Core holder and experimental method for thermal stress fracturing experiment

Abstract

This invention discloses a core holder and experimental method for thermal stress fracturing experiments, comprising: an insulated pipe kit having a through cavity; a heating device at one end of the insulated pipe kit, and an insulation layer in the area outside the heating device; a first temperature sensor on the upper side of the area opposite the insulation layer, and a transparent glass-encased steel container on the lower side of the area opposite the insulation layer; a second temperature sensor on the heating device; a clamping device for clamping the insulated pipe kit; a piston kit disposed on the clamping device for introducing gas or liquid into the cavity of the insulated pipe kit; and a device for clamping the experimental core placed in the cavity of the insulated pipe kit. This experimental apparatus, in addition to thermal stress fracturing displacement experiments, can also meet the equipment requirements of conventional body experiments, exhibiting strong functionality.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and more specifically to a core holder and experimental method for thermal stress fracturing experiments. Background Technology

[0002] Deep shale gas development faces challenges due to its deep burial depth, including high temperatures, high pressures, underdeveloped natural fractures, and significant differences in horizontal principal stresses. These challenges lead to difficulties in constructing artificial fractures, insufficient permeability enhancement capacity of conventional fracture networks, and accelerated decline in post-fracturing production—a series of engineering and technical difficulties distinct from those encountered in shallow shale gas development. Consequently, deep shale gas development has been less effective, resulting in significantly lower returns on investment. Post-fracturing well shut-in (i.e., shutting in the well for a period after fracturing the shale gas fracture network before performing a shut-in operation) is a production enhancement technology that promotes the development of microfractures in the matrix, increases the complexity of the fracture network, and improves the initial production of a single well. It is a crucial guarantee for the economical and efficient development of deep shale gas. The extended shut-in period after fracturing provides ample time for the adsorption-hydration between the reservoir rock and the fracturing fluid. Since the temperature of the fracturing fluid is much lower than that of the deep shale reservoir (fracturing fluid is generally at room temperature when injected on the surface), a large temperature gradient is generated between the rock and fluid contact surfaces when the high-temperature rock in the bottom layer comes into contact with the relatively low-temperature fracturing fluid. This temperature gradient leads to uneven thermal stress between reservoir rocks, affecting the microstructure of the rock pores and consequently the rock permeability.

[0003] Existing equipment and related experimental methods are primarily designed for testing permeability and microstructure of core samples under isothermal conditions. Few methods adequately consider the impact of temperature gradients during fracturing on core permeability and microstructure. This fails to meet the research needs of oil and gas field development, necessitating a novel physical model for displacement experiments to further satisfy the demands of microscopic experimental research, building upon existing models. Summary of the Invention

[0004] The purpose of this invention is to provide a core holder and experimental method for thermal stress fracturing experiments, in order to solve the technical problems in the background art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A core holder for thermal stress fracturing experiments includes:

[0007] The insulated pipe kit has a through cavity; a heating device is provided at one end of the insulated pipe kit, and an insulation layer is provided in the area of ​​the insulated pipe kit other than the area where the heating device is located; a first temperature sensor is provided on the upper side of the area opposite to the insulation layer, and a transparent glass-encased steel container is provided on the lower side of the area opposite to the insulation layer; a second temperature sensor is provided on the heating device; a clamping device is used to clamp the insulated pipe kit; a piston kit is provided on the clamping device for introducing gas or liquid into the cavity of the insulated pipe kit; and for clamping an experimental core placed in the cavity of the insulated pipe kit.

[0008] In some embodiments, the insulated pipe kit includes two concentric pipes nested together, with an insulation layer filling the space between the two concentric pipes, and an enhanced thermally conductive copper pipe filling the space between the two concentric pipes whose right ends are wrapped by a heating device.

[0009] In some embodiments, several mounting holes are drilled above and below the two concentric pipes. The first temperature sensor is located in the mounting hole above the concentric pipes, and the transparent glass-enclosed steel container is located in the mounting hole below the concentric pipes.

[0010] In some embodiments, the heating device is an elliptical concentric copper tube with a sandwich layer, in which a heating resistor is wound, a second temperature sensor is disposed above the right end of the elliptical concentric copper tube, and a connecting head is disposed below the elliptical concentric copper tube.

[0011] In some embodiments, the clamping device includes a glass frame and a tube sleeve. The two tube sleeves are respectively arranged on the left and right sides of the frame in an axially symmetrical manner. The left and right tube sleeves each have a groove on their opposite side. The groove diameter of the left tube sleeve is smaller than that of the right tube sleeve. The insulation pipe kit is clamped by the grooves of the left and right tube sleeves.

