A test device and method for simulating water injection-induced rock fracture sliding in an environment

Abstract

The application discloses a kind of test device and method of water injection induced rock fissure sliding in simulated environment, it is related to rock mass engineering technical field, device includes rigid loading frame, confining pressure system, heating and heat insulation system, sample assembly system, shear loading system, pore water pressure system, displacement measurement system, temperature measurement system, sealing system and general control system;Through horizontal and vertical ball mechanism, the low friction single degree of freedom motion of sample is realized, the rotation of sample around its axial is limited by the cooperation of anti-rotation groove and anti-rotation key, the precise measurement of fissure surface displacement is realized by external displacement meter and displacement transmission rod, and the confining pressure is servo-controlled based on displacement feedback by general control system, to realize constant normal stiffness boundary simulation.The technical problems of traditional device boundary condition distortion, insufficient measurement accuracy, sample unexpected deflection and poor sealing effect are solved, the process of water injection induced rock fissure sliding in deep geological environment can be truly simulated, and the authenticity and reliability of test results are improved.

Description

Technical Field

[0001] This invention relates to the field of indoor testing technology in rock mass engineering, and in particular to a test device for simulating fluid injection-induced rock mass fracture initiation and shearing in deep geological environments, as well as a test method based on the device. Background Technology

[0002] In deep rock engineering activities such as deep oil and gas resource extraction, geothermal resource development, carbon dioxide geological storage, and hydraulic fracturing, high-pressure fluids are often injected into the formation to modify the rock fracture network. The injection of high-pressure fluids increases the pore water pressure within the rock fractures, reducing the effective normal stress on the fracture surface and thus inducing shear slip (fracture initiation). This process is the core mechanism for inducing microseismic events and even leading to engineering disasters such as fault activation and wellbore instability in deep engineering. Indoor physical simulation experiments are a crucial means to study the mechanism of fluid-induced rock fracture initiation and to establish initiation criteria and constitutive relationships.

[0003] Currently, the industry commonly uses conventional triaxial rock testing equipment or direct shear testing devices to conduct related tests. However, these devices face numerous insurmountable technical bottlenecks when simulating the water injection-induced fracture initiation and sliding process under deep, high-temperature, and high-pressure geological conditions. The test conditions are significantly out of sync with the actual geological environment of deep engineering projects, as detailed below:

[0004] First, the structural stiffness and degree-of-freedom control capability of the device are insufficient, making it impossible to achieve zero-deflection and low-friction single-degree-of-freedom shearing of the specimen. During the shearing process, conventional shearing devices are prone to unexpected deflection and torsion of the specimen, and there is a large frictional resistance between the specimen and the clamping structure and sealing components. As a result, the collected stress-displacement data cannot truly reflect the pure shear mechanical behavior of the crack surface, and the accuracy of the experimental data is seriously insufficient.

[0005] Secondly, accurate displacement measurement under high temperature and high pressure in a confined environment is difficult to achieve. Displacement sensors in conventional devices are mostly located on the loading cylinder outside the device, making it impossible to directly measure the actual displacement of the crack surface. Gaps and deformations in the transmission chain can lead to significant errors in the measurement results. Furthermore, displacement sensors operating under high temperature and high pressure also face challenges such as insufficient high-temperature and high-pressure resistance and difficulties in signal transmission, making accurate measurement of the normal and tangential displacements of the crack surface impossible. Consequently, servo control based on displacement feedback cannot be implemented.

[0006] Third, the boundary condition simulation is seriously inconsistent with the actual situation of deep engineering. The rock mass in the deep strata is constrained by the surrounding rock, and its boundary condition is a constant normal stiffness boundary. However, conventional test devices mostly adopt a constant confining pressure loading mode, which can only simulate a constant normal stress boundary and cannot reproduce the real constraint state of the deep rock mass. This leads to a significant deviation between the test results and the actual situation on the engineering site. At the same time, the temperature sensors of conventional devices are mostly placed on the outer wall of the chamber or sleeve, far away from the fracture surface of the core. They cannot accurately measure the real temperature of the fracture surface, resulting in a distortion of the temperature field simulation.

[0007] Fourth, the sealing effect of the fractured specimen is poor, and pore water is prone to leakage. Conventional sealing methods are difficult to achieve effective sealing of the fracture surface under high temperature and high pressure shear conditions. Pore water is prone to leak along the side of the fracture, which makes it impossible for the pore water pressure inside the fracture surface to stably reach the test set value, seriously affecting the normal conduct of the test and the reliability of the results.

[0008] The aforementioned technical deficiencies severely restrict the industry's in-depth research on the mechanism of fluid-induced rock fracture initiation and sliding. Therefore, there is an urgent need to develop a new type of test device and method that can achieve high stiffness constraint, accurate displacement measurement, simulation of real boundary conditions, and reliable sealing. Summary of the Invention

[0009] To address the shortcomings of the existing technologies, this invention provides a test apparatus and method for inducing rock fissures to initiate sliding under simulated conditions by water injection. This method solves the technical problems existing in the prior art, such as unexpected sample deflection and excessive frictional resistance, insufficient accuracy in measuring fissure surface displacement, inability to simulate constant normal stiffness boundary conditions, temperature measurement distortion, and poor sample sealing effect. Thus, it can realistically reproduce the deep high-temperature and high-pressure geological environment, accurately simulate the entire process of rock fissure initiation induced by water injection, and significantly improve the authenticity and reliability of the test results.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is: a test device for inducing rock fractures and sliding under simulated conditions by water injection, comprising:

[0011] A rigid loading frame serves as the load-bearing structure; a confining pressure system is used to apply confining pressure to the specimen; and a heating and insulation system is used to regulate the temperature environment around the specimen.

