Integrity detection method and device for cementing interface of carbon dioxide injection well

Abstract

The present application discloses a method and device for detecting the integrity of the cementing interface of a carbon dioxide injection well, which belongs to the field of cementing engineering. The method determines whether the second cementing interface is cracked by obtaining the shear stress generated at the second cementing interface of the carbon dioxide injection well under the action of chemical and mechanical coupling; in response to the cracking of the second cementing interface, the failure length is calculated according to the principle of conservation of energy, and the integrity of the second cementing interface is determined by the failure length as a calculation index. The method takes into account the influence of the change of the stress-strain state of the formation under the action of chemical-mechanical coupling after carbon dioxide injection on the second cementing interface, and can scientifically reflect the failure process of the second cementing interface during carbon dioxide oil recovery and storage, and can further clarify the failure conditions, making the selection range of injection and production construction parameters more accurate.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of cementing engineering, and in particular to a method and device for detecting the integrity of cementing interfaces in a carbon dioxide injection well. Background Art

[0002] Cementing is an important operation in the drilling process. Its purpose is to isolate loose, easy to collapse, easy to leak and other complex formations, isolate the oil, gas and water layers in the annular space outside the casing, prevent them from communicating with each other, and control the flow of oil and gas, so as to facilitate safe drilling and ensure the long-term production of the oil well. Cementing operation is to lower the casing into the well and inject cement into the annular space between the wellbore and the casing. The second interface of cementing is the bonding surface between the cement ring and the formation. Therefore, the integrity of the second interface of cementing directly affects the quality of cementing. It is necessary to test the integrity of the second interface of cementing.

[0003] At present, the integrity detection methods of cementing interface can be summarized into two categories, namely logging detection method and interface bonding strength detection method. The logging detection method mainly includes: using the acoustic logging instrument to determine the cement bonding state outside the casing through the acoustic wave propagation time, first wave amplitude, first wave attenuation and full wave train; using the gamma density instrument to record the selected cement curve and the integral cement curve to determine the cement density and cement sealing effect, and using the casing wall thickness curve to determine the casing wall thickness, casing damaged section and casing centralizer position; finally, using the acoustic logging and gamma density logging data to comprehensively analyze the integrity of the cementing interface. The interface bonding strength detection method is: first, a layer of drilling fluid filter cake is coated on the artificial core; then the core with the filter cake is placed in the consolidation mold, and the gap between the core and the consolidation mold is injected with cement slurry for curing; finally, the cured bonding model is placed on the pressure testing machine for testing, and the core is pressed off by shearing to test the bonding strength between the core and the cement ring.

[0004] However, for CO2 injection wells, the relevant cementing interface integrity detection method only considers the logging data and interface bonding strength, and cannot accurately describe the dynamic failure process of the cementing interface in CO2 injection wells. Summary of the invention

[0005] In order to solve the problems existing in the related technologies, the embodiment of the present application provides a method and device for detecting the integrity of the cementing interface of a carbon dioxide injection well. The technical solution is as follows:

[0006] On the one hand, an embodiment of the present application provides a method for detecting the integrity of a cementing interface in a carbon dioxide injection well, the method comprising:

[0007] Obtaining the shear stress generated at the cementing interface of the carbon dioxide injection well under the chemical and mechanical coupling effects;

[0008] Based on the shear stress and cement sheath bonding strength, determining whether the cementing second interface is cracked;

[0009] In response to the second cementing interface cracking, according to the energy conservation principle, obtaining the cracking length of the second cementing interface;

[0010] Based on the cracking length, the failure length of the second cementing interface is obtained, and the integrity of the second cementing interface is detected by the failure length.

[0011] In a possible implementation manner, obtaining the shear stress generated at the cementing interface of the carbon dioxide injection well under the chemical and mechanical coupling effect includes:

[0012] Obtaining the additional axial stress generated at the cementing second interface under the chemical and mechanical coupling effects;

[0013] Based on the additional axial stress and the horizontal compressive stress of the formation on the second cementing interface, the shear stress at the second cementing interface is obtained.

[0014] In a possible implementation manner, obtaining the additional axial stress generated at the cementing interface under the chemical and mechanical coupling action includes:

[0015] Based on the influence of chemical dissolution of acidic solution on the elastic modulus of formation rock, the elastic modulus of formation rock after dissolution is obtained;

[0016] Based on the elastic modulus of the dissolved formation rock, the axial additional stress on the cementing interface caused by the increase in formation pore pressure is obtained.

