, pushing the piston to move towards the end of chamber A, and the carbon dioxide in chamber A is discharged into the carbon dioxide absorption tank 6.

[0073] S5, Cyclic Boost: (e.g., ...) Figure 5 As shown, when the piston in the reciprocating piston cylinder 4 moves to the end of chamber A, the first switching valve V5 and the fourth switching valve V8 open, the second switching valve V6 and the third switching valve V7 close, and the high-pressure carbon dioxide in the oil pipe pushes the piston from chamber A to chamber B. The casing protection fluid in chamber B is injected into the casing annulus through the fourth switching valve V8.

[0074] Return to step S4 to reverse the piston, and then proceed to step S5 for cyclic pressurization, gradually increasing the casing pressure.

[0075] S6. Stop pressure replenishment: When the pressure difference between the oil pipe and the casing is less than the stop pressure replenishment setting value of 1MPa, the first switching valve V5 and the fourth switching valve V8 are closed, and the pressure replenishment device stops working.

[0076] S7. When the pressure difference between the tubing and the casing exceeds the starting pressure replenishment setting value of 3MPa again, the first switching valve V5 and the fourth switching valve V8 are opened, and the second switching valve V6 and the third switching valve V7 are closed; then return to step S3 and start the next round of casing pressure replenishment.

[0077] S8. Stop Injection State: When the well stops injecting gas, the tubing pressure gradually decreases. When it is lower than the casing pressure, the pressure relief valve V9 is opened to release the casing pressure, and the casing protection fluid in the annulus flows back to the casing protection fluid storage tank 5. When the casing pressure drops to 3 MPa below the tubing pressure and reaches the stop pressure relief setting value, the pressure relief valve V9 is closed to stop the pressure relief.

[0078] like Figure 7 , Figure 8As shown, the control system is equipped with an MCU, which uses an STM32F103RET6 chip. The signal line output of the oil pipe pressure transmitter E1 outputs an oil pipe pressure current signal proportional to the oil pipe air pressure. The negative terminal of the oil pipe pressure transmitter E1 is grounded, and the positive terminal is connected to one end of resistor R6. The other end of resistor R6 is grounded, converting the oil pipe air pressure current signal into a voltage sampling signal. After being current-limited by resistor R5, the voltage sampling signal enters the non-inverting input of AD8552 operational amplifier U2. The output of AD8552 operational amplifier U2 provides the oil pipe air pressure voltage signal to the PC1 port of the MCU. The MCU calculates the actual oil pipe air pressure value and provides it to the storage unit for storage.

[0079] The signal line output of the bushing pressure transmitter E2 is a bushing pressure current signal proportional to the bushing pressure. The negative terminal of the bushing pressure transmitter E2 is grounded, and the positive terminal is connected to one end of resistor R8. The other end of resistor R8 is grounded, converting the bushing pressure current signal into a voltage sampling signal. This voltage sampling signal is current-limited by resistor R7 and then enters the non-inverting input of AD8552 operational amplifier U3. The output of AD8552 operational amplifier U3 provides the bushing pressure voltage signal to the PC2 port of the MCU. The MCU calculates the actual bushing pressure value and provides it to the storage unit for storage.

[0080] A first Hall proximity switch K1 is provided on the outer side of the end of chamber A of the reciprocating piston cylinder 4 to detect when the piston arrives at the end of chamber A, and a second Hall proximity switch K2 is provided on the outer side of the end of chamber B of the reciprocating piston cylinder to detect when the piston arrives at the end of chamber B.

[0081] The first Hall effect proximity switch K1 is connected in series between the +24VDC converter and the input terminal of optocoupler U9. The output terminal of optocoupler U9 is connected to the PC6 port of the MCU. The second Hall effect proximity switch K2 is connected in series between the +24VDC converter and the input terminal of optocoupler U10. The output terminal of optocoupler U10 is connected to the PC6 port of the MCU. When the MCU receives the signal from either the first Hall effect proximity switch K1 or the second Hall effect proximity switch K2, it controls the opening and closing of the first to fourth switching valves and the pressure relief valve through the DCF1 port to the DCF5 port according to the executed steps.

[0082] The first switching valve control circuit includes an optocoupler U4 and a transistor Q1. Pin 1 of optocoupler U4 is connected to a +5V power supply, pin 2 is connected to the DCF1 port of the MCU, pin 3 is connected to the base of transistor Q1, the collector of transistor Q1 is grounded, pin 4 is connected to a +24V power supply, and the emitter of transistor Q1 is connected to the +24V power supply and the control coil interface JV5 of the first switching valve V5. When the DCF1 port of the MCU outputs a low level, optocoupler U4 is triggered, transistor Q1 conducts, and the first switching valve V5 is energized and opens.

[0083] The second switching valve control circuit includes an optocoupler U5 and a transistor Q2. Pin 1 of optocoupler U5 is connected to a +5V power supply, pin 2 is connected to the DCF2 port of the MCU, pin 3 is connected to the base of transistor Q2, the collector of transistor Q2 is grounded, pin 4 is connected to a +24V power supply, and the emitter of transistor Q2 is connected to the +24V power supply and the control coil interface JV2 of the second switching valve V6. When the DCF2 port of the MCU outputs a low level, optocoupler U5 is triggered, transistor Q2 conducts, and the second switching valve V6 is energized and opens.

