A quantitative testing device and method for hydraulic fracturing gas displacement under true triaxial conditions

Abstract

This invention relates to the field of coalbed methane disaster control technology, specifically disclosing a quantitative testing device and method for hydraulic fracturing displacement of methane under true triaxial conditions. The device includes a true triaxial confining pressure assembly, a fracturing assembly, a methane storage cylinder, a reference tank, a vacuum pump, a back pressure valve, and a gas-liquid separator. The test sample is fixed in the sample chamber of the true triaxial confining pressure assembly, which applies confining pressure to the sample. The methane storage cylinder is connected to the inlet of the reference tank. The outlet of the reference tank, the vacuum pump's extraction port, and the back pressure valve's inlet are all connected to the test sample inside the sample chamber via pipelines. The outlet of the back pressure valve is connected to the inlet of the gas-liquid separator, and the outlet of the gas-liquid separator is connected to a flow rate acquisition element. A first pressure acquisition element for monitoring the internal pressure of the reference tank is connected to the reference tank, and a second pressure acquisition element is connected to the fracturing assembly. This device can meet the requirements for quantitative research on hydraulic fracturing displacement of coalbed methane.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane disaster control technology, specifically to a quantitative testing device and method for hydraulic fracturing displacement of methane under true triaxial conditions. Background Technology

[0002] Coal resources occupy a dominant position in my country's energy structure. However, with the depletion of shallow resources, the depth of coal mining has been increasing year by year, leading to serious coal and gas outburst accidents. Hydraulic fracturing technology, as an efficient gas control method, is being increasingly applied in deep mines. Practice has shown that during in-seam hydraulic fracturing in the intake airway of a coal seam, there is an increase in gas concentration in the return airway, thus demonstrating the displacement effect of hydraulic fracturing on coal seam gas.

[0003] However, the mechanism of hydraulic fracturing in displacing coal seam gas remains unclear, thus preventing large-scale industrial applications and currently only remaining at the stage of similar laboratory experiments. Existing research on hydraulic fracturing gas displacement has the following shortcomings: 1. Triaxial stress cannot be applied to coal samples; 2. It is impossible to distinguish between gas displacement and natural gas release; 3. The coal samples used are small in size, making it difficult to conduct fracturing tests normally. These reasons all prevent the quantitative study of the efficiency of hydraulic fracturing in displacing coal seam gas. Summary of the Invention

[0004] The present invention provides a quantitative testing device and method for hydraulic fracturing gas displacement under true triaxial conditions, which can meet the requirements for quantitative research on hydraulic fracturing gas displacement in coal seams.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a quantitative testing device for hydraulic fracturing and gas displacement under true triaxial conditions, comprising a true triaxial confining pressure assembly, a fracturing assembly, a methane storage cylinder, a reference tank, a vacuum pump, a back pressure valve, and a gas-liquid separator; the test sample is fixed in the sample chamber of the true triaxial confining pressure assembly, and confining pressure is applied to the test sample through the true triaxial confining pressure assembly; the fracturing assembly includes a fracturing tube arranged in the test sample and a fracturing pump connected to the fracturing tube; the methane storage cylinder is connected to the inlet of the reference tank, the outlet of the reference tank, the vacuum pump outlet, and the back pressure valve inlet are all connected to the test sample inside the sample chamber through pipelines, the outlet of the back pressure valve is connected to the inlet of the gas-liquid separator, and the outlet of the gas-liquid separator is connected to a flow acquisition element; a first pressure acquisition element for monitoring the internal pressure of the reference tank is connected to the reference tank, and a second pressure acquisition element for monitoring the outlet pressure of the fracturing pump is connected to the pipeline between the fracturing pump and the fracturing tube.

[0007] Furthermore, the reference tank outlet is connected to the first inlet of the three-way valve, the vacuum pump outlet is connected to the second inlet of the three-way valve, and the outlet of the three-way valve is connected to the test sample inside the sample chamber through a pipeline.

[0008] Furthermore, a first shut-off valve is connected to the pipeline between the outlet of the reference tank and the first inlet of the three-way valve; a second shut-off valve and a vacuum gauge are connected to the pipeline between the vacuum pump outlet and the second inlet of the three-way valve, with the vacuum gauge located between the second shut-off valve and the vacuum pump.

[0009] Furthermore, a third shut-off valve is connected to the pipeline between the fracturing pump and the fracturing pipe; a fourth shut-off valve is connected to the air inlet of the back pressure valve.

