Method for evaluating sealing integrity of cement sheath under working condition of alternating internal pressure of casing

Abstract

The invention discloses a cement sheath sealing integrity evaluation method under a casing alternating internal pressure working condition. The method mainly solves the problem that an existing cement sheath sealing performance evaluation method cannot determine the cement sheath cementation index attenuation rule under the internal pressure alternating condition and the cementation index during cement sheath sealing failure. The method is characterized by comprising the following steps: preparing an experimental cement sheath, circularly providing an alternating load into a sleeve, drawing a change rule of a cementation index along with an internal pressure alternating round under the conditions of upper limit pressure and lower limit pressure of alternating internal pressure of different sleeves, and recording the circulating round and the cementation index of the alternating load of the sleeve when the sealing of the cement sheath fails; fitting to obtain a change rule expression of the cementation index along with the internal pressure alternating turns under different casing pipe alternating internal pressures; and determining the safe service life according to the cement sheath cementation index and the operation upper and lower limit pressure of the transfer injection well. According to the evaluation method, the change rule of the cement sheath cementation index along with internal pressure alternating turns can be determined, and the safe service life of the gas well is evaluated according to the well cementation quality and the designed operation pressure of the target well section of the field transfer gas injection well.

Description

Technical Field

[0001] The invention relates to the technical field of wellbore integrity evaluation for converting old oilfield wells into gas injection wells, in particular to a method for evaluating cement ring seal integrity under casing alternating internal pressure conditions. Background Art

[0002] At present, some oil fields in my country have entered the middle and late stages of development, and the development targets have gradually shifted to peripheral low-permeability reservoirs. However, the permeability of low-permeability reservoirs is low and the water drive effect is poor. In order to improve the recovery rate of oil fields, domestic oil fields have successively carried out field tests of gas injection drive. In order to reduce the cost of oil field development, the gas injection test area mostly uses water drive old wells to convert to gas injection wells for continued production. However, the completion time of the early water drive old wells was relatively early, and the current technical status of the wellbore is unclear. Since the injection pressure of gas injection drive is higher than that of water injection, and the injection method of water and gas alternation is adopted, there is a risk of sealing failure of the cement sheath under the high-pressure alternating load after the old well is converted to a gas injection well, thereby affecting the effect of gas injection development; even the high-pressure injected gas may escape to the surface along the cement sheath interface, bringing great safety hazards. Therefore, it is necessary to carry out cement sheath sealing evaluation under different production conditions, guide the feasibility and safe operation limit analysis of old wells converted to gas injection wells, and ensure the safe and efficient development of oil field gas injection drive.

[0003] The evaluation of cement ring sealing is currently mainly carried out through indoor simulation experiment methods, such as a device and method for measuring the damage of cement ring integrity by alternating internal pressure of casing (CN111766166A), and a device for evaluating the effective sealing section of cement ring under alternating internal pressure (CN202210661640). The above two methods cannot clearly define the attenuation law of cement ring bonding index under alternating internal pressure conditions, and the bonding index when the cement ring seal fails. They cannot evaluate the sealing ability of the cement ring after bearing alternating loads when the cementing quality is not excellent. When the cementing quality of the target well section is not excellent, the above methods cannot evaluate the safe service period of the transfer gas well, and therefore cannot effectively guide the feasibility evaluation and production parameter optimization of the transfer gas well.

[0004] Based on the above analysis, the existing technology is still unable to effectively evaluate the sealing integrity of the cement sheath under the condition of alternating internal pressure of the casing, and thus guide the feasibility analysis of gas injection wells and the optimization of safe operation parameters. Summary of the invention

[0005] In order to overcome the deficiency of existing cement ring sealing evaluation methods that cannot clearly define the attenuation law of cement ring bonding index under internal pressure alternating conditions and the bonding index when cement ring sealing fails, the present invention provides a cement ring sealing integrity evaluation method under casing alternating internal pressure conditions. The evaluation method can clearly define the change law of cement ring bonding index with the number of internal pressure alternation cycles, and evaluate its safe service life according to the cementing quality of the target well section of the on-site gas injection well and the designed operating pressure.

