A shale gas core fracturing-displacement integrated experimental device and method

Abstract

The present invention discloses an integrated experimental device and method for shale gas core fracturing and displacement. The experimental device includes an input system, a core holder, an output system, and a metering system. The core holder is provided with a core, and threaded core fixtures are provided at both ends to secure the core. A hollow metal needle is axially inserted through the core fixture, one end of the metal needle is embedded in the core, and the other end is connected to the input system or the output system. The input system includes a liquid carbon dioxide input system and a fracturing fluid input system arranged in parallel. The output system is used to collect the fluid output by the core holder. The metering system includes a first pressure gauge, a second pressure gauge, and a flow meter. The present invention can create fractures in the core through the liquid carbon dioxide input system and the metal needle, simulating the perforation of a reservoir by a real gas well, and simulates the hydraulic fracturing process through the fracturing fluid input system.

Description

Technical Field

[0001] The present invention relates to the technical field of shale gas reservoir exploration and development, and in particular to a shale gas core fracturing-displacement integrated experimental device and method. Background Art

[0002] my country's shale gas reservoirs are widespread, thick, and generally gas-rich, capable of long-term, stable gas production. However, shale gas reservoirs have low permeability, making extraction challenging. The primary method for extracting these reservoirs is horizontal well hydraulic fracturing. The effectiveness of post-fracture core reservoir reconstruction is primarily evaluated by permeability, making it crucial to simulate permeability changes in cores using test fluids after hydraulic fracturing. While extremely dense shale cores have very low permeability, hydraulic fracturing can significantly increase permeability. However, the effects of hydraulic fracturing in actual formations are difficult to simulate experimentally.

[0003] Currently, there are two main methods for creating fractures in natural core chambers. One uses a Brazilian splitting apparatus or a rock mechanics triaxial testing system, generally employing radial tension and axial compression. This method creates irregular fracture morphologies, making it impossible to control the fracture shape, orientation, and aperture. The other method involves cutting the core into two equal halves and simulating or calculating the fracture width based on the desired fracture aperture using the thickness of the intermediate gasket or the diameter of the sand filling particles. Both methods require the fracture to be created before transferring it to the core holder. This process may alter and affect the original fracture morphology of the core, making it impossible to perform experiments immediately after fracturing, which is inconsistent with the actual reservoir fracturing process. Summary of the Invention

[0004] In view of the above problems, the present invention aims to provide a shale gas core fracturing-displacement integrated experimental device and method.

[0005] The technical solutions of the present invention are as follows:

[0006] On the one hand, a shale gas core fracturing-displacement integrated experimental device is provided, comprising an input system, a core holder, an output system, and a metering system;

[0007] A core is provided in the core holder, and threaded core fixing devices are provided at both the left and right ends of the core holder for fixing the core. A hollow metal needle is axially passed through the core fixing device, and one end of the metal needle is embedded in the core. The other end of one metal needle is connected to the input system, and the other end of the other metal needle is connected to the output system.

[0008] The input system includes a liquid carbon dioxide input system and a fracturing fluid input system arranged in parallel. The liquid carbon dioxide input system is used to input liquid carbon dioxide into the core holder, and use the liquid carbon dioxide in combination with the metal needle to fracture the core to form cracks; the fracturing fluid input system is used to input fracturing fluid into the core holder, and use the fracturing fluid to displace the core; the output system is used to collect the fluid output by the core holder;

[0009] The metering system includes a first pressure gauge, a second pressure gauge, and a flow meter. The first pressure gauge and the second pressure gauge are used to monitor the pressure at the input and output ends of the core holder, respectively. The flow meter is used to monitor the flow rate of the fluid output by the core holder.

[0010] Preferably, the liquid carbon dioxide input system comprises an ultra-high pressure pump, a liquid carbon dioxide intermediate container, and a valve 1 connected in sequence, wherein the output end of the valve 1 is connected to the input end of the core holder;

[0011] The fracturing fluid input system includes a displacement pump, a fracturing fluid intermediate container, and a second valve connected in sequence, wherein the output end of the second valve is connected to the input end of the core holder;

[0012] The output system includes a fluid collecting device, which is connected to the output end of the core holder, and a valve three is provided on the connected pipeline.

