Leaking stoppage and sealing method for production pipe column of gas injection well
By calculating the annular protective fluid level and selecting appropriate plugging agents, combined with inert gas injection, and controlling the annular pressure, the sealing problem caused by alternating formation pressure changes in gas injection wells was solved, achieving long-term sealing of gas injection wells and improving safety and production stability.
Patent Information
- Application Number
- CN202411023963.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-29
- Publication Date
- 2026-01-30
AI Technical Summary
Existing technologies in gas injection wells suffer from poor long-term sealing performance of production tubing due to alternating formation pressure changes, especially severe pressure-bearing phenomena in the annulus of the oil casing. Furthermore, existing plugging methods fail to effectively address formation pressure changes, leading to a drop in the annulus protection fluid level and increasing safety hazards.
By calculating the minimum liquid level of the annular protective fluid and selecting an appropriate type of plugging agent, combined with the injection of inert gas, the annular pressure is controlled to balance the formation pressure, ensuring the long-term sealing performance of the packer and plugging agent. Ultrafine particle sedimentation and suspension plugging agents are used to seal the leakage points respectively, and the leakage is plugged by gravity difference and extrusion.
It achieves long-term sealing of the annulus under alternating formation pressure, avoids gas exchange, improves the safety and production stability of gas injection wells, and reduces operating costs.
Smart Images
Figure CN121429322A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of oil and gas exploitation, in particular to a method for plugging and sealing a production string of a gas injection well. BACKGROUND
[0002] In the process of natural gas development and storage, CO2 underground storage, the completion string of injection-production well is designed with packer, downhole safety valve, setting nipple, circulating sliding sleeve and other completion tools. The completion tubing and completion tools all use metal gas seal thread. After the completion string is lowered into the wellbore, the packer is set to seal the annulus between the oil casing and the tubing, and the annulus protection fluid is poured into the annulus, generally to the wellhead. The above process protects the outer wall of the production casing and tubing above the permanent packer, and achieves the purpose of sealing the integrity of the wellbore. However, with the continuous service of the wellbore, the annulus pressure becomes more and more serious, especially in the oil casing annulus, and the leakage points are mainly in the tubing thread, the packer, the upper insertion seal of the packer, the circulating sliding sleeve and other places, which brings great difficulty to the control and treatment of the well with annulus pressure.
[0003] At present, for the well with serious annulus pressure, the tubing and the oil casing annulus have already leaked, so the large repair operation of replacing the production string is adopted for treatment, that is, after the original well string is pulled out, the new tubing and downhole tools are lowered again, which has high operation cost and needs to shut down the production. For the well with not serious annulus pressure and the completion string with certain sealing capacity, the main method is to strengthen the monitoring and release the annulus pressure, but the leakage points still exist, the gas exchanges with the annulus protection fluid through the leakage points, which leads to more and more gas in the annulus and lower and lower liquid level of the annulus protection fluid, and the annulus pressure is aggravated, which brings great safety hidden danger to the gas storage and the production operation of the production string and the environmental protection.
[0004] At present, there are several treatment methods for the operation without moving the production string: one is to use resin or gel, which is injected into the annulus protection fluid at the wellhead to accumulate and block the leakage channel at the leakage point; the other is to use alloy powder which is sent into the packer in the oil casing annulus, and the alloy powder is melted by a heating device to make the tubing, casing and packer become one, so as to separate the oil and gas. The two processes do not consider the influence of the changing formation pressure on the pressure-bearing capacity of the plugging agent, such as the alternating change of the formation pressure in the process of gas storage operation with gas injection and gas production, and the gradual rise of the formation pressure in the CO2 injection well with CO2 injection. The alternating change of the formation pressure easily leads to the plugging failure of the plugging agent, and with the more and more common phenomenon of annulus pressure in the gas well, further research is needed to develop a more suitable and effective process for field operation. SUMMARY
[0005] The present application provides a method for plugging and sealing a production string of a gas injection well, which solves the problem of poor long-term sealing of the production string in the prior art when the formation pressure changes alternately.
