Rock thermal shock experiment device, experiment method and rock fracture evaluation method

Abstract

This disclosure relates to a rock thermal shock experimental apparatus, experimental method, and rock fracture evaluation method. The rock thermal shock experimental apparatus includes a true triaxial system, a liquid supply system, and a temperature measurement system. The true triaxial system is used for triaxial confining pressure loading and heating of the rock sample. Thermal shock boreholes and temperature measurement boreholes are drilled on the rock sample. The liquid supply system includes an inlet pipeline for injecting liquid into the thermal shock boreholes and a supply pump connected to the inlet pipeline, as well as an outlet pipeline for discharging the liquid. The temperature measurement system includes multiple temperature measuring devices, with temperature measuring devices arranged at least inside the thermal shock boreholes and inside the temperature measurement boreholes. The rock thermal shock experimental apparatus of this disclosure can realistically simulate the impact of underground fluids on rocks, achieving the thermal shock effect by creating an effective temperature difference between the heated rock sample and the injected cold liquid. The rock fracture evaluation method can quantitatively analyze the relationship between temperature and rock fracture under thermal shock.

Description

Technical Field

[0001] This disclosure relates to the field of rock mechanical failure research technology, and in particular to a rock thermal shock experimental apparatus, experimental method and rock fracture evaluation method. Background Technology

[0002] Thermal shock is a common phenomenon in nature. When rocks are rapidly heated or cooled, a large amount of heat exchange occurs within a very short time, causing drastic temperature changes. This temperature gradient leads to impact thermal stress within the rock mass, resulting in thermal shock fracturing. The essence of rock thermal shock fracturing is the instantaneous and enormous thermal stress caused by changes in the internal temperature field of the rock, leading to the initiation, propagation, and eventual connection of internal cracks—a process from microscopic damage to macroscopic failure. Rock thermal shock fracturing results in numerous fissures and cracks at the microscopic level, and at the macroscopic level, deterioration of mechanical properties and increased permeability. These characteristics of rock thermal shock fracturing are attracting significant attention from the scientific community and are being widely applied in the permeability enhancement of hot dry rocks, oil, and natural gas reservoirs.

[0003] Some experimental studies on rock thermal shock fracture have been presented in related technologies. However, existing rock thermal shock experimental devices cannot realistically simulate the impact of underground fluids on rocks. Therefore, the experimental data obtained by these devices have poor guiding significance for field engineering applications. Thus, there is an urgent need for an experimental device that can realistically simulate the thermal shock process of underground rocks, as well as a method that can evaluate the fracture effect of rock thermal shock. Summary of the Invention

[0004] To solve the above-mentioned technical problems, or at least partially solve them, this disclosure provides a rock thermal shock test apparatus, method, and rock fracture evaluation method.

[0005] This disclosure provides a rock thermal shock experimental apparatus, including a true triaxial system, a liquid supply system, and a temperature measurement system;

[0006] The true triaxial system includes a pressure bearing device for applying triaxial confining pressure to rock samples;

[0007] The rock sample is provided with thermal impact boreholes and temperature measurement boreholes. The liquid supply system includes an inlet pipeline for injecting liquid into the thermal impact boreholes and a liquid supply pump connected to the inlet pipeline, as well as a drain pipeline for discharging the liquid injected into the thermal impact boreholes.

[0008] The temperature measurement system includes multiple temperature measuring devices, and at least the temperature measuring devices are respectively arranged inside the thermal shock borehole and inside the temperature measuring borehole;

[0009] The true triaxial system further includes a heating device for heating the rock sample, and / or the liquid supply system further includes a heating module for heating the liquid before it enters the liquid supply pump.

[0010] Optionally, a thermal impact borehole is drilled on the rock sample, and the inlet pipeline and the outlet pipeline are both arranged inside the thermal impact borehole.

[0011] Optionally, two thermal impact boreholes are formed on the rock sample, one of which contains the inlet pipeline and the other contains the outlet pipeline, and the rock sample is provided with prefabricated cracks for connecting the two thermal impact boreholes.

[0012] Optionally, the inlet line extends to the bottom of the thermal shock borehole, and the outlet line extends to the top of the thermal shock borehole.

[0013] Optionally, the liquid supply system further includes a high-pressure pump connected to the liquid inlet line, the high-pressure pump being used to inject liquid into the thermal shock borehole through the liquid inlet line.

[0014] This disclosure also provides a method for testing the thermal shock of rocks, including the following steps:

[0015] S11, using a true triaxial system to apply triaxial confining pressure to the rock sample and bring the temperature of the rock sample to the first temperature;

[0016] S12, a liquid with a second temperature is injected into the thermal shock borehole of the rock sample using a liquid supply pump until the temperature in the thermal shock borehole or the temperature measuring borehole of the rock sample stabilizes. The liquid injection is then stopped, and the difference between the temperature of the rock sample in the temperature measuring borehole and the temperature in the thermal shock borehole is recorded.

[0017] S13, take out the rock sample and perform CT scan on the rock sample, observe and record the microcracks in the rock sample, and the recorded crack parameters and the temperature difference recorded during the experiment form the first set of data.

[0018] S14, increase or decrease the liquid injection flow rate, repeat steps S11 to S13, and obtain multiple sets of crack parameters and corresponding temperature difference data;

[0019] S15 establishes a functional relationship between the temperature difference under triaxial confining pressure and the microcracks formed after the rock sample is subjected to thermal shock, with crack parameters as the dependent variable and temperature difference as the independent variable.

[0020] Optionally, after step S15, the following steps are also included:

[0021] S16, Increase or decrease the triaxial confining pressure, repeat steps S11-S15, and establish the functional relationship between the temperature difference under multiple different triaxial confining pressure conditions and the microcracks formed after the rock sample is subjected to thermal shock.

