High-frequency pressure real-time cement sheath damage identification method

Abstract

The invention discloses a high-frequency pressure real-time cement sheath damage identification method, which comprises the following steps: carrying out data acquisition by using existing wellhead pressure monitoring equipment, ensuring that the precision of the equipment is within + / -0.1%, and meanwhile, ensuring that the equipment is firmly mounted and calibrated; drawing a wellhead pressure and derivative curve and observing a specific slope line segment; the bottom hole pressure of the Laplace space is calculated; and comparing a calculation result with a normal condition to judge whether damage occurs and evaluate the damage degree. According to the method, on the basis of the spherical well testing theory, the complex fluid flowing condition after the cement sheath is damaged is comprehensively considered, in the process of deducing the well bottom pressure expression of the cement sheath damaged well, different boundary conditions including fluid flowing equations under gas cap, bottom water, upper top sealing, lower bottom sealing and the like are considered in detail, and the well bottom pressure expression of the cement sheath damaged well is deduced. The accurate modeling mode can more accurately reflect the actual situation after the cement sheath is damaged, and compared with a traditional simple model, the method has higher accuracy in the aspect of identifying the damage of the cement sheath.

Description

Technical Field

[0001] This invention relates to the field of oil extraction, specifically to a method for real-time identification of cement sheath damage using high-frequency pressure. Background Technology

[0002] Cement sheaths play a crucial role in oil extraction, serving to secure casing, isolate different formations, and prevent fluid cross-contamination. However, due to various factors such as formation stress variations and corrosion, cement sheaths can be damaged. Damage to cement sheaths not only affects normal well production but can also lead to safety hazards and environmental pollution. Accurately identifying cement sheath damage is essential for timely repair measures, ensuring well lifespan, and improving extraction efficiency.

[0003] Traditional cement sheath testing methods, such as ultrasonic testing and radiometric testing, can directly detect the physical state of the cement sheath. However, these methods often require specialized equipment to be lowered into the well for testing, making the operation complex and costly. Moreover, these methods can only be used to detect changes in the cement sheath at specific points in time, and cannot monitor changes in the cement sheath's condition in real time.

[0004] For example, ultrasonic testing requires lowering the ultrasonic probe into the vicinity of the cement sheath. In complex downhole environments, the lowering and operation of the equipment faces many difficulties, and the test results may be affected by factors such as downhole fluids and casing.

[0005] Some analytical methods based on simple theoretical models fail to adequately consider the complex fluid flow conditions following cement sheath damage. When the cement sheath fails, the fluid flow patterns in the formation change, exhibiting both radial and vertical flow, and are also influenced by factors such as gas caps and bottom water. Traditional simplistic models often neglect these factors or oversimplify them, leading to inaccurate assessments of cement sheath damage. Summary of the Invention

[0006] The purpose of this invention is to provide a method for real-time identification of cement ring damage under high-frequency pressure, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for real-time identification of cement sheath damage under high-frequency pressure includes the following steps:

[0009] Step S1: Determine the high-frequency pressure data acquisition frequency based on the pressure change characteristics that may be caused by cement sheath damage and the dynamic characteristics of downhole fluid flow. Use existing wellhead pressure monitoring equipment to acquire data, and ensure that the accuracy of the equipment is within ±0.1%. At the same time, ensure that the equipment is securely installed and calibrated.

[0010] Step S2: Clean the data using statistical methods to remove outliers, and smooth the data using the moving average method;

[0011] Step S3: Analyze the pressure change rate to detect water hammer waves, and plot the wellhead pressure and derivative curves to observe specific slope segments;

[0012] Step S4: Determine the parameters of the spherical well test theoretical equation based on the oil well boundary conditions, calculate the bottom-hole pressure in the Laplace space, and consider wellbore storage and skin effect to obtain the relationship between the bottom-hole pressure in the real space and time.

[0013] Step S5: Compare the calculation results with those under normal conditions to determine whether there is damage and assess the degree of damage.

[0014] In this invention, in step S1, the sampling frequency is 10-20 times per second to collect pressure data.

[0015] In this invention, in step S2, outliers in the collected pressure data are removed using the statistical method 3σ principle, and the pressure data after cleaning is smoothed using the moving average method.