[0010] Furthermore, the true triaxial confining pressure assembly includes a test vessel, a cover, a confining pressure pump, a base, and a loading shaft. The cover and the upper opening of the test vessel are connected and enclose each other to form a confining pressure cavity. The base is arranged at the bottom of the confining pressure cavity, and the sample chamber is arranged on the base. The outlet of the confining pressure pump is connected to the confining pressure cavity through a pipeline. The loading shaft passes through the test vessel and acts on the sample chamber.

[0011] Furthermore, the sample chamber includes a sealing sleeve for covering the sample to be tested. The bottom of the sealing sleeve is provided with a first interface that corresponds to the fracturing tube and a second interface that connects to the air outlet of the reference tank and the air extraction port of the vacuum pump. The side and top of the sealing sleeve are provided with a third interface that connects to the air inlet of the back pressure valve.

[0012] Furthermore, the sealing sleeve is fitted around the loading plate, and the loading plate is provided with through holes for avoiding the third interface.

[0013] Furthermore, the upper opening of the sealing sleeve is sealed to the plug.

[0014] Furthermore, the first pressure acquisition element, the second pressure acquisition element, and the flow acquisition element are connected to the data acquisition instrument.

[0015] Secondly, the present invention provides a quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions, which uses the quantitative testing device for hydraulic fracturing gas displacement under true triaxial conditions described in the present invention to test the test sample, and includes the following steps:

[0016] S1, fix the test sample in the sample chamber of the true triaxial confining pressure assembly;

[0017] S2, start the vacuum pump to evacuate the sample to be tested;

[0018] S3, applying confining pressure to the test sample using a true triaxial confining pressure assembly;

[0019] S4, connect the methane storage cylinder and the reference tank, fill the reference tank with methane gas from the methane storage cylinder, and use the first pressure acquisition element to obtain the initial pressure P1 of the reference tank after the methane gas is filled.

[0020] S5, connect the reference tank and the sample chamber, and introduce methane gas into the sample to be tested. When the pressure curve of the first pressure acquisition element no longer decreases, it indicates that the sample to be tested has reached the adsorption equilibrium state. Use the first pressure acquisition element to obtain the equilibrium pressure P2 in the reference tank at this time.

[0021] S6, set the allowable pressure of the back pressure valve to the equilibrium pressure P2 to ensure that the methane gas in the test sample in equilibrium cannot pass through the back pressure valve.

[0022] S7, start the fracturing assembly, inject fracturing fluid into the test sample at a constant flow rate, observe the data curve of the second pressure acquisition element, and shut down the fracturing assembly after the test sample is fractured.

[0023] S8, read the flow meter data to obtain the amount of methane displacement during the fracturing process, calculate the amount of methane gas adsorbed on the test sample using P1, P2 and the volume V of the reference tank, and calculate the displacement efficiency of hydraulic fracturing for methane gas based on the preset formula.

[0024] The beneficial effects of this invention are:

[0025] 1. The device and method for quantitative testing of gas displacement by hydraulic fracturing under true triaxial conditions of the present invention can realize hydraulic fracturing experiments on large-scale test samples, i.e., gas-containing coal samples, and can apply triaxial stress to the coal sample using a true triaxial confining pressure component. At the same time, it solves the problem of difficulty in measuring the amount of gas displacement caused by the superposition of the natural gas release effect and the water displacement effect.

[0026] 2. In this invention, a back pressure valve is installed on the pipeline between the sample chamber and the gas-liquid separator inlet. During the test, the allowable pressure of the back pressure valve is set to the equilibrium pressure in the reference tank when the test sample reaches the adsorption equilibrium state. This ensures that the methane gas in the test sample in equilibrium cannot pass through the back pressure valve, thereby preventing the methane gas from entering the gas-liquid separator before fracturing and ensuring the accuracy of the test results.

[0027] 3. This invention connects a flow acquisition element to the outlet of a gas-water separator, uses the flow acquisition element to obtain the amount of methane displacement during the fracturing process, uses a first pressure acquisition element, a second pressure acquisition element and the internal chamber volume of a reference tank to calculate the amount of methane gas adsorbed on the test sample, and calculates the displacement efficiency of hydraulic fracturing for methane gas based on a preset formula, thus realizing the quantitative testing of the efficiency of hydraulic fracturing in displacing coal seam gas. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the quantitative testing device for hydraulic fracturing and gas displacement under true triaxial conditions described in this invention.

