A coiled tubing gas injection process string and method of operating the same

Abstract

The application belongs to the technical field of oilfield downhole gas injection and discloses a coiled tubing gas injection process pipe column and an operating method thereof. The pipe column comprises, from top to bottom, a gas injection wellhead, a coiled tubing wellhead suspension device, a coiled tubing, a gas-tight coiled tubing connector, a gas-tight sliding sleeve and a gas injection packer. The gas injection packer is provided with a constant-pressure switch and a setting valve. The pipe column further comprises a rubber plug one, a rubber plug two and a pressure-retaining ball. The rubber plug one is used in cooperation with the gas-tight sliding sleeve. The rubber plug two is used in cooperation with the constant-pressure switch. The pressure-retaining ball is used in cooperation with the setting valve. The coiled tubing gas injection process pipe column and the operating method thereof provided by the application can not only effectively solve the problem of many potential leakage risk points of a conventional gas-tight pipe column, prolong the full life cycle of the pipe column, but also can realize slurry replacement, setting, long-term gas injection and later workover operation by one trip of the pipe column, simplify the operation process and reduce the operation cost.

Description

Technical Field

[0001] This invention belongs to the field of downhole gas injection technology in oilfields, specifically relating to a continuous tubing gas injection process string and its operation method. Background Technology

[0002] Gas injection is an effective technology for improving oil recovery in low-permeability reservoirs, especially ultra-low-permeability and extra-low-permeability reservoirs where water injection is difficult. The coiled tubing gas injection process string is crucial for gas-driven oil recovery; it must simultaneously meet requirements such as high pressure resistance, corrosion resistance, long-term sealing, and operation under pressure. Currently, the main coiled tubing gas injection process string used in oilfields is still the general injection string of "gas-tight tubing + packer" to achieve effective downhole gas injection.

[0003] Regarding downhole gas injection tubing, existing patent (1) CN203308443U discloses a recirculating gas injection tubing. This tubing, from top to bottom, consists of tubing, anchor, gas injection backwash valve, sealing insert, release reconnector, packer, disc safety valve, and gas injection check valve. The operation process involves first lowering the gas injection release tubing (the part below the release reconnector), then setting and releasing the release tubing before lowering the tubing above the sealing insert for gas injection. When mud replacement or well control is required, the tubing can be used… The annular pressure difference can be used to open the circulation hole of the gas injection backwash valve; Patent (2) CN102536183A discloses a downhole gas injection string, which consists of a tubing string, a casing pressure valve, a sealing plug, a release reconnector, a packer and a gas injection valve from top to bottom. The casing pressure valve and the gas injection valve are one-way valves. The gas injection valve is used to prevent the injected gas from being spit out, and the casing pressure valve is used to replace the annular protective fluid; Patent (3) CN107178347A discloses a long-lasting CO2 The gas injection string and its operation method: This string, from top to bottom, consists of tubing, circulating well-washing sleeve, hydraulic anchor, hanging ring, sealing tubing, sealing cylinder, permanent packer, setting ball seat, and two-stage check valve. The operation process involves first lowering the gas injection release string (below the sealing cylinder), then lowering the string above the sealing tubing after setting and releasing the seal for fluid replacement. When the casing pressure reaches the predetermined value, the piston of the circulating well-washing sleeve moves downward to achieve the well-washing operation, utilizing a two-stage check valve. The valve enables well shut-in at the bottom of the well; Patent (4) CN107605443A discloses a CO2-driven continuous tubing gas injection process tubing structure. The tubing structure consists of tubing, reverse circulation valve, insert pipe, Y445 packer, setting ball seat, one-way valve and guide shoe from top to bottom. First, the entire tubing is lowered into the well. The reverse circulation valve is used to replace the slurry. After the soluble ball is used to set the packer, gas injection is carried out. Later, the one-way valve is used to realize the internal connection of the tubing for tubing tripping operations.

