A device and method for testing triaxial mechanical parameters of rock under carbon dioxide contact
By designing a testing device for triaxial mechanical parameters of rocks under carbon dioxide contact, the problem that existing technologies cannot test the triaxial mechanical parameters of rocks under direct carbon dioxide contact is solved. This enables the simulation and testing of rock mechanical properties in a real reservoir environment and is applicable to experiments with cores of different sizes.
Patent Information
- Application Number
- CN202210749043.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-06-29
- Publication Date
- 2026-01-20
- Estimated Expiration
- 2042-06-29
AI Technical Summary
Existing technologies cannot experimentally test the triaxial mechanical parameters of rocks under direct contact with carbon dioxide, nor can they simulate the changes in the triaxial mechanical properties of rocks under the interaction of carbon dioxide with underground reservoir rocks.
Design a device for testing the triaxial mechanical parameters of rocks under carbon dioxide contact, including a rock-carbon dioxide contact and triaxial compression testing system, combined with a control system for axial pressure, confining pressure, temperature and carbon dioxide pressure, and conduct experiments through a computer data recording and control system.
It enables the testing of rock mechanical parameters during simulated carbon dioxide drilling, fracturing, displacement, and storage processes. It can test changes in the mechanical properties of rocks in real reservoir environments, is suitable for experiments with cores of different sizes, and is stable, reliable, and has low maintenance costs.
Smart Images
Figure CN115165585B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a device and method for testing triaxial mechanical parameters of rock under carbon dioxide contact. BACKGROUND
[0002] With the increasing dependence of China's oil and gas on foreign countries, how to increase the intensity of oil and gas exploration and development under the background of "double carbon" and ensure China's energy security is an important problem that needs to be solved at present. Through supercritical carbon dioxide for efficient and low-carbon exploitation of unconventional resources such as shale oil and gas, especially through carbon dioxide, a clean fluid for drilling and completion, reservoir fracturing modification, oil and gas displacement replacement, improving oil and gas single well production and oil and gas reservoir recovery, and at the same time realizing carbon dioxide geological storage, which has important significance.
[0003] The influence of carbon dioxide on the mechanical properties of oil and gas reservoir rocks is one of the most critical factors for supercritical carbon dioxide drilling and completion, fracturing, oil displacement, and formation storage. Laboratory testing is the most direct and effective way, but the current experiments on the influence of carbon dioxide on rock mechanical parameters cannot achieve triaxial mechanical parameter testing under the condition of direct contact between carbon dioxide and rock, thereby simulating the changes in rock triaxial mechanical properties under the interaction between carbon dioxide and underground reservoir rocks during carbon dioxide drilling and completion, fracturing, displacement, and storage to the greatest extent. This limitation has not been solved. SUMMARY
[0004] The present application aims to solve the above problems and proposes a device and method for testing triaxial rock mechanical parameters under the condition of direct contact between carbon dioxide and rock core under certain temperature and pressure conditions.
[0005] The technical solution of the present application is as follows:
[0006] The present application proposes a device for testing triaxial mechanical parameters of rock under carbon dioxide contact.
[0007] A device for testing triaxial mechanical parameters of rock under carbon dioxide contact, comprising a rock and carbon dioxide contact and triaxial compression testing system, and an axial pressure control system, a confining pressure control system, a temperature control system, and a carbon dioxide pressure control system connected to the rock and carbon dioxide contact and triaxial compression testing system, and a computer data recording and control system; the axial pressure control system, the confining pressure control system, the temperature control system, and the carbon dioxide pressure control system are connected to the computer data recording and control system;
[0008] The triaxial compression test system for testing the rock and carbon dioxide comprises a cavity, a strain testing device is arranged in the cavity, and the strain testing device is connected to a computer data recording and control system; the cavity is divided into a core chamber and a hydraulic oil chamber, a core is arranged in the core chamber; the hydraulic oil chamber is filled with hydraulic oil; an upper core holder is arranged at an upper end of the core chamber, the upper core holder is sequentially provided with an upper groove, a first channel and an upper carbon dioxide chamber from bottom to top, and a top end of the upper carbon dioxide chamber is connected to an axial compression control system; a lower core holder is arranged at a lower end of the core chamber, the lower core holder is sequentially provided with a lower groove, the first channel, a lower carbon dioxide chamber and a second channel from top to bottom, and the second channel is connected to a carbon dioxide pressure control system; the upper core holder is in dynamic sealing with a top end of the cavity, and the lower core holder is fixedly connected with a bottom end of the cavity.
