Simulation test method and system for supercritical CO2 fracturing displacement of saline layer

Abstract

The application discloses a simulation test method and system for supercritical CO2 fracturing displacement of a saline layer, and the simulation test system comprises an air-tightness detection gas source tank, a saline water tank, a carbon dioxide gas source tank, a sample chamber, a gas collection device, a gas component analyzer, a vacuum pump, an infrasound wave monitoring unit, a data monitoring workstation and a nondestructive testing instrument. The sample chamber is a container capable of bearing high pressure, the inner wall of the sample chamber is provided with a first heating device and a three-axis clamping device, the gas inlet of the sample chamber is outwardly connected with a first pipeline, the gas outlet is outwardly connected with a second pipeline, and a sensor group is arranged on the first pipeline and the second pipeline respectively at positions close to the sample chamber, and the sensor group comprises a gas flow meter, a pressure sensor and a temperature sensor. The first pipeline is provided with a second heating device, the air-tightness detection gas source tank, the saline water tank and the carbon dioxide gas source tank are connected with the first pipeline through pipelines respectively, and the gas collection device and the vacuum pump are connected with the second pipeline respectively.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fracturing stimulation, in particular to a simulation test method and system for supercritical CO2 fracturing displacement of a saltwater layer. BACKGROUND

[0002] CO2 fracturing has the technical advantages of small reservoir damage, easy flowback after fracturing, phase change energy enhancement, and viscosity reduction by dissolution, and has developed rapidly and has been widely used in fracturing reconstruction tests of low-permeability formations in the oil and gas exploitation industry. However, research on supercritical CO2 fracturing displacement of a saltwater layer is still relatively rare, which has affected the further development of CO2 fracturing technology in engineering practice. Therefore, how to provide a simulation test method and system for supercritical CO2 fracturing displacement of a saltwater layer to conduct related technical research has become a technical problem to be solved by those skilled in the art. SUMMARY

[0003] Therefore, the present application provides a simulation test method and system for supercritical CO2 fracturing displacement of a saltwater layer, which facilitates experimental research on supercritical CO2 fracturing displacement of a saltwater layer, thereby providing a reference for optimizing injection well parameters in engineering practice.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0005] A simulation test system for supercritical CO2 fracturing displacement of a saltwater layer, comprising:

[0006] a sample chamber, which is a container capable of withstanding high pressure, the inner wall of the sample chamber is provided with a first heating device and a triaxial clamping device, the gas inlet of the sample chamber is connected to a first pipeline, the gas outlet of the sample chamber is connected to a second pipeline, the first pipeline and the second pipeline are respectively provided with a sensor group near the sample chamber, the sensor group comprises a gas flow meter, a pressure sensor and a temperature sensor;

[0007] a infrasound wave monitoring unit comprising a plurality of infrasound wave sensors arranged outside the sample chamber and an infrasound wave monitor connected to the infrasound wave sensors;

[0008] a second heating device arranged in the first pipeline;

[0009] a gas collection device and a vacuum pump connected to the second pipeline, respectively;

[0010] a gas component analyzer connected to the gas collection device through a pipeline;

[0011] A data monitoring workstation is connected with the gas component analyzer, the infrasound monitor, the first heating device, the three-axis clamping device and the sensor group through wires respectively;

[0012] A non-destructive testing instrument is used to detect the interior of the rock sample; and

[0013] Airtightness detection gas source tanks, salt water tanks and carbon dioxide gas source tanks are connected with the part of the first pipeline on the side of the second heating device away from the sample chamber through pipelines.

[0014] Optionally, in the simulation test system, the infrasound sensors are six and are arranged on three coordinate axes with the sample chamber as the coordinate origin.

[0015] Optionally, in the simulation test system, the airtightness detection gas source tanks and the salt water tanks are connected with the first pipeline through a first booster pump.

[0016] Optionally, in the simulation test system, the carbon dioxide gas source tank is connected with the first pipeline through a second booster pump.

[0017] Optionally, in the simulation test system, the gas collection device is provided with a gas release valve.

[0018] Optionally, in the simulation test system, the non-destructive testing instrument is a CT scanner.

