Device and method for evaluating the self-healing effect of cement sheath and interface in well cementing

Abstract

This invention discloses a device and method for evaluating the self-repair effect of cement sheaths and interfaces in well cementing. The device includes an annular simulation unit, a temperature and pressure control unit, a multiphase flow control unit, an in-situ monitoring unit, and a data acquisition control unit. The annular simulation unit comprises an inner casing, a cement sheath incorporating self-repairing material, and a formation core, forming a coaxially nested annular structure from the inside out, as well as a sealing cap. The temperature and pressure control unit applies combined temperature and pressure to the annular simulation unit. The multiphase flow control unit injects multiphase fluid generated by the decomposition of natural gas hydrates into the annular simulation unit. The in-situ monitoring unit performs non-destructive online monitoring of the cement sheath and interfaces, acquiring dynamic information on damage evolution and the entire self-repair process. The data acquisition control unit evaluates the self-repair effect of the cement sheath and interfaces based on the fusion processing results of the data collected from each unit. This invention improves the accuracy of evaluating the self-repair effect of cement sheaths and interfaces in well cementing.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well integrity testing technology, and in particular to a device and method for evaluating the self-repair effect of cement sheaths and two interfaces. Background Technology

[0002] With the continuous development of deep-sea and unconventional natural gas resources, the safe and efficient extraction of natural gas hydrates, as a clean energy source with enormous potential, has become a global research hotspot. The decomposition process of natural gas hydrate extraction can cause drastic changes in the formation environment around the wellbore, subjecting the cement sheath to multi-field coupling effects. This can easily induce the initiation and propagation of micro-cracks within the cement sheath and disrupt the cementing integrity of the interface between the cement sheath and the formation, thereby easily leading to major safety risks such as annular pressure and gas leakage.

[0003] Existing cement sheath integrity evaluation devices are mostly developed for conventional oil and gas wells operating under high temperature and high pressure conditions. They can only achieve single-temperature and pressure loading, static performance testing, or offline microstructure characterization, and their simulation and reproduction capabilities for more complex actual operating conditions are relatively low. Furthermore, existing solutions largely rely on static performance parameters of the cement sheath and interface before and after repair for evaluation and analysis, failing to study and analyze the damage and self-repair evolution of the cement sheath and interface. Current technologies struggle to achieve a comprehensive and accurate evaluation of the self-repair effect of the cement sheath and interface, as well as a systematic study of its dynamic evolution. Summary of the Invention

[0004] This invention provides a device and method for evaluating the self-repair effect of cementing sheaths and two interfaces, in order to solve the technical problems of insufficient accuracy in evaluating the self-repair effect of cementing sheaths and two interfaces, and the difficulty in systematically analyzing the dynamic evolution law of self-repair.

[0005] According to one aspect of the present invention, a device for evaluating the self-healing effect of cement sheath and two-interface is provided. The device includes annular simulation unit, temperature and pressure control unit, multiphase flow control unit, in-situ monitoring unit, and data acquisition control unit; wherein: The annular simulation unit includes an inner casing, a cement sheath, a formation core, and a sealing cap; wherein, the inner casing, cement sheath, and formation core are coaxially nested from the inside to the outside to form a ring structure, and the ring structure is used to simulate the cement sheath body and the two interfaces cementing state; the cement sheath is a cementing cement sheath with added self-healing material; the sealing cap is assembled at both ends of the ring structure. The temperature and pressure control unit is used to apply a combined effect of temperature and pressure to the annular simulation unit to simulate the temperature and pressure changes during the decomposition process of natural gas hydrates. The multiphase flow control unit is used to inject multiphase fluid generated by the decomposition of natural gas hydrate into the annular simulation unit to simulate the intrusion and chemical corrosion of the multiphase fluid on the cement ring and the two interfaces. The in-situ monitoring unit is used to perform non-destructive online monitoring of the cement ring and the two interfaces within the annular simulation unit, and to obtain dynamic information on the entire process of damage evolution and self-repair of the cement ring and the two interfaces. The data acquisition and control unit is used to perform timing coordination control and data fusion processing on each unit in the device, and to evaluate the self-healing effect of the cement ring and the two interfaces based on the data fusion processing results.

[0006] According to another aspect of the present invention, a method for evaluating the self-repair effect of cementing sheath and two-interface is provided, wherein the method is implemented using the self-repair effect evaluation device for cementing sheath and two-interface as described in any embodiment of the present invention.

[0007] The technical solution of this invention, by configuring the annular simulation unit as a coaxially nested annular structure of inner casing, cement sheath, and formation core from the inside out, can simulate the annular structure between the casing, cement sheath, and formation. A sealing cap seals the ends of the annular structure to ensure the airtightness of the simulation environment, thereby improving the accuracy of simulating the cement sheath body and the bonding state of the two interfaces. The cement sheath is a cementing cement sheath with added self-healing materials, capable of simulating the self-healing effect of the cementing cement sheath. By applying combined temperature and pressure to the annular simulation unit through a temperature and pressure control unit, the dynamic temperature and pressure changes during the decomposition of natural gas hydrates can be simulated, enabling the annular simulation unit to simulate thermal stress cracks caused by the decomposition of natural gas hydrates, thus improving the accuracy of simulating the bonding state of the cement sheath body and the two interfaces. The multiphase flow control unit can inject multiphase flow generated by the decomposition of natural gas hydrates into the annular simulation unit. Multiphase fluid simulation can model the intrusion and chemical corrosion of cement sheaths and interfaces by multiphase fluids. Through multiphysics coupling, the simulated environment more closely resembles actual working conditions, improving the realism of cement sheath and interface damage simulation and thus enhancing the accuracy of simulating the self-healing behavior of cement sheaths and interfaces. In-situ monitoring units enable non-destructive online monitoring of the cement sheath and interfaces, continuously capturing dynamic information throughout the damage evolution and self-healing process. This avoids offline detection that damages the sample structure and loses key process data, thus improving the completeness and timeliness of monitoring data. Data acquisition and control units enable sequential coordinated control and data fusion processing of each unit, unifying the experimental process and integrating multi-dimensional monitoring information. This avoids asynchronous actions and data fragmentation between units, thereby improving the accuracy and automation level of evaluating the self-healing effect of cement sheaths and interfaces. Based on the above technical solutions, by simulating the annular structure between the casing, cement sheath, and formation, as well as the complex working environment under the conditions of natural gas hydrate decomposition, the realism of the simulation of cement sheath and interface damage can be improved. Furthermore, by conducting in-situ dynamic monitoring of the entire self-repair process of the cement sheath and interface, the technical problems of insufficient accuracy in evaluating the self-repair effect of cement sheath and interface, and the difficulty in systematically analyzing the dynamic evolution law of self-repair can be solved. This can improve the experimental verification capability of evaluating the damage evolution and self-repair effect of cement sheath and interface, thereby improving the reliability and efficiency of the research and development and engineering application evaluation of self-repairing cementing materials.

[0008] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0010] Figure 1 This is a structural schematic diagram of a cementing sheath and a two-interface self-healing effect evaluation device provided according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the annular simulation unit provided according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the temperature and pressure control unit provided according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the interaction logic of each unit in a well cement sheath and two-interface self-healing effect evaluation device provided according to an embodiment of the present invention; Figure 5 This is a first schematic diagram of the fiber Bragg grating sensor deployment location according to an embodiment of the present invention; Figure 6 This is a second schematic diagram of the fiber Bragg grating sensor deployment location provided in an embodiment of the present invention; Figure 7 This is a third schematic diagram of the fiber optic grating sensor deployment location according to an embodiment of the present invention; Figure 8 This is a fourth schematic diagram of the fiber optic grating sensor deployment location according to an embodiment of the present invention; Figure 9 This is a schematic diagram of the interaction logic between the in-situ monitoring unit and the data acquisition and control unit according to an embodiment of the present invention; Figure 10 This is a schematic diagram of the execution logic of a method for evaluating the self-healing effect of cementing sheath and two interfaces according to an embodiment of the present invention. Detailed Implementation

[0011] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0012] It should be noted that the terms "candidate," "target," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0013] Figure 1 This is a schematic diagram of a device for evaluating the self-healing effect of cementing sheath and two interfaces provided in an embodiment of the present invention. This embodiment is applicable to the evaluation of cementing quality and the development of self-healing cementing systems for wells with complex working conditions such as natural gas hydrates, deepwater oil and gas, shale gas, geothermal energy, and carbon dioxide capture, utilization and storage. It is especially applicable to the evaluation of the damage evolution and self-healing effect of cementing sheath and two interfaces under the action of self-healing materials during the decomposition of natural gas hydrates under laboratory conditions.

[0014] See Figure 1 and Figure 2 The well cement sheath and two-interface self-repair effect evaluation device provided in this embodiment of the invention includes annular simulation unit 100, temperature and pressure control unit 200, multiphase flow control unit 300, in-situ monitoring unit 400, and data acquisition control unit 500; wherein: The annular simulation unit 100 includes an inner casing 110, a cement sheath 120, a formation core 130, and a sealing cap 140. The inner casing 110, cement sheath 120, and formation core 130 are coaxially nested from the inside to the outside to form an annular structure. The annular structure is used to simulate the cement sheath body and the bonding state between the two interfaces. The cement sheath 120 is a cementing sheath with self-healing material added. The sealing cap 140 is assembled at both ends of the annular structure. The temperature and pressure control unit 200 is used to apply a combined effect of temperature and pressure to the annular simulation unit to simulate the temperature and pressure changes during the decomposition process of natural gas hydrates; The multiphase flow control unit 300 is used to inject multiphase fluid generated by the decomposition of natural gas hydrate into the annular simulation unit to simulate the intrusion and chemical corrosion of the multiphase fluid on the cement ring and the two interfaces. The in-situ monitoring unit 400 is used to perform non-destructive online monitoring of the cement ring and the two interfaces within the annular simulation unit, and to obtain dynamic information on the entire process of damage evolution and self-repair of the cement ring and the two interfaces. The data acquisition and control unit 500 is used to perform timing coordination control and data fusion processing on each unit in the device, and to evaluate the self-healing effect of the cement ring and the two interfaces based on the data fusion processing results.

[0015] Specifically, the annular simulation unit 100 can refer to an experimental structural unit used to simulate the annular spatial morphology and cementing interface between the inner casing, cement sheath, and formation after downhole cementing. The inner casing 110 is used to simulate the cylindrical component of the well casing; the cement sheath 120 can refer to the annular structure used to simulate downhole cement stone, and the cement sheath 120 contains self-healing materials to simulate the self-healing effect of the cement sheath; the formation core 130 can be a natural or artificially prepared rock sample, and the formation core 130 is used to simulate the annular component of the downhole formation medium; the sealing cap 140 can refer to a sealing component assembled at the end of the simulation structure, and the sealing cap 140 is used to achieve sealing and pressure bearing of the annular composite structure; the cementing surface between the inner casing 110 and the cement sheath 120 is one interface, and the cementing surface between the cement sheath 120 and the formation core 130 is two interfaces.