[0022] This disclosure also provides a method for evaluating rock fracture, including the following steps:

[0023] S21, the first rock sample is subjected to triaxial confining pressure loading using a true triaxial system, and the temperature of the first rock sample is brought to the first temperature.

[0024] S22, a liquid with a second temperature is injected into the thermal impact borehole of the first rock sample using a liquid supply pump until the temperature in the thermal impact borehole or the temperature measuring borehole of the first rock sample stabilizes. The liquid injection is then stopped, and the difference between the temperature of the rock sample in the temperature measuring borehole and the temperature in the thermal impact borehole is recorded.

[0025] S23, shut off the drain line used to discharge the liquid injected into the thermal shock borehole, use a high-pressure pump to inject liquid into the thermal shock borehole of the first rock sample, continuously increase the pressure in the thermal shock borehole until the pressure decreases, and the maximum pressure observed is the fracture pressure of the rock sample after thermal shock.

[0026] Optionally, after step S23, the following steps are also included:

[0027] S24, increase or decrease the liquid injection flow rate, repeat steps S21-S23, and obtain the fracture pressure of rock samples under thermal shock under multiple different temperature difference conditions.

[0028] S25. Using the fracture pressure of the rock sample after thermal shock as the dependent variable and the temperature difference as the independent variable, a functional relationship between the temperature difference and the fracture pressure of the rock sample after thermal shock is established.

[0029] Optionally, the rock fracture evaluation method further includes the following steps:

[0030] S31, the second rock sample is subjected to triaxial confining pressure loading using a true triaxial system, and the temperature of the second rock sample is brought to the first temperature.

[0031] S32, a high-pressure pump is used to inject liquid into the thermal shock borehole of the second rock sample, and the pressure inside the thermal shock borehole is continuously increased until the pressure decreases. The maximum pressure observed is the fracture pressure of the original rock sample that has not been subjected to thermal shock.

[0032] The technical solution provided in this disclosure has the following advantages compared with the prior art:

[0033] The rock thermal shock experimental apparatus disclosed herein is equipped with a true triaxial system. This true triaxial system can apply triaxial confining pressure to the rock sample, thereby realistically simulating and reproducing the environment of rock samples at different underground locations from the perspective of confining pressure. The rock thermal shock experimental apparatus is equipped with liquid inlet and outlet pipelines inside the rock sample, thereby injecting liquid into the thermal shock borehole through the liquid supply pump and the liquid inlet pipeline, which can realistically simulate the impact of underground fluids on the rock sample. At the same time, the rock is heated by the heating device of the true triaxial system, so that an effective temperature difference is formed between the hot rock sample and the cold liquid injected into the rock thermal shock borehole through the liquid supply pump, thereby realizing the thermal shock effect. Alternatively, the heating module of the liquid supply system heats the liquid before it enters the liquid supply pump, so that an effective temperature difference is formed between the cold rock sample and the hot liquid injected into the rock sample thermal shock borehole through the liquid supply pump, thereby realizing the thermal shock effect. In this way, the working conditions of thermal shock to underground rocks can be realistically simulated.

[0034] The rock thermal shock test method and rock fracture evaluation method disclosed herein can realistically reproduce the operation of different thermal shock engineering projects in the field by setting different confining pressures of rock samples and different flow rates of injected liquids. The rock thermal shock test method uses CT scanning of microcracks in rock samples after thermal shock and conducts multiple sets of thermal shock experiments under different liquid injection flow rates. Through correlation analysis of the microcracks formed in the rock samples and temperature differences, a functional relationship between temperature difference and the formation of microcracks after thermal shock is established. Finally, a quantitative relationship between thermal shock and the formation of microcracks in rock samples under different temperature difference conditions is obtained, providing accurate reference data for field engineering applications. The rock fracture evaluation method can obtain the fracture pressure of rock samples after thermal shock, so as to obtain the impact of thermal shock on the brittleness and strength of rock samples based on the fracture pressure after thermal shock, providing data reference for field engineering applications. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0036] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the rock thermal shock test apparatus according to an embodiment of the present disclosure;

[0038] Figure 2This is a schematic diagram of the rock sample and the pipelines and temperature measuring device arranged on it in an embodiment of the rock thermal shock test apparatus described in this disclosure.

[0039] Figure 3 This is a schematic diagram of the rock sample and the pipelines and temperature measuring device arranged on it in another embodiment of the rock thermal shock test apparatus described in this disclosure.

[0040] Figure 4 This is a schematic diagram of the rock thermal shock experimental apparatus according to another embodiment of the present disclosure;

[0041] Figure 5 This is a schematic diagram of the rock thermal shock test apparatus according to another embodiment of the present disclosure;

[0042] Figure 6 This is a schematic flowchart of the rock thermal shock test method described in the embodiments of this disclosure.

[0043] Among them, 1-True triaxial system; 11-Pressure holding device; 12-Heating device; 2-Rock sample; 21-Thermal impact drilling; 22-Temperature measuring drilling; 23-Pre-fabricated crack; 3-Liquid supply system; 31-Liquid supply pump; 32-Liquid inlet pipeline; 33-Liquid outlet pipeline; 34-Liquid outlet collection device; 35-Flow meter; 36-High pressure pump; 37-Heating module; 4-Temperature measuring system; 41-Temperature measuring device. Detailed Implementation

[0044] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0045] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0046] like Figure 1As shown in some embodiments of this disclosure, a rock thermal shock experimental apparatus includes a true triaxial system 1, a liquid supply system 3, and a temperature measurement system 4. The true triaxial system 1 includes a pressure holding device 11 for applying triaxial confining pressure to a rock sample 2, and a heating device 12 for heating the rock sample 2. The rock sample 2 has a thermal shock borehole 21 and a temperature measurement borehole 22. The liquid supply system 3 includes an inlet pipeline 32 for injecting liquid into the thermal shock borehole 21, a liquid supply pump 31 connected to the inlet pipeline 32, and a drain pipeline 33 for discharging the liquid injected into the thermal shock borehole 21. The temperature measurement system 4 includes multiple temperature measuring devices 41, and heating devices 12 are respectively arranged inside the thermal shock borehole 21 and the temperature measurement borehole 22.