[0029] Figure 2 This is a schematic diagram of the sample chamber described in this invention.

[0030] In the diagram, 1—methane storage cylinder, 2—reference tank, 3—first pressure acquisition element, 4—first shut-off valve, 5—three-way valve, 6—second shut-off valve, 7—vacuum gauge, 8—vacuum pump, 9—fracturing pump, 10—second pressure acquisition element, 11—third shut-off valve, 12—confining pressure pump, 13—fracturing pipe, 14—base, 15—test vessel, 16—loading shaft, 17—sample chamber, 171—sealing sleeve, 172—plug, 173—first interface, 174—second interface, 175—third interface, 176—loading plate, 177—metal hoop, 18—cover, 19—sample to be tested, 20—fourth shut-off valve, 21—back pressure valve, 22—gas-water separator, 23—flow meter, 24—data acquisition instrument, 25—pressure reducing valve. Detailed Implementation

[0031] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0032] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0033] See Figure 1The quantitative testing device for hydraulic fracturing and gas displacement under true triaxial conditions, as shown, includes a true triaxial confining pressure assembly, a fracturing assembly, a methane storage cylinder 1, a reference tank 2, a vacuum pump 8, a back pressure valve 21, and a gas-liquid separator 22. The test sample 19 is fixed in the sample chamber 17 of the true triaxial confining pressure assembly. The true triaxial confining pressure assembly applies confining pressure to the test sample 17 to simulate the real stress environment of the coal sample, making the test results closer to the actual situation. The fracturing assembly includes a fracturing pipe 13 arranged in the test sample 19 and a fracturing pump 9 connected to the fracturing pipe 13. Fracturing fluid is pumped into the fracturing pipe 13 by the fracturing pump 9. As the fracturing fluid is continuously pumped in, the test sample 19 is fractured. The fracturing tube 13 is fixed in the pre-drilled test sample 193 with strong adhesive. The length of the fracturing tube 13 extending into the test sample 193 is denoted as L1, and the height of the test sample 19 is denoted as L2, where 1 / 3·L2≤L1≤1 / 2·L2. Since the fracturing tube 13 and the test sample 19 are connected by strong adhesive, it is necessary to ensure that there is sufficient adhesive length between them to prevent the fracturing tube 13 from falling off during fracturing. In addition, the hydraulic fracture needs to have sufficient development space in the test sample 19, and the end of the fracturing tube 13 should not be close to the edge of the test sample 19. Therefore, 1 / 3·L2≤L1≤1 / 2·L2 is limited.

[0034] The methane storage cylinder 1 is connected to the inlet of the reference tank 2. The outlet of the reference tank 2, the suction port of the vacuum pump 8, and the inlet of the back pressure valve 21 are all connected to the test sample 19 inside the sample chamber 17 through pipelines. The outlet of the back pressure valve 21 is connected to the inlet of the gas-liquid separator 22. The back pressure valve serves two purposes: 1) After the methane gas in the test sample 19 reaches adsorption-desorption equilibrium, it is necessary to ensure that the pressure inside the sample chamber 17 remains stable even if the fourth shut-off valve 20 is opened; otherwise, the test sample 19 will... 1) When methane is directly connected to the atmosphere through a pipeline, it will naturally diffuse through the gas-liquid separator 22. During fracturing, the amount of methane displaced by fracturing cannot be quantitatively characterized. 2) After the pressure liquid enters the sample 19 to be tested, the adsorption sites that originally belonged to methane molecules are occupied by liquid molecules. The free gas in the sample chamber 17 increases, which leads to an increase in the pressure in the sample chamber 17, exceeding the set value P2 of the back pressure valve 21. At this time, the displaced free methane can pass through the back pressure valve 21. This measure can effectively avoid the interference of the natural diffusion of methane on the actual amount of methane displaced.

[0035] The outlet of the gas-liquid separator 22 is connected to a flow acquisition element 23; the reference tank 2 is connected to a first pressure acquisition element 3 for monitoring the internal pressure of the reference tank 2; and the pipeline between the fracturing pump 9 and the fracturing pipe 13 is connected to a second pressure acquisition element 9 for monitoring the pressure at the outlet of the fracturing pump.