[0016] By coaxially nesting the inner casing, a cement sheath incorporating self-healing material, and a formation core from the inside out, an annular structure simulating the space between the casing, cement sheath, and formation is formed. This annular structure is then sealed at both ends with sealing caps, creating an experimental body that accurately simulates the cementing annular structure for evaluating the self-healing effect of the cement sheath and the two-interface. For example, the inner casing 110 can be made of steel with an outer diameter of 88.9 mm and a length of 300-400 mm. The surface of the inner casing 110 can be sandblasted to simulate the roughness of the well casing under actual working conditions and to ensure that the outer wall of the inner casing 110 can support pre-embedded sensing components. The cement sheath 120 can be cast using oil well cement containing self-healing material, with a thickness of 15-20 mm, to simulate the cement sheath body and to study the damage and self-healing behavior of the cement sheath; the self-healing material can be microcapsules, shape memory polymers, etc. The formation core 130 can be a synthetic core or a natural core to simulate the mechanical and permeability characteristics of the formation rocks. The inner diameter of the formation core 130 should match the outer diameter of the cement ring 120, and the length of the formation core 130 should be consistent with the length of the inner sleeve 110. The synthetic core can be sandstone, mudstone, etc. The sealing cap 140 can be made of stainless steel, and an O-ring is embedded inside the sealing cap 140. The sealing cap 140 is assembled at both ends of the annular structure to ensure axial high-pressure sealing of the annular simulation unit, preventing fluid leakage from the ends of the annular structure and ensuring the airtight and stable high-pressure experimental environment inside the annular simulation unit.

[0017] The temperature and pressure control unit 200 refers to a control execution unit capable of providing coupled temperature and pressure loading to the experimental simulation environment and dynamically adjusting temperature and pressure parameters. Based on the environmental temperature and pressure changes during natural gas hydrate decomposition, by applying the combined effects of temperature and pressure to the simulation structure formed by the annular simulation unit 100 through the temperature and pressure control unit 200, the downhole temperature and pressure environment during natural gas hydrate decomposition can be simulated and reproduced. This ensures that the experimental conditions match the actual formation conditions as closely as possible, avoiding the lack of reliability in the evaluation results due to simulation distortion of temperature and pressure conditions.

[0018] The multiphase flow control unit 300 can refer to a fluid supply control unit used for transporting and regulating the multiphase fluid generated by the decomposition of natural gas hydrates. By injecting the multiphase fluid generated by the decomposition of natural gas hydrates into the annular simulation unit through the multiphase flow control unit, the intrusion behavior and chemical corrosion of the multiphase fluid on the cement annulus body and the two interfaces are simulated using fluid action.

[0019] The temperature and pressure control unit 200 and the multiphase flow control unit 300 can simulate the multi-physics coupling in the complex fluid environment downhole, making the experimental environment more consistent with the actual working conditions. This can improve the accuracy and rationality of the simulation of cement sheath and two-interface damage and the evaluation of self-repair effect. Among them, multi-physics coupling simulation can refer to the integrated simulation of the effects of multiple physical fields such as temperature, pressure, fluid intrusion and chemical corrosion in actual working conditions.

[0020] The in-situ monitoring unit 400 refers to a set of monitoring components that perform real-time online monitoring of the cement ring 120 and the bonding state of the two interfaces without damaging the structure of the annular simulation unit 100 or the experimental simulation environment. By using the in-situ monitoring unit 400 to perform non-destructive online monitoring of the cement ring 120 and the two interfaces within the annular simulation unit 100, dynamic monitoring information on the cement ring 120 and the two interfaces from damage initiation and development to self-repair can be continuously collected. This avoids damage to the annular structure and loss of evolution process data caused by offline monitoring, and improves the completeness and timeliness of the monitoring information.

[0021] The data acquisition and control unit 500 can refer to a control processing unit that performs timing control, data acquisition and integration, and data analysis and evaluation functions on the annular simulation unit 100, the temperature and pressure control unit 200, the multiphase flow control unit 300, and the in-situ monitoring unit 400. The data acquisition and control unit 500 coordinates the operation of each functional unit through timing-based collaborative control and integrates the multi-source monitoring information acquired by each functional unit through data fusion processing. This solves the problem of fragmented multi-source monitoring information, providing more complete information support for the self-repair effect evaluation, thereby improving the scientific rigor and accuracy of the self-repair effect evaluation. See Figure 2Optionally, based on any of the above embodiments, the annular simulation unit 100 may further include a mud cake layer 150, which is located between the cement ring 120 and the formation core 130.

[0022] The mud cake layer 150 is used to simulate the mud cake interface between the cement sheath and the formation during actual downhole operations. The mud cake interface refers to the thin layer of mud deposits formed at the interface between the cement sheath and the formation during cementing operations.

[0023] By adding a mud cake layer 150 to the annular simulation unit 100, the inner casing 110, cement sheath 120, mud cake layer 150, and formation core 130 are coaxially nested from the inside out, forming a multi-layer annular simulation structure that more closely resembles actual downhole conditions. This allows for a more accurate simulation of the cementation conditions at the downhole interface when mud cake is present, thereby improving the accuracy of simulating the interface cementation state. For example, the mud cake layer can be a replaceable filter cake simulation sheet, placed between the cement sheath 120 and the formation core 130. By switching between different filter cake simulation sheets, the influence of different mud cake properties on the interface cementation quality can be studied. Different mud cake properties can refer to different mud cake layer thicknesses, water content, permeability, etc. For example, the thickness of the filter cake simulation sheet is typically 2-3 mm.

[0024] Optionally, based on any of the above embodiments, the annular simulation unit 100 further includes a first temperature and pressure sensor and a second temperature and pressure sensor; wherein, the first temperature and pressure sensor is disposed at the inlet of the annular simulation unit 100 and is used to monitor the pressure and temperature of the fluid injected into the annular simulation unit 100; the second temperature and pressure sensor is disposed at the outlet of the annular simulation unit 100 and is used to monitor the pressure and temperature of the fluid flowing out of the annular simulation unit 100.

[0025] Specifically, the first temperature and pressure sensor can refer to a sensing component installed at the inlet of the annular simulation unit to detect the temperature and pressure parameters of the fluid injected into the annular simulation unit 100. Detecting the injected fluid temperature ensures that it meets the expected experimental requirements, and monitoring changes in the injected fluid pressure records dynamic pressure data during the pressure shock process. The second temperature and pressure sensor can refer to a sensing component installed at the outlet of the annular simulation unit to detect the temperature and pressure parameters of the fluid flowing out of the annular simulation unit 100. Detecting changes in the outflowing fluid temperature reflects the thermal conduction effect and the thermal impact of the phase change process within the cement ring, and allows for real-time monitoring of the pressure decay process of the outflowing fluid.

[0026] By coordinating the deployment of the first and second temperature and pressure sensors, synchronous monitoring of the temperature and pressure parameters at the inlet and outlet of the fluid within the annular simulation unit 100 can be achieved, enabling real-time capture of temperature and pressure changes during fluid flow through the simulation unit. Based on the pressure data synchronously detected by the first and second temperature and pressure sensors, the fluid pressure difference at the inlet and outlet of the annular simulation unit 100 can be obtained. Furthermore, the change in the permeability of the cement ring 120 can be calculated based on the fluid pressure difference. The permeability of the cement ring 120 can serve as a parameter or quantitative indicator for evaluating the self-healing effect of the cement ring.

[0027] Optionally, the first and second temperature and pressure sensors can be integrated sensing elements that combine temperature and pressure detection functions, or they can be temperature and pressure sensing components composed of separately arranged temperature and pressure sensors.

[0028] Optionally, based on any of the above embodiments, the annular simulation unit 100 further includes a leakage collection and measurement device, which is installed at the outlet of the annular simulation unit 100. The annular simulation unit 100 is used to collect and measure the volume of fluid seeping from the cement ring body and the two interfaces in real time.

[0029] A leakage collection and measurement device is positioned at the outlet of the annular simulation unit 100. It can be used to collect fluid seeping from the cement ring body and the second interface in real time, and to perform high-precision measurement of the seepage volume. This enables dynamic monitoring and quantitative characterization of the leakage characteristics of the cement ring and the second cemented interface. Optionally, a high-precision electronic balance or mass flow meter is built into the leakage collection and measurement device. By configuring the annular simulation unit 100 with a leakage collection and measurement device, the degree of leakage of the cement ring and the second interface can be quickly and accurately quantified, intuitively reflecting the sealing integrity and self-healing effect of the cement ring and the second interface. Furthermore, the measurement data from the leakage collection and measurement device can serve as parameter information or quantitative indicators for evaluating the self-healing effect of the cement ring and the second interface, and can also be used as an auxiliary parameter in the inversion calculation of the cement ring permeability.

[0030] Optionally, based on any of the above embodiments, the temperature and pressure control unit 200 includes a refrigerant tank 210, a fluid circulation pump 220, a methane cylinder 230, and a pressure controller 240; wherein: The coolant tank 210 is connected to the outer jacket layer 160 of the annular simulation unit 100 via the fluid circulation pump 220. The coolant tank 210 is used to supply coolant to the annular simulation unit 100, and the fluid circulation pump 220 is used to drive the coolant from the coolant tank 210 to the outer jacket layer 160 of the annular simulation unit 100. The outer jacket layer 160 of the annular simulation unit 100 is a sandwich structure outside the stratum core 130 in the annular simulation unit 100. Methane cylinder 230 is used to supply methane gas into the annular simulation unit 100, and pressure controller 240 is used to control the methane gas injection pressure, pressurization rate and holding time.

[0031] The annular simulation unit 100 is encased in an outer jacket 160 that surrounds the formation core 130. A coolant can circulate within the outer jacket 160, cooling the annular simulation unit 100 via heat conduction to simulate the formation's heat absorption process. A fluid circulation pump 220 drives the coolant circulation to ensure the uniformity of the temperature field around the annular simulation unit 100 and its dynamic response speed.