[0047] The rock thermal shock experimental apparatus provided in the above embodiments of this disclosure includes a true triaxial system 1. This true triaxial system 1 is used to apply triaxial confining pressure (i.e., pressurize the rock sample 2 in the x, y, and z directions) and high-temperature heating to the rock sample 2, thereby realistically simulating and restoring the pressure and temperature state of the in-situ underground rock sample 2 in terms of confining pressure and temperature. The rock thermal shock experimental apparatus has thermal shock boreholes 21 and temperature measuring boreholes 22 drilled on the rock sample 2. An inlet pipe 32 and a drain pipe 33 are arranged in the thermal shock borehole 21. The liquid used for thermal shock (such as cold liquid) is injected into the thermal shock borehole 21 of the rock sample 2 using a liquid supply pump 31 and an inlet pipe 32. The rock sample 2 heated by the heating device 12 of the true triaxial system 1 and the injected rock sample The cold liquid in the thermal shock borehole 21 forms an effective temperature difference, thereby realizing the thermal shock effect and realistically simulating the impact of cold flow on underground rocks. The drainage pipeline 33 is used to discharge the liquid injected into the thermal shock borehole 21, and the discharged liquid can be collected in the drainage collection device 34. The temperature measurement system 4 includes multiple temperature measuring devices 41. Temperature measuring devices 41 are respectively arranged inside the thermal shock borehole 21 and the temperature measuring borehole 22. The temperature of the rock sample 2 is detected online through the temperature measuring devices 41, which can accurately reflect the local temperature of the rock sample 2 under thermal shock, that is, the temperature difference of the rock sample 2. This facilitates the quantitative analysis of the relationship between the temperature difference and the fracture effect of the rock under thermal shock through rock thermal shock experiments, thereby providing accurate reference data for field engineering applications.

[0048] In a specific implementation, the pressure-applying device 11 of the true triaxial system 1 includes pressure plates for applying pressure to the rock sample 2 in the x-axis, y-axis, and z-axis directions. Specifically, the pressure-applying device 11 may include six pressure plates for applying pressure to the six surfaces of the rock sample 2. The six pressure plates may be referred to as the upper pressure plate, lower pressure plate, front pressure plate, rear pressure plate, left pressure plate, and right pressure plate according to their orientation. Figure 1Only the left and right pressure plates of the true triaxial system 1 are shown; the other pressure plates are not shown. To avoid interference between the pressure plates and the inlet and outlet pipes of the liquid supply system 3 and the temperature measuring device 41 of the temperature measuring system 4 when the pressure plates pressurize the rock sample 2, grooves can be provided on the upper pressure plate to avoid the inlet pipe 32, outlet pipe 33, and temperature measuring device 41. When the upper pressure plate is pressed down, the inlet pipe 32, outlet pipe 33, and temperature measuring device 41 are located in the corresponding grooves on the upper pressure plate. The heating device 12 of the true triaxial system 1 The device includes at least one heating plate. Specifically, the heating device 12 may include five heating plates for heating five of the six surfaces (excluding the top surface) of the rock sample 2. The heating plates can be moved by pressure plates corresponding to them, causing the heating plates to adhere to the corresponding surfaces of the rock sample 2, thus achieving the purpose of heating the rock sample 2 through the heating plates. Alternatively, the rock sample 2 can be placed in a true triaxial chamber, and heating plates can be installed on the walls of the true triaxial chamber and fixed to the walls, achieving the purpose of heating the rock sample 2 through the heating plates. Of course, the specific structure of the true triaxial system 1 is not limited to the above specific limitations; as long as it can achieve triaxial confining pressure loading and high-temperature heating of the rock sample 2 using the true triaxial system 1, it is acceptable. Those skilled in the art can make reasonable settings according to actual conditions.

[0049] In some embodiments of this disclosure, such as Figure 2 As shown, a thermal impact borehole 21 is drilled on rock sample 2, and the inlet pipe 32 and the outlet pipe 33 are both arranged within this thermal impact borehole 21. Preferably, the thermal impact borehole 21 is a circular hole, and the inner diameter of the thermal impact borehole 21 is larger than the sum of the inner diameters of the inlet pipe 32 and the outlet pipe 33. Arranging the inlet pipe 32 and the outlet pipe 33 within the same thermal impact borehole 21 makes the processing of rock sample 2 and the layout of the pipes more convenient. Of course, there can also be multiple thermal impact boreholes 21, with the inlet pipe 32 and the outlet pipe 33 arranged within one of them.