[0006] The technical solution of the present invention is: a method for evaluating the sealing integrity of cement ring under alternating internal pressure conditions of casing, comprising:

[0007] S1. Prepare the experimental formation rock ring using the cement ring sealing integrity evaluation experimental device, fill the space between the formation rock ring and the casing with cement slurry, detect the acoustic amplitude after curing according to the on-site temperature and pressure conditions, and calculate the cement ring initial bonding index BI 0 ;

[0008] S2. Pressurize the casing to the upper limit pressure P max1 , stabilize the pressure, and reduce the pressure inside the casing to the lower limit pressure P min , then stabilize the pressure, and then detect the sound amplitude to calculate the cement sheath bonding index BI 1 ; At the same time, high-pressure gas is injected into the bottom of the cement sheath, and gas leakage is detected at the top of the cement sheath;

[0009] S3, repeat step S2, cyclically provide alternating load to the casing for N times, and calculate the cement sheath bonding index BI after each cycle n When continuous gas flow is detected at the top of the cement sheath, it is considered that the cement sheath seal has failed, and the number of cycles of the casing alternating load at this time is recorded. d1 and cementation index BI n1 ;

[0010] S4. Draw the upper limit pressure P of the casing alternating internal pressure max1 , lower limit pressure P min The variation law of cementation index BI with the number of internal pressure alternation cycles N under the condition;

[0011] S5, repeat steps S1 to S4, and set the casing upper limit pressure to P in each round of experiment. maxn , obtain the upper limit pressure P of the casing alternating internal pressure maxn , lower limit pressure P min The change law of the cementation index with the internal pressure alternation cycle under the condition, and the cycle number N of the casing alternating load when the cement ring seal fails is recorded. dn and cementation index BI nn ;

[0012] S6. Fit the results of steps S4 and S5 to obtain the expression of the change rule of the cementation index with the internal pressure alternation rounds under different casing alternating internal pressures, BI = f(N);

[0013] S7. Determine the cement sheath bonding index BI of the target section of the old well for gas injection g , determine the design service life N of the old wells for gas injection f and the number of alternating production cycles M within each year;

[0014] S8. Calculate the upper limit pressure P of the old well for gas injectionmax1 , lower limit pressure P min The safe service life T at that time;

[0015] S9. Compare the safe service life T and the designed service life N f , if T <N f , then reduce the upper limit pressure P max1 , repeat step S8 until T ≥ N f , then the old well that is converted to gas injection will produce according to this operating parameter.

[0016] Furthermore, the cement sheath bonding index BI is:

[0017]

[0018] Among them: A max A is the acoustic amplitude of the free casing section, mv; E A is the first wave sound amplitude, mv; min is the minimum sound amplitude, mv.

[0019] Furthermore, the voltage stabilization time in step S2 is at least 5 minutes.

[0020] Further, in step S4, according to the upper limit pressure P of the casing alternating internal pressure max1 , internal pressure alternation rounds N, cement sheath bonding index BI after each internal pressure alternation n , with the number of internal pressure alternation cycles N as the horizontal axis and the cementation index BI as the vertical axis, the upper limit pressure P of the casing alternating internal pressure is plotted. max1 , lower limit pressure P min Under the conditions, the cementation index BI changes with the number of internal pressure alternation cycles N.

[0021] Further, the cement sheath bonding index BI of the target well section for evaluating the gas injection in the old well in step S7 is g is the average value of the cementation index of the target well section.

[0022] Further, the safe service life T in step S8 is,

[0023] T=(N d1 -N g ) / M (5)

[0024] Where: N g BI is the cementation index g The corresponding casing internal pressure cycle number; N d1 is the number of casing internal pressure cycles corresponding to cement ring seal failure, and M is the number of alternating production cycles per year.

[0025] Furthermore, if no seal failure occurs after N cycles of alternating the upper and lower limit operating pressures in the experimental design, the cycle number corresponding to the cementing index when the cement sheath seal fails is taken as N according to the formula in step S6. d1 , re-use formula (5) to calculate the safe service life T.

[0026] Further, if the cement sheath bonding index of the gas injection well is not reached after N rounds of internal pressure alternation in the experimental design, the cement sheath bonding index is reduced to the bonding index of the target well section of the gas injection well, and the number of cycles at this time is calculated according to the formula in step S6 as N g , the cycle number corresponding to the bonding index when the cement ring seal fails is taken as N d1 , and then use formula (5) again to calculate the safe service life T.

[0027] Furthermore, the operating parameters in step S9 include the upper limit pressure P of the casing alternating internal pressure. maxn , lower limit pressure P min , Design service life N f And the production cycle M is alternating every year.

