Wellbore structure strain transmission physical model device and experimental method

Abstract

The application relates to a wellbore structure strain transmission physical model device and an experimental method, and relates to the technical field of petroleum. The wellbore structure strain transmission physical model device comprises a wellbore structure, a support structure, a pressure loading device and a strain detection device. The wellbore structure is cylindrically arranged, and the wellbore structure comprises a casing, a cement ring and a rock ring in sequence from inside to outside along the radial direction. The inner wall of the casing, the outer wall of the casing and the outer wall of the cement ring are linearly arranged with optical fibers along the axial direction. The support structure comprises a support structure, a loading column head and a chassis structure. The chassis structure is arranged on the support structure and located at the bottom. The lower surface of the loading column head is arranged as a concave arc surface matched with the outer surface of the wellbore structure and matched with the outer surface of the rock ring. The chassis structure bears the wellbore structure. The pressure loading device is installed on the support structure and located above the wellbore structure.

Description

Technical Field

[0001] This invention relates to the field of petroleum technology, and in particular to a strain transfer model device and experimental method for wellbore structures. Background Technology

[0002] Under conditions such as hydraulic fracturing, post-fracturing shut-in, and adjacent well cross-contamination, formation strain is transmitted step by step to the casing through three layers of media (rock-cement sheath-casing) and multiple interfaces (rock-cement sheath interface, cement-casing interface). During this process, the strain is affected by the material mechanical parameters, geometric dimensions, and interface bonding state of the rock, cement sheath, and casing, resulting in varying degrees of attenuation or distortion, which affects the accuracy and reliability of formation strain monitoring results.

[0003] Currently, the transmission and attenuation mechanisms of strain in rock-cement sheath-casing structures remain unclear, and the influence of interfacial adhesion degradation, frictional slip, and complete debonding on strain lacks systematic experimental support. Existing experimental devices mostly focus on single interfaces or simplified structures, and their strain acquisition methods are outdated and lack precision, making it difficult to accurately capture the strain transmission process in a three-layer structure. Distributed fiber optic strain monitoring technology can perform distributed, dynamic, and high-precision strain monitoring. Therefore, it is necessary to combine this technology to develop a strain transmission model device and dynamic monitoring method for rock-cement sheath-casing structures to reveal the transmission mechanism and laws of strain through the three-layer structure, providing experimental means for research on formation deformation and wellbore integrity evaluation.

[0004] The above content is only used to help understand the technical solution of the present invention and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The main objective of this invention is to provide a strain transfer model device and experimental method for well shaft structures, aiming to solve the aforementioned technical problems in the prior art.

[0006] To achieve the above objectives, the present invention provides a strain transfer model device for wellbore structures, the strain transfer model device for wellbore structures comprising: The wellbore structure is cylindrical in shape and includes, from the inside to the outside, a casing, a cement sheath, and a rock sheath in a radial direction. Optical fibers are arranged in a straight line along the axial direction on the inner wall of the casing, the outer wall of the casing, and the outer wall of the cement sheath. The supporting structure includes a bracket structure, a loading column head, and a base frame structure. The base frame structure is mounted on the bracket structure and located at the bottom. The lower surface of the loading column head and the upper surface of the base frame structure are concave arc surfaces, and both are matched with the outer surface of the wellbore structure and are fitted to the outer surface of the rock annulus. The base frame structure supports the wellbore structure. A pressure loading device is installed on the support structure and located above the wellbore structure, and applies a compressive load radially toward the wellbore structure; A strain detection device, connected to the optical fiber, is used to measure strain data distributed along the optical fiber.

[0007] Preferably, in the wellbore structure strain transfer model device, the determination of the parameters of the wellbore structure includes: Determine the main dimensionless parameters controlling strain transfer under radial loading conditions, including geometric parameters, material stiffness parameters, Poisson's ratio parameters, interface parameters, and loading parameters; The geometric parameters include: (1) (2) (3) Material stiffness parameters include: (4) (5) Poisson's ratio parameters include: (6) (7) (8) Interface parameters include: (9) (10) Loading parameters include: (11) in, Let be the nth master dimensionless parameter in k, where k is w or d. When k is w, it represents the shaft structure of the model, and when k is d, it represents the shaft structure of the mine. n takes an integer between 1 and 11. t c,k t p,k H k R s,k These represent the thickness of the cement ring, the thickness of the rock ring, the sample thickness, and the outer radius of the casing in k, respectively, in meters. E c,k E s,k E p,k、 These are the elastic moduli of the cement ring, the elastic moduli of the casing, and the elastic moduli of the rock ring in k, respectively, in Pa. ν p,k ν c,k νs,k These are the Poisson's ratios of the rock ring, cement ring, and casing in k, respectively. , Let be the tangential equivalent stiffness at the interface between the rock sheath and the cement sheath, and the tangential equivalent stiffness at the interface between the cement sheath and the casing, respectively, in Pa·m. -1 ; R s,k Let be the outer radius of the sleeve in k, in meters. Let Pa be the characteristic stress corresponding to radial loading in k; Based on the determined master dimensionless parameters of strain transfer under radial loading conditions, equations (12) to (15) are obtained, including... (12) (13) (14) (15) Based on the selected outer radius of the model casing and Equation (12), calculate the thickness of the cement ring, the thickness of the rock layer, and the height of the sample in the model; Based on equation (12) and the elastic modulus of the selected model rock ring material, calculate the elastic modulus of the cement ring and the casing in the model. Based on the Poisson's ratio of the model rock ring material and Equation (14), determine the Poisson's ratio of the model cement ring and the casing; Based on the tangential equivalent stiffness of the interface between the rock ring and cement ring in the mine, the tangential equivalent stiffness of the interface between the cement ring and the casing, and Equation (13), the tangential equivalent stiffness of the interface between the rock ring and cement ring in the model and the tangential equivalent stiffness of the interface between the cement ring and the casing are calculated. Based on the characteristic stress corresponding to radial loading in the mine and Equation (15), the characteristic stress corresponding to radial loading in the model is calculated.