[0016] In this invention, in step S3, water hammer is detected by analyzing the rate of change of pressure data and calculating the pressure difference between adjacent data points. When the pressure difference exceeds the threshold determined based on the historical data and theoretical analysis of the specific oil well, it is considered that water hammer may exist.

[0017] In this invention, in step S3, the wellhead pressure and derivative curves are plotted, and the presence of a straight line segment with a slope of -1 / 2 is observed under a double logarithmic coordinate system to determine whether it conforms to the characteristics of cement sheath damage.

[0018] In this invention, in step S4, the boundary conditions of the well with cement sheath damage are determined according to the actual situation of the oil well. Based on the boundary conditions, the parameters of the relevant equations in the spherical well test theory are determined. The bottom hole pressure of the instantaneous source without considering wellbore storage and skin factor is Laplace transformed according to the method in the spherical well test theory. If it is a bounded formation, the corresponding bottom hole pressure is obtained by the product method and then Laplace transformation is performed.

[0019] In this invention, in step S4, the obtained pressure is further substituted to obtain the bottom hole pressure in Laplace space considering wellbore storage and skin factor, and then the numerical relationship between the bottom hole pressure and time in the cement sheath damaged well in real space is obtained by Laplace numerical inversion.

[0020] In this invention, in step S5, the calculated bottom hole pressure versus time relationship and pressure curve characteristic analysis results are compared with the values ​​and characteristics under normal conditions. Based on the comparison analysis results, when the calculated bottom hole pressure changes significantly differently from the normal situation over a certain period of time and the pressure curve characteristics conform to the cement sheath damage characteristics, if the pressure curve characteristics deviate significantly from the normal situation and the bottom hole pressure changes significantly, the cement sheath damage is determined to be severe; if there are only slight characteristic changes and pressure fluctuations, the damage is determined to be mild.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. This invention is based on the spherical well test theory and comprehensively considers the complex fluid flow situation after cement sheath damage. In the process of deriving the bottom pressure expression of wells with cement sheath damage, it takes into account different boundary conditions, including fluid flow equations under gas cap, bottom water, top cap closure, and bottom cap closure. This precise modeling method can more accurately reflect the actual situation after cement sheath damage. Compared with the traditional simple model, it has higher accuracy in identifying cement sheath damage.

[0023] 2. This invention utilizes the characteristics of wellhead pressure and derivative curves when cement sheaths are damaged, including abnormal water hammer and spherical features in the wellhead pressure and derivative curves, to identify cement sheath damage. These characteristics are a direct reflection of fluid flow changes on the pressure curves after cement sheath damage. By accurately analyzing these curve characteristics, it is possible to precisely determine whether the cement sheath is damaged and the extent of the damage. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a typical closed curve at the top and bottom of the present invention;

[0025] Figure 2 This is a schematic diagram of typical pressure constant curves at the top and bottom of the present invention;

[0026] Figure 3 This is a schematic diagram of a typical curve where the upper top and lower bottom are mixed boundaries according to the present invention;

[0027] Figure 4 This is a schematic diagram of the closed semi-logarithmic diagram of the top and bottom of the present invention;

[0028] Figure 5 This is a schematic diagram of a typical curve with a closed radial discontinuity at the top and bottom of the present invention.

[0029] Figure 6 This is a schematic diagram of the horizontal well location according to the present invention;

[0030] Figure 7 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0031] 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.

[0032] Please see Figure 7 The present invention provides a technical solution:

[0033] A method for real-time identification of cement sheath damage under high-frequency pressure includes the following steps:

[0034] Step S1: Determine the high-frequency pressure data acquisition frequency based on the pressure change characteristics that may be caused by cement sheath damage and the dynamic characteristics of downhole fluid flow. Use existing wellhead pressure monitoring equipment to acquire data, and ensure that the accuracy of the equipment is within ±0.1%. At the same time, ensure that the equipment is firmly installed and calibrated. The acquisition frequency is 10-20 times of pressure data per second.