[0050] In one specific embodiment, rock sample 2 is prepared as follows: Figure 2As shown, the rock sample 2 is processed into a regular shape, such as a cube, and the size can be matched with the true triaxial system 1, such as 300×300×300mm. Holes are drilled on the surface of the regular rock sample 2, including a thermal shock borehole 21 and a temperature measurement borehole 22. There is one thermal shock borehole 21, located at the center of the rock sample 2 surface. The inner diameter of the thermal shock borehole 21 should be at least greater than the sum of the inner diameters of the inlet pipe 32 and the outlet pipe 33 to ensure the proper functioning of the inlet pipe 32 and the outlet pipe 33. Liquid pipelines 33 are all laid out in the thermal shock borehole 21. The depth range of the thermal shock borehole 21 is preferably 1 / 3 to 3 / 4 of the side length of the rock sample 2. The number of temperature measuring boreholes 22 is not limited, and is generally 1 to 4. When the number of temperature measuring boreholes 22 is greater than or equal to 2, the temperature measuring boreholes 22 are evenly distributed around the thermal shock borehole 21 so that the temperature measuring device 41 laid out in multiple temperature measuring boreholes 22 can be used to calibrate the temperature measuring results. Furthermore, when the temperature measuring device 41 in one of the temperature measuring boreholes 22 fails, the normal operation of the rock thermal shock experimental device can still be ensured. After the drilling of rock sample 2 is completed, the liquid inlet line 32 and the liquid outlet line 33 are sealed inside the thermal shock borehole 21. The sealing method can be high-temperature sealant, copper sleeve, etc. The liquid inlet line 32 extends to the bottom of the thermal shock borehole 21, and the liquid outlet line 33 extends to the upper part of the thermal shock borehole 21, so that more liquid injected into the thermal shock borehole 21 can be stored in the thermal shock borehole 21 for heat exchange.

[0051] In other embodiments of this disclosure, such as Figure 3 As shown, rock sample 2 has two thermal impact boreholes 21. One of the thermal impact boreholes 21 contains an inlet pipe 32, and the other contains a drain pipe 33. Rock sample 2 has prefabricated cracks 23 for connecting the two thermal impact boreholes 21. When there are two thermal impact boreholes 21, prefabricated cracks 23 need to be machined inside rock sample 2 to connect the two thermal impact boreholes 21 through the prefabricated cracks 23, forming a channel for liquid inflow and outflow.

[0052] In one specific embodiment, such as Figure 3 As shown, the shape of rock sample 2 can be adopted as follows: Figure 2The rock sample 2 shown has the same shape. The two thermal impact boreholes 21 can be symmetrically arranged on the surface of the rock sample 2 relative to the center of the surface. The depth of the thermal impact boreholes 21 is preferably 1 / 3 to 3 / 4 of the side length of the rock sample 2. The number of temperature measuring boreholes 22 is not limited, generally 1 to 4. When there is only one temperature measuring borehole 22, it can be set between the two thermal impact boreholes 21. When there are two or more temperature measuring boreholes 22, they can be symmetrically distributed on the vertical midline of the line connecting the two thermal impact boreholes 21 relative to the center of the surface of the rock sample 2. After the drilling of the rock sample 2 is completed, the liquid inlet pipe 32 and the liquid outlet pipe 33 are sealed inside the two thermal impact boreholes 21 respectively. The sealing method can be high-temperature sealant, copper sleeve, etc. The liquid inlet pipe 32 extends to the bottom of the thermal impact borehole 21, and the liquid outlet pipe 33 extends to the top of the thermal impact borehole 21.

[0053] In some embodiments of this disclosure, the temperature measuring system 4 includes multiple temperature measuring devices 41. Each temperature measuring device 41 is a device capable of real-time detection of the temperature of the rock sample 2, specifically a thermocouple, etc. The temperature measuring devices 41 are not limited to being installed inside the thermal shock borehole 21 or the temperature measuring borehole 22; they can also be installed at multiple points on the surface and inside the rock sample 2, such as... Figure 2 As shown, temperature measuring devices 41 are respectively installed inside the thermal shock borehole 21, inside the temperature measuring borehole 22, and on the outer wall of the rock sample 2.

[0054] In some embodiments of this disclosure, such as Figure 4 As shown, the liquid supply system 3 also includes a high-pressure pump 36 connected to the liquid inlet pipeline 32. This high-pressure pump 36 injects high-pressure liquid into the thermal shock borehole 21 through the liquid inlet pipeline 32 to perform a fracturing test on the rock sample 2. Specifically, it can perform a high-pressure fracturing test on the rock sample 2 after thermal shock, or on the original rock sample 2 before thermal shock. By comparing the fracture pressure of the rock sample 2 after thermal shock with that of the rock sample 2 before thermal shock, the changes in the brittleness and strength of the rock sample 2 after thermal shock can be quantitatively analyzed. In practice, the high-pressure pump 36 and the liquid supply pump 31 can be connected in parallel. The liquid inlet pipeline 32 is connected to both the high-pressure pump 36 and the liquid supply pump 31 via a tee connector. Furthermore, to control the branch pipes connected to the high-pressure pump 36 and the liquid supply pump 31, on / off valves are installed on both the branch pipe connected to the high-pressure pump 36 and the branch pipe connected to the liquid supply pump 31.

[0055] like Figure 5As shown, some embodiments of this disclosure provide a rock thermal shock experimental apparatus, including a true triaxial system 1, a liquid supply system 3, and a temperature measurement system 4. The true triaxial system 1 includes a pressure holding device 11 for applying triaxial confining pressure to a rock sample 2; the rock sample 2 has a thermal shock borehole 21 and a temperature measurement borehole 22. The liquid supply system 3 includes an inlet pipeline 32 for injecting liquid into the thermal shock borehole 21, a liquid supply pump 31 connected to the inlet pipeline 32, and a drain pipeline 33 for discharging the liquid injected into the thermal shock borehole 21. The liquid supply system 3 also includes a heating module 37 connected to the liquid supply pump 31, which heats the liquid before it enters the liquid supply pump 31. The temperature measurement system 4 includes multiple temperature measuring devices 41, with heating devices 12 arranged inside at least the thermal shock borehole 21 and the temperature measurement borehole 22.