[0012] The sample assembly system includes an upper shear box, a lower shear box, a horizontal ball bearing mechanism, a lateral limiting guide rail, and a vertical ball bearing mechanism. The sample is positioned between the upper and lower shear boxes. The lower shear box, through the cooperation of the horizontal ball bearing mechanism and the lateral limiting guide rail, is constrained to slide only in a single horizontal direction, achieving low-friction movement in the shearing direction. The upper shear box, through the cooperation of the vertical ball bearing mechanism, is constrained to move only along the normal direction of the crack surface, adapting to the shear expansion / contraction deformation of the crack surface during shearing. The top and bottom of the sample are provided with horizontally extending anti-rotation grooves. Corresponding positions on the inner walls of the upper and lower shear boxes are provided with anti-rotation protrusions that match and fit into the anti-rotation grooves. Through the cooperation of the anti-rotation protrusions and the anti-rotation grooves, the torsional torque generated during shearing can be effectively resisted, limiting the rotation of the crack sample around its axis and achieving zero-deflection fixed-axis shearing of the sample.

[0013] The shear loading system is used to apply shear force to the specimen; the pore water pressure system is used to inject fluid into the specimen; the displacement measurement system is used to measure the normal and tangential displacements of the specimen's fracture surface during the test; the temperature measurement system is used to measure the temperature of the specimen's fracture surface; and the sealing system is used to dynamically seal the specimen's fracture surface.

[0014] The central control system receives data from the displacement measurement system and temperature measurement system, analyzes the data, and controls the confining pressure system, heating and insulation system, shear loading system, and pore water pressure system to realize the water injection-induced rock fracture initiation and sliding test.

[0015] Furthermore, the confining pressure system includes a fifth plunger pump, a high-temperature rubber sealing sleeve, a right-side positioning guide sleeve, and a left-side positioning guide sleeve installed inside a rigid pressure-bearing outer sleeve. The high-temperature rubber sealing sleeve encloses the upper and lower shear boxes. The right-side and left-side positioning guide sleeves are located on both sides of the high-temperature rubber sealing sleeve, so that the inner wall of the rigid pressure-bearing outer sleeve, one end of the right-side positioning guide sleeve, one end of the left-side positioning guide sleeve, and the outer surface of the high-temperature rubber sealing sleeve form a confining pressure chamber. The confining pressure chamber is connected to the fifth plunger pump through a confining pressure injection channel. The fifth plunger pump injects a high-pressure confining pressure medium into the confining pressure chamber to provide confining pressure that simulates a deep geostress environment for the sample.

[0016] Furthermore, the heating and insulation system includes an outer heat-insulating protective sleeve that wraps around the rigid pressure-bearing outer sleeve, a resistance heating rod located between the rigid pressure-bearing outer sleeve and the outer heat-insulating protective sleeve, and a temperature controller electrically connected to the resistance heating rod. The temperature controller is used to precisely control the heating power of the resistance heating rod, achieving precise control and constant temperature maintenance of the test temperature. The outer heat-insulating protective sleeve is used to reduce heat loss, improve heating efficiency, and ensure test safety.

[0017] Furthermore, the shear loading system includes a right shear head and a left shear head symmetrically arranged on both sides of the sample, a right tangential loading hydraulic cavity separator cylinder that cooperates with the right shear head to form a right tangential loading hydraulic cavity, a left tangential loading hydraulic cavity separator cylinder that cooperates with the left shear head to form a left tangential loading hydraulic cavity, a first plunger pump connected to the right tangential loading hydraulic cavity through a right tangential loading hydraulic injection channel, and a second plunger pump connected to the left tangential loading hydraulic cavity through a left tangential loading hydraulic injection channel. Through independent control of the first and second plunger pumps, unidirectional shear loading of the sample can be achieved, as well as bidirectional cyclic shear loading and unloading.

[0018] Furthermore, the pore water pressure system includes an L-shaped pore water pressure injection channel connected to the sample fracture inlet, an L-shaped pore water pressure outlet channel connected to the sample fracture outlet, a third plunger pump connected to the injection channel, a fourth plunger pump connected to the outlet channel, and a first and second movable baffles disposed within the pore water pressure injection channel. The third plunger pump is used to precisely apply a set pore water pressure to the fracture surface, the fourth plunger pump is used to control the fluid pressure at the fracture surface outlet to achieve accurate simulation of the seepage conditions on the fracture surface, and the first and second movable baffles are used to guide and seal the injected fluid within the fracture surface to prevent fluid leakage to other areas.

[0019] Furthermore, the displacement measurement system includes a normal displacement measurement unit and a tangential displacement measurement unit. The normal displacement measurement unit includes a first normal displacement transmission rod, a first normal displacement measuring gauge, a second normal displacement transmission rod, and a second normal displacement measuring gauge. The first and second normal displacement transmission rods are fixedly connected to both sides of the upper shear box, respectively, to transmit the normal displacement of the upper shear box to the first and second normal displacement measuring gauges outside the device. The tangential displacement measurement unit includes a first tangential displacement transmission rod, a first tangential displacement measuring gauge, a second tangential displacement transmission rod, and a second tangential displacement measuring gauge. The first and second tangential displacement transmission rods are fixedly connected to the right shear head and the left shear head, respectively, to transmit the tangential displacement of the fracture sample to the first and second tangential displacement measuring gauges outside the device. This structure achieves interference-free, high-precision direct measurement of the fracture surface displacement within a high-temperature, high-pressure sealed chamber, avoiding error interference from intermediate links in the transmission chain.

[0020] Furthermore, the temperature measurement system includes a first temperature sensor and a second temperature sensor, both of which are directly inserted into the upper shear box with their ends near the crack surface of the sample. This arrangement enables real-time and accurate measurement of the true temperature near the crack surface, solving the problem of temperature measurement distortion in traditional devices.

[0021] Furthermore, the sealing system includes side sealing strips and end sealing strips for sealing the surface of the sample cracks, an arc-shaped rigid pressure plate for pressing the sealing strips, and a flexible pad disposed between the arc-shaped rigid pressure plate and the shear box. Under the confining pressure of the confining chamber, the arc-shaped rigid pressure plate, together with the flexible pad, applies a pressing force to the side sealing strips and end sealing strips that changes synchronously with the confining pressure. The higher the confining pressure, the greater the pressing force, thereby achieving dynamic adaptive sealing of the sample crack surface under high temperature and high pressure shearing conditions and effectively preventing pore water from leaking along the crack side.

