A method for testing the permeability of salt rock core samples

Abstract

The invention relates to a permeability testing method for a salt rock core sample, comprising the following steps: S1: using a core drilling machine to drill and coring block salt rock to obtain a core sample; S2: using 3D printing technology to print a hollow sample mold according to the internal dimensions of a sample slot of a permeability testing instrument, so that the internal dimensions of the sample mold are equal to the internal dimensions of the sample slot; S3: loading the core sample into the center of the sample mold, and injecting a castable between the core sample and the inner wall of the sample mold; after the castable is solidified, forming a protective layer on the outer side of the core sample; removing the sample mold, and then removing all or part of the protective layers at both ends of the core sample facing a test gas input pipe and an output pipe, respectively, to obtain a sample block; and S4: placing the sample block into the sample slot of the permeability testing instrument, and inputting and outputting the test gas from the exposed parts at both ends of the core sample, respectively, to perform a permeability test.

Description

Technical Field

[0001] The invention belongs to the technical field of salt rock permeability testing, and in particular relates to a permeability testing method for a salt rock core sample. Background Art

[0002] Salt rock is internationally recognized as an excellent place for underground storage due to its low porosity, low permeability, and water-soluble mining. The permeability of the surrounding rock is an important indicator for geological storage. The professional instrument for measuring the permeability of core samples requires that the samples be columnar in shape. When applying confining pressure during the test, the existing triaxial seepage test device is used. Currently, when making core samples in this field, large rock samples with few cracks and relatively complete rock blocks are selected and drilled using a vertical coring machine. During drilling, the rotation speed must be strictly controlled to ensure that the drill bit drills evenly and the core is intact. After coring, the cored coal sample is cut into a columnar salt rock sample using an automatic double-sided rock grinder, and polished smooth so that the two end faces are parallel, forming a columnar salt rock sample with a standard height-to-diameter ratio.

[0003] However, when a columnar salt rock sample is placed in the sample slot of a permeability tester, the salt contained in the sample can corrode the inner wall of the sample slot, causing damage to the instrument. Furthermore, due to tectonic stress, the original structure and texture undergo severe cracking and destruction, resulting in structural changes such as fragmentation, wrinkling, and polished surfaces. This makes the existing process for preparing columnar salt rock samples extremely prone to failure, resulting in a low yield rate and seriously affecting the efficiency of permeability testing. Therefore, permeability testing of salt rock samples is a difficult problem. Summary of the Invention

[0004] In response to the above problems, the present invention provides a method for testing the permeability of a salt rock core sample, comprising:

[0005] S1: Use a core drilling machine to drill and coring the massive salt rock to obtain a core sample;

[0006] S2: Using 3D printing technology, print a hollow sample mold according to the inner dimensions of the sample tank of the permeability test instrument, so that the inner dimensions of the sample mold are equal to the inner dimensions of the sample tank;

[0007] S3: Place the core sample in the center of the sample mold, and inject a castable between the core sample and the inner wall of the sample mold; after the castable solidifies, a protective layer is formed on the outer side of the core sample; remove the sample mold, and then remove all or part of the protective layer at both ends of the core sample facing the test gas input pipe and output pipe, thereby obtaining a sample block;

[0008] S4: Place the sample block into the sample slot of the permeability test instrument, and the test gas is input and output from the exposed parts at both ends of the core sample to perform permeability testing.

[0009] To prevent the salt substances in the salt rock sample from corroding the instrument, the present invention creates a protective layer formed of castable material on the outside of the core sample, separating the core sample from the instrument sample slot and protecting the instrument sample slot. Because the outer shape of the protective layer is the same as the inner shape of the sample slot, the core sample production requirements are reduced, the sample production efficiency and success rate are improved, and the efficiency of salt rock sample testing is greatly accelerated. The core sample is rod-shaped, with the two ends of its central axis pointing to the two ends of the core sample. During testing, one end of the core sample faces the test gas input tube, and the other end faces the test gas output tube, allowing the test gas to pass through the core sample.