[0056] The rock thermal shock experimental apparatus provided in this disclosure embodiment is similar to... Figure 1 The main difference in the rock thermal shock experimental apparatus shown is that the heating device of the true triaxial system can be eliminated (of course, the heating device of the true triaxial system can also be retained), and a heating module 37 connected to the liquid supply pump 31 is set up. The heating module 37 can be used to heat the liquid before it enters the liquid supply pump 31, thereby realizing the injection of hot liquid into the thermal shock borehole 21 of the rock sample 2. This allows the hot liquid to form an effective temperature difference with the cold rock sample 2, which can also simulate the impact of underground fluid on the rock sample 2, thereby realizing the thermal shock effect.

[0057] In some embodiments of this disclosure, such as Figure 1 , Figure 4 and Figure 5 As shown, a flow meter 35 is installed on the liquid inlet pipeline 32 to control the flow rate of the liquid injected into the thermal shock borehole 21 of the rock sample 2.

[0058] like Figure 6 As shown in the embodiments of this disclosure, a method for conducting a rock thermal shock test is also provided, comprising the following steps:

[0059] S11, using the true triaxial system 1 to apply triaxial confining pressure to rock sample 2, and bring the temperature of rock sample 2 to the first temperature;

[0060] S12, a liquid with a second temperature is injected into the thermal impact borehole 21 of the rock sample 2 using a liquid supply pump 31 until the temperature in the thermal impact borehole 21 or the temperature measuring borehole 22 of the rock sample 2 stabilizes. The liquid injection is then stopped, and the difference between the temperature of the rock sample in the temperature measuring borehole 22 and the temperature in the thermal impact borehole 21 is recorded.

[0061] S13, take out rock sample 2 and perform CT scan on rock sample 2, observe and record the microcracks of the rock sample, and the recorded crack parameters and the temperature difference recorded during the experiment form the first set of data; specifically, the crack parameters may include at least one of the number of cracks, length, and area.

[0062] S14, increase or decrease the liquid injection flow rate, repeat steps S11-S13, and obtain multiple sets of crack parameters and corresponding temperature difference data;

[0063] S15 establishes a functional relationship between the temperature difference under triaxial confining pressure and the microcracks formed after the rock sample is subjected to thermal shock, with crack parameters as the dependent variable and temperature difference as the independent variable.

[0064] It should be understood that the rock thermal shock test method of the embodiments of this disclosure can be adopted as follows: Figure 1 The rock thermal shock experimental setup shown is used to conduct thermal shock experiments. A true triaxial heating system heats the rock sample to a predetermined temperature to form a hot rock sample. A liquid (specifically, a room-temperature cold liquid) is injected into the thermal shock borehole of the rock sample using a liquid supply pump, creating an effective temperature difference between the hot rock sample and the cold liquid. This results in thermal shock to the rock sample, thus simulating thermal shock under different temperature difference conditions. Alternatively, a similar setup can be used... Figure 5 The rock thermal shock experimental apparatus shown is used to conduct thermal shock experiments. The heating module of the liquid supply system heats the liquid before it enters the liquid supply pump to form a hot liquid. The rock sample can be a cold rock sample (specifically, a cold rock sample at room temperature). This creates an effective temperature difference between the cold rock sample and the hot liquid, which has a thermal shock effect on the rock sample 2, thereby simulating the thermal shock of the cold rock sample and the hot liquid under different temperature difference conditions.

[0065] It should be noted that the temperature difference refers to the difference between the temperature of the rock sample in the thermometer borehole 22 and the temperature in the thermal shock borehole 21 after the temperature of the liquid injected into the thermal shock borehole 21 has stabilized during the thermal shock experiment.

[0066] The rock thermal shock test method of the above embodiments of this disclosure can set triaxial confining pressure on the rock sample according to the simulated formation pressure, and set the liquid injection velocity according to the flow velocity of underground fluid impacting the rock. By setting different confining pressures and different flow velocities of the injected liquid, the operation of different thermal shock engineering projects in the field can be realistically reproduced. The rock fracture evaluation method performs CT scans on the microcracks of the rock sample after thermal shock and conducts multiple sets of thermal shock experiments under different liquid injection velocity conditions. By analyzing the correlation between the microcracks formed in the rock sample and the temperature difference, a functional relationship between the temperature difference and the microcracks formed after the rock sample is subjected to thermal shock is established. Finally, a quantitative relationship between thermal shock and the formation of microcracks in the rock sample under different temperature difference conditions is obtained, providing accurate reference data for field engineering applications.

[0067] In some embodiments of this disclosure, after step S15, the following steps are further included:

[0068] S16, Increase or decrease the triaxial confining pressure, repeat steps S11-S15, and establish the functional relationship between the temperature difference under multiple different triaxial confining pressure conditions and the microcracks formed after the rock sample is subjected to thermal shock.

[0069] In the above embodiments, by changing the triaxial confining pressure during the thermal shock experiment, a functional relationship between the temperature difference under multiple different triaxial confining pressure conditions and the microcracks formed in the rock sample after thermal shock was finally established. The quantitative relationship between thermal shock and the formation of microcracks in the rock sample under different confining pressures and temperature differences was obtained, providing accurate reference data for field engineering applications.

[0070] It should be noted that, for the use of, such as Figure 1 The rock thermal shock test method of the experimental apparatus shown can not only set the cold liquid injection flow rate and triaxial confining pressure, but also the temperature at which the true triaxial system heats the rock sample, that is, the final temperature of the rock sample. By changing the final temperature of the rock sample during the thermal shock test, a functional relationship between the temperature difference under different rock sample temperature conditions and the microcracks formed after the rock sample is subjected to thermal shock can be established. Finally, a quantitative relationship between thermal shock and the formation of microcracks in the rock sample under different confining pressures, different rock sample temperatures, and different temperature differences can be obtained, providing accurate reference data for field engineering applications.