[0012] In some embodiments, the piston assembly includes a piston, a piston cap, a piston rod, and a piston top plate. The piston and piston cap are provided in pairs and are symmetrical along the diagonal of the glass frame. The piston caps are respectively embedded in the grooves of the sleeve. One end of the piston rod is connected to the piston top plate, and the other end of the piston rod passes through the left sleeve and is connected to the left piston. The two ends of the elliptical concentric copper tube pass vertically through the piston caps embedded in the sleeve and are then vertically embedded in the concentric tube. A horizontal through hole is provided in the middle of the piston along the horizontal direction, and the horizontal through hole passes through the piston rod and the piston top plate. A liquid / gas inlet is provided on the left side of the piston, which is perpendicular to the horizontal through hole. A liquid / gas outlet is provided at one end of the right piston, which is fixed by a clamping screw. The other end of the right piston passes through the right sleeve and is located in the cavity. The liquid / gas outlet is perpendicular to the horizontal through hole. Both the liquid / gas inlet and outlet are provided with matching plugs and gas-liquid quick connectors.

[0013] In some embodiments, the glass frame is cuboid in shape, with grooves at the front and back for mounting the observation glass, and pre-drilled channels at the bottom left and right sides; a slot is provided at the bottom, and liquid / gas channels are provided on both sides of the glass frame, with the liquid / gas channels flush with the piston rod and the middle part of the concentric pipe.

[0014] In some embodiments, the clamping device further includes a T-shaped sleeve located at one end of the right side of the glass frame, with threaded holes on all four sides, and the T-shaped plate is fixed by tightening screws; the T-shaped plate has an elliptical channel in the middle, and a silicone pad is provided in the elliptical channel, which is larger than the right piston; the right piston is fixed in position after passing vertically through the elliptical channel of the T-shaped plate.

[0015] In some embodiments, the clamping device further includes a U-shaped square clip, which is located at one end of the left piston. The U-shaped square clip has threaded holes at both ends and is placed vertically in the slots on the glass frame and fixed to the glass frame by tightening screws. The inner side of the U-shaped square clip is in close contact with the left piston.

[0016] This embodiment also provides an experimental method for a core holder in a thermal stress fracturing experiment, based on the aforementioned holder, including the following steps:

[0017] 1) Assemble the piston rod and piston top plate and pass them through the piston cap. Place the piston cap with the piston rod into the groove of the tube sleeve on the left side of the glass frame and press it to fit tightly. Place the piston cap into the groove of the tube sleeve on the right side of the glass frame and press it to fit tightly.

[0018] 2) Combine the piston with the horizontal fluid channel and liquid / gas inlet with the U-shaped square clamp, insert the piston rod assembled in step 1 into the piston, then put both ends of the U-shaped square clamp into the slots of the glass frame, tighten the screws to fix the piston on the left side, and put the T-shaped tube sleeve through the clamping bracket into the slots of the glass frame, and fix it to the glass frame with screws.

[0019] 3) Place the heating device on the right side of the insulated pipe kit where there is no insulation layer, and put the dried experimental core into the pipe from the right side; vertically fit the left side of the insulated pipe kit with the heating device on it onto the assembled piston rod, and after fitting it, put the right side of the insulated pipe kit into the piston cap on the right side of the frame.

[0020] 4) Connect the power supply, temperature control device, temperature sensor, and computer's thermal resistance and sensor wires through the prefabricated holes in the frame to the insulation pipe kit and heating device.

[0021] 5) Place the observation light source into the light source placement slot of the frame;

[0022] 6) Use the quick connector to pump nitrogen into the liquid / gas inlet, remove the plug from the liquid / gas outlet, and purge the remaining gas from the clamp.

[0023] 7) After the gas is drained, turn on the power of the heating device, set the initial core temperature for the experiment, and record the current time when the temperatures of all the first temperature sensors at the core position on the insulation pipe and the second temperature sensor on the device are the same as the set initial core temperature.

[0024] 8) Remove the plugs from the liquid / air inlet and the liquid / air outlet. Use the quick connector to pump the experimental liquid into the liquid / air inlet. The temperature of the experimental liquid is significantly lower than the initial core temperature. Record the time when the temperature of all the first temperature sensors at the core location begins to change for the first time, the time when the first liquid appears in the transparent glass-enclosed steel container, and the flow rate of the liquid / air outlet.