[0010] Optionally, in step S1, a salt rock block sample to be tested is taken, and the salt rock block is drilled, cut and cored using an existing vertical drilling and coring machine, and then polished into a cylindrical or approximately cylindrical core sample; and then dried to remove moisture from the core sample.

[0011] Since there will be castable material wrapped around the outside of the core sample, the core sample only needs to be made into an approximately columnar or cylindrical shape. The volume of the core sample can be smaller than the internal size of the sample slot of the testing instrument, and the specific shape and size requirements are not high.

[0012] Optionally, step S1 may be followed by a step of measuring the structure and size of the core sample. Specifically, the core sample is scanned using a laser and / or a 3D scanner to obtain three-dimensional size data of the core sample. Image processing software (such as CAD software) is then used to obtain the relationship between the cross-sectional area in the direction of fluid flow in the core sample and the corresponding position.

[0013] For example, for a core sample with a regular shape, the direction of the fluid flow inside it is parallel to the central axis of the core sample, and the cross section is perpendicular to the central axis; for a core sample with an irregular shape, the direction of the fluid flow inside it has an angle α with its own central axis, and the cross section perpendicular to the central axis also has an angle α with the effective seepage cross section.

[0014] Alternatively, the three-dimensional dimension data of the core sample is imported into the CAD software to measure the maximum length L of the core sample along the central axis. max , and the minimum cross-sectional area A min ;

[0015] For core samples with regular shapes, L max and A min It can be calculated by combining the three-dimensional size data with common formulas, L max is the effective seepage length, A min is the effective seepage cross-sectional area;

[0016] For irregularly shaped core samples, Lmax is the distance between the upper and lower limits of the core sample, L is the effective seepage length of the core sample, and the inclination angle α of the irregularly shaped core sample is determined by the following formula:

[0017] cosα=L / L max

[0018] The effective seepage cross-sectional area A of the irregularly shaped core sample is determined by the inclination angle α and A min Determined using the following formula:

[0019] A=A min / cosα

[0020] Optionally, in step S2, the sample mold is cylindrical and has a removable cover on the top, and all inner walls of the sample mold are smooth; the cover is provided with at least one through hole for injecting castable into the sample mold, and preferably, the position of the through hole corresponds to the space between the core sample and the inner wall of the sample mold.

[0021] Optionally, in step S3, the core sample is placed in a sample mold and a lid is put on, with the upper and lower ends of the core sample respectively resting against the bottom surface of the sample mold and the lower surface of the lid to fix the core sample; the lid is sealed around to prevent the castable from overflowing; the castable is injected through the through hole on the lid; and the residual air in the sample mold is evacuated, and the castable is then naturally solidified to obtain a sample block.

[0022] The casting material is epoxy resin, which is transparent, not adsorbed by the core sample, and does not react with the core sample.

[0023] The permeability test method in step S4 is the same as that in the prior art, that is, the dried sample block is placed in the core holder (i.e., the sample slot) of the gas permeability tester, the permeability test is performed on the sample block, and the test results are recorded.

[0024] In the present invention, in order to reduce the difficulty of making the core sample, no requirement or low requirement is made for the smoothness and flatness of the side of the core sample (because the side is a curved surface and it is difficult to cut or polish it), while the flatness requirement for the end surfaces of the core sample depends on the specific situation (because the difficulty of cutting or polishing the end surfaces is not high).

[0025] For example, for samples with good structural conditions and ample time, both ends of the core sample can be polished into a flat surface. The two ends of the core sample are flat and can be respectively fitted against the bottom surface of the sample mold and the lower surface of the lid. The sides of the core sample are wrapped with castables, and the end faces at both ends are not covered with a protective layer, or are only covered with a thin layer of protective layer. Before testing, the protective layers on both end faces of the core sample are peeled off to expose the salt rock end faces for easy detection of the test gas.