[0035] In this step, the acquisition frequency of high-frequency pressure data is determined based on the pressure change characteristics that may be caused by cement sheath damage and the dynamic characteristics of downhole fluid flow. Since rapid pressure fluctuations (such as water hammer anomalies) may occur when the cement sheath is damaged, the acquisition frequency needs to be high enough to capture these subtle changes. The initial acquisition frequency is set at 10-20 pressure data points per second. This frequency is determined based on the timescale of pressure changes after cement sheath damage, ensuring both the ability to capture rapidly changing pressure signals and the capacity for data storage and processing.

[0036] Specifically, data acquisition is carried out using existing wellhead pressure monitoring equipment to ensure that the accuracy of the equipment meets the requirements for identifying cement sheath damage. Generally, the pressure measurement accuracy is required to be within ±0.1%. In terms of installation, it is necessary to ensure that the equipment is installed firmly to avoid the measurement results being affected by factors such as wellhead vibration. In addition, the equipment should be calibrated to ensure that its measurement reference is accurate.

[0037] Step S2: Use statistical methods to clean the data and remove outliers, use the moving average method to smooth the data, use the 3σ principle of statistical methods to remove outliers in the collected pressure data, use the moving average method to smooth the cleaned pressure data, detect water hammer by analyzing the rate of change of pressure data, calculate the pressure difference between adjacent data points, and when the pressure difference exceeds the threshold determined based on the historical data and theoretical analysis of the specific oil well, it is considered that water hammer may exist.

[0038] In this step, outliers in the collected pressure data are first removed. Outliers may be caused by temporary equipment malfunctions, external interference, or other factors. For example, statistical methods such as the 3σ rule (a data point is considered an outlier if it deviates from the mean by more than three standard deviations) can be used to identify and remove outliers. This step is to ensure the data quality for subsequent analysis and avoid outliers misleading the results by smoothing the cleaned pressure data. Methods such as moving averages can be used; for example, a 5-point moving average is used, where for each data point, the average of the two data points before and after it is taken as the smoothed value for that point. Smoothing reduces noise in the data, making the pressure curve smoother and facilitating subsequent analysis of the pressure curve's characteristics.

[0039] Step S3: Analyze the pressure change rate to detect water hammer waves, plot the wellhead pressure and derivative curves, observe specific slope segments, plot the wellhead pressure and derivative curves, and observe whether there is a straight line segment with a slope of -1 / 2 in the pressure derivative curve under double logarithmic coordinates to determine whether it meets the characteristics of cement sheath damage.

[0040] In this step, water hammer detection is performed on the preprocessed pressure data. Water hammer is a key characteristic of cement sheath damage, manifesting as sudden fluctuations in pressure data. Water hammer is detected by analyzing the rate of change in pressure data. For example, the pressure difference between adjacent data points is calculated; if the pressure difference exceeds a certain set threshold (determined based on historical data and theoretical analysis of the specific well, such as 0.5 MPa / s), water hammer is considered likely to be present. This step is based on the characteristic that cement sheath damage causes abnormal water hammer; detecting water hammer can provide a preliminary assessment of the potential for cement sheath damage.

[0041] Specifically, plotting the wellhead pressure and derivative curves is based on the spherical well testing theory. When the cement sheath is damaged, the wellhead pressure and derivative curves will exhibit a spherical shape. The shape of the curves is analyzed to determine if it matches the characteristics of cement sheath damage. For example, in a logarithmic coordinate system, observe whether the pressure derivative curve has a straight line segment with a slope of -1 / 2 (spherical flow segment). If it does, it further indicates that the cement sheath may be damaged. This step is an analysis based on the specific shape characteristics of the wellhead pressure and derivative curves when the cement sheath is damaged, which corresponds to the spherical well testing theory.

[0042] Step S4: Determine the parameters of the spherical well test theory equations based on the well boundary conditions. Calculate the bottom-hole pressure in the Laplace space and consider wellbore storage and skin effect to obtain the relationship between the bottom-hole pressure and time in the real space. Determine the boundary conditions of the cement sheath-damaged well based on the actual situation of the well. Determine the parameters of the relevant equations in the spherical well test theory based on the boundary conditions. Perform Laplace transformation on the bottom-hole pressure of the instantaneous source without considering wellbore storage and skin factor according to the method in the spherical well test theory. If it is a bounded formation, use the product method to obtain the corresponding bottom-hole pressure and then perform Laplace transformation. Substitute the obtained pressure to obtain the bottom-hole pressure in the Laplace space considering wellbore storage and skin factor. Then use Laplace numerical inversion to obtain the numerical relationship between the bottom-hole pressure and time in the real space of the cement sheath-damaged well.