[0004] Although the above-mentioned tubing string technology can meet the basic requirements of gas injection wells, the inventors of this application have discovered at least the following problems in the process of implementing the inventive technical solution in the embodiments of this application:

[0005] 1. Patents (1)(2)(3)(4) all use conventional gas-tight tubing as the downhole working string, and the tubing is connected by gas-tight couplings. There are many potential leakage risks during the gas injection process, which increases the well control risk. At the same time, in order to ensure the sealing performance of the entire tubing string of the gas injection well, torque and gas tightness tests need to be performed on each gas-tight coupling tubing that enters the well during on-site construction, which results in a long construction period.

[0006] 2. All of the patents (1)(2)(3) involve the loss of the tubing string, which requires setting and then reconnecting the sealing tube above the tubing string for air injection. Therefore, two tubing operations are required to achieve the slurry replacement and setting operations, which is complicated and costly.

[0007] 3. Both patents (3) and (4) use a single-flow valve to seal the internal passage of the tubing. When corrosive gas is injected for a long period of time, it is difficult to guarantee the reliability of the single-flow valve, which increases the difficulty and cost of well control in the later stage.

[0008] 4. Both patents (3) and (4) use soluble ball dissolution for setting. Dissolution takes a certain amount of time. When dissolution is insufficient, the residue of the soluble ball can easily block the flow valve channel or the solution may contaminate the formation.

[0009] Therefore, it is urgent to conduct research on gas injection processes and supporting tools with higher reliability and safety in order to solve the above problems at the same time. Summary of the Invention

[0010] The present invention aims to solve at least one technical problem existing in the background art, and provides a continuous tubing gas injection process string and its operation method, which can not only effectively solve the problem of many potential leakage risk points of conventional gas-tight tubing strings and extend the entire life cycle of the tubing string, but also realize the replacement of slurry, setting, long-term gas injection and subsequent well workover operations in one tubing string, simplifying the operation process and reducing the operation cost.

[0011] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0012] A coiled tubing injection process string includes, from top to bottom, an injection wellhead, a coiled tubing wellhead suspension device, a coiled tubing, a gas-tight coiled tubing connector, a gas-tight sliding sleeve, and an injection packer; the injection packer includes a pressure regulating switch and a setting valve; the lower end of the coiled tubing is clamped and anchored to the gas-tight coiled tubing connector by slips; the gas-tight coiled tubing connector, the gas-tight sliding sleeve, and the injection packer are connected in sequence by a gas-tight buckle; the pressure regulating switch and the setting valve are both located inside the injection packer, with the pressure regulating switch located above the setting valve;

[0013] It also includes:

[0014] Rubber plug one is used in conjunction with the gas-tight sliding sleeve; rubber plug one is inserted into the continuous tube and enters the inner cavity of the gas-tight sliding sleeve. By applying pressure, the gas-tight sliding sleeve is opened, thereby opening the oil sleeve annulus.

[0015] Rubber plug two is used in conjunction with a constant pressure switch. Rubber plug two is inserted into the inside of the coiled tubing and enters the inner cavity of the constant pressure switch. Pressure is applied to close or open the constant pressure switch, thereby blocking or opening the internal passage of the coiled tubing.

[0016] The pressure ball is used in conjunction with the setting valve; the pressure ball is inserted into the continuous tubing and enters the inner cavity of the setting valve, thereby setting the continuous tubing string by pressurizing it.

[0017] Furthermore, the pressure ball is a steel ball.

[0018] Furthermore, the setting valve is provided with a pressure-holding ball positioning shoulder.

[0019] Furthermore, the constant pressure switch is provided with a rubber stopper and a two-positioning shoulder.

[0020] Furthermore, a rubber plug and a positioning shoulder are provided at the upper end of the gas-tight sliding sleeve.

[0021] Meanwhile, the present invention also provides an operation method for a continuous tube gas injection process string, using a continuous tube gas injection process string as described above, the operation method specifically including:

[0022] Step S01: Well workover and kill, lift the original well tubing string, replace the wellhead, install the large four-way valve and coiled tubing wellhead suspension device at the gas injection wellhead. After lowering the gas injection tubing string, which consists of coiled tubing, gas-tight coiled tubing connector, gas-tight sliding sleeve and gas injection packer, into the designed position, inject annular protective fluid to replace the kill fluid in the annulus of the oil casing according to the design requirements.

