Shale core hydration experimental device and experimental method based on CT (Computed Tomography) scanning
Through the shale core hydration experimental device and method based on CT scan, the impact of hydration on shale micro-fractures was studied, and the problem that the existing technology could not effectively understand the impact of hydration on the formation of shale micro-fractures was solved, and the rules of hydration secondary fractures were clarified, providing theoretical support for fracturing design.
Patent Information
- Application Number
- CN202311751316.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-19
- Publication Date
- 2025-06-20
AI Technical Summary
The prior art cannot effectively understand the impact of hydration on the formation of shale micro-fractures, resulting in poor flow of fracturing fluid and the occurrence of water-locking effects.
The shale core hydration experimental device and method based on CT scan was used to evaluate the secondary fractures of shale hydration through CT scan, and the influence of different pore pressure and confining pressure conditions on the expansion morphology and formation mechanism of secondary fractures was studied.
The generation and distribution rules of hydrated secondary cracks were clarified, and theoretical support was provided for optimizing the design and construction of shale reservoir fracturing, solving the problems of water lock effect and poor flow.
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Figure CN120177525A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of shale oil and gas reservoirs, in particular to a shale core hydration experimental device and an experimental method based on CT scanning. Background Art
[0002] As an important replacement resource for conventional oil and gas, shale is composed of fine-grained sediments, rich in clay minerals and organic matter, with a large number of micro-nano pores. The reservoir is highly heterogeneous and prone to spontaneous imbibition based on capillary force. During the fracturing process, the invasion of fracturing fluid leads to an increase in water saturation in the near-wellbore area, an increase in the capillary resistance of the oil-water interface in the pores, an enhancement of the Jamin effect, poor flow of fracturing fluid, and a water lock effect. Under the capillary force of the hydrophilic small pores, the fracturing fluid originally retained in the shale flow channel will diffuse into the reservoir matrix, and the flow channel will gradually open, that is, the water lock is released. After the fracturing fluid is immersed in the shale reservoir, the shale will undergo hydration, resulting in dissolution pores and mineral shedding, changing the internal microstructure of the shale. After hydration, the average pore size of the shale becomes larger, and microcracks continue to develop and interpenetrate each other. However, at the same time, clay minerals will absorb water and swell, resulting in the dispersion and migration of particles to block the pore throat, making it possible to reduce the connectivity of the pore structure. However, there is currently no experimental method to understand the impact of hydration on the formation of microfractures in shale. Summary of the invention
[0003] In order to overcome the deficiency of the prior art that it is unable to understand the influence of hydration on the formation of shale microcracks, the present invention provides a shale core hydration experimental device and an experimental method based on CT scanning. The experimental device evaluates shale hydration secondary cracks through CT scanning core experiments, evaluates the influence of different pore pressure and confining pressure conditions on the secondary crack distribution morphology and the formation mechanism of hydration secondary cracks, and clarifies the generation and distribution rules of hydration secondary cracks.
[0004] The technical solution of the present invention is: a shale core hydration experimental device based on CT scanning, including a core clamp, a core arranged in the core clamp, a hydration experimental device and a CT scanning device, the hydration experimental device includes a liquid inlet device and a waste liquid device, when the hydration experiment is carried out on the core, the liquid inlet device and the waste liquid device are respectively connected to the two ends of the core clamp; when the core is subjected to CT scanning, the core clamp is placed inside the CT scanning device.
[0005] Furthermore, the liquid inlet device comprises an injection liquid tank, which is connected to one end of the core holder through a horizontal flow pump, and a liquid inlet switch and a pressure gauge are provided on the liquid inlet pipeline.
[0006] Furthermore, the waste liquid device comprises a waste liquid tank, which is connected to the core clamp via a waste liquid pipeline, and a waste liquid switch is provided on the waste liquid pipeline.
[0007] Furthermore, the hydration experimental device further includes a hand pump, which is connected to the side wall of the core holder through a confining pressure inlet pipeline for applying confining pressure to the core holder, and a confining pressure switch is provided on the confining pressure inlet pipeline.