[0013] Preferably, the liquid carbon dioxide in the liquid carbon dioxide intermediate container is injected through a gas pressurization system.

[0014] Preferably, the gas boosting system includes an air compressor, a boosting pump, a fourth valve, and a carbon dioxide gas storage tank connected in sequence. The carbon dioxide gas storage tank is connected to the liquid carbon dioxide intermediate container, and the connected pipelines are provided with a pressure regulating valve, a third pressure gauge, and a fifth valve in sequence.

[0015] Preferably, a confining pressure pump is further included, and the output end of the confining pressure pump is connected to the confining pressure input port of the core holder.

[0016] On the other hand, a shale gas core fracturing-displacement integrated experimental method is also provided, and the experiment is carried out using any of the shale gas core fracturing-displacement integrated experimental devices described above.

[0017] Preferably, the shale gas core fracturing-displacement integrated experimental method comprises the following steps:

[0018] S1: Obtain a core from the target shale gas reservoir, dry the core, and place it in the core holder. Rotate the core fixing devices at the left and right ends of the core holder to bury the metal needle in the core, and evacuate the core holder.

[0019] S2: using the liquid carbon dioxide input system to input liquid carbon dioxide into the core holder, and using the liquid carbon dioxide in combination with the metal needle to fracture the core to form cracks;

[0020] S3: using the fracturing fluid input system to input fracturing fluid into the core holder, and when liquid flows out of the output system, closing the valve of the output system to hold back the pressure, so that the core is saturated with the fracturing fluid;

[0021] S4: Open the valve of the output system, use the fracturing fluid input system to input fracturing fluid into the core holder, use the fracturing fluid to displace the core, and record the pressure and flow rate when the pressure monitored by the pressure gauge 1 and the pressure gauge 2 stabilizes, and calculate the liquid-measured permeability of the core after fracturing.

[0022] Preferably, the shale gas core fracturing-displacement integrated experimental method further comprises the following steps:

[0023] S5: Adjust the input pump pressure of the liquid carbon dioxide input system and repeat steps S2-S4 until the target number of times is reached;

[0024] S6: fitting the liquid permeability data under different input pump pressure conditions to obtain a correlation formula between the input pump pressure and the liquid permeability of the core after fracturing;

[0025] S7: Calculate the liquid-measured permeability of the core after fracturing at the target input pump pressure according to the correlation formula.

[0026] Preferably, in step S4, the liquid permeability of the core after fracturing is calculated by the following formula:

[0027]

[0028] Where: k is the fluid permeability of the core after fracturing, mD; μ is the viscosity of the fracturing fluid, mPa·s; L is the core length, cm; Q is the flow rate through the core, cm 3 / s; A is the core cross-sectional area, cm 2 ; P is the pressure difference between seepage sections, MPa.

[0029] Preferably, in step S6, the correlation formula between the input pump pressure and the liquid-measured permeability of the core after fracturing is:

[0030] k f=ax 3 +bx 2 +cx+k m (2)

[0031] Where: k f is the predicted value of the liquid permeability of the core after fracturing, mD; a, b, c are all fitting coefficients, dimensionless; x is the pump pressure, MPa; k m is the liquid permeability of the core before fracturing, mD.

[0032] The beneficial effects of the present invention are:

[0033] The present invention uses the liquid carbon dioxide input system and the metal needle to create fractures in the core, simulating the perforation of a real gas well into a reservoir, and the fracturing fluid input system to simulate the hydraulic fracturing process. The device has a simple structure, a convenient and easy method, and simple operation. It can transform fractured cores of varying permeabilities by controlling pump parameters according to actual needs, thereby simulating actual gas reservoir production conditions and providing technical support for the development of shale gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is a schematic structural diagram of the shale gas core fracturing-displacement integrated experimental device of the present invention;

[0036] Figure 2 Schematic diagram of the fitting relationship between the input pump pressure and the liquid-measured permeability of the core after fracturing in a specific embodiment.