[0032] Specifically, see Figure 3 The refrigerant tank 210 is connected to the outer jacket layer 160 of the annular simulation unit 100 via a fluid circulation pump 220. The refrigerant tank 210 stores and supplies refrigerant to the annular simulation unit 100. The fluid circulation pump 220 provides power to drive the refrigerant from the refrigerant tank 210 to the outer jacket layer 160 of the annular simulation unit 100, and maintains the circulating flow of the refrigerant to simulate the endothermic cooling process during the decomposition of natural gas hydrates. Figure 3 The blue arrows indicate the direction of refrigerant flow. The refrigerant tank 210 provides a low-temperature, constant-temperature environment for the refrigerant. For example, the temperature control range within the refrigerant tank 210 can typically be set from -30°C to 25°C, with a temperature control accuracy maintained at ±0.5°C. The refrigerant can be an ethylene glycol solution. The methane cylinder 230 stores high-pressure methane gas, serving as a pressure shock source. It supplies methane gas to the annular simulation unit 100 to simulate the rapid expansion effect of gas produced by the decomposition of natural gas hydrates. For example, the pressure within the methane cylinder 230 can typically provide a pressure control range of 0-30 MPa. The pressure controller 240 precisely controls the injection pressure, pressurization rate, and holding time of the methane gas. The pressure controller 240 also has a closed-loop feedback function to ensure the stability of the pressure inside the annular simulation unit 100. Figure 3 The red arrow in the middle indicates the flow direction of high-pressure methane gas. By coordinating the control of temperature and pressure, the temperature change characteristics and pressure dynamic changes during the decomposition of natural gas hydrates can be simulated, providing the annular simulation unit 100 with test conditions that closely resemble actual downhole conditions, further improving the authenticity and reliability of the evaluation test results.

[0033] Optionally, see Figure 3The temperature and pressure control unit 200 can receive a programmed control signal and automatically execute temperature and pressure control based on the programmed control signal, wherein the programmed control signal can be issued by the data acquisition control unit 500. For example, the data acquisition control unit 500 sends a programmed control signal to the temperature and pressure control unit 200 by running a preset temperature and pressure control program. The programmed control signal can indicate the temperature and pressure control operation and the temperature and pressure control parameters. According to the received programmed control signal, each component or element within the temperature and pressure control unit 200 performs automatic control operations.

[0034] Based on any of the above embodiments, optionally, the multiphase flow control unit 300 includes a fluid storage tank assembly 310, a multiphase flow pump 320, a fluid switching valve assembly 330, and a conductivity sensor 340; wherein: The fluid storage tank group 310 includes multiple fluid storage tanks, which are used to store the single-phase fluids produced by the decomposition of natural gas hydrates. The fluid storage tank group 310 is connected to the multiphase flow pump 320 through the fluid switching valve group 330. The fluid switching valve assembly 330 is used for automatic switching and mixing of different fluids; Multiphase flow pump 320 is used to inject multiphase fluid into annular simulation unit 100; The conductivity sensor 340 is used to monitor the conductivity of the multiphase flow emanating from the annular simulation unit 100.

[0035] Specifically, see Figure 4 In the multiphase flow control unit 300, multiple fluid storage tanks store the various single-phase fluids produced by the decomposition of natural gas hydrates. Each fluid storage tank is connected to the multiphase flow pump 320 via a fluid switching valve assembly 330. According to the experimental environmental simulation requirements, the fluid switching valve assembly 330 automatically switches and mixes the different single-phase fluids to form a multiphase fluid that conforms to actual downhole operating conditions. The multiphase flow pump 320 then provides power to stably inject the mixed multiphase fluid into the annulus simulation unit 100, maintaining the continuous circulation of the multiphase fluid. Figure 4 The green arrows in the diagram illustrate the fluid flow direction within the multiphase flow control unit. Simultaneously, a conductivity sensor 340 monitors the conductivity of the multiphase fluid seeping from the annular simulation unit 100 in real time. Based on the monitored conductivity, the dynamic changes in fluid composition can be captured, indirectly reflecting the dissolution of cementitious material and the crack healing process within the cement sheath. The conductivity measured by the conductivity sensor 340 can serve as a quantitative indicator for evaluating the self-healing effect of the cement sheath and the two-interface.

[0036] The fluid switching valve assembly 330 can be composed of multiple solenoid valves. It can receive programmed control signals and control the multiphase fluid mixing type, ratio, and injection sequence based on these signals. The programmed control signals can be issued by the data acquisition and control unit 500. The multiphase flow pump 320 injects the mixed multiphase fluid into the annulus simulation unit 100 at a preset flow rate. The multiphase flow pump 320 has precise flow control capabilities; for example, it can control a flow rate range of 0.1-50 ml / min. The multiphase flow pump 320 can be used to simulate the dynamic characteristics of actual downhole fluid invasion while ensuring multiphase fluid injection. It supports various fluid injection modes, such as continuous or pulsed fluid injection. Optionally, the multiphase flow pump 320 can have its flow rate manually adjusted locally, or it can receive programmed control signals and control the multiphase fluid injection flow rate based on these signals. The programmed control signals can be issued by the data acquisition and control unit 500. In addition, the multiphase flow pump 320 can regulate the pressure of the multiphase fluid by adjusting the flow rate of the multiphase fluid. By controlling the pressure fluctuation of the multiphase fluid, it can control the triggering of microcapsule rupture or responsive material activation in the cement ring 120, thereby improving the controllability of the self-healing process of the cement ring and the two interfaces.

[0037] Optionally, based on any of the above embodiments, a fluid temperature controller is provided between the multiphase flow pump 320 and the annular simulation unit 100. The fluid temperature controller is used to control the temperature of the multiphase fluid injected into the annular simulation unit 100.

[0038] In the fluid delivery pipeline of the multiphase flow control unit 300, a fluid temperature controller is installed between the multiphase flow pump 320 and the annular simulation unit 100. The multiphase fluid, after its flow rate is adjusted by the multiphase flow pump, first flows through the fluid temperature controller. The fluid temperature controller precisely regulates the temperature of the multiphase fluid according to the preset downhole operating temperature requirements. Once the multiphase fluid temperature reaches the preset standard, it is then delivered to the annular simulation unit. This ensures that the temperature of the multiphase fluid injected into the annular simulation unit 100 is as similar as possible to the fluid temperature during the actual downhole natural gas hydrate decomposition process, thus reducing the interference of temperature disturbances on the experimental results. Furthermore, by adjusting the multiphase flow temperature through the fluid temperature controller, it can be used to control the triggering of microcapsule rupture or responsive material activation within the cement sheath 120, thereby improving the controllability of the self-healing process of the cement sheath and the two interfaces.

[0039] Optionally, based on any of the above embodiments, the fluid storage tank group 310 includes a methane gas storage tank, a formation water storage tank, and an acidic fluid storage tank; wherein: The methane gas storage tank is used to store methane gas. A gas flow controller is installed between the methane gas storage tank and the fluid switching valve group 330. The gas flow controller is used to control the injection rate of methane gas. Acidic fluid storage tanks are used to store acidic corrosive fluids to simulate the chemical corrosion environment following the decomposition of natural gas hydrates.

[0040] The fluid storage tank group 310 includes a methane gas storage tank, a formation water storage tank, and an acidic fluid storage tank, which are used to store high-pressure methane gas, formation water, and acidic corrosive fluid generated during the decomposition of natural gas hydrates, respectively. The high-pressure methane gas is used to simulate the intrusion of gas from natural gas hydrate decomposition onto the cement sheath and the interface between the two surfaces. The formation water is prepared by adding salts of different mineralization levels according to the experimental environmental simulation requirements, and is used to simulate the intrusion of formation fluids onto the cement sheath and the interface between the two surfaces. The formation water storage tank can be encased in a temperature control jacket to regulate the formation water temperature through heating or cooling. The acidic corrosive fluid can refer to an acidic fluid containing carbon dioxide or sulfur dihydrogen hydride and possessing corrosive properties, used to simulate the chemical corrosion environment after the decomposition of natural gas hydrates. The acidic fluid storage tank can be made of corrosion-resistant materials, such as nickel-based corrosion-resistant alloys, and is also equipped with a pressure balancing device.

[0041] A gas flow controller is installed on the gas pipeline between the methane gas storage tank and the fluid switching valve assembly 330 to precisely control the injection rate of methane gas. For example, the flow rate range of the gas flow controller can typically be set to 0-500 ml / min, and the control accuracy can typically be set to ±1%. Optionally, a pressure reducing valve can also be installed on the gas pipeline between the methane gas storage tank and the gas flow controller to reduce and stabilize the pressure of the high-pressure methane gas in the storage tank. This adjusts the pressure of the high-pressure gas source in the storage tank to the rated inlet pressure required for the normal operation of the gas flow controller, preventing excessively high or fluctuating gas source pressure from affecting the control accuracy of the gas flow controller and ensuring stable and reliable flow control.

[0042] By specifically configuring multiple fluid storage tanks as methane gas tanks, formation water tanks, and acidic fluid tanks, the main single-phase fluids generated by the decomposition of natural gas hydrates can be accurately stored, closely matching the actual fluid composition characteristics in the well. This allows for the separate storage and precise supply of each fluid component. The deployment of gas flow controllers can precisely control the injection rate of methane gas, avoiding imbalances in the multiphase flow composition caused by excessively fast or slow methane gas injection, thereby improving the accuracy of multiphase fluid simulation. The acidic corrosive fluid stored in the acidic fluid tanks can realistically simulate the chemical corrosion environment after the decomposition of natural gas hydrates, avoiding deviations between the experimental conditions and the actual downhole environment due to the lack of acidic corrosion simulation. This more realistically reflects the corrosive effect of acidic fluids on the cement sheath and the interface, further enhancing the realism and comprehensiveness of multiphase flow simulation. This provides more realistic fluid composition and corrosion environment support for evaluating the damage and self-repair effect of the cement sheath and the interface, ensuring the scientific validity and reliability of the evaluation results.

[0043] Optionally, the multiphase flow control unit 300 also includes a pH sensor, which is installed in the outlet pipe of the annular simulation unit 100 and is used to monitor the pH value of the multiphase flow emanating from the annular simulation unit 100.

[0044] In the structural layout of the multiphase flow control unit 300, a pH sensor can be added. The pH sensor is installed at the outlet pipe of the annular simulation unit 100, allowing the multiphase flow seeping from the annular simulation unit 100 to pass through the pH sensor. The pH sensor can monitor the acidity / alkalinity information of the seeping multiphase flow in real time. The monitored acidity / alkalinity information can characterize the acidity / alkalinity changes after the multiphase flow interacts chemically with the cement ring and the interface, indirectly reflecting the degree of corrosion of the cement ring and interface by the acidic fluid, the chemical response of the repair material, and the dynamic changes in fluid characteristics during the self-healing process of the cement ring. This can compensate for the deficiency of monitoring only conductivity, which cannot comprehensively reflect the fluid corrosion characteristics. The acidity / alkalinity information can serve as a parameter or quantitative indicator for evaluating the self-healing effect of the cement ring and interface.

[0045] Optionally, the multiphase flow control unit 300 also includes a back pressure regulating valve, which is installed in the outlet pipeline of the annular simulation unit 100 and is used to regulate the pressure fluctuation range within the annular simulation unit 100.