[0009] The triaxial compression test system for testing the rock and carbon dioxide comprises a cavity, a strain testing device is arranged in the cavity, and the strain testing device is connected to a computer data recording and control system; the cavity is divided into a core chamber and a hydraulic oil chamber, a core is arranged in the core chamber; the hydraulic oil chamber is filled with hydraulic oil; an upper core holder is arranged at an upper end of the core chamber, the upper core holder is sequentially provided with an upper groove, a first channel and an upper carbon dioxide chamber from bottom to top, and a top end of the upper carbon dioxide chamber is connected to an axial compression control system; a lower core holder is arranged at a lower end of the core chamber, the lower core holder is sequentially provided with a lower groove, the first channel, a lower carbon dioxide chamber and a second channel from top to bottom, and the second channel is connected to a carbon dioxide pressure control system; the upper core holder is in dynamic sealing with a top end of the cavity, and the lower core holder is fixedly connected with a bottom end of the cavity.
[0010] The carbon dioxide pressure control system comprises a carbon dioxide cylinder, a carbon dioxide booster system and a carbon dioxide buffer tank which are sequentially connected; the output end of the carbon dioxide buffer tank is respectively connected with a carbon dioxide recovery device and a vacuumizing device; the output end of the carbon dioxide buffer tank is also connected to the second channel; a carbon dioxide pressure sensor is arranged on a connecting pipeline between the output end of the carbon dioxide buffer tank and the second channel, and the carbon dioxide pressure sensor and the carbon dioxide booster system are respectively connected to the computer data recording and control system.
[0011] The axial compression control system comprises an axial compression loading system and a load sensor; the load sensor is connected to the top end of the upper carbon dioxide chamber; one end of the axial compression loading system is connected to the upper carbon dioxide chamber, and the other end is connected to the computer data recording and control system; the confining pressure control system comprises a confining pressure loading system and a confining pressure sensor; the confining pressure sensor is arranged in the hydraulic oil chamber, one end of the confining pressure loading system is connected to the hydraulic oil chamber, and the other end is connected to the computer data recording and control system; the temperature control system comprises a heating system and a temperature sensor, the temperature sensor is arranged in the hydraulic oil chamber, one end of the heating system is connected to the hydraulic oil chamber, and the other end is connected to the computer data recording and control system; the load sensor, the confining pressure sensor and the temperature sensor are all connected to the computer data recording and control system.
[0012] The strain testing device comprises an extensometer or a strain gauge; the extensometer is arranged in the hydraulic oil chamber and attached to the outer wall of the soft sleeve; the strain gauge is arranged in the core chamber and adhered to the core.
[0013] The confining pressure loading system comprises a booster pump connected with hydraulic oil through an oil inlet line and an oil return line; the heating system comprises an external resistance heating belt wrapped outside the cavity; the carbon dioxide booster system is an electric plunger pump; the carbon dioxide recovery device comprises a pressure reducing valve and a recovery tank connected in sequence; the vacuumizing device comprises a needle valve and a vacuum pump connected in sequence.
[0014] The first hole channel has five holes, and the diameter of the first hole channel is equal to the cross-sectional diameter of the upper and lower grooves; the cross section of the upper and lower grooves is semicircular; the diameter of the second hole channel is 1.5-2.5 times the diameter of the first hole channel.
[0015] The second hole channel is connected with the output end of the carbon dioxide buffer tank, the carbon dioxide recovery device and the vacuumizing device through a four-way joint.
[0016] The present application provides a method for testing triaxial mechanical parameters of rock under carbon dioxide contact.