[0037] Numbers in the figure:

[0038] 1-Air compressor, 2-Booster pump, 3-Valve 4, 4-CO2 storage tank, 5-Pressure regulating valve, 6-Pressure gauge 3, 7-Valve 5, 8-Liquid CO2 intermediate container, 9-Ultra-high pressure pump, 10-Fracturing fluid intermediate container, 11-Valve 2, 12-Valve 1, 13-Pressure gauge 1, 14-Displacement pump, 15-Confining pressure pump, 16-Metal needle, 17-Core holder, 18-Core fixing device, 19-Pressure gauge 2, 20-Flow meter, 21-Valve 3, 22-Fluid collection device. DETAILED DESCRIPTION

[0039] The present invention is further described below with reference to the accompanying drawings and examples. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those commonly understood by those of ordinary skill in the art to which this application belongs. The use of similar words such as "include" or "comprising" in the present invention means that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0040] On the one hand, if Figure 1 As shown, the present invention provides a shale gas core fracturing-displacement integrated experimental device, including an input system, a core holder 17, an output system and a metering system;

[0041] The core holder 17 contains a core. Threaded core fixing devices 18 are provided at both the left and right ends of the core holder 17 for fixing the core. A hollow metal needle 16 is axially passed through the core fixing device 18. One end of the metal needle 16 is embedded in the core. The other end of one metal needle 16 is connected to the input system, and the other end of the other metal needle 16 is connected to the output system.

[0042] The input system includes a liquid carbon dioxide input system and a fracturing fluid input system arranged in parallel. The liquid carbon dioxide input system is used to input liquid carbon dioxide into the core holder 17, and use the liquid carbon dioxide in combination with the metal needle 16 to fracture the core to form cracks; the fracturing fluid input system is used to input fracturing fluid into the core holder 17, and use the fracturing fluid to displace the core; the output system is used to collect the fluid output by the core holder 17;

[0043] The metering system includes a pressure gauge 13, a pressure gauge 2 19 and a flow meter 20. The pressure gauge 13 and the pressure gauge 2 19 are used to monitor the pressure at the input and output ends of the core holder 17 respectively, and the flow meter 20 is used to monitor the flow rate of the fluid output by the core holder 17.

[0044] In a specific embodiment, the liquid carbon dioxide input system includes an ultra-high pressure pump 9, a liquid carbon dioxide intermediate container 8, and a valve 12 connected in sequence, wherein the output end of the valve 12 is connected to the input end of the core holder 17;

[0045] The fracturing fluid input system includes a displacement pump 14, a fracturing fluid intermediate container 10, and a valve 2 11 connected in sequence, wherein the output end of the valve 2 11 is connected to the input end of the core holder 17;

[0046] The output system includes a fluid collecting device 22 , which is connected to the output end of the core holder 17 , and a valve 3 21 is provided on the connected pipeline.

[0047] In a specific embodiment, the liquid carbon dioxide in the liquid carbon dioxide intermediate container 8 is injected through a gas pressurization system. Optionally, the gas pressurization system includes an air compressor 1, a booster pump 2, a valve 4 3, and a carbon dioxide gas storage tank 4 connected in sequence. The carbon dioxide gas storage tank 4 is connected to the liquid carbon dioxide intermediate container 8, and the connected pipelines are sequentially provided with a pressure regulating valve 5, a pressure gauge 3 6, and a valve 5 7.

[0048] In a specific embodiment, the experimental apparatus further includes a confining pressure pump 15, the output end of which is connected to the confining pressure input port of the core holder 17. In this embodiment, the provision of the confining pressure pump 15 can simulate formation confining pressure conditions, making the results more consistent with actual operating conditions. Furthermore, to simulate formation temperature conditions, the experimental apparatus of the present invention may further include a constant temperature chamber or a heating device, which is used to bring the core in the core holder to a simulated formation temperature, thereby simulating formation temperature conditions.