[0071] In one specific embodiment, the rock thermal shock test method includes the following steps:

[0072] Step 1: Rock Sample Preparation

[0073] like Figure 2As shown, the rock sample 2 is processed into a regular shape, such as a cube, and the size can be matched with the true triaxial system 1, such as 300×300×300mm. Drilling is performed on the surface of the regular rock sample 2, including thermal shock drilling 21 and temperature measuring drilling 22. There is one thermal shock drilling 21, located at the center of the rock sample 2 surface. The inner diameter of the thermal shock drilling 21 should be at least greater than the sum of the inner diameters of the inlet pipe 32 and the outlet pipe 33. The depth of the thermal shock drilling 21 is preferably 1 / 3 to 3 / 4 of the side length of the rock sample. The number of temperature measuring drilling 22 is unlimited, generally 1 to 4, and the temperature measuring drilling 22 are evenly distributed around the thermal shock drilling 21. After the drilling of rock sample 2 is completed, the liquid inlet pipe 32 and the liquid outlet pipe 33 are sealed inside the thermal shock borehole 21. The sealing method can be high-temperature sealant, copper sleeve, etc. The liquid inlet pipe 32 extends to the bottom of the thermal shock borehole 21, and the liquid outlet pipe 33 extends to the upper part of the thermal shock borehole 21, so that more liquid injected into the thermal shock borehole 21 can be stored in the thermal shock borehole 21 for heat exchange.

[0074] Optionally, such as Figure 3 As shown, there can be two thermal shock boreholes 21. One of the two thermal shock boreholes 21 is equipped with an inlet pipe 32, and the other is equipped with a drain pipe 33. In this case, pre-fabricated cracks 23 need to be processed inside the rock sample 2 to connect the two thermal shock boreholes 21, forming a channel for liquid inflow and outflow. For the preparation of rock samples in this embodiment, please refer to the description of rock sample preparation in the section on rock thermal shock experimental apparatus of this disclosure, which will not be repeated here.

[0075] Step 2: Thermal Shock Test

[0076] (1) Experimental preparation: such as Figure 1 As shown, install and connect each device and pipeline in sequence, as follows: Figure 2 As shown, temperature measuring devices 41 are installed inside the temperature measuring borehole 22, inside the thermal shock borehole 21, and on the outer wall of the rock sample, respectively.

[0077] (2) True triaxial system 1 is activated: as follows Figure 1As shown, turn on the power of the true triaxial system 1 and set the triaxial confining pressure for the rock sample 2. At this time, the pressure of the rock sample along the x-axis, y-axis, and z-axis can be set according to the simulated formation pressure. The reference setting range is that the pressure increases by 10 MPa for every 1 km increase in underground depth. For example, if simulating the pressure at 5 km underground, the pressure of the x-axis, y-axis, and z-axis of the true triaxial system 1 can be set to 50 MPa, 50 MPa, and 50 MPa, respectively. The triaxial confining pressures of the x-axis, y-axis, and z-axis do not need to be the same. After the triaxial pressure is set and pressurized, the temperature is set. The final temperature can be determined according to the simulated formation temperature, generally ranging from room temperature to 400℃. The heating rate is generally 5 to 20℃ / hour. The heating rate should not be too fast to avoid the thermal damage effect on the rock.

[0078] (3) Liquid Injection: After heating is complete, cold liquid is injected using a liquid supply pump 31. This cold liquid can be water or fracturing fluid, etc. The injection flow rate range is 0.2 L / min-5 L / min. The temperature of each temperature measuring point on rock sample 2 is observed. Liquid injection is stopped when the temperature inside the thermal shock borehole 21 or the temperature measuring borehole 22 stabilizes. Optionally, the cold liquid can be replaced by a cold energy-containing substance such as liquid nitrogen or supercritical carbon dioxide.

[0079] (4) Stop the experiment: Stop heating, cool the system to room temperature, disassemble the experimental devices and pipelines, and take out the experimental rock sample 2.

[0080] Step 3: Evaluation of rock sample fracture

[0081] The extracted experimental rock samples were subjected to CT scans, and detailed observations and records of microcracks were made. Correlation analysis was performed with the experimental parameters, including triaxial confining pressure and temperature difference changes. The temperature difference refers to the difference between the rock temperature in the thermometer borehole 22 and the temperature in the thermal shock borehole 21 after the temperature of the cold liquid injected into the thermal shock borehole 21 has stabilized during the thermal shock experiment. The analysis results can be used to reconstruct and guide on-site engineering construction applications.

[0082] The correlation analysis method specifically includes: ① Collecting and recording the number, length, and area of ​​cracks formed based on CT scans; ② Recording the data in conjunction with the triaxial confining pressure and temperature difference during the experiment to form the first set of data; ③ Increasing or decreasing the cold liquid injection flow rate and repeating the thermal shock experiment, obtaining the crack parameters and corresponding temperature differences to form the second set of data; ④ Similarly, continuing to increase or decrease the cold liquid injection flow rate and repeating the thermal shock experiment to obtain multiple sets of data. Using the number, length, and area of ​​cracks as dependent variables and the temperature difference as the independent variable, performing equation regression to obtain parametric equations, and establishing a functional relationship between the temperature difference under the triaxial confining pressure condition and the microcracks formed after thermal shock on the rock sample; ⑤ Similarly, changing the triaxial confining pressure and repeating the above experimental steps to establish a functional relationship between the temperature difference and the microcracks formed after thermal shock on the rock sample under another triaxial confining pressure condition. Finally, a quantitative relationship between thermal shock and the formation of microcracks in rock samples under different triaxial confining pressures and temperature differences is obtained.