[0025] 9) Turn off the power after the second temperature sensor first detects a temperature change;

[0026] 10) For the same block and size as in steps 1-9, repeat steps 1-9 without heating, and record the time when liquid first appears in the transparent glass container and the flow rate of the liquid / gas outlet.

[0027] 11) The experiment is over.

[0028] The beneficial effects of this invention compared to the prior art are:

[0029] 1. This experimental setup has a novel structure and strong practicality. Different initial core temperatures can be precisely set using the heating device and temperature sensor.

[0030] 2. This experiment flexibly combines piston kits, insulation pipe kits, and heating devices. By using the length of the rock core placed in the insulation pipe and the initial temperature set by the heating device, an experimental environment with arbitrary temperature gradients can be established for the experimental rock core to test the effect of thermal stress of any magnitude on rock permeability.

[0031] 3. In addition to thermal stress cracking and displacement experiments, this experimental apparatus can also meet the equipment requirements for conventional body experiments, making it highly functional.

[0032] 4. This device can accurately calculate the relationship between displacement rate and temperature gradient using a fiberglass container. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the present invention;

[0034] Figure 2 This is a schematic diagram of the stainless steel tube sleeve structure of the present invention;

[0035] Figure 3This is a schematic diagram of the stainless steel piston assembly structure of the present invention;

[0036] Figure 4 This is a schematic diagram of the combination of the thermal insulation pipe kit and the heating device of the present invention; Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The described embodiments are some, but not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0038] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0039] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an indirect connection through an intermediate medium, or the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0040] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0041] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or display that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or display.

[0042] The following will combine Figure 1-4This application provides a detailed description of a core holder and experimental method for thermal stress fracturing experiments, as described in the embodiments of this application. It is worth noting that the following embodiments are merely illustrative of this application and do not constitute a limitation thereof.

[0043] Example 1:

[0044] like Figure 1-4 As shown, a core holder for a thermal stress fracturing experiment includes: an insulated pipe kit having a through cavity; a heating device at one end of the insulated pipe kit, and an insulation layer in the area of ​​the insulated pipe kit other than the area where the heating device is located; a first temperature sensor on the upper side of the area opposite to the insulation layer, and a transparent glass-encased steel container on the lower side of the area opposite to the insulation layer; a second temperature sensor on the heating device; a clamping device for clamping the insulated pipe kit; a piston kit disposed on the clamping device for introducing gas or liquid into the cavity of the insulated pipe kit; and a core holder for clamping the experimental core placed in the cavity of the insulated pipe kit.

[0045] The insulated pipe kit consists of two concentric pipes 8-3 and 8-4, with an insulation layer 8-5 filling the space between them. The section of the pipe at the right end of the kit, enclosed by the heating device, lacks an insulation layer and is filled with a reinforced thermally conductive copper pipe 8-6. Ten small holes are drilled at both the top and bottom of the kit. A first temperature sensor 8-1 is installed in the top hole, and a 1ml transparent glass-encased steel container (equipped with a weight sensor) 8-2 is installed in the bottom hole. The insulated pipe kit is positioned by embedding both ends of the pipe into grooves in the stainless steel sleeve 1.

[0046] The clamping device includes a glass frame and a tube sleeve, which can be made of stainless steel. There is one stainless steel tube sleeve on each side of the stainless steel glass frame, symmetrically arranged along the axis, and fixed to the stainless steel glass frame by screws 1-1. Both tube sleeves have grooves near the concentric pipes, with the diameter of the left groove slightly smaller than the right groove, because the right groove also needs to enclose the heating device. Sealing silicone rings 1-2 are placed in the grooves.

[0047] The piston assembly can be made of stainless steel. The stainless steel piston assembly includes a stainless steel piston 2, a stainless steel piston cap 3, a stainless steel piston rod 2-4, and a piston top plate 2-5. The stainless steel piston 2 and stainless steel piston cap 3 are a pair and symmetrically arranged along the diagonal of the stainless steel glass frame. The stainless steel piston caps are respectively embedded in the grooves of the stainless steel sleeve. The stainless steel piston rod 2-4 and piston top plate 2-5 are connected to the left piston 2. Specifically, one end of the piston rod is connected to the piston top plate, and the other end of the piston rod passes through the left sleeve and connects to the left piston.