[0017] A method for testing triaxial mechanical parameters of rock under carbon dioxide contact, using the carbon dioxide contact rock triaxial mechanical parameter testing device as described above, the process is as follows:
[0018] Step 1: Place the core between the upper and lower core clamps, and apply axial pressure to fix the core; the soft sleeve is sleeved outside the core chamber, and the upper limit of the soft sleeve is higher than the upper groove, and the lower limit of the soft sleeve is lower than the lower groove; install the strain testing device; fill hydraulic oil into the hydraulic oil chamber to apply confining pressure and keep the axial pressure continue to load, keep the core stable balance;
[0019] Step 2: Close the carbon dioxide buffer tank and the carbon dioxide recovery device, and vacuumize the core chamber through the vacuumizing device;
[0020] Step 3: Close the vacuumizing device, open the carbon dioxide buffer tank, and control the carbon dioxide booster system through the computer data recording and control system to fill carbon dioxide into the core chamber through the carbon dioxide buffer tank, the second hole channel, the lower carbon dioxide chamber and the first hole channel in sequence, so that the carbon dioxide is in direct contact with the rock; the carbon dioxide pressure is always lower than the confining pressure by 5-10 MPa; at the same time, the heating system heats the hydraulic oil;
[0021] Step 4: Continue to fill carbon dioxide into the core chamber until the preset carbon dioxide pressure and carbon dioxide temperature are reached; start the contact soaking;
[0022] Step 5: After reaching the preset contact soaking time, perform the rock triaxial compression experiment, control the axial pressure loading system to axially pressurize the core through the computer data recording and control system, and record the load and strain changes in the axial pressure experiment process;
[0023] Step 6: After the rock triaxial compression experiment is completed, the carbon dioxide buffer tank and the carbon dioxide booster system are closed, and the carbon dioxide recovery device is opened to recover the carbon dioxide in the core chamber. When the carbon dioxide in the core chamber is completely discharged into the carbon dioxide recovery device, the confining pressure of the core chamber is unloaded.
[0024] In the step 1, the axial pressure is 100-1000N, and the confining pressure is 0-80MPa; in the step 4, the carbon dioxide pressure is 0-60MPa, and the carbon dioxide temperature is 0-100℃; in the step 5, the preset contact soaking time is 0-120h.
[0025] More preferably, in the step 1, the axial pressure is 500N, and the confining pressure is 15MPa; in the step 4, the carbon dioxide pressure is 10MPa, and the carbon dioxide temperature is 45℃; in the step 5, the preset contact soaking time is 2h.
[0026] The technical effect of the present application is that:
[0027] 1. The present application can simulate the triaxial rock mechanics parameter test in the process of direct contact between underground reservoir rock and carbon dioxide in the process of carbon dioxide drilling, fracturing, displacement, and storage, etc., and can obtain the rock mechanics parameters in the process of direct contact between carbon dioxide and rock under the closest real reservoir environment and engineering conditions.
[0028] 2. The present application can make carbon dioxide and core fully and directly contact and carry out soaking reaction under certain time, temperature and pressure conditions, and can realize the instantaneous replenishment of a small amount of consumption in the process of contact reaction between carbon dioxide and core.
[0029] 3. The present application can be applied to rock triaxial compression experiments of any reservoir rock and carbon dioxide contact.
[0030] 4. The present application can realize experimental testing of different size cylindrical cores by changing the size, material grade, etc. of the carbon dioxide core contact and rock triaxial compression test device.
[0031] 5. The present application can realize random and continuous changes of experimental conditions such as temperature, pressure, contact soaking time, etc. in the process of direct contact and soaking of carbon dioxide and core.
[0032] 6. The present application can realize that the experimental conditions such as carbon dioxide temperature and pressure are not limited by changing the material, size and steel grade of the equipment and instruments.
[0033] 7. The present application has wide application range, is stable and reliable, is convenient to assemble and disassemble, and has low maintenance and repair cost. BRIEF DESCRIPTION OF DRAWINGS
[0034] Figure 1 It is a structural schematic diagram of a rock triaxial mechanical parameter testing device under carbon dioxide contact.
[0035] Figure 2 It is a schematic diagram of a rock and carbon dioxide contact and triaxial compression testing system.
[0036] Figure 3 It is an end surface schematic diagram of an upper core holder and a lower core holder.