[0008] Preferably, in the wellbore structure strain transfer model device, the bonding state of the rock sheath and the cement sheath interface, and the cement sheath and the casing interface, includes a fully bonded state, a partially bonded state, a frictional slip state, and a completely debonded state.

[0009] Preferably, in the well shaft structure strain transfer model device, the support structure includes an upper crossbeam, a lower crossbeam, and a plurality of supporting columns, the upper crossbeam being located above the lower crossbeam, and the supporting columns connecting the upper crossbeam and the lower crossbeam; The base frame structure is mounted on the lower crossbeam.

[0010] Preferably, in the wellbore structure strain transfer model device, the pressure loading device is a hydraulic loading assembly, which includes a hydraulic cylinder and a hydraulic piston disposed in the hydraulic cylinder. The hydraulic cylinder is mounted on the upper crossbeam, and the hydraulic piston is disposed in the hydraulic cylinder and can move radially along the wellbore structure.

[0011] Preferably, in the wellbore structure strain transfer model device, the center of the rock annulus has a mounting hole, the casing is placed in the mounting hole, and an annular gap is formed between the casing and the rock annulus; a cement ring is inserted into the annular gap. The optical fiber is placed at the interface between the rock ring and the cement ring.

[0012] Preferably, in the wellbore structure strain transfer model device, the strain detection device is a distributed optical fiber demodulator.

[0013] To achieve the above objectives, the present invention also provides an experimental method utilizing the above-described well shaft structure strain transfer model device, the experimental method comprising: The wellbore structure is loaded using a pressure loading device, and strain data distributed along the optical fiber is collected using a strain detection device to obtain measured strain data. Based on the predetermined material mechanical parameters, geometric dimensions, and the influence of interface cementation state on strain transfer efficiency, the actual formation strain and deformation are calculated using the total strain transfer efficiency and measured strain.

[0014] Preferably, in the experimental method using the strain transfer model device of the well shaft structure, the step of determining the influence of predetermined material mechanical parameters, geometric dimensions, and interface bonding state on strain transfer efficiency includes: Obtain the material mechanical parameters and geometric dimensions of the casing, cement ring, and rock ring; Based on the interface bonding state of the first interface and the second interface, the interface transfer coefficients of the first interface and the second interface are determined respectively, wherein the first interface is the interface between the rock ring and the cement ring, and the second interface is the interface between the cement ring and the casing. Establish displacement and strain field models for each layer, as well as interface continuity and boundary conditions; Based on the displacement field, calculate the target strain at key radial positions of the casing, cement ring, and rock ring; based on the strain field, calculate the strain transfer efficiency of the rock ring and cement ring, the strain transfer efficiency of the cement ring and casing, and the strain transfer efficiency inside the casing wall. The total strain transfer efficiency is calculated based on the strain transfer efficiency of the rock ring and cement ring, the strain transfer efficiency of the cement ring and casing, and the strain transfer efficiency inside the casing wall. By changing the material mechanical parameters, geometric dimensions, and interfacial bonding state of the casing, cement ring, and rock ring, the process is repeated cyclically to determine the influence of these parameters on strain transfer efficiency.

[0015] Preferably, in the experimental method using the strain transfer model device of the well casing structure, the radial strain is used as the target strain to obtain the inner wall strain r=r i The measured radial strain and the total radial strain transfer efficiency were measured. Based on the total radial strain transfer efficiency and the inner wall of the casing, r=r i Measured radial strain at the location, inverted and compared with the inner wall of the casing r=r i Rock rings located in the same radial direction, r=r m The actual radial strain is ; Calculate r at any two positions of the rock ring a and r b The radial deformation between them is calculated using the following formula: ; in, The inner radius of the casing is r = r i Radial strain; The radius of the rock ring is r = r m Radial strain; The total radial strain transfer efficiency; A p These are the constant coefficients in the general solution of rock ring displacement; B p represents the constant coefficients in the general solution of rock ring displacement.

[0016] The present invention has at least the following beneficial effects: The wellbore structure provided by this invention is cylindrical in shape and includes, from the inside to the outside, a casing, a cement sheath, and a rock sheath in a radial direction. Optical fibers are arranged in a straight line along the axial direction on the inner wall of the casing, the outer wall of the casing, and the outer wall of the cement sheath. The support structure includes a bracket structure, a loading head, and a base frame structure. The base frame structure is mounted on the bracket structure and located at the bottom. The lower surface of the loading head is a concave arc surface that matches the outer surface of the wellbore structure and is fitted to the outer surface of the rock sheath. The base frame structure supports the wellbore structure. A pressure loading device is installed on the bracket structure and located above the wellbore structure, applying a compressive load radially to the wellbore structure. A strain detection device is connected to the optical fibers to measure strain data distributed along the optical fibers. This allows for the simulation of the mechanical transmission behavior of strain in the rock sheath-cement sheath-casing structure under laboratory conditions, providing experimental means for research on formation deformation and wellbore integrity evaluation. Attached Figure Description

[0017] Figure 1 A schematic diagram of a strain transfer model device for a well shaft structure provided by the present invention; Figure 2 for Figure 1 A schematic diagram of a column head under load; Figure 3 for Figure 1 Schematic diagram of the mid-base frame structure; Figure 4 for Figure 3 A schematic diagram of the mid-frame structure from another perspective; Figure 5 This is a flowchart of the experimental method for the strain transfer model device using a well shaft structure according to the present invention.