[0019] A simulation test method for supercritical CO2 fracturing and displacement of a salt water layer, using the simulation test system disclosed in any one of the above simulation test systems, comprises the following steps:

[0020] Sample heating and pressurization: the rock sample taken from the salt water layer is placed into the sample chamber through the sample inlet and fixed on the three-axis clamping device, the first heating device continuously heats at a preset temperature for a preset time to ensure that the rock sample is fully dried, the sample inlet is closed after the weight loss of the rock sample is determined, the first heating device maintains the test temperature, and the three-axis clamping device slowly pressurizes the rock sample to the target pressure at a preset pressurization speed to simulate the confining pressure suffered by the rock in the salt water layer;

[0021] Airtightness check: the detection gas from the airtightness detection gas source tank is heated by the second heating device and then introduced into the sample chamber, the introduction of the detection gas is stopped when the air pressure in the sample chamber reaches a preset value, and the detection gas in the system is discharged by the vacuum pump after it is determined that the airtightness meets the requirements according to the air pressure change in the sample chamber;

[0022] Salt water injection: the salt water from the salt water tank is heated by the second heating device and then introduced into the sample chamber, and the introduction of the salt water is stopped when the rock sample returns to the weight before sample heating.

[0023] Fracturing and displacement: carbon dioxide from the carbon dioxide gas source tank and detection gas from the airtight detection gas source tank are mixed in a preset ratio, heated by the second heating device, and then introduced into the sample chamber. The pipeline between the gas collection device and the sample chamber is turned on, the process data of fracturing and displacement are collected and monitored by the data monitoring workstation, the test gas components are tested and analyzed by the gas component analyzer, when the gas component analyzer tests the CO2 content of the test gas to reach the CO2 content of the mixed gas before being introduced into the sample chamber, the carbon dioxide gas source tank and the airtight detection gas source tank are closed to stop introducing gas into the sample chamber, then the first heating device and the second heating device are closed, the sample chamber is depressurized and cooled;

[0024] Sample detection: after the rock sample is taken out from the sample chamber, it is placed into the nondestructive testing instrument, and the fracturing effect is analyzed by the nondestructive testing instrument.

[0025] Optionally, in the simulation test method described above, the preset pressurization speed is not greater than 1 MPa / min.

[0026] Optionally, in the simulation test method described above, the preset time is not less than 10 hours.

[0027] Optionally, in the simulation test method described above, in the fracturing and displacement step, the rate of the mixed gas of carbon dioxide and detection gas introduced into the sample chamber is not greater than 50 ml / min.

[0028] The simulation test system provided in the application can achieve the following beneficial effects:

[0029] Through simulation test, the change characteristics of the three-dimensional structure of the salt water layer rock at different times in the CO2 fracturing of the salt water layer are obtained, and the effect of CO2 fracturing of the salt water layer under different working conditions and the relationship between the effect and the salt water production are obtained through simulation test;

[0030] The triaxial pressurization (cubic shape) is used to simulate the deep pressure condition (the pressure in different axes can be different), the salt water layer rock sample is in close contact with the inner wall of the high-pressure reaction device (i.e. the sample chamber) without gap, and the salt water layer rock sample is directly pressurized, so that the simulation effect is close to the real environment;

[0031] Carbon dioxide can be directly and continuously injected into the salt water layer rock sample, and migrates from one end of the rock sample to the other end. The pressure change in the sample chamber is caused by the injection of gas, and the whole process is a continuous process of dynamic fracturing and displacement;

[0032] Through simulation test, the fracturing process and the salt water displacement process of the supercritical CO2 during the reconstruction of the salt water layer can be organically integrated together for targeted research, which is convenient for guiding actual engineering practice. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the accompanying drawings in the following description only represent some of the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of the provided drawings.

[0034] Figure 1 is a schematic diagram of a simulation test system for supercritical CO2 fracturing displacement of a saline aquifer provided by an embodiment of the present application;

[0035] Figure 2 is a schematic diagram of the arrangement of infrasound wave sensors around the sample chamber in the simulation test system provided by an embodiment of the present application.