[0017] In a possible implementation, the acidic solution is a carbonic acid solution generated when carbon dioxide is injected into a well and contacts with formation water.

[0018] In a possible implementation, judging whether the second cementing interface is cracked based on the shear stress and the cement sheath bonding strength includes:

[0019] If the shear stress is less than the cement sheath bonding strength, the cementing interface will not crack;

[0020] If the shear stress is greater than or equal to the cement sheath bonding strength, cracks will occur at the cementing interface.

[0021] In a possible implementation, in response to the second cementing interface cracking, obtaining the cracking length of the second cementing interface according to the energy conservation principle includes:

[0022] Obtaining a cracking energy dissipation rate during the cracking process of the cementing second interface;

[0023] Obtaining a cement sheath potential energy release rate at the second cementing interface;

[0024] The crack length of the second cementing interface is obtained according to the cracking energy dissipation rate and the cement sheath potential energy release rate.

[0025] In a possible implementation manner, obtaining the cement sheath potential energy release rate of the second cementing interface includes:

[0026] Obtaining the total potential energy of the elastic body at the second cementing interface;

[0027] Assuming that the friction force of the cementing interface is constant during the cracking process, the potential energy release rate of the cement sheath of the cementing interface is obtained based on the total potential energy of the elastic body.

[0028] In a possible implementation, the obtaining of the failure length of the second cementing interface based on the cracking length, and detecting the integrity of the second cementing interface by the failure length includes:

[0029] The failure length of the cementing interface is obtained by subtracting the thickness range from the carbon dioxide injection point to the reservoir from the crack length;

[0030] The failure length of the second cementing interface is used as a judgment index to detect the integrity of the second cementing interface.

[0031] In a possible implementation manner, the failure length of the cementing second interface is used as a discrimination index to detect the integrity of the cementing second interface, including:

[0032] When the failure length of the cementing second interface is less than 0, the integrity of the cementing second interface is not destroyed;

[0033] When the failure length of the second cementing interface is greater than or equal to 0, the integrity of the second cementing interface is destroyed.

[0034] On the other hand, a device for detecting the integrity of a cementing interface of a carbon dioxide injection well is provided, the device comprising:

[0035] A first acquisition unit is used to acquire the shear stress generated at the cementing interface of the carbon dioxide injection well under the chemical and mechanical coupling effect;

[0036] A judging unit, used for judging whether cracking occurs at the cementing second interface based on the shear stress and the cement sheath bonding strength;

[0037] A second acquisition unit is used for acquiring the crack length of the second cementing interface according to the energy conservation principle in response to the cracking of the second cementing interface;

[0038] The detection unit is used to obtain the failure length of the second cementing interface based on the cracking length, and detect the integrity of the second cementing interface through the failure length.

[0039] In a possible implementation, the first acquisition unit is used to acquire the axial additional stress generated at the second cementing interface under the chemical and mechanical coupling action; and to acquire the shear stress at the second cementing interface based on the axial additional stress and the horizontal compressive stress of the formation exerted on the second cementing interface.

[0040] In a possible embodiment, the first acquisition unit is also used to obtain the elastic modulus of the formation rock after dissolution based on the influence of the chemical dissolution of the acidic solution on the elastic modulus of the formation rock; based on the elastic modulus of the formation rock after dissolution, obtain the axial additional stress on the second interface of the cementing caused by the increase in formation pore pressure.

[0041] In a possible implementation, the acidic solution is a carbonic acid solution generated when carbon dioxide is injected into a well and contacts with formation water.

[0042] In a possible implementation, the judgment unit is used to judge that if the shear stress is less than the cement sheath bonding strength, the second cementing interface will not crack; if the shear stress is greater than or equal to the cement sheath bonding strength, the second cementing interface will crack.

[0043] In a possible implementation, the second acquisition unit is used to acquire the cracking energy dissipation rate during the cracking process of the second cementing interface; acquire the cement sheath potential energy release rate of the second cementing interface; and acquire the cracking length of the second cementing interface according to the cracking energy dissipation rate and the cement sheath potential energy release rate.

[0044] In a possible implementation, the second acquisition unit is further used to acquire the total potential energy of the elastic body at the second cementing interface; assuming that the friction force of the second cementing interface is a constant during the cracking process, the cement sheath potential energy release rate of the second cementing interface is acquired based on the total potential energy of the elastic body.