[0084] The third switching valve control circuit includes an optocoupler U6 and a transistor Q3. Pin 1 of optocoupler U6 is connected to a +5V power supply, pin 2 is connected to the DCF3 port of the MCU, pin 3 is connected to the base of transistor Q3, the collector of transistor Q3 is grounded, pin 4 is connected to a +24V power supply, and the emitter of transistor Q3 is connected to the +24V power supply and the control coil interface JV7 of the third switching valve V7. When the DCF3 port of the MCU outputs a low level, optocoupler U6 is triggered, transistor Q3 conducts, and the third switching valve V7 is energized and opens.

[0085] The fourth switching valve control circuit includes an optocoupler U7 and a transistor Q4. Pin 1 of optocoupler U7 is connected to the +5V power supply, pin 2 is connected to the DCF4 port of the MCU, pin 3 is connected to the base of transistor Q4, the collector of transistor Q4 is grounded, pin 4 is connected to the +24V power supply, and the emitter of transistor Q4 is connected to the +24V power supply and the control coil interface JV8 of the fourth switching valve V8. When the DCF4 port of the MCU outputs a low level, optocoupler U7 is triggered, transistor Q4 conducts, and the fourth switching valve V8 is energized and opens.

[0086] The pressure relief valve control circuit includes an optocoupler U8 and a transistor Q5. Pin 1 of optocoupler U8 is connected to a +5V power supply, pin 2 is connected to the DCF5 port of the MCU, pin 3 is connected to the base of transistor Q5, the collector of transistor Q5 is grounded, pin 4 is connected to a +24V power supply, and the emitter of transistor Q5 is connected to the +24V power supply and the control coil interface JV9 of pressure relief valve V9. When the DCF5 port of the MCU outputs a low level, optocoupler U8 is triggered, transistor Q5 conducts, and pressure relief valve V9 is energized and opens to relieve pressure.

[0087] The above description is merely a preferred embodiment of the present invention, showing and describing the basic principles, main features, and advantages of the present invention. It is not intended to limit the scope of patent protection of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. In addition to the above embodiments, the present invention may have other implementations without departing from the spirit and scope of the invention. Various changes and modifications to the present invention are possible, and all technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents. Technical features not described in the present invention can be implemented by or using existing technology, and will not be elaborated here.

Claims

1. A method for automatic pressure replenishment of casing in a carbon dioxide flooding injection well, comprising an automatic pressure replenishment device for the casing in a carbon dioxide flooding injection well, the device comprising: A carbon dioxide storage tank, containing carbon dioxide; The high-pressure injection pump has its inlet connected to the outlet of the carbon dioxide storage tank and its outlet connected to the inlet of the first oil pipe valve. A casing protection fluid storage tank, containing casing protection fluid; A reciprocating piston cylinder is equipped with a piston, with chamber A on one side of the piston and chamber B on the other side of the piston; The upper port of the A chamber of the reciprocating piston cylinder is connected to the outlet of the second oil pipe valve through the first switching valve, and the lower port of the A chamber of the reciprocating piston cylinder is connected to the carbon dioxide absorption tank through the second switching valve; the outlet of the casing protection fluid storage tank is connected to the upper port of the B chamber of the reciprocating piston cylinder through the third switching valve, and the lower port of the B chamber of the reciprocating piston cylinder is connected to the protection fluid injection pipeline through the fourth switching valve, and the outlet of the protection fluid injection pipeline is connected to the inlet of the casing valve. A damper is installed in the pipeline between the outlet of the second oil pipe valve and the inlet of the first switching valve; The bypass port of the protective fluid injection pipeline is connected to a pressure relief valve, and the outlet pipeline of the pressure relief valve is connected to the return port of the casing protective fluid storage tank. The reciprocating piston cylinder has a first Hall proximity switch on the outer side of the end of chamber A to detect when the piston arrives at the end of chamber A, and a second Hall proximity switch on the outer side of the end of chamber B to detect when the piston arrives at the end of chamber B. The method is characterized by comprising the following steps in sequence: S1. Initial state: Before carbon dioxide injection, the piston in the reciprocating piston cylinder is located at the end of chamber A, and chamber B is filled with sleeve protection fluid; the first switching valve, the second switching valve, the third switching valve, the fourth switching valve and the pressure relief valve are all in the closed state. S2, Gas Injection: The high-pressure injection pump starts and injects carbon dioxide downhole, increasing the tubing pressure. When the pressure difference between the tubing and the annulus exceeds the start-up pressure setting value, the first and fourth switching valves open, and the second and third switching valves close. S3, Casing Pressure Replenishment: The high-pressure carbon dioxide in the tubing is first depressurized by the damper and then enters the A chamber of the reciprocating piston cylinder, pushing the piston to move to the opposite side, which in turn pushes the casing protection pressure in the B chamber of the reciprocating piston cylinder into the annulus, increasing the casing pressure. S4, Piston Reversal: When the piston moves to the end of chamber B, the first switching valve and the fourth switching valve are closed, and the second switching valve and the third switching valve are opened; the casing protection fluid in the casing protection fluid storage tank flows automatically into chamber B of the reciprocating piston cylinder by gravity difference, pushing the piston to the end of chamber A, and the carbon dioxide in chamber A is discharged into the carbon dioxide absorption tank. S5. Cyclic pressurization: When the piston moves to the end of chamber A of the reciprocating piston cylinder, the first switching valve and the fourth switching valve open, and the second switching valve and the third switching valve close. The high-pressure carbon dioxide in the oil pipe pushes the piston from chamber A to chamber B again, and presses the casing protection fluid in chamber B back into the casing annulus. Then, return to step S4 to cyclically increase the casing pressure.

2. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 1, characterized in that: A tubing pressure transmitter for monitoring tubing pressure is installed at the inlet of the first switching valve or the outlet of the second switching valve, and a casing pressure transmitter for monitoring casing pressure is installed at the inlet of the casing valve. The signal lines of the tubing pressure transmitter and the casing pressure transmitter are respectively connected to the pressure signal input terminal of the control system.

3. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 2, characterized in that: The first switching valve, the second switching valve, the third switching valve, the fourth switching valve, and the pressure relief valve are all electric valves or pneumatic valves, and their opening and closing are controlled by the control signals of the control system.

4. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 3, characterized in that: The control system is equipped with an MCU, which uses an STM32F103RET6 chip. The signal line of the oil pipe pressure transmitter outputs an oil pipe pressure current signal proportional to the oil pipe air pressure. The negative terminal of the oil pipe pressure transmitter is grounded, and the positive terminal is connected to one end of resistor R6. The other end of resistor R6 is grounded, converting the oil pipe air pressure current signal into a voltage sampling signal. After being current-limited by resistor R5, the voltage sampling signal enters the non-inverting input of AD8552 operational amplifier U2. The output of AD8552 operational amplifier U2 provides the oil pipe air pressure voltage signal to the PC1 port of the MCU. The MCU calculates the actual oil pipe air pressure value and provides it to the storage unit for storage.

5. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 4, characterized in that: The signal line output of the bushing pressure transmitter is a bushing pressure current signal proportional to the bushing pressure. The negative terminal of the bushing pressure transmitter is grounded, and the positive terminal is connected to one end of resistor R8. The other end of resistor R8 is grounded, converting the bushing pressure current signal into a voltage sampling signal. This voltage sampling signal is current-limited by resistor R7 and then enters the non-inverting input of AD8552 operational amplifier U3. The output of AD8552 operational amplifier U3 provides the bushing pressure voltage signal to the PC2 port of the MCU. The MCU calculates the actual bushing pressure value and provides it to the storage unit for storage.

6. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 5, characterized in that: The first switching valve control circuit includes an optocoupler U4 and a transistor Q1. Pin 1 of the optocoupler U4 is connected to a +5V power supply, pin 2 of the optocoupler U4 is connected to the DCF1 port of the MCU, pin 3 of the optocoupler U4 is connected to the base of the transistor Q1, the collector of the transistor Q1 is grounded, pin 4 of the optocoupler U4 is connected to a +24V power supply, and the emitter of the transistor Q1 is connected to the +24V power supply and the control coil interface JV5 of the first switching valve.

7. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 6, characterized in that: The first Hall proximity switch (K1) is connected in series between the +24VDC and the input terminal of the optocoupler U9, and the output terminal of the optocoupler U9 is connected to the PC6 port of the MCU; the second Hall proximity switch (K2) is connected in series between the +24VDC and the input terminal of the optocoupler U10, and the output terminal of the optocoupler U10 is connected to the PC6 port of the MCU; when the MCU receives the signal from the first Hall proximity switch (K1) or the second Hall proximity switch (K2), it controls the opening and closing of the first to fourth switching valves and the pressure relief valve through the DCF1 port to the DCF5 port.

8. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 1, characterized in that, The method further includes the following steps: S6. Stop pressure replenishment: When the pressure difference between the oil pipe and the casing is less than the stop pressure replenishment setting value, the first switching valve and the fourth switching valve are closed, and the pressure replenishment device stops working.

9. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 8, characterized in that, The method further includes the following steps: S7. When the pressure difference between the tubing and the casing exceeds the starting pressure replenishment setting value again, the first switching valve and the fourth switching valve open, and the second switching valve and the third switching valve close; then return to step S3 and start the next round of casing pressure replenishment.

10. The automatic pressure replenishment method for the casing of a carbon dioxide flooding injection well according to claim 9, characterized in that, After the well stops injecting gas, the tubing pressure gradually decreases. When it falls below the casing pressure, the pressure relief valve is opened to release pressure in the casing, and the casing protection fluid in the annulus flows back to the casing protection fluid storage tank. When the casing pressure drops below the tubing pressure and reaches the stop pressure relief set value, the pressure relief valve is closed to stop pressure relief.

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