[0006] To solve the above technical problems, the technical scheme of the blowout sealing method for the gas injection well production string is as follows:
[0007] A blowout sealing method for a gas injection well production string, comprising the following steps:
[0008] (1) According to the running lower limit pressure of the gas injection well or the initial formation pressure P i , the residual pressure bearing capacity P f of the packer, the minimum liquid level height h of the annulus protection fluid required to balance the pressure of the packer is calculated and injected into the oil casing annulus;
[0009] (2) According to the leakage position of the gas injection well production string, the type of plugging agent is selected and injected into the oil casing annulus;
[0010] (3) During the gas injection period of the gas injection well, inert gas is injected into the oil casing annulus to ensure that the difference between the formation pressure and the sum of the liquid column pressure of the annulus protection fluid and the pressure of the inert gas does not exceed the residual pressure bearing capacity of the upper and lower end faces of the packer.
[0011] The present application is an improvement on the prior art. The blowout sealing method for the gas injection well production string provided by the present application selects different types of plugging agents for different leakage positions, and during the gas injection stage of the gas injection well, the sum of the liquid column pressure of the annulus protection fluid and the pressure of the injected inert gas is adjusted to balance the formation pressure during the gas injection stage, ensuring that the difference between the formation pressure and the sum of the liquid column pressure of the annulus protection fluid and the pressure of the inert gas does not exceed the residual pressure bearing capacity of the upper and lower end faces of the packer, achieving long-term sealing of the packer and the plugging agent, and further achieving long-term sealing of the oil casing annulus, thereby solving the problem of poor long-term sealing of the oil casing annulus caused by alternating changes in the formation pressure of the gas injection well.
[0012] To further balance the annulus pressure and the formation pressure, preferably, the calculation method of the minimum liquid level height h of the annulus protection fluid in step (1) is as follows:
[0013]
[0014] Wherein, P i is the running lower limit pressure of the gas injection well or the formation pressure before gas injection, unit: MPa; P f is the residual pressure bearing capacity of the packer, unit: MPa; ρ h is the density of the annulus protection fluid, unit: g / cm 3 .
[0015] To further simplify the injection frequency of inert gas during the gas injection stage and avoid frequent operations, preferably, in step (3), whenever the formation pressure rises to the residual pressure bearing capacity P f0.6-0.8 times of the formation pressure, inert gas is injected into the oil casing annulus, and the inert gas pressure is P f 0.6-0.8 times of the formation pressure. In order to avoid frequent inert gas injection operation, the method of phased inert gas injection is adopted, so that the difference between the formation pressure and the pressure of the annulus protection fluid and the inert gas does not exceed the residual pressure bearing capacity of the end face of the packer away from the annulus protection fluid, the pressure difference between the upper and lower end faces of the packer during the inert gas injection stage is ensured to be small, the leakage of the formation gas through the packer and the exchange with the annulus protection fluid are avoided, and the long-term sealing effectiveness is improved.
[0016] In order to further improve the sealing performance of the oil casing annulus, preferably, the plugging agent comprises an ultra-fine particle deposition type plugging agent for plugging the leakage of the packer and / or an ultra-fine particle suspension type plugging agent for plugging the leakage of the threaded connection of the production string. For the annulus pressure caused by the leakage of the packer, the ultra-fine particle deposition type plugging agent is injected into the oil casing annulus carried by the annulus protection fluid, and naturally settles on the top of the packer by using the gravity difference. For the annulus pressure caused by the leakage of the threaded connection of the tubing, the insert seal or the circulating sliding sleeve and the like, the ultra-fine particle suspension type plugging agent is injected into the oil casing annulus carried by the annulus protection fluid, and is spontaneously accumulated in the leakage channel by extrusion, so as to realize the plugging of the leakage channel. If the packer and the threaded connection of the production string both have leakage, the ultra-fine particle deposition type plugging agent and the ultra-fine particle suspension type plugging agent are simultaneously injected into the oil casing annulus carried by the annulus protection fluid, so as to respectively plug the leakage points of the packer and the threaded connection of the production string.
[0017] In order to further improve the sealing performance of the oil casing annulus when the threaded connection of the production string has leakage, preferably, in the step (2), when the threaded connection of the production string has leakage and the leakage position is higher than h, the liquid level of the annulus protection fluid in the oil casing annulus is higher than the leakage position.
[0018] In order to further improve the sealing performance of the production string during production, preferably, the liquid level of the annulus protection fluid is monitored during the gas production process of the gas injection well and is not lower than h. If the threaded connection of the production string has leakage and the leakage position is higher than h, the liquid level of the annulus protection fluid is monitored during the gas production process and is higher than the leakage position.