[0008] A shale core hydration experimental method based on CT scanning includes:
[0009] S1. Fabricate an artificial fracture core and clamp the core in the core holder;
[0010] S2. Connect the core holder to the core hydration device and apply confining pressure;
[0011] S3. Remove the core holder from the core hydration device and place it in the CT scanning device to perform CT scanning on the core and record the core porosity;
[0012] S4. Remove the core holder from the CT scanning device and connect it to the core hydration device, apply pore pressure to the core, inject the gel-breaking fluid, and then let it stand;
[0013] S5. Remove the core holder from the core hydration device and place it in the CT scanning device to observe the changes in the core fracture length and the number of fractures after hydration, and record the core porosity;
[0014] S6. Increase the pore pressure and continue to inject the gel-breaking fluid into the core, and repeat steps S4 and S5;
[0015] S7. Replace the different gel-breaking fluids and repeat steps S2 to S6.
[0016] Furthermore, in step S1, the direction of the artificial fracture of the core is perpendicular to the shale bedding direction.
[0017] Furthermore, the pore pressure in step S4 is 5 MPa and the standing time is at least 24 hours; the pore pressure in step S6 is 10 MPa and the standing time is at least 24 hours.
[0018] Furthermore, the gel-breaking fluid is one of a slickwater gel-breaking fluid, a guar gum gel-breaking fluid, and a mixed gel-breaking fluid, and the ratio of the slickwater gel-breaking fluid to the guar gum gel-breaking fluid in the mixed gel-breaking fluid is 2:8.
[0019] Furthermore, before applying confining pressure to the core holder, close the inlet switch and the waste liquid switch.
[0020] Furthermore, before applying pore pressure to the core holder, close the confining pressure switch.
[0021] The present invention has the following beneficial effects: By adopting the above solution, the present invention solves the problem that the existing indoor core experiments cannot understand the internal complex microfractures generated by core hydration. Through CT scanning of core experiments, the secondary fractures caused by shale hydration are evaluated, and the influence of different pore pressure and confining pressure conditions on the distribution pattern of secondary fractures and the formation mechanism of hydration secondary fractures is evaluated, so as to clarify the generation and distribution law of hydration secondary fractures, providing theoretical support for optimizing the fracturing design and construction of shale reservoirs. Description of the Drawings
[0022] Figure 1 is a schematic diagram of the hydration device in the present invention;
[0023] Figure 2 is a schematic diagram of the CT scanning device in the present invention;
[0024] Figure 3 are the CT scanning results of the core under different pore pressure conditions when the breaker fluid is a slickwater breaker fluid;
[0025] Figure 4 are the CT scanning results of the core under different pore pressure conditions when the breaker fluid is a guar gum breaker fluid;
[0026] Figure 5 are the CT scanning results of the core under different pore pressure conditions when the breaker fluid is a mixed breaker fluid.
[0027] In the figure, 1 is the CT scanning device, 2 is the core holder, 3 is the core, 4 is the core fixing rubber, 5 is the waste liquid switch, 6 is the pressure gauge, 7 is the liquid inlet switch, 8 is the waste liquid pipeline, 9 is the first liquid inlet pipeline, 10 is the confining pressure liquid inlet pipeline, 11 is the waste liquid tank, 12 is the peristaltic pump, 13 is the hand pump, 14 is the second liquid inlet pipeline, 15 is the confining pressure switch, and 16 is the injection liquid tank. Detailed Embodiments
[0028] The present invention will be further described below with reference to the accompanying drawings:
[0029] As shown in Figure 1 and Figure 2 , a shale core hydration experiment device based on CT scanning includes a core holder 2. A core 3 is arranged inside the core holder 2, and a core fixing rubber 4 is arranged outside the core 3, which can prevent the core 3 from being damaged when the core holder 2 clamps it. The device further includes a hydration experiment device and a CT scanning device 1. The hydration experiment device is used to inject the breaker fluid into the core holder 2 and apply confining pressure, and the CT scanning device 1 is used to observe the crack length, the number of cracks and the porosity of the core. The hydration experiment device includes a liquid inlet device, a waste liquid device and a confining pressure device. When conducting a hydration experiment on the core 3, the liquid inlet device and the waste liquid device are respectively connected to both ends of the core holder 2, and the confining pressure device is connected to one side of the core holder 2. When performing a CT scan on the core, the core holder 2 is placed inside the CT scanning device 1.