[0036] To reduce the number of pipelines, the outlet of the reference tank 2 is connected to the first inlet of the three-way valve 5, the suction port of the vacuum pump 8 is connected to the second inlet of the three-way valve 5, and the outlet of the three-way valve 5 is connected to the test sample 19 inside the sample chamber 17 via a pipeline. Furthermore, to prevent the vacuum pump 8 from acting on the reference tank 2 through the three-way valve 5, a first shut-off valve 4 is connected to the pipeline between the outlet of the reference tank 2 and the first inlet of the three-way valve 6. A second shut-off valve 6 and a vacuum gauge 7 are connected to the pipeline between the suction port of the vacuum pump 8 and the second inlet of the three-way valve. The vacuum gauge 7 is located between the second shut-off valve 6 and the vacuum pump 8, and the vacuum gauge 7 can better obtain the vacuum level inside the sample chamber 17, adjusting the vacuum pump 8 to turn on or off based on the monitored vacuum level.

[0037] To control the flow of fracturing fluid, a third shut-off valve 11 is connected to the pipeline between the fracturing pump 9 and the fracturing pipe 13. To control the flow of the pipeline containing the back pressure valve 21, a fourth shut-off valve 20 is connected to the air inlet of the back pressure valve 21.

[0038] In order to enable the connection and disconnection between methane storage cylinder 1 and reference tank 2, a pressure reducing valve 25 is connected to the outlet of methane storage cylinder 1.

[0039] In this embodiment, the true triaxial confining pressure assembly includes a test vessel 15, a cover 18, a confining pressure pump 12, a base 14, and a loading shaft 16. The cover 18 and the upper opening of the test vessel 15 are connected, and the two together form a confining pressure chamber. The base 14 is arranged at the bottom of the confining pressure chamber, and the sample chamber 17 is arranged on the base 14. The outlet of the confining pressure pump 12 is connected to the confining pressure chamber through a pipeline. The loading shaft 16 passes through the test vessel 15 and acts on the sample chamber 17. During operation, the confining pressure pump 12 injects confining pressure fluid into the confining pressure chamber to simulate the confining pressure environment around the coal sample. The loading shaft 16 applies a preset pressure to the sample chamber 17 to simulate the geostress environment of the coal sample, allowing the test sample 19 to undergo gas displacement testing under conditions closer to the real environment, thus improving the accuracy of the test results.

[0040] In this embodiment, see Figure 2 The sample chamber 17 includes a sealing sleeve 171 for covering the sample to be tested. The bottom of the sealing sleeve 171 is provided with a first interface 173 that corresponds to the fracturing tube 13 and a second interface 174 that connects to the air outlet of the reference tank 2 and the air extraction port of the vacuum pump 8. The side and top of the sealing sleeve 171 are provided with a third interface 175 that connects to the air inlet of the back pressure valve 21.

[0041] The sealing sleeve 171 is fitted to the loading plate 176 on all four sides. The loading shaft 16 passes through the test vessel 15 and acts on the loading plate 176. The loading force is then transmitted to the side wall of the sealing sleeve 171 through the loading plate 176, thereby making the test sample 19 inside the sealing sleeve 171 more uniformly stressed. To ensure normal pipeline connectivity, a through hole is provided on the loading plate 176 to avoid the third interface 175.

[0042] To improve the ease of assembly of the test sample 19, an opening is provided at the upper part of the sealing sleeve 172. When fixing the test sample 19, it can be directly placed into the sealing sleeve 172 through the upper opening. To improve the overall sealing performance of the sample chamber 17, the upper opening of the sealing sleeve 171 is sealed to the plug 172.

[0043] To improve the calculation speed, the first pressure acquisition element 3, the second pressure acquisition element 10, and the flow acquisition element 23 are connected to the data acquisition instrument 24.

[0044] Example 2: A quantitative testing method for gas displacement caused by hydraulic fracturing under true triaxial conditions. The method uses the quantitative testing device for gas displacement caused by hydraulic fracturing under true triaxial conditions described in Example 1 to test a gas-bearing coal sample, i.e., the test sample. The method includes the following steps:

[0045] S1, fix the test sample 19 in the sample chamber 17 of the true triaxial confining pressure assembly;

[0046] S2, close the first shut-off valve 4, the third shut-off valve 11, and the fourth shut-off valve 20, and open the second shut-off valve 6 and the vacuum pump 8 to evacuate the test sample 19. Observe the reading of the vacuum gauge 7. After reaching the set vacuum level, close the second shut-off valve 6 and the vacuum pump 8 in sequence. In this embodiment, the target vacuum level is set to 200 Pa.