[0018] 100-Strain transfer model device for wellbore structure; 1-Wellbore structure; 11-Casing; 12-Cement sheath; 13-Rock sheath; 2-Support structure; 21-Support structure; 211-Upper crossbeam; 212-Lower crossbeam; 213-Bearing column; 22-Base frame structure; 23-Loading column head; 3-Pressure loading device; 31-Hydraulic cylinder; 32-Hydraulic piston; 4-Strain detection device; 5-Fiber optic cable.

[0019] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0021] In this embodiment of the invention, the term "and / or" describes the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following associated objects have an "or" relationship.

[0022] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0023] In this embodiment of the invention, the term "multiple" refers to two or more, and other quantifiers are similar.

[0024] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the embodiments of the present invention to facilitate a better understanding of the invention. However, the technical solutions claimed in the present invention can be implemented even without these technical details and various variations and modifications based on the following embodiments. The division of the following embodiments is for ease of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with and referenced by each other without contradiction.

[0026] This invention provides a strain transfer model device for wellbore structures. Please refer to [link / reference]. Figures 1 to 4The wellbore structure strain transfer model device 100 includes a wellbore structure 1, a support structure 2, a pressure loading device 3, and a strain detection device 4. The wellbore structure 1 is cylindrical and includes, from the inside to the outside, a casing 11, a cement sheath 12, and a rock sheath 13. Optical fibers 5 are arranged axially along the inner and outer walls of the casing 11 and the cement sheath 12. The support structure 2 includes a bracket structure 21 and a base structure 22. The base structure 22 is mounted on the bracket structure 21 and located at the bottom. The upper surface of the base structure 22 is a concave arc surface that matches the outer surface of the wellbore structure 1 to support the wellbore structure 1 and fits against the outer surface of the rock sheath 13. The pressure loading device 3 is mounted on the bracket structure 21 and located above the wellbore structure 1, applying a compressive load radially to the wellbore structure 1. The strain detection device 4 is connected to the optical fibers 5 and is used to measure strain data distributed along the optical fibers 5.

[0027] The present invention utilizes a cylindrical wellbore structure 1, which comprises, from the inside to the outside, a casing 11, a cement sheath 12, and a rock sheath 13. Optical fibers 5 are arranged axially in a straight line on the inner and outer walls of the casing 11 and the cement sheath 12. The support structure 2 includes a bracket structure 21, a loading head 23, and a base frame structure 22. The base frame structure 22 is mounted on the bracket structure 21 and located at the bottom. The lower surface of the loading head 23 and the upper surface of the base frame structure 22 are concave arc surfaces, both matching the outer surface of the wellbore structure 1 and fitting snugly against the outer surface of the rock sheath 13. The base frame structure 22 supports the wellbore structure 1. The pressure loading device 3 is installed on the support structure 21 and located above the well structure 1, and applies a compressive load in the radial direction of the well structure 1; the strain detection device 4 is connected to the optical fiber 5 and is used to measure the strain data distributed along the optical fiber 5, so that the strain transmission law and attenuation mechanism under different interface states, different loading methods and different casing 11 types can be studied.

[0028] Before conducting strain transfer experiments on the three-layer structure of rock ring 13-cement ring 12-casing 11, a calculation system was established between the indoor model and the mine prototype based on the geometric dimensions, material parameters, and stress conditions of the mine shaft structure 1. Based on this, the geometric dimensions, material parameters, interface state, and loading regime of the indoor sample were determined through back-calculation, ensuring that the indoor experiment was representative of the mine shaft structure 1 in terms of strain transfer path, attenuation law, and interface failure behavior. Since the experimental method of this invention involves placing the three-layer structure sample of rock ring 13-cement ring 12-casing 11 flat on a uniaxial compressor and applying a compressive load radially along the casing 11, the construction was based on the mechanical response of the three-layer cylindrical structure under radial loading conditions.

[0029] Please see Figure 5 The method for determining the parameters of wellbore structure 1 includes steps S100 to S700.

[0030] Step S100 involves determining the main dimensionless parameters controlling strain transfer under radial loading conditions, including geometric parameters, material stiffness parameters, Poisson's ratio parameters, interface parameters, and loading parameters.

[0031] The geometric parameters include: (1) (2) (3) Material stiffness parameters include: (4) (5) Poisson's ratio parameters include: (6) (7) (8) Interface parameters include: (9) (10) Loading parameters include: (11) in, Let be the nth master dimensionless parameter in k, where k is w or d. When k is w, it represents the shaft structure 1 of the model. When k is d, it represents the shaft structure 1 of the mine. n is an integer between 1 and 11. t c,k t p,k H k R s,k The thicknesses of cement ring 12, rock ring 13, sample thickness, and outer radius of sleeve 11 in k are respectively, in meters. E c,k E s,k E p,k、 The elastic modulus of the cement ring 12, the elastic modulus of the sleeve 11, and the elastic modulus of the rock ring 13 in k are respectively, in Pa. ν p,k ν c,k ν s,k These are the Poisson's ratios of rock ring 13, cement ring 12, and casing 11 in k, respectively. , The values ​​are the tangential equivalent stiffness at the interface between rock ring 13 and cement ring 12, and the tangential equivalent stiffness at the interface between cement ring 12 and casing 11, respectively, in Pa·m. -1 ; R s,k Let the outer radius of sleeve 11 in k be m; Let Pa be the characteristic stress corresponding to radial loading in k; Step S200, based on the determined master dimensionless parameters of strain transfer under radial loading conditions, yields equations (12) to (15). Step S200 includes... (12) (13) (14) (15) Step S300 calculates the thickness of the cement ring 12, the thickness of the rock layer, and the height of the sample in the model based on the selected outer radius of the model sleeve 11 and formula (12).

[0032] According to equation (12), we can obtain: (12.1) (12.2) (12.3). The outer radius R of the selected model sleeve 11 is... s,w Substituting into equations (12.1) to (12.3), the thickness of the cement ring 12, the thickness of the rock layer, and the height of the sample in the model can be calculated respectively.