[0023] Step S02: Insert a pressure-pressurizing ball into the continuous tube, pressurize it to pump the pressure-pressurizing ball into the inner cavity of the setting valve, and pressurize to achieve sealing of the continuous tube string;

[0024] Step S03: Continuously pressurize and push the piston of the gas-injecting packer to compress and expand the sealing sleeve of the corrosion-resistant gas material to seal the annulus of the packer oil sleeve, expand the slip to open the anchoring sleeve, step lock the position, and complete the setting and anchoring; after successful sealing verification, continue to pressurize to the predetermined pressure P1, remove the pressure ball and the setting valve, and the inside of the continuous tube is unobstructed.

[0025] Step S04: Insert rubber plug two into the coiled tubing, pressurize and pump rubber plug two into the inner cavity of the constant pressure switch. When the pressure reaches the predetermined pressure P2, rubber plug two seals the internal passage of the coiled tubing and releases pressure from the pump truck. At this time, the pressure inside the coiled tubing observed from the wellhead is 0 MPa.

[0026] Step S05: Suspend, shear, and seal the continuous tubing, and install the gas production tree at the injection wellhead;

[0027] Step S06: Pressurize from the injection wellhead. When the pressure reaches the predetermined pressure P3, the pressure regulating switch opens, the inside of the continuous tube is unobstructed, and gas can be injected.

[0028] Furthermore, the operation method also includes:

[0029] Step S07: When performing well workover operations in the later stage of gas injection, simply insert rubber plug one into the coiled tubing, pressurize and pump rubber plug one into the inner cavity of the gas-tight sliding sleeve, continue pressurizing to the predetermined pressure P4, the gas-tight sliding sleeve opens, the oil casing annulus is connected, and circulation well kill operations can be carried out.

[0030] Step S08: After the well is successfully killed, disassemble the gas production tree at the injection wellhead, connect the surface coiled tubing to the downhole coiled tubing, and lift the tubing string with a predetermined force of 5-8t through the injection head to detach the coiled tubing from the gas injection packer. Then, pull out the coiled tubing, gas-tight coiled tubing connector, and gas-tight sliding sleeve from top to bottom.

[0031] Step S09: Use the lower milling cylinder to drill away the rubber sleeve and slips of the gas injection packer, and retrieve the remaining tools.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) Conventional gas-tight tubing uses conventional gas-tight tubing, with a single tubing length of only about 10m. Multiple tubings need to be connected with threaded joints at the top and bottom, which poses a risk of leakage. However, the continuous tubing gas injection process tubing and its operation method provided by this invention use continuous tubing that can be several kilometers long to replace conventional tubing. There are only two connection points, one at the top and one at the bottom. At the same time, the invention improves and uses tools such as gas-tight sliding sleeves, gas-tight packers, and constant pressure switches. This not only effectively solves the problem of multiple potential leakage risk points in conventional gas-tight tubing and extends the entire life cycle of the tubing, but also enables the replacement of slurry, setting, long-term gas injection, and secondary well workover operations in one tubing run. This simplifies the operation process and significantly reduces the operating cost.

[0034] (2) The present invention provides a continuous tubing gas injection process string and its operation method, which uses rubber plugs to seal the continuous tubing. It does not require the use of conventional check valves. The rubber plugs are knocked to the bottom of the well before the gas injection operation. When corrosive gas is injected for a long period of time, there is no problem that the steel ball in the check valve is in a corrosive environment for a long time and it is difficult to guarantee the reliability of the check valve. This effectively reduces the difficulty of well control and the cost of investment in the later stage. At the same time, the pressure ball is used for setting. The pressure ball is a steel ball. Compared with soluble balls, it will not dissolve and affect the formation or block the internal channel of the tubing string due to insufficient dissolution. Attached Figure Description

[0035] Figure 1 A schematic diagram of the overall structure of the continuous tubing gas injection process string;

[0036] Figure 2 Schematic diagram of continuous tubing gas injection;

[0037] Figure 3 A schematic diagram of the structure for sealing the internal passage of the coiled tubing with a rubber plug, dismantling the wellhead, connecting the coiled tubing, and lifting the tubing string.