[0028] Furthermore, it also includes an experimental device for evaluating the sealing integrity of a cement ring, the experimental device includes a casing, a formation rock ring is arranged on the outside of the casing, a cement ring is filled between the casing and the formation rock ring, and a cementing quality detector is arranged inside the casing; an air injection pump is connected to the bottom of the cement ring, and a gas flow meter is connected to the top of the cement ring; and a casing internal booster pump is arranged at the upper end of the experimental device.

[0029] The present invention has the following beneficial effects: due to the adoption of the above scheme, the method can truly simulate the temperature, pressure and cementing quality conditions of the on-site cement ring service, test the change law of the cement ring bonding index with the alternating internal pressure load and round of the casing, establish the cement ring sealing capacity expression based on the experimental results, and accurately evaluate the safe service life according to the bonding index and design production parameters of the old wells converted to gas injection, thereby guiding the feasibility analysis of the old wells converted to gas injection and the optimization of safe operation parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of the present invention;

[0031] Figure 2 is a schematic diagram of the experimental apparatus used in the present invention;

[0032] Figure 3 It is the curve showing the change of cement sheath bonding index with the number of cycles of internal pressure alternation when the operating pressure is 50MPa-10MPa;

[0033] Figure 4It is a curve showing the change of cement sheath bonding index with the number of internal pressure alternation cycles when the operating pressures are 50MPa-10MPa, 40MPa-10MPa, and 30MPa-10MPa respectively.

[0034] In the figure, 1 is the experimental device, 2 is the booster pump in the casing, 3 is the cementing quality detector, 4 is the gas injection pump, and 5 is the gas flow meter. DETAILED DESCRIPTION

[0035] Depend on Figure 1 , Figure 2 As shown, a cement ring sealing integrity evaluation method under casing alternating internal pressure conditions includes an experimental device 1 for cement ring sealing integrity evaluation. The experimental device 1 includes a casing. During the experiment, a formation rock ring is arranged outside the casing, a cement ring is filled between the casing and the formation rock ring, and a cementing quality detector 3 is arranged inside the casing; the bottom of the cement ring is connected to an air injection pump 4, and the upper part is connected to a gas flow meter 5; the upper end of the experimental device 1 is provided with a casing internal booster pump 2 and a pressure relief valve. During the experiment, the casing is pressurized by the casing internal booster pump 2, and high-pressure gas is injected into the bottom of the cement ring by the air injection pump 4. Whether there is gas leakage is detected by the gas flow meter 5 at the top, so as to determine the sealing integrity of the cement ring.

[0036] At the same time, the average cementation index of the target well section is taken as the cementation index of the well section.

[0037] The present invention will be further described below in conjunction with specific embodiments:

[0038] S1. Taking the casing outer diameter of 139.7mm and cement ring thickness of 38.1mm in the gas injection drive field as an example, according to the inner diameter of 400mm in the full-size cement ring sealing integrity evaluation device, the formation rock ring with an outer diameter of 400mm and an inner diameter of 215.9mm is prepared using the cement ring sealing integrity evaluation device, and the formation rock ring is placed in the cement ring sealing integrity evaluation device. The cement slurry is prepared using the G-grade cement used in the gas injection drive field, and the cement slurry is filled in the annular space formed by the casing and the formation. The pouring height is the maximum height of the experimental device, 1m, and the cementing quality logging instrument is pre-placed in the casing.

[0039] The cement sheath was cured according to the on-site temperature and pressure. After 48 hours of curing, the acoustic amplitude curve was detected using the cementing quality logging instrument. The acoustic amplitude of the free casing section was 159.872 mv, the first wave acoustic amplitude was 21.886 mv, and the minimum acoustic amplitude was 15.631 mv. The initial cementation index BI of the cement sheath was calculated according to formula (1): 0 is 0.86,

[0040]

[0041] Among them: A maxA is the acoustic amplitude of the free casing section, mv; E A is the first wave sound amplitude, mv; min is the minimum sound amplitude, mv.

[0042] S2. After obtaining a cement sheath test piece with excellent cementing quality, the casing is pressurized to the upper limit pressure of 50MPa required for the experiment through the casing booster pump. After stabilizing the pressure for 5 minutes, the casing pressure relief valve is used to reduce the casing pressure to the lower limit pressure of 10MPa, and the pressure is stabilized for another 5 minutes. After the pressure relief and stabilization are completed, the sound amplitude is detected by the cementing quality logging instrument, and the cement sheath bonding index BI is calculated according to formula (1): 1 At the same time, a gas injection pump is used to inject 0.5MPa high-pressure gas into the bottom of the cement sheath. The high-pressure gas is usually N 2 , use a flow meter to detect whether there is any gas leakage at the top of the cement sheath.