[0036] In the drawings, the following are marked:

[0037] 1, helium gas source tank; 11, helium gas inlet valve; 2, saline water tank; 21, saline water inlet valve; 3, carbon dioxide gas source tank; 31, carbon dioxide gas inlet valve; 4, first booster pump; 41, helium gas booster valve; 5, second booster pump; 51, carbon dioxide booster valve; 6, second heating device; 61, sample chamber gas inlet valve; 7, sample chamber; 71, sample chamber gas outlet valve; 8, first heating device; 9, three-axis clamping device; 10, rock sample; 12, vacuum pump; 121, vacuum outlet valve; 13, gas collection device; 131, gas collection inlet valve; 132, gas release valve; 14, gas component analyzer; 141, gas analysis inlet valve; 15, data monitoring workstation; 16, nondestructive testing instrument; 17, infrasound wave monitoring unit; 171, infrasound wave sensor; 172, infrasound wave monitor; a, temperature sensor; b, pressure sensor; c, gas flow meter. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments only represent some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] Referring to Figure 1 and Figure 2The embodiment of the application provides a simulation test system for supercritical CO2 fracturing displacement of a salt water layer, which comprises a helium gas source tank 1, a salt water tank 2, a carbon dioxide gas source tank 3, a sample chamber 7, a vacuum pump 12, a gas collection device 13, a gas component analyzer 14, a data monitoring workstation 15, a nondestructive testing instrument 16 and a infrasound wave monitoring unit 17. The helium gas source tank 1 is filled with high-purity helium, the carbon dioxide gas source tank 3 is filled with high-purity carbon dioxide, the salt water tank 2 is filled with salt water prepared according to the salt water composition and concentration of the salt water layer, the sample chamber 7 is a container capable of bearing high pressure, the inner wall of the sample chamber 7 is provided with a first heating device 8 and a three-axis clamping device 9, the first heating device 8 is used for heating and maintaining the test temperature of the sample chamber 7, the three-axis clamping device 9 is used for applying pressure to the rock sample 10 from three axial directions to simulate the confining pressure suffered by the rock of the salt water layer, the vacuum pump 12 is used for exhausting the detection gas in the system after the system is subjected to air tightness detection, the gas component analyzer 14 is connected with the gas collection device 13 through a pipeline, the gas collection device 13 is used for collecting test gas from the sample chamber 7, the gas component analyzer 14 is used for detecting the components and contents of the test gas from the gas collection device 13, the data monitoring workstation 15 is used for collecting and monitoring the related data of the test process from each instrument and equipment in the system, the nondestructive testing instrument 16 is used for detecting the inside of the rock sample 10 after the test, and the fracturing condition is accurately described, so that the fracturing effect analysis is carried out subsequently. The infrasound wave monitoring unit 17 comprises a plurality of infrasound wave sensors 171 arranged outside the sample chamber 7 and an infrasound wave monitor 172 connected with the infrasound wave sensors 171, which is used for real-time monitoring, recording and storing infrasound wave data in the fracturing process, so that the fracturing displacement process is analyzed subsequently.

[0040] As Figure 1As shown, the first heating device 8 and the triaxial clamping device 9 are arranged on the inner wall of the sample chamber 7, that is, the first heating device 8 and the triaxial clamping device 9 almost do not occupy the cavity of the sample chamber 7, and the rock sample 10 is in close contact with the inner wall of the sample chamber 7 without gap, and the rock sample 10 is directly pressurized by the triaxial clamping device 9, that is, the rock sample 10 should be made in advance according to the size of the cavity of the sample chamber 7, for example, in the embodiment, the sample chamber 7 is a whole cube, so the rock sample 10 should be made in the shape of a cube. The sample chamber 7 has a door that can be opened and closed as a sample inlet for taking and placing the rock sample 10, that is, the rock sample 10 enters and exits the sample chamber 7 through the sample inlet. In addition, the sample chamber 7 is provided with an air inlet and an air outlet, and since the rock sample 10 is in close contact with the inner wall of the sample chamber 7 without gap, the injected carbon dioxide can be directly and continuously injected into the rock sample 10, transported from one end to the other end of the rock sample 10, and finally discharged from the sample chamber 7 through the air outlet. In a preferred embodiment, the air inlet and the air outlet are respectively arranged on the opposite two side walls of the sample chamber 7. It should be noted that in order to simplify the structure, the salt water from the salt water tank 2 also enters the sample chamber 7 through the air inlet, and a separate liquid inlet is not arranged for the salt water, that is, the above-mentioned air inlet and / or air outlet can be used for liquid to enter and exit the sample chamber 7. The air inlet of the sample chamber 7 is connected to the first pipeline, and the air outlet of the sample chamber 7 is connected to the second pipeline, and the first pipeline and the second pipeline are respectively provided with a sensor group near the sample chamber 7, and the sensor group includes a gas flow meter c, a pressure sensor b and a temperature sensor a. The first pipeline is provided with a second heating device 6, and the gas-tight detection gas source tank, the salt water tank 2 and the carbon dioxide gas source tank 3 are respectively connected to the part of the first pipeline away from the sample chamber 7 on the side of the second heating device 6. The second heating device 6 is used for heating the passing liquid or gas, so that the liquid and gas can enter the sample chamber 7 at the test temperature, and the influence of temperature difference on the test process is avoided as much as possible. The gas collection device 13 and the vacuum pump 12 are respectively connected to the second pipeline, that is, the end of the second pipeline away from the sample chamber 7 is divided into two paths, one of which is connected to the vacuum pump 12, and the other of which is connected to the gas collection device 13. The data monitoring workstation 15 is connected to the gas component analyzer 14, the infrasound wave monitor 172, the first heating device 8, the triaxial clamping device 9 and the sensor group through wires respectively.

