An experimental method for quantitatively monitoring deformation of a cement sheath assembly

Abstract

The present application belongs to the technical field of cementing of oil and gas well, and particularly relates to an experimental method for quantitatively monitoring deformation process of cement sheath combination. The present application obtains the deformation synchronism of the simulated casing, the cement sheath and the simulated surrounding rock and the volume change of the cement sheath by the following steps: configuring cement slurry, recording the original inner and outer radii of the simulated casing and the simulated surrounding rock, preparing the cement sheath, judging the operation process of generating the deformation of the combination, applying temperature or pressure value according to different operation processes, obtaining the data of the inner and outer diameters of the cement sheath combination changing with time and the time points of the changes in the whole change process, and processing the obtained data, thereby providing support for the integrity research of the cement sheath.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas well cementing technology, specifically relating to an experimental method for quantitatively monitoring the deformation process of cement sheath assemblies. Background Technology

[0002] The cement sheath assembly, composed of casing, cement sheath, and surrounding formation rock, is a crucial component in oil and gas well cementing. Good cement sheath integrity is essential for ensuring the normal operation of oil and gas wells. The main function of the cement sheath is to effectively seal the annular space between the casing and the formation rock, preventing fluid cross-flow during drilling, production, and enhanced production operations, while also providing effective protection and support for the internal casing. However, during subsequent operations (such as secondary density drilling, fracturing, and heavy oil thermal recovery), the temperature and pressure inside the casing will change, sometimes significantly, affecting or even destroying the cement sheath's integrity. Therefore, understanding the deformation process of the cement sheath assembly under varying temperature and pressure within the casing—such as the synchronicity of deformation among the casing, cement sheath, and surrounding formation rock, and changes in cement stone volume—is of significant practical importance for deepening the industry's understanding of cement sheath integrity failure processes, reversing the failure process under different operating conditions, and ultimately proposing technical approaches, research directions, and key research areas for improving the sealing integrity of cement sheaths during subsequent production processes.

[0003] In recent years, many scholars have studied the stress state of cement sheath assemblies under high temperature and high pressure based on mechanical models, such as Xu Xinniu, Ruan Biao, Du Zonghe, Huang Hong, Zhang Wei, Yang Hu, and Zhou Penggao's article "Mechanical Integrity of Cement Sheaths During Trial Production of High Temperature and High Pressure Oil and Gas Reservoirs—Taking Gaotan 1 Well in the Southern Margin of Junggar Basin as an Example" [J], Science, Technology and Engineering, 2021, 21(19):7924-7930. However, no method for quantitatively monitoring the deformation process of cement sheath assemblies based on experimental devices has been provided. In subsequent studies on cement sheath integrity, Andrade et al., based on their self-developed experimental device, investigated the integrity of a scaled-down "casing-cement sheath-formation" assembly under cyclic loading (temperature and pressure). Although the device was simple to operate, its temperature and pressure were relatively low, and it did not measure the deformation of the cement sheath assembly, limiting its use to qualitative evaluation and judgment of whether the cement sheath integrity had failed. Zhu Qingjie et al. invented an indoor simulation experimental device for casing-cement sheath damage under formation loading (Zhu Qingjie, Chen Yanhua, Zhang Yumin, Liao Yong, Diao Hengqiang, Li Lifeng, Wang Zhanhui, Indoor Simulation Experimental Device for Casing-Cement Sheath Damage under Formation Loading, Patent Publication No.: CN101725345A). Although this device can measure the strain and deformation of the casing-cement sheath, it is limited to studying the influence of temperature and pressure on the integrity of the cement sheath. Therefore, there is an urgent need for a method based on an experimental device to quantitatively monitor the deformation process of the cement sheath assembly. Summary of the Invention

[0004] This invention provides an experimental method for quantitatively monitoring the deformation process of a cement ring assembly. The purpose is to provide a means and method that can clearly identify the deformation of the casing, cement ring, and surrounding rock, as well as the synchronicity between them, and understand the changes in the volume of the cement ring, thereby providing a means and method for quantitatively understanding and studying the deformation process of the cement ring assembly.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An experimental method for quantitatively monitoring the deformation process of a cement ring assembly includes the following steps:

[0007] Step 1: Prepare cement slurry;

[0008] Step 2: Record the inner radius and outer radius values ​​of the simulated casing and simulated surrounding rock before the experiment;

[0009] Step 3: Prepare cement rings;

[0010] Step 4: Determine the operational process that causes deformation of the assembled structure.

[0011] If the process that causes the deformation of the assembly is a simulated single loading-unloading process of the internal pressure of the casing with constant temperature and changing pressure, then proceed to step five; if the process that causes the deformation of the assembly is a process simulation with changing temperature and constant pressure, then proceed to step seven.

[0012] Step 5: According to the downhole working conditions, pressurize or depressurize the simulated casing to the preset value, maintain it for the preset time, and then restore the pressure inside the simulated casing. Obtain the data on the changes in the inner and outer diameters of the cement sheath assembly over time and the time points of the changes during the entire pressure change process.

[0013] Step Six: Process the data obtained in Step Five;

[0014] Step 7: According to the downhole working conditions, heat or cool the simulated casing to the preset value and maintain it for the preset time. Then restore the temperature inside the simulated casing and obtain the data on the changes in the inner and outer diameters of the cement sheath assembly over time during the entire temperature change process.

[0015] Step 8: Process the data obtained in Step 7.

[0016] The method for preparing the cement ring in step three is the same as that used in step one. Specifically, the cement slurry prepared in step one is injected into the dynamic testing device for the sealing capacity of the cement ring. The cement slurry is cured at set time intervals. During the curing process, internal pressure is applied to the simulated casing and external pressure is applied to the simulated surrounding rock until it solidifies and forms a cement ring.

[0017] The time interval for curing the cement slurry is set to 4h, 6h, 8h, 1d, 2d or 28d.

[0018] The specific method for processing the data in step six is ​​as follows:

[0019] The first step is to determine the deformation sequence of the casing, the surrounding rock, and the casing itself based on the changes in the inner and outer diameters of the assembly.

[0020] The second step is to determine the deformation process of the cement ring assembly based on the changes in the inner and outer diameters of the assembly:

[0021] The third step is to calculate the volume change of the cement ring before the integrity failure caused by the tensile cracks in the cement ring during loading and before the integrity failure caused by the interface bonding failure during unloading, based on the changes in the inner and outer diameters of the cement ring assembly at different times.