[0045] In a possible implementation, the detection unit is used to obtain the failure length of the second cementing interface by subtracting the thickness range from the carbon dioxide injection point to the reservoir from the crack length; and detect the integrity of the second cementing interface using the failure length of the second cementing interface as a judgment indicator.

[0046] In a possible implementation, the detection unit is further used to ensure that when the failure length of the second cementing interface is less than 0, the integrity of the second cementing interface is not destroyed; when the failure length of the second cementing interface is greater than or equal to 0, the integrity of the second cementing interface is not destroyed.

[0047] The technical solution for detecting the integrity of the second interface of cementing in a carbon dioxide injection well provided in the embodiment of the present application takes the failure length of the second interface of cementing as a calculation index, establishes a calculation model for the failure length of the second interface of cementing from the principle of energy conservation, and improves the calculation method for the integrity of the second interface of cementing. Compared with the related art, the embodiment of the present application has at least the following beneficial effects: 1. The influence of the change of the stress-strain state of the formation under the chemical-mechanical coupling after carbon dioxide injection on the second interface of cementing is considered, and the failure process of the second interface during carbon dioxide oil recovery and storage is more scientifically reflected; 2. The calculation model for the failure length of the second interface of cementing is established based on the law of conservation of energy, and the failure length of the second interface of cementing under the condition of carbon dioxide injection can be more accurately obtained by analyzing its energy transfer process; 3. Taking the failure length of the second interface of cementing as a calculation index, the failure condition of the integrity of the second interface of cementing during carbon dioxide injection can be further clarified on the basis of ensuring the quality of cementing, so that the range of injection and production construction parameters is more accurate, and a more reliable theoretical basis is provided for carbon dioxide storage projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0049] Figure 1 This is a flow chart of a method for detecting the integrity of cementing interfaces in a carbon dioxide injection well provided in an embodiment of the present application;

[0050] Figure 2 It is a structural schematic diagram of a carbon dioxide injection well cementing second interface integrity detection device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0051] Unless otherwise defined, all technical terms used in the embodiments of the present application have the same meanings as those generally understood by those skilled in the art. To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the embodiments of the present application will be described in detail in a possible implementation in conjunction with the accompanying drawings.

[0052] First, the application scenarios of the embodiments of the present application are introduced.

[0053] Carbon dioxide (CO2) geological storage refers to the separation and collection of carbon dioxide emitted by factories and produced by human life, and the injection into suitable deep geological structures to store CO2 underground for a long time. Geological structures that can be used for CO2 geological storage include: abandoned oil and gas fields, unexploitable coal seams, saline structures on land or in the deep sea, and oil and gas layers that need to improve recovery. CO2 geological storage can not only effectively reduce the content of carbon dioxide in the air and solve a series of environmental problems such as the greenhouse effect, but also increase oil and gas production. In order to achieve the purpose of a storage period of up to thousands of years, it is necessary to ensure that CO2 cannot leak into the atmosphere or upper aquifers along faults or wellbores.

[0054] The CO2 formation storage system mainly includes the cement sheath-formation cementing interface, reservoir and interlayer. One of the prerequisites for the implementation of the CO2 geological storage project is to test the integrity of the CO2 injection formation, that is, whether the cementing interface, reservoir and interlayer can leak gas. During the construction process, CO2 is continuously injected and flows in the direction of the outer diameter of the hole. The formation pressure in the rock near the injection well gradually increases, causing the reservoir to be continuously decompacted and undergo a certain displacement in the vertical direction. Since the cement sheath is well bonded to the formation, the cementing interface will be affected by the shear stress generated by the formation decompacting. And since it contacts the formation water after being injected into the formation and dissolves in the formation water to form a carbonic acid (H2CO3) solution, the H2CO3 solution is acidic, and the mechanical properties of the formation change under the dissolution of the acidic solution, and the elastic modulus is greatly reduced. Similarly, during the depressurization process, the pressure in the wellbore drops sharply, which will also cause the interface to be subjected to shear stress. When the shear stress on the cementing interface is greater than the interface bonding strength, cracks will occur on the cementing interface, thereby affecting the cementing quality. Therefore, a set of calculation methods is needed to determine the integrity of the cementing interface.

[0055] The present application embodiment provides a method for detecting the integrity of the cementing interface of a carbon dioxide injection well. Figure 1 As shown, the method includes the following steps 101 to 104.