[0083] The rock thermal shock test method of this disclosure embodiment can be adopted as follows: Figure 5 The rock thermal shock experimental setup shown was used to conduct thermal shock experiments, compared with the setup used as follows: Figure 1 The rock thermal shock experimental apparatus shown differs from others in that it does not require heating the rock sample 2 using a true triaxial system 1. Instead, the heating module 37 heats the liquid before it enters the supply pump 31. The supply pump 31 injects the hot liquid into the thermal shock borehole 21 of the rock sample 2, creating an effective temperature difference between the hot liquid and the cold rock sample. This also induces thermal shock in the rock sample 2, thus simulating thermal shock between the cold rock sample and the hot liquid under different temperature differences. The specific experimental process will not be detailed here. The hot liquid can also be a fluid containing thermal energy, such as steam or oil.

[0084] This disclosure also provides a method for evaluating rock fracture, including conducting a fracture pressure test on a rock sample after thermal shock and comparing it with the fracture pressure of a rock sample that has not been subjected to thermal shock, thereby enabling quantitative analysis of the changes in the brittleness and strength of the rock sample after thermal shock.

[0085] This method for evaluating rock fracture includes the following steps:

[0086] S21, the first rock sample is subjected to triaxial confining pressure loading using the true triaxial system 1, and the temperature of the rock sample 2 is brought to the first temperature;

[0087] S22, a liquid with a second temperature is injected into the thermal impact borehole 21 of the first rock sample using a liquid supply pump 31 until the temperature in the thermal impact borehole 21 or the temperature measuring borehole 22 of the first rock sample stabilizes. The liquid injection is then stopped, and the difference between the temperature of the rock sample in the temperature measuring borehole 22 and the temperature in the thermal impact borehole 21 is recorded.

[0088] S23, close the drain line 33, use the high pressure pump 36 to inject liquid into the thermal shock borehole 21 of rock sample 2, continuously increase the pressure in the thermal shock borehole 21 until the pressure decreases, and the maximum pressure observed is the fracture pressure of the rock sample after thermal shock.

[0089] The fracture pressure of the rock sample after thermal shock can be obtained using the above method, so as to determine the effect of thermal shock on the brittleness and strength of the rock sample. It should be noted that, in specific implementation, the liquid injected into the thermal shock borehole 21 of the rock sample 2 by the high-pressure pump 36 in step S23 can be the same as the liquid injected into the thermal shock borehole 21 of the rock sample 2 by the liquid supply pump 31 in step S22, or they can be different; the timing of closing the drain line 33 in step S23 can be either immediately after stopping the liquid injection in step S22, or after injecting a certain amount of liquid into the thermal shock borehole 21 of the rock sample 2 by the high-pressure pump 36 in step S23 and then closing the drain line 33.

[0090] Furthermore, following step 23, the following steps are also included:

[0091] S24, increase or decrease the liquid injection flow rate (i.e. change the temperature difference), repeat steps S21-S23 to obtain multiple sets of fracture pressures of rock samples under different temperature difference conditions after thermal shock.

[0092] S25. Using the fracture pressure of the rock sample after thermal shock as the dependent variable and the temperature difference as the independent variable, a functional relationship between the temperature difference and the fracture pressure of the rock sample after thermal shock is established.

[0093] The above method can be used to obtain the fracture pressure of rock samples after thermal shock under different temperature difference conditions, establish the functional relationship between temperature difference and fracture pressure of rock samples after thermal shock, and thus quantitatively analyze the changes in brittleness and strength of rock samples after thermal shock.

[0094] The rock fracture evaluation method also includes the following steps:

[0095] S31, the second rock sample is subjected to triaxial confining pressure loading using the true triaxial system 1, and the temperature of the second rock sample 2 is brought to the first temperature;

[0096] S32, using a high-pressure pump 36, liquid is injected into the thermal shock borehole 21 of the second rock sample, continuously increasing the pressure inside the thermal shock borehole 21 until the pressure decreases. The maximum pressure observed is the fracture pressure of the original rock sample that has not been subjected to thermal shock.

[0097] The fracture pressure of the original rock sample that has not been subjected to thermal shock can be obtained by the above method. By comparing the fracture pressure of the rock sample after thermal shock with that of the original rock sample that has not been subjected to thermal shock, the changes in the brittleness and strength of the rock sample after thermal shock can be obtained.

[0098] The rock fracture evaluation method provided in this disclosure compares the fracture pressure of rock samples subjected to thermal shock with that of rock samples not subjected to thermal shock. The comparison reveals that the fracture pressure of the rock samples subjected to thermal shock is lower than that of the un-thermally-shocked samples, indicating a decrease in brittleness and strength after thermal shock. This result suggests that the rock samples are more prone to microcrack formation after thermal shock. Furthermore, by experimentally obtaining the fracture pressure of rock samples subjected to thermal shock under different temperature differences, a functional relationship between temperature difference and fracture pressure after thermal shock is established, thereby enabling quantitative analysis of changes in the brittleness and strength of the rock samples after thermal shock. In summary, the rock thermal shock experimental apparatus provided in this disclosure, by setting up a true triaxial system, can realistically simulate and reproduce the environment of rock samples at different locations and temperatures underground in terms of confining pressure and temperature. Simultaneously, the apparatus incorporates liquid inlet and outlet pipelines inside the rock sample, simulating the thermal shock conditions experienced by underground rocks in the field, and enabling thermal shock simulation of cold rock samples and hot liquid under different temperature differences. The rock thermal shock experimental method and rock fracture evaluation method provided in this disclosure, by setting different confining pressures, temperatures, and different flow rates of the liquid injected into the rock sample, can realistically reproduce the operational conditions of different thermal shock engineering projects in the field. By performing CT scans on the microcracks of the rock sample after thermal shock and obtaining the fracture pressure through high-pressure fracturing, the formation of microcracks and changes in brittleness and strength of the rock after thermal shock are evaluated, providing accurate reference data for field engineering applications.