[0022] The first step, determining the deformation sequence of the casing, the casing itself, and the surrounding rock based on changes in the inner and outer diameters of the assembly, is as follows: if the simulated casing deforms first, i.e., the radial displacement value of the simulated casing's inner wall... r1 0, simulated radial displacement value of the outer wall of the surrounding rock. If r4=0), then the cement ring deformation is asynchronous, and the deformation sequence is from the inside out. The stress is transmitted from the simulated sleeve to the cement ring and then to the simulated surrounding rock. If the simulated surrounding rock deforms first, i.e., the radial displacement value of the simulated surrounding rock outer wall is... r4 0, simulated radial displacement value of the inner wall of the casing If r1=0, the cement ring deforms asynchronously, and the deformation sequence is from the outside to the inside. The stress is transferred from the simulated surrounding rock to the cement ring and then to the simulated casing. If the simulated casing and the simulated surrounding rock deform at the same time, the cement ring deforms synchronously.

[0023] The second step, judging the deformation process of the cement ring assembly based on the changes in the inner and outer diameters of the assembly, is as follows: During the loading and unloading process under small pressure differences (i.e., within the elastic range of the cement ring-casing-surrounding rock), the cement ring assembly as a whole is within the elastic deformation range. The cement ring can maintain its integrity during both loading and unloading, and the inner and outer diameters of the assembly can be restored to their initial values. As the pressure difference increases, the deformation of the cement ring assembly increases. When the pressure difference is insufficient to cause tensile cracking failure of the cement ring, the cement ring can maintain its integrity during loading, but during unloading, there will be a point where the integrity fails due to interface cementation failure. This point is the inflection point where the elastic deformation of the cement ring is fully restored. Based on this, the elastic deformation, plastic deformation, and total deformation of the cement ring during the loading and unloading process can be obtained. If the pressure difference during the loading and unloading process increases to the maximum pressure difference (i.e., outside the elastic range of the cement ring-casing-surrounding rock), the cement ring will experience irreversible tensile cracking failure during loading.

[0024] The specific method for calculating the volume change of the cement ring before the integrity failure caused by tensile cracks in the cement ring during loading and before the integrity failure caused by interfacial bonding failure during unloading, based on the changes in the inner and outer diameters of the cement ring assembly at different times, in the third step is as follows:

[0025] When the internal pressure of the simulated casing changes, the volume of the simulated casing remains constant. At this time, the inner radius of the simulated casing is r1′=r1+ r1, thus obtaining r2′:

[0026]

[0027] Where: r1 is the original inner radius of the simulated sleeve;

[0028] r1′ is the inner radius of the simulated casing when the internal pressure changes; the unit is mm.

[0029] r2 is the simulated original outer radius of the sleeve, in mm;

[0030] r2′ is the outer radius of the simulated casing when the internal pressure changes; the unit is mm.

[0031] h represents the instrument height, in mm;

[0032] Similarly, when the pressure inside the simulated casing changes, the volume of the simulated surrounding rock remains constant. In this case, the outer radius of the simulated surrounding rock is r4′ = r4 + r4, thus r3′:

[0033]

[0034] Where: r3 is the original inner radius of the simulated surrounding rock, in mm;

[0035] The inner radius of the surrounding rock is simulated to represent the pressure change within the casing; the unit is mm.

[0036] r4 is the original outer radius of the simulated surrounding rock, in mm;

[0037] r4′ is the simulated outer radius of the surrounding rock when simulating changes in the internal pressure of the casing, in mm;

[0038] Therefore, we can conclude that

[0039]

[0040] in: The volume change of the cement sheath is measured in mm to simulate changes in internal pressure within the casing. 3 .

[0041] The volume change of the cement ring can be used to determine the expansion and contraction of the cement ring at a certain moment, and can also be used to determine the volume change of the cement ring during loading and unloading.

[0042] The method for processing the data obtained in step seven in step eight is as follows:

[0043] The first step is to determine the deformation sequence of the casing, the surrounding rock, and the casing itself based on the changes in the inner and outer diameters of the assembly.

[0044] The second step is to calculate the volume change of the cement ring and determine its expansion / contraction at different times, thereby reversing the process of cement ring integrity change under this working condition.

[0045] The first step, determining the deformation sequence of the casing, the casing itself, and the surrounding rock based on changes in the inner and outer diameters of the assembly, is as follows: if the simulated casing deforms first, i.e., the radial displacement value of the simulated casing's inner wall... r1 0, simulated radial displacement value of the outer wall of the surrounding rock. If r4=0, the cement ring deforms asynchronously, and the deformation sequence is from the inside out. The stress is transferred from the simulated sleeve to the cement ring and then to the simulated surrounding rock. If the simulated surrounding rock deforms first, i.e., the radial displacement value of the simulated surrounding rock outer wall is... r4 0, simulated radial displacement value of the inner wall of the casing If r1=0, the cement ring deforms asynchronously, and the deformation sequence is from the outside to the inside. The stress is transferred from the simulated surrounding rock to the cement ring and then to the simulated casing. If the simulated casing and the simulated surrounding rock deform at the same time, the cement ring deforms synchronously.

[0046] The second step involves calculating the volume change of the cement ring and determining its expansion / contraction at different times. Based on this, the specific method for reconstructing the cement ring integrity change process under this working condition is as follows.

[0047] Given the coefficient of volume expansion β of the object, and from:

[0048]

[0049] in: This represents the change in the total volume of an object when the temperature changes, expressed in mm. 3 ;

[0050] The original volume of the object, in mm. 3 ;

[0051] This represents the change in temperature of an object, expressed in °C.

[0052] From the above formula, the total volume change of the simulated casing and surrounding rock under temperature changes can be obtained. Considering that the downhole casing is cemented and axial volume changes are not taken into account, when the volumes of the simulated casing and surrounding rock change, only the radial volume change is considered. This radial volume change is 3 / 10 to 4 / 10 of the total volume change. Assuming the simulated casing is uniformly heated and the temperature is uniformly transferred within the cement sheath assembly, when the temperature inside the simulated casing rises, the inner radius r of the simulated casing at this time... 1温 =r1+ r 1温 , thus obtaining r 2温 ′:

[0053]

[0054] in:

[0055] The simulated outer radius of the bushing is given in mm when the internal temperature of the bushing rises.

[0056] This represents the radial volume change of the simulated casing as the internal temperature rises, expressed in mm. 3 ;

[0057] r 1温 This represents the change in the inner radius of the simulated sleeve when the temperature changes, in mm.

[0058] Similarly, when the temperature inside the simulated casing rises, the outer radius of the simulated surrounding rock is r4′=r4+ r 4温 , thus obtaining r 3温 ′:

[0059]

[0060] in:

[0061] - The simulated inner radius of the surrounding rock when the temperature inside the casing rises, in mm;

[0062] - The radial volume change of the simulated surrounding rock when the temperature inside the casing rises, in mm. 3 ;

[0063] r 4温 - The change in the outer radius of the simulated surrounding rock when simulating temperature changes inside the casing, in mm;

[0064] Therefore, we can conclude that

[0065]

[0066] in: - The volume change of the cement sheath during the temperature rise inside the casing, in mm. 3 ;

[0067] After the internal and external temperatures stabilize, the fracturing condition can be simulated. The simulated casing temperature is reduced, and the simulated casing and simulated surrounding rock should shrink in volume. At this time, the initial internal and external diameters of the simulated casing and simulated formation are the final internal and external diameters of the simulated casing and simulated formation calculated in the above process when the internal and external temperatures stabilize.