[0056] Step 101: Obtain the shear stress generated at the cementing interface of the CO2 injection well under the chemical and mechanical coupling effect.

[0057] It should be noted that the research object of the embodiment of the present application is the vertical section from the CO2 injection point to the cementing interface with a reservoir thickness of l in the CO2 injection well.

[0058] In a possible implementation, in step 101, the shear stress generated at the cementing interface of the CO2 injection well under the chemical and mechanical coupling is obtained, including the following steps 1011 to 1012.

[0059] Step 1011, obtaining the axial additional stress generated at the second cementing interface under the chemical and mechanical coupling effect.

[0060] After CO2 is injected into the formation, it contacts the formation water and dissolves in the formation water to form H2CO3 solution. Since the H2CO3 solution is acidic, it will react chemically with the formation rock, i.e., dissolution. This causes a large number of secondary pores and even microcracks to form in the formation rock, changing the porosity and mechanical properties of the formation, thereby changing the stress-strain state of the cementing interface.

[0061] In a possible implementation, obtaining the axial additional stress generated at the cementing interface of the CO2 injection well under the chemical and mechanical coupling effect includes the following sub-steps 1011-1 to 1011-2.

[0062] 1011-1: Based on the influence of chemical dissolution of acidic solution on the elastic modulus of formation rock, the elastic modulus of formation rock after dissolution is obtained.

[0063] The elastic modulus of rock refers to the ratio of stress to strain in the elastic range of rock. The stress-strain curves of most rocks are not straight lines, so the elastic modulus of rock is not a constant. The elastic modulus of rock varies with the type, composition, particle size, water content, pore size and other properties of the rock. When chemical dissolution occurs in the formation rock, the microstructure of the rock changes, which is manifested as an increase in micropores or voids, and its elastic modulus also changes accordingly.

[0064] The elastic modulus of the dissolved stratum rock is calculated by the following formula:

[0065] E y =(1-D)E0 (1)

[0066] Where E0 represents the initial elastic modulus of rock before dissolution, in MPa; D represents the microscopic chemical damage variable of formation rock, dimensionless; E y Represents the elastic modulus of the stratum after dissolution, in MPa.

[0067] Among them, the initial elastic modulus of rock before dissolution can be obtained from the stress-strain curve of rock. Any point on the stress-strain curve of rock has a tangent elastic modulus and a secant elastic modulus; according to the range of stress in rock engineering, the elastic modulus is obtained from the test results.

[0068] The change of rock mesostructure under chemical corrosion is the fundamental reason for the change of rock mechanical properties. Therefore, the rock mesochemical damage variable is established based on the change of porosity, which is equal to the percentage of porosity increase after dissolution.

[0069] 1011-2: Based on the elastic modulus of the formation rock after dissolution, the axial additional stress on the cementing interface caused by the increase in formation pore pressure is obtained.

[0070] As CO2 is continuously injected, the gas penetrates into the formation and flows toward the outer diameter of the hole, and the pore pressure in the formation rock will continue to increase, causing the formation to be continuously de-compacted and undergo a certain vertical displacement. Since the cement sheath and casing are well bonded to the formation, the cement sheath will be subjected to the tensile stress induced by the axial force generated by the de-compacting of the formation.

[0071] Among them, the additional axial stress of cement sheath induced by pore pressure change can be calculated according to the following formula:

[0072]

[0073] Among them, C f Represents the compression coefficient of the formation, in MPa -1 ; φ represents the porosity of the formation, in %; σ ye represents the effective stress of the overlying rock layer, in MPa; E s represents the elastic modulus of cement sheath, in MPa; Δp represents the pore pressure increment, in MPa; σ sz Represents the additional axial stress in the cement sheath induced by the change in pore pressure, in MPa.

[0074] Optionally, the compression coefficient of the formation is generally taken as 0.9; the pore pressure increment is the difference between the bottom hole pressure after gas injection and the initial pore pressure; the remaining parameters in the above formula (2) can be obtained from indoor experiments.

[0075] Step 1012, based on the axial additional stress and the horizontal compressive stress of the formation on the second cementing interface, the shear stress at the second cementing interface is obtained.