[0033] Step S400: Calculate the elastic modulus of the cement ring 12 and the sleeve 11 in the model according to Equation (12) and the elastic modulus of the selected model rock ring 13 material.

[0034] According to equation (12), we can obtain: (12.4) (12.4) Substituting the elastic modulus of the selected model rock ring 13 material into equations (12.4) and (12.4), the elastic modulus of the cement ring 12 and the sleeve 11 in the model can be calculated respectively.

[0035] Step S500 determines the Poisson's ratio of the model cement ring 12 and the sleeve 11 based on the Poisson's ratio of the model rock ring 13 material and formula (14).

[0036] According to equation (14), we can obtain: = = (14.1) Substituting the Poisson's ratio of the model rock ring 13 material into equation (14.1), we can obtain the Poisson's ratio of the model cement ring 12 and the sleeve 11.

[0037] Step S600: Based on the tangential equivalent stiffness of the interface between the rock ring 13 and the cement ring 12, the tangential equivalent stiffness of the interface between the cement ring 12 and the casing 11, and Equation (13), calculate the tangential equivalent stiffness of the interface between the rock ring 13 and the cement ring 12, and the tangential equivalent stiffness of the interface between the cement ring 12 and the casing 11.

[0038] According to equation (13), we can obtain: (13.1) (13.2) By substituting the tangential equivalent stiffness of the interface between the rock ring 13 and the cement ring 12, and the tangential equivalent stiffness of the interface between the cement ring 12 and the casing 11 into equations (13.1) and (13.2), respectively, the tangential equivalent stiffness of the interface between the rock ring 13 and the cement ring 12, and the tangential equivalent stiffness of the interface between the cement ring 12 and the casing 11 can be calculated.

[0039] Step S700: Calculate the characteristic stress corresponding to the radial loading of the model based on the characteristic stress corresponding to the radial loading of the mine and Equation (15).

[0040] According to equation (15), we can obtain: (15.1) Substituting the characteristic stress corresponding to the radial loading of the mine into equation (15.1), the characteristic stress corresponding to the radial loading of the model can be calculated.

[0041] In specific experiments, the bonding state of the interfaces between the rock sheath 13 and the cement sheath 12, and between the cement sheath 12 and the casing 11, can be preset and controlled. By changing the interface treatment method, material properties, and contact conditions, different interface mechanical states can be constructed to simulate various interface bonding situations that may occur during actual wellbore cementing. The interface bonding conditions include, but are not limited to, the following: complete bonding state, partial bonding state, frictional slip state, and complete debonding state.

[0042] More specifically, a fully bonded state can be achieved by thoroughly cleaning the interface (such as degreasing and dust removal), mechanically roughening it (such as sandblasting and etching), and applying a high-strength adhesive material (such as epoxy resin or a special adhesive), followed by curing under certain pressure and temperature conditions, so that a continuous and dense adhesive layer is formed at the interface, thereby achieving near-ideal full bonding.

[0043] Partial bonding can be achieved by applying a release agent to local areas of the interface, setting a local isolation layer, or controlling the roughness distribution, so that the interface forms a non-uniform state in which bonded and unbonded areas coexist, thereby simulating the complex working conditions of discontinuous bonding at the interface in field cementing.

[0044] Friction slip can be simulated by setting controllable friction pads (such as polytetrafluoroethylene sheets) or coating a thin layer of low-friction material between the interfaces and adjusting the interface roughness to give the interfaces a certain coefficient of friction. After reaching the critical shear stress, relative slip occurs, which can be used to simulate the interface shear failure behavior.

[0045] Complete debonding can be achieved by covering the entire surface with a release film, continuously spraying a release agent, or artificially leaving tiny gaps, so that there is no effective adhesion between the interfaces, allowing free sliding or separation to occur during loading.

[0046] During installation, the sleeve 11 and optical fiber 5 can be pre-assembled. The optical fiber 5 is laid axially along the inner and outer walls of the sleeve 11. Depending on experimental requirements, a straight-line bonding or spiral winding method can be chosen for its placement, and stable attachment of the optical fiber 5 can be achieved through adhesives or mechanical fixation. To improve the realism and sensitivity of strain transfer, bare optical fiber 5 or unsheathed optical fiber 5 is preferred to reduce the attenuation effect of the sheath material on strain transfer. Simultaneously, a sufficiently long lead-out section should be reserved at the end of the optical fiber 5, and a protective sleeve 11 or buffer structure should be installed to prevent damage or breakage during subsequent installation and loading.

[0047] After the fiber optic cable 5 is installed in the sleeve 11, the fiber optic cable 5 is further installed in the interface area between the rock ring 13 and the cement ring 12. Depending on the research focus, the fiber optic cable 5 can be placed on the inner interface (close to the sleeve 11) or the outer interface (close to the rock) of the cement ring 12. Multiple fibers 5 can also be installed simultaneously to achieve multi-location monitoring. The installation method can be embedded (pre-embedded in cement grout) or attached (adhered to the interface surface), and appropriate fixing measures (such as fine groove embedding and thin-layer bonding) can be used to ensure that the fiber optic cable 5 is stable in position and does not drift during the casting process.

[0048] Alternatively, the wellbore can be installed as follows: a mounting hole is provided in the center of the rock annulus 13, the casing 11 is placed in the mounting hole, and an annular gap is formed between the casing 11 and the rock annulus 13; a cement ring 12 is inserted into the annular gap; and the optical fiber 5 is placed at the interface between the rock annulus 13 and the cement ring 12. In specific operation, the pre-assembled casing 11 and optical fiber 5 are placed as a whole in a sample casting container, forming an annular gap between the casing 11 and the rock annulus 13, and cement slurry is injected into the annular gap to form a cement ring 12, thus obtaining the wellbore structure 1.