[0068] Beneficial effects:

[0069] (1) The present invention is simple and quick to operate, without the need for various cumbersome operations, which is conducive to the rapid evaluation of the integrity of cement rings on site.

[0070] (2) The present invention makes full use of existing experimental equipment, and the test results obtained are highly accurate, which can provide cementing quality assurance for subsequent construction of oil and gas wells.

[0071] (3) This invention can not only determine the synchronous deformation of the casing, cement ring and surrounding rock, but also determine the volume change of the cement ring, which provides a new idea and method for the study of cement ring integrity.

[0072] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0073] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0074] Figure 1 This is a schematic diagram of the internal cross-section of the experimental apparatus of the present invention.

[0075] In the diagram: 1. Simulated casing; 2. Simulated surrounding rock; 3. Cement ring. Detailed Implementation

[0076] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0077] Example 1:

[0078] Reference Figure 1 As shown, an experimental method for quantitatively monitoring the deformation process of a cement ring assembly includes the following steps:

[0079] Step 1: Prepare cement slurry;

[0080] Step 2: Record the inner radius and outer radius of the simulated casing 1 and simulated surrounding rock 2 before the experiment, respectively;

[0081] Step 3: Prepare cement ring 3;

[0082] Step 4: Determine the operational process that causes deformation of the assembled structure.

[0083] If the process that causes the deformation of the assembly is a simulated single loading-unloading process of the internal pressure of the casing with constant temperature and changing pressure, then proceed to step five; if the process that causes the deformation of the assembly is a process simulation with changing temperature and constant pressure, then proceed to step seven.

[0084] Step 5: According to the downhole working conditions, pressurize or depressurize the simulated casing to the preset value, maintain it for the preset time, and then restore the pressure inside the simulated casing. Obtain the data on the changes in the inner and outer diameters of the cement sheath assembly over time and the time points of the changes during the entire pressure change process.

[0085] Step Six: Process the data obtained in Step Five;

[0086] Step 7: According to the downhole working conditions, heat or cool the simulated casing to the preset value and maintain it for the preset time. Then restore the temperature inside the simulated casing and obtain the data on the changes in the inner and outer diameters of the cement sheath assembly over time during the entire temperature change process.

[0087] Step 8: Process the data obtained in Step 7.

[0088] The technical solution of this invention is not only simple and quick to operate, eliminating the need for various cumbersome procedures, but also facilitates rapid on-site evaluation of the integrity of the cement ring.

[0089] This invention makes full use of existing experimental equipment, namely a dynamic testing device for cementing sheath sealing capacity in patent publication number CN106771096B, which yields high-precision test results and can provide cementing quality assurance for subsequent oil and gas well construction.

[0090] This invention can not only determine the synchronous deformation of the casing, cement ring, and surrounding rock, but also the volume change of the cement ring, providing a new approach and method for studying the integrity of the cement ring.

[0091] Example 2:

[0092] Reference Figure 1 An experimental method for quantitatively monitoring the deformation process of cement ring assemblies differs from Example 1 in that the method for preparing the cement ring in step three is the same as that in step one, the cement slurry prepared in step one is injected into the dynamic testing device for the sealing capacity of cement rings, the cement slurry is cured at set time intervals, and internal pressure is applied to the simulated casing and external pressure is applied to the simulated surrounding rock during curing until it solidifies to form a cement ring.

[0093] Furthermore, the time interval for the curing cement slurry is set to 4h, 6h, 8h, 1d, 2d, or 28d. The pressure value for applying internal pressure to the simulated casing can be calculated based on the fluid column pressure inside the casing and the actual operating conditions, i.e., actual fluid column pressure inside the casing + actual operating pressure (such as fracturing pressure); the pressure value for applying external pressure to the simulated surrounding rock can be calculated based on the actual formation pressure gradient of each oilfield, i.e., formation pressure gradient of this block or this well * actual vertical depth of a single well.

[0094] Furthermore, the specific method for processing the data in step six is ​​as follows:

[0095] The first step is to determine the deformation sequence of the casing, the surrounding rock, and the casing itself based on the changes in the inner and outer diameters of the assembly.

[0096] The second step is to determine the deformation process of the cement ring assembly based on the changes in the inner and outer diameters of the assembly:

[0097] The third step is to calculate the volume change of the cement ring before the integrity failure caused by the tensile cracks in the cement ring during loading and before the integrity failure caused by the interface bonding failure during unloading, based on the changes in the inner and outer diameters of the cement ring assembly at different times.

[0098] Furthermore, the method for determining the deformation sequence of the casing, the casing itself, and the surrounding rock based on the changes in the inner and outer diameters of the assembly in the first step is as follows: if the simulated casing deforms first, i.e., the radial displacement value of the simulated casing's inner wall... r1 0, simulated radial displacement value of the outer wall of the surrounding rock. If r4=0, the cement ring deforms asynchronously, and the deformation sequence is from the inside out. The stress is transferred from the simulated sleeve to the cement ring and then to the simulated surrounding rock. If the simulated surrounding rock deforms first, i.e., the radial displacement value of the simulated surrounding rock outer wall is... r4 0, simulated radial displacement value of the inner wall of the casing If r1=0, the cement ring deforms asynchronously, and the deformation sequence is from the outside to the inside. The stress is transferred from the simulated surrounding rock to the cement ring and then to the simulated casing. If the simulated casing and the simulated surrounding rock deform at the same time, the cement ring deforms synchronously.

[0099] Furthermore, the second step, which determines the deformation process of the cement ring assembly based on changes in the inner and outer diameters of the assembly, is as follows: During the loading and unloading process under small pressure differences (i.e., within the elastic range of the cement ring-casing-surrounding rock), the cement ring assembly as a whole is within the elastic deformation range. The cement ring maintains good integrity during both loading and unloading, and both the inner and outer diameters of the assembly can recover to their initial values. As the pressure difference increases, the deformation of the cement ring assembly increases. When the pressure difference is insufficient to cause tensile cracking failure of the cement ring, the cement ring can maintain good integrity during loading, but during unloading, a point of integrity failure due to interface cementation failure will occur. This point is the inflection point where the elastic deformation of the cement ring fully recovers. Based on this, the elastic deformation, plastic deformation, and total deformation of the cement ring during the loading and unloading process can be obtained. If the pressure difference during the loading and unloading process increases to a maximum pressure difference (i.e., outside the elastic range of the cement ring-casing-surrounding rock), the cement ring will experience irreversible tensile cracking failure during loading.