[0076] In a possible implementation, the relationship between the shear stress at the cementing interface under CO2 injection conditions and the horizontal compressive stress and axial additional stress of the formation on the cementing interface is:

[0077]

[0078] Wherein, τ represents shear stress, in MPa; r1 represents the inner diameter of cement sheath, in m; r2 represents the outer diameter of cement sheath, in m; p w represents the pressure in the casing, in MPa; μ represents the friction coefficient at the two interfaces, dimensionless; σ1 represents the horizontal formation stress, in MPa; z represents the microelement length from the injection point to the reservoir thickness, and is taken as 0 <z<l。

[0079] Among them, the formation horizontal compressive stress σ1 is the difference between the maximum horizontal principal stress and the minimum horizontal principal stress of the formation, which can be obtained from well logging data.

[0080] According to the above calculation relationship, the friction coefficient at the two interfaces is taken as 0.2, the inner diameter and outer diameter of the cement sheath are obtained by measurement, and the pressure inside the casing is obtained by the casing pressure gauge, and the shear stress at the two interfaces of cementing can be obtained.

[0081] Step 102: Based on the shear stress and the cement sheath bonding strength, determine whether cracking occurs at the second cementing interface.

[0082] In a possible implementation manner, the cement sheath bonding strength is obtained by indoor experiments.

[0083] Based on the obtained shear stress and cement sheath bonding strength, the rule for judging whether the cementing interface has cracked is:

[0084] When τ<τ eff When the shear stress is less than the cement sheath bonding strength, the cementing interface will not crack;

[0085] When τ ≥ τ eff When the shear stress is greater than or equal to the cement sheath bonding strength, the cementing interface begins to crack.

[0086] In a possible implementation, when the shear stress generated by the second cementing interface is concentrated at the second cementing interface of the reservoir section, the integrity of the second cementing interface will not be destroyed because the upper part is blocked by the barrier layer; when the shear stress generated by the second cementing interface is concentrated at the second cementing interface of the barrier section, at this time, the second cementing interface is prone to form a gas channel and its integrity is destroyed.

[0087] Therefore, the failure range of the cementing interface, that is, the crack length of the cementing interface, affects the integrity of the cementing interface.

[0088] Step 103: In response to the cracking of the second cementing interface, the cracking length of the second cementing interface is obtained according to the energy conservation principle.

[0089] The energy conservation principle states that the change in the total energy of a system can only be equal to the amount of energy transferred into or out of the system. The total energy is the sum of the system's mechanical energy, thermal energy, and any internal energy forms other than thermal energy. Therefore, according to the energy dissipation rate of the cracking and the potential energy release rate of the two interfaces during the cracking process of the cementing interface, the cracking length of the cementing interface can be obtained.

[0090] In a possible implementation, in response to cracking of the second cementing interface, according to the energy conservation principle, obtaining the cracking length of the second cementing interface includes the following steps 1031 to 1033.

[0091] Step 1031, obtaining the cracking energy dissipation rate during the cracking process of the second cementing interface.

[0092] Optionally, the calculation formula for the cracking energy dissipation rate is:

[0093]

[0094] Where Γ represents the energy dissipation rate of the cementing interface crack, and the unit is J / m 2 ; A represents the debonding area of ​​cement sheath, unit is m 2 ; σ r A r du r Represents the energy consumed by unit displacement of formation rock under the action of horizontal formation stress, in J; σ c A c du c Represents the energy consumed by the unit displacement of cement sheath under the horizontal stress of the formation, in J; u f represents the total displacement caused by the decompression of the stratum, in m; p f du f represents the work done by the horizontal stress of the formation, with the unit of J; τ(z)du(z,l1) represents the energy consumed by the interface shear stress at any point in the failure zone under shear action, with the unit of J.

[0095] In one possible implementation, it is assumed that there is no external load and there is no energy replenishment on the slip interface, that is, the displacement caused by shear stress at any point on the interface depends only on the shear stress at that point, and τ(z) remains unchanged when the crack length of the two interfaces increases from l1 to dl1. Therefore, τ(z) can be considered to be a function of z only, and τ(z)du(z,l1) can be rewritten as d[τ(z)du(z,l1)].

[0096] Step 1032, obtaining the cement sheath potential energy release rate of the second cementing interface.

[0097] The potential energy release rate, also known as the crack extension force, is an important fracture parameter in linear elastic fracture mechanics, which refers to the change of potential energy with crack area.

[0098] In a possible implementation, obtaining the cement sheath potential energy release rate of the second cementing interface includes sub-steps 1032 - 1 to 1032 - 2 .