[0030] The liquid inlet device includes an injection liquid tank 16. The injection liquid tank 16 is connected to a peristaltic pump 12 through a second liquid inlet pipeline 14. The peristaltic pump 12 is connected to one end of a core holder 2 through a first liquid inlet pipeline 9, and a liquid inlet switch 7 and a pressure gauge 6 are provided on the first liquid inlet pipeline 9.
[0031] The waste liquid device includes a waste liquid tank 11. The waste liquid tank 11 is connected to the core holder 2 through a waste liquid pipeline 8, and a waste liquid switch 5 is provided on the waste liquid pipeline 8.
[0032] The confining pressure device includes a hand pump 13. The hand pump 13 is connected to the side wall of the core holder 2 through a confining pressure liquid inlet pipeline 10 for applying confining pressure to the core holder 2, and a confining pressure switch 15 is provided on the confining pressure liquid inlet pipeline 10.
[0033] A shale core hydration experiment method based on CT scanning includes the following steps:
[0034] S1. Fabricate a 2.5 cm × 5 cm artificial fracture core with the direction of the artificial fracture of the core perpendicular to the shale bedding direction, and clamp the core in the core holder.
[0035] S2. Connect the core holder to the hydration device, inject the gel-breaking liquid into the injection liquid tank, close the liquid inlet switch and the waste liquid switch, open the confining pressure switch, and use the hand pump to apply confining pressure to the core holder.
[0036] S3. Remove the core holder from the hydration device and place it in the CT scanning device to perform CT scanning on the core, observe the length of the core fracture, and record the porosity of the core before hydration.
[0037] S4. Remove the core holder from the CT scanning device and connect it to the hydration device. Open the liquid inlet switch, apply a pore pressure of 5 MPa to the core holder through the peristaltic pump, and then let it stand for 24 hours.
[0038] S5. Remove the core holder from the hydration device and place it in the CT scanning device to observe the change in the length of the core fracture and the number of fractures after hydration, and record the porosity of the core.
[0039] S6. Remove the core holder from the CT scanning device and connect it to the hydration device. Open the liquid inlet switch, apply a pore pressure of 10 MPa to the core holder through the peristaltic pump, and then let it stand for 24 hours. Remove the core holder from the hydration device and place it in the CT scanning device to observe the change in the length of the core fracture and the number of fractures after hydration, and record the porosity of the core.
[0040] S7. Replace with different gel-breaking fluids and repeat steps S2 to S6. Observe the changes in the core fracture length and the number of fractures after hydration during each CT scan, and record the core porosity. After the last CT scan, connect the core holder to the hydration experiment device, open the waste liquid switch and the confining pressure switch, remove the confining pressure and the injection pressure, drain the waste liquid into the waste liquid tank, remove the core holder after disconnecting the connecting pipeline, take out the core, and the experiment ends.
[0041] The gel-breaking fluid is one of a slickwater gel-breaking fluid, a guar gum gel-breaking fluid, and a mixed gel-breaking fluid, where the ratio of the slickwater gel-breaking fluid to the guar gum gel-breaking fluid in the mixed gel-breaking fluid is 2:8.