[0041] In the embodiment, the helium gas source tank 1 and the salt water tank 2 are connected to the first pipeline through the first booster pump 4, as shown in the figure. Figure 1 The helium and the salt water pass through the first booster pump 4 to the sample chamber 7, which simplifies the structure of the system and reduces the equipment investment cost. Of course, in other embodiments, the helium gas source tank 1 and the salt water tank 2 can be respectively provided with a booster pump. Since the carbon dioxide is mixed with the helium and then goes to the sample chamber 7, a booster pump can be provided for the carbon dioxide gas source tank 3, as shown in the figure. Figure 1As shown, in the embodiment, the carbon dioxide gas source tank 3 is connected with the first pipeline through the second booster pump 5. In order to improve the control accuracy of the test, the application can be connected with a booster valve after the booster pump. In the embodiment, the first booster pump 4 is provided with a helium booster valve 41 between the first pipeline, and the second booster pump 5 is provided with a carbon dioxide booster valve 51 between the first pipeline. It should be noted that when the booster pump or the booster valve is used alone to meet the requirements of the test on the gas pressure, only one of the two booster pumps and booster valves can be provided, and the other one can be omitted.

[0042] The gas collection device 13 has a container for collecting the test gas. In order to quickly exhaust the test gas in the gas collection device 13 after the test, the application can be provided with a gas release valve 132. The test gas in the gas collection device 13 enters the gas component analyzer 14 through the pipeline. The gas component analyzer 14 transmits the detection result to the data monitoring workstation 15 through the wire, and discharges the test gas to a designated place, such as directly to the atmospheric environment, or a gas storage tank connected with the gas component analyzer 14 through the pipeline, and the gas component analyzer 14 discharges the test gas to the gas storage tank for subsequent processing.

[0043] Specifically, the non-destructive testing instrument 16 has multiple types to choose from, such as an ultrasonic detector, a CT scanner, an X-ray camera, etc. It should be noted that the non-destructive testing instrument 16 can be configured as multiple instruments, including two or more types of instruments, for example, the application can simulate a test system including a CT scanner and an ultrasonic detector.

[0044] The infrasound wave monitoring unit 17 should be arranged to surround the sample chamber 7 as much as possible, and the infrasound wave sensor 171 is arranged on the three coordinate axes with the sample chamber 7 as the coordinate origin, that is, the sample chamber 7 is arranged on the upper side, the lower side, the front side, the rear side, the left side and the right side. Figure 2 As shown, in the embodiment, the carbon dioxide gas source tank 3 is connected with the first pipeline through the second booster pump 5. In order to improve the control accuracy of the test, the application can be connected with a booster valve after the booster pump. In the embodiment, the first booster pump 4 is provided with a helium booster valve 41 between the first pipeline, and the second booster pump 5 is provided with a carbon dioxide booster valve 51 between the first pipeline. It should be noted that when the booster pump or the booster valve is used alone to meet the requirements of the test on the gas pressure, only one of the two booster pumps and booster valves can be provided, and the other one can be omitted.