[0099] 1032-1: Obtain the total potential energy of the elastic body at the cementing interface.

[0100] Optionally, the total potential energy of the elastic body is the sum of the strain potential energy and the external force potential energy, and the external force potential energy is the external force work with a negative sign. Therefore, the calculation formula for the total potential energy of the elastic body is:

[0101]

[0102] Among them, Π represents the total potential energy of the elastic body, the unit is J; V represents the total volume of the elastic body, the unit is m 3 ; T represents external load, unit is MPa; S T Represents the surface area of ​​the external load T, in m 2 ; σ0 represents the prestress of the elastic body when there is no external load, and the unit is MPa; ε0 represents the prestrain of the elastic body when there is no external load, and the unit is dimensionless; σ represents the additional stress of the elastic body under the external load T, and the unit is MPa; ε represents the strain of the elastic body under the external load T, and the unit is dimensionless; u represents the displacement of the elastic body under the external load T, and the unit is m; S represents the relative slip between the cement sheath and the formation at the inner interface of the crack, and the unit is m.

[0103] In a possible implementation, the elastic body is the cementing interface, i.e., the cement sheath; the external load T is the shear stress generated by the cementing interface; the action surface of the external load T is the cementing area of ​​the cementing interface; σ=σ1+σ sz , which is the sum of the horizontal compressive stress and the axial additional stress on the cement sheath. Substituting the calculated parameters obtained by measurement into the above formula, the total potential energy of the cement sheath elastic body can be obtained.

[0104] 1032-2: Assuming that the friction force of the cementing interface is constant during the cracking process, the potential energy release rate of the cement sheath at the cementing interface is obtained based on the total potential energy of the elastic body.

[0105] Optionally, the calculation formula for the cement sheath potential energy release rate is:

[0106]

[0107] Where G represents the potential energy release rate, in J / m 2 ; a represents the characteristic size of the crack, in m 2 ; S F Represents the internal interface area with friction, in m 2 ; τ0 represents the tangential component of the internal interface prestress, in MPa. represents the partial differential function.

[0108] In a possible implementation, the inner interface with friction is the cementing second interface between the cement sheath and the formation; the external load T is the shear stress generated by the cementing second interface; the tangential component of the inner interface prestress is the friction force at the cementing second interface, which is regarded as a constant. Substituting the calculated parameters obtained by measurement into the above formula (6), the potential energy release rate of the cement sheath can be obtained.

[0109] Step 1033, obtaining the crack length of the second cementing interface according to the obtained cracking energy dissipation rate and cement sheath potential energy release rate.

[0110] In a possible implementation, the relationship between the energy difference at the cementing interface and the crack length of the two interfaces is:

[0111]

[0112] Among them, the energy difference is the difference between the cracking energy dissipation rate and the cement sheath potential energy release rate. The cracking energy dissipation rate Γ and the cement sheath potential energy release rate G obtained according to the above formula (4) and formula (6), and the shear stress τ obtained according to formula (3), are substituted into the above relationship (7) to obtain the crack length l1 of the cementing interface.

[0113] Step 104: Based on the crack length, the failure length of the second cementing interface is obtained, and the integrity of the second cementing interface is detected by the obtained failure length.

[0114] Failure of cementing interface refers to the formation of annular gaps at the interface, which forms a gas channel, destroying its integrity, losing its sealing ability, and causing failure of fracturing operation. However, the crack length of cementing interface will not affect the integrity of cementing interface within a certain range. Therefore, the integrity of cementing interface can be detected by the failure length of cementing interface.

[0115] In a possible implementation, the thickness range from the CO2 injection point to the reservoir is subtracted from the crack length to obtain the failure length of the cementing interface. The integrity of the cementing interface is detected using the failure length of the cementing interface as a criterion.

[0116] Among them, the calculation formula of the failure length of the cementing interface is:

[0117] l s =l1-l (8)

[0118] Among them, l s , l1, and l are the failure length of the cementing interface, the crack length, and the thickness from the injection point to the reservoir, respectively.

