A kind of fracture network shear amplification follow-up seal injection-production heat exchange test device and method

Abstract

The application discloses a kind of fissure network shear amplification and translation servo seal injection-production heat exchange test device and method, belong to rock mechanics and geothermal development test technical field.The device includes shear loading system, constant normal stiffness loading system, injection-production heat exchange system, temperature control system and servo seal system;Servo seal system is located in the upper and lower ends of main fissure, is composed of continuous flexible coating, rubber filling body, friction reduction component and negative Poisson's ratio structure, respectively bears liquid tight, contour support, friction reduction and normal spacing compensation function.After shear, in the condition of maintaining the shear position of sample, normal boundary and temperature state, through porous end plate in situ continuous injection-production heat exchange, force, displacement, pressure, flow and temperature parameters are synchronously collected.The application can solve the problems of seal failure, friction interference test and heat exchange test distortion caused by sample state change after shear, and is suitable for quantitative evaluation of fissure network shear amplification and translation effect and injection-production heat exchange performance.

Description

Technical Field

[0001] This invention belongs to the field of rock mechanics and geothermal development testing technology, specifically relating to a fracture network shear permeability enhancement follow-up sealing injection-production heat transfer test device and method, which is particularly suitable for evaluating the shear permeability enhancement effect and testing the in-situ injection-production heat transfer characteristics of rough main fractures containing secondary fracture networks under constant normal stiffness boundaries. Background Technology

[0002] Enhanced geothermal systems (EGS) are a core technological approach for the development of deep geothermal resources. Their reservoirs typically consist of a complex fracture network formed by naturally occurring primary fractures and surrounding secondary fractures. Inducing shear displacement in the primary fractures to generate a dilatation effect can enhance the overall conductivity of the fracture network (i.e., shear permeability enhancement), a crucial technique for improving reservoir heat transfer efficiency. The normal deformation accompanying the shearing of the primary fractures and the alteration of the connectivity of secondary fractures directly affect the seepage path of the heat transfer fluid and the heat exchange process. Therefore, accurate characterization of the seepage and heat transfer characteristics of the fracture network before and after shear permeability enhancement is necessary through laboratory experiments.

[0003] Existing fracture shear-seepage coupling test devices mostly use flexible rubber strips, sealing gaskets, or integral rubber sleeves to seal the edges of the main fracture to prevent fluid leakage along the fracture ends. However, during actual shearing, the rock masses on both sides simultaneously experience shear displacement along the fracture extension direction and spacing changes (shear dilatation or shear contraction) along the fracture normal. The aforementioned single flexible seal will simultaneously bear shear kneading, normal compression, and local tension, easily leading to torsional deformation, local detachment, or extrusion failure. Increasing the sealing preload to improve sealing reliability will significantly increase the relative motion resistance of the rock masses on both sides, interfering with the accurate measurement of shear load; decreasing the preload will easily lead to end leakage, affecting the accuracy of seepage testing. Existing sealing structures cannot simultaneously meet the requirements of continuous liquid tightness, low-friction follow-up, and adaptive compensation of normal spacing.

[0004] On the other hand, existing testing procedures typically involve removing the load, disassembling and transferring the specimen after shearing, and then connecting the specimen to a seepage or heat transfer testing system. This process inevitably alters the contact state, aperture distribution, and residual stress level of the fracture surface, causing subsequent injection-production heat transfer tests to fail to correspond to the actual fracture structure at the end of shearing, resulting in significant errors in the test results. If attempts are made to conduct injection-production heat transfer directly in situ under load, it is also necessary to address issues such as how to adapt the injection-production endplate and fluid pipeline to the rock mass shear dilatation displacement, and how to achieve uniform injection-production to eliminate the local effects of single-point inflow. Furthermore, the surrounding rock of actual underground reservoirs has finite stiffness, forming an elastic constraint on fracture shear dilatation, while most existing testing devices can only achieve constant normal load or constant normal displacement boundaries, failing to accurately simulate the stiffness constraint conditions of real surrounding rock.

[0005] In summary, the existing technology has not yet provided a test device that can maintain a reliable low-friction seal throughout the shearing process, simulate the stiffness boundary of the surrounding rock, and carry out continuous in-situ injection-production heat exchange without unloading and transferring the sample after shearing. This restricts the in-depth study of the shear permeability enhancement mechanism and heat transfer characteristics of fracture networks. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a fracture network shear-enhanced dynamic sealing injection-production heat transfer test device and method. This invention aims to solve the technical problems of conventional single flexible seals being prone to failure under the combined action of shear slip and normal deformation, frictional resistance interfering with test accuracy, and changes in fracture state and distortion of injection-production heat transfer test caused by sample unloading and transfer after shearing. At the same time, it achieves constant normal stiffness surrounding rock boundary simulation and multi-pore uniform injection-production test.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a fracture network shear permeability enhancement follow-up sealing injection-production heat exchange test device, comprising a rigid reaction steel frame, a temperature control system, a fracture network rock mass sample, a shear loading system, a constant normal stiffness loading system, an injection-production heat exchange system, a follow-up sealing system, and a monitoring and control system.

[0008] The fractured network rock mass sample includes a left-side fractured rock mass and a right-side fractured rock mass arranged opposite each other. The opposing surfaces of the two together form a vertically rough penetrating main fracture. The left-side fractured rock mass contains left-side secondary fractures, and the right-side fractured rock mass contains right-side secondary fractures. At least some of the secondary fractures are connected to the main fractures and / or the injection-production boundary of the fractured network rock mass sample, forming a complete seepage heat exchange channel.

[0009] The shear loading system includes an upper shear loading device and a lower shear loading device arranged symmetrically, as well as corresponding upper and lower loading force transmission plates. The upper and lower shear loading devices are supported on the rigid reaction steel frame by upper and lower loading fixed support assemblies, respectively, and drive the right-side fractured rock mass to generate shear displacement along the extension direction of the vertical rough penetration main fracture through the upper and lower loading force transmission plates.