[0049] The water-cement ratio, additive type, and proportion of the cement slurry can be adjusted according to experimental requirements. During the pouring process, layered injection, vibration venting, or vacuuming should be used to reduce the generation of air bubbles and pores, ensuring the density and uniformity of the cement ring 12 structure. After pouring, curing should be carried out under constant temperature and humidity conditions. The curing time can be determined according to the type of cement (e.g., 7 days, 14 days, or 28 days) until the cement ring 12 reaches its design strength, thus forming a stable three-layer composite structure of rock ring 13-cement ring 12-casing 11.

[0050] The well shaft structure 1 is installed on the base frame structure 22. The geometric center axis of the well shaft structure 1 needs to be kept coaxial with the loading axis to facilitate operation and control.

[0051] The strain detection device 4 is a distributed fiber optic demodulator. Each distributed fiber optic cable 5 in the well structure 1 is connected to the distributed fiber optic demodulator via fiber optic jumpers, and the fiber optic channels are identified and calibrated. The distributed fiber optic demodulator acquires the spatial positioning information along the fiber optic cable 5, establishing a correspondence between the fiber optic cable 5 measuring points and the actual spatial positions of the well structure 1. Simultaneously, initial signal testing and noise assessment can be performed to ensure stable fiber optic signal transmission without significant anomalies.

[0052] After completing system debugging and connecting fiber optic cable 5, axial stress is applied to the wellbore structure 1 according to the preset loading scheme. The loading method can employ constant-rate loading, graded loading, cyclic loading, or a combination of loading and unloading to simulate different geostress paths and engineering conditions. During the loading process, load, displacement, and strain response should be monitored in real time to ensure a smooth and impact-free loading process and to prevent unexpected instability of the wellbore structure 1.

[0053] Throughout the loading process, a distributed fiber optic demodulator is used to acquire and record strain data distributed along fiber optic 5 in real time, and synchronize this data with the load and displacement data acquired by the loading system. By filtering, denoising, and spatially reconstructing the data, the strain evolution process inside the specimen and at the interface can be obtained, thereby achieving a fine characterization of the strain transmission path and interface response characteristics.

[0054] By analyzing the above experimental data, the interfacial strain transfer coefficient, attenuation characteristics and interfacial failure behavior can be further inverted, thereby revealing the strain transfer mechanism of the rock-cement ring 12-casing 11 structure.

[0055] The distributed fiber optic 5 strain demodulation system can record the spatial distribution of strain at different interface states, different loading paths, and different time points during the loading process in real time, thereby realizing the integration of stress loading and dynamic strain monitoring. The distributed fiber optic 5 strain demodulation system can use monitoring technologies such as Rayleigh scattering-based distributed strain sensing (RFS-DSS), optical frequency domain reflection (OFDR)-based distributed strain sensing, or low-frequency distributed acoustic sensing (LF-DAS) to obtain high spatial resolution dynamic strain data along the 5-axis of the fiber.

[0056] To ensure uniform loading, the upper surface of the base frame structure 22 is tightly fitted to the outer surface of the well shaft structure 1. The support structure 21 includes an upper crossbeam 211, a lower crossbeam 212, and several supporting columns 213. The upper crossbeam 211 is located above the lower crossbeam 212, and the supporting columns 213 connect the upper crossbeam 211 and the lower crossbeam 212. The base frame structure 22 is mounted on the lower crossbeam 212.

[0057] The pressure loading device 3 is a hydraulic loading assembly, which includes a hydraulic cylinder 31 and a hydraulic piston 32 disposed on the hydraulic cylinder 31. The hydraulic cylinder 31 is mounted on the upper crossbeam 211, and the hydraulic piston 32 is disposed within the hydraulic cylinder 31 and can move radially along the well shaft structure 1. The strain detection device 4 is a distributed optical fiber demodulator 5.

[0058] The present invention also provides an experimental method using the strain transfer model device 100 of the well shaft structure 1 described above, the experimental method using the strain transfer model device 100 of the well shaft structure 1 includes steps S810 and S820.

[0059] In step S810, the wellbore structure 1 is loaded by the pressure loading device 3, and strain data distributed along the optical fiber 5 is collected by the strain detection device 4 to obtain the measured strain data. Step S820: Based on the predetermined material mechanical parameters, geometric dimensions, and the influence of interface cementation state on strain transfer efficiency, the actual formation strain and deformation are calculated using the total strain transfer efficiency and the measured strain.

[0060] Step S820 includes steps S821 to S826.

[0061] Step S821: Obtain the material mechanical parameters and geometric dimensions of the sleeve 11, cement ring 12, and rock ring 13. The material mechanical parameters of the sleeve 11, cement ring 12, and rock ring 13 include the elastic modulus and Poisson's ratio, specifically the elastic modulus and Poisson's ratio of the rock ring 13, the elastic modulus and Poisson's ratio of the cement ring 12, and the elastic modulus and Poisson's ratio of the sleeve 11.

[0062] The geometric dimensions of the casing 11, cement ring 12, and rock ring 13 include the outer boundary radius r of the rock. R Cement ring 12 outer radius r c Outer radius r of sleeve 11 o The inner radius of sleeve 11 is r i Among them, r i < r o <r c <r R .

[0063] Step S822 determines the interface transfer coefficients of the first and second interfaces based on their interfacial bonding states. The first interface is the interface between the rock ring 13 and the cement ring 12, and the second interface is the interface between the cement ring 12 and the sleeve 11. The interface transfer coefficient of the interface between the rock ring 13 and the cement ring 12 is k. pc The interfacial transfer coefficient of cement ring 12-sleeve 11 is k. cs .

[0064] Where 0 < k pc ≤1, 0<k cs ≤1; When the interface is fully bonded, the corresponding interface transfer coefficient is 1; When there is micro-slip, debonding or weak bonding at the interface, the corresponding interface transfer coefficient is less than 1.