[0022] A test method for inducing rock fractures to initiate sliding under simulated conditions using water injection, implemented with the above-mentioned test apparatus, includes the following steps:

[0023] S1. Sample Installation and Sealing: Install the sample with pre-fabricated through-crack between the upper and lower shear boxes, so that the anti-rotation key of the shear box is embedded in the anti-rotation groove of the sample; install the side sealing strip, end sealing strip, arc-shaped rigid pressure plate and flexible pad in sequence to complete the sealing assembly of the sample crack to form the shear box assembly; wrap the entire shear box assembly with a high-temperature rubber sealing sleeve, place it on the semi-arc support rod for positioning, and then install it into the rigid pressure-bearing outer sleeve; assemble the positioning guide sleeves on both sides, the shear head, and the hydraulic cavity dividing cylinder in sequence, tighten the rigid fastening sleeve to complete the internal component compression, and finally anchor the rigid pressure-bearing outer sleeve to the concave rigid loading base with rigid fastening bolts to complete the overall assembly of the device;

[0024] S2. Temperature and Pressure Environment Application: After completing the connection of all pipelines and electrical circuits, start the heating and insulation system, set the target test temperature through the temperature controller, control the resistance heating rod to heat the device, and keep it at a constant temperature after the temperature reaches the target temperature to make the internal temperature field of the sample uniform and stable; start the confining pressure system, inject the confining pressure medium into the confining pressure chamber through the fifth plunger pump, gradually increase the pressure to the preset test confining pressure value and keep it stable;

[0025] S3. Shear stress preloading: Start the shear loading system, and control the first plunger pump through the main control system to inject high-pressure oil into the right tangential loading hydraulic chamber, drive the right shear head to push the lower shear box to slide in the horizontal direction, apply shear stress to the crack surface of the crack sample, and collect shear stress and tangential displacement data in real time until the shear stress reaches the critical state of crack initiation and then maintain the shear load stability.

[0026] S4. Water Injection Induces Fracture Slip Initiation: The pore water pressure system is activated, and the third plunger pump is controlled by the main control system to inject high-pressure fluid into the fracture surface through the L-shaped pore water pressure injection channel, gradually increasing the pore water pressure in the fracture surface. The increase in pore water pressure causes the effective normal stress on the fracture surface to continuously decrease. When the effective normal stress drops to a critical value, shear slip occurs on the fracture surface, completing the simulation of water injection induced fracture slip initiation.

[0027] S5. Real-time Data Monitoring: During the experiment, the normal and tangential displacement data of the fracture surface are collected in real time through the displacement measurement system, and the temperature data near the fracture surface is collected in real time through the temperature measurement system. The data are then transmitted to the central control system for recording and storage, which is used for subsequent analysis of the fracture initiation characteristics. Based on the real-time feedback of the normal displacement data and the preset normal stiffness parameters, the central control system calculates the confining pressure value to be adjusted in real time, dynamically adjusts the confining pressure of the confining pressure chamber, and maintains the normal stiffness of the fracture surface constant.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. This invention, through the multi-dimensional degree-of-freedom constraint design of the sample assembly system, uses a horizontal ball bearing mechanism in conjunction with a transverse limiting guide rail to constrain the shear box to slide with low friction only along the shear direction; the vertical ball bearing mechanism constrains the upper shear box to move only along the normal direction, adapting to crack shear expansion deformation; at the same time, the cooperation between the sample anti-rotation groove and the shear box anti-rotation convex key effectively restricts the torsion of the sample around its axis, fundamentally solving the problems of sample deflection, torsion, and high frictional resistance in traditional devices, significantly improving the accuracy of shear test data, and realizing zero deflection and low-friction single-degree-of-freedom shearing of the sample.

[0030] 2. This invention combines an external displacement measuring instrument with a rigid displacement transmission rod. The displacement transmission rod is directly and rigidly connected to the shear box and shear head, transmitting the normal and tangential displacements of the crack surface to the external displacement measuring instrument without gaps or interference. This avoids the problem of insufficient high-temperature and high-pressure resistance of built-in sensors, and eliminates the errors caused by transmission chain deformation and gaps in traditional indirect measurement methods. The measurement accuracy is greatly improved, and accurate direct measurement of crack surface displacement is achieved in a high-temperature and high-pressure sealed environment.

[0031] 3. The overall control system of this invention is based on the accurately acquired normal displacement data and controls the output pressure of the confining pressure system in real time. It dynamically adjusts the confining pressure to maintain the preset constant normal stiffness, breaking through the limitation of traditional devices that can only simulate constant normal stress boundaries. It can realistically reproduce the actual boundary conditions of deep rock masses constrained by surrounding rock, significantly improving the fit between the test results and the actual situation on the engineering site. For the first time in this type of test device, the simulation of constant normal stiffness boundary based on displacement closed-loop feedback has been realized.

[0032] 4. The temperature sensor of this invention is directly inserted into the shear box near the crack surface, which can accurately measure the real temperature of the crack surface and avoid distortion of the temperature field simulation. The sealing system uses the confining pressure to drive the arc-shaped rigid pressure plate to press the sealing strip, realizing dynamic sealing that adapts to the confining pressure. This effectively solves the problem of pore water leakage under high temperature and high pressure shear conditions, ensures the stability and accuracy of pore water pressure loading, and further improves the reliability of the test.

[0033] 5. The device of the present invention adopts an integrated high-rigidity rigid frame design. The symmetrical shear loading system can realize multi-mode loading of unidirectional shear and cyclic shear. It can simulate the whole process of water injection-induced rock fracture initiation and sliding under different deep geological environments and different load conditions. The device has a wide range of applications and strong experimental scalability, providing a reliable experimental platform for in-depth research on the mechanism of fluid-induced rock fracture initiation and sliding. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0035] Figure 2 This is a partially enlarged structural diagram of the lower shear box, the horizontal ball bearing mechanism, and the shear loading head area in this invention.