[0010] The constant normal stiffness control device is used to simulate a finite stiffness surrounding rock boundary. It includes a normal servo actuator, a normal loading rod, a normal force detection unit, a normal displacement detection unit, and a controller. The controller is connected to the normal servo actuator, the normal force detection unit, and the normal displacement detection unit. Based on the real-time acquired normal displacement increment and preset normal stiffness parameters, the controller dynamically adjusts the normal load: increasing the normal load when the main fracture dilates and decreasing the normal load when the main fracture contracts, thus maintaining a constant ratio between the normal stress increment and the normal displacement increment.

[0011] The injection-production heat exchange system includes an injection end plate and a production end plate respectively attached to the outer surfaces of the left and right rock bodies. Both end plates adopt an integrated load-bearing and injection-production structure, including a rigid load-bearing part of the end plate, an internal shared fluid cavity, multiple hemispherical fluid holes distributed in a matrix, and a main fluid pipe. The rigid load-bearing part of the end plate simultaneously undertakes the functions of normal load transmission and fluid distribution cavity support. It includes an outer rigid frame and a central rigid orifice plate set within the outer rigid frame. The outer rigid frame and the central rigid orifice plate are fixedly connected as a whole. The shared fluid cavity is formed inside the rigid load-bearing part of the end plate. All the hemispherical fluid holes of the injection end plate are connected to the shared fluid cavity of the same end plate, and all the hemispherical fluid holes of the production end plate are connected to the shared fluid cavity of the other end plate, forming a boundary between non-zonal multi-hole uniformly distributed injection and confluence production. The main fluid pipe passes through the internal through holes of the loading component and support assembly along the normal direction and is connected to an external fluid supply and collection device.

[0012] The following sealing system includes an upper following sealing component and a lower following sealing component, respectively spanning the upper and lower ends of the main fracture. Each component adopts a functionally divided composite structure: a continuous flexible coating layer serves as the outer water-blocking structure, continuously covering the internal components and sealingly connecting with the structures on both sides, undertaking the main liquid-tight function; two rubber fillers connect the fixed structure on the left and the movable structure on the right, respectively, with a hardness higher than that of the continuous flexible coating layer, and their relative edges form a staggered mating interface to maintain the contour of the sealing component; friction-reducing components are respectively set above and below the negative Poisson's ratio structure at the relative misalignment interface; the negative Poisson's ratio structure is set in the middle of the staggered mating interface. When the right fracture rock mass undergoes shear displacement and normal spacing change relative to the left fracture rock mass, the friction-reducing components reduce the relative displacement resistance by rolling or sliding, and the negative Poisson's ratio structure compensates for the normal spacing change through reversible deformation, achieving spacing compensation; the continuous flexible coating layer maintains continuous sealing against vertical roughness penetrating the upper and lower ends of the main fracture.

[0013] The temperature control system includes a heating component, a heat preservation component, a temperature detection component, and a temperature controller. The temperature detection component detects the temperature of the left-side fractured rock mass, the right-side fractured rock mass, and the area adjacent to the vertically roughened main fracture. The temperature controller adjusts the heating component according to the detected temperature to keep the fractured network rock mass sample within a preset temperature range during the shearing stage and the injection-production heat exchange stage.

[0014] The monitoring and control system coordinates the operation of the entire system and includes a computer, stress-temperature monitoring components, normal force detection unit, shear force detection unit, normal displacement detection unit, shear displacement detection unit, inlet pressure detection unit, outlet pressure detection unit, inlet temperature detection unit, outlet temperature detection unit, total flow rate detection unit, and synchronous data acquisition unit. The stress-temperature monitoring components are respectively arranged on the upper and lower parts of the left and right fractured rock masses and include adjacent or integrated stress detection units and temperature detection units. The system is used to synchronously collect force, displacement, stress, temperature, pressure, and flow rate parameters. During the shearing stage, it maintains reliable sealing and stable normal stiffness boundaries. After reaching the preset shear displacement, it keeps the rock mass position and load state unchanged and directly starts the injection-production heat exchange system to carry out in-situ continuous testing.

[0015] Furthermore, the left-side fractured rock mass is supported on the left side of the rigid reaction steel frame via a water injection end plate and a left-side axial fixed support assembly; the outer side of the right-side fractured rock mass is sequentially equipped with a extraction end plate, a constant normal stiffness control device, and a right-side axial telescopic support assembly. The right-side axial telescopic support assembly is connected to the right side of the rigid reaction steel frame and can extend and retract along the normal direction of the main fracture to accommodate the normal dilatation or contraction displacement of the right-side rock mass. The rigid reaction steel frame surrounds the fractured network rock mass sample, the shear loading system, and the constant normal stiffness loading system; the left-side axial fixed support assembly, the upper loading fixed support assembly, and the lower loading fixed support assembly are respectively fixedly connected to the rigid reaction steel frame; the right-side axial telescopic support assembly includes a fixed support section and a movable support section that cooperate with each other and can extend and retract relative to each other along the normal direction of the main fracture. The fixed support section is connected to the rigid reaction steel frame, and the movable support section is connected to the constant normal stiffness control device.

[0016] Furthermore, each hemispherical fluid orifice includes a cylindrical pipe section and a hemispherical opening connected to one end of the cylindrical pipe section facing the fractured rock mass sample. The other end of the cylindrical pipe section is connected to the end plate via a shared fluid cavity. Multiple hemispherical fluid orifices are arranged in a multi-row, multi-column matrix. The rigid load-bearing portion of the injection end plate, facing the left fractured rock mass, is provided with a flexible sealing strip surrounding the multiple hemispherical fluid orifices. The left axial fixed support assembly, the right axial telescopic support assembly, and the normal loading member located inside both are all provided with axial through holes adapted to the main fluid pipe. The main fluid pipe of the injection end plate passes sequentially through the axial through holes of the left normal loading member and the left axial fixed support assembly and is connected to the injection supply device. The main fluid pipe of the extraction end plate passes sequentially through the axial through holes of the right normal loading member and the right axial telescopic support assembly and is connected to the extraction collection device.