[0037] Reference signs: 1, hydraulic oil chamber; 2, core chamber; 3, upper core holder; 4, lower core holder; 5, first hole; 6, upper carbon dioxide chamber; 7, second hole; 8, soft sleeve; 9, lower carbon dioxide chamber. DETAILED DESCRIPTION
[0038] Example 1 - A rock triaxial mechanical parameter testing device under carbon dioxide contact
[0039] A rock triaxial mechanical parameter testing device under carbon dioxide contact, comprising a rock and carbon dioxide contact and triaxial compression testing system and an axial pressure control system, a confining pressure control system, a temperature control system and a carbon dioxide pressure control system connected with the rock and carbon dioxide contact and triaxial compression testing system respectively, and further comprising a computer data recording and control system; the axial pressure control system, the confining pressure control system, the temperature control system and the carbon dioxide pressure control system are all connected with the computer data recording and control system;
[0040] The rock and carbon dioxide contact and triaxial compression testing system comprises a cavity, a strain testing device is arranged in the cavity, and the strain testing device is connected with the computer data recording and control system; the cavity is divided into a core chamber 2 and a hydraulic oil chamber 1, and a core is arranged in the core chamber 2; the hydraulic oil chamber 1 is filled with hydraulic oil; an upper end of the core chamber 2 is provided with an upper core holder 3, the upper core holder 3 is sequentially provided with an upper groove, a first hole 5 and an upper carbon dioxide chamber 6 from bottom to top, and the upper carbon dioxide chamber 6 is connected to the axial pressure control system at a top end; a lower end of the core chamber 2 is provided with a lower core holder 4, the lower core holder 4 is sequentially provided with a lower groove, the first hole 5, a lower carbon dioxide chamber 9 and a second hole 7 from top to bottom, and the second hole 7 is connected to the carbon dioxide pressure control system; the upper core holder 3 is dynamically sealed with a top end of the cavity, and the lower core holder 4 is fixedly connected with a bottom end of the cavity; further comprising a soft sleeve 8 which is open at top and bottom, the soft sleeve 8 is wrapped outside the core, an upper limit of the soft sleeve 8 is higher than the upper groove, and a lower limit of the soft sleeve 8 is lower than the lower groove; the core chamber 2 and the hydraulic oil chamber 1 are separated by the soft sleeve 8; the upper carbon dioxide chamber 6 and the lower carbon dioxide chamber 9 store carbon dioxide.
[0041] The cross section of the upper groove / lower groove is a semicircle with a diameter of 1-2 mm, facilitating the flow of carbon dioxide gas and increasing the contact area between carbon dioxide and the core; the first hole 5 is 5 in number and has a diameter of 1-2 mm; the diameter of the first hole 5 is equal to the diameter of the cross section of the upper groove / lower groove; the 5 first holes 5 increase the airflow channel, in combination with the upper groove / lower groove, so that the carbon dioxide and the core are more fully and quickly contacted; the upper carbon dioxide chamber 6 and the lower carbon dioxide chamber 9 are both cylindrical, with a height of 50-100 mm and a diameter of 25-100 mm; the diameter of the second hole 7 is 1.5-2.5 times the diameter of the first hole 5. In the embodiment, the diameter of the upper groove / lower groove and the first hole 5 is 1 mm; the height of the upper carbon dioxide chamber 6 and the lower carbon dioxide chamber 9 is 25 mm, and the diameter is 30 mm; the diameter of the second hole 7 is 2 mm.
[0042] Embodiment 2
[0043] Based on the embodiment 1, further comprising:
[0044] The carbon dioxide pressure control system comprises a carbon dioxide gas cylinder, a carbon dioxide booster system and a carbon dioxide buffer tank connected in sequence; the output end of the carbon dioxide buffer tank is connected with a carbon dioxide recovery device and a vacuum pumping device respectively; the output end of the carbon dioxide buffer tank is also connected to the second hole 7; a carbon dioxide pressure sensor is arranged on the connecting pipeline between the output end of the carbon dioxide buffer tank and the second hole 7, and the carbon dioxide pressure sensor and the carbon dioxide booster system are connected to a computer data recording and control system respectively.
[0045] The axial pressure control system comprises an axial pressure loading system and a load sensor; the load sensor is connected to the top end of the upper carbon dioxide chamber 6; one end of the axial pressure loading system is connected to the upper carbon dioxide chamber 6, and the other end is connected to the computer data recording and control system; the confining pressure control system comprises a confining pressure loading system and a confining pressure sensor; the confining pressure sensor is located in the hydraulic oil chamber 1, and one end of the confining pressure loading system is connected to the hydraulic oil chamber 1, and the other end is connected to the computer data recording and control system; the temperature control system comprises a heating system and a temperature sensor, and the temperature sensor is located in the hydraulic oil chamber 1; one end of the heating system is connected to the hydraulic oil chamber 1, and the other end is connected to the computer data recording and control system; the load sensor, the confining pressure sensor and the temperature sensor are all connected to the computer data recording and control system.
[0046] The strain testing device comprises an extensometer or a strain gauge; the extensometer is located in the hydraulic oil chamber 1 and attached to the outer wall of the soft sleeve 8; the strain gauge is located in the core chamber 2 and adhered to the core.
