Shale gas core fracturing-displacement integrated experimental device and method

Abstract

The invention discloses a shale gas core fracturing-displacement integrated experimental device and method. The experimental device comprises an input system, a core holder, an output system and a metering system, a rock core is arranged in the rock core holder, rock core fixing devices with threads for fixing the rock core are arranged at the left end and the right end of the rock core holder, hollow metal needle heads axially penetrate through the rock core fixing devices, one end of each metal needle head is embedded into the rock core, and the other end of each metal needle head is connected with the input system or the output system; the input system comprises a liquid carbon dioxide input system and a fracturing fluid input system which are arranged in parallel; the output system is used for collecting the fluid output by the core holder; the metering system comprises a first pressure gauge, a second pressure gauge and a flow meter. According to the invention, the liquid carbon dioxide input system and the metal needle head can be used for forming a crack on a rock core, the perforation of a real gas well on a reservoir is simulated, and the hydraulic fracturing process is simulated through the fracturing fluid input system.

Description

Technical Field

[0001] The 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 widely distributed, thick, and generally contain gas, which can produce gas stably for a long time. However, the permeability of shale gas reservoirs is low, making them difficult to exploit. The main exploitation method for this type of gas reservoir is horizontal well hydraulic fracturing development. The effect of core reservoir transformation after fracturing is mainly evaluated by permeability. Therefore, it is extremely important to simulate the change in permeability of the test fluid after hydraulic fracturing of the core. For extremely dense shale cores, the permeability is extremely low, and the permeability can be greatly improved after hydraulic fracturing. The effect of fracturing in actual formations is difficult to simulate experimentally.

[0003] At present, there are two main methods for creating fractures in natural core chambers. One is to use the Brazilian splitting instrument or the rock mechanics triaxial testing system, generally using radial tension and axial compression. The fractures formed by this method are irregular in shape and the fracture shape, orientation and opening cannot be controlled. The other is to cut the core into two equal halves, and simulate or calculate the fracture width based on the required fracture opening using the thickness of the intermediate gasket or the diameter of the sand filling particles. Both methods require the fracture to be created before being transferred to the core holder. During this period, the original fracture morphology of the core may be changed and affected, and it is impossible to ensure that the experiment can be carried out 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 solution of the present invention is 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] The core holder is provided with a core, and both left and right ends of the core holder are provided with threaded core fixing devices for fixing the core, and the core fixing device is axially penetrated by a hollow metal needle, one end of the metal needle is buried in the core, the other end of one of the metal needles 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 comprises a liquid carbon dioxide input system and a fracturing fluid input system arranged in parallel, wherein 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 for displacement; the output system is used to collect the fluid output by the core holder;

[0009] The metering system includes a pressure gauge 1, a pressure gauge 2 and a flow meter. The pressure gauge 1 and the pressure gauge 2 are used to monitor the pressure at the input end and the output end of the core holder respectively, and 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 which are connected in sequence, and the output end of the valve 1 is connected to the input end of the core holder;

[0011] The fracturing fluid input system comprises 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 comprises a fluid collecting device, which is connected to the output end of the core holder, and a valve three is arranged 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 comprises an air compressor, a boosting pump, a valve four, and a carbon dioxide storage tank connected in sequence; the carbon dioxide storage tank is connected to the liquid carbon dioxide intermediate container, and a pressure regulating valve, a pressure gauge three, and a valve five are provided in sequence on the connected pipelines.

[0015] Preferably, a confining pressure pump is further included, and an 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 shale gas core fracturing-displacement integrated experimental device described in any one of the above is used to conduct experiments.

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

[0018] S1: Obtain a core of a 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 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 when the pressure monitored by the pressure gauge 1 and the pressure gauge 2 is stable, record the pressure and flow at this time, 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: adjusting the input pump pressure of the liquid carbon dioxide input system, and repeating 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 liquid 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 can simulate the perforation of a reservoir by a real gas well by creating fractures in the core through the liquid carbon dioxide input system and the metal needle, and simulate the hydraulic fracturing process through the fracturing fluid input system. The device has a simple structure, a convenient and easy method, and simple operation; it can transform fractured cores with different 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative labor.