[0100] Furthermore, the specific method for calculating the volume change of the cement ring before the integrity failure caused by tensile cracks in the cement ring during loading and before the integrity failure caused by interfacial bonding failure during unloading, based on the changes in the inner and outer diameters of the cement ring assembly at different times, in the third step is as follows:

[0101] When the internal pressure of the simulated casing changes, the volume of the simulated casing remains constant. At this time, the inner radius of the simulated casing is r1′=r1+ r1, thus obtaining r2′:

[0102]

[0103] Where: r1 is the original inner radius of the simulated sleeve;

[0104] r1′ is the inner radius of the simulated casing when the internal pressure changes; the unit is mm.

[0105] r2 is the simulated original outer radius of the sleeve, in mm;

[0106] r2′ is the outer radius of the simulated casing when the internal pressure changes; the unit is mm.

[0107] h represents the instrument height, in mm;

[0108] Similarly, when the pressure inside the simulated casing changes, the volume of the simulated surrounding rock remains constant. In this case, the outer radius of the simulated surrounding rock is r4′ = r4 + r4, thus r3′:

[0109]

[0110] Where: r3 is the original inner radius of the simulated surrounding rock, in mm;

[0111] The inner radius of the surrounding rock is simulated to represent the pressure change within the casing; the unit is mm.

[0112] r4 is the original outer radius of the simulated surrounding rock, in mm;

[0113] r4′ is the simulated outer radius of the surrounding rock when simulating changes in the internal pressure of the casing, in mm;

[0114] Therefore, we can conclude that

[0115]

[0116] in: The volume change of the cement sheath is measured in mm to simulate changes in internal pressure within the casing. 3

[0117] The volume change of the cement ring can be used to determine the expansion and contraction of the cement ring at a certain moment, and can also be used to determine the volume change of the cement ring during loading and unloading.

[0118] Furthermore, the method for processing the data obtained in step seven in step eight is as follows:

[0119] The first step is to determine the deformation sequence of the casing, the surrounding rock, and the casing itself based on the changes in the inner and outer diameters of the assembly.

[0120] The second step is to calculate the volume change of the cement ring and determine its expansion / contraction at different times, thereby reversing the process of cement ring integrity change under this working condition.

[0121] Furthermore, the method for determining the deformation sequence of the casing, the casing itself, and the surrounding rock based on the changes in the inner and outer diameters of the assembly in the first step is as follows: if the simulated casing deforms first, i.e., the radial displacement value of the simulated casing's inner wall... r1 0, simulated radial displacement value of the outer wall of the surrounding rock. If r4=0, the cement ring deforms asynchronously, and the deformation sequence is from the inside out. The stress is transferred from the simulated sleeve to the cement ring and then to the simulated surrounding rock. If the simulated surrounding rock deforms first, i.e., the radial displacement value of the simulated surrounding rock outer wall is... r4 0, simulated radial displacement value of the inner wall of the casing If r1=0, the cement ring deforms asynchronously, and the deformation sequence is from the outside to the inside. The stress is transferred from the simulated surrounding rock to the cement ring and then to the simulated casing. If the simulated casing and the simulated surrounding rock deform at the same time, the cement ring deforms synchronously.

[0122] Furthermore, the second step involves calculating the volume change of the cement ring and determining its expansion / contraction at different times. Based on this, the specific method for reconstructing the cement ring integrity change process under this working condition is as follows:

[0123] Given the coefficient of volume expansion β of the object, and from:

[0124]

[0125] in: This represents the change in the total volume of an object when the temperature changes, expressed in mm. 3 ;

[0126] The original volume of the object, in mm. 3 ;

[0127] This represents the change in temperature of an object, expressed in °C.

[0128] From the above formula, the total volume change of the simulated casing and surrounding rock under temperature changes can be obtained. Considering that the downhole casing is cemented and axial volume changes are not taken into account, when the volumes of the simulated casing and surrounding rock change, only the radial volume change is considered. This radial volume change is 3 / 10 to 4 / 10 of the total volume change. Assuming the simulated casing is uniformly heated and the temperature is uniformly transferred within the cement sheath assembly, when the temperature inside the simulated casing rises, the inner radius r of the simulated casing at this time... 1温 =r1+ r 1温 , thus obtaining r 2温 ′:

[0129]

[0130] in:

[0131] The simulated outer radius of the bushing is given in mm when the internal temperature of the bushing rises.

[0132] This represents the radial volume change of the simulated casing as the internal temperature rises, expressed in mm. 3 ;

[0133] r 1温 This represents the change in the inner radius of the simulated sleeve when the temperature changes, in mm.

[0134] Similarly, when the temperature inside the simulated casing rises, the outer radius of the simulated surrounding rock is r4′=r4+ r 4温 , thus obtaining r 3温 ′:

[0135]

[0136] in:

[0137] - The simulated inner radius of the surrounding rock when the temperature inside the casing rises, in mm;

[0138] - The radial volume change of the simulated surrounding rock when the temperature inside the casing rises, in mm. 3 ;

[0139] r 4温 - The change in the outer radius of the simulated surrounding rock when simulating temperature changes inside the casing, in mm;

[0140] Therefore, we can conclude that

[0141]

[0142] in: - The volume change of the cement sheath during the temperature rise inside the casing, in mm. 3 ;

[0143] After the internal and external temperatures stabilize, the fracturing condition can be simulated. The simulated casing temperature is reduced, and the simulated casing and simulated surrounding rock should shrink in volume. At this time, the initial inner and outer diameters of the simulated casing and simulated formation are the final inner and outer diameters of the simulated casing and simulated formation calculated in the above process when the internal and external temperatures stabilize. The calculation method for the change in cement sheath volume is the same as above.

[0144] In practical applications, the cement slurry is prepared and cured according to the standard "Test Methods for Cement in Oil Wells" (GB / T19139-2003). The cement slurry is then injected into a dynamic testing device for the sealing capacity of cement sheaths in well cementing, which has patent publication number CN106771096B. A certain temperature and pressure are set, and the cement slurry is cured for a set time to allow it to solidify and form a cement sheath.

[0145] Data Acquisition and Processing: Since the original data of the experimental setup are known, the original inner radius r1 (i.e., the original inner radius of the inner casing) and the original outer radius r2 (i.e., the original outer radius of the inner casing) of simulated casing 1, the original inner radius r3 (i.e., the original inner radius of the outer casing) of simulated surrounding rock 2, and the original outer radius r4 (i.e., the original outer radius of the outer casing) of simulated surrounding rock 2 are as follows: Figure 1 As shown, the experimental setup can measure the radial displacement value of the simulated inner wall of the casing. r1, simulated radial displacement value of the outer wall of the surrounding rock r4.