[0049] On the other hand, the present invention also provides a shale gas core fracturing-displacement integrated experimental method, which uses any of the above-mentioned shale gas core fracturing-displacement integrated experimental devices to conduct experiments.

[0050] In a specific embodiment, the shale gas core fracturing-displacement integrated experimental method includes the following steps:

[0051] S1: Obtain a core from the target shale gas reservoir, dry the core, and place it in the core holder 17. Rotate the core fixing devices 18 at the left and right ends of the core holder 17 to bury the metal needle 16 in the core, and evacuate the core holder 17.

[0052] S2: using the liquid carbon dioxide input system to input liquid carbon dioxide into the core holder 17, and using the liquid carbon dioxide in combination with the metal needle 16 to fracture the core to form cracks;

[0053] S3: Using the fracturing fluid input system to input fracturing fluid into the core holder 17, and when liquid flows out of the output system, closing the valve of the output system to hold back the pressure, so that the core is saturated with the fracturing fluid;

[0054] S4: Open the valve of the output system, use the fracturing fluid input system to input 17 fracturing fluid into the core holder, use the fracturing fluid to displace the core, and when the pressure monitored by the pressure gauge 13 and the pressure gauge 2 19 stabilizes, record the pressure and flow at this time, and calculate the liquid permeability of the core after fracturing.

[0055] In a specific embodiment, the liquid permeability of the core after fracturing is calculated by the following formula:

[0056]

[0057] Where: k is the fluid permeability of the core after fracturing, mD; μ is the viscosity of the fracturing fluid, mPa·s; L is the core length, cm; Q is the flow rate through the core, cm 3 / s; A is the core cross-sectional area, cm 2 ; P is the pressure difference between seepage sections, MPa.

[0058] In a specific embodiment, the shale gas core fracturing-displacement integrated experimental method further includes the following steps:

[0059] S5: Adjust the input pump pressure of the liquid carbon dioxide input system and repeat steps S2-S4 until the target number of times is reached;

[0060] S6: fitting the liquid permeability data under different input pump pressure conditions to obtain a correlation formula between the input pump pressure and the liquid permeability of the core after fracturing;

[0061] In a specific embodiment, the correlation formula between the input pump pressure and the liquid permeability of the core after fracturing is:

[0062] k f =ax 3 +bx 2 +cx+k m (2)

[0063] Where: k f is the predicted value of the liquid permeability of the core after fracturing, mD; a, b, c are all fitting coefficients, dimensionless; x is the pump pressure, MPa; k m is the liquid permeability of the core before fracturing, mD.

[0064] S7: Calculate the liquid-measured permeability of the core after fracturing at the target input pump pressure according to the correlation formula.

[0065] In a specific embodiment, taking a shale gas reservoir as an example, a core fracturing-displacement integrated experimental method for shale gas is used to conduct a core fracturing-displacement integrated experiment, which specifically includes the following steps:

[0066] (1) Obtain a core from the target shale gas reservoir, dry the core, and place it in the core holder 17. Rotate the core fixing devices 18 at the left and right ends of the core holder 17 to bury the metal needle 16 in the core.

[0067] In this embodiment, the core has a length of 5 cm, a diameter of 2.5 cm, and an initial liquid permeability of 0.00021 mD.

[0068] (2) The carbon dioxide is stored in the carbon dioxide gas storage tank 4, and the fracturing fluid is placed in the fracturing fluid intermediate container 10. The viscosity of the fracturing fluid is tested to be 1.2 mP·s.

[0069] (3) Press Figure 1 The shale gas core fracturing-displacement integrated experiment shown here connects the various components, checks for air tightness, and then performs vacuuming.