[0048] The two ends of the elliptical concentric copper tube pass vertically through the stainless steel piston caps 3 embedded in the stainless steel sleeve 1, and then vertically embed into the insulated pipe 8. A horizontal through hole 2-1 is provided in the middle of the stainless steel piston 2, extending through the piston rod 2-4 and the piston top plate 2-5. A liquid / gas inlet 2-2 is provided on the left side of the stainless steel piston, perpendicular to the horizontal through hole 2-1. A liquid / gas outlet 2-3 is provided on the side of the stainless steel piston 2 that is fixed by the clamping screw 6-1. A liquid / gas outlet is provided on the right side of the piston that is fixed by the clamping screw, and the other end of the right piston passes through the right sleeve and is located within the cavity. The liquid / gas outlet 2-3 is perpendicular to the horizontal through hole 2-1. Both the liquid / gas inlet and outlet are equipped with matching plugs and quick-connect gas-liquid couplings.

[0049] The stainless steel glass frame 4 is rectangular in shape, with grooves at the front and back allowing for easy disassembly and observation of the glass 4-1. Silicone pads are placed within the grooves to prevent damage to the glass. Pre-drilled channels 4-3 are located at the bottom left and right sides of the stainless steel glass frame to facilitate the passage of sensors and thermal resistors. A slot 4-2 is located at the bottom of the stainless steel frame, within which an observation light source can be placed to observe the liquid droplets inside the first temperature sensor 8-1 and the 1ml transparent glass-steel container 8-2. Liquid / gas channels are located on both sides of the stainless steel glass frame 4, and these channels are flush with the middle of the piston assembly 2 and the insulation pipe assembly 8.

[0050] It should be noted that the 1ml transparent fiberglass container is a small container made of fiberglass with a capacity of only 1 ml, similar to a small graduated cylinder. Fiberglass is used for corrosion resistance and transparency for easy observation, allowing for the use of corrosive liquids in experiments.

[0051] A stainless steel T-shaped tube sleeve 5 is provided, located at one end of the right side of the glass frame 4. It has four threaded holes on its four sides, and four tightening screws 5-1 are used to fix the T-shaped plate to the right side of the stainless steel glass 4. An oval channel is provided in the middle of the T-shaped plate, and a silicone gasket is placed inside the channel. The channel is slightly larger than the right-side piston channel 2. The right-side piston is fixed in position after passing vertically through the stainless steel T-shaped plate.

[0052] A stainless steel U-shaped square card 7 is provided and located at one end of the entrance channel. The U-shaped square card has threaded holes at both ends and is placed vertically in the slots on the stainless steel glass frame 4. It is fixed to the stainless steel glass frame by tightening screws 7-1. The inner side of the U-shaped square card 7 is close to the stainless steel piston 2, which facilitates the fixing of the stainless steel piston.

[0053] The heating device 9 is an elliptical concentric copper tube with a jacket. A heating resistor 9-3 is wound inside the jacket, and a second temperature sensor 9-1 is installed above the rightmost end of the tube. A connecting connector 9-2 is located below the heating device and is connected to a motor. The heating device is installed on the right side of the insulated pipe assembly, on the section without insulation.

[0054] The present invention provides a core holder and experimental method for thermal stress fracturing experiments, and the specific assembly and experimental steps are as follows:

[0055] 1) Assemble the piston rod 2-4 and piston top plate 2-5 and pass them through the stainless steel piston cap 3. Place the stainless steel cap with the piston rod into the groove of the stainless steel tube sleeve on the left side of the glass frame 4 and press it to fit tightly. Place the stainless steel piston cap into the groove of the stainless steel tube sleeve on the right side of the glass frame 4 and press it to fit tightly.

[0056] 2) Combine the stainless steel piston with the horizontal fluid channel 2-1 and the liquid / gas inlet 2-2 with the U-shaped square clip, insert the piston rod assembled in step 1 into the piston, then put both ends of the U-shaped square clip 7 into the slots of the stainless steel glass frame 4, and tighten the screw 7-1 to fix the stainless steel piston 2 on the left side. Pass the stainless steel T-shaped tube sleeve 5 through the clamping bracket 6 and put it into the slot of the stainless steel glass frame 4, and connect and fix it to the stainless steel glass frame 4 with the screw 5-1.

[0057] 3) Place the heating device 9 on the right side of the insulated pipe kit where there is no insulation layer, and insert the dried experimental core from the right side of the pipe. Vertically fit the left side of the insulated pipe kit with the heating device over the piston rod assembled in steps 1) and 2). After fitting, place the right side of the insulated pipe kit into the stainless steel piston cap 3 on the right side of the stainless steel frame 4.