[0017] Furthermore, the continuous flexible coating layer has corrugated sections or reserved relaxation in the area near the staggered mating interface to disperse the tensile deformation caused by the relative misalignment of the two side structures; the friction reduction component includes multiple cylindrical rollers arranged along the shear direction and a retaining structure that restricts the relative position of the cylindrical rollers. The axis of the cylindrical rollers is perpendicular to the longitudinal section of the corresponding follow-up sealing component, and the main deformation direction of the negative Poisson's ratio structure is adapted to the change direction of the normal distance between the left fixed structure and the right movable structure.

[0018] Furthermore, the present invention also provides a test method for fracture network shear permeability enhancement and follow-up sealing injection-production heat transfer, implemented using the above-mentioned apparatus, including the following steps: S1. Sample preparation: Process two fractured rock masses containing secondary fractures, and assemble them to form a vertical roughness that penetrates the main fracture, ensuring that the secondary fractures are connected to the main fracture and the injection-production boundary. Record the initial fracture parameters and sample size.

[0019] S2. Assembly and Leak Detection: Assemble the sample, injection and sampling end plate, follow-up sealing assembly, various loading systems and support assemblies onto the rigid reaction steel frame, connect the fluid pipeline and sensor, and complete the low-pressure sealing check and system calibration.

[0020] S3. Heating and Reference Correction: The temperature control system is activated to heat the sample to the preset temperature and maintain it stable. The force, displacement, stress, and temperature detection signals are corrected at high temperature to eliminate the influence of temperature drift.

[0021] S4. Normal loading and mode switching: Apply initial normal load, and after the load and displacement stabilize, switch to constant normal stiffness control mode.

[0022] S5. Constant normal stiffness shear penetration enhancement: Drives the right rock mass to generate a preset shear displacement, and adjusts the normal load in real time according to the normal displacement increment; during shearing, the friction reduction component releases the relative displacement displacement, the negative Poisson's ratio structure adaptively compensates for the change in normal spacing, and the continuous flexible coating layer maintains the end liquid tightness.

[0023] S6. In-situ state maintenance: After reaching the preset shear displacement, the shear position is locked, the normal load is not removed, the specimen is not disassembled or transferred, and the constant normal stiffness boundary and temperature conditions are maintained to keep the crack contact state and sealing performance unchanged.

[0024] S7. In-situ injection-production heat exchange test: Start the injection-production heat exchange system. The heat exchange fluid is uniformly injected into the fracture network through the porous end plate. After flowing through the main fracture and secondary fracture, it is collected and discharged by the production end plate.

[0025] S8. Data Acquisition and Analysis: Simultaneously record mechanical, displacement, temperature, pressure, and flow parameters throughout the entire process; calculate shear penetration enhancement factor, conductivity, heat extraction power, and thermal breakthrough characteristics; and evaluate the shear penetration enhancement and heat transfer performance of the fracture network. Specifically, determine the overall conductivity change of the fracture network before and after shearing based on the total flow rate and inlet / outlet pressure difference; determine the heat extracted by the heat transfer fluid from the fracture network rock mass sample based on the inlet temperature, outlet temperature, and total flow rate; and determine the thermal breakthrough characteristics based on the change of outlet temperature over time.

[0026] Furthermore, in step S5, taking the direction of shear dilatation of the main crack as the positive direction of the normal displacement, the normal load is adjusted according to the following formula:

[0027] In the formula, For the current target normal load, For the initial normal load, To preset the normal stiffness, The nominal area of ​​the main fracture The normal displacement increment is relative to the initial state, with the dilatation direction of the main crack as the positive direction of the normal displacement increment. When the main crack undergoes dilatation, the normal load is increased; when the main crack undergoes contraction, the normal load is decreased, so that the ratio of the normal stress increment to the normal displacement increment remains at the preset normal stiffness.

[0028] Furthermore, in steps S5 to S7, the right-side axial expansion and contraction support assembly expands and contracts axially with the normal shear dilatation displacement of the right-side fractured rock mass, so that the rigid bearing part of the end plate of the extraction end plate remains in contact with the outer surface of the right-side fractured rock mass; the friction reduction assembly rolls with the relative misalignment of the left-side fixed structure and the right-side movable structure; the negative Poisson's ratio structure compensates for the change in the distance between the two structures through deformation, and the continuous flexible coating layer keeps the upper and lower ends of the main fracture closed.

[0029] Compared with the prior art, the present invention has the following advantages: 1. This invention features a novel functionally divided composite follow-up sealing structure, in which liquid tightness maintenance, interface friction reduction, normal spacing compensation, and contour support are respectively undertaken by a continuous flexible coating layer, a friction-reducing component, a negative Poisson's ratio structure, and a rubber filler. This avoids the problem of rubbing failure caused by a single seal being subjected to shearing, compression, and tension simultaneously. The friction-reducing component significantly reduces shear slip resistance and minimizes the interference of sealing friction on load testing. The negative Poisson's ratio structure adaptively compensates for changes in normal spacing caused by shear expansion / contraction, and in conjunction with the corrugated flexible coating layer, it can maintain reliable liquid tightness even under large shear displacements.

[0030] 2. This invention enables in-situ continuous injection and extraction heat transfer testing after shearing. After shearing, there is no need to unload, disassemble, or transfer the sample. The heat transfer test can be carried out directly while keeping the crack opening, contact state, residual stress, normal boundary, and temperature state completely unchanged. This fundamentally eliminates the state error caused by sample transfer and significantly improves the accuracy and repeatability of the test results.

[0031] 3. The present invention adopts a constant normal stiffness loading mode during the test, which can dynamically adjust the normal load according to the stiffness of the target surrounding rock, and more realistically simulate the elastic constraint boundary of the surrounding rock of the underground reservoir. The test results are more in line with the actual engineering. By adjusting the preset stiffness parameters, comparative tests under different surrounding rock conditions can be carried out flexibly.

[0032] 4. The injection and production end plate of the present invention adopts an integrated design of rigid load bearing and fluid distribution. The matrix-type hemispherical fluid holes, together with the shared fluid cavity, realize large-area uniform injection and production, and weaken the local effect of single-point injection. The built-in arrangement of the main fluid pipe saves end space. With the right-side axial telescopic support component, it can move synchronously with the rock mass shear dilation and keep the end plate tightly attached, adapting to normal deformation while maintaining the stability of the injection and production boundary.