[0036] Figure 3 This is a partially enlarged structural diagram of the upper shear box and vertical ball bearing mechanism area in this invention.

[0037] Figure 4 This is a longitudinal cross-sectional view of the sealing system in this invention.

[0038] In the figure: 1-Concave rigid loading base; 2-Rigid fastening bolt; 3-Rigid pressure bearing outer sleeve; 4-Resistance heating rod; 5-Outer heat insulation protective sleeve; 6-Temperature controller; 7-Sample; 8-Upper shear box; 9-Lower shear box; 10-Horizontal ball bearing mechanism; 11-Horizontal limiting guide rail; 12-High temperature rubber sealing sleeve; 13-Semi-arc support rod; 14-Vertical ball bearing mechanism; 15-Right side positioning guide sleeve; 16-Right side tangential loading hydraulic cavity dividing cylinder; 17-Right rigid fastening sleeve; 18-Limiting insertion rod; 19-Right shearing head; 20-Left side positioning guide sleeve; 21-Left side tangential loading hydraulic cavity dividing cylinder; 22-Left rigid fastening sleeve; 23-First normal displacement transmission rod; 24-First normal displacement measuring gauge; 25-First temperature sensor; 26-Second normal displacement transmission rod; 27-Second normal displacement measuring gauge; 28-Second temperature sensor; 2 9-Left shear head; 30-First tangential displacement transmission rod; 31-First tangential displacement measuring gauge; 32-Second tangential displacement measuring gauge; 33-Second tangential displacement transmission rod; 34-Right tangential loading hydraulic chamber; 35-Sealing ring; 36-First plunger pump; 37-First movable baffle; 38-Second movable baffle; 39-L-shaped pore water pressure injection channel; 40-Third plunger pump; 41-Second plunger pump; 42-L-shaped pore water pressure injection channel 43-Water pressure outflow channel; 44-Fourth plunger pump; 45-Containing pressure chamber; 46-Containing pressure injection channel; 47-Fifth plunger pump; 48-Right side tangential loading hydraulic injection channel; 49-First limiter; 50-Second limiter; 51-Third limiter; 52-Curved rigid pressure plate; 53-Flexible pad; 54-End sealing strip; 55-Side sealing strip; 56-Sample anti-rotation groove; 57-Shear box anti-rotation protrusion key. Detailed Implementation

[0039] The present invention will be further described below.

[0040] This embodiment provides a test device for simulating water injection-induced rock fracture initiation and sliding under simulated conditions. Its overall structure is as follows: Figure 1 As shown, it includes a rigid loading frame, a confining pressure system, a heating and insulation system, a sample assembly system, a shear loading system, a pore water pressure system, a displacement measurement system, a temperature measurement system, a sealing system, and a central control system 51.

[0041] The rigid loading frame is the main load-bearing component of the entire device. It consists of a concave rigid loading base 1 and a rigid pressure-bearing outer sleeve 3, which are anchored by multiple sets of rigid fastening bolts 2 to form an integrated closed high-rigidity structure. This structure can effectively resist high-pressure loads during the test and prevent frame deformation from interfering with the test results.

[0042] The confining pressure system is used to provide a confining pressure environment simulating deep geostress for sample 7, including a confining pressure chamber 44, a confining pressure injection channel 45, and a fifth plunger pump 46. The confining pressure chamber 44 is a sealed chamber formed by a rigid pressure-bearing outer sleeve 3, a high-temperature rubber sealing sleeve 12, a right-side positioning guide sleeve 15, and a left-side positioning guide sleeve 20. The confining pressure injection channel 45 is located on the wall of the rigid pressure-bearing outer sleeve 3, with one end connected to the confining pressure chamber 44 and the other end connected to the fifth plunger pump 46. The fifth plunger pump 46 is a high-precision servo plunger pump, capable of injecting hydraulic oil and other confining pressure media into the confining pressure chamber 44, precisely controlling the application and dynamic adjustment of the confining pressure.

[0043] The heating and insulation system is used to simulate the high-temperature environment of deep underground formations, including resistance heating rods 4, an outer heat-insulating protective sleeve 5, and a temperature controller 6. Multiple sets of resistance heating rods 4 are evenly arranged in the grooves on the outer wall of the rigid pressure-bearing outer sleeve 3. The outer heat-insulating protective sleeve 5 wraps around the outside of the resistance heating rods 4 to reduce heat loss and provide safety protection. The temperature controller 6 is electrically connected to all resistance heating rods 4 and has a PID precise temperature control function. It can adjust the heating power in real time according to temperature feedback to achieve precise control and constant temperature maintenance of the test temperature, and can simulate high-temperature environments above 200℃.

[0044] The specimen assembly system is one of the core components of this device, used to clamp the cylindrical fracture specimen 7 with a pre-fabricated through-crack, while simultaneously constraining the multi-dimensional degrees of freedom of the specimen 7. For example... Figure 1 , Figure 2 and Figure 3 As shown, the sample assembly system includes an upper shear box 8, a lower shear box 9, a horizontal ball bearing mechanism 10, a transverse limiting guide rail 11, and a vertical ball bearing mechanism 14. The outer arc surface of the lower shear box 9 has a guide groove extending along the X-axis (horizontal direction). The horizontal ball bearing mechanism 10 is disposed within this guide groove, and the transverse limiting guide rail 11 is matched and engaged with the guide groove. The rolling friction of the balls replaces the traditional sliding friction, significantly reducing motion resistance. Simultaneously, it strictly constrains the lower shear box 9 to slide horizontally only along the X-axis (horizontal direction), limiting its displacement along the Y-axis (tangential to the crack surface) and Z-axis (normal to the crack surface). The upper shear box 8 has protruding structures on its left and right sides, which cooperate with the vertical ball bearing mechanism 14. The vertical ball bearing mechanism 14 is fixed to the inner wall of the rigid pressure-bearing outer sleeve 3, allowing the upper shear box 8 to move only along the Z-axis (normal to the crack surface). This allows it to freely adapt to the shear expansion or contraction deformation of the crack surface during shearing, while simultaneously limiting its displacement along the X-axis.