[0058] 4) Connect the power supply and temperature control device 10 and the temperature sensor recording computer 11, along with their heat transfer resistors and sensor wires, through the prefabricated holes 4-3 in the stainless steel frame 4 to the insulation pipe kit and heating device.

[0059] 5) Install the transparent glass observation surfaces 4-1 of the stainless steel frame on the front and rear sides of the stainless steel frame 4 onto the stainless steel frame 4, press them to fit tightly, and fix all the parts in the middle of the piston by tightening the screws on the clamping screws 6-1 on the bracket 6.

[0060] 6) Place the observation light source into the stainless steel frame light source placement slot 4-2 of the stainless steel frame 4;

[0061] 7) Use the quick connector to pump nitrogen into the liquid / gas inlet 2-2, remove the plug from the liquid / gas outlet 2-3, and purge the remaining gas in the experimental apparatus.

[0062] 8) After the gas is drained, turn on the power supply 10 of the heating device, set the initial core temperature of the experiment, and record the current time when the temperatures of all the first temperature sensors 8-1 at the core position on the insulation pipe and the second temperature sensor 9-1 on the feeding device 9 are the same as the set initial core temperature of the experiment.

[0063] 9) Remove the plugs from the liquid / air inlet 2-2 and the liquid / air outlet 2-3. Use the quick connector to pump the experimental liquid (liquid with a temperature significantly lower than the initial core temperature) into the liquid / air inlet 2-2. Record the time when the temperature of all the first temperature sensors 8-1 at the core location begins to change for the first time, the time when liquid first appears in the 1ml transparent glass container 8-2 (equipped with a weight sensor), and the flow rate of the liquid / air outlet 2-3.

[0064] 10) After the second temperature sensor 9-1 first generates a temperature change, turn off the power;

[0065] 11) For the same block and size as in step 1-10, perform step 1-10 without heating, and record the time when the first liquid appears in the 1ml transparent glass container 8-2 and the flow rate of the liquid / gas outlet 2-3.

[0066] 12) The experiment is over.

[0067] This experiment flexibly combines piston kits, insulated pipe kits, and heating devices. By adjusting the length of the rock core placed in the insulated pipes and the initial temperature set by the heating device, an experimental environment with arbitrary temperature gradients can be established for the experimental rock core to test the effect of thermal stress of any magnitude on rock permeability. In addition to thermal stress fracturing and displacement experiments, this experimental device can also meet the equipment requirements of conventional body experiments, making it highly functional.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A core holder for thermal stress fracturing experiments, characterized in that, include: The insulated pipe kit has a through cavity; a heating device is provided at one end of the insulated pipe kit, and an insulation layer is provided in the area of ​​the insulated pipe kit other than the area where the heating device is provided; a first temperature sensor is provided on the upper side of the area opposite to the insulation layer, and a transparent glass-enclosed steel container is provided on the lower side of the area opposite to the insulation layer; a second temperature sensor is provided on the heating device. A clamping device for clamping the thermal insulation pipe kit; A piston assembly, disposed on the clamping device, is used to introduce gas or liquid into the cavity of the insulated pipe assembly; and to clamp an experimental core placed inside the cavity of the insulated pipe assembly. The insulated pipe kit includes two concentric pipes nested together, with an insulation layer filling the space between the two concentric pipes. The right end of the insulated pipe is wrapped by a heating device, and the space between the two concentric pipes is filled with a heat-conducting copper pipe. Several mounting holes are drilled above and below the two concentric pipes. The first temperature sensor is located in the mounting hole above the concentric pipe, and the transparent glass-enclosed steel container is located in the mounting hole below the concentric pipe. The heating device is an elliptical concentric copper tube with a jacket, in which a heating resistor is wound. A second temperature sensor is located above the elliptical concentric copper tube on the right end, and a connecting head is located below the elliptical concentric copper tube. The clamping device includes a glass frame and a tube sleeve. The two tube sleeves are respectively arranged on the left and right sides of the frame in an axially symmetrical manner. The left and right tube sleeves each have a groove on their opposite side. The groove diameter of the left tube sleeve is smaller than that of the right tube sleeve. The insulation pipe kit is clamped by the grooves of the left and right tube sleeves. The piston assembly includes a piston, piston cap, piston rod, and piston top plate. A pair of pistons and piston caps are provided and symmetrically arranged along the diagonal of the glass frame. The piston caps are respectively embedded in the grooves of the sleeve. One end of the piston rod is connected to the piston top plate, and the other end of the piston rod passes through the left sleeve and connects to the left piston. The two ends of an elliptical concentric copper tube pass vertically through the piston caps embedded in the sleeve and are then vertically embedded into the concentric tube. A horizontal through-hole is provided in the middle of the piston, passing through the piston rod and piston top plate. A liquid / gas inlet is provided on the left side of the piston, perpendicular to the horizontal through-hole. A liquid / gas outlet is provided on the right side of the piston, fixed by a clamping screw. The other end of the right piston passes through the right sleeve and is located in the cavity, perpendicular to the horizontal through-hole. Both the liquid / gas inlet and outlet are equipped with matching plugs and quick-connect gas-liquid couplings.