[0033] 5. The multi-parameter synchronous acquisition system of the present invention can acquire full mechanical, seepage and thermal data under a unified time reference, and can systematically evaluate the shear permeability enhancement effect, seepage evolution law and heat transfer performance, providing a reliable experimental means for the study of shear permeability enhancement mechanism and development parameter optimization of fractured geothermal reservoirs. Attached Figure Description

[0034] Figure 1 This is a three-dimensional structural diagram of the experimental device of the present invention.

[0035] Figure 2 for Figure 1 A schematic diagram of the longitudinal section inside a medium-rigid reaction steel frame.

[0036] Figure 3 This is a schematic diagram of the planar structure of the contact surface between the water injection end plate and the rock mass of the present invention.

[0037] Figure 4 for Figure 2 A schematic diagram of the longitudinal cross-sectional structure of the injection and extraction end plate.

[0038] Figure 5 This is a partially enlarged longitudinal cross-sectional view of the follow-up sealing assembly of the present invention.

[0039] Figure 6 This is a flowchart of the test method of the present invention.

[0040] In the diagram: 1-Temperature control system; 2-Rigid load-bearing part of end plate; 3-Lower shear loading device; 4-Lower loading force transmission plate; 5-Common fluid cavity of end plate; 6-Left secondary fracture; 7-Main fracture; 8-Lower follow-up sealing assembly; 9-Upper follow-up sealing assembly; 10-Left upper stress-temperature monitoring assembly; 11-Right upper stress-temperature monitoring assembly; 12-Upper shear loading device; 13-Upper loading force transmission plate; 14-Right lower stress-temperature monitoring assembly; 15-Left fractured rock mass; 16-Computer; 17-Injection supply device; 18-Production collection device; 19-Inlet pressure detection unit; 20 21-Outlet pressure detection unit; 22-Inlet temperature detection unit; 23-Outlet temperature detection unit; 24-Constant normal stiffness control device; 25-Right side fractured rock mass; 26-Right side secondary fracture; 27-Left side lower stress-temperature monitoring component; 28-Hemispherical fluid orifice; 29-Flexible sealing strip; 30-Main fluid pipe; 31-Right side axial expansion support component; 32-Continuous flexible coating layer; 33-Negative Poisson's ratio structure; 34-Friction reduction component; 35-Rubber filler; 36-Rigid reaction steel frame; 37-Left side axial fixed support component; 38-Upper loading fixed support component; 39-Lower loading fixed support component. Detailed Implementation

[0041] The present invention will be further described below.

[0042] Example 1: This example is a preferred embodiment of the fracture network shear-enhanced permeability follow-up sealing injection-production heat transfer test device. The overall structure is as follows: Figure 1 and Figure 2 As shown.

[0043] The core of this device is a closed reaction frame provided by a rigid reaction steel frame 35. The fractured network rock mass sample, shear loading system, constant normal stiffness loading system, and follow-up sealing system are all arranged inside the steel frame. The temperature control system 1 is set around the entire loading and sample area to form a temperature-controlled test environment.

[0044] The fractured rock mass sample is formed by assembling a fractured rock mass 15 on the left and a fractured rock mass 24 on the right. The opposing surfaces of the two are split or carved to form a vertically roughened main fracture 7 with complementary roughness morphology. The main fracture 7 extends to the upper and lower boundaries of the sample. A secondary fracture 6 is pre-fabricated inside the fractured rock mass 15 on the left, and a secondary fracture 25 is pre-fabricated inside the fractured rock mass 24 on the right. The secondary fractures can be obtained by cutting, pre-embedding thin sections for extraction, 3D printing casting, or processing natural rock samples. At least some of the secondary fractures intersect with the main fracture 7, and some of the secondary fractures extend to the injection and production boundaries on the left and right sides of the sample, forming a complete seepage channel from the injection end to the production end. In the comparative test of the same group, the initial fracture aperture, roughness, network topology parameters and dimensions of the sample are kept consistent.

[0045] The left side of the fractured rock mass 15 is attached to the water injection end plate and fixed to the left column of the rigid reaction steel frame 35 via the left axial fixed support assembly 36. The right side of the fractured rock mass 24 is attached to the extraction end plate and connected outward in sequence to the constant normal stiffness control device 23 and the right axial telescopic support assembly 30. The right axial telescopic support assembly 30 consists of a fixed support section and a movable support section. The fixed support section is fixed to the right column of the rigid reaction steel frame 35, and the movable support section can slide and expand along the normal (horizontal direction) of the main fracture 7. It is equipped with a guide structure to limit out-of-plane deflection and provide follow-up support for the shear dilatation displacement of the right rock mass.

[0046] The temperature control system 1 includes an electric heating element, an insulation layer, multi-point temperature sensors, and a temperature controller, which can uniformly heat and insulate the sample and the loading area. For high-temperature test scenarios, the end plates, seals, sensors, and pipelines are all made of temperature-resistant and adaptable materials. The heating adopts a staged heating strategy. The temperature is considered stable after the temperature fluctuation at the measuring points inside the rock mass is lower than a preset threshold (e.g., 0.5℃ / h). Subsequently, sensor benchmark correction under high temperature is performed to eliminate the influence of temperature drift on force and displacement tests.

[0047] The shear loading system employs a dual-actuator arrangement with upper and lower components. The upper shear loading device 12 is mounted on top of the rigid reaction steel frame 35 via an upper loading fixed support assembly 37, while the lower shear loading device 3 is mounted on the bottom of the steel frame via a lower loading fixed support assembly 38. The loading devices can utilize electro-hydraulic servo cylinders, electric servo cylinders, or mechanical loading mechanisms. Shear force is transmitted to the upper and lower end faces of the right-side fractured rock mass 24 via the upper loading force transmission plate 13 and the lower loading force transmission plate 4, driving it to generate relative shear displacement vertically. A master-slave synchronous control strategy can be adopted to ensure that the shear displacement of the right-side rock mass is consistent with the preset path. The shear force and shear displacement are detected by high-precision force sensors and displacement sensors, respectively.