[0047] The confining pressure loading system comprises a booster pump connected with hydraulic oil through an oil inlet line and an oil return line; the heating system comprises an external resistance heating belt wrapped outside the cavity; the carbon dioxide pressurizing system is an electric plunger pump; the carbon dioxide recovery device comprises a pressure reducing valve and a recovery tank connected in sequence; the pressure reducing valve is made of austenitic 022Cr17Ni12Mo2 stainless steel (316L), with a maximum inlet pressure of 60 MPa and an outlet pressure of 0-8 MPa; the recovery tank is made of 2205 duplex stainless steel, with a maximum pressure resistance of 20 MPa and a volume of 1000 L. The vacuum pumping device comprises a needle valve and a vacuum pump connected in sequence, with a pumping rate of 3.6 m3 / h and a limit vacuum of 0.1 MPa.
[0048] The application provides a method for testing triaxial mechanical parameters of rock under carbon dioxide contact.
[0049] The application provides a method for testing triaxial mechanical parameters of rock under carbon dioxide contact.
[0050] Step 1: Place the core between the upper core holder 3 and the lower core holder 4, and apply an axial pressure of 500 N to fix the core; the soft sleeve 8 is a double-wall heat-shrinkable sleeve containing glue, with a thickness of 0.5 mm and composed of an outer polyolefin alloy and an inner hot melt glue; the double-wall heat-shrinkable sleeve containing glue is sealed by hot air blow molding; the soft sleeve 8 is wrapped outside the core, and the upper limit of the soft sleeve 8 is higher than the upper groove, and the lower limit of the soft sleeve 8 is lower than the lower groove; the strain testing device is an extensometer located in the hydraulic oil chamber 1 and attached to the outer wall of the soft sleeve 8; the axial deformation of the extensometer is 0-8 mm, the radial deformation is 0-4 mm, the measurement resolution is 0.0001 mm, the measurement accuracy is ±1%, and the core strain change can be measured; fill the hydraulic oil chamber 1 with hydraulic oil to apply confining pressure and continue to load the axial pressure to keep the core stable and balanced; the confining pressure is 15 MPa, and the confining pressure loading rate is 0.05 MPa / s;
[0051] Step 2: Close the carbon dioxide buffer tank and the carbon dioxide recovery device, and pump the core chamber 2 through the vacuum pumping device;
[0052] Step 3: Close the vacuum pumping device, open the carbon dioxide buffer tank, and control the carbon dioxide pressurizing system to sequentially pass through the carbon dioxide buffer tank, the second hole 7, the lower carbon dioxide chamber 9 and the first hole 5 to fill the core chamber 2 with 10 MPa pressure carbon dioxide to directly contact the carbon dioxide with the rock; at the same time, the heating system heats the hydraulic oil;
[0053] Step 4: Continue to fill the core chamber 2 with carbon dioxide until the preset carbon dioxide pressure of 10 MPa and carbon dioxide temperature of 45℃ are reached; start the contact soaking;
[0054] Step 5: After reaching the preset contact soaking time of 2h, perform the rock triaxial compression test. The computer data recording and control system controls the axial pressure loading system to apply axial pressure to the core at a loading rate of 0.25 kN / s (continuous) until the core is destroyed, and records the load and strain changes during the axial pressure loading process;
[0055] Step 6: After the rock triaxial compression test is completed, turn off the carbon dioxide buffer tank and carbon dioxide booster system, and turn on the carbon dioxide recovery device to recover the carbon dioxide in the core chamber 2. When the carbon dioxide in the core chamber 2 is completely discharged into the carbon dioxide recovery device, unload the confining pressure of the core chamber 2.
[0056] The computer data recording and control system is a Chaoyang triaxial rock-soil mechanics comprehensive test system 2017SR539588. It uses a 10 kHz system frequency, with a basic unit of 100 µs (0.1 ms) for adjustable control and sampling frequency. In the parameter input interface, load, confining pressure, temperature, pressure, etc. can be input. Through data transmission, axial load loading, confining pressure loading, temperature heating, and carbon dioxide pressurization are controlled. The relevant sensors feed back the actual stress, strain, load, confining pressure, temperature, etc. to the computer data recording and control system. The interface can output axial load, confining pressure, temperature, and pressure. It can also output stress and strain parameters during the rock triaxial compression test.