[0119] In a possible implementation, the failure length of the cementing interface is used as a judgment index, and the judgment rule for detecting whether the cementing interface is complete is:

[0120] When l s When <0, the failure length of the cementing interface is less than 0, which is equivalent to the cracking length being less than the thickness from the injection point to the reservoir. At this time, the integrity of the cementing interface is not destroyed. s When ≥0, the failure length of the cementing interface is greater than or equal to 0, which is equivalent to the cracking length being greater than or equal to the thickness from the injection point to the reservoir. This means that the cracking length of the cementing interface exceeds the range from the injection point to the reservoir thickness and extends to the interlayer. At this time, the integrity of the cementing interface is not destroyed.

[0121] Repeat steps 101 to 104 under different CO2 injection conditions, calculate the crack length of the cementing interface II, compare it with the thickness range from the injection point to the reservoir, and calculate the failure length of the cementing interface II. Whether the failure length of the cementing interface II is greater than zero is used as a discrimination index, that is, whether the crack length of the cementing interface II exceeds the thickness range from the injection point to the reservoir is used as a discrimination index, and a method for detecting the integrity of the cementing interface II during CO2 flooding and burial is formed, and the integrity of the cementing interface II under different gas injection conditions is detected.

[0122] The integrity detection method of the second interface of cementing in a CO2 injection well provided in the embodiment of the present application takes the failure length of the second interface of cementing as a calculation index, establishes a calculation model of the failure length of the second interface of cementing from the principle of energy conservation, and improves the calculation method of the integrity of the second interface of cementing. The embodiment of the present application has at least the following beneficial effects: considering the influence of the change of the stress-strain state of the formation under the chemical-mechanical coupling after CO2 injection on the second interface of cementing, it can more scientifically reflect the failure process of the second interface during CO2 oil displacement and storage; according to the law of conservation of energy, a calculation model of the failure length of the second interface of cementing is established, and by analyzing its energy transfer process, the failure length of the second interface of cementing under the condition of CO2 injection can be more accurately obtained; taking the failure length of the second interface of cementing as a calculation index, it can further clarify the failure condition of the integrity of the second interface of cementing during CO2 injection on the basis of ensuring the quality of cementing, so that the selection range of injection and production construction parameters is more accurate; it is targeted at CO2 storage projects, and can provide a reliable theoretical basis for the study of the failure process of the second interface of cementing during CO2 oil displacement and storage.

[0123] The present application embodiment provides a device 20 for detecting the integrity of a carbon dioxide injection well cementing interface. Figure 2 As shown, the device comprises:

[0124] The first acquisition unit 21 is used to acquire the shear stress generated at the cementing interface of the CO2 injection well under the chemical and mechanical coupling effect;

[0125] A judging unit 22, used to judge whether cracking occurs at the cementing interface based on shear stress and cement sheath bonding strength;

[0126] The second acquisition unit 23 is used for acquiring the crack length of the second cementing interface according to the energy conservation principle in response to the cracking of the second cementing interface;

[0127] The detection unit 24 is used to obtain the failure length of the cementing interface based on the cracking length, and detect the integrity of the cementing interface through the failure length.

[0128] In a possible implementation, the first acquisition unit 21 is used to acquire the axial additional stress generated at the cementing interface under the chemical and mechanical coupling action; based on the axial additional stress and the horizontal compressive stress of the formation on the cementing interface, the shear stress at the cementing interface is acquired.

[0129] In a possible implementation, the first acquisition unit 21 is also used to obtain the elastic modulus of the formation rock after dissolution based on the influence of the chemical dissolution of the acidic solution on the elastic modulus of the formation rock; based on the elastic modulus of the formation rock after dissolution, obtain the axial additional stress on the cementing interface caused by the increase in formation pore pressure.

[0130] In a possible embodiment, the acidic solution is an H2CO3 solution generated when CO2 is injected into a well and contacts with formation water.

[0131] In a possible implementation, the judgment unit 22 is used to judge that if the shear stress is less than the cement sheath bonding strength, the cementing interface will not crack; if the shear stress is greater than or equal to the cement sheath bonding strength, the cementing interface will crack.

[0132] In a possible implementation, the second acquisition unit 23 is used to acquire the cracking energy dissipation rate during the cracking process of the cementing interface; acquire the cement sheath potential energy release rate of the cementing interface; and acquire the cracking length of the cementing interface according to the cracking energy dissipation rate and the cement sheath potential energy release rate.

[0133] In a possible implementation, the second acquisition unit 23 is also used to acquire the total potential energy of the elastic body at the cementing interface; assuming that the friction force at the cementing interface is a constant during the cracking process, the cement sheath potential energy release rate at the cementing interface is acquired based on the obtained total potential energy of the elastic body.