[0048] The constant normal stiffness control device 23 is used to simulate the elastic constraints of the surrounding rock. Its core components include a normal servo actuator, a normal force sensor, a normal displacement sensor, and a closed-loop controller. The control principle is as follows: First, apply the initial normal load. After the load and displacement stabilize, record the initial normal position. Switch to constant normal stiffness control mode. The controller reads the real-time normal displacement at a fixed sampling period. Calculate the normal displacement increment And calculate the target normal load using the following formula:

[0049] In the formula, The normal stiffness per unit area is preset, and the unit is Pa / m; The nominal load area of ​​the main fracture is given. The corresponding normal stress relationship is... .

[0050] The controller uses the difference between the target load and the measured load as the control error, and drives the normal actuator to adjust the output force through PID or model prediction algorithms: when the main fracture dilatation ( When the main fracture shrinks ( ), the normal load increases linearly with displacement; when the main fracture shrinks ( When the normal load decreases accordingly, an elastic constraint boundary equivalent to the stiffness of the surrounding rock is achieved. This can be achieved by setting different... The value can simulate surrounding rock conditions with different stiffnesses; when At that time, the system degenerates into a constant normal load mode.

[0051] A gap is reserved between the loading force transmission plate and the guide surface to match the maximum shear expansion displacement, ensuring that shear and normal deformations do not interfere with each other; the overall flexibility of the device needs to be calibrated by standard rigid body loading before the test to deduct the influence of the deformation of the loading system itself.

[0052] The water injection end plate and the production end plate have basically the same structure, both being integrated load-bearing and injection-production designs, as shown in the following diagram. Figure 3 and Figure 4 As shown. The main body of the end plate is the rigid load-bearing part 2, which is formed by the outer rigid frame and the central rigid orifice plate. The whole has sufficient bending and compressive strength and can uniformly transmit normal loads. The end plate has a common fluid cavity 5, which is a single, unpartitioned, connected cavity that serves as a buffer space for fluid distribution and collection. Multiple hemispherical fluid holes 27 are machined on the central rigid orifice plate and are uniformly arranged in a multi-row, multi-column matrix. Each hemispherical fluid hole 27 consists of an inner cylindrical pipe section and a hemispherical opening facing the rock mass. The cylindrical pipe section is connected to the common fluid cavity 5 of the end plate. The edge of the hemispherical opening is flush with the bearing surface of the end plate, which ensures smooth fluid flow and avoids stress concentration at the hole opening. The coverage area of ​​the hole array matches the fracture exposure area to ensure that the injected and produced fluids fully act on the fracture network.

[0053] On the rock mass contact surface of the water injection end plate, an annular flexible sealing strip 28 is embedded around the periphery of the hemispherical fluid hole array 27. After being pre-tightened in the normal direction, it fits the rock mass surface to prevent fluid from leaking from the periphery of the end plate. The sealing strip can be made of materials such as heat-resistant silicone rubber or fluororubber.

[0054] The main fluid pipe 29 extends from the middle of the back side of the end plate, runs along the normal direction, and passes through the axial through holes inside the normal loading component and the support assembly, finally connecting to the external fluid system. The main fluid pipe 29 at the injection end connects to the injection supply device 17, with an inlet pressure detection unit 19 and an inlet temperature detection unit 21 sequentially installed on the pipe. The main fluid pipe 29 at the production end connects to the production collection device 18, with an outlet pressure detection unit 20 and an outlet temperature detection unit 22 sequentially installed on the pipe. The total flow detection unit can be arranged in either the injection or production main pipe. The production side main fluid pipe is connected to the external fixed pipeline via a temperature- and pressure-resistant flexible hose or a corrugated metal pipe, with sufficient allowance to accommodate the normal displacement during shear dilation of the right-side rock mass, avoiding strain on the pipe joints. The fluid volume of the end plate cavity can be pre-calibrated for subsequent data processing to correct for fluid residence time and heat capacity effects.

[0055] The upper follower-type sealing assembly 9 and the lower follower-type sealing assembly 8 have the same structure, respectively bridging the upper and lower ends of the main crack 7, and are used to seal the fluid leakage path at the end of the crack. The detailed structure of the assembly is as follows... Figure 5 As shown.

[0056] The outer layer of the component is a continuous flexible covering layer 31, made of a low-modulus, high-elongation flexible water-blocking material (such as fluororubber-coated fabric or silicone rubber membrane). Its left and right edges are respectively sealed and bonded to the left fixed structure (left rock mass / left end plate extension) and the right movable structure (right rock mass / right end plate extension), forming a continuous liquid-tight barrier that performs the core sealing function. Inside the covering layer are two independent rubber fillers 34, which are fixed to the left fixed structure and the right movable structure, respectively. The rubber fillers 34 are made of rubber or elastic composite materials with a hardness higher than the continuous flexible covering layer 31, used to maintain the overall contour of the sealing component, limit the deformation area, and prevent the flexible covering layer from collapsing inward. The relative edges of the two rubber fillers 34 are machined into staggered mating interfaces, forming two relative sliding surfaces and a middle receiving space. A set of friction-reducing components 33 is installed at each of the upper and lower sliding surfaces, and a negative Poisson's ratio structure 32 is installed in the middle receiving space.

[0057] The friction-reducing component 33 consists of multiple cylindrical rollers arranged along the shear direction and a cage. The roller axes are perpendicular to the longitudinal section, allowing them to roll freely at the relative misalignment interface of the rubber fillers on both sides. This converts sliding friction into rolling friction, significantly reducing the motion resistance of shear misalignment and minimizing the interference of sealing friction on the shear force test. The friction-reducing component can also take the form of needle rollers, low-friction sliding plates, etc. All rolling / sliding components are encapsulated inside the coating layer, isolating them from the test fluid.

[0058] The negative Poisson's ratio structure 32 adopts a concave honeycomb or rotating unit type elastic lattice structure, with its main deformation direction arranged along the normal direction. A certain amount of preload is applied during assembly. When the shear dilatancy of the rock mass on the right side causes the normal distance between the two structures to increase, the negative Poisson's ratio structure contracts laterally and elongates normally, continuously providing elastic support. When the distance decreases, the structure is compressed, and the reversible deformation adaptively compensates for the change in normal distance, always maintaining the interface fit and avoiding gaps or excessive compression in the seal.