[0047] S3, the test sample 19 is subjected to confining pressure by the true triaxial confining pressure component, creating a triaxial stress environment around the sample chamber 12 and reaching the set value. In this embodiment, the specific set values ​​of the triaxial stress are: maximum horizontal principal stress σH = 21MPa, minimum horizontal principal stress σh = 11MPa, and vertical principal stress σV = 20MPa. This setting meets the actual stress state of deep coal seams in my country.

[0048] S4, open the pressure reducing valve 25 to connect the methane storage cylinder 1 and the reference tank 2, and fill the reference tank 2 with methane gas from the methane storage cylinder 1. Use the first pressure acquisition element 3 to obtain the initial pressure P1 of the reference tank after the methane gas is filled, and then close the pressure reducing valve 25. In this embodiment, the internal chamber volume of the reference tank 2 is V = 1000 mL.

[0049] S5, open the first shut-off valve 4 to connect the reference tank 2 and the sample chamber 17, and introduce methane gas into the test sample 19. When the pressure curve of the first pressure acquisition element 3 no longer decreases, it indicates that the test sample 19 has reached the adsorption equilibrium state. Use the first pressure acquisition element 3 to obtain the equilibrium pressure P2 in the reference tank at this time, and close the first shut-off valve 4.

[0050] S6, set the allowable pressure of the back pressure valve 21 to the equilibrium pressure P2 to ensure that the methane gas in the test sample 19, which is in equilibrium, cannot pass through the back pressure valve.

[0051] S7, start the fracturing assembly, that is, turn on the fracturing pump 9 and the third shut-off valve 11 in sequence, inject fracturing fluid into the test sample 19 at a constant flow rate, observe the data curve of the second pressure acquisition element 10, and turn off the third shut-off valve 11 and the fracturing pump 9 in sequence after the test sample is fractured.

[0052] S8, read the data from flow meter 23 to obtain the methane displacement Q1 during the fracturing process. Calculate the methane gas adsorption amount Q2 of the test sample using P1, P2, and the volume V of the reference tank.

[0053] Q2=nV mol Z, In the formula, n is the amount of methane gas; P1 is the initial pressure of the reference tank after the methane gas is introduced; P2 is the equilibrium pressure inside the reference tank; V is the volume of the reference tank; R is the ideal gas state constant; T is the temperature of the methane gas; Vmol is the molar volume of the methane gas; and Z is the gas compressibility factor.

[0054] The displacement efficiency of hydraulic fracturing for methane gas was calculated based on a pre-defined formula.

[0055] Based on the actual experiment, P1 = 4 MPa, P2 = 1.531 MPa, the experimental environment temperature was 20℃ (293 K), and the ideal gas state constant R was 8.314 J / (mol·K). Therefore, in this example:

[0056]

[0057] According to the query, under the experimental conditions, the methane gas compressibility factor Z is 0.975, so the methane gas adsorption capacity of the test sample is Q2 = 1.01325 × 22.4 × 0.975 = 22.1 L.

[0058] Based on the data from flow meter 23, the gas volume Q1 passing through during fracturing is 1578.5 ml. Therefore, the displacement efficiency of the methane gas is...