[0019] In order to further make the sealing of the oil casing annulus long-term effective, preferably, the gas injection and gas production of the gas injection well are alternately operated, the gas injection stage and the gas production stage are one cycle, and the minimum liquid level h of the annulus protection fluid is calculated once in each cycle. With the alternate operation of the gas injection and gas production cycles of the gas injection well, the residual pressure bearing capacity of the packer will decrease, and it is necessary to reevaluate and recalculate the minimum liquid level of the annulus protection fluid in each cycle.
[0020] In order to further improve the sealing performance of the production string of the gas storage injection and production well or the CO2 injection well, preferably, the gas injection well is the gas storage injection and production well or the CO2 injection well. BRIEF DESCRIPTION OF DRAWINGS
[0021] Figure 1 The schematic diagram of the production string plugging and sealing method for the injection-production well of the gas storage of the embodiment 1 is shown in the figure.
[0022] In the figure: 1, production string; 2, casing; 3, packer; 4, inert gas; 5, annular protection fluid; 6, ultra-fine particle suspension plugging agent; 7, ultra-fine particle precipitation plugging agent. DETAILED DESCRIPTION
[0023] The technical concept of the production string plugging and sealing method for the gas injection well of the present application is as follows:
[0024] The production string plugging and sealing method for the gas injection well comprises the following steps:
[0025] (1) According to the running lower limit pressure of the gas injection well or the initial formation pressure P i , the residual pressure bearing capacity of the packer P f , the minimum liquid level height h of the annular protection fluid required to balance the pressure of the packer is calculated and the casing annulus is injected;
[0026] (2) According to the corresponding selection of the plugging agent type according to the leakage position of the production string of the gas injection well, the casing annulus is injected;
[0027] (3) During the gas injection of the gas injection well, inert gas is injected into the casing annulus to make the difference between the formation pressure and the sum of the liquid column pressure of the annular protection fluid and the pressure of the inert gas not exceed the residual pressure bearing capacity of the upper and lower end faces of the packer.
[0028] The production string plugging and sealing method for the gas injection well provided by the present application selects different types of plugging agents for plugging different leakage positions, and during the gas injection stage of the gas injection well, the pressure of the casing annulus is adjusted by adjusting the liquid column pressure of the annular protection fluid and the pressure of the injected inert gas, to balance the formation pressure, ensure that the difference between the formation pressure and the sum of the liquid column pressure of the annular protection fluid and the pressure of the inert gas does not exceed the residual pressure bearing capacity of the upper and lower end faces of the packer, realize the long-term sealing of the packer and the plugging agent, and further realize the long-term sealing of the casing annulus, thereby solving the problem of poor long-term sealing of the casing annulus of the gas injection well caused by the alternating change of the formation pressure.
[0029] The embodiments of the present application will be further described below in combination with specific examples.
[0030] First, the specific embodiments of the production string plugging and sealing method for the gas injection well of the present application
[0031] The embodiment 1 of the production string plugging and sealing method for the gas injection well of the present application is described by taking the injection-production well of the gas storage as an example, and the schematic diagram of the production string plugging and sealing method for the injection-production well of the gas storage is shown in the figure. Figure 1As shown, the wellbore of the gas storage injection-production well consists of a production tubing string 1, a casing 2, and a packer 3. The wellhead is sealed by a wellhead device. After the packer 3 is set, an annulus is formed, and annulus protection fluid 5 is injected into the annulus.
[0032] The method for sealing leaks in the gas injection well production tubing in this embodiment is as follows:
[0033] (1) Based on the lower operating pressure P of the gas storage facility i The remaining pressure bearing capacity P of the packer f Calculate the minimum annular fluid level h required to achieve pressure balance in the packer and inject it into the annulus. The calculation method for the minimum fluid level h is as follows:
[0034]
[0035] Among them, P i P represents the lower limit operating pressure of the gas storage facility, in MPa. f ρ represents the remaining pressure-bearing capacity of the packer, in MPa. h Density of the annular protective fluid, unit: g / cm³ 3 .