[0070] (4) Apply a confining pressure of 40 MPa to the core holder 17 through the confining pressure pump 15, close valve 12 and valve 2 11, open valve 5 7, start the air compressor 1 and the booster pump 2, open valve 4 3, increase the pressure of carbon dioxide in the carbon dioxide storage tank 4, and control the pressure through the pressure regulating valve 5. When the pressure gauge 3 6 shows 10 MPa, stop pressurizing and the gaseous carbon dioxide becomes liquid.

[0071] (5) Close valve five 7, open valve one 12, and use the ultra-high pressure pump 9 to quickly pump the liquid carbon dioxide in the liquid carbon dioxide intermediate container 8 to 25 MPa and quickly pump it into the pump. The gas is ejected from the metal needle 16, and the high-pressure gas fractures the core to form cracks and is driven out from the metal needle 16 at the outlet end.

[0072] (6) Open valve one 12, open valve two 11, start the displacement pump 14 to displace the fracturing fluid, and close valve three 21 when liquid outflow is detected in the fluid collection device 22. Continue to increase the pressure to build up pressure in the core. After the pressure indicator reaches 10 MPa, maintain it for 3 hours to make the core saturated with the fracturing fluid.

[0073] (7) Open valve three 21, use fracturing fluid to displace the core and measure the liquid permeability. After the pressure gauge 13 and pressure gauge two 19 indicate stable readings, record the pressure and flow at this time, and calculate the liquid permeability of the core after fracturing using formula (1).

[0074] In this embodiment, the data recorded after the pressure gauge 13 and the pressure gauge 2 19 readings stabilized were an inlet pressure of 5.69 MPa, an outlet pressure of 5.08 MPa, and a flow rate of 1.2 mL / s. The calculated liquid permeability of the core after fracturing was 2.405 mD, which was four orders of magnitude higher than the initial liquid permeability of 0.00021 mD before the core was fractured. The experimental device described in the present invention can well improve the permeability performance of the core.

[0075] (8) Close valve 11, change the pressure of carbon dioxide through the pressure regulating valve 5, adjust the pump pressure of the ultra-high pressure pump 9 to 30 MPa, open valve 12 to pump liquid carbon dioxide into the core for the second fracture transformation, and measure the liquid permeability after the second fracture transformation, the result is 4.025 mD.

[0076] (9) Repeat step (8) and continue to test the liquid permeability under the conditions of pump pressure of 35MPa and 40MPa. The results are 4.981mD and 5.668mD respectively.

[0077] (10) According to the liquid permeability test results under the above four pump pressure conditions, the results are Figure 2 As shown in Figure 2, the correlation formula between the input pump pressure obtained by fitting and the liquid permeability of the core after fracturing is:

[0078] k f =0.0427x 3 -0.5482x 2 +2.9262x+0.00021 (3)

[0079] The correlation formula shown in formula (3) can be used to obtain the fractured core with the target liquid permeability by controlling the input pump pressure according to actual needs, thereby better simulating the actual working conditions.

[0080] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A shale gas core fracturing-displacement integrated experimental device, characterized in that: Including input system, core holder, output system and metering system; A core is provided in the core holder, and threaded core fixing devices are provided at both the left and right ends of the core holder for fixing the core. A hollow metal needle is axially passed through the core fixing device, and one end of the metal needle is embedded in the core. The other end of one metal needle is connected to the input system, and the other end of the other metal needle is connected to the output system. The input system includes a liquid carbon dioxide input system and a fracturing fluid input system arranged in parallel. The liquid carbon dioxide input system is used to input liquid carbon dioxide into the core holder, and use the liquid carbon dioxide in combination with the metal needle to fracture the core to form cracks; the fracturing fluid input system is used to input fracturing fluid into the core holder, and use the fracturing fluid to displace the core; the output system is used to collect the fluid output by the core holder; The metering system includes a first pressure gauge, a second pressure gauge, and a flow meter. The first pressure gauge and the second pressure gauge are used to monitor the pressure at the input and output ends of the core holder, respectively. The flow meter is used to monitor the flow rate of the fluid output by the core holder.