[0043] S3, repeat step S2 until the experiment requires weeks. This time, take 60 rounds of alternating load as an example, provide alternating load to the casing 60 times, detect the sound amplitude after each loading and unloading, and calculate the cement sheath bonding index BI n When continuous gas flow is detected at the top of the cement sheath, it is considered that the cement sheath seal has failed, and the number of cycles N of the casing alternating load at this time is recorded. d1 and cementation index BI n1 .

[0044] The cement ring bonding index after each round of casing internal pressure alternation is shown in Table 1. The experiment shows that the cement ring seal failure round is 22, and the bonding index at this time is 0.10.

[0045] S4. According to the upper limit pressure of casing alternating internal pressure of 50MPa, 60 cycles of internal pressure alternation, and the cement sheath bonding index after each internal pressure alternation (as shown in Table 1), with the internal pressure alternation cycle N as the abscissa and the bonding index BI as the ordinate, the change law of the bonding index BI with the internal pressure alternation cycle N under the conditions of the upper limit pressure of casing alternating internal pressure of 50MPa and the lower limit pressure of 10MPa is plotted, as shown in Figure 3 .

[0046] S5. Repeat steps S1 to S4 for many times. In each round of experiments, the upper limit pressure of the casing is set to the required pressure of the experiment. In this experiment, the two experimental conditions of upper limit pressure of 40MPa and 30MPa are taken as examples to obtain the change law of the bonding index with the number of cycles of casing internal pressure alternation under the conditions of upper limit pressure of 40MPa and 30MPa and lower limit pressure of 10MPa. The number of cycles of casing alternating load and the bonding index when the cement ring seal fails are recorded, as shown in Table 1. Under the experimental conditions of upper limit pressure of 40MPa and 30MPa, the cement ring did not fail in 60 cycles.

[0047] Draw the curve of cementation index changing with the number of internal pressure alternation cycles under the condition of casing alternating internal pressure upper limit 50MPa, 40MPa, 30MPa and lower limit 10MPa, as shown in Figure 4 .

[0048] Table 1 Changes of cementation index with internal pressure alternation cycles

[0049]

[0050]

[0051] S6. Based on the experimental results, mathematical fitting is performed on the results of steps S4 and S5 to obtain the expression of the change rule of the cementation index with the number of internal pressure alternation cycles under different casing alternating internal pressure conditions.

[0052] BI=f(N)

[0053] In this experiment, the expression of the change law of the cementation index with the internal pressure alternation cycle under the working conditions of upper limit pressure of 50MPa, 40MPa, 30MPa and lower limit pressure of 10MPa was obtained.

[0054] BI 50-10 =1.5419N -0.723 (2)

[0055] BI 40-10 =0.9552e -0.011N (3)

[0056] BI 30-10 =0.8601e -0.003N (4).

[0057] S7. Count the historical cementing data of old wells in the test area that have been converted to gas injection, determine the cement sheath bonding index of the target well section for evaluation of old wells that have been converted to gas injection, and take the average bonding index of the target well section as the bonding index BI of the well section g . This time, one gas injection well was counted, and the cementation index of the target well section was 0.8. According to the gas injection development and production plan, the design service life of the old well converted to gas injection was determined as N. f The period is 30 years, and the number of alternating production cycles M is 4 each year.

[0058] S8. Calculate the safe service life T of old wells converted to gas injection: Based on the obtained cement sheath bonding index and sealing change law under different alternating loads, when the cement sheath bonding index of the target well section of the old well converted to gas injection is 0.8, according to the operating upper limit pressure of 50MPa and the lower limit pressure of 10MPa, according to Table 1, it can be known that the corresponding casing internal pressure cycle N when the bonding index is 0.8 g =2, when the cement ring seal fails, the bonding index is 0.1, corresponding to the number of casing internal pressure cycles N d1=22, then use formula (5) to calculate the safe service life T:

[0059] T=(N d1 -N g ) / M (5)

[0060] Safe service life T = (N d1 -N g ) / M=(22-2) / 4=5 years.