[0036] (2) Select the type of plugging agent according to the leakage location of the gas injection well production tubing and inject it into the annulus;
[0037] Specifically, first determine the location of the leakage in the production tubing of the gas storage injection and production wells. If the leakage is determined to be caused by the failure of the packer 3 seal, prepare an ultrafine particle precipitated plugging agent 7 on the surface. The amount of plugging agent prepared is calculated based on the annular volume with a stacking height of 0.3m on the packer. Add the prepared ultrafine particle precipitated plugging agent 7 to the annular protective fluid 5 and inject it into the annulus through the four-way valve of the tubing head, ensuring that the liquid level of the annular protective fluid 5 is not less than h. Allow it to stand and allow the ultrafine particle precipitated plugging agent 7 to naturally settle to the top of the packer 3 in the annular protective fluid 5.
[0038] If the leakage is determined to be caused by the failure of the threaded connection of production string 1 (such as tubing, insertion seal, circulating sleeve, or downhole safety valve), prepare ultrafine particle suspended plugging agent 6 on the surface and add it to the annulus protection fluid 5. Inject it into the annulus through the four-way valve of the tubing head, ensuring that the liquid level of the annulus protection fluid 5 is not lower than h. When the leakage location is higher than h, add more annulus protection fluid 5 to make the liquid level higher than the leakage location. Let it stand until the ultrafine particle suspended plugging agent 6 is squeezed and spontaneously accumulates in the threaded leakage channel, thereby sealing the threaded leakage channel.
[0039] If it is determined that the leakage is simultaneously occurring in the connecting threads of packer 3 and production tubing 1, ultrafine particle precipitating plugger 7 and ultrafine particle suspension plugger 6 are prepared on the ground. The amount of ultrafine particle precipitating plugger 7 is calculated based on the annular volume with a stacking height of 0.3m on the packer. The ultrafine particle suspension plugger 6 and ultrafine particle precipitating plugger 7 are added to the annular protective fluid 5 and injected into the annulus through the four-way flank of the tubing head, ensuring that the liquid level of the annular protective fluid 5 is not lower than h. When the leakage position of the connecting threads of production tubing 1 is higher than h, annular protective fluid 5 is added to make the liquid level higher than the leakage position. The ultrafine particle suspension plugger 6 is allowed to stand and spontaneously accumulate under compression in the thread leakage channel, while the ultrafine particle precipitating plugger 7 naturally settles to the top of packer 3 in the annular protective fluid 5, thus sealing the leakage channel.
[0040] (3) During the gas injection period of the gas storage injection-production well, inert gas 4 is injected into the annulus of the oil casing to make the formation pressure equal to the liquid column pressure of the annulus protective fluid 5 and the pressure P of the inert gas 4. g The difference between the sums does not exceed the remaining pressure-bearing capacity of the packer.
[0041] Specifically, during the gas injection period, each time the formation pressure rises to the packer's remaining pressure-bearing capacity P... f Inert gas 4 is injected into the annulus of the oil sleeve at a pressure of 0.6 to 0.8 times that of the original gas, at a pressure P. g For P f 0.6 to 0.8 times. Inert gas 4 can be nitrogen, helium, etc.
[0042] (4) During the production process of the gas storage injection and production wells, monitor the liquid level of the annular protective fluid 5 and ensure that it is not lower than h.
[0043] Specifically, when the level of the annular protective fluid 5 is lower than h, the annular protective fluid 5 is replenished to a level h using the surface replenishment process. If there is leakage in the connecting threads of the production tubing of the gas storage injection and production wells, when the level of the annular protective fluid 5 h is lower than the leakage location, the annular protective fluid 5 is replenished using the surface replenishment process to make the level higher than the leakage location.
[0044] II. Specific Application Examples of the Gas Injection Well Production Tubing Leakage Sealing Method of the Present Invention
[0045] Taking a well in a gas storage facility with annular pressure as an example, the specific implementation method is explained. The lower operating pressure of this gas storage facility is 13 MPa. The well is under annular pressure, with a shut-in oil pressure of 13 MPa and a casing pressure of 10 MPa. The current annular fluid level is 1654 m. Analysis shows that the annular pressure in this well is caused by packer leakage. The packer has a remaining pressure-bearing capacity of 9 MPa. The production tubing sealing method implemented for this well is as follows:
[0046] (1) Based on the lower operating pressure P of the gas storage facilityi =13MPa, residual pressure bearing capacity P of the packer f =9MPa, the minimum fluid level h required to balance the pressure of the packer is calculated using the following formula and injected into the annulus of the oil casing. The minimum fluid level h of the well is calculated to be 2245m.