2. The shale gas core fracturing-displacement integrated experimental device according to claim 1, characterized in that: The liquid carbon dioxide input system includes an ultra-high pressure pump, a liquid carbon dioxide intermediate container, and a valve 1 connected in sequence, wherein the output end of the valve 1 is connected to the input end of the core holder; The fracturing fluid input system includes a displacement pump, a fracturing fluid intermediate container, and a second valve connected in sequence, wherein the output end of the second valve is connected to the input end of the core holder; The output system includes a fluid collecting device, which is connected to the output end of the core holder, and a valve three is provided on the connected pipeline.

3. The shale gas core fracturing-displacement integrated experimental device according to claim 2, characterized in that: The liquid carbon dioxide in the liquid carbon dioxide intermediate container is injected through a gas pressurization system.

4. The shale gas core fracturing-displacement integrated experimental device according to claim 3, characterized in that: The gas boosting system includes an air compressor, a boosting pump, a fourth valve, and a carbon dioxide gas storage tank connected in sequence. The carbon dioxide gas storage tank is connected to the liquid carbon dioxide intermediate container, and the connected pipelines are provided with a pressure regulating valve, a third pressure gauge, and a fifth valve in sequence.

5. The shale gas core fracturing-displacement integrated experimental device according to any one of claims 1 to 4, characterized in that: It also includes a confining pressure pump, the output end of which is connected to the confining pressure input port of the core holder.

6. A shale gas core fracturing-displacement integrated experimental method, characterized in that: The experiment is carried out using the shale gas core fracturing-displacement integrated experimental device described in any one of claims 1 to 5.

7. The shale gas core fracturing-displacement integrated experimental method according to claim 6, characterized in that: The following steps are involved: S1: Obtain a core from the target shale gas reservoir, dry the core, and place it in the core holder. Rotate the core fixing devices at the left and right ends of the core holder to bury the metal needle in the core, and evacuate the core holder. S2: using the liquid carbon dioxide input system to input liquid carbon dioxide into the core holder, and using the liquid carbon dioxide in combination with the metal needle to fracture the core to form cracks; S3: using the fracturing fluid input system to input fracturing fluid into the core holder, and when liquid flows out of the output system, closing the valve of the output system to hold back the pressure, so that the core is saturated with the fracturing fluid; S4: Open the valve of the output system, use the fracturing fluid input system to input fracturing fluid into the core holder, use the fracturing fluid to displace the core, and record the pressure and flow rate when the pressure monitored by the pressure gauge 1 and the pressure gauge 2 stabilizes, and calculate the liquid-measured permeability of the core after fracturing.

8. The shale gas core fracturing-displacement integrated experimental method according to claim 7, characterized in that: The following steps are also included: S5: Adjust the input pump pressure of the liquid carbon dioxide input system and repeat steps S2-S4 until the target number of times is reached; S6: fitting the liquid permeability data under different input pump pressure conditions to obtain a correlation formula between the input pump pressure and the liquid permeability of the core after fracturing; S7: Calculate the liquid-measured permeability of the core after fracturing at the target input pump pressure according to the correlation formula.

9. The shale gas core fracturing-displacement integrated experimental method according to claim 8, characterized in that: In step S4, the liquid permeability of the core after fracturing is calculated using the following formula: Where: k is the fluid permeability of the core after fracturing, mD; μ is the viscosity of the fracturing fluid, mPa·s; L is the core length, cm; Q is the flow rate through the core, cm 3 / s; A is the core cross-sectional area, cm 2 ; P is the pressure difference between seepage sections, MPa.

10. The shale gas core fracturing-displacement integrated experimental method according to claim 8, characterized in that: In step S6, the correlation formula between the input pump pressure and the liquid-measured permeability of the core after fracturing is: k f =ax 3 +bx 2 +cx+k m (2) Where: k f is the predicted value of the liquid permeability of the core after fracturing, mD; a, b, c are all fitting coefficients, dimensionless; x is the pump pressure, MPa; k m is the liquid permeability of the core before fracturing, mD.

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