2. The core holder for thermal stress fracturing experiments according to claim 1, characterized in that, The glass frame is rectangular in shape, with grooves at the front and back for mounting the observation glass. The glass frame has pre-made channels at the bottom on both sides. A slot is provided at the bottom, and liquid / gas channels are provided on both sides of the glass frame, with the liquid / gas channels flush with the piston rod and the middle part of the concentric pipe.

3. The core holder for thermal stress fracturing experiments according to claim 2, characterized in that, The clamping device also includes a T-shaped sleeve, which is located at one end of the right side of the glass frame and has threaded holes on all four sides. The T-shaped plate is fixed by tightening screws. The T-shaped plate has an elliptical channel in the middle, and a silicone pad is placed inside the elliptical channel. The elliptical channel is larger than the right piston. The right piston passes vertically through the elliptical channel of the T-shaped plate and is fixed in position.

4. The core holder for thermal stress fracturing experiments according to claim 3, characterized in that, The clamping device also includes a U-shaped square clip, which is located at one end of the left piston. The U-shaped square clip has threaded holes at both ends and is placed vertically in the slots on the glass frame, and is fixed to the glass frame by tightening screws; the inner side of the U-shaped square clip is in close contact with the left piston.

5. An experimental method for a core holder in a thermal stress fracturing experiment, comprising using the core holder for a thermal stress fracturing experiment as described in claim 4, characterized in that, Includes the following steps: 1) Assemble the piston rod and piston top plate and pass them through the piston cap. Place the piston cap with the piston rod into the groove of the tube sleeve on the left side of the glass frame and press it to fit tightly. Place the other piston cap into the groove of the tube sleeve on the right side of the glass frame and press it to fit tightly. 2) Combine the piston with the horizontal fluid channel and liquid / gas inlet with the U-shaped square clamp, insert the piston rod assembled in step 1 into the piston, then put both ends of the U-shaped square clamp into the slots of the glass frame, tighten the screws to fix the piston on the left side, and put the T-shaped tube sleeve through the clamping bracket into the slots of the glass frame, and fix it to the glass frame with screws. 3) Place the heating device on the right side of the insulated pipe kit where there is no insulation layer, and put the dried experimental core into the pipe from the right side; vertically fit the left side of the insulated pipe kit with the heating device on it onto the assembled piston rod, and after fitting it, put the right side of the insulated pipe kit into the piston cap on the right side of the frame. 4) Connect the power supply, temperature control device, temperature sensor, and the computer's thermal resistance and sensor wires through the prefabricated holes in the frame to the insulation pipe kit and heating device. 5) Place the observation light source into the light source placement slot of the frame; 6) Use the quick connector to pump nitrogen into the liquid / gas inlet, remove the plug from the liquid / gas outlet, and purge the remaining gas from the clamp. 7) After the gas is drained, turn on the power of the heating device, set the initial core temperature for the experiment, and record the current time when the temperatures of all the first temperature sensors at the core position on the insulation pipe and the second temperature sensor on the heating device are the same as the set initial core temperature. 8) Remove the plugs from the liquid / air inlet and the liquid / air outlet. Use the quick connector to pump the experimental liquid into the liquid / air inlet. The temperature of the experimental liquid is significantly lower than the initial core temperature. Record the time when the temperature of all the first temperature sensors at the core location begins to change for the first time, the time when the first liquid appears in the transparent glass-enclosed steel container, and the flow rate of the liquid / air outlet. 9) Turn off the power after the second temperature sensor first detects a temperature change; 10) For the same block and size as in steps 1-9, repeat steps 1-9 without heating, and record the time when liquid first appears in the transparent glass container and the flow rate of the liquid / gas outlet. 11) The experiment is over.

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