[0065] In some implementations, the interface transfer coefficient can be obtained through experimental calibration, i.e., by loading an experiment to measure the strain or displacement on both sides of the interface and calculating it according to their ratio, or by numerical simulation inversion, i.e. by establishing a rock-cement ring 12-casing 11 coupled model, adjusting the interface parameters to match the simulation results with the measured data, thereby determining the corresponding interface transfer coefficient.

[0066] Step S823 establishes the displacement and strain field models for each layer, as well as the interface continuity and boundary conditions. Specifically, the radial displacement of each layer satisfies: ; Simplified to: ; The radial strain, circumferential strain, and axial strain of each layer are as follows: ; ; ; The interface continuity condition and boundary condition include: When the target strain is radial strain, at the interface between the rock and cement ring 12, r = r c The following conditions must be met: Displacement compatibility conditions: ; Interfacial stress continuity condition: ; At the interface between cement ring 12 and sleeve 11, r=r o At this location, the following conditions must be met: Displacement compatibility conditions: ; Interfacial stress continuity condition: ; On the inner wall of sleeve 11, r=r i At this location, the inner wall of sleeve 11 bears the internal pressure p. i ,So ; At the outer boundary of rock ring 13, r=r R At this location, the outer boundary of rock ring 13 is subjected to an external load p. R ,So ; When the displacement of the outer boundary of rock ring 13 is known, and the displacement of the outer boundary of rock ring 13 is u R hour, .

[0067] Step S824 calculates the target strain at key radial positions of the casing 11, cement ring 12, and rock ring 13 based on the displacement field; and calculates the strain transfer efficiency of the rock ring 13 and cement ring 12, the strain transfer efficiency of the cement ring 12 and casing 11, and the strain transfer efficiency inside the casing 11 wall based on the strain field. The calculation of the strain transfer efficiency of the rock ring 13 and cement ring 12 includes: The radial strain transfer efficiency of rock ring 13 and cement ring 12 is: ; The circumferential strain transfer efficiency of rock ring 13 and cement ring 12 is: ; The axial strain transfer efficiency of rock ring 13 and cement ring 12 is: in, The radial propagation effect within rock ring 13 is calculated using the following formula: ; The formula for calculating the radial transmission effect at the interface between rock ring 13 and cement ring 12 is as follows: ; The calculation formula for the circumferential propagation effect within rock ring 13 is as follows: ; The formula for calculating the circumferential transmission effect at the interface between rock ring 13 and cement ring 12 is as follows: ; The calculation formula for the axial propagation effect inside rock ring 13 is as follows: ; The formula for calculating the axial transmission effect at the interface between rock ring 13 and cement ring 12 is as follows: .

[0068] The radial strain transfer efficiency of cement ring 12 and sleeve 11 is: : in, The formula for calculating the radial propagation effect of cement ring 12 is as follows: ; The formula for calculating the radial transmission effect at the interface between cement ring 12 and sleeve 11 is as follows: ; The radial strain transfer efficiency of cement ring 12 and sleeve 11 is simplified as follows: ; The circumferential strain transfer efficiency of cement ring 12 and sleeve 11 is: ; The engineering approximation of the circumferential strain transfer efficiency of cement ring 12 and sleeve 11 is: ; The axial strain transfer efficiency of cement ring 12 and sleeve 11 is: .

[0069] The strain transfer efficiency inside the wall of the sleeve 11 includes: The radial strain transfer efficiency of the outer wall and inner wall of sleeve 11 is: ; The circumferential strain transfer efficiency of the outer wall and inner wall of sleeve 11 is: ; The axial strain transfer efficiency of the outer wall and inner wall of sleeve 11 is: .

[0070] Step S825 calculates the total strain transfer efficiency based on the strain transfer efficiencies of the rock ring 13 and cement ring 12, the strain transfer efficiency of the cement ring 12 and casing 11, and the strain transfer efficiency inside the casing 11 wall. The total radial strain transfer efficiency is: ; The overall circumferential strain transfer efficiency is: ; The overall axial strain transfer efficiency is: .

[0071] Step S826 involves cyclically changing the material mechanical parameters, geometric dimensions, and interface bonding state of the sleeve 11, cement ring 12, and rock ring 13 to determine the influence of the material mechanical parameters, geometric dimensions, and interface bonding state on the strain transfer efficiency.

[0072] By studying the influence of material mechanical parameters, geometric dimensions, and interfacial bonding state on strain transfer efficiency, the A layer of each layer can be determined. j and B j Thus, the actual formation strain and deformation are calculated based on the measured strain using the total strain transfer efficiency. Step S826 includes steps S8261 to S8263.

[0073] Step S8261 uses radial strain as the target strain to obtain the inner wall strain r=r of sleeve 11. i Measured radial strain at the specified location and total radial strain transfer efficiency; based on the total radial strain transfer efficiency and the measured radial strain at r=ri on the inner wall of sleeve 11, inversely calculate the radial strain at r=ri on the inner wall of sleeve 11. i Rock rings located in the same radial direction 13r=r m The actual radial strain is ; Calculate the value of r at any two positions in rock ring 13 a and r b The radial deformation between them is calculated using the following formula: .

[0074] Step S8262 uses circumferential strain as the target strain to obtain the inner wall strain r=r of sleeve 11. i The measured circumferential strain and the total circumferential strain transfer efficiency were measured. Based on the total circumferential strain transfer efficiency and the inner wall r=r of sleeve 11i The measured circumferential strain was used to invert the position r=r in rock ring 13. m The actual circumferential strain of the formation at that location is given by the following formula: ; Calculate the rock ring 13r m The formula for calculating the circumferential deformation at the location is: .