[0045] To prevent the specimen 7 from twisting around the X-axis (its own axial direction) during shearing, a specimen anti-rotation groove 56 extending horizontally along the X-axis is provided at both the top and bottom of the specimen 7. Corresponding positions on the inner walls of the upper shear box 8 and the lower shear box 9 are provided with shear box anti-rotation protrusions 57, matching the dimensions of the specimen anti-rotation grooves 56. During assembly, the shear box anti-rotation protrusions 57 are embedded in the specimen anti-rotation grooves 56 to form a sliding fit, and the embedding depth of the shear box anti-rotation protrusions 57 is less than the groove depth of the specimen anti-rotation grooves 56, avoiding interference between the keyway fit and the normal deformation of the specimen 7. Through the contact limiting on the side of the keyway, the torsional torque generated during shearing can be effectively resisted, completely restricting the rotation of the specimen 7 around the X-axis, thereby achieving zero-deflection fixed-axis pure shearing of the upper and lower specimens, fundamentally eliminating the interference of specimen 7's torsion on the test results.

[0046] The shear loading system is used to apply shear load to specimen 7. It adopts a symmetrical double-end loading design, such as... Figure 1 and Figure 2 As shown, the sample 7 includes a right shear head 19, a left shear head 29, a right tangential loading hydraulic chamber separating cylinder 16, a left tangential loading hydraulic chamber separating cylinder 21, a first plunger pump 36, and a second plunger pump 41. The right shear head 19 and the left shear head 29 are symmetrically arranged on the left and right sides of the sample 7. The left end of the right shear head 19 is connected to the right end of the lower shear box 9 through a lever-groove structure. Specifically, the lever protrusion on the left wall of the right shear head 19 is embedded in the corresponding groove on the right end of the lower shear box 9. This structure can further limit the Z-axis displacement of the lower shear box 9 while transmitting the X-axis horizontal shear load, thus preventing the lower sample 7 from vertically deflecting.

[0047] A right-side tangential loading hydraulic chamber partition cylinder 16 is fitted outside the right shear head 19, forming a sealed right-side tangential loading hydraulic chamber 34 in cooperation with the right shear head 19; a left-side tangential loading hydraulic chamber partition cylinder 21 is fitted outside the left shear head 29, forming a sealed left-side tangential loading hydraulic chamber in cooperation with the left shear head 29. A right-side tangential loading hydraulic injection channel 47 is located within the right-side tangential loading hydraulic chamber partition cylinder 16 and the rigid pressure-bearing outer sleeve 3, with one end connected to the right-side tangential loading hydraulic chamber 34 and the other end connected to the first plunger pump 36; a left-side tangential loading hydraulic injection channel is connected to the left-side tangential loading hydraulic chamber, with the other end connected to the second plunger pump 41. Both the first plunger pump 36 and the second plunger pump 41 are high-precision servo plunger pumps, capable of independently controlling output pressure. A single pump drive can achieve unidirectional shear loading of the sample 7, while alternating dual pump drive can achieve bidirectional cyclic shear loading and unloading of the sample 7, meeting the needs of different test scenarios.

[0048] The inner walls of both ends of the rigid pressure-bearing outer sleeve 3 are provided with internal threads. The right rigid fastening sleeve 17 and the left rigid fastening sleeve 22 are respectively connected to the rigid pressure-bearing outer sleeve 3 through internal threads. After the right rigid fastening sleeve 17 is tightened, it presses the right positioning guide sleeve 15 and the right tangential loading hydraulic cavity dividing cylinder 16. After the left rigid fastening sleeve 22 is tightened, it presses the left positioning guide sleeve 20 and the left tangential loading hydraulic cavity dividing cylinder 21. Axial limiting is achieved by the first limiter 48, the second limiter 49 and the third limiter 50, so as to realize the rigid fastening of the shear loading system and the rigid loading frame, and further improve the overall rigidity and loading stability of the device.

[0049] Pore ​​water pressure systems are used to apply precise and controllable pore water pressure to fracture surfaces, simulating high-pressure fluid injection processes, such as... Figure 1 As shown, the system includes an L-shaped pore water pressure injection channel 39, an L-shaped pore water pressure outlet channel 42, a third plunger pump 40, a fourth plunger pump 43, a first movable baffle plate 37, and a second movable baffle plate 38. The L-shaped pore water pressure injection channel 39 is located within the right shear head 19 and the lower shear box 9, with one end connected to the inlet of the fracture surface of the sample 7 and the other end connected to the third plunger pump 40. The L-shaped pore water pressure outlet channel 42 is located within the left shear head 29 and the lower shear box 9, with one end connected to the outlet of the fracture surface of the fractured sample 7 and the other end connected to the fourth plunger pump 43. The third plunger pump 40 is used to inject high-pressure fluid into the fracture surface to precisely apply pore water pressure, while the fourth plunger pump 43 is used to control the fluid pressure at the outlet of the fracture surface, enabling the simulation of different seepage gradients on the fracture surface. The first movable baffle plate 37 and the second movable baffle plate 38 are disposed in one of the L-shaped pore water pressure injection channel 39 and the L-shaped pore water pressure outflow channel 42, or both. They can guide and seal the injected fluid in the fracture surface area, preventing fluid leakage into the gap between the shear box and the pressure head, and ensuring the stability of the pore water pressure loading. In addition, the right shear pressure head 19 and the left shear pressure head 29 are each provided with a sealing ring 35 at their ends to further prevent fluid leakage from the gap during the seepage test.