[0046] In the multiphase flow control unit structure 300 layout, a back pressure regulating valve is installed at the outlet position of the annular simulation unit. Through the regulating function of the back pressure regulating valve, it can respond to the pressure changes inside the annular simulation unit 100 in real time. By adjusting the valve opening, the flow rate of fluid flowing out of the annular simulation unit 100 is controlled, thereby regulating the pressure inside the annular simulation unit 100 and keeping the pressure within a preset fluctuation range. This can avoid large pressure fluctuations caused by multiphase flow injection, ensuring that the pressure inside the annular simulation unit 100 always matches the actual pressure conditions during the decomposition of natural gas hydrates during multiphase fluid injection and testing. This can reduce the interference of frequent or large pressure fluctuations on the cement sheath and the two-interface damage evolution and self-repair process.

[0047] Based on any of the above embodiments, optionally, the in-situ monitoring unit 400 includes a fiber optic grating monitoring subunit, an acoustic emission monitoring subunit, and an ultrasonic monitoring subunit; wherein: The fiber Bragg grating monitoring subunit includes a fiber Bragg grating sensor 411 and a fiber Bragg grating demodulator 412. The fiber Bragg grating sensor 411 is arranged inside the annular simulation unit 100. The fiber Bragg grating demodulator 412 is used to transmit optical signals to the fiber Bragg grating sensor 411 and receive the optical signals reflected by the fiber Bragg grating sensor 411. The fiber Bragg grating demodulator 412 is also used to calculate the strain distribution and temperature change of the cement ring and the two interfaces in real time based on the received optical signals. The acoustic emission monitoring subunit includes an acoustic emission sensor 421 and an acoustic emission acquisition card 422; the acoustic emission sensor 421 array is attached to the outer wall of the formation core 130, and the acoustic emission acquisition card 422 is used to receive acoustic emission signals and perform feature extraction based on the acoustic emission signals; The ultrasonic monitoring subunit includes an ultrasonic pulse excitation source, a first transducer, a second transducer, and an ultrasonic acquisition card 431. The ultrasonic pulse excitation source is used to output an electrical pulse signal. The first transducer is installed inside the sealing cap 140 at the inlet end of the annular simulation unit 100 and is used to transmit ultrasonic signals into the cement ring 120 according to the electrical pulse signal. The second transducer is installed inside the sealing cap 140 at the outlet end of the annular simulation unit 100 and is used to receive the ultrasonic signal after penetrating the cement ring 120 and convert the received ultrasonic signal into an electrical signal for output. The ultrasonic acquisition card 431 is used to acquire the electrical signal output by the second transducer and obtain the acoustic response characteristics of the cement ring 120 based on the electrical signal.

[0048] The in-situ monitoring unit 400 consists of a fiber optic grating monitoring subunit, an acoustic emission monitoring subunit, and an ultrasonic monitoring subunit. The three work together to achieve comprehensive monitoring of the state of the cement ring and the two interfaces within the annular simulation unit 100.

[0049] Specifically, the fiber Bragg grating monitoring subunit is installed within the annular simulation unit 100 using a fiber Bragg grating sensor 411 to sense the strain distribution and temperature changes of the cement ring and the two interfaces. The fiber Bragg grating sensor 411 is encapsulated with a corrosion-resistant material and has good temperature adaptability. For example, after encapsulation, the fiber Bragg grating sensor 411 can adapt to a wide temperature range from -30 degrees Celsius to 150 degrees Celsius. In the fiber Bragg grating monitoring subunit, a fiber Bragg grating demodulator 412 emits optical signals, receives reflected optical signals, and calculates the center wavelength drift of the fiber Bragg grating sensor 411 in real time. Based on the center wavelength drift of the fiber Bragg grating sensor 411, physical quantities such as strain and temperature can be obtained to evaluate the self-repair status of the cement ring and the two interfaces. The sampling frequency and wavelength resolution of the fiber Bragg grating demodulator 412 can be set according to the accuracy requirements of the experimental data. For example, the sampling frequency of the fiber Bragg grating demodulator 412 can be set to no less than 100 Hz, and the wavelength resolution can be set to no more than 1 picometer.

[0050] See Figure 4 The purple dashed lines indicate the transmission direction of various signals. The acoustic emission monitoring subunit is attached to the outer wall of the formation core 130 via an array of acoustic emission sensors 421. It can capture elastic wave signals generated by cement sheath damage, and the acoustic emission acquisition card 422 receives the signals and extracts features. Each acoustic emission sensor is equipped with an independent shielded cable, providing good anti-interference capability. The acoustic emission acquisition card 422 can be a multi-channel synchronous acquisition card, used to receive acoustic emission signals, perform analog-to-digital conversion and waveform recording, and extract features from the processed acoustic emission signals to analyze the evolution and self-repair of cement sheath and interface damage. The evolution and self-repair of cement sheath and interface damage can refer to the initiation time of microcracks, the location of microcracks, the progress of microcrack propagation, and the progress of microcrack repair. The acoustic emission acquisition card 422 supports continuous waveform acquisition and feature parameter extraction. The acquisition parameters can be set according to the accuracy requirements of the experimental data. For example, the sampling rate of the acoustic emission acquisition card 422 can be set to not less than 10 MHz.

[0051] Optionally, acoustic emission sensors 421 can be arranged in a circumferential and axially layered staggered manner along the core of the formation. This can form a three-dimensional spatial positioning array of acoustic emission sensors 421. The three-dimensional spatial positioning array can realize the three-dimensional spatial positioning of the sound source of internal damage and debonding fracture of the cement sheath and the two-interface, thereby improving the accuracy of locating the damage of the cement sheath and the two-interface.

[0052] Optionally, the acoustic emission monitoring subunit also includes an acoustic emission signal amplifier. The acoustic emission signal amplifier receives and amplifies the elastic wave signal captured by the acoustic emission sensor 421, and sends the amplified elastic wave signal to the acoustic emission acquisition card 422. The acoustic emission signal amplifier is connected between the acoustic emission sensor 421 and the acoustic emission acquisition card 422, and can amplify the weak elastic wave signal captured by the acoustic emission sensor 421. The configuration parameters of the acoustic emission signal amplifier can be set according to the accuracy requirements of the experimental data. For example, the adjustable gain range of the acoustic emission signal amplifier can be set to 20-60 dB, and the bandwidth matching sensor frequency range can be set to 100-800 kHz.

[0053] The ultrasonic monitoring subunit includes an ultrasonic pulse excitation source, a first transducer, a second transducer, and an ultrasonic acquisition card 431. The ultrasonic pulse excitation source is used to output an electrical pulse signal. The first transducer is installed inside the sealing cap 140 at the inlet end of the annular simulation unit 100 and is used to transmit ultrasonic signals into the cement ring 120 according to the electrical pulse signal. The second transducer is installed inside the sealing cap 140 at the outlet end of the annular simulation unit 100 and is used to receive the ultrasonic signal after penetrating the cement ring 120 and convert the received ultrasonic signal into an electrical signal for output. The ultrasonic acquisition card 431 is used to acquire the electrical signal output by the second transducer and obtain the acoustic response characteristics of the cement ring 120 based on the electrical signal.

[0054] The ultrasonic monitoring subunit outputs an electrical pulse signal through an ultrasonic pulse excitation source. The first transducer inside the sealing cap at the inlet end of the annular simulation unit 100 converts the received electrical pulse signal into an ultrasonic signal and transmits it to the cement ring 120. The second transducer inside the sealing cap at the outlet end of the annular simulation unit 100 receives the ultrasonic signal after it penetrates the cement ring 120 and converts it into an electrical signal. The ultrasonic acquisition card 431 then acquires this electrical signal and obtains the acoustic response characteristics of the cement ring 120. (See also...) Figure 4 The ultrasonic pulse excitation source, the first transducer, and the second transducer can be implemented using an ultrasonic probe 432 that integrates electrical pulse transmission, ultrasonic transmission / reception, and signal conversion functions.

[0055] Specifically, the ultrasonic acquisition card 431 has high-speed analog-to-digital conversion and waveform storage functions. Based on the converted signal and waveform information, it calculates parameters such as sound velocity and amplitude attenuation in real time. The damage of the cement ring and the two interfaces can be analyzed based on the calculated parameters. The configuration parameters of the ultrasonic acquisition card 431 can be set according to the accuracy requirements of the experimental data. For example, the sampling rate of the ultrasonic acquisition card 431 can be set to not less than 50 MHz.

[0056] The first transducer is installed inside the sealing cap 140 at the inlet end of the annular simulation unit 100. It is used to transmit longitudinal or transverse ultrasonic signals into the cement ring 120 according to the electrical pulse signal. For example, the center frequency of the ultrasonic signal emitted by the first transducer is typically selectable in the range of 200 kHz to 1 MHz. The second transducer is installed inside the sealing cap 140 at the outlet end of the annular simulation unit 100. The second transducer is used to receive the ultrasonic signal after penetrating the cement ring 120 and convert the received ultrasonic signal into an electrical signal for output. The second transducer and the first transducer constitute a transmission scanning mode, which can improve the completeness of capturing the damage of the cement ring and the two interfaces. Since the inner sleeve 110, cement ring 120 and formation core 130 in the annular simulation unit 100 are coaxially nested from the inside to the outside to form an annular structure, and both ends of the annular structure are equipped with sealing caps 140, the annular simulation unit 100 has a symmetrical structure at both ends. The inlet and outlet ends of the annular simulation unit 100 are merely functional definitions of the fluid injection and outflow ends. The annular simulation unit 100 itself does not distinguish or limit fixed inlet and outlet ends. Any end of the annular simulation unit 100 can be used as the inlet end and the other end as the outlet end. In a single evaluation process, it is sufficient to keep the settings of the inlet and outlet ends consistent.

[0057] Optionally, the ultrasonic pulse excitation source can receive a programmed control signal and adjust the pulse voltage, pulse width, and repetition frequency based on the programmed control signal to adapt to the acoustic characteristics of different formation cores and cement sheaths; wherein the programmed control signal can be issued by the data acquisition and control unit 500. For example, the pulse voltage of the ultrasonic pulse excitation source is typically configured to 100-500 volts. The ultrasonic pulse excitation source can also have internal signal reception, synchronous triggering, and self-testing functions, which can be used to establish an ultrasonic emission time reference.

[0058] The in-situ monitoring unit 400, through online collaborative monitoring of multiple sub-units, eliminates the need to disassemble the annular simulation unit 100. It enables real-time, comprehensive monitoring of the cement ring and its interface during damage evolution and self-healing. The fiber optic grating monitoring sub-unit accurately captures strain and temperature changes, promptly determining the state changes of the cement ring and its interface. The acoustic emission monitoring sub-unit captures signals generated by cement ring damage, accurately extracting damage characteristics. The ultrasonic monitoring sub-unit reflects the density and structural integrity of the cement ring through penetrating monitoring. These three sub-units complement each other, avoiding the limitations of single monitoring methods. Furthermore, the monitoring data from each sub-unit can corroborate each other, ensuring the accuracy and comprehensiveness of the monitoring results. This provides rich and reliable data support for evaluating the self-healing effect of the cement ring, improving the objectivity and accuracy of the self-healing evaluation.