[0038] The markings in the diagram are as follows: 1-Injection wellhead; 2-Continuous tubing wellhead suspension device; 3-Continuous tubing; 4-Gas-tight continuous tubing connector; 5-Gas-tight sliding sleeve; 6-Injection packer; 7-Pressure control switch; 8-Setting valve; 9-Plug 1; 10-Plug 2; 11-Pressure-holding ball; 12-Gas-tight buckle. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] Combination Figure 1 As shown, this embodiment of the invention provides a continuous tubing injection process string, including an injection wellhead 1, a continuous tubing wellhead suspension device 2, a continuous tubing 3, a gas-tight continuous tubing connector 4, a gas-tight sliding sleeve 5, and an injection packer 6 connected sequentially from top to bottom; the injection packer 6 includes a pressure regulating switch 7 and a setting valve 8; the lower end of the continuous tubing 3 is pressed and anchored to the gas-tight continuous tubing connector 4 by slips; the gas-tight continuous tubing connector 4, the gas-tight sliding sleeve 5, and the injection packer 6 are connected sequentially by a gas-tight buckle 12, and the pressure regulating switch 7 and the setting valve 8 are both located inside the injection packer 6, with the pressure regulating switch 7 located above the setting valve 8.

[0042] It also includes rubber stopper 9, rubber stopper 10 and pressure ball 11; among them, rubber stopper 9 is used in conjunction with the gas-sealing sliding sleeve 5, rubber stopper 10 is used in conjunction with the constant pressure switch 7, and pressure ball 11 is used in conjunction with the setting valve 8.

[0043] Specifically, the upper end of the gas-tight sliding sleeve 5 is provided with a rubber plug positioning shoulder. The rubber plug 9 can pass through the continuous tube 3 and the gas-tight continuous tube connector 4 to enter the rubber plug positioning shoulder inside the gas-tight sliding sleeve 5. By pressing, the gas-tight sliding sleeve 5 is opened, thereby opening the oil sleeve annulus.

[0044] The constant pressure switch 7 is provided with a rubber plug second positioning shoulder. The rubber plug second 10 can pass through the continuous tube 3, the gas-tight continuous tube connector 4, the gas-tight sliding sleeve 5, and the gas injection packer 6 to enter the rubber plug second positioning shoulder inside the constant pressure switch 7. By pressing, the constant pressure switch 7 is closed or opened, thereby blocking or unblocking the internal channel of the continuous tube 3.

[0045] The pressure ball 11 can pass through the continuous tube 3, the gas-tight continuous tube connector 4, the gas-tight sliding sleeve 5, the gas injection packer 6, and the constant pressure switch 7 to enter the positioning shoulder of the pressure ball in the setting valve 8, and set the continuous tube string by pressurizing it.

[0046] The pressure-retaining ball 11 is a steel ball, which, compared to soluble balls, will not dissolve and affect the formation or cause insufficient dissolution and blockage of the internal channels of the tubing.

[0047] Example 2

[0048] Combination Figure 1-3 As shown, this embodiment of the invention provides an operation method for a continuous tubing gas injection process string, using the continuous tubing gas injection process string described in Embodiment 1. The specific operation method is as follows:

[0049] Step S01: Well workover and kill, lift the original well string, replace the wellhead, install the large four-way valve of the gas injection wellhead 1 and the coiled tubing wellhead suspension device 2. After the gas injection string consisting of coiled tubing 3, gas-tight coiled tubing connector 4, gas-tight sliding sleeve 5 and gas injection packer 6 is lowered into the design position, inject annular protective fluid to replace the kill fluid in the oil casing annulus according to the design requirements.