[0045] Using the simulation test system provided by the application, the application also provides a simulation test method for supercritical CO2 fracturing displacement of a salt water layer. Before the test, a rock sample 10 and salt water need to be prepared. The rock sample 10 is obtained from the underground salt water layer during mining, and a part of the water sample is brought back during mining. In the laboratory, the salt water is prepared according to the components and concentration of the water sample and is stored in a salt water tank 2 for use. The simulation test method mainly includes the following steps:

[0046] (1) Sample heating and pressurization: the rock sample 10 taken from the saline layer is placed into the sample chamber 7 through the sample inlet and fixed on the triaxial clamping device 9, the first heating device 8 continuously heats at a preset temperature for a preset time to ensure that the rock sample 10 is fully dried, the sample inlet is closed after the weight loss of the rock sample 10 is determined, the first heating device 8 maintains the test temperature, and the triaxial clamping device 9 slowly pressurizes the rock sample 10 to the target pressure at a preset pressurization speed to simulate the confining pressure of the rock in the saline layer.

[0047] Specifically, the rock sample 10 is placed into the sample chamber 7 without closing the sample inlet, i.e., the sample is heated in the whole open sample chamber 7, so that the water in the rock sample 10 is completely discharged, and the weight of the dried rock sample 10 is reduced. The determined weight loss of the rock sample 10 serves as a reference value for the subsequent saline water injection amount. The weight loss of the rock sample 10 can be determined by placing the sample chamber 7 on a weighing device, so that the weight loss of the rock sample 10 can be obtained without taking out the rock sample 10. During the sample heating stage, the continuous heating time is generally not less than 10 hours, for example, it can be 12 hours, and the heating temperature can be set as needed, for example, it can be 80°-120°. After the sample inlet is closed, the sample chamber 7 is in a sealed state, and the first heating device 8 maintains the test temperature to provide a constant temperature environment. The test temperature is generally 100-160℃, and the temperature change of the constant temperature environment is controlled within 0.2℃ as soon as possible during the test process. The pressure applied by the triaxial clamping device 9 is generally provided by a hydraulic cylinder, and the pressurization speed should not be too large, which is generally set to be not greater than 1 MPa / min, for example, it can be 0.5 MPa / min. When the pressure reaches the target pressure, the triaxial clamping device 9 maintains the target pressure, and the target pressure is set according to the simulated saline layer environment, for example, it can be 10-30 MPa.

[0048] (2) Gas tightness check: helium from the helium gas source tank 1 is heated by the second heating device 6 and then introduced into the sample chamber 7. When the gas pressure in the sample chamber 7 reaches a preset value, the introduction of the detection gas is stopped. After the gas tightness is determined to meet the requirements according to the gas pressure change in the sample chamber 7, the helium in the system is exhausted by the vacuum pump 12.

[0049] The gas tightness check is mainly to confirm that the system can operate safely and prevent test safety accidents. Specifically, if the gas tightness of the system does not meet the requirements, the test cannot be continued, and the system needs to be repaired. Figure 1As shown, the helium inlet valve 11 and the sample chamber inlet valve 61 are opened, the sample chamber outlet valve 71 is closed, and high-purity helium is injected into the sample chamber 7. The injection pressure is higher than the system design pressure by 1 MPa. After the pressure is stabilized, the helium inlet valve 11 and the sample chamber inlet valve 61 are closed, and the system airtightness is detected, i.e., whether the system has a gas leakage phenomenon is checked. After confirming that there is no gas leakage phenomenon, it is determined that the airtightness meets the requirements, and then the system is vacuumized. The vacuum pump 12 is turned on, the sample chamber outlet valve 71 and the vacuum outlet valve 121 are opened, and the other valves are in the closed state. The vacuumization is performed for 10-12 hours to remove the residual gas in the system. The vacuum pump 12 is closed, and the sample chamber outlet valve 71 and the vacuum outlet valve 121 are closed.

[0050] (3) Saltwater injection: The saltwater from the saltwater tank 2 is heated by the second heating device 6 and then introduced into the sample chamber 7. The introduction of the saltwater is stopped when the rock sample 10 returns to the weight before the sample heating.