[0146] When the temperature inside the casing remains constant, the cement ring assembly does not undergo thermal expansion or contraction. When the internal pressure of the simulated casing is changed, the simulated casing and the simulated surrounding rock are both made of steel circular tubes. Due to their large elastic modulus, the volume change of the cement ring assembly during deformation is very small. Therefore, for the convenience of analyzing the deformation of the casing, cement ring, and surrounding rock, it is ignored and regarded as having a constant volume.

[0147] Existing indoor cement ring integrity studies indicate that during the simulated casing loading-unloading process, since both the simulated casing 1 and the simulated surrounding rock 2 are steel circular pipes, they are mostly within the elastic deformation range. After unloading, their inner and outer diameters can be restored to their initial values. However, the cement ring 3 has a small elastic modulus and is relatively brittle, so it is prone to plastic deformation, and its inner and outer diameters are difficult to fully recover after unloading.

[0148] Based on the above assumptions, the following two cases can be considered:

[0149] 1. Simulating the single loading-unloading process of casing internal pressure, i.e., simulating the fracturing process.

[0150] Under the condition that the internal temperature of the simulated casing 1 is equal to and remains unchanged with the external temperature of the simulated surrounding rock 2, due to the presence of formation pressure, in order to make the quantitative monitoring of the deformation process of the cement ring assembly more accurate, the internal pressure of the simulated casing and the external pressure of the simulated surrounding rock are set while the cement ring 3 is being cured.

[0151] After the cement sheath is cured, the simulated casing internal pressure is increased to the preset value according to the downhole working conditions, maintained for a period of time, and then reduced to the initial value. During this process, the changes in the inner and outer diameters of the cement sheath assembly and the time when the changes begin are monitored.

[0152] Based on the measurement data, the deformation sequence of the casing, the casing itself, and the surrounding rock can be determined by the changes in the inner and outer diameters of the assembly: during the simulated casing internal pressure loading-unloading process, if the simulated casing deforms first, i.e., the radial displacement value of the simulated casing inner wall... r1 0, simulated radial displacement value of the outer wall of the surrounding rock. r4=0 indicates that the cement ring deforms asynchronously, with the deformation sequence from the inside out. The stress is transmitted from the simulated sleeve to the cement ring and then to the simulated surrounding rock. If the simulated surrounding rock deforms first, it means the radial displacement value of the simulated surrounding rock outer wall is... r4 0, simulated radial displacement value of the inner wall of the casing r1=0 indicates that the cement ring deforms asynchronously, and the deformation sequence is from the outside to the inside. The stress is transferred from the simulated surrounding rock to the cement ring and then to the simulated casing. If the simulated casing and the simulated surrounding rock deform at the same time, it can be said that the cement ring deforms synchronously.

[0153] Secondly, the deformation process of the cement ring assembly can be determined based on the changes in its inner and outer diameters. Existing indoor cement ring integrity experiments show that during loading and unloading under small pressure differences (i.e., within the elastic range of the cement ring-casing-surrounding rock), the cement ring assembly remains within the elastic deformation range. The cement ring maintains good integrity during both loading and unloading, and both the inner and outer diameters of the assembly can recover to their initial values. As the pressure difference increases, the deformation of the cement ring assembly increases. Since the simulated casing and simulated surrounding rock are both steel circular pipes with strong elastic deformation capabilities, but the cement stone has weak deformation capabilities and is prone to plastic deformation, when the pressure difference is insufficient to cause tensile cracking failure of the cement ring, the cement ring can... During loading, the cement ring maintains good integrity, but when unloading reaches a certain point, integrity failure will occur due to interface cementation failure. This point is the inflection point where the elastic deformation of the cement ring is fully recovered. Based on this, the elastic deformation, plastic deformation, and total deformation of the cement ring during the loading-unloading process can be obtained. If the pressure difference during the loading-unloading process increases to the maximum pressure difference, i.e., the pressure difference outside the elastic range of the cement ring-casing-surrounding rock, the cement ring will experience irreversible tensile crack failure during loading, thus causing its integrity to fail in subsequent loading and unloading processes. Combining the changes in the inner and outer diameters of the assembly, the inner and outer diameters and their volume changes when tensile cracks appear in the cement ring can be calculated.

[0154] Furthermore, based on the changes in the inner and outer diameters of the cement ring assembly at different times, the volume changes of the cement ring before the integrity failure caused by tensile cracks during loading and before the integrity failure caused by interfacial bonding failure during unloading can be calculated. The specific method is as follows:

[0155] When the internal pressure of the simulated casing changes, the volume of the simulated casing remains constant. At this time, the inner radius of the simulated casing is r1′=r1+ r1, thus obtaining r2′:

[0156]

[0157] Where: r1 is the original inner radius of the simulated sleeve, in mm;

[0158] r1′ is the inner radius of the simulated casing when the internal pressure changes; the unit is mm.

[0159] r2 is the simulated original outer radius of the sleeve, in mm;

[0160] r2′ is the outer radius of the simulated casing when the internal pressure changes; the unit is mm.

[0161] h represents the instrument height, in mm;

[0162] Similarly, when the pressure inside the simulated casing changes, the volume of the simulated surrounding rock remains constant. In this case, the outer radius of the simulated surrounding rock is r4′ = r4 + r4, thus r3′:

[0163]

[0164] Where: r3 is the original inner radius of the simulated surrounding rock, in mm;

[0165] The inner radius of the surrounding rock is simulated to represent the pressure change within the casing; the unit is mm.

[0166] r4 is the original outer radius of the simulated surrounding rock, in mm;

[0167] r4′ is the simulated outer radius of the surrounding rock when simulating changes in the internal pressure of the casing, in mm;

[0168] Therefore, we can conclude that

[0169]

[0170] in: The volume change of the cement sheath is measured in mm to simulate changes in internal pressure within the casing. 3 ;

[0171] The volume change of the cement ring can be used to determine the expansion and contraction of the cement ring at a certain moment, and can also be used to determine the volume change of the cement ring during loading and unloading.

[0172] 2. Simulate the casing internal pressure drop process, i.e., simulate the initial density reduction drilling.

[0173] Following the same procedure and method, a cement ring is formed through curing. Then, according to the set working conditions, the pressure inside the simulated casing is reduced to the preset value and maintained for a period of time. At the same time, the changes in the inner and outer diameters of the cement ring assembly and the time when these changes begin to occur are monitored.

[0174] Using the same method, by combining the time sequence of changes in the simulated outer diameter of the casing and the simulated inner diameter of the surrounding rock, the order of deformation can be determined. At the same time, the volume change of the cement sheath can be calculated, and its expansion / contraction at different times can be determined, thereby reversing the process of cement sheath integrity change under this working condition.

[0175] When the pressure remains constant, the internal temperature of the simulated casing is changed. Both the simulated casing and the simulated surrounding rock are casings, i.e., steel round pipes. The volume changes of the simulated casing and the simulated surrounding rock under large temperature differences need to be considered.