[0075] Step S8263 uses axial strain as the target strain to obtain the inner wall strain r=r of sleeve 11. i The measured axial strain and the total axial strain transfer efficiency were obtained; based on the total axial strain transfer efficiency and the inner wall r=r of sleeve 11. i The measured axial strain was used to invert the position r=r in rock ring 13. m The actual axial strain of the formation at the specified location is given by the following formula: ; Calculate rock ring 13 from axial coordinate z a To z b The axial deformation is calculated using the following formula: ; in, Let be the radial strain of the j-th layer of material at radius r; Let be the circumferential strain of the j-th layer of material at radius r; Let be the axial strain of the j-th layer of material at radius r; where, Let z be the axial strain at the z-axis position of the j-th layer of material; j is p, c, or s, where the p-th layer is rock ring 13, the c-th layer is cement ring 12, and the s-th layer is casing 11; r is the radial coordinate in the cylindrical coordinate system, that is, the distance from the center of the wellbore outwards; r can be, but is not limited to, r i r m、 r c、 r o、 r R .

[0076] , , These are the total radial strain transfer efficiency, the total circumferential strain transfer efficiency, and the total axial strain transfer efficiency, respectively. A j These are the constant coefficients in the general solution of the displacement of the j-th layer material; B j denoted as the constant coefficient in the general solution of the displacement of the j-th layer material.

[0077] in, For rock ring 13, r=r m Circumferential deformation at the location; E j Let J be the elastic modulus of the j-th layer material; , , These are the radial stress, circumferential stress, and axial stress of the j-th layer material, respectively. Let be the Poisson's ratio of the j-th layer material; Let r be the radial displacement of the j-th layer of material at point r; k pc k cs These are the interface transfer coefficients for the first interface and the second interface, respectively. , , The strain transfer efficiencies of the cement ring 12 and the sleeve 11 in the radial, circumferential, and axial directions are respectively. , , These are the strain transfer efficiencies of the outer wall and inner wall of sleeve 11 in the radial, circumferential, and axial directions, respectively. , , These are the total radial strain transfer efficiency, the total circumferential strain transfer efficiency, and the total axial strain transfer efficiency, respectively. , , These are the strain transfer efficiencies of the outer wall and inner wall of sleeve 11 in the radial, circumferential, and axial directions, respectively. , , The strain transfer efficiencies of the rock ring 13 and the cement ring 12 in the radial, circumferential, and axial directions are respectively.

[0078] Example A typical oilfield wellbore structure was selected as the prototype system. The geometric parameters included: casing outer radius 69.85 mm, wall thickness 10.54 mm; cement sheath outer diameter 15.9 mm; cement sheath thickness 15.9 mm; the outer edge of the formation rock sheath was 100 m from the casing center; the rock sheath thickness was calculated as the distance from the outer edge of the formation rock sheath to the casing center minus (casing outer radius + cement sheath outer diameter), which was 99913.25 mm; and the well section length was taken as 2 m.

[0079] The material mechanical parameters include: the cement sheath uses a conventional cementing system, and its elastic modulus is 2.5 × 10⁻⁶. 5 Pa, Poisson's ratio is 0.22: Taking sandstone as an example, the elastic modulus of the rock ring is 3.0 × 10⁻⁶. 10 Pa, Poisson's ratio is 0.2; taking P110 material as an example, its elastic modulus is 2.1×10. 11 Pa, Poisson's ratio is 0.3.

[0080] Loading parameters: Set the formation radial stress to 10 MPa.

[0081] The outer radius of the model casing was selected as 12.5 mm. Using the parameter determination method of well structure 1 in this invention, the thickness of the cement sheath of the model was calculated to be 2.85 mm, and the axial length of the model sample was 358 mm.

[0082] In the model, to ensure experimental feasibility, it is only necessary to ensure that the outer boundary of the rock is large enough so that the boundary effect does not affect strain transmission. Typically, the outer radius of the rock is taken as 5-10 times the outer radius of the casing.

[0083] Here, the outer radius of the model rock ring is set to 10 times the outer radius of the casing, which is 125mm.

[0084] The thickness of the rock ring in the model is 109.65 mm.

[0085] The selected model rock ring elastic modulus is 3×10. 9 Pa was calculated, and the required elastic modulus of the cement ring and sleeve in the model was calculated in reverse. The elastic modulus of the cement ring was 2.5 × 10⁻⁶. 9 Pa, the elastic modulus of the sleeve is 2.1 × 10 Pa. 10 Pa. The Poisson's ratio of the cement ring in the model is 0.22, and the Poisson's ratio of the sleeve is 0.3. The model is loaded with a stress of 1.0 MPa.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An experimental method for a strain transfer model device using a well shaft structure, characterized in that, include: The wellbore structure is loaded using a pressure loading device, and strain data distributed along the optical fiber is collected using a strain detection device to obtain measured strain data. Based on the influence of predetermined material mechanical parameters, geometric dimensions, and interface cementation state on strain transfer efficiency, the actual formation strain and deformation are calculated using the total strain transfer efficiency and measured strain. The influence of predetermined material mechanical parameters, geometric dimensions, and interface cementation state on strain transfer efficiency includes: Obtain the material mechanical parameters and geometric dimensions of the casing, cement ring, and rock ring; Based on the interface bonding state of the first interface and the second interface, the interface transfer coefficients of the first interface and the second interface are determined respectively, wherein the first interface is the interface between the rock ring and the cement ring, and the second interface is the interface between the cement ring and the casing. Establish displacement and strain field models for each layer, as well as interface continuity and boundary conditions; Based on the displacement field, calculate the target strain at key radial positions of the casing, cement ring, and rock ring; based on the strain field, calculate the strain transfer efficiency of the rock ring and cement ring, the strain transfer efficiency of the cement ring and casing, and the strain transfer efficiency inside the casing wall. The total strain transfer efficiency is calculated based on the strain transfer efficiency of the rock ring and cement ring, the strain transfer efficiency of the cement ring and casing, and the strain transfer efficiency inside the casing wall. By varying the material mechanical parameters, geometric dimensions, and interfacial bonding state of the casing, cement ring, and rock ring, the experiment was cyclically executed to determine the influence of these parameters on strain transfer efficiency. Using radial strain as the target strain, the strain r=r on the inner wall of the casing was obtained. i The measured radial strain and the total radial strain transfer efficiency were measured. Based on the total radial strain transfer efficiency and the inner wall of the casing, r=r i Measured radial strain at the location, inverted and compared with the inner wall of the casing r=r i Rock rings located in the same radial direction, r=r m The actual radial strain is ; Calculate r at any two positions of the rock ring a and r b The radial deformation between them is calculated using the following formula: ； in, The inner radius of the casing is r = r i Radial strain; The radius of the rock ring is r = r m Radial strain; The total radial strain transfer efficiency; A p These are the constant coefficients in the general solution of rock ring displacement; B p These are the constant coefficients in the general solution of rock ring displacement; The wellbore structure strain transfer model device includes: The wellbore structure is cylindrical in shape and includes, from the inside to the outside, a casing, a cement sheath, and a rock sheath in a radial direction. Optical fibers are arranged in a straight line along the axial direction on the inner wall of the casing, the outer wall of the casing, and the outer wall of the cement sheath. The supporting structure includes a bracket structure, a loading column head, and a base frame structure. The base frame structure is mounted on the bracket structure and located at the bottom. The lower surface of the loading column head and the upper surface of the base frame structure are concave arc surfaces, and both are matched with the outer surface of the wellbore structure and are fitted to the outer surface of the rock annulus. The base frame structure supports the wellbore structure. A pressure loading device is installed on the support structure and located above the wellbore structure, and applies a compressive load radially toward the wellbore structure; A strain detection device, connected to the optical fiber, is used to measure strain data distributed along the optical fiber.