[0059] The continuous flexible covering layer 31 has corrugated sections or reserved relaxation margins in the area corresponding to the misalignment interface. It can gradually expand or contract with the relative misalignment of the two sides of the structure, dispersing the shear displacement to a longer section and avoiding local excessive stretching that could lead to cracking.

[0060] This sealing structure achieves a three-in-one "liquid tightness-friction reduction-compensation" through functional decomposition: the continuous flexible coating layer 31 is dedicated to water blocking and does not bear the main friction and extrusion loads; the friction reduction component 33 is dedicated to releasing shear displacement and reducing resistance; the negative Poisson's ratio structure 32 is dedicated to adapting to normal deformation. The three work together to significantly improve the sealing reliability and service life under conditions of large shear displacement and large normal deformation.

[0061] The monitoring and control system is based on a computer 16, and is equipped with a synchronous data acquisition unit and various sensors.

[0062] Mechanical and displacement monitoring: including normal force, shear force, normal displacement, and shear displacement sensors, used for load closed-loop control and mechanical parameter recording; Internal monitoring of rock mass: The upper left stress-temperature monitoring component 10, the upper right stress-temperature monitoring component 11, the lower right stress-temperature monitoring component 14, and the lower left stress-temperature monitoring component 26 are respectively buried in the upper and lower parts of the left and right rock masses, and can simultaneously detect local stress and temperature changes. Fluid parameter monitoring: Inlet pressure detection unit 19, outlet pressure detection unit 20, inlet temperature detection unit 21, outlet temperature detection unit 22 and total flow sensor are used for collecting seepage and heat exchange parameters.

[0063] All monitoring channels are triggered by a unified clock to achieve synchronous acquisition of multiple parameters. The control system can realize the time-series linkage of shear loading, normal stiffness control, temperature control and injection-production system, and automatically execute the entire process of "heating-loading-shearing-holding-injection-acquisition".

[0064] Example 2: This example describes a test method using the above-mentioned device, the process of which is as follows. Figure 6 As shown, the specific steps are as follows: S1. Sample Preparation: Based on the experimental target, lithology was selected, and the samples were processed into rectangular rock blocks of a predetermined size. Left-side fractured rock mass 15 and right-side fractured rock mass 24, with complementary roughness surfaces, were prepared using a splitting method. These were then joined to form a vertically rough, through-type main fracture 7. Secondary fractures 6 on the left and 25 on the right were prefabricated within the rock masses on both sides using cutting and pre-embedding techniques, ensuring that the secondary fractures were connected to the main fracture and that at least some of the secondary fractures extended to the injection-production boundaries on the left and right sides. The sample dimensions, nominal area of ​​the main fracture, initial fracture aperture, and roughness coefficient were measured and recorded.

[0065] S2. System Assembly and Leak Detection: Assemble the rigid reaction steel frame 35 and all supporting components. Sequentially install the left-side fractured rock mass 15, the water injection end plate, the right-side fractured rock mass 24, and the extraction end plate. Install the upper follow-up sealing component 9 and the lower follow-up sealing component 8, ensuring the continuous flexible coating layer 31 completely covers the leakage paths at the upper and lower ends of the main fracture, and complete the pre-tightening of the seal. Install the shear loading device and the constant normal stiffness control device 23, deploy various sensors, and connect the fluid pipelines. After assembly, introduce low-pressure water for a leak test. After confirming there are no end leaks or pipeline leaks, perform zero-point calibration on each sensor channel.

[0066] S3. Heating and Reference Correction: Activate temperature control system 1 and heat the sample to the target temperature in stages according to the set heating rate. Continue heating until the temperature at multiple points inside the rock mass reaches the preset range and the fluctuation is stable, indicating thermal equilibrium. At this temperature, perform reference correction on the force, displacement, and stress sensors to eliminate systematic errors caused by temperature drift.

[0067] S4. Initial Normal Loading and Mode Switching: Activate the constant normal stiffness control device 23 to apply the initial normal load in load control mode. Maintain the load until the normal displacement tends to stabilize. Record the initial normal position in this state. Switch the control mode to constant normal stiffness mode. If it is necessary to determine the baseline seepage and heat transfer parameters before shearing, an injection-production test can be carried out at this stage to record the initial flow rate, pressure difference, and temperature data.

[0068] S5. Constant Normal Stiffness Shear Transparency Enhancement: The shear loading system is activated, driving the right-side fractured rock mass 24 to generate vertical shear displacement using displacement control. The shear rate is set according to the test requirements. During the shearing process, the constant normal stiffness control device 23 collects the normal displacement in real time and dynamically adjusts the normal load according to the preset stiffness formula to maintain a constant normal stiffness boundary. During this process, the right-side rock mass undergoes shear displacement relative to the left-side rock mass. The friction-reducing component 33 in the dynamic sealing assembly rolls and releases the shear displacement, reducing the displacement resistance. If accompanied by shear dilatation or shear contraction, the negative Poisson's ratio structure 32 synchronously generates deformation to compensate for the change in normal spacing. The continuous flexible coating layer 31 always maintains the closed state at the end of the main fracture, with no fluid leakage.

[0069] S6. In-situ State Preservation: When the shear displacement reaches the preset value, the shear loading stops and the shear position of the right-side rock mass is locked. The normal load is not removed, no components are disassembled, and the sample is not transferred throughout the process. The constant normal stiffness control mode and temperature setting value are maintained continuously, so that the crack opening, contact state, residual stress, and sealing state are completely preserved in their original state at the end of the shearing.

[0070] S7. In-situ injection-production heat exchange test: Start the injection supply device 17 and set the injection flow rate and injection temperature. The heat exchange fluid enters the common fluid cavity 5 of the water injection end plate through the main fluid pipe 29, and is evenly injected into the left secondary fracture 6 through the matrix hemispherical fluid holes 27. Then it flows into the vertical rough penetrating main fracture 7, and then flows into the production end plate through the right secondary fracture 25, and finally flows into the production collection device 18. During the test, the right axial telescopic support assembly 30 expands and contracts synchronously with the normal deformation of the rock mass, keeping the production end plate in close contact with the rock mass surface; the follow-up sealing assembly continuously maintains the end seal.