[0061] S9. Compare the safe service life T and the designed service life N f Since the safe service life T = 5 years is less than the design service life N f =30 years, indicating that the old wells converted to gas injection cannot meet the requirements of safe production within the designed service life under the upper and lower limit operating pressures of 50MPa and 10MPa, so it is necessary to optimize and lower the upper limit operating pressure.

[0062] S10, lower the upper limit pressure of the casing to 40MPa and the lower limit pressure to 10MPa, and recalculate the safe service life of the old wells converted to gas injection. According to the working condition analysis of the upper limit operating pressure of 40MPa and the lower limit operating pressure of 10, the cementation index of 0.8 corresponds to N cycles of casing pressure. g =16, when the cement ring bonding index is 0.1, the seal fails. According to the formula (3) in step S6, the number of casing internal pressure cycles corresponding to the failure of the cement ring seal is N. d1 =201, then the safe service life is calculated using formula (5):

[0063] T=(N d1 -N g ) / M=(201-16) / 4=46 years.

[0064] Since the safe service life T = 46 years is greater than the designed service life N f =30 years, indicating that the old wells converted to gas injection meet the requirements of safe production within the designed service life under the conditions of upper and lower limit operating pressures of 40MPa and 10MPa. The old wells converted to gas injection on site can produce under the conditions of upper limit pressure of 40MPa, lower limit pressure of 10MPa and a service life of 30 years.

[0065] In addition, consider two special cases:

[0066] (1) If the cement sheath bonding index of the gas injection well is relatively high, for example, the bonding index is 0.8, and the upper and lower limit operating pressures of the field design are relatively low, for example, the upper limit operating pressure is 30 MPa and the lower limit operating pressure is 10 MPa, and no seal failure occurs after 60 cycles of internal pressure alternation in the experimental design, then according to the formula (4) in step S6, the number of cycles corresponding to the cement sheath sealing failure when the bonding index is 0.1 is calculated as N.d1 =702, the bonding index is 0.8, corresponding to round N g =21, and then use formula (5) to calculate the safe service life, then the safe service life is:

[0067] T=(N d1 -N g ) / M=(702-21) / 4=170 years.

[0068] It shows that the gas injection well is relatively safe under the service conditions of upper limit operating pressure of 30MPa and lower limit operating pressure of 10MPa.

[0069] (2) If the cement sheath bonding index of the gas injection well is relatively low, for example, the bonding index is 0.6, and the upper and lower limit operating pressures of the field design are relatively low, for example, the upper limit operating pressure is 30 MPa and the lower limit operating pressure is 10 MPa, and the cement sheath bonding index of the gas injection well is still not reached after 60 cycles of internal pressure alternation in the experimental design, then according to the formula (4) in step S6, the number of cycles corresponding to the cement sheath bonding index of 0.6 is calculated to be N. g =118, calculate the number of cycles corresponding to the cement sheath seal failure with a bonding index of 0.1 as N d1 =702, and then use formula (5) to calculate the safe service life, then the safe service life is:

[0070] T = (702-118) / 4 = 146 years.

[0071] It shows that the gas injection well is relatively safe under the service conditions of upper limit operating pressure of 30MPa and lower limit operating pressure of 10MPa.

Claims

1. A method for evaluating cement sheath seal integrity under casing alternating internal pressure conditions. Features include: S1. Prepare the experimental formation rock ring using the cement ring sealing integrity evaluation experimental device, fill the space between the formation rock ring and the casing with cement slurry, detect the acoustic amplitude after curing according to the on-site temperature and pressure conditions, and calculate the initial cementation index BI of the cement ring 0 ; S2. Pressurize the casing to the upper limit pressure P max1 , stabilize the pressure, and reduce the pressure inside the casing to the lower limit pressure P min , then stabilize the pressure, and then detect the sound amplitude to calculate the cement sheath bonding index BI 1 ; At the same time, high-pressure gas is injected into the bottom of the cement sheath, and gas leakage is detected at the top of the cement sheath; S3. Repeat step S2, cyclically apply an alternating load to the casing for N times, and calculate the cement sheath bond index BI after each cycle. n When continuous gas flow is detected at the top of the cement sheath, it is determined that the cement sheath seal has failed, and record the number of cycles N of the alternating load on the casing at this time. d1 and the bond index BI. n1 ; S4. Draw the upper limit pressure P of the casing alternating internal pressure max1 , lower limit pressure P min The variation law of cementation index BI with the number of internal pressure alternation cycles N under the condition; S5, repeat steps S1 to S4, and set the casing upper limit pressure to P in each round of experiment. maxn , obtain the upper limit pressure P of the casing alternating internal pressure maxn , lower limit pressure P min The change law of the cementation index with the internal pressure alternation cycle under the condition, and the cycle number N of the casing alternating load when the cement ring seal fails is recorded. dn and cementation index BI nn ; S6. Fit the results of steps S4 and S5 to obtain the expression of the change rule of the cementation index with the internal pressure alternation rounds under different casing alternating internal pressures, BI = f(N); S7. Determine the cement sheath bonding index BI of the target section of the old well for gas injection g , determine the design service life N of the old wells for gas injection f and the number of alternating production cycles M within each year; S8. Calculate the upper limit pressure P of the old well for gas injection max1 , lower limit pressure P min The safe service life T at that time; S9. Compare the safe service life T and the designed service life N f , if T <N f , then reduce the upper limit pressure P max1 , repeat step S8 until T ≥ N f , then the old well that is converted to gas injection will produce according to this operating parameter.