[0047]
[0048] Among them, P i P represents the lower limit operating pressure of the gas storage facility, in MPa. f ρ represents the remaining pressure-bearing capacity of the packer, in MPa. h Density of the annular protective fluid, unit: g / cm³ 3 ;
[0049] (2) The leakage in this well was caused by packer seal failure, and ultrafine particle sedimentation plugging agent was used for plugging. The inner diameter of the tubing in this well is Φ = 73.02 mm, and the inner diameter of the production casing is Φ = 121.4 mm. The amount of plugging agent required is calculated to be 0.002 m³ based on the annulus volume with a stacking height of 0.3 m on the packer. 3 The calculated plugging agent was added to the annular protective fluid, and the annular protective fluid was injected into the oil jacket annulus to the lowest liquid level height of 2245m.
[0050] (3) During the gas injection period of the gas storage well, each time the formation pressure rises to the packer's remaining pressure-bearing capacity P f Nitrogen gas is injected into the annulus at a pressure 0.6 to 0.8 times the pressure of the packer. The upper operating pressure of the gas storage tank in this well is 27 MPa. Based on the current remaining pressure-bearing capacity of the packer (9 MPa), the nitrogen injection pressure will be between 5.4 and 7.2 MPa each time. For example, for every 7 MPa increase in formation pressure, nitrogen gas will be injected into the annulus at a pressure of 7 MPa.
[0051] (4) During the operation of the gas storage facility, monitor the level of the annulus protection fluid in the well and ensure that it is not lower than 2245m.
[0052] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method of plugging and sealing a gas injection well production string, characterized in that, The method comprises the following steps: (1) the operating lower limit pressure of the injection well or the initial formation pressure P i , the remaining pressure capacity of the packer P f , the minimum liquid level h of the annular protective fluid required to balance the pressure of the packer is calculated and injected into the oil casing annulus; (2) Selecting the plugging agent type according to the leakage position of the production string of the gas injection well and injecting the plugging agent into the oil-casing annulus; (3) During the gas injection of the gas injection well, inert gas is injected into the oil-casing annulus to make the difference between the formation pressure and the sum of the liquid column pressure of the annulus protection fluid and the pressure of the inert gas not exceed the residual pressure bearing capacity of the packer.
2. The method of sealing a gas injection well production string leak of claim 1, wherein, The calculation method of the minimum liquid level height h of the annulus protection fluid in the step (1) is as follows: Wherein, P i is the lower limit pressure of the operation of the gas injection well or the formation pressure before gas injection, unit MPa; P f is the residual pressure-bearing capacity of the packer, unit MPa; p h is the density of the annular protection fluid, unit g / cm 3 .
3. The method of sealing a gas injection well production string leak of claim 1, wherein, The step (3) is that when the formation pressure rises to 0.6-0.8 times of the residual pressure-bearing capacity P of the packer, inert gas is injected into the oil jacket annulus, and the inert gas pressure is 0.6-0.8 times of P. f The step (3) is that when the formation pressure rises to 0.6-0.8 times of the residual pressure-bearing capacity P of the packer, inert gas is injected into the oil jacket annulus, and the inert gas pressure is 0.6-0.8 times of P. f The step (3) is that when the formation pressure rises to 0.6-0.8 times of the residual pressure-bearing capacity P of the packer, 4. The method of sealing a gas injection well production string leak of claim 1, wherein, The plugging agent comprises an ultra-fine particle deposition type plugging agent for plugging the leakage of the packer and / or an ultra-fine particle suspension type plugging agent for plugging the leakage of the thread of the production string.
5. The method of sealing a gas injection well production string leak of claim 1, wherein, In the step (2), the thread of the connection of the production string has leakage, and when the leakage position is higher than h, the liquid level height of the annulus protection fluid in the oil-casing annulus is higher than the leakage position.
6. The method of sealing a gas injection well production string leak of claim 1, wherein, The liquid level height of the annulus protection fluid is monitored during the gas production of the gas injection well and is not lower than h.
7. A method of plugging and sealing a gas injection well production string as defined in claim 1 or 2, characterized in that, The gas injection and gas production of the gas injection well are alternately operated, the gas injection stage and the gas production stage are one cycle, and the minimum liquid level height h of the annulus protection fluid is calculated once in each cycle.
8. The method of sealing a gas injection well production string leak of claim 1, wherein, The gas injection well is a gas storage injection-production well or a CO2 injection well.