[0059] Optionally, based on any of the above embodiments, the fiber optic grating sensor 411 may be pre-embedded at least in one of the following locations: the outer wall of the inner sleeve 110, the inner wall of the cement ring 120, the interior of the cement ring 120, the outer wall of the cement ring 120, and the inner wall of the stratum core 130.

[0060] The inner wall can refer to the side wall of each annular component closest to the central axis of the annular simulation unit 100, and the outer wall can refer to the side wall of each annular component away from the central axis of the annular simulation unit 100. Each annular component refers to the inner sleeve 110, cement ring 120, and formation core 130 in the annular simulation unit 100. Specifically, during the assembly of the annular simulation unit 100, fiber optic grating sensors 411 can be pre-embedded. The pre-embedded position of the fiber optic grating sensors 411 should be selected from at least one of the following locations: the outer wall of the inner sleeve 110, the inner wall of the cement ring 120, the interior of the cement ring 120, the outer wall of the cement ring 120, and the inner wall of the formation core 130. This allows the fiber optic grating sensors 411 to directly contact the monitoring parts, so as to fully sense the strain distribution and temperature changes of each monitoring part during the experiment, and provide real and direct optical signal feedback for the fiber optic grating demodulator 412, thereby realizing accurate in-situ monitoring of the state of the cement ring and related interfaces.

[0061] If the fiber Bragg grating sensor 411 is embedded in the outer wall of the inner sleeve 110 or the inner wall of the cement ring 120, it is equivalent to the fiber Bragg grating sensor 411 being located at an interface. The fiber Bragg grating sensor 411 can directly monitor the state changes of the interface and the inner wall of the cement ring. (See [link to relevant documentation]). Figure 5 This demonstrates the situation where the fiber optic grating sensor 411 is pre-embedded in the outer wall of the inner sleeve 110.

[0062] If the fiber Bragg grating sensor 411 is embedded inside the cement ring 120, it can directly monitor changes in the state of the cement ring. In this case, the causes of these changes include strain and damage to the cement ring itself, changes in the stress state of the cement ring due to damage or failure of the cementing interface between the cement ring and the adjacent medium, and the combined effect of damage to the cement ring itself and failure of the cementing interface. The specific causes of these changes need to be analyzed and determined in conjunction with data from other monitoring subunits. (See [reference needed]). Figure 6 This demonstrates the situation where the fiber optic grating sensor 411 is embedded inside the cement ring 120.

[0063] If the fiber optic grating sensor 411 is embedded in the outer wall of the cement ring 120 or the inner wall of the stratum core 130, it is equivalent to the fiber optic grating sensor 411 being located at the two interfaces. The fiber optic grating sensor 411 can directly monitor the state changes of the outer wall of the cement ring and the two interfaces.

[0064] Optionally, if a mud cake layer 150 is configured between the cement sheath 120 and the formation core 130 in the annular simulation unit 100, the fiber Bragg grating sensor 411 can also be pre-embedded in the mud cake layer 150. If the fiber Bragg grating sensor 411 is embedded in the mud cake layer 150, it can directly monitor the state changes of the mud cake layer and the two interfaces; if the fiber Bragg grating sensor 411 is arranged on the inner wall of the mud cake layer 150, it can directly monitor the state changes of the mud cake layer, the outer wall of the cement sheath, and the two interfaces; if the fiber Bragg grating sensor 411 is arranged on the outer wall of the mud cake layer 150, it can directly monitor the state changes of the mud cake layer and the two interfaces. See also Figure 7 This demonstrates the case where the fiber optic grating sensor 411 is embedded in the mud cake layer 150.

[0065] In this embodiment, during the assembly of the annular simulation unit 100, fiber Bragg grating sensors 411 can be pre-embedded in multiple locations to improve the accuracy of condition monitoring, or to simultaneously monitor condition changes at one interface, the cement ring, and the second interface. For example, see... Figure 8 This demonstrates the situation where fiber optic grating sensors 411 are pre-embedded in the inner wall of cement ring 120, inside cement ring 120, and inner wall of formation core 130. In this example, by deploying fiber optic grating sensors at multiple pre-embedded locations, the state changes at one interface, cement ring, and two interfaces can be monitored simultaneously.

[0066] Optionally, based on any of the above embodiments, the data acquisition control unit 500 includes a data acquisition processor 510, a computer control terminal 520, and a data storage server 530; wherein: The data acquisition processor 510 is used to synchronously acquire various signals generated in the annular simulation unit 100, the multiphase flow control unit 300 and the in-situ monitoring unit 400, and process the acquired signals to obtain first data. The first data is used to indicate the real-time damage status and self-healing effect of the cement ring and the two interfaces. Data storage server 530 is used to store various signals and initial data; The computer control terminal 520 is used to control each unit to automatically perform corresponding functional operations and to display the first data in real time; the computer control terminal 520 is also used to generate a self-healing effect evaluation report of the cement ring and the second interface based on the information stored in the data storage server 530.

[0067] Specifically, the data acquisition processor 510 has a built-in time synchronization module. The data acquisition processor 510 is used to synchronously acquire various signals generated by the annular simulation unit 100, the multiphase flow control unit 300, and the in-situ monitoring unit 400. The acquired signals are processed by alignment, filtering, feature extraction, etc., to obtain various parameter information. The processed various parameter information is fused and analyzed to generate first data. The first data can intuitively reflect the real-time damage and self-repair effect of the cement ring and the second interface. Among them, the various parameter information can refer to the information acquired by each unit that can reflect the real-time damage and self-repair effect of the cement ring and the second interface. For example, various parameter information may include the permeability of the cement ring 120 and the volume of the leakage fluid in the cement ring body and the two interfaces obtained by the annular simulation unit 100; the pH value and conductivity of the multiphase flow emanating from the annular simulation unit 100 obtained by the multiphase flow control unit 300; and the fiber grating information, acoustic emission information, and ultrasonic information obtained by the in-situ monitoring unit 400. Among these, the fiber grating information may refer to physical quantities such as strain and temperature that have undergone demodulation and conversion processing; the acoustic emission information may refer to the three-dimensional damage location information and / or waveform characteristic information that have undergone signal processing; and the ultrasonic information may refer to the acoustic parameter information that has been obtained through inversion calculation processing.

[0068] The data storage server 530 is used to store all monitoring signals and initial data, which can ensure that the data is not lost and is traceable. Based on the time-series stored initial data, the system can analyze the damage evolution and self-healing process of the cement ring and the two interfaces.

[0069] The computer control terminal 520 can have a built-in programmable controller; the programmable controller can generate multiple program control signals according to a preset control program, and send the corresponding program control signals to each unit in the device according to the timing and process sequence specified by the preset program; after receiving the program control signals, each unit executes the corresponding matching function operation. For example, the programmed controller can sequentially execute the following control flow according to a preset program: First, control the temperature and pressure control unit 200 to perform a temperature drop condition; after the temperature drop condition has been running for a first preset duration, control the temperature and pressure control unit 200 to inject high-pressure methane gas into the annular simulation unit 100 to simulate the formation pressure impact; after the internal temperature of the annular simulation unit 100 drops to a preset temperature threshold, maintain a constant temperature state; after the internal pressure rises to a preset pressure threshold, maintain a stable pressure state; after completing the constant temperature and stable pressure, the programmed controller controls the multiphase flow control unit 300 to mix the multiphase fluid through the fluid switching valve group 330, and starts the multiphase flow pump 320 to inject multiphase fluid into the annular simulation unit 100; after the multiphase fluid has been continuously injected for a second preset duration, control the temperature and pressure control unit 200 to stop the active cooling and high-pressure methane gas injection, so that the annular simulation unit 100 enters a natural temperature recovery and natural pressure recovery state, and at the same time shuts down the multiphase flow pump 320, thereby triggering the self-healing reaction of the cement ring and the two interfaces inside the annular simulation unit 100. Optionally, a preset program is used to implement dynamic coupling loading of multiphysics fields to simulate the complex environment of actual downhole. The preset program can refer to the level code written in a programming language, or it can refer to the experimental procedure indicated by curves containing temperature, pressure and multiphase flow injection timing.

[0070] The computer control terminal 520 may be equipped with a display; the display is used to visualize the first data output by the data acquisition processor 510 in real time, and can also retrieve and display historical monitoring data stored in the data storage server 530, and can display a comprehensive evaluation report on the self-repair effect of the cement sheath and the second interface. The comprehensive evaluation report on the self-repair effect of the cement sheath and the second interface can be generated by the computer control terminal 520 after comprehensively analyzing and processing the multi-source monitoring information stored in the data storage server 530. Optionally, the comprehensive evaluation report on the self-repair effect of the cement sheath and the second interface includes the original data source, analysis conclusions, and evaluation indicators; wherein, the original data source is the original monitoring signal and first data stored in the data storage server 530; the analysis conclusion is the qualitative and quantitative comprehensive evaluation result of the self-repair effect of the cement sheath and the second interface obtained based on the original data source; the evaluation indicators are the parameter categories and corresponding parameter thresholds and parameter values ​​used to construct the analysis conclusions. Optionally, based on the comprehensive evaluation results of the self-repair effect of the cement sheath and the second interface, decision support and risk assessment can be provided for subsequent oil and gas well development and the research and development of self-repairing cement systems.

[0071] Based on any of the above embodiments, optionally, the data acquisition processor 510, according to various synchronously acquired signals, outputs a damage evolution cloud map, crack location results, and repair progress curve of the cement ring and the second interface through a built-in damage localization algorithm and a self-repair effect evaluation model; the damage localization algorithm is an algorithm that inverts the three-dimensional spatial distribution and expansion characteristics of cracks in the cement ring and the second interface based on the acoustic emission three-dimensional array signal monitored by the acoustic emission monitoring subunit; the self-repair effect evaluation model is a model used to quantitatively characterize the self-repair effect of the cement ring and the second interface based on the acoustic response characteristics of the cement ring monitored by the ultrasonic monitoring subunit, the conductivity of the multiphase flow exudated from the annular simulation unit 100 monitored by the conductivity sensor 340, and the acoustic emission three-dimensional array signal monitored by the acoustic emission monitoring subunit; the damage evolution cloud map is used to visually display the spatial distribution of damage in the entire cement ring and the second interface; the crack location results are used to determine the three-dimensional spatial location information of cracks in the cement ring and the second interface; the repair progress curve is used to dynamically characterize the evolution law of damage repair of the cement ring and the second interface over time.