2. The cement sheath seal integrity evaluation method under casing alternating internal pressure conditions according to claim 1, Features: The cement sheath bonding index BI is: Among them: A max A is the acoustic amplitude of the free casing section, mv; E A is the first wave sound amplitude, mv; min is the minimum sound amplitude, mv.

3. The cement sheath seal integrity evaluation method under casing alternating internal pressure conditions according to claim 1, Features: The voltage stabilization time in step S2 is at least 5 minutes.

4. The cement sheath seal integrity evaluation method under casing alternating internal pressure conditions according to claim 1, Features: In step S4, according to the upper limit pressure P of the casing alternating internal pressure max1 , internal pressure alternation rounds N, cement sheath bonding index BI after each internal pressure alternation n , with the number of internal pressure alternation cycles N as the horizontal axis and the cementation index BI as the vertical axis, the upper limit pressure P of the casing alternating internal pressure is plotted. max1 , lower limit pressure P min Under the conditions, the cementation index BI changes with the number of internal pressure alternation cycles N.

5. The cement sheath seal integrity evaluation method under casing alternating internal pressure conditions according to claim 1, Features: The step S7 of evaluating the cement sheath bonding index BI of the target well section in the old well for gas injection g is the average value of the cementation index of the target well section.

6. The method for evaluating cement sheath sealing integrity under casing alternating internal pressure conditions according to claim 1, Features: The safe service life T in step S8 is, T=(N d1 -N g ) / M (5) Where: N g BI is the cementation index g The corresponding casing internal pressure cycle number; N d1 is the number of casing internal pressure cycles corresponding to cement ring seal failure, and M is the number of alternating production cycles per year.

7. The method for evaluating cement sheath seal integrity under casing alternating internal pressure conditions according to any one of claims 1 to 6, Features: If the seal failure does not occur after N cycles of alternating the upper and lower limit operating pressures in the experimental design, then according to the formula in step S6, the cycle number corresponding to the cementation index when the cement ring seal fails is taken as N d1 , re-use formula (5) to calculate the safe service life T.

8. The method for evaluating cement sheath seal integrity under casing alternating internal pressure conditions according to claims 1-6, Features: If the cement sheath bonding index of the gas injection well is not reached after N rounds of internal pressure alternation in the experimental design, the cement sheath bonding index is reduced to the bonding index of the target well section of the gas injection well, and the number of cycles at this time is calculated as N according to the formula in step S6. g , the cycle number corresponding to the bonding index when the cement ring seal fails is taken as N d1 , and then use formula (5) again to calculate the safe service life T.

9. The cement sheath seal integrity evaluation method under casing alternating internal pressure conditions according to claim 1, Features: The operating parameters in step S9 include the upper limit pressure P of the casing alternating internal pressure maxn , lower limit pressure P min , Design service life N f And the production cycle M is alternating every year.

10. The method for evaluating cement sheath sealing integrity under casing alternating internal pressure conditions according to claim 1, Features: It also includes an experimental device (1) for evaluating the sealing integrity of a cement ring, wherein the experimental device (1) includes a casing, a formation rock ring is arranged outside the casing, a cement ring is filled between the casing and the formation rock ring, and a cementing quality detector (3) is arranged inside the casing; the bottom of the cement ring is connected to an air injection pump (4), and the top of the cement ring is connected to a gas flow meter (5); and the upper end of the experimental device (1) is provided with an inner casing booster pump (2).

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