[0051] The injection of the saltwater is to restore the dry rock sample 10 to the weight before the sample heating, so as to simulate the water-bearing state of the rock in the underground saltwater layer. Specifically, as shown in FIG. 4, the saltwater inlet valve 21 is opened to slowly inject the saltwater into the sample chamber 7 until the injection amount reaches the required value, and then the first booster pump 4 is closed. It should be noted that the injection speed of the saltwater should not be too large, so as to ensure that the saltwater injected into the sample chamber 7 does not flow out of the gas outlet of the sample chamber 7, that is, to ensure that all the injected saltwater is absorbed by the rock sample 10. Figure 1

[0052] (4) Fracturing and displacement: The carbon dioxide from the carbon dioxide gas source tank 3 and the helium from the helium gas source tank 1 are mixed at a predetermined ratio, heated by the second heating device 6, and then introduced into the sample chamber 7. The pipeline between the gas collection device 13 and the sample chamber 7 is conducted, the process data of the fracturing and displacement are collected and monitored by the data monitoring workstation 15, the test gas components are tested and analyzed by the gas component analyzer 14, and when the gas component analyzer 14 tests that the CO2 content of the test gas reaches the CO2 content of the mixed gas before being introduced into the sample chamber 7, the carbon dioxide gas source tank 3 and the helium gas source tank 1 are closed to stop the introduction of the gas into the sample chamber 7. Then, the first heating device 8 and the second heating device 6 are closed, the sample chamber 7 is depressurized and cooled.

[0053] Specifically, as shown in FIG. 4, Figure 1 ​As shown, open the carbon dioxide gas inlet valve 31, the helium gas inlet valve 11, the sample chamber gas inlet valve 61, open the first booster pump 4 and the second booster pump 5, inject the carbon dioxide and helium gas into the sample chamber 7 after heating by the second heating device 6 according to the mixing ratio of the test design, and quickly open the sample chamber gas outlet valve 71, the gas collection gas inlet valve 131 and the gas analysis gas inlet valve 141. The test process data (data of various sensors, the three-axis clamping device 9, the first heating device 8, the infrasound monitoring unit 17, etc.) are collected and monitored by the data monitoring workstation 15. When the gas component analyzer 14 (for example, a gas chromatograph) tests that the CO2 content of the test gas is consistent with the CO2 content of the previous designed mixing ratio, it indicates that the carbon dioxide is no longer absorbed by the rock sample 10, at which time the fracturing and displacement phase can be ended, and the gas source valves, the booster pumps and the heating device are sequentially closed, and the sample chamber 7 slowly depressurizes and cools down. The designed mixing ratio of the carbon dioxide and helium gas can be that the CO2 content in the mixed gas is 50% to 70%. During the fracturing and displacement process, the gas inlet rate into the sample chamber 7 is generally set to be not greater than 50 ml / min, for example, can be 30 ml / min or 40 ml / min.

[0054] In other embodiments, other gases can also be used instead of helium as the gas for air tightness detection and mixing with carbon dioxide. It should be noted that when other gases are selected, gases that are not easy to be injected into the rock sample 10 should be selected, so that when the mixed gas passes through the rock sample 10 in the sample chamber 7, only carbon dioxide is injected into the rock sample 10, so that the CO2 content of the test gas from the gas collection device 13 detected by the gas component analyzer 14 can determine whether the amount of carbon dioxide injected into the rock sample 10 in the sample chamber 7 has reached the saturation value (i.e., the storage capacity of the rock sample 10).

[0055] (5) Sample detection: After the rock sample 10 is taken out from the sample chamber 7, it is placed into the nondestructive testing instrument 16, and the fracturing effect analysis is performed by the nondestructive testing instrument 16.

[0056] The simulation test system provided in the application can perform simulation tests of supercritical CO2 fracturing of a saline aquifer and simultaneous production of saline water, that is, simulation of the fracturing of a saline aquifer and water displacement in the field of engineering practice, so that the influence of supercritical CO2 injection pressure, injection rate and injection amount on the fracturing effect of a saline aquifer and the production of saline water can be studied, the influence of temperature on the modification of a saline aquifer by critical CO2 can be studied, and then the optimal injection conditions of critical CO2 fracturing of a specific saline aquifer are obtained.