[0176] Based on the above assumptions, the simulation is divided into two cases: the casing temperature increases (heavy oil thermal recovery) or decreases (fracturing).

[0177] Following the same procedure and method described above, a cement ring is formed through curing. Then, based on the set working conditions, the simulated sleeve internal temperature is adjusted to the preset value and maintained for a period of time. At the same time, the changes in the inner and outer diameters of the cement ring assembly and the time when these changes begin to occur are monitored.

[0178] The same method can be used to determine the order of deformation of the casing, cement sheath, and surrounding rock by combining the time sequence of changes in the simulated outer diameter of the casing and the simulated inner diameter of the surrounding rock.

[0179] However, calculating the volume change of the cement ring and determining its expansion / contraction at different times requires considering the volume changes of the simulated casing and the simulated surrounding rock caused by temperature changes.

[0180] Given the coefficient of volume expansion β of the object, and from:

[0181]

[0182] in: This represents the change in the total volume of an object when the temperature changes, expressed in mm. 3 ;

[0183] The original volume of the object, in mm. 3 ;

[0184] This represents the change in temperature of an object, expressed in °C.

[0185] From the above formula, the total volume change of the simulated casing and surrounding rock under temperature changes can be obtained. Considering that the downhole casing is cemented and axial volume changes are not taken into account, when the volumes of the simulated casing and surrounding rock change, only the radial volume change is considered. This radial volume change is 3 / 10 to 4 / 10 of the total volume change. Assuming the simulated casing is uniformly heated and the temperature is uniformly transferred within the cement sheath assembly, when the temperature inside the simulated casing rises, the inner radius r of the simulated casing at this time... 1温 =r1+ r 1温 We can obtain r 2温 ′:

[0186]

[0187] in:

[0188] The simulated outer radius of the bushing is given in mm when the internal temperature of the bushing rises.

[0189] This represents the radial volume change of the simulated casing as the internal temperature rises, expressed in mm. 3 ;

[0190] r 1温 This represents the change in the inner radius of the simulated sleeve when the temperature changes, in mm.

[0191] Similarly, when the temperature inside the simulated casing rises, the outer radius of the simulated surrounding rock is r4′=r4+ r 4温 , thus obtaining r 3温 ′:

[0192]

[0193] in:

[0194] - The simulated inner radius of the surrounding rock when the temperature inside the casing rises, in mm;

[0195] - The radial volume change of the simulated surrounding rock when the temperature inside the casing rises, in mm. 3 ;

[0196] r 4温 - The change in the outer radius of the simulated surrounding rock when simulating temperature changes inside the casing, in mm;

[0197] Therefore, we can conclude

[0198]

[0199] in: - The volume change of the cement sheath during the temperature rise inside the casing, in mm. 3 ;

[0200] Example 3:

[0201] An experimental method for quantitatively monitoring the deformation process of cement ring assemblies, the specific steps of which are as follows:

[0202] (1) Prepare cement slurry with a water-cement ratio of 0.44 according to the standard "Test Methods for Cement in Oil Wells" (GB / T19139-2003).

[0203] (2) Assuming that the temperature inside the casing and the temperature outside the formation are both 20℃, and the pressure inside the casing and the pressure of the formation are both 35MPa, the cement slurry is placed in the experimental device with the preset temperature and pressure, and cured for 7 days to form a cement ring. The experimental device simulates the original inner radius of the casing r1=29.75mm, the original outer radius of the casing r2=31.75mm, the original inner radius of the surrounding rock r3=37.3mm, the original outer radius of the surrounding rock r4=39.3mm, and the instrument height h=1340mm.

[0204] (3) Reduce the pressure inside the simulated casing to 5MPa, record the radial displacement value of the inner wall of the simulated casing and the radial displacement value of the outer wall of the simulated surrounding rock at each moment, and organize the recorded radial displacement values ​​of the inner wall of the simulated casing and the radial displacement values ​​of the outer wall of the simulated surrounding rock at each moment and the calculated change in cement ring volume. The results are shown in Table 1.

[0205] Table 1. Relationship between radial displacement values ​​of the simulated casing inner wall and simulated surrounding rock outer wall and the volume change of the cement sheath.

[0206]

[0207] In Table 1 above, negative radial displacement values ​​for the simulated casing inner wall and the simulated surrounding rock outer wall indicate inward movement of the simulated casing inner wall relative to its original position, and negative changes in cement sheath volume indicate compression of the cement sheath volume. Under this condition, the simulated casing actively contracts inward, followed by the cement sheath passively contracting inward and being compressed relative to its initial volume. Finally, the simulated surrounding rock passively contracts inward. Furthermore, the cement sheath undergoes elastic deformation, with an elastic deformation of 118.0746 mm. 3 .

[0208] Example 4:

[0209] An experimental method for quantitatively monitoring the deformation process of cement ring assemblies, the specific steps of which are as follows:

[0210] (1) Prepare cement slurry with a water-cement ratio of 0.44 according to the standard "Test Methods for Cement in Oil Wells" (GB / T19139-2003).

[0211] (2) Assuming that the casing temperature and formation temperature are both 20℃, and the casing pressure and formation pressure are both 5MPa, the cement slurry is placed in the experimental device with the preset temperature and pressure and cured for 7 days to form a cement ring.

[0212] (3) The pressure inside the simulated casing was increased to 55 MPa, and then decreased to 5 MPa. The radial displacement values ​​of the inner wall of the simulated casing and the outer wall of the simulated surrounding rock were recorded at each time point until gas channeling occurred, at which point the experiment ended. The recorded radial displacement values ​​of the inner wall of the simulated casing and the outer wall of the simulated surrounding rock at each time point, along with the calculated change in cement sheath volume, were compiled, and the results are shown in Table 2.

[0213] Table 2. Relationship between radial displacement values ​​of the simulated casing inner wall and simulated surrounding rock outer wall and cement sheath volume change.

[0214]

[0215] In Table 2 above, a positive radial displacement value of the simulated casing inner wall indicates that the simulated casing inner wall moves outward relative to its original position, while a negative change in cement sheath volume indicates that the cement sheath volume is compressed. Under this condition, the simulated casing actively expands outward, followed by the cement sheath passively expanding outward and being compressed relative to its initial value. Finally, the simulated surrounding rock passively expands outward. Furthermore, the cement sheath undergoes elastoplastic deformation, with an elastic deformation of 297.2235 mm. 3 The amount of plastic deformation is 26.1629 mm. 3 The failure of the cement ring integrity was caused by the breakdown of the interfacial bonding.

[0216] Example 5:

[0217] An experimental method for quantitatively monitoring the deformation process of cement ring assemblies, the specific steps of which are as follows:

[0218] (1) Prepare cement slurry with a water-cement ratio of 0.44 according to the standard "Test Methods for Cement in Oil Wells" (GB / T19139-2003).