[0099] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0100] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rock thermal shock experimental apparatus, characterized in that, It includes a true triaxial system (1), a liquid supply system (3), and a temperature measurement system (4); The true triaxial system (1) includes a pressure holding device (11) for applying triaxial confining pressure to the rock sample (2); The rock sample (2) has a thermal impact borehole (21) and a temperature measurement borehole (22). The liquid supply system (3) includes an inlet pipeline (32) for injecting liquid into the thermal impact borehole (21), a liquid supply pump (31) connected to the inlet pipeline (32), and a drain pipeline (33) for discharging the liquid injected into the thermal impact borehole (21). The temperature measurement system (4) includes multiple temperature measuring devices (41), and the temperature measuring devices (41) are respectively arranged inside the thermal shock borehole (21) and the temperature measuring borehole (22) to record the difference between the rock sample temperature in the temperature measuring borehole (22) and the temperature in the thermal shock borehole (21) during the thermal shock experiment using the temperature measuring devices (41). The true triaxial system (1) further includes a heating device (12) for heating the rock sample (2), and / or the liquid supply system (3) further includes a heating module (37) for heating the liquid before it enters the liquid supply pump (31).

2. The rock thermal shock experimental apparatus according to claim 1, characterized in that, A thermal impact borehole (21) is formed on the rock sample (2), and the liquid inlet pipeline (32) and the liquid outlet pipeline (33) are both arranged in the thermal impact borehole (21).

3. The rock thermal shock experimental apparatus according to claim 1, characterized in that, Two thermal impact boreholes (21) are formed on the rock sample (2). One of the two thermal impact boreholes (21) is equipped with an inlet pipe (32) and the other is equipped with a drain pipe (33). The rock sample (2) is provided with a prefabricated crack (23) for connecting the two thermal impact boreholes (21).

4. The rock thermal shock experimental apparatus according to claim 1, characterized in that, The inlet pipe (32) extends into the bottom of the thermal shock borehole (21), and the outlet pipe (33) extends into the upper part of the thermal shock borehole (21).

5. The rock thermal shock experimental apparatus according to any one of claims 1 to 4, characterized in that, The liquid supply system (3) also includes a high-pressure pump (36) connected to the liquid inlet line (32), the high-pressure pump (36) being used to inject liquid into the thermal shock borehole (21) through the liquid inlet line (32).

6. A method for testing the thermal shock of rocks, characterized in that, Includes the following steps: S11, the rock sample (2) is subjected to triaxial confining pressure loading using a true triaxial system (1), and the temperature of the rock sample (2) is brought to the first temperature; S12, a liquid with a second temperature is injected into the thermal impact borehole (21) of the rock sample (2) using a liquid supply pump (31) until the temperature in the thermal impact borehole (21) or the temperature measuring borehole (22) of the rock sample (2) stabilizes, the liquid injection is stopped, and the difference between the temperature of the rock sample in the temperature measuring borehole (22) and the temperature in the thermal impact borehole (21) is recorded, wherein the first temperature is greater than or less than the second temperature; S13, take out rock sample (2) and perform CT scan on rock sample (2), observe and record the microcracks of rock sample (2), and the recorded crack parameters and the temperature difference recorded during the experiment form the first set of data; S14, increase or decrease the liquid injection flow rate, repeat steps S11-S13, and obtain multiple sets of crack parameters and corresponding temperature difference data; S15 establishes a functional relationship between the temperature difference under triaxial confining pressure and the microcracks formed after the rock sample is subjected to thermal shock, with crack parameters as the dependent variable and temperature difference as the independent variable.

7. The rock thermal shock test method according to claim 6, characterized in that, Following step S15, the following steps are also included: S16, Increase or decrease the triaxial confining pressure, repeat steps S11-S15, and establish the functional relationship between the corresponding temperature difference under multiple different triaxial confining pressure conditions and the microcracks formed after the rock sample is subjected to thermal shock.

8. A method for evaluating rock fracture, characterized in that, Includes the following steps: S21, the first rock sample is subjected to triaxial confining pressure loading using a true triaxial system (1), and the temperature of the first rock sample reaches the first temperature; S22, a liquid with a second temperature is injected into the thermal impact borehole (21) of the first rock sample using a liquid supply pump (31) until the temperature in the thermal impact borehole (21) or the temperature measuring borehole (22) of the first rock sample stabilizes. The liquid injection is then stopped, and the difference between the temperature of the rock sample in the temperature measuring borehole (22) and the temperature in the thermal impact borehole (21) is recorded, wherein the first temperature is greater than or less than the second temperature. S23, shut off the drain line (33) used to drain the liquid injected into the thermal shock borehole (21), use a high-pressure pump (36) to inject liquid into the thermal shock borehole (21) of the first rock sample, continuously increase the pressure in the thermal shock borehole (21) until the pressure decreases, and the maximum pressure observed is the fracture pressure of the rock sample after thermal shock.

9. The rock fracture evaluation method according to claim 8, characterized in that, Following step S23, the following steps are also included: S24, increase or decrease the liquid injection flow rate, repeat steps S21-S23, and obtain the fracture pressure of rock samples under thermal shock under multiple different temperature difference conditions. S25. Using the fracture pressure of the rock sample after thermal shock as the dependent variable and the temperature difference as the independent variable, a functional relationship between the temperature difference and the fracture pressure of the rock sample after thermal shock is established.

10. The rock fracture evaluation method according to claim 8, characterized in that, It also includes the following steps: S31, the second rock sample is subjected to triaxial confining pressure loading using a true triaxial system (1), and the temperature of the second rock sample reaches the first temperature; S32, a high-pressure pump (36) is used to inject liquid into the thermal shock borehole (21) of the second rock sample, and the pressure in the thermal shock borehole (21) is continuously increased until the pressure decreases. The maximum pressure observed is the fracture pressure of the original rock sample that has not been subjected to thermal shock.

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