[0059] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions, characterized in that, The test sample was tested using a true triaxial hydraulic fracturing displacement gas quantitative test device, which includes a true triaxial confining pressure assembly, a fracturing assembly, a methane storage cylinder (1), a reference tank (2), a vacuum pump (8), a back pressure valve (21), and a gas-liquid separator (22). The test sample (19) is fixed in the sample chamber (17) of the true triaxial confining pressure assembly, and confining pressure is applied to the test sample (19) through the true triaxial confining pressure assembly; The fracturing assembly includes a fracturing tube (13) arranged in the test sample (19) and a fracturing pump (9) connected to the fracturing tube (13). The methane storage cylinder (1) is connected to the inlet of the reference tank (2). The outlet of the reference tank (2), the suction port of the vacuum pump (8), and the inlet of the back pressure valve (21) are all connected to the test sample (19) inside the sample chamber (17) through pipelines. The outlet of the back pressure valve (21) is connected to the inlet of the gas-water separator (22). The outlet of the gas-water separator (22) is connected to a flow meter (23). The reference tank (2) is connected to a first pressure acquisition element (3) for monitoring the internal pressure of the reference tank (2), and the pipeline between the fracturing pump (9) and the fracturing pipe (13) is connected to a second pressure acquisition element (10) for monitoring the pressure at the outlet of the fracturing pump. The testing method includes the following steps: S1, fix the test sample (19) in the sample chamber (17) of the true triaxial confining pressure assembly; S2, start the vacuum pump (8) to evacuate the test sample (19); S3, apply confining pressure to the test sample (19) using the true triaxial confining pressure assembly; S4, connect the methane storage cylinder (1) and the reference tank (2), fill the reference tank (2) with methane gas from the methane storage cylinder (1), and use the first pressure acquisition element (3) to obtain the initial pressure P1 of the reference tank (2) after filling with methane gas; S5, connect the reference tank (2) and the sample chamber (17), introduce methane gas into the test sample (19), when the pressure curve of the first pressure acquisition element (3) no longer decreases, it indicates that the test sample (19) has reached the adsorption equilibrium state, and use the first pressure acquisition element (3) to obtain the equilibrium pressure P2 in the reference tank (2) at this time; S6, set the allowable pressure of the back pressure valve (21) to the equilibrium pressure P2 to ensure that the methane gas in the test sample (19) in equilibrium cannot pass through the back pressure valve (21). S7, start the fracturing assembly and inject fracturing fluid into the test sample (19) at a constant flow rate, observe the data curve of the second pressure acquisition element (10), and shut down the fracturing assembly after the test sample (19) is fractured; S8, read the flow meter (23) data to obtain the methane displacement Q1 during the fracturing process, and calculate the methane gas adsorption amount Q2 of the test sample (19) based on P1, P2 and the volume V of the reference tank. The displacement efficiency of hydraulic fracturing for methane gas was calculated. .

2. The quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions according to claim 1, characterized in that: The air outlet of the reference tank (2) is connected to the first inlet of the three-way valve (5), the air extraction port of the vacuum pump (8) is connected to the second inlet of the three-way valve (5), and the outlet of the three-way valve (5) is connected to the test sample (19) inside the sample chamber (17) through a pipeline.

3. The quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions according to claim 2, characterized in that: A first shut-off valve (4) is connected to the pipeline between the air outlet of the reference tank (2) and the first inlet of the three-way valve (5); A second shut-off valve (6) and a vacuum gauge (7) are connected on the pipeline between the vacuum pump (8) extraction port and the second inlet of the three-way valve (5). The vacuum gauge (7) is located between the second shut-off valve (6) and the vacuum pump (8).

4. The quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions according to claim 2, characterized in that: A third shut-off valve (11) is connected to the pipeline between the fracturing pump (9) and the fracturing pipe (13); a fourth shut-off valve (20) is connected to the air inlet of the back pressure valve (21).

5. The quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions according to claim 1 or 2, characterized in that: The true triaxial confining pressure assembly includes a test vessel (15), a cover (18), a confining pressure pump (12), a base (14), and a loading shaft (16). The cover (18) and the test vessel (15) are connected at the upper opening and enclosed to form a confining pressure cavity. The base (14) is arranged at the bottom of the confining pressure cavity, and the sample chamber (17) is arranged on the base (14). The outlet of the confining pressure pump (12) is connected to the confining pressure cavity through a pipeline. The loading shaft (16) passes through the test vessel (15) and acts on the sample chamber (17).

6. The quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions according to claim 1 or 2, characterized in that: The sample chamber (17) includes a sealing sleeve (171) for covering the sample to be tested. The bottom of the sealing sleeve (171) is provided with a first interface (173) that corresponds to the fracturing tube (13) and a second interface (174) that connects to the air outlet of the reference tank (2) and the air extraction port of the vacuum pump (8). The side and top of the sealing sleeve (171) are provided with a third interface (175) that connects to the air inlet of the back pressure valve (21).

7. The quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions according to claim 6, characterized in that: The outer walls of the sealing sleeve (171) are fitted to the loading plate (176), and the loading plate (176) is provided with a through hole for avoiding the third interface (175).

8. The quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions according to claim 6, characterized in that: The upper opening of the sealing sleeve (171) is sealed to the plug (172).

9. The quantitative testing method for hydraulic fracturing gas displacement under true triaxial conditions according to claim 1 or 2, characterized in that: The first pressure acquisition element (3), the second pressure acquisition element (10) and the flow meter (23) are connected to the data acquisition instrument (24).

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