[0219] (2) Assuming that the casing temperature and formation temperature are both 120℃, and the casing pressure and formation pressure are both 5MPa, the cement slurry is placed in the experimental device with the preset temperature and pressure, and cured for 7 days to form a cement ring. The coefficient of volume expansion of steel is β=3.6x10 -5 / ℃

[0220] (3) Reduce the temperature of the simulated casing to 40℃ and record the radial displacement value of the inner wall of the simulated casing and the radial displacement value of the outer wall of the simulated surrounding rock at each time point. Compile the recorded radial displacement values ​​of the inner wall of the simulated casing and the radial displacement values ​​of the outer wall of the simulated surrounding rock at each time point and the calculated change in cement ring volume. Due to the large amount of data involved, only representative data are selected. The results are shown in Table 3.

[0221] Table 3. Relationship between radial displacement values ​​of the simulated casing inner wall and simulated surrounding rock outer wall and the volume change of the cement sheath.

[0222]

[0223] The above experiments show that a negative radial displacement value for the simulated casing inner wall and the simulated surrounding rock outer wall indicates that the simulated casing inner wall is moving inward relative to its original position, and a negative change in cement ring volume indicates that the cement ring volume is compressed. Under this condition, the simulated casing actively contracts inward, followed by the cement ring passively contracting inward and being compressed relative to its initial value. Finally, the simulated surrounding rock passively contracts inward. Furthermore, the cement ring undergoes elastic deformation, with a deformation of 81.3365 mm. 3 .

[0224] Example 6:

[0225] An experimental method for quantitatively monitoring the deformation process of cement ring assemblies, the specific steps of which are as follows:

[0226] (1) Prepare cement slurry with a water-cement ratio of 0.44 according to the standard "Test Methods for Cement in Oil Wells" (GB / T19139-2003).

[0227] (2) Assuming that the casing temperature and formation temperature are both 20℃, and the casing pressure and formation pressure are both 5MPa, the cement slurry is placed in the experimental device with the preset temperature and pressure and cured for 7 days to form a cement ring.

[0228] (3) Raise the temperature of the simulated casing from 30℃ to 250℃ and wait for a period of time until the gas channeling experiment ends. Record the radial displacement values ​​of the inner wall of the simulated casing and the outer wall of the simulated surrounding rock at each moment. Compile the recorded radial displacement values ​​of the inner wall of the simulated casing and the outer wall of the simulated surrounding rock at each moment and the calculated change in cement ring volume. Due to the large amount of data involved, only representative data are selected. The results are shown in Table 4.

[0229] Table 4. Relationship between radial displacement values ​​of the simulated casing inner wall and simulated surrounding rock outer wall and cement sheath volume change.

[0230]

[0231] The above experiments show that a positive radial displacement value of the simulated casing inner wall indicates that the simulated casing inner wall moves outward relative to its original position, while a negative change in the cement ring volume indicates that the cement ring volume is compressed. Under this condition, the simulated casing actively expands outward, followed by the cement ring passively expanding outward and being compressed relative to its initial value. Finally, the simulated surrounding rock passively expands outward. Furthermore, the cement ring undergoes elastoplastic deformation, with a plastic deformation of 278.2018 mm³ and an elastic deformation of 11.9158 mm³. The failure of the cement ring's integrity is due to the breakdown of the interface bonding.

[0232] Where there is no conflict, those skilled in the art can combine the relevant technical features in the above examples according to the actual situation to achieve the corresponding technical effects. Specific details of the various combinations will not be elaborated here.

[0233] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0234] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0235] The above description is merely a preferred embodiment of the present invention. The present invention is not limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. Any simple modifications, equivalent variations, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the present invention.

Claims

1. An experimental method for quantifying the deformation process of a cement sheath assembly, characterized by: It comprises the following steps, Step one: configure cement slurry; Step two: record the inner radius and outer radius of the simulated casing and simulated surrounding rock before the experiment respectively; Step three: prepare the cement sheath; Step four: determine the operation process that causes the deformation of the combination; If the operation process that causes the deformation of the combination is a single loading-unloading process of the simulated casing inner pressure with unchanged temperature and changed pressure, then step five is entered, and if the operation process that causes the deformation of the combination is a process simulation with changed temperature and unchanged pressure, then step seven is entered; Step five: according to the downhole working condition, increase or decrease the pressure in the simulated casing to a preset value, keep for a preset time, then restore the pressure in the simulated casing, and obtain the data of the changes of the inner diameter and outer diameter of the cement sheath combination with time and the time points of the changes in the whole pressure change process; Step six: process the data obtained in step five; The specific method for processing the data in step six is as follows, First step, determine the deformation sequence of the casing and the formation surrounding rock according to the changes of the inner diameter and outer diameter of the combination; Second step, determine the deformation process of the cement sheath combination according to the changes of the inner diameter and outer diameter of the combination; Third step, calculate the volume change of the cement sheath before the integrity failure of the cement sheath caused by the tensile crack of the cement sheath in the loading process and before the integrity failure of the cement sheath caused by the interface cementation damage in the unloading process according to the changes of the inner diameter and outer diameter of the cement sheath combination at different times; Step seven: according to the downhole working condition, increase or decrease the temperature in the simulated casing to a preset value, keep for a preset time, then restore the temperature in the simulated casing, and obtain the data of the changes of the inner diameter and outer diameter of the cement sheath combination with time in the whole temperature change process; Step eight: process the data obtained in step seven; The method for processing the data obtained in step seven is as follows, First step, determine the deformation sequence of the casing and the formation surrounding rock according to the changes of the inner diameter and outer diameter of the combination; Second step, calculate the volume change of the cement sheath, determine the swelling / shrinking condition at different times, and inversely calculate the process of the integrity change of the cement sheath under the working condition.

2. An experimental method for monitoring the deformation process of a cemented annulus assembly as claimed in claim 1, characterized in that: The method for preparing the cement sheath in step three is the same, which is to inject the cement slurry configured in step one into the cement sheath sealing capacity dynamic testing device, maintain the cement slurry at a set time interval, and at the same time, apply internal pressure to the simulated casing and external pressure to the simulated surrounding rock until the cement sheath is formed by setting.

3. An experimental method for monitoring the deformation process of a cemented annulus assembly as claimed in claim 2, characterized in that: The set time interval for maintaining the cement slurry is 4h, 6h, 8h, 1d, 2d or 28d.