[0071] S8. Data Acquisition and Performance Evaluation: Throughout the test, parameters such as normal load, shear load, normal displacement, shear displacement, internal stress and temperature of the rock mass, fluid inlet and outlet pressures, inlet and outlet temperatures, and total flow rate were collected synchronously. After the test, data processing and performance evaluation were performed using the following methods: (1) Evaluation of shear penetration enhancement effect Based on the pressure difference between inlet and outlet With total flow Calculate the overall conductivity of the fracture network :

[0072] in, For inlet pressure, This is due to export pressure.

[0073] By comparing the conductivity before and after shearing, the shear penetration enhancement factor is obtained. If the equivalent flow length L and equivalent flow area A of the sample are known... fIf the hydrodynamic viscosity μ can be reasonably determined, and the Darcy-type linear flow assumption is satisfied at the corresponding stage, then the equivalent permeability can be further calculated: .

[0074] (2) Evaluation of heat exchange performance According to fluid density Specific heat capacity at constant pressure ,flow Calculate the instantaneous heat extraction power based on the temperature difference between the inlet and outlet. :

[0075] Integrating over time yields the cumulative heat output. .

[0076] Based on the decay curve of the outlet temperature over time, the thermal breakthrough time and characteristics are determined, and the reservoir's continuous heat exchange capacity is evaluated.

[0077] Example 3: This example is one of several optional implementation methods. Adjustments can be made as follows without departing from the core concept of this invention: Normal boundary mode: In addition to constant normal stiffness, it can also be switched to constant normal load or constant normal displacement mode according to experimental requirements to adapt to different research scenarios.

[0078] End plate hole array: The arrangement of hemispherical fluid holes can be staggered array, ring array, etc., and can be adjusted according to the sample shape and crack distribution.

[0079] Sealing component materials: Negative Poisson's ratio structures can be made of metal, heat-resistant polymers, or rubber-based composite materials; friction-reducing components can be paired with solid lubricating coatings to further reduce the coefficient of friction.

[0080] Heat exchange medium: In addition to water, other heat exchange media such as heat transfer oil and supercritical CO2 can be used, with matching sealing and piping materials.

Claims

1. A fractured network shear permeability enhancement follow-up sealing injection-production heat transfer test device, comprising a temperature control system, a fractured network rock mass sample, a shear loading system, a constant normal stiffness loading system, and a monitoring and control system, characterized in that, It also includes the injection-extraction heat exchange system and the follow-up sealing system; The fractured network rock mass sample includes a left-side fractured rock mass and a right-side fractured rock mass containing secondary fractures, with a main fracture forming between them, and some secondary fractures communicating with the main fracture and / or the injection-production boundary of the fractured network rock mass sample; the shear loading system is used to induce shear displacement in the right-side fractured rock mass along the extension direction of the main fracture. The constant normal stiffness control device is used to adjust the normal load applied to the fracture network rock mass sample in real time according to the preset normal stiffness and normal displacement increment. The injection-production heat exchange system is used to conduct injection-production heat exchange tests on fractured network rock mass samples. The following sealing system includes an upper following sealing assembly and a lower following sealing assembly, which are respectively positioned across the upper and lower ends of the main crack. Both the upper and lower following sealing assemblies include a continuous flexible covering layer, two rubber fillers, a negative Poisson's ratio structure, and a friction-reducing component. The two rubber fillers are respectively connected to the left fixed structure and the right movable structure. The friction-reducing component is located at the relative misalignment interface of the two rubber fillers. The negative Poisson's ratio structure is located between the two rubber fillers. The continuous flexible covering layer continuously covers the rubber fillers, the negative Poisson's ratio structure, and the friction-reducing component, and is sealed to the left fixed structure and the right movable structure, respectively. The monitoring and control system is used to coordinate and control the shear loading system, the constant normal stiffness loading system, the temperature control system, and the injection-production heat exchange system.

2. The apparatus according to claim 1, characterized in that, The injection-production heat exchange system includes an injection end plate and a production end plate respectively attached to the outer surfaces of the left and right fractured rock masses. Both the injection end plate and the production end plate include a rigid load-bearing part, a common fluid cavity, multiple hemispherical fluid holes, and a main fluid pipe. The multiple hemispherical fluid holes are distributed in a matrix and are respectively connected to the corresponding common fluid cavity of the end plate. The main fluid pipe is connected to the common fluid cavity of the end plate.

3. The apparatus according to claim 2, characterized in that, The left-side fractured rock mass is supported on the left side of the rigid reaction steel frame via a water injection end plate and a left-side axial fixed support assembly. On the outer side of the right-side fractured rock mass, a extraction end plate, a constant normal stiffness control device, and a right-side axial telescopic support assembly are sequentially installed, with the right-side axial telescopic support assembly connected to the right side of the rigid reaction steel frame. The rigid reaction steel frame surrounds the fractured network rock mass sample, the shear loading system, and the constant normal stiffness loading system. The left-side axial fixed support assembly, the upper loading fixed support assembly, and the lower loading fixed support assembly are respectively fixedly connected to the rigid reaction steel frame. The right-side axial telescopic support assembly includes components that cooperate with each other and can move along the main axis... The structure includes a fixed support section and a movable support section with relative expansion and contraction in the fracture normal direction. The fixed support section is connected to a rigid reaction steel frame, and the movable support section is connected to a constant normal stiffness control device. The rigid load-bearing part of the end plate includes an outer rigid frame and a central rigid orifice plate set in the outer rigid frame. The outer rigid frame and the central rigid orifice plate are fixedly connected as a whole. A common fluid cavity is formed inside the rigid load-bearing part of the end plate. All hemispherical fluid holes of the water injection end plate are connected to the common fluid cavity of the same end plate, and all hemispherical fluid holes of the extraction end plate are connected to the common fluid cavity of another end plate to form a non-zoned injection and extraction structure with multi-hole uniform injection and multi-hole confluence extraction.