[0050] Step S02: Insert the pressure ball 11 into the continuous tube 3, and pump the pressure ball 11 into the inner cavity of the setting valve 8 by the pump truck to set the continuous tube string.

[0051] Step S03: Continuously pressurize and push the piston of the gas-injecting packer 6 to compress and expand the sealing sleeve of the corrosion-resistant gas material to seal the annulus of the packer oil sleeve, expand the slip to open the anchoring sleeve, step lock the position, and complete the setting and anchoring; after the seal is successfully verified, continue to pressurize to the predetermined pressure of 20MPa, and remove the pressure ball 11 and the setting valve 8 to make the inside of the continuous tube 3 unobstructed.

[0052] Step S04: Insert rubber plug 2 10 into the continuous tube 3 and pump it into the inner cavity of the constant pressure switch 7 by the pump truck. When the pressure is increased to the predetermined pressure of 15MPa, rubber plug 2 10 seals the internal channel of the continuous tube 3 and the pressure is released from the pump truck. At this time, observe that the pressure inside the continuous tube at the wellhead is 0MPa.

[0053] Step S05: Suspend, shear, and seal the continuous tubing, and install the gas production tree at injection wellhead 1;

[0054] Step S06: Pressurize from the gas injection wellhead until the pressure reaches the predetermined pressure of 28 MPa, then the pressure regulating switch 7 opens. Figure 2 Once the internal flow of the continuous tube 3 is unobstructed, gas can be injected.

[0055] Step S07: When performing well workover operations in the later stage of gas injection, simply insert rubber plug 9 into the coiled tubing 3, pressurize it with a pump truck to send rubber plug 9 into the inner cavity of the gas-sealed sliding sleeve 5, and continue pressurizing to the predetermined pressure of 15MPa. When the gas-sealed sliding sleeve 5 opens, the oil casing annulus is connected, and circulation well kill operations can be carried out.

[0056] Step S08: After successful well control, dismantle the production tree at the injection wellhead 1, connect the coiled tubing 3 to the lifting device, and lift the tubing string with a predetermined force of 8t to detach it from the injection packer 6 and pull out the tubing string. Figure 3 From top to bottom, they are: continuous tube 3, gas-tight continuous tube connector 4, and gas-tight sliding sleeve 5.

[0057] Step S09: The lower milling cylinder removes the rubber sleeve and slips of the gas-filled packer 6, and retrieves the remaining tools.

[0058] The above description is merely an embodiment of this application and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the scope of this application should be included within the protection scope of this invention.

Claims

1. A continuous tubing injection process string, characterized in that, The assembly includes, from top to bottom, a gas injection wellhead (1), a coiled tubing wellhead suspension device (2), a downhole coiled tubing (3), a gas-tight coiled tubing connector (4), a gas-tight sliding sleeve (5), and a gas injection packer (6); the gas injection packer (6) includes a pressure regulating switch (7) and a setting valve (8); the lower end of the downhole coiled tubing (3) is sealed and anchored to the gas-tight coiled tubing connector (4) by clamps; the gas-tight coiled tubing connector (4), the gas-tight sliding sleeve (5), and the gas injection packer (6) are connected in sequence by a gas-tight buckle (12); the pressure regulating switch (7) and the setting valve (8) are both located inside the gas injection packer (6), and the pressure regulating switch (7) is located above the setting valve (8); It also includes: Rubber plug 1 (9) is used in conjunction with gas-tight sliding sleeve (5); rubber plug 1 (9) is inserted into the downhole coiled tubing (3) and enters the inner cavity of gas-tight sliding sleeve (5). By pressurizing, gas-tight sliding sleeve (5) is opened, thereby opening the annulus of the oil sleeve; Rubber plug 2 (10) is used in conjunction with pressure switch (7); rubber plug 2 (10) is inserted into the downhole coiled tubing (3) and enters the inner cavity of pressure switch (7). Pressure is applied to close or open pressure switch (7), thereby blocking or opening the internal passage of downhole coiled tubing (3); The pressure ball (11) is used in conjunction with the setting valve (8); the pressure ball (11) is inserted into the downhole coiled tubing (3) and enters the inner cavity of the setting valve (8), and the gas injection process string is injected by pressurizing the setting coiled tubing.