2. The experimental method for using a strain transfer model device based on a well shaft structure as described in claim 1, characterized in that, The parameters for the wellbore structure are determined as follows: Determine the main dimensionless parameters controlling strain transfer under radial loading conditions, including geometric parameters, material stiffness parameters, Poisson's ratio parameters, interface parameters, and loading parameters; The geometric parameters include: ；（1） ；（2） ；（3） Material stiffness parameters include: ；（4） ；（5） Poisson's ratio parameters include: ；（6） ；（7） ；（8） Interface parameters include: ；（9） ；（10） Loading parameters include: ；（11） in, Let be the nth master dimensionless parameter in k, where k is w or d. When k is w, it represents the shaft structure of the model, and when k is d, it represents the shaft structure of the mine. n takes an integer between 1 and 11. t c,k t p,k H k R s,k These represent the thickness of the cement ring, the thickness of the rock ring, the sample thickness, and the outer radius of the casing in k, respectively, in meters. E c,k E s,k E p,k、 These are the elastic moduli of the cement ring, the elastic moduli of the casing, and the elastic moduli of the rock ring in k, respectively, in Pa. ν p,k ν c,k ν s,k These are the Poisson's ratios of the rock ring, cement ring, and casing in k, respectively. , Let be the tangential equivalent stiffness at the interface between the rock sheath and the cement sheath, and the tangential equivalent stiffness at the interface between the cement sheath and the casing, respectively, in Pa·m. -1 ; R s,k Let be the outer radius of the sleeve in k, in meters. Let Pa be the characteristic stress corresponding to radial loading in k; Based on the determined master dimensionless parameters of strain transfer under radial loading conditions, equations (12) to (15) are obtained, including... (12) ；（13） ；（14） ；（15） Based on the selected outer radius of the model casing and Equation (12), calculate the thickness of the cement ring, the thickness of the rock layer, and the height of the sample in the model; Based on equation (12) and the elastic modulus of the selected model rock ring material, calculate the elastic modulus of the cement ring and the casing in the model. Based on the Poisson's ratio of the model rock ring material and Equation (14), determine the Poisson's ratio of the model cement ring and the casing; Based on the tangential equivalent stiffness of the interface between the rock ring and cement ring in the mine, the tangential equivalent stiffness of the interface between the cement ring and the casing, and Equation (13), the tangential equivalent stiffness of the interface between the rock ring and cement ring in the model and the tangential equivalent stiffness of the interface between the cement ring and the casing are calculated. Based on the characteristic stress corresponding to radial loading in the mine and Equation (15), the characteristic stress corresponding to radial loading in the model is calculated.

3. The experimental method for using a strain transfer model device based on a well shaft structure as described in claim 1, characterized in that, The bonding states of the rock ring and cement ring interface, and the cement ring and casing interface include fully bonded state, partially bonded state, frictional slip state, and completely debonded state.

4. The experimental method for using a strain transfer model device based on a well shaft structure as described in claim 1, characterized in that, The support structure includes an upper crossbeam, a lower crossbeam, and several supporting columns. The upper crossbeam is located above the lower crossbeam, and the supporting columns connect the upper crossbeam and the lower crossbeam. The base frame structure is mounted on the lower crossbeam.

5. The experimental method for using a strain transfer model device based on a well shaft structure as described in claim 4, characterized in that, The pressure loading device is a hydraulic loading assembly, which includes a hydraulic cylinder and a hydraulic piston disposed in the hydraulic cylinder. The hydraulic cylinder is mounted on the upper crossbeam, and the hydraulic piston is disposed in the hydraulic cylinder and can move radially along the well shaft structure.

6. The experimental method for using a strain transfer model device based on a well shaft structure as described in claim 1, characterized in that, The rock ring has a central mounting hole, the sleeve is placed in the mounting hole, and an annular gap is formed between the sleeve and the rock ring; a cement ring is inserted into the annular gap. The optical fiber is placed at the interface between the rock ring and the cement ring.

7. The experimental method for using a strain transfer model device based on a well shaft structure as described in claim 1, characterized in that, The strain detection device is a distributed fiber optic demodulator.

Images