[0042] Table 1 shows the porosity values of the shale core hydration fractures under different pore pressure conditions. Figures 3 - 5 The following is the CT scan results of the core under different fracturing fluids and different pore pressure conditions. From the experimental results, it can be seen that when the experimental temperature and confining pressure are constant, as the pore pressure increases, the porosity of the hydration secondary fractures increases, the length of the hydration fractures extends, and the number of hydration secondary fractures increases significantly, fully indicating that at a certain confining pressure, increasing the pore pressure helps the generation and extension of hydration fractures. Comparing when the pore pressure increases from 5 MPa to 10 MPa, the increase in the porosity of the hydration fractures is the most obvious for the guar gum gel-breaking fluid, followed by the mixed gel-breaking fluid.
[0043] Table 1 Porosity of Hydration Fractures under Different Pore Pressure Conditions
[0044]
Claims
1. A CT-scan-based shale core hydration experiment device, comprising a core holder (2), with a core (3) disposed inside the core holder (2), characterized in that: It also includes a hydration experiment device and a CT scanning device (1). The hydration experiment device includes a liquid inlet device and a waste liquid device. When conducting a hydration experiment on the core (3), the liquid inlet device and the waste liquid device are respectively connected to both ends of the core holder (2). When performing a CT scan on the core, the core holder (2) is placed inside the CT scanning device (1).
2. The CT-scan-based shale core hydration experiment device according to claim 1, characterized in that: The liquid inlet device includes an injection liquid tank (16). The injection liquid tank (16) is connected to one end of the core holder (2) through a peristaltic pump (12), and a liquid inlet switch (7) and a pressure gauge (6) are provided on the liquid inlet pipeline.
3. The CT-scan-based shale core hydration experiment device according to claim 2, characterized in that: The waste liquid device includes a waste liquid tank (11). The waste liquid tank (11) is connected to the core holder (2) through a waste liquid pipeline (8), and a waste liquid switch (5) is provided on the waste liquid pipeline (8).
4. The CT-scan-based shale core hydration experiment device according to claim 3, characterized in that: The hydration experiment device also includes a hand pump (13). The hand pump (13) is connected to the side wall of the core holder (2) through a confining pressure inlet pipeline (10) for applying confining pressure to the core holder (2), and a confining pressure switch (15) is provided on the confining pressure inlet pipeline (10).
5. A CT-scan-based shale core hydration experiment method, characterized in that: S1. Fabricate an artificial fracture core and clamp the core in the core holder; S2. Connect the core holder to the core hydration device and apply confining pressure; S3. Remove the core holder from the core hydration device and place it in the CT scanning device to perform a CT scan on the core and record the core porosity; S4. Remove the core holder from the CT scanning device and connect it to the core hydration device, apply pore pressure to inject the gel-breaking fluid and then let it stand; S5. Remove the core holder from the core hydration device and place it in the CT scanning device to observe the changes in the core fracture length and the number of fractures after hydration, and record the core porosity; S6. Increase the pore pressure and continue to inject the gel-breaking fluid into the core, and repeat steps S4 and S5; S7. Replace with different gel-breaking fluids and repeat steps S2 to S6.
6. The CT-scan-based shale core hydration experiment method according to claim 5, characterized in that: In step S1, the direction of the artificial fracture of the core is perpendicular to the shale bedding direction.
7. The CT-scan-based shale core hydration experiment method according to claim 5, characterized in that: In step S4, the pore pressure is 5 MPa and the standing time is at least 24 hours; in step S6, the pore pressure is 10 MPa and the standing time is at least 24 hours.
8. The CT-scan-based shale core hydration experiment method according to claim 5, characterized in that: The gel-breaking fluid is one of a slickwater gel-breaking fluid, a guar gum gel-breaking fluid, and a mixed gel-breaking fluid. The ratio of the slickwater gel-breaking fluid to the guar gum gel-breaking fluid in the mixed gel-breaking fluid is 2:
8.
9. The CT-scan-based shale core hydration experiment method according to claim 5, characterized in that: Before applying confining pressure to the core holder, close the liquid inlet switch and the waste liquid switch.
10. The CT-scan-based shale core hydration experiment method according to claim 5, characterized in that: Before applying pore pressure to the core holder, close the confining pressure switch.