[0050] Displacement measurement systems are used to accurately measure the normal and tangential displacements of crack surfaces, such as... Figure 1As shown, the device includes a normal displacement measurement unit and a tangential displacement measurement unit. The normal displacement measurement unit includes a first normal displacement transmission rod 23, a first normal displacement measuring instrument 24, a second normal displacement transmission rod 26, and a second normal displacement measuring instrument 27. The first normal displacement transmission rod 23 and the second normal displacement transmission rod 26 are rigid rods resistant to high temperature and high pressure. One end of each rod is threaded to the protruding parts on the left and right sides of the upper shear box 8, and the other end passes through the rigid pressure-bearing outer sleeve 3, respectively, and contacts the probes of the first normal displacement measuring instrument 24 and the second normal displacement measuring instrument 27 outside the device. This allows the normal displacement of the upper shear box 8 to be directly transmitted to the external displacement measuring instruments without gaps, thus achieving accurate measurement of the normal displacement of the crack surface.

[0051] The tangential displacement measurement unit includes a first tangential displacement transmission rod 30, a first tangential displacement measuring instrument 31, a second tangential displacement transmission rod 33, and a second tangential displacement measuring instrument 32. Both the first tangential displacement transmission rod 30 and the second tangential displacement transmission rod 33 are rigid rods. One end of each rod is threaded to the ends of the right shear head 19 and the left shear head 29, respectively, while the other end extends through a rigid fastening sleeve and contacts the probes of the first tangential displacement measuring instrument 31 and the second tangential displacement measuring instrument 32 outside the device. This allows the displacement of the two shear heads to be directly transmitted to the external measuring instruments, thereby accurately obtaining the tangential displacement of the crack surface. The above design places the displacement measuring instruments in a normal temperature and pressure environment outside the device, avoiding the influence of high temperature and high pressure environments on sensor performance, while eliminating errors associated with traditional indirect measurement methods and significantly improving measurement accuracy.

[0052] The temperature measurement system is used to accurately monitor the temperature near the crack surface. It includes a first temperature sensor 25 and a second temperature sensor 28, both of which use high-precision armored thermocouples that are directly inserted into the upper shear box 8. The temperature measuring end of the sensor is set close to the crack surface of the sample 7, which can measure the real temperature near the crack surface in real time and accurately, thus solving the measurement distortion problem caused by the temperature sensor being far away from the crack surface in traditional devices.

[0053] The sealing system is used to achieve dynamic adaptive sealing of the crack surface of sample 7 to prevent pore water leakage. Its structure is as follows: Figure 4As shown, the system includes a side sealing strip 55, an end sealing strip 54, an arc-shaped rigid pressure plate 52, and a flexible pad 53. The side sealing strip 55 is adhered to the side seam of the crack in sample 7, and the end sealing strip 54 is adhered to both ends of the crack, with the two overlapping to form a complete sealing structure. The arc-shaped rigid pressure plate 52 is positioned at the connection between the upper and lower shear boxes, completely abutting against the side sealing strip 55 from the outside. The flexible pad 53 is positioned between the arc-shaped rigid pressure plate 52 and the upper and lower shear boxes to achieve uniform pressure transmission. When confining pressure is applied in the confining chamber 44, the high-pressure confining medium pushes the arc-shaped rigid pressure plate 52 to move inward, which, together with the flexible pad 53, applies a uniform and continuous clamping force to the side sealing strip 55 and the end sealing strip 54. This clamping force increases synchronously with the increase of the confining pressure, achieving dynamic adaptive sealing under high-temperature and high-pressure shear conditions and effectively preventing pore water leakage along the side of the crack.

[0054] The central control system 51 serves as the core of the device's control and data acquisition. It employs an industrial control computer and is electrically connected to the first plunger pump 36, the second plunger pump 41, the third plunger pump 40, the fourth plunger pump 43, the fifth plunger pump 46, the temperature controller 6, all displacement gauges, and temperature sensors. The central control system 51 enables coordinated control of all systems, including closed-loop temperature control, pressure and flow control of each plunger pump, and automatic control of the loading process. Simultaneously, it can synchronously acquire all displacement, temperature, and pressure data for real-time display, storage, and subsequent processing.

[0055] Specifically, the main control system 51 is equipped with a constant normal stiffness boundary servo control mode, which can receive real-time feedback of normal displacement data from the normal displacement measuring instrument, calculate the required confining pressure value in real time based on preset normal stiffness parameters, and send control commands to the fifth plunger pump 46 to servo adjust its output pressure, dynamically changing the confining pressure of the confining pressure chamber 44, thereby maintaining a constant normal stiffness on the fracture surface throughout the test, realistically simulating the confined boundary conditions of deep rock masses. Simultaneously, the main control system 51 is equipped with a cyclic shear control mode, which can alternately control the start / stop and output pressure of the first plunger pump 36 and the second plunger pump 41 to achieve cyclic shear loading and unloading of the sample 7, expanding the experimental functions of the device.

[0056] A test method for inducing rock fractures and sliding under high temperature and high pressure conditions by water injection, implemented using the above-mentioned test apparatus, specifically includes the following steps:

[0057] S1. Sample installation and sealing:

[0058] S1.1 First, prepare a cylindrical rock sample 7 with a pre-fabricated through-crack. Process anti-rotation grooves 56 extending along the X-axis on the top and bottom of the sample 7. Place the sample 7 in the lower shear box 9, close the upper shear box 8, and make the anti-rotation protrusion 57 of the shear box accurately embedded in the anti-rotation groove 56 of the sample.

[0059] S1.2. Attach a side sealing strip 55 to the side seam of the crack in sample 7 and an end sealing strip 54 to the end, so that the two overlap to form a complete sealing strip; install the arc-shaped rigid pressure plate 52 and the flexible pad 53 in sequence, so that the arc-shaped rigid pressure plate 52 completely abuts against the side sealing strip 55 to form a shear box assembly.