[0072] Specifically, the data acquisition processor 510 first receives various signals, such as the acoustic emission three-dimensional array signal from the acoustic emission monitoring subunit, the acoustic characteristic signal of the cement ring from the ultrasonic monitoring subunit, and the fluid conductivity signal from the conductivity sensor 340. Then, through the built-in damage localization algorithm, it analyzes and inverts the acoustic emission three-dimensional array signal to determine the spatial distribution and propagation characteristics of the cement ring and the two-interface cracks, and obtains the crack localization result. At the same time, through the built-in self-healing effect evaluation model, it integrates multiple types of data, such as the acoustic response characteristics of the cement ring, the conductivity of the exudate fluid, and the acoustic emission three-dimensional signal, to quantitatively evaluate the self-healing effect. Finally, the data acquisition processor 510 outputs the corresponding damage evolution cloud map, crack localization result, and repair process curve, which are displayed by the computer control terminal 520. The damage evolution cloud map, crack localization result, and repair process curve can respectively realize the visualization of damage distribution, the precise location of cracks, and the dynamic presentation of the repair process.

[0073] For example, Figure 9 The data acquisition and control unit 500 synchronously acquires various signals generated by the in-situ monitoring unit 400, ensuring that the acquisition of various signals is based on a unified time reference. The acquired signals are processed and analyzed, and damage location results and repair progress curves are output.

[0074] The technical solution of this invention, by configuring the annular simulation unit as a coaxially nested annular structure of inner casing, cement sheath, and formation core from the inside out, can simulate the annular structure between the casing, cement sheath, and formation. A sealing cap seals the ends of the annular structure to ensure the airtightness of the simulation environment, thereby improving the accuracy of simulating the cement sheath body and the bonding state of the two interfaces. The cement sheath is a cementing cement sheath with added self-healing materials, capable of simulating the self-healing effect of the cementing cement sheath. By applying combined temperature and pressure to the annular simulation unit through a temperature and pressure control unit, the dynamic temperature and pressure changes during the decomposition of natural gas hydrates can be simulated, enabling the annular simulation unit to simulate thermal stress cracks caused by the decomposition of natural gas hydrates, thus improving the accuracy of simulating the bonding state of the cement sheath body and the two interfaces. The multiphase flow control unit can inject multiphase flow generated by the decomposition of natural gas hydrates into the annular simulation unit. Multiphase fluid simulation can model the intrusion and chemical corrosion of cement sheaths and interfaces by multiphase fluids. Through multiphysics coupling, the simulated environment more closely resembles actual working conditions, improving the realism of cement sheath and interface damage simulation and thus enhancing the accuracy of simulating the self-healing behavior of cement sheaths and interfaces. In-situ monitoring units enable non-destructive online monitoring of the cement sheath and interfaces, continuously capturing dynamic information throughout the damage evolution and self-healing process. This avoids offline detection that damages the sample structure and loses key process data, thus improving the completeness and timeliness of monitoring data. Data acquisition and control units enable sequential coordinated control and data fusion processing of each unit, unifying the experimental process and integrating multi-dimensional monitoring information. This avoids asynchronous actions and data fragmentation between units, thereby improving the accuracy and automation level of evaluating the self-healing effect of cement sheaths and interfaces. Based on the above technical solutions, by simulating the annular structure between the casing, cement sheath, and formation, as well as the complex working environment under the decomposition conditions of natural gas hydrates, the realism of the simulation of cement sheath and interface damage can be improved. Furthermore, by conducting in-situ dynamic monitoring of the entire self-repair process of the cement sheath and interface, the technical problems of insufficient accuracy in evaluating the self-repair effect of cement sheath and interface, and the difficulty in systematically analyzing the dynamic evolution law of self-repair can be solved. This can improve the experimental verification capability of evaluating the damage evolution and self-repair effect of cement sheath and interface, thereby enhancing the reliability and efficiency of research on the long-term sealing integrity of natural gas hydrate wells, the development of self-repairing cementing materials, and the performance evaluation of engineering applications.

[0075] The following is an exemplary description of the method for evaluating the self-repair effect of cementing sheath and two-interface self-repair effect using the cementing sheath and two-interface self-repair effect evaluation device provided in any embodiment of the present invention, but it is not intended to limit the present invention.

[0076] Figure 10This is a schematic diagram of the execution logic of a method for evaluating the self-healing effect of cementing sheath and two interfaces provided in an embodiment of the present invention. First, an annular simulation unit suitable for simulating the cementing process is assembled based on the characteristics of the well to be evaluated. Then, a temperature and pressure control unit is used to simulate the cooling process of natural gas hydrate decomposition, followed by high-pressure impact. Subsequently, a multiphase flow control unit injects multiphase flow to simulate multiphysics coupling. By executing the above steps, the complex environment under actual working conditions is simulated, allowing the cement sheath and interface in the annular simulation unit to reproduce damage conditions such as microcracks. Then, the self-healing behavior of the cement sheath and interface is triggered by pressure fluctuations or temperature changes, such as activating responsive materials or causing microcapsule rupture. The self-healing process of the cement sheath and interface can be monitored in real time by an in-situ monitoring unit. Combined with parameters such as temperature, pressure, and permeability obtained from other units, the self-healing effect of the cement sheath and interface can be analyzed to generate an evaluation report. In addition, based on the evaluation report, adjustments can be made to the self-healing materials, formation cores, and dimensions. The influence of formation stiffness and self-healing material type on the self-healing effect of the cement sheath and interface can be analyzed. The trigger threshold of self-healing behavior can also be analyzed, providing optimization directions for cementing quality evaluation and the development of self-healing cement systems.

[0077] For example, when using the cementing sheath and two-interface self-healing effect evaluation device provided in any embodiment of the present invention to evaluate the entire process of damage repair of self-healing microcapsule cement sheath in sandstone formation, the annulus simulation unit is first assembled. API standard P110 grade steel inner casing, G-grade oil well cement sheath with added self-healing microcapsules, and artificially compacted sandstone formation core are selected. A mud cake layer simulation sheet is placed between the cement sheath and the formation core. High-pressure sealing is achieved through a stainless steel sealing cap with double O-ring seals. Pressure and temperature sensors are installed at the annulus inlet and outlet, and a leakage collection and measurement device is connected. Subsequently, a multi-dimensional in-situ monitoring network is deployed outside the inner casing. A fiber optic strain-temperature composite sensor is pre-embedded inside the wall and cement annulus. A three-dimensional array of acoustic emission sensors is arranged on the outer wall of the formation core. An ultrasonic transducer is embedded in the center of the upper and lower sealing caps. Each sensor is connected to a demodulator, amplifier, and acquisition card. Then, the functional units are connected. The low-temperature constant temperature bath, phase change fluid circulation pump, and annulus outer jacket are connected to form a temperature control loop. The high-pressure methane cylinder and precision pressure controller are connected to the annulus to form a pressure loading loop. The multiphase flow pump, fluid switching valve group, various fluid storage tanks, fluid temperature controller, online pH and conductivity sensors, and back pressure regulating valve are sequentially connected to form a multiphase flow simulation loop. All acquisition devices are connected to a unified interface. The data acquisition and control unit is networked with a computer control terminal and a data storage server. The experiment is automatically executed by a programmed control module. First, the annular simulation unit is evacuated, reverse-saturated with formation water, and allowed to stabilize. Baseline acquisition is completed under set initial temperature and pressure conditions. Next, the decomposition of natural gas hydrates is simulated by rapidly cooling the cryogenic constant temperature bath while applying linear pressure shocks to simulate the endothermic and gas expansion effects of natural gas hydrate decomposition. Subsequently, the cryogenic and high-pressure conditions are maintained, and simulated formation water containing carbon dioxide and saturated methane is injected to simulate multiphase flow intrusion and acid corrosion. Online sensors monitor the chemical parameters of the outlet fluid in real time. Afterward, cooling and fluid injection are stopped. The system is allowed to naturally recover and enter the self-repair phase. The data acquisition and control unit synchronously acquires fiber optic grating strain temperature, acoustic emission waveform and location data, ultrasonic velocity and attenuation, inlet and outlet temperature and pressure, pH, conductivity and cumulative leakage throughout the process using a unified time base. All data are displayed and stored in real time. Finally, based on multi-source monitoring data, the location of crack initiation and propagation is identified, and the self-repair process is dynamically tracked. The repair efficiency is quantitatively evaluated through data on permeability changes, strain recovery, sound velocity recovery, conductivity evolution and leakage. This fully realizes the in-situ monitoring, dynamic characterization and scientific evaluation of the damage evolution and self-repair effect of cement sheath and two-interface under the multi-field coupling condition of natural gas hydrate decomposition.

[0078] Specifically, by monitoring data changes, damage to the cement sheath and the interface can be identified and located. For example, during the rapid temperature drop phase, the acoustic emission event rate rises sharply from the background value, reaching a peak of 180 acoustic emission events per minute when the temperature drops to -15 degrees Celsius. The background value is the baseline acoustic emission event rate measured under the original environmental conditions, which is usually the upper limit of the acoustic emission event rate caused by noise, such as 5 acoustic emission events per minute. The three-dimensional localization results of acoustic emission show that the acoustic emission events are concentrated in the circumferential region in the middle of the cement sheath and at the interface between the cement sheath and the mud cake layer. Therefore, it can be assumed that the microcracks induced by thermal stress first originated at the location where the acoustic emission events were concentrated. Furthermore, the circumferential tensile strain exceeding 600 με was monitored by the fiber optic grating sensor embedded in the middle of the cement ring, which is consistent with the acoustic emission location results. The fiber optic grating sensor on the outer wall of the inner sleeve monitored a non-uniform strain distribution, which indicates that the bonding state of the two interfaces has changed. The ultrasonic monitoring results show that the longitudinal wave velocity decreased from the initial 3200 m / s to 2950 m / s, a decrease of about 8%, and the attenuation of the sound wave amplitude increased, which can be considered as the generation of a microcrack network within the cement ring.

[0079] The self-healing process can be dynamically monitored by monitoring data changes. For example, after entering the natural warming stage, as the temperature gradually rises to about 30°C, acoustic emission activity decreases significantly, and the acoustic emission event rate drops to less than 20 times per minute within 24 hours. Fiber grating monitoring shows that the tensile strain in the damaged area begins to recover slowly. After 48 hours, the strain value drops to within ±150με, and after 72 hours, it further recovers to within ±50με, indicating that the crack is gradually closing. The ultrasonic velocity rises to 3150m / s after 72 hours, recovering to 98% of the initial value, and the attenuation of the acoustic amplitude is also significantly reduced.