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

[0036] Figure 2 It is a 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-boosting pump, 3-valve four, 4-carbon dioxide storage tank, 5-pressure regulating valve, 6-pressure gauge three, 7-valve five, 8-liquid carbon dioxide intermediate container, 9-ultra-high pressure pump, 10-fracturing fluid intermediate container, 11-valve two, 12-valve one, 13-pressure gauge one, 14-displacement pump, 15-confining pressure pump, 16-metal needle, 17-core holder, 18-core fixing device, 19-pressure gauge two, 20-flow meter, 21-valve three, 22-fluid collecting device. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with the accompanying drawings and embodiments. 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 generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean 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 has a core in it, and both left and right ends of the core holder 17 are provided with threaded core fixing devices 18 for fixing the core, and the core fixing device 18 is axially penetrated by a hollow metal needle 16, one end of the metal needle 16 is buried in the core, the other end of one of the metal needles 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, wherein 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 for displacement; 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 19 and a flow meter 20. The pressure gauge 13 and the pressure gauge 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 which are connected in sequence, and 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 which are connected in sequence, and the output end of the valve 2 11 is connected to the input end of the core clamp 17;

[0046] The output system comprises 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 four 3, and a carbon dioxide gas storage tank 4 connected in sequence, and the carbon dioxide gas storage tank 4 is connected to the liquid carbon dioxide intermediate container 8, and a pressure regulating valve 5, a pressure gauge three 6, and a valve five 7 are sequentially arranged on the connected pipeline.

[0048] In a specific embodiment, the experimental device further includes a confining pressure pump 15, and the output end of the confining pressure pump 15 is connected to the confining pressure input port of the core holder 17. In this embodiment, the confining pressure condition of the formation can be simulated by setting the confining pressure pump 15, so that the result is more in line with the actual working conditions. In addition, in order to simulate the formation temperature condition, the experimental device of the present invention may also include a constant temperature box or a heating device, through which the core in the core holder reaches the formation simulation temperature, thereby simulating the formation temperature condition.

[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 comprises the following steps:

[0051] S1: Obtain a core of 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 is stable, record the pressure and flow at this time, and calculate the liquid-measured 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 liquid 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: adjusting the input pump pressure of the liquid carbon dioxide input system, and repeating 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-measured 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 according to the present invention is used to conduct a core fracturing-displacement integrated experiment, which specifically includes the following steps:

[0066] (1) Obtain a core of 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, and 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) Carbon dioxide is stored in a carbon dioxide gas storage tank 4, and fracturing fluid is placed in a fracturing fluid intermediate container 10. The tested viscosity of the fracturing fluid is 1.2 mP·s.

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

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

[0071] (5) Close valve five 7, open valve one 12, and use 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) Valve 1 12 is opened, valve 2 11 is opened, and displacement pump 14 is started to displace the fracturing fluid. When liquid outflow is detected in the fluid collection device 22, valve 3 21 is closed, and the pressure is continued to be increased to build up pressure in the core. After the pressure reading reaches 10 MPa, it is maintained 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 to measure the liquid permeability, and record the pressure and flow rate after the pressure gauge 13 and pressure gauge two 19 indicate stable readings. 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 19 indicate stable readings are 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 is 2.405 mD, which is four orders of magnitude higher than the initial liquid permeability of 0.00021 mD before the core is fractured. The experimental device described in the present invention can well transform 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 pump pressures of 35 MPa and 40 MPa. The results are 4.981 mD and 5.668 mD, respectively.

[0077] (10) According to the test results of liquid permeability under the above four pump pressure conditions, the results are Figure 2 As shown in the figure, 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] By using the correlation formula shown in formula (3), the fractured core with target liquid permeability can be obtained by controlling the input pump pressure according to actual needs, thereby better simulating the actual working conditions.

[0080] The above description is only 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 the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification 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 still falls 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: It includes input system, core holder, output system and metering system; The core holder is provided with a core, and both left and right ends of the core holder are provided with threaded core fixing devices for fixing the core, and the core fixing device is axially penetrated by a hollow metal needle, one end of the metal needle is buried in the core, the other end of one of the metal needles is connected to the input system, and the other end of the other metal needle is connected to the output system; The input system comprises a liquid carbon dioxide input system and a fracturing fluid input system arranged in parallel, wherein 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 for displacement; the output system is used to collect the fluid output by the core holder; The metering system includes a pressure gauge 1, a pressure gauge 2 and a flow meter. The pressure gauge 1 and the pressure gauge 2 are used to monitor the pressure at the input end and the output end of the core holder respectively, and 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 comprises an ultra-high pressure pump, a liquid carbon dioxide intermediate container, and a valve 1 which are connected in sequence, and the output end of the valve 1 is connected to the input end of the core holder; The fracturing fluid input system comprises 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 comprises a fluid collecting device, which is connected to the output end of the core holder, and a valve three is arranged 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 comprises an air compressor, a boosting pump, a fourth valve, and a carbon dioxide gas storage tank which are connected in sequence. The carbon dioxide gas storage tank is connected to the liquid carbon dioxide intermediate container, and a pressure regulating valve, a third pressure gauge, and a fifth valve are arranged in sequence on the connected pipelines.

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 of a 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 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 when the pressure monitored by the pressure gauge 1 and the pressure gauge 2 is stable, record the pressure and flow at this time, 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: adjusting the input pump pressure of the liquid carbon dioxide input system, and repeating 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 by the following formula: Where: k is the liquid 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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