[0026] For another example, when cutting or polishing a sample with poor structural conditions, a slight mistake may cause the sample to crack or break.

[0027] Optionally, step S1 further includes polishing a flat portion at the center of both ends of the core sample, which is used to connect with the sample mold and to receive or output the test gas during subsequent testing.

[0028] Further optionally, the areas of the end faces at both ends of the core sample are equal, the areas of the flat parts at both ends are also equal, and the ratio of the area of the flat parts to the area of the end faces of the core sample is not less than 0.5.

[0029] Further optionally, in step S2, a lower support platform protruding upward is provided at the center of the bottom of the sample mold, and an upper support platform protruding downward is provided at the center of the lower surface of the cover;

[0030] The lower support platform is in the shape of an inverted truncated cone, with a top diameter larger than a bottom diameter. The top surface of the lower support platform is used to contact and support the flat portion at the center of the bottom end of the core sample.

[0031] The upper support platform is in a truncated cone shape, with a top diameter smaller than a bottom diameter. The bottom surface of the upper support platform is used to contact and support the flat portion at the top center of the core sample.

[0032] After the pouring and solidification in step S3, except for the flat parts at both ends of the core sample, the rest of the parts, whether raised or concave, will be wrapped in the castable, and only the flat parts can expose the protective layer, which is used to receive or output the test gas during testing. Moreover, the two ends of the formed sample block each have a truncated cone-shaped opening, the diameter of the side of the opening away from the core sample is small, and the diameter of the side of the opening close to the core sample is large. After the test gas enters the opening, it can also diffuse along the inner wall of the opening, try to occupy most of the area on the cross section of the core sample, and make the test gas form a form of diffusion toward the outside of the cross section and the effective diffusion direction, and then enter the core sample to continue to diffuse. After the test gas leaves the core sample, it gathers in another opening and then leaves the sample block.

[0033] In the traditional permeability test of salt rock samples, the cut and polished cylindrical samples are directly placed into the sample slot, and then confining pressure is applied to simulate the underground formation environment. The confining pressure acts directly on the sample surface. In the present invention, a protective layer is added to the core sample to completely wrap its side, and the epoxy resin has a certain strength after curing. The confining pressure first acts directly on the protective layer and then indirectly acts on the core sample. Therefore, the core sample of the present invention is slightly different from the prior art in terms of the pressure environment. During the test, the core sample may have some effect on the permeability due to the difference in the stress state. The present invention takes these deviations into consideration, and after repeated experimental comparisons, the protection of the protective layer on the side of the core sample on the permeability test is integrated into a correction factor. When determining the permeability after the test, the correction factor needs to be introduced to correct the deviation and improve the accuracy of the test.

[0034] The correction factor F1 is determined by the following formula:

[0035] ;

[0036] Wherein, D is the total average thickness of the protective layer of the sample block, in cm; B is the inner diameter of the sample tank, in cm;

[0037] The corrected gas permeability is then determined by the following formula:

[0038] ;

[0039] Where: is the corrected gas permeability, in μm 2 ; Kg is the gas permeability, unit is μm 2 ; Q0 is the gas flow rate, unit is cm 3 / s;P o is atmospheric pressure, in Psi; μ g is the viscosity of the gas under atmospheric pressure and test temperature, in mPa·s; L is the effective seepage length of the core sample, in cm; A is the effective seepage cross-sectional area of the core sample, in cm 2 ; P1 is the upstream pressure, unit is Psi; P2 is the downstream pressure, unit is Psi.

[0040] The total average thickness D of the sample block's protective layer is the difference between the diameter of one end of the sample block and the diameter of one end of the core sample. The volume of the core sample can be determined experimentally by assuming the core sample is a standard cylinder and inferring its end diameter from its volume. For example, if the core sample is immersed in a liquid (which is not absorbed by the core sample), the change in liquid volume before and after immersion is the core sample's volume.