2. The continuous tube gas injection process string according to claim 1, characterized in that, The pressure ball (11) is a steel ball.

3. The continuous tube gas injection process string according to claim 1, characterized in that, The setting valve (8) is provided with a pressure ball positioning shoulder.

4. The continuous tube gas injection process string according to claim 1, characterized in that, The constant pressure switch (7) is provided with a rubber stopper and a positioning shoulder.

5. The continuous tube gas injection process string according to claim 1, characterized in that, The upper end of the gas-tight sliding sleeve (5) is provided with a rubber plug and a positioning shoulder.

6. A method for operating a continuous tubing gas injection process string, using a continuous tubing gas injection process string as described in any one of claims 1-5, characterized in that, The specific operation method includes: Step S01: Well workover and kill, lift the original well tubing string, replace the wellhead, install the large four-way valve and coiled tubing wellhead suspension device at the gas injection wellhead. After the gas injection tubing string consisting of the downhole coiled tubing (3), gas-tight coiled tubing connector (4), gas-tight sliding sleeve (5) and gas injection packer (6) is lowered into the design position, inject annular protective fluid to replace the kill fluid in the oil casing annulus according to the design requirements. Step S02: Insert a pressure-absorbing ball (11) into the downhole coiled tubing (3), pressurize it to pump the pressure-absorbing ball (11) into the inner cavity of the setting valve (8), and pressurize it to achieve the sealing of the coiled tubing gas injection process string; Step S03: Continuously pressurize and push the piston of the gas-injection packer (6) to compress and expand the sealing sleeve of the corrosion-resistant gas material to seal the annulus of the oil sleeve, expand the slip to open the anchoring sleeve, step and lock the position to complete the setting and anchoring; after the seal is successfully verified, continue to pressurize to the predetermined pressure P1, and remove the pressure ball (11) and the setting valve (8) to make the inside of the downhole coiled tubing (3) unobstructed; Step S04: Insert rubber plug 2 (10) into the downhole coiled tubing (3), pressurize and pump rubber plug 2 (10) into the inner cavity of the constant pressure switch (7). When the pressure is increased to the predetermined pressure P2, rubber plug 2 (10) seals the internal passage of the downhole coiled tubing (3) and releases pressure from the pump truck. At this time, the pressure inside the downhole coiled tubing (3) observed from the wellhead is 0 MPa. Step S05: Suspend, shear, and seal the downhole coiled tubing (3), and install the gas production tree at the injection wellhead; Step S06: Pressurize from the injection wellhead. When the pressure reaches the predetermined pressure P3, the pressure regulating switch (7) is opened, and the inside of the downhole continuous pipe (3) is unobstructed, so gas can be injected.

7. The method for operating a continuous tubing gas injection process string according to claim 6, characterized in that, The operation method further includes: Step S07: When performing well repair operations in the later stage of gas injection, simply insert rubber plug 1 (9) into the downhole continuous tubing (3), pressurize and pump rubber plug 1 (9) into the inner cavity of the gas-sealed sliding sleeve (5), and continue to pressurize to the predetermined pressure P4. When the gas-sealed sliding sleeve (5) opens and the oil casing annulus is connected, circulation well killing operations can be carried out. Step S08: After the well is successfully killed, the gas production tree at the injection wellhead is dismantled, the surface coiled pipe is connected to the downhole coiled pipe, and the downhole coiled pipe (3) is lifted with a predetermined force of 5-8t through the injection head, so that the downhole coiled pipe (3) is separated from the gas injection packer (6), and the downhole coiled pipe (3), gas-tight coiled pipe connector (4), and gas-tight sliding sleeve (5) are lifted from top to bottom. Step S09: The lower milling cylinder removes the rubber sleeve and slips of the gas injection packer (6) and retrieves the remaining structure of the continuous tube gas injection process string.

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