4. The apparatus according to claim 3, characterized in that, Each hemispherical fluid orifice includes a cylindrical pipe section and a hemispherical opening connected to one end of the cylindrical pipe section facing the fractured rock mass sample. The other end of the cylindrical pipe section is connected to the end plate via a shared fluid cavity. Multiple hemispherical fluid orifices are arranged in a matrix with multiple rows and columns. The rigid load-bearing part of the water injection end plate is provided with a flexible sealing strip surrounding the multiple hemispherical fluid orifices on the side facing the fractured rock mass on the left.

5. The apparatus according to claim 3, characterized in that, The left axial fixed support assembly, the right axial telescopic support assembly, and the normal loading member located inside both are all provided with axial through holes adapted to the main fluid pipe; the main fluid pipe of the water injection end plate passes through the axial through holes of the left normal loading member and the left axial fixed support assembly in sequence and is connected to the injection supply device; the main fluid pipe of the extraction end plate passes through the axial through holes of the right normal loading member and the right axial telescopic support assembly in sequence and is connected to the extraction collection device.

6. The apparatus according to claim 1, characterized in that, The hardness of both rubber fillers is greater than that of the continuous flexible overlay, and their relative edges form a staggered mating interface. The continuous flexible overlay has corrugated sections or reserved relaxation in the area near the staggered mating interface to disperse the tensile deformation caused by the relative misalignment of the two structures. The negative Poisson's ratio structure is located in the middle of the staggered mating interface, and the friction-reducing components are respectively located above and below the negative Poisson's ratio structure at the relatively misaligned interfaces. The friction-reducing components include multiple cylindrical rollers arranged along the shear direction and a retaining structure that restricts the relative position of the cylindrical rollers. The axis of the cylindrical rollers is perpendicular to the longitudinal section of the corresponding follow-up sealing component. The main deformation direction of the negative Poisson's ratio structure is adapted to the direction of change of the normal distance between the left fixed structure and the right movable structure.

7. The apparatus according to claim 1, characterized in that, The temperature control system includes a heating component, a heat preservation component, a temperature detection component, and a temperature controller. The temperature detection component detects the temperature of the left fractured rock mass, the right fractured rock mass, and the area adjacent to the main fracture, respectively. The temperature controller adjusts the heating component according to the detected temperature to keep the fractured network rock mass sample within the preset temperature range during the shearing stage and the injection-production heat exchange stage.

8. A test method for heat transfer during injection and production using a fractured network shear-enhanced permeability system, characterized in that, The test is carried out using the test apparatus according to any one of claims 1 to 7, and includes the following steps: S1. Prepare a fracture network rock mass sample including a fractured rock mass on the left and a fractured rock mass on the right, so that a main fracture is formed between the fractured rock mass on the left and the fractured rock mass on the right. S2. Install the left-side fractured rock mass, right-side fractured rock mass, water injection end plate, production end plate, upper follow-up sealing assembly, lower follow-up sealing assembly, shear loading system and constant normal stiffness loading system on the rigid reaction steel frame, so that the continuous flexible coating layer continuously covers the leakage path at the upper and lower ends of the main fracture, so that the main fluid pipe passes through the axial through hole inside the corresponding loading component, and complete the pipeline connection, sensor installation and sealing check. S3. The fractured network rock mass sample is heated using a temperature control system. After the fractured network rock mass sample reaches the preset temperature range and remains stable, the force, displacement, stress and temperature measurement signals are corrected for temperature state reference. S4. Apply an initial normal load to the fractured network rock mass sample, and switch to constant normal stiffness control mode after the normal load and normal displacement stabilize. S5. The shear loading system drives the right-side fractured rock mass to generate a preset shear displacement, and adjusts the normal load in real time according to the normal displacement increment generated during the shearing process, so that the normal load increment and the normal displacement increment satisfy the preset normal stiffness relationship; during the shear displacement of the right-side fractured rock mass relative to the left-side fractured rock mass, the friction reduction component rolls or slides at the relative displacement interface of the two rubber fillers, and the negative Poisson's ratio structure undergoes reversible deformation as the normal spacing changes. S6. When the right-side fractured rock mass reaches the preset shear displacement, maintain the shear position of the right-side fractured rock mass. Without removing the normal load or disassembling or transferring the fracture network rock mass sample, continue to maintain the constant normal stiffness boundary conditions and preset temperature conditions, and continue to maintain the liquid-sealed state of the upper and lower ends of the main fracture by the continuous flexible coating layer. S7. The heat exchange fluid enters the common fluid cavity of the end plate of the water injection end plate through the injection supply device via the main fluid pipe, and is evenly injected into the shear-enhanced fracture network through multiple hemispherical fluid holes. The heat exchange fluid flowing through the fracture network merges into the common fluid cavity of the end plate of the production end plate through multiple hemispherical fluid holes, and is then discharged into the production collection device through the main fluid pipe. S8. Simultaneously record normal load, shear load, normal displacement, shear displacement, inlet and outlet pressure, inlet and outlet temperature, and total flow rate, and evaluate the shear permeability enhancement effect of the fracture network, the overall seepage characteristics, and the injection-production heat exchange performance based on this.

9. The method according to claim 8, characterized in that, In step S5, taking the direction of shear dilatation of the main crack as the positive direction of the normal displacement, the normal load is adjusted according to the following formula: In the formula, For the current target normal load, For the initial normal load, To preset the normal stiffness, The nominal area of ​​the main fracture The normal displacement increment is relative to the initial state, with the dilatation direction of the main crack as the positive direction of the normal displacement increment. When the main crack undergoes dilatation, the normal load is increased; when the main crack undergoes contraction, the normal load is decreased, so that the ratio of the normal stress increment to the normal displacement increment remains at the preset normal stiffness.

10. The method according to claim 8, characterized in that, In steps S5 to S7, the right-side axial expansion and contraction support assembly expands and contracts axially with the normal shear dilatation displacement of the right-side fractured rock mass, keeping the rigid bearing part of the end plate of the extraction end plate in contact with the outer surface of the right-side fractured rock mass; the friction reduction assembly rolls with the relative displacement of the left-side fixed structure and the right-side movable structure; the negative Poisson's ratio structure compensates for the change in the distance between the two structures through deformation, and the continuous flexible coating layer keeps the upper and lower ends of the main fracture closed.

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