[0080] By monitoring data changes, the self-healing effect of the cement ring and the two interfaces can be quantitatively evaluated. For example, after the experiment, the cumulative leakage was recorded by a leakage collection and measurement device, and the gas permeability of the repaired cement ring was calculated. Compared with the permeability after damage, it was significantly reduced. The gas permeability of the cement ring can be tested with nitrogen, while the permeability after damage can be calculated by measuring the pressure difference of the annular simulation unit. Data from the online conductivity sensor showed that the conductivity increased slightly in the early stage of the self-healing phase, which can indicate the release of the repair agent. Subsequently, it gradually decreased and tended to stabilize, indicating that the ion dissolution was reduced after the cracks healed. After the experiment, the cement ring was removed and subjected to micro-CT scanning. The results were compared with the acoustic emission three-dimensional localization results, which confirmed that the main cracks were effectively filled by the repair agent.

[0081] By employing the cementing sheath and two-interface self-healing effect evaluation device provided in any embodiment of the present invention, the coupling effect of temperature drop and pressure shock during the decomposition process of natural gas hydrate can be simulated and reproduced. The combined application of fiber optic grating and acoustic emission can realize real-time positioning and monitoring of the entire process of crack initiation, propagation and repair. Furthermore, the repair efficiency of the self-healing microcapsule cement sheath can be quantitatively evaluated by indicators such as permeability. The synchronous acquisition and correlation analysis of multiple physical field parameters can be realized, thus providing rich data support for the study of self-healing mechanism.

[0082] For example, when studying the influence of different formation stiffness on the damage and self-repair behavior of the two-interface using the cementing sheath and two-interface self-repair effect evaluation device provided in any embodiment of the present invention, the annulus simulation unit is first assembled. High-stiffness, high-strength cement-synthetic rock core and low-stiffness artificially compacted mudstone are selected as formation rock cores, respectively. The same specification inner casing and cement sheath with added self-repair microcapsules are matched. The mud cake layer is removed to form a clean contact interface and the sealing cap is assembled. Then, fiber optic strain-temperature composite sensors, acoustic emission sensor arrays and ultrasonic transducers are deployed according to standards to construct a multi-dimensional in-situ monitoring network. Then, the temperature and pressure control unit, multiphase flow control unit, in-situ monitoring unit and data acquisition control unit are connected by pipelines and circuits to ensure the consistency of test conditions. The entire test process is automatically executed by programmed control. First, the annulus simulation unit is evacuated, reverse-saturated with formation water and allowed to stand still and stabilize. The uniform initial temperature and pressure are set to complete the baseline acquisition. Then, the natural gas hydrate decomposition working condition simulation is carried out. The proposed method involves a rapid temperature drop in a cryogenic constant-temperature bath, while simultaneously applying matched pressure impact loads to formations of varying stiffness to prevent core damage. Subsequently, while maintaining these temperature and pressure conditions, simulated formation water containing carbon dioxide and saturated methane is injected to simulate multiphase flow intrusion and acid corrosion. The outlet fluid status is monitored in real-time by online pH and conductivity sensors. Cooling and fluid injection are then stopped, allowing the system to naturally recover and enter the self-healing phase. The data acquisition and control unit synchronously collects multi-source signals throughout the process, including fiber optic gratings, acoustic emission, ultrasound, temperature and pressure, pH, conductivity, and leakage. Finally, based on the collected data, comparative analysis is conducted on the damage modes, self-healing responses, leakage changes, and chemical parameter evolution of the cement sheath and interface under formations of different stiffness. This quantitatively reveals the influence mechanism of formation stiffness on damage evolution and self-healing efficiency, enabling precise evaluation of the self-healing effect of cement sheaths and interfaces under different formation conditions. This provides experimental basis for the engineering adaptability screening and formulation optimization of self-healing cementing materials.

[0083] Specifically, by monitoring changes in data, the influence of different formation stiffness on the damage modes of the cement sheath and the interface can be analyzed. For example, for high-stiffness formations, acoustic emission events are mainly concentrated in two regions: one is the middle of the cement sheath, usually with circumferential cracks, and the other is near the interface between the cement sheath and the formation core. Acoustic emission events at the interface account for about 40% of the total, indicating that the high-stiffness formation exerts strong radial constraint on the cement sheath, which may lead to shear slip and micro-gap at the interface under thermo-mechanical coupling. Fiber Bragg grating monitoring results show that the fiber Bragg grating sensor on the outer wall of the inner sleeve shows uneven axial strain distribution, with a significant strain gradient near the interface. Ultrasonic monitoring results show a decrease in longitudinal wave velocity and a significant attenuation of sound wave amplitude, reflecting damage to both the cement sheath and the interface. For low-stiffness formations, acoustic emission events are mainly concentrated in the middle of the cement sheath, with events at the interface accounting for only about 15%. This indicates that the low-stiffness formation provides weaker constraint on the cement sheath, making it more prone to internal cracking under thermal stress, while the interface remains relatively intact. Fiber Bragg grating monitoring results show that the maximum tensile strain detected by the circumferential fiber Bragg grating sensor inside the cement sheath is slightly higher than that in the high-stiffness formation experimental group. However, the strain gradient displayed by the fiber Bragg grating sensor on the outer wall of the inner sleeve is smaller, indicating a better interfacial cementation state. Ultrasonic monitoring results show a decrease in longitudinal wave velocity, mainly reflecting damage to the cement sheath itself.

[0084] By monitoring changes in data, we can analyze the dynamic monitoring of the self-healing process under different formation stiffness. For example, for high-stiffness formations, acoustic emission activity gradually decreases during the natural warming stage, but a small number of acoustic emission events still occur in the interface area, indicating that the healing process of the interface gap is slow. Fiber grating data show that the strain of the cement sheath recovers to within ±150με within 48 hours, but the strain recovery of the sensor near the interface area is slower, and there is still a residual strain of about ±80με after 72 hours. The ultrasonic velocity recovers to 95% of the initial value after 72 hours. After the experiment, the gas permeability test shows that the permeability after repair decreases from 2.0mD after the damage to 0.3mD, with a repair efficiency of 85%. Due to the incomplete healing of the interface gap, the remaining permeability is slightly higher. For low-stiffness formations, acoustic emission activity rapidly decreased during the natural warming phase, dropping to background levels within 24 hours. Fiber Bragg grating data showed that the strain of the cement sheath recovered to within ±50 με within 48 hours, with minimal residual strain. The ultrasonic velocity recovered to 99% of its initial value after 72 hours. Gas permeability testing after the experiment showed that the repaired permeability decreased from 1.8 mD after the damage to 0.1 mD, achieving a repair efficiency of 94.4%. A well-maintained interface is beneficial for restoring overall sealing.

[0085] By monitoring changes in data, the effects of different formation stiffness on the self-healing effect of the cement sheath and the two-interface can be quantitatively evaluated. For example, for high-stiffness formations, the leakage collection and measurement device recorded that the leakage rate increased rapidly during the damage stage and decreased slowly during the self-healing stage, with a cumulative leakage of approximately 15 mL after 72 hours. For low-stiffness formations, the leakage rate increased slightly more slowly during the damage stage and decreased rapidly during the self-healing stage, with a cumulative leakage of approximately 8 mL after 72 hours, significantly lower than that of the high-stiffness formation experimental group. According to the conductivity sensor data, the conductivity of both high-stiffness and low-stiffness formations increased during the damage stage, indicating that ions were dissolved from the cement stone in both groups. During the self-healing stage, the conductivity of the low-stiffness formation group decreased faster, indicating that the ion dissolution channels were blocked after the cracks healed. The high-stiffness formation group decreased more slowly, consistent with the slow healing process of the interfacial gaps.

[0086] By employing the self-repair effect evaluation device for cement sheath and two interfaces provided in any embodiment of the present invention, the influence of formation stiffness on the damage mode and self-repair effect of cement sheath can be analyzed. High-stiffness formations cause damage to be concentrated in the cement sheath body and the two interfaces, the interface damage heals slowly, and the residual leakage after repair is high. Low-stiffness formations cause damage to mainly occur in the cement sheath body, the interface remains intact, and the self-repair material can more effectively heal the body cracks, resulting in higher repair efficiency.

[0087] For example, when using the self-healing effect evaluation device for cement sheath and two-interface provided in any embodiment of the present invention to conduct trigger threshold determination and long-term cyclic stability testing of self-healing materials, the annulus simulation unit is first assembled. Cement sheath samples with different microcapsule wall thicknesses, matching inner casing, formation cores, and sealing caps are selected and assembled. The mud cake layer is removed to form a clean interface. At the same time, fiber optic grating sensors, acoustic emission sensor arrays, and ultrasonic transducers are deployed as required to construct a full-coverage in-situ monitoring network. Then, the temperature and pressure control unit, multiphase flow control unit, in-situ monitoring unit, and data acquisition control unit are connected by pipelines and circuits to enhance pressure control accuracy and data acquisition stability. The entire experimental process is automatically executed by the programmed control module. First, the trigger threshold determination stage is entered. The annulus simulation unit is evacuated, reverse-saturated with formation water, and allowed to stand still for stability. A constant temperature and initial pressure are set to complete baseline acquisition. Then, a step-by-step sinusoidal pressure fluctuation loading is used to gradually increase the fluctuation amplitude. The data acquisition control unit simultaneously acquires acoustic emission, fiber optic grating, conductivity, and leakage rate signals. Based on the sudden increase of high-frequency components in acoustic emission, the response is determined. The activation time of microcapsules is determined by comprehensively considering abnormal fluctuations, instantaneous changes in conductivity, and inflection points in leakage rate, thus establishing the dynamic activation pressure threshold for the corresponding sample. After threshold determination, the long-term cyclic stability test phase begins. Target samples are selected, and a control group of ordinary cement sheaths is set up. A coupled load of sudden temperature drop and pressure impact is applied to induce microcracks. Then, a pressure fluctuation slightly higher than the trigger threshold is used to activate the self-healing function. Repair is completed by static incubation at room temperature. Subsequently, a set number of sinusoidal pressure cycles are applied to simulate long-term service loads. Loading is paused at certain intervals, and static permeability testing, ultrasonic scanning, and acoustic emission background noise acquisition are carried out sequentially. The data acquisition and control unit synchronously acquires and stores all signals using a unified time base, recording the evolution of acoustic emission cumulative energy, fiber optic strain, ultrasonic velocity amplitude, and cumulative leakage in real time. Finally, based on multi-source monitoring data, the fatigue degradation characteristics, sealing performance changes, and long-term structural stability of the cement sheath are quantitatively analyzed. This completes the accurate calibration of the trigger threshold of the self-healing material, verification of the repair effect, and evaluation of long-term service performance, providing experimental support for the optimization of self-healing cementing material formulations, performance screening, and engineering applications.