[0134] In a possible implementation, the detection unit 24 is used to subtract the thickness range from the CO2 injection point to the reservoir from the crack length to obtain the failure length of the second cementing interface; and use the failure length of the second cementing interface as a judgment indicator to detect the integrity of the second cementing interface.

[0135] In a possible implementation, the detection unit 24 is also used to determine that when the failure length of the cementing interface 2 is less than 0, the integrity of the cementing interface 2 is not destroyed; when the failure length of the cementing interface 2 is greater than or equal to 0, the integrity of the cementing interface 2 is not destroyed.

[0136] The integrity detection device for the cementing interface of a CO2 injection well provided in the embodiment of the present application uses the failure length of the cementing interface as a calculation index and establishes a calculation model for the failure length of the cementing interface based on the energy conservation principle. The device can scientifically reflect the failure process of the interface during CO2 oil recovery and storage, more accurately derive the failure length of the cementing interface under CO2 injection conditions, make the selection range of injection and production construction parameters more accurate, and provide a more reliable detection device for CO2 storage projects.

[0137] It should be understood that the above Figure 2 When the device provided realizes its functions, only the division of the above-mentioned functional modules is used as an example for illustration. In practical applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above. In addition, the device and method embodiments provided in the above embodiments belong to the same concept, and their specific implementation process is detailed in the method embodiment, which will not be repeated here.

[0138] In an exemplary embodiment, a computer-readable storage medium is also provided, in which at least one program code is stored. The at least one program code is loaded and executed by a processor to enable a computer to implement any of the above-mentioned methods for detecting the integrity of cementing interfaces in carbon dioxide injection wells.

[0139] Optionally, the computer-readable storage medium may be a read-only memory (ROM), a random access memory (RAM), a compact disc (CD-ROM), a magnetic tape, a floppy disk, an optical data storage device, etc.

[0140] In an exemplary embodiment, a computer program or a computer program product is also provided, wherein at least one computer instruction is stored in the computer program or the computer program product, and the at least one computer instruction is loaded and executed by a processor so that a computer implements any of the above-mentioned methods for detecting the integrity of the cementing interface of a carbon dioxide injection well.

[0141] The above description is only an illustrative embodiment of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for detecting the integrity of the cementing interface of a carbon dioxide injection well, characterized in that: The method comprises: Obtaining the shear stress generated at the cementing interface of the carbon dioxide injection well under the chemical and mechanical coupling effects; If the shear stress is less than the cement sheath bonding strength, the cementing interface will not crack; If the shear stress is greater than or equal to the cement sheath bonding strength, the cementing second interface will crack; In response to the second cementing interface cracking, obtaining a cracking energy dissipation rate during the cracking of the second cementing interface; Obtaining the total potential energy of the elastic body at the second cementing interface; Assuming that the friction force of the cementing interface is constant during the cracking process, the potential energy release rate of the cement sheath at the cementing interface is obtained based on the total potential energy of the elastic body; According to the cracking energy dissipation rate and the cement sheath potential energy release rate, obtaining the cracking length of the cementing second interface; Subtract the thickness range from the carbon dioxide injection point to the reservoir from the crack length to obtain the failure length of the cementing second interface; When the failure length of the cementing second interface is less than 0, the integrity of the cementing second interface is not destroyed; When the failure length of the second cementing interface is greater than or equal to 0, the integrity of the second cementing interface is destroyed.

2. The method according to claim 1, characterized in that The step of obtaining the shear stress generated at the cementing interface of the carbon dioxide injection well under the chemical and mechanical coupling effect comprises: Obtaining the additional axial stress generated at the cementing second interface under the chemical and mechanical coupling effects; Based on the additional axial stress and the horizontal compressive stress of the formation on the second cementing interface, the shear stress at the second cementing interface is obtained.

3. The method according to claim 2, characterized in that The step of obtaining the additional axial stress generated at the cementing interface under the chemical and mechanical coupling action includes: Based on the influence of chemical dissolution of acidic solution on the elastic modulus of formation rock, the elastic modulus of formation rock after dissolution is obtained; Based on the elastic modulus of the dissolved formation rock, the axial additional stress on the cementing interface caused by the increase in formation pore pressure is obtained.

4. The method according to claim 3, characterized in that The acidic solution is a carbonic acid solution produced when carbon dioxide is injected into a well and contacts with formation water.

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