4. An experimental method for monitoring the deformation process of a cemented annulus assembly as claimed in claim 1, characterized in that: The first step in the sixth step is to determine the deformation sequence of the casing and the formation surrounding rock according to the change of the combined inner diameter and outer diameter, that is, if the simulated casing deforms first, that is, the radial displacement value of the inner wall of the simulated casing is r1 0, the radial displacement value of the outer wall of the simulated surrounding rock is r4=0, then the cement sheath deforms asynchronously, the deformation sequence is from inside to outside, and the stress is transmitted from the simulated casing to the cement sheath and then to the simulated surrounding rock; if the simulated surrounding rock deforms first, that is, the radial displacement value of the outer wall of the simulated surrounding rock is r4 0, the radial displacement value of the inner wall of the simulated casing is r1=0, then the cement sheath deforms asynchronously, the deformation sequence is from outside to inside, and the stress is transmitted from the simulated surrounding rock to the cement sheath and then to the simulated casing; if the simulated casing and the simulated surrounding rock deform at the same time, the cement sheath deforms synchronously.

5. An experimental method for monitoring the deformation process of a cemented annulus assembly as claimed in claim 1, characterized in that: The method for determining the deformation process of the cement sheath combination according to the changes of the inner diameter and outer diameter of the combination in the second step of step six is that in the process of differential pressure loading-unloading in the elastic range of the cement sheath-casing-surrounding rock, the whole cement sheath combination is in the elastic deformation range, the cement sheath can maintain integrity during the loading and unloading processes, and the inner diameter and outer diameter of the combination can be restored to the initial values; With the increase of pressure difference, the deformation of cement sheath assembly increases, when the pressure difference is not enough to make the cement sheath appear tensile crack failure, the cement sheath can maintain integrity during the loading process, but will appear the point of integrity failure caused by the interface cementation failure during the unloading process, and the point is the inflection point of the complete recovery of the elastic deformation of the cement sheath, and thus the elastic deformation, plastic deformation and total deformation of the cement sheath during the loading-unloading process can be obtained; if the pressure difference during the loading-unloading process increases to the maximum pressure difference, i.e. the pressure difference outside the elastic range of the cement sheath-casing-surrounding rock, the cement sheath will appear the un-recoverable tensile crack failure during the loading process.

6. An experimental method for monitoring the deformation process of a cemented annulus assembly as claimed in claim 1, characterized in that: The specific method for calculating the volume change of the cement sheath before the cement sheath integrity failure caused by the tensile crack of the cement sheath during the loading process and before the cement sheath integrity failure caused by the interface cementation failure during the unloading process according to the changes of the inner diameter and the outer diameter of the cement sheath assembly at different times in the third step of the sixth step is as follows, When the pressure in the simulation casing is changed, the volume of the simulation casing is constant, at this time the simulation casing inner radius r1'=r1+ r1, r2' is obtained: Wherein: r1 is the original inner radius of the simulation casing, unit: mm; r1' is the inner radius of the simulation casing when the inner pressure of the simulation casing changes, unit: mm; r2 is the original outer radius of the simulation casing, unit: mm; r2' is the outer radius of the simulation casing when the inner pressure of the simulation casing changes, unit: mm; h is the height of the instrument, unit: mm; Similarly, the inner pressure of the casing is changed, and the volume of the surrounding rock is constant, at this time the outer radius of the surrounding rock r4'=r4 r4, r3' can be obtained: Wherein: r3 is the original inner radius of the simulation surrounding rock, unit: mm; R is the radius of the surrounding rock, unit is mm; r4 is the original outer radius of the simulation surrounding rock, unit: mm; r4' is the outer radius of the simulation surrounding rock when the inner pressure of the simulation casing changes, unit: mm; Therefore, the following can be obtained wherein: is the volume change of the cement sheath when the pressure in the casing changes, in mm 3 ; The volume change of the cement sheath can be used to determine the expansion and contraction of the cement sheath at a certain time, and the volume change of the cement sheath during the loading and unloading process can also be determined.

7. An experimental method for monitoring the deformation process of a cemented annulus assembly as claimed in claim 1, characterized in that: The first step in the eighth step is to determine the deformation sequence of the casing and the formation surrounding rock according to the change of the combined inner diameter and outer diameter, that is, if the simulated casing deforms first, that is, the radial displacement value of the inner wall of the simulated casing r1 0, the radial displacement value of the outer wall of the simulated surrounding rock r4=0, then the cement sheath deforms asynchronously, the deformation sequence is from inside to outside, and the stress is transmitted from the simulated casing to the cement sheath and then to the simulated surrounding rock; if the simulated surrounding rock deforms first, that is, the radial displacement value of the outer wall of the simulated surrounding rock r4 0, the radial displacement value of the inner wall of the simulated casing r1=0, then the cement sheath deforms asynchronously, the deformation sequence is from outside to inside, and the stress is transmitted from the simulated surrounding rock to the cement sheath and then to the simulated casing; if the simulated casing and the simulated surrounding rock deform at the same time, then the cement sheath deforms synchronously.

8. An experimental method for monitoring the deformation process of a cemented annulus assembly as claimed in claim 1, characterized in that: The specific method for calculating the volume change of the cement sheath and determining the expansion / contraction of the cement sheath at different times in the second step of the eighth step is as follows, It is known that the volume expansion coefficient of the object is β, and the following is obtained: wherein: Vtot is the total volume change of the object when the temperature changes, in mm 3 ; Original volume of the object, in mm 3 ; T is the temperature change of the object, in °C; The total volume change of the simulated casing and simulated surrounding rock can be obtained from the above formula. According to the cementing of the casing in the well, the axial volume change is not considered. When the volume of the simulated casing and simulated surrounding rock changes, only the radial volume change is considered, which is 3 / 10-4 / 10 of the total volume change. It is assumed that the simulated casing is uniformly heated and the temperature is uniformly transmitted in the cement ring combination. When the temperature in the simulated casing rises, the inner radius r 1温 ′ of the simulated casing is r r 1温 , and r 2温 ′ is obtained. Wherein: Rsim is the outer radius of the simulation sleeve, in mm; To simulate the change of the radial volume of the simulation sleeve when the temperature in the simulation sleeve rises, in mm 3 ; r 1温 r is the change in the inner radius of the simulation sleeve when the temperature changes, in mm; Similarly, when the temperature in the simulation casing rises, at this time the simulation surrounding rock outer radius r4'=r4+ r 4温 , we can get r 3温 ′: Wherein: - simulated radius in the surrounding rock when the temperature in the simulation casing is rising, in mm; - simulated radial volume change of surrounding rock when the temperature in the simulation casing rises, in mm 3 ; r 4温 - the change in the radius of the surrounding rock when simulating the change in the temperature in the casing, in mm; Therefore, the following is obtained wherein: - the volume change of the cement sheath when the temperature in the casing is raised, in mm 3 ; After waiting for the inner and outer temperatures to be stable, the fracturing working condition can be simulated, the temperature of the simulation casing is reduced, and the simulation casing and the simulation surrounding rock should be volume contracted, at this time, the initial inner and outer diameters of the simulation casing and the simulation formation are the final inner and outer diameters of the simulation casing and the simulation formation calculated in the above process when the inner and outer temperatures are stable.

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