[0057] The above description of disclosed embodiments enables one of ordinary skill in the art to make and use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A simulated test system for supercritical CO2 fracturing displacement of saline aquifers, characterized in that, The simulation test system comprises: a sample chamber which is a container capable of bearing high pressure, the inner wall of the sample chamber is provided with a first heating device and a three-axis clamping device, the gas inlet of the sample chamber is connected to a first pipeline outside, the gas outlet of the sample chamber is connected to a second pipeline outside, the first pipeline and the second pipeline are respectively provided with a sensor group near the sample chamber, the sensor group comprises a gas flow meter, a pressure sensor and a temperature sensor; an infrasound wave monitoring unit comprising a plurality of infrasound wave sensors arranged outside the sample chamber and an infrasound wave monitor connected to the infrasound wave sensors; a second heating device arranged on the first pipeline; a gas collection device and a vacuum pump connected to the second pipeline respectively; a gas component analyzer connected to the gas collection device through a pipeline; a data monitoring workstation connected to the gas component analyzer, the infrasound wave monitor, the first heating device, the three-axis clamping device and the sensor group through wires respectively; a non-destructive testing instrument for detecting the interior of the rock sample; and an air tightness detection gas source tank, a salt water tank and a carbon dioxide gas source tank connected to the first pipeline through pipelines on the side of the second heating device away from the sample chamber.

2. The simulation test system of claim 1, wherein, The six infrasound wave sensors are dispersedly arranged on three coordinate axes with the sample chamber as the coordinate origin.

3. The analog test system of claim 1, wherein The air tightness detection gas source tank and the salt water tank are connected to the first pipeline through a first booster pump.

4. The simulation test system of claim 3, wherein The carbon dioxide gas source tank is connected to the first pipeline through a second booster pump.

5. The analog test system of claim 1, wherein, The gas collection device is provided with a gas release valve.

6. The simulation test system according to any one of claims 1 to 5, characterized in that, The non-destructive testing instrument is a CT scanner.

7. A method of simulating a supercritical CO2 fracturing displacement of a saline layer, characterized in that, The simulation test system according to any one of claims 1-6 comprises the following steps: sample heating and pressurization: a rock sample taken from a salt water layer is placed into the sample chamber through a sample inlet and fixed on the three-axis clamping device, the first heating device continuously heats at a preset temperature for a preset time to ensure that the rock sample is fully dried, the sample inlet is closed after the weight loss of the rock sample is determined, the first heating device maintains the test temperature, and the three-axis clamping device slowly pressurizes the rock sample to the target pressure at a preset pressurization speed to simulate the confining pressure of the rock in the salt water layer; air tightness check: detection gas from the air tightness detection gas source tank is heated by the second heating device and then introduced into the sample chamber, the introduction of the detection gas is stopped when the air pressure in the sample chamber reaches a preset value, and the air tightness is determined to meet the requirements according to the air pressure change in the sample chamber, and the detection gas in the system is discharged by the vacuum pump; salt water injection: salt water from the salt water tank is heated by the second heating device and then introduced into the sample chamber, and the introduction of the salt water is stopped when the rock sample returns to the weight before sample heating; Fracturing and displacement: carbon dioxide from the carbon dioxide gas source tank and detection gas from the airtight detection gas source tank are mixed in a preset ratio, heated by the second heating device, and then introduced into the sample chamber. The pipeline between the gas collection device and the sample chamber is turned on. The process data of fracturing and displacement are collected and monitored by the data monitoring workstation. The test gas components are tested and analyzed by the gas component analyzer. When the gas component analyzer tests the CO2 content of the test gas to reach the CO2 content of the mixed gas before being introduced into the sample chamber, the carbon dioxide gas source tank and the airtight detection gas source tank are closed to stop the introduction of gas into the sample chamber. Then the first heating device and the second heating device are turned off. The sample chamber is depressurized and cooled. Sample detection: after the rock sample is taken out from the sample chamber and placed in the nondestructive testing instrument, the fracturing effect is analyzed by the nondestructive testing instrument.

8. The simulation test method according to claim 7, characterized by, The preset pressurizing speed is not greater than 1 MPa / min.

9. The simulation test method according to claim 8, characterized by, The preset time is not less than 10 hours.

10. The simulation test method according to any one of claims 7 to 9, characterized in that, In the fracturing and displacement step, the rate at which the mixed gas of carbon dioxide and detection gas is introduced into the sample chamber is not greater than 50 ml / min.

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