[0043] In this step, due to the damage to the cement sheath, fluid flow occurs both from the fracture and outwards from the cement sheath. The fluid flow in the formation includes not only radial but also vertical flow. Because of the vertical flow, the gas cap or bottom water in the reservoir will affect the bottom hole pressure. This results in a complex bottom hole pressure curve with many factors to consider. If the skin factor and wellbore storage are not considered, the bottom hole pressure solution for the cement sheath-damaged well under transient source conditions can be obtained using the product method. Applying a Laplace transform to this bottom hole pressure yields the bottom hole pressure in Laplace space under transient source conditions for the cement sheath-damaged well. Substituting this pressure into equation (5-1) yields the Laplace space solution considering C... D Cement sheath damage and bottom hole pressure under S conditions Finally, Laplace numerical inversion was performed to obtain the bottom hole pressure P of the cement sheath damaged well in real space. WD Numerical relationship with time.

[0044] In an infinitely large formation, the dimensionless equation for a well with cement sheath damage can be written as follows:

[0045]

[0046] P D (r D ,z D ,t D =0)=0 (5-50b)

[0047] P D (r D ,z D =0,t D ) = 0 (air cap) (5-50c-1)

[0048]

[0049] P D (r D ,z D =h D ,t D ) = 0 (bottom water)(5-50d-1)

[0050]

[0051] P D (r D →∞,z D ,t D )=0 (5-50e)

[0052]

[0053] Applying the Laplace transform to equation (5-50), we get...

[0054]

[0055] In the formula

[0056]

[0057] u --- the variable of the Laplace transform;

[0058]

[0059] Solve equation (5-51) using the method of separation of variables, thus letting

[0060]

[0061] Substituting equation (5-52) into equation (5-51), we can obtain the equation satisfied by Θ and its boundary conditions.

[0062] Θ (z) + λ 2 Θ(z)=0 (5-53a)

[0063] Θ(z D =0)=0 (Air top) (5-53b-1)

[0064] Θ'(z D =0)=0 (top closed) (5-53b-2)

[0065] Θ(z D =h D ) = 0 (bottom water) (5-53c-1)

[0066] Θ'(z D =h D ) = 0 (bottom closed) (5-53c-2)

[0067] The general solution of equation (5-53) is

[0068] Θ(z D )=Asin(λz D )+Bcos(λz D (5-54)

[0069] Based on the boundary conditions of the upper and lower datum, the eigenvalues ​​λ and eigenfunctions Θ can be obtained.

[0070] 1. Damaged wells with cement sheaths that are sealed at both the top and bottom.

[0071]

[0072] Θ(z D )=cos(λz D (5-55a-2)

[0073] 2. For wells with damaged cement sheaths containing air caps and bottom water.

[0074]

[0075] Θ(z D )=sin(λz D (5-55b-2)

[0076] 3. For wells with a damaged cement sheath but no bottom water,

[0077]

[0078] Θ(z D )=sin(λz D (5-55c-2)

[0079] 4. For wells with damaged cement sheaths but no air cap, where there is bottom water.

[0080]

[0081] Θ(z D )=cos(λz D (5-55d-2)

[0082] The radial characteristic function can be written as

[0083]

[0084] Therefore, the bottom hole pressure of a cement sheath-damaged well in the Laplace space can be expressed as...

[0085]

[0086] Expanding the boundary conditions (5-51e) using a special function as a Fouier series, we can find the following: 1. For reservoirs without bottom water and gas cap.

[0087]

[0088] 2. Damaged well with a cement ring containing bottom water and an air cap.

[0089]

[0090] 3. Damaged wells with bottom water but no air cap and cement ring

[0091]

[0092]

[0093] 4. Damaged well with an air-filled top but no bottom water.