[0088] Specifically, by monitoring changes in data, the influence of different formation stiffness on the damage mode of the cement sheath and the two-interface can be analyzed. For example, for a sample with a wall thickness of 5 micrometers, when the pressure fluctuation reaches ±3.2 MPa, the acoustic emission event rate suddenly increases from the background value to >150 times / min, and the proportion of high-frequency components increases significantly, where high frequency can refer to greater than 300 kHz; the fiber optic grating sensor detects local micro-strain abnormal fluctuations (approximately ±30 με), which recover after about 5 minutes; the online conductivity sensor shows that the conductivity increases instantaneously by 0.5 MS / cm, and then slowly decreases. Based on the above monitoring results, the self-healing activation threshold for a sample with a wall thickness of 5 micrometers can be considered to be ±3.2 MPa. For a sample with a wall thickness of 10 micrometers, similar characteristics appear when the fluctuation reaches ±4.8 MPa: the acoustic emission event rate suddenly increases to >200 times / min, and the conductivity increases by 0.8 MS / cm. Based on the above monitoring results, the self-healing activation threshold for a sample with a wall thickness of 10 micrometers can be considered to be ±4.8 MPa. For samples with a wall thickness of 15 micrometers, when the fluctuation amplitude reaches ±6.2 MPa, the acoustic emission event rate suddenly increases to >180 times / min. However, the fiber grating strain fluctuation is more severe than that of samples with wall thicknesses of 5 micrometers and 10 micrometers (approximately ±50 με), indicating a greater fracture energy. Based on the above monitoring results, the self-healing activation threshold for samples with a wall thickness of 10 micrometers can be considered to be ±6.2 MPa. By using the cementing sheath and two-interface self-healing effect evaluation device provided in any embodiment of the present invention, the dynamic activation threshold of microcapsules can be accurately determined. This allows for the analysis of the positive correlation between wall thickness and triggering pressure, providing key parameters for the optimized design of self-healing materials.

[0089] By monitoring data changes, the long-term cyclic stability of cement rings with self-healing materials can be analyzed. For example, after damage induction and activation, the initial permeability of the sample containing self-healing material after repair is 0.2 mD, while that of the sample without self-healing material is 1.8 mD. The ultrasonic velocity recovers to 97% of the initial value, which indicates that the self-healing material used has a good repair effect. During the cycling process, the acoustic emission event rate of the sample containing the self-healing material remained at <5 times / min in the first 2,000 cycles, with no obvious new crack activity. After 3,000 cycles, the acoustic emission event rate slowly increased to 8 times / min, but it was mainly friction-type signals, with no sudden rupture signals. The circumferential strain monitored by the fiber optic grating was basically stable in the first 2,000 cycles, and showed a slow decay trend after 3,000 cycles, indicating that the material underwent slight fatigue softening. The longitudinal wave velocity monitored by the ultrasonic wave remained stable in the first 2,000 cycles, slowly decreased after 3,000 cycles, and slightly decreased after 10,000 cycles, with a slight decrease in dynamic elastic modulus. The cumulative leakage volume monitored by the leakage volume increased by about 2.5 mL after 10,000 cycles, and the permeability slowly increased from 0.2 mD to 0.28 mD, which was still far lower than the 1.8 mD after damage. Samples without self-healing materials exhibited continuous acoustic emission activity from the start of cycling, with an event rate maintained at 20-30 times / min, including numerous burst signals, indicating continuous initiation of new cracks. Circumferential strain monitored by fiber optic gratings continuously increased; ultrasonic velocity continuously decreased, showing a significant decrease of approximately 15% after 10,000 cycles, with a significant attenuation of dynamic elastic modulus; cumulative leakage increased by approximately 12 mL after 10,000 cycles, with permeability rising from 1.8 mD to 2.3 mD, indicating a continuous deterioration in sealing performance. By employing the cement sheath and two-interface self-healing effect evaluation device provided in any embodiment of this invention, the improvement effect of self-healing materials on the long-term fatigue performance of the cement sheath can be quantified, and multi-source monitoring data shows that the introduction of self-healing materials can delay the accumulation process of fatigue damage.

[0090] The method for evaluating the self-repairing effect of cementing sheath and two-interface self-repairing effect using the cementing sheath and two-interface self-repairing effect evaluation device provided by any embodiment of the present invention can not only be used for simulation evaluation of extreme working conditions such as hydrate decomposition, but also extended to the fine characterization and long-term performance verification of self-repairing materials, thereby providing an experimental platform for the research and development of high-performance self-repairing cementing materials.

[0091] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0092] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A device for evaluating the self-healing effect of cement sheath and two interfaces in well cementing, characterized in that, The device includes an annular simulation unit, a temperature and pressure control unit, a multiphase flow control unit, an in-situ monitoring unit, and a data acquisition and control unit; wherein: The annular simulation unit includes an inner casing, a cement sheath, a formation core, and a sealing cap; wherein, the inner casing, cement sheath, and formation core are coaxially nested from the inside to the outside to form a ring structure, and the ring structure is used to simulate the cement sheath body and the two interfaces cementing state; the cement sheath is a cementing cement sheath with added self-healing material; the sealing cap is assembled at both ends of the ring structure. The temperature and pressure control unit is used to apply a combined effect of temperature and pressure to the annular simulation unit to simulate the temperature and pressure changes during the decomposition process of natural gas hydrates. The multiphase flow control unit is used to inject multiphase fluid generated by the decomposition of natural gas hydrate into the annular simulation unit to simulate the intrusion and chemical corrosion of the multiphase fluid on the cement ring and the two interfaces. The in-situ monitoring unit is used to perform non-destructive online monitoring of the cement ring and the two interfaces within the annular simulation unit, and to obtain dynamic information on the entire process of damage evolution and self-repair of the cement ring and the two interfaces. The data acquisition and control unit is used to perform timing coordination control and data fusion processing on each unit in the device, and to evaluate the self-healing effect of the cement ring and the two interfaces based on the data fusion processing results.

2. The apparatus according to claim 1, characterized in that, The annular simulation unit also includes a mud cake layer, which is located between the cement annulus and the formation core.

3. The apparatus according to claim 1, characterized in that, The annular simulation unit further includes a first temperature and pressure sensor and a second temperature and pressure sensor; wherein, the first temperature and pressure sensor is installed at the inlet of the annular simulation unit and is used to monitor the pressure and temperature of the fluid injected into the annular simulation unit; the second temperature and pressure sensor is installed at the outlet of the annular simulation unit and is used to monitor the pressure and temperature of the fluid flowing out of the annular simulation unit.

4. The apparatus according to claim 1, characterized in that, The temperature and pressure control unit includes a refrigerant tank, a fluid circulation pump, a methane cylinder, and a pressure controller; wherein: The coolant tank is connected to the outer jacket layer of the annular simulation unit through the fluid circulation pump. The coolant tank is used to supply coolant to the annular simulation unit. The fluid circulation pump is used to drive the coolant from the coolant tank to the outer jacket layer of the annular simulation unit. The outer jacket layer of the annular simulation unit is the interlayer structure outside the formation core in the annular simulation unit. The methane cylinder is used to supply methane gas into the annular simulation unit, and the pressure controller is used to control the methane gas injection pressure, pressurization rate, and holding time.

5. The apparatus according to claim 1, characterized in that, The multiphase flow control unit includes a fluid storage tank assembly, a multiphase flow pump, a fluid switching valve assembly, and a conductivity sensor; wherein: The fluid storage tank group includes multiple fluid storage tanks, which are used to store the single-phase fluids produced by the decomposition of natural gas hydrates. The fluid storage tank group is connected to the multiphase flow pump through the fluid switching valve group. The fluid switching valve assembly is used for automatic switching and mixing of different fluids; The multiphase flow pump is used to inject multiphase fluid into the annular simulation unit; The conductivity sensor is used to monitor the conductivity of the multiphase flow seeping out of the annular simulation unit.

6. The apparatus according to claim 5, characterized in that, The fluid storage tank group includes methane gas storage tanks, formation water storage tanks, and acidic fluid storage tanks; wherein: The methane gas storage tank is used to store methane gas. A gas flow controller is installed between the methane gas storage tank and the fluid switching valve group. The gas flow controller is used to control the injection rate of methane gas. The acidic fluid storage tank is used to store acidic corrosive fluids to simulate the chemical corrosion environment after the decomposition of natural gas hydrates.

7. The apparatus according to claim 1, characterized in that, The in-situ monitoring unit includes a fiber optic grating monitoring subunit, an acoustic emission monitoring subunit, and an ultrasonic monitoring subunit; wherein: The fiber Bragg grating monitoring subunit includes a fiber Bragg grating sensor and a fiber Bragg grating demodulator; the fiber Bragg grating sensor is deployed within the annular simulation unit; the fiber Bragg grating demodulator is used to transmit optical signals to the fiber Bragg grating sensor and receive optical signals reflected by the fiber Bragg grating sensor; the fiber Bragg grating demodulator is also used to calculate the strain distribution and temperature change of the cement ring and the two interfaces in real time based on the received optical signals. The acoustic emission monitoring subunit includes an acoustic emission sensor and an acoustic emission acquisition card; the acoustic emission sensor array is attached to the outer wall of the formation core, and the acoustic emission acquisition card is used to receive the acoustic emission signal and perform feature extraction based on the acoustic emission signal; The ultrasonic monitoring subunit includes an ultrasonic pulse excitation source, a first transducer, a second transducer, and an ultrasonic acquisition card. The ultrasonic pulse excitation source is used to output an electrical pulse signal. The first transducer is installed inside the sealing cap at the inlet end of the annular simulation unit and is used to transmit an ultrasonic signal into the cement ring according to the electrical pulse signal. The second transducer is installed inside the sealing cap at the outlet end of the annular simulation unit and is used to receive the ultrasonic signal after penetrating the cement ring and convert the received ultrasonic signal into an electrical signal for output. The ultrasonic acquisition card is used to acquire the electrical signal output by the second transducer and obtain the acoustic response characteristics of the cement ring based on the electrical signal.

8. The apparatus according to claim 7, characterized in that, The fiber optic grating sensor is pre-embedded at least in one of the following locations: the outer wall of the inner sleeve, the inner wall of the cement ring, the interior of the cement ring, the outer wall of the cement ring, and the inner wall of the formation core.

9. The apparatus according to claim 1, characterized in that, The data acquisition and control unit includes a data acquisition processor, a computer control terminal, and a data storage server; wherein: The data acquisition processor is used to synchronously acquire various signals generated in the annular simulation unit, the multiphase flow control unit and the in-situ monitoring unit, and process the acquired signals to obtain first data. The first data is used to indicate the real-time damage status and self-healing effect of the cement ring and the two interfaces. The data storage server is used to store the various signals and the first data; The computer control terminal is used to control each unit to automatically perform corresponding functional operations and to display the first data in real time; the computer control terminal is also used to generate a self-healing effect evaluation report of the cement ring and the two interfaces based on the information stored in the data storage server.

10. A method for evaluating the self-healing effect of cementing sheaths and two interfaces, characterized in that, The method is achieved using the cementing sheath and two-interface self-repair effect evaluation device as described in any one of claims 1-9.

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