[0060] S1.3 Wrap the entire shear box assembly with a high-temperature rubber sealing sleeve 12, position it on the semi-circular support rod 13, and then insert the whole assembly into the rigid pressure-bearing outer sleeve 3; assemble the right side positioning guide sleeve 15, the right shear head 19, and the right side tangential loading hydraulic chamber dividing cylinder 16 in sequence, and tighten the right rigid fastening sleeve 17 to complete the clamping and positioning of the right side assembly; assemble the left side in the same way; finally, anchor the rigid pressure-bearing outer sleeve 3 to the concave rigid loading base 1 with multiple sets of rigid fastening bolts 2 to complete the overall assembly of the device.

[0061] S1.4 Connect all hydraulic lines and electrical lines, and conduct pipeline sealing tests and electrical line continuity tests to ensure that the device is leak-free and the line connections are normal.

[0062] S2, Temperature and pressure environment applied:

[0063] S2.1 Start the heating and insulation system, set the target test temperature through the temperature controller 6, control the resistance heating rod 4 to heat the device at the set heating rate, and keep it at the target temperature for more than 2 hours to make the temperature field inside the sample 7 uniform and stable.

[0064] S2.2 Start the confining pressure system. Control the fifth plunger pump 46 through the main control system 51 to inject hydraulic oil into the confining pressure chamber 44 at the set pressure increase rate, gradually increase the confining pressure to the preset test confining pressure value, and maintain the confining pressure stable after stabilization, so as to provide a confining pressure environment that simulates deep ground stress for the sample 7.

[0065] S3, Shear stress preloading:

[0066] S3.1 Start the shear loading system. Control the first plunger pump 36 through the main control system 51 to inject high-pressure oil into the right tangential loading hydraulic chamber 34 at the set loading rate. Drive the right shear head 19 to push the lower shear box 9 to slide along the X-axis and apply shear stress to the crack surface of the sample 7.

[0067] S3.2 During the test, the main control system 51 collects shear stress and tangential displacement data in real time and plots the shear stress-displacement curve. When the shear stress reaches the critical state of crack initiation (the shear stress-displacement curve enters the yield stage), the shear loading is stopped and the current shear load is kept stable.

[0068] S3.3 When a cyclic shear test is required, the first plunger pump 36 and the second plunger pump 41 are alternately started by the main control system 51 to perform a cyclic operation of positive shear loading and reverse shear unloading on the sample 7, simulating the stress state of the crack under cyclic loading.

[0069] S4. Water injection induces crack initiation and sliding:

[0070] S4.1 Start the pore water pressure system. Control the third plunger pump 40 through the main control system 51 to inject high-pressure distilled water into the fracture surface through the L-shaped pore water pressure injection channel 39 at the set pressure increase rate, and gradually increase the pore water pressure in the fracture surface.

[0071] S4.2 As the pore water pressure continues to increase, the effective normal stress (effective normal stress = normal stress - pore water pressure) on the fracture surface continues to decrease. When the effective normal stress drops to a critical value, the shear strength of the fracture surface is insufficient to resist the applied shear stress, and shear slip occurs on the fracture surface, thus completing the physical simulation of water injection-induced rock fracture initiation and slip.

[0072] S4.3 During the water injection-induced slip process described above, constant normal stiffness boundary servo control is simultaneously activated: when shear slip accompanied by shear dilatation occurs on the crack surface, the upper shear box 8 generates an upward normal displacement. The first normal displacement transmission rod 23 and the second normal displacement transmission rod 26 transmit this displacement in real time to the external first normal displacement measuring instrument 24 and the second normal displacement measuring instrument 27; the central control system 51 reads the two normal displacement data in real time, takes the average value as the real-time normal displacement Δd, and bases it on the preset normal stiffness K. n According to the formula Δσ n =K n *Δd, the required increase in confining pressure Δσ calculated in real time. n The main control system 51 sends a control command to the fifth plunger pump 46 based on the calculation results, servo-increasing its output pressure and raising the confining pressure in the confining pressure chamber 44 by Δσ. n Through this closed-loop servo control, the normal stiffness K of the fracture surface is maintained throughout the entire fracture initiation and sliding process. n It is constant and accurately reflects the actual boundary conditions of deep rock masses constrained by the surrounding rock.

[0073] S5. Real-time data monitoring:

[0074] During the experiment, the normal and tangential displacement data of the fracture surface were collected in real time by the displacement measurement system, and the temperature data near the fracture surface were collected in real time by the temperature measurement system. At the same time, the pressure data of each plunger pump were collected simultaneously. All data were transmitted to the central control system 51 in real time at a sampling frequency of 100Hz for recording, storage and real-time curve display, which will be used for subsequent analysis of the fracture initiation mechanical characteristics and evolution law.

[0075] After the above test was completed, the pore water pressure was gradually reduced to 0, then the shear load was gradually reduced to 0, and then the heating and insulation system was stopped. After the device cooled to room temperature, the confining pressure was gradually reduced to 0. Finally, the device was disassembled, sample 7 was taken out, and the test was completed.