[0094]

[0095] In equation (5-58) In the substitution (5-1) Thus, we obtain the expression for the bottom hole pressure of a cement sheath-damaged well, considering wellbore storage and skin effect. Then, using Laplace numerical inversion, we obtain the numerical relationship between the bottom hole pressure and time in real space (where S should represent the wellbore skin).

[0096] Figure 1 , Figure 2 and Figure 3 These are typical curves for the following conditions in a well with cement sheath damage: top and bottom sealing, top and bottom pressure control, and top and bottom as a mixed boundary. Due to the use of combined parameter C... D e 2S Thus, h in equation 2-58 DR become at the same time

[0097] like Figure 1 As shown, Part I is the wellbore storage section. Part II is the transition section from the wellbore storage section to radial flow in the vertical direction. Part III is the radial flow section in the vertical direction. Part IV is the spherical flow section, where the double logarithmic derivative curve is a straight line segment with a slope of -1 / 2 (pressure derivative); Part V is the total radial flow section of the entire formation. It can be seen from the pressure derivative curve that wells with cement sheath damage may exhibit two radial flow sections and one spherical flow. Figure 4 Is with Figure 1 The corresponding semi-logarithmic curve.

[0098] For bounded formations, the product method can still be used to obtain the bottomhole pressure of the instantaneous source without considering wellbore storage and skin factor. Applying a Laplace transform to this bottomhole pressure yields the bottomhole pressure of the instantaneous source in Laplace space without considering wellbore storage and skin factor. Substituting this pressure into equation (5-1) yields the bottomhole pressure in Laplace space considering wellbore storage and skin factor. Finally, Laplace numerical inversion is used to obtain the numerical relationship between bottomhole pressure and time. Figure 5 This is a typical curve for a well with a fault in a closed formation with an upper and lower top.

[0099] The well test analysis method for wells with cement sheath damage is largely the same as that for wells with full perforation. If it's single-stage production pressure drop data, simply plot the combined curves of lgt~lgΔP and lgt~lgΔP' (ΔP'=dΔP / dlnt), and perform curve fitting using typical pressure drop curves. If it's pressure data for multi-stage production (including pressure recovery), the pressure derivatives for multi-stage production need to be corrected according to equation (4-126). Then, calculate typical multi-stage flow curves and perform curve fitting. After curve fitting, obtain the time fitting value TM, pressure fitting value PM, and C. D e 2S z aD z bD h 2CD and L iD e S Based on these values, the following explanation can be derived.

[0100] From the pressure fitting value

[0101]

[0102] The value obtained from time fitting

[0103]

[0104] By C D e 2S get

[0105]

[0106] ΔP S =S t / PM

[0107] S P ---Given by equation (1-64)

[0108] By h 2CD get

[0109]

[0110] By zaD z bD get

[0111] z a =h·z aD (5-63a)

[0112] z b =h·z bD (5-63b)

[0113] By L iD e S Obtain the distance from the well to the outer boundary.

[0114] L i =r w e -S L i e S (5-64)

[0115] Step S5: Compare the calculation results with the normal situation to determine whether there is damage and assess the degree of damage. By comparing the calculated bottom hole pressure with the time and the pressure curve characteristic analysis results with the values ​​and characteristics under normal conditions, according to the comparison analysis results, when the trend of the calculated bottom hole pressure in a certain period of time is significantly different from that under normal conditions and the pressure curve characteristics are consistent with the cement sheath damage characteristics, if the pressure curve characteristics deviate significantly from the normal situation and the bottom hole pressure changes significantly, it is determined that the cement sheath damage is more serious; if there are only slight characteristic changes and pressure fluctuations, it is determined that the damage is less serious.

[0116] In this step, the calculated bottomhole pressure versus time relationship and the pressure curve characteristic analysis results are compared with the values ​​and characteristics under normal conditions. The values ​​and characteristics under normal conditions can be calculated using historical well data or theoretical models. For example, if the calculated bottomhole pressure trend over a certain period differs significantly from normal conditions, and the pressure curve characteristics (such as water hammer, spherical flow section, etc.) also conform to the characteristics of cement sheath damage, then it can be determined that the cement sheath is damaged. Based on the comparative analysis results, the degree of cement sheath damage is assessed. If the pressure curve characteristics deviate significantly from normal conditions and the bottomhole pressure changes considerably, then the cement sheath damage is considered severe; if there are only slight characteristic changes and pressure fluctuations, then the damage is considered minor. This step, based on the analysis results of all previous steps, comprehensively assesses the cement sheath damage, thus providing a basis for subsequent repair measures.