[0057] The axial pressure loading control rate of the axial pressure loading system is 0.1-20 kN / s (continuous), with a maximum axial load of 1000 KN. The load sensor has a range of 10-1000 KN and a value accuracy of 1%. The axial loading displacement range is 120 mm (continuous), with a measurement accuracy of ±1% FS, a measurement resolution of 0.001 mm, and an axial loading displacement control rate of 0.1-50 mm / min (continuous).
[0058] The confining pressure loading system pressurizes the hydraulic oil through the carbon dioxide pressurization system, enters the hydraulic oil chamber 1, and can provide a pressure of 0-70 MPa. The maximum hydraulic oil flow is 18 L / min, and the pressurization rate is 0.01-1 MPa / s (continuous). The confining pressure sensor can test a pressure range of 0-70 MPa with an accuracy of 0.01 MPa.
[0059] The heating system is an external resistance heating band. The experimental device is wrapped with an external resistance heating band for heating and insulation. The internal heating range is 0-100℃, and the external resistance heating band has an external surface temperature of up to 50℃. The internal temperature sensor can measure a temperature range of 0-100℃ with an accuracy of ±0.1℃.
[0060] Carbon dioxide cylinder pressure 4 MPa, capacity of 20 L, 6 bottles in parallel gas supply; carbon dioxide booster system for electric plunger pump, flow 0.2 m3 / h, the maximum pressure can reach 30 MPa; carbon dioxide buffer tank material for 2205 duplex stainless steel, capacity of 10 L, the highest pressure 38 MPa, the outlet is equipped with a direct reading pressure gauge, range of 0-45 MPa.
Claims
1. A device for testing triaxial mechanical parameters of rock under carbon dioxide contact, comprising a rock and carbon dioxide contact and triaxial compression test system, an axial pressure control system, a confining pressure control system, a temperature control system and a carbon dioxide pressure control system connected with the rock and carbon dioxide contact and triaxial compression test system respectively, and a computer data recording and control system; the axial pressure control system, the confining pressure control system, the temperature control system and the carbon dioxide pressure control system are connected with the computer data recording and control system. wherein The rock and carbon dioxide contact and triaxial compression test system comprises a cavity, a strain testing device is arranged in the cavity, and the strain testing device is connected with the computer data recording and control system; the cavity is divided into a core chamber (2) and a hydraulic oil cavity chamber (1), a core is placed in the core chamber (2); the hydraulic oil cavity chamber (1) is filled with hydraulic oil; an upper core holder (3) is arranged at the upper end of the core chamber (2), the upper core holder (3) is sequentially provided with an upper groove, a first channel (5) and an upper carbon dioxide cavity (6) from bottom to top, and the upper carbon dioxide cavity (6) is connected to the axial pressure control system at the top end; a lower core holder (4) is arranged at the lower end of the core chamber (2), the lower core holder (4) is sequentially provided with a lower groove, a first channel (5), a lower carbon dioxide cavity (9) and a second channel (7) from top to bottom, and the second channel (7) is connected to the carbon dioxide pressure control system; the upper core holder (3) is dynamically sealed with the top end of the cavity, and the lower core holder (4) is fixedly connected with the bottom end of the cavity. Further comprising a soft sleeve (8) with upper and lower openings, the soft sleeve (8) is wrapped outside the core, the upper limit of the soft sleeve (8) is higher than the upper groove, and the lower limit of the soft sleeve (8) is lower than the lower groove; the core chamber (2) and the hydraulic oil cavity chamber (1) are separated by the soft sleeve (8); the upper carbon dioxide cavity (6) and the lower carbon dioxide cavity (9) contain carbon dioxide; The carbon dioxide pressure control system comprises a carbon dioxide cylinder, a carbon dioxide booster system and a carbon dioxide buffer tank connected in sequence; a carbon dioxide recovery device and a vacuum pumping device are respectively connected to the output end of the carbon dioxide buffer tank; the output end of the carbon dioxide buffer tank is also connected to the second channel (7); a carbon dioxide pressure sensor is arranged on the connecting pipeline between the output end of the carbon dioxide buffer tank and the second channel (7), and the carbon dioxide pressure sensor and the carbon dioxide booster system are respectively connected to the computer data recording and control system. The specific use process is as follows: Step 1: place the core between the upper core holder (3) and the lower core holder (4), and apply axial pressure to fix the core; the soft sleeve (8) is wrapped outside the core chamber (2), the upper limit of the soft sleeve (8) is higher than the upper groove, and the lower limit of the soft sleeve (8) is lower than the lower groove; install the strain testing device; fill the hydraulic oil cavity chamber (1) with hydraulic oil to apply confining pressure and keep the axial pressure continue to load, and keep the core stable and balanced; Step 2: close the carbon dioxide buffer tank and the carbon dioxide recovery device, and vacuumize the core chamber (2) by the vacuum pumping device. Step 3: close the vacuum device, open the carbon dioxide buffer tank, and control the carbon dioxide booster system to sequentially pass through the carbon dioxide buffer tank, the second channel (7), the lower carbon dioxide chamber (9), and the first channel (5) to the core chamber (2) to fill carbon dioxide, and the carbon dioxide is in direct contact with the rock; the carbon dioxide pressure is always 5-10 MPa lower than the confining pressure; at the same time, the hydraulic oil is heated by the heating system; Step 4: continue to fill carbon dioxide into the core chamber (2) until the preset carbon dioxide pressure and carbon dioxide temperature are reached; start the contact soaking; Step 5: after reaching the preset contact soaking time, perform a rock triaxial compression experiment, control the axial pressure loading system to axially pressurize the core by the computer data recording and control system, and record the load and strain changes in the axial pressure experiment process; Step 6: after the rock triaxial compression experiment is completed, close the carbon dioxide buffer tank and the carbon dioxide booster system, open the carbon dioxide recovery device to recover the carbon dioxide in the core chamber (2), and unload the confining pressure of the core chamber (2) after the carbon dioxide in the core chamber (2) is completely discharged into the carbon dioxide recovery device.
2. The device according to claim 1, wherein: The axial pressure control system includes an axial pressure loading system and a load sensor; the load sensor is connected to the top end of the upper carbon dioxide chamber (6); one end of the axial pressure loading system is connected to the upper carbon dioxide chamber (6), and the other end is connected to the computer data recording and control system; the confining pressure control system includes a confining pressure loading system and a confining pressure sensor; the confining pressure sensor is located in the hydraulic oil chamber (1), one end of the confining pressure loading system is connected to the hydraulic oil chamber (1), and the other end is connected to the computer data recording and control system; the temperature control system includes a heating system and a temperature sensor, the temperature sensor is located in the hydraulic oil chamber (1), one end of the heating system is connected to the hydraulic oil chamber (1), and the other end is connected to the computer data recording and control system; the load sensor, the confining pressure sensor, and the temperature sensor are connected to the computer data recording and control system.
3. The device according to claim 2, wherein the device is characterized by: The strain testing device includes an extensometer or a strain gauge; the extensometer is located in the hydraulic oil chamber (1) and attached to the outer wall of the soft sleeve (8); the strain gauge is located in the core chamber (2) and adhered to the core.
4. The device according to claim 3, wherein the device is characterized by: The confining pressure loading system includes a booster pump, which is connected to the hydraulic oil through an oil inlet line and an oil return line; the heating system includes an external resistance heating band, which is wrapped outside the cavity; the carbon dioxide booster system is an electric plunger pump; the carbon dioxide recovery device includes a pressure reducing valve and a recovery tank connected in sequence; the vacuum device includes a needle valve and a vacuum pump connected in sequence.
5. The device according to claim 4, wherein: The first channel (5) has five channels, and the diameter of the first channel (5) is equal to the cross-sectional diameter of the upper / lower groove; the cross section of the upper / lower groove is a semicircle; the diameter of the second channel (7) is 1.5-2.5 times the diameter of the first channel (5).
6. The device according to claim 5, wherein: The second channel (7) is connected to the output end of the carbon dioxide buffer tank, the carbon dioxide recovery device, and the vacuum device through a four-way connection.
7. The device according to claim 6, wherein the device is characterized by: The axial pressure in the step 1 is 100-1000N, the confining pressure is 0-80MPa; the carbon dioxide pressure in the step 4 is 0-60MPa, the carbon dioxide temperature is 0-100℃; the preset contact soaking time in the step 5 is 0-120h.
8. The device according to claim 7, wherein the device is characterized by: The axial pressure in the step 1 is 500N, the confining pressure is 15MPa; the carbon dioxide pressure in the step 4 is 10MPa, the carbon dioxide temperature is 45℃; the preset contact soaking time in the step 5 is 2h.