Claims

1. A test apparatus for simulating water injection-induced rock fracture initiation and sliding under simulated conditions, comprising a rigid loading frame, a heating and insulation system, a pore water pressure system, a confining pressure system, and a temperature measurement system, characterized in that, Also includes: The sample assembly system includes an upper shear box, a lower shear box, a horizontal ball bearing mechanism, a lateral limiting guide rail, and a vertical ball bearing mechanism; the sample is located between the upper and lower shear boxes. The lower shear box is constrained to slide only in a single horizontal direction by cooperating with the transverse ball bearing mechanism and the transverse limiting guide rail; the upper shear box is constrained to move only along the normal direction of the crack surface by cooperating with the vertical ball bearing mechanism; the top and bottom of the specimen are provided with specimen anti-rotation grooves extending in the horizontal direction, and the inner walls of the upper and lower shear boxes are provided with anti-rotation protrusions that match and fit into the specimen anti-rotation grooves to restrict the specimen from rotating around its axis. A shear loading system is used to apply shear force to a specimen. The displacement measurement system includes a normal displacement measurement unit and a tangential displacement measurement unit. The normal displacement measurement unit includes a first normal displacement transmission rod, a first normal displacement measuring gauge, a second normal displacement transmission rod, and a second normal displacement measuring gauge. The first and second normal displacement transmission rods are fixedly connected to both sides of the upper shear box, respectively, to transmit the normal displacement of the upper shear box to the first and second normal displacement measuring gauges outside the device. The tangential displacement measurement unit includes a first tangential displacement transmission rod, a first tangential displacement measuring gauge, a second tangential displacement transmission rod, and a second tangential displacement measuring gauge. The first and second tangential displacement transmission rods are fixedly connected to the right shear head and the left shear head, respectively, to transmit the tangential displacement of the fractured sample to the first and second tangential displacement measuring gauges outside the device. The sealing system includes side sealing strips and end sealing strips for sealing the surface of the sample cracks, an arc-shaped rigid pressure plate for pressing the sealing strips, and a flexible pad disposed between the arc-shaped rigid pressure plate and the shear box; the arc-shaped rigid pressure plate, in conjunction with the flexible pad, can apply a pressing force that changes synchronously with the confining pressure to the side sealing strips and end sealing strips under the confining pressure of the confining chamber, thereby achieving dynamic sealing of the sample crack surface; The confining pressure system includes a fifth plunger pump, a high-temperature rubber sealing sleeve, a right-side positioning guide sleeve, and a left-side positioning guide sleeve installed inside a rigid pressure-bearing outer sleeve. The high-temperature rubber sealing sleeve encloses the upper and lower shear boxes. The right-side and left-side positioning guide sleeves are located on both sides of the high-temperature rubber sealing sleeve, so that the inner wall of the rigid pressure-bearing outer sleeve, one end of the right-side positioning guide sleeve, one end of the left-side positioning guide sleeve, and the outer surface of the high-temperature rubber sealing sleeve form a confining pressure chamber. The confining pressure chamber is connected to the fifth plunger pump through a confining pressure injection channel, and the confining pressure is adjusted by controlling the injection of the fifth plunger pump. The central control system is used to receive data from the displacement measurement system and temperature measurement system, and to control the confining pressure system, heating and insulation system, shear loading system, and pore water pressure system to realize the water injection-induced rock fracture initiation and sliding test.

2. The test device for simulating water injection induced rock fracture slip in an environment according to claim 1, characterized in that, The heating and insulation system includes an outer heat-insulating protective sleeve that wraps around a rigid pressure-bearing outer sleeve, a resistance heating rod located between the rigid pressure-bearing outer sleeve and the outer heat-insulating protective sleeve, and a temperature controller electrically connected to the resistance heating rod.

3. The experimental apparatus for inducing rock fractures and sliding under simulated conditions by water injection as described in claim 1, characterized in that, The shear loading system includes a right shear head and a left shear head symmetrically arranged on both sides of the sample; a right tangential loading hydraulic cavity separator cylinder that cooperates with the right shear head to form a right tangential loading hydraulic cavity; a left tangential loading hydraulic cavity separator cylinder that cooperates with the left shear head to form a left tangential loading hydraulic cavity; a first plunger pump connected to the right tangential loading hydraulic cavity through a right tangential loading hydraulic injection channel; and a second plunger pump connected to the left tangential loading hydraulic cavity through a left tangential loading hydraulic injection channel. The injection control of the first and second plunger pumps enables the right and left shear heads to apply corresponding shear forces to the sample.

4. The device of claim 1, wherein, The pore water pressure system includes a pore water pressure injection channel connected to the sample fracture inlet, a pore water pressure outflow channel connected to the sample fracture outlet, a third plunger pump connected to the injection channel, a fourth plunger pump connected to the outflow channel, and a first movable baffle and a second movable baffle disposed within the pore water pressure injection channel.

5. The test device for simulating water injection induced rock fracture slip in an environment according to claim 1, characterized in that, The temperature measurement system includes a first temperature sensor and a second temperature sensor, both of which are directly inserted into the upper shear box with their ends close to the crack surface of the sample.

6. The test device for simulating water injection induced rock fracture slip in an environment according to claim 1, characterized in that, The overall control system continuously receives data from the normal displacement measurement unit and the tangential displacement measurement unit, and based on the feedback data, servo controls the output pressure of the fifth plunger pump to achieve a simulation test under constant normal stiffness boundary conditions.

7. A test method for a simulated environment water injection-induced rock fracture initiation and sliding test device according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Sample installation and sealing: Install the sample with pre-fabricated through crack between the upper and lower shear boxes, and seal the crack of the sample through the sealing system. After the assembled shear box assembly is installed into the high-temperature rubber sealing sleeve, it is installed into the rigid loading frame to complete the overall assembly. S2. Temperature and pressure environment application: Start the heating and insulation system, and use the temperature controller to control the resistance heating rod to heat the device to the preset test temperature and keep it at that temperature; Start the confining pressure system and inject the confining pressure medium into the confining pressure chamber through the fifth plunger pump to apply the preset confining pressure to the test set value; S3. Shear stress preloading: Start the shear loading system and drive the shear head on the corresponding side through the first plunger pump or the second plunger pump to apply shear stress to the crack surface of the sample until the shear stress reaches the critical state of crack initiation. S4. Water injection to induce fracture slip: Start the pore water pressure system and inject high-pressure fluid into the fracture surface through the pore water pressure injection channel via the third plunger pump to apply pore water pressure, reduce the effective normal stress on the fracture surface, until shear slip occurs on the fracture surface. S5. Real-time data monitoring: During the test, the normal and tangential displacement data of the crack surface are collected in real time through the displacement measurement system, and the temperature data near the crack surface is collected in real time through the temperature measurement system. The data are then transmitted to the central control system for recording and storage. Based on the real-time feedback of the normal displacement data and the preset normal stiffness parameters, the central control system calculates the confining pressure value to be adjusted in real time, dynamically adjusts the confining pressure of the confining pressure chamber, and maintains the normal stiffness of the crack surface constant.

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