[0117] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0118] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for real-time identification of cement ring damage using high-frequency pressure, characterized in that, Includes the following steps: Step S1: Determine the high-frequency pressure data acquisition frequency based on the pressure change characteristics that may be caused by cement sheath damage and the dynamic characteristics of downhole fluid flow. Use existing wellhead pressure monitoring equipment to acquire data, and ensure that the accuracy of the equipment is within ±0.1%. At the same time, ensure that the equipment is securely installed and calibrated. Step S2: Clean the data using statistical methods to remove outliers, and smooth the data using the moving average method; Step S3: Analyze the pressure change rate to detect water hammer waves, and plot the wellhead pressure and derivative curves to observe specific slope segments; Step S4: Determine the parameters of the spherical well test theoretical equation based on the oil well boundary conditions, calculate the bottom-hole pressure in the Laplace space, and consider wellbore storage and skin effect to obtain the relationship between the bottom-hole pressure in the real space and time. Step S5: Compare the calculation results with those under normal conditions to determine whether there is damage and assess the degree of damage.

2. The method for real-time identification of cement ring damage by high-frequency pressure according to claim 1, characterized in that: In step S1, the sampling frequency is 10-20 times per second to collect pressure data.

3. The method for real-time identification of cement ring damage by high-frequency pressure according to claim 1, characterized in that: In step S2, outliers in the collected pressure data are removed using the statistical method of the 3σ principle, and the pressure data after cleaning is smoothed using the moving average method.

4. The method for real-time identification of cement ring damage by high-frequency pressure according to claim 1, characterized in that: In step S3, water hammer is detected by analyzing the rate of change of pressure data and calculating the pressure difference between adjacent data points. When the pressure difference exceeds the threshold determined based on the historical data and theoretical analysis of the specific oil well, it is considered that water hammer may exist.

5. The method for real-time identification of cement ring damage by high-frequency pressure according to claim 1, characterized in that: In step S3, the wellhead pressure and derivative curves are plotted, and the pressure derivative curve is observed under a double logarithmic coordinate system to determine whether there is a straight line segment with a slope of -1 / 2 to determine whether it conforms to the characteristics of cement sheath damage.

6. The method for real-time identification of cement ring damage by high-frequency pressure according to claim 1, characterized in that: In step S4, the boundary conditions of the well with cement sheath damage are determined according to the actual situation of the oil well. Based on the boundary conditions, the parameters of the relevant equations in the spherical well test theory are determined. The bottom hole pressure of the instantaneous source without considering wellbore storage and skin factor is Laplace transformed according to the method in the spherical well test theory. If it is a bounded formation, the corresponding bottom hole pressure is obtained by the product method and then Laplace transformation is performed.

7. The method for real-time identification of cement ring damage by high-frequency pressure according to claim 1, characterized in that: In step S4, the obtained pressure is further substituted to obtain the bottom hole pressure in Laplace space considering wellbore storage and skin factor, and then the numerical relationship between the bottom hole pressure and time in the cement sheath damaged well in real space is obtained by Laplace numerical inversion.

8. The method for real-time identification of cement ring damage by high-frequency pressure according to claim 1, characterized in that: In step S5, the calculated bottom hole pressure versus time relationship and pressure curve characteristic analysis results are compared with the values ​​and characteristics under normal conditions. Based on the comparison analysis results, when the calculated bottom hole pressure changes significantly differently from the normal situation over a certain period of time and the pressure curve characteristics match the cement sheath damage characteristics, if the pressure curve characteristics deviate significantly from the normal situation and the bottom hole pressure changes significantly, the cement sheath damage is determined to be severe. If there are only slight characteristic changes and pressure fluctuations, the damage is determined to be mild.

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