[0041] The thickness of the curved side of the sample block should not be too thin. If it is too thin, the gap between the sample mold and the core sample will be small, the castable will be unevenly distributed, and it will have a negative impact on the test; if it is too thick, it will also have a negative impact on the test. Therefore, in the study of the correction factor, the present invention limits the value of D / B to 1 / 5-1 / 10, which includes the vast majority of sample block cases. Sample blocks within this range have a high production success rate and a stable and good test state. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic diagram of the sample block of Example 1;

[0043] Figure 2 Schematic diagram of the sample block of Example 2.

[0044] In the accompanying drawings, 1-core sample, 2-protective layer, 3-upper support platform, 4-lower support platform. DETAILED DESCRIPTION

[0045] Example 1

[0046] A method for testing the permeability of a salt rock core sample in this embodiment includes:

[0047] S1: Use a core drill to drill and coring machine to obtain core samples from massive salt rock;

[0048] S2: Using 3D printing technology, print a hollow sample mold according to the inner dimensions of the sample tank of the permeability test instrument, so that the inner dimensions of the sample mold are equal to the inner dimensions of the sample tank;

[0049] S3: Place the core sample in the center of the sample mold, and inject a castable between the core sample and the inner wall of the sample mold; after the castable solidifies, a protective layer is formed on the outer side of the core sample; remove the sample mold, and then remove all or part of the protective layer at both ends of the core sample facing the test gas input pipe and output pipe, thereby obtaining a sample block;

[0050] S4: Place the sample block into the sample slot of the permeability test instrument, and the test gas is input and output from the exposed parts at both ends of the core sample to perform permeability testing.

[0051] In step S1, a salt rock block sample to be tested is taken, and the salt rock block is drilled, cut and cored using an existing vertical drilling and coring machine, and then polished into a cylindrical or approximately cylindrical core sample; and then dried to remove moisture from the core sample.

[0052] Since the core sample will be covered with castable material later, the core sample only needs to be made into a columnar or cylindrical shape, and the volume of the core sample is smaller than the internal size of the sample slot of the testing instrument. The sample construction conditions of this embodiment are better, and both ends of the core sample are polished into a flat surface.

[0053] After step S1, the step of measuring the structure and size of the core sample is also included. Specifically, the core sample is scanned using a laser and / or a 3D scanner to obtain three-dimensional size data of the core sample; then, image processing software (such as CAD software) is used to obtain the relationship between the cross-sectional area in the direction of fluid flow in the core sample and the corresponding position in the direction.

[0054] Import the three-dimensional dimension data of the core sample into the CAD software and measure the maximum length L of the core sample along the central axis. max , and the minimum cross-sectional area A min ;

[0055] For the irregularly shaped core sample in this example, L max is the distance between the upper and lower limits of the core sample, L is the effective seepage length of the core sample, and the inclination angle α of the irregularly shaped core sample is determined by the following formula:

[0056] cosα=L / L max

[0057] The effective seepage cross-sectional area A of the irregularly shaped core sample is determined by the inclination angle α and A min Determined using the following formula:

[0058] A=A min / cosα.

[0059] In step S2, the sample mold is cylindrical and has a removable cover on the top, and all inner walls of the sample mold are smooth; a through hole is provided on the cover for injecting castable into the sample mold, and the position of the through hole corresponds to the space between the core sample and the inner wall of the sample mold.

[0060] In step S3, the core sample is placed in a sample mold and covered with a lid. The upper and lower ends of the core sample are placed against the bottom surface of the sample mold and the lower surface of the lid, respectively, to secure the core sample. The lid is sealed to prevent the castable from overflowing. The castable (epoxy resin) is injected through the through-holes in the lid. Residual air in the sample mold is then evacuated, and the castable is allowed to cure naturally to form a sample block. The sides of the core sample are covered with the castable, while the end surfaces are either not covered with protective layer 2 or covered only with a thin layer of protective layer. Before testing, the protective layer is peeled off from both ends of the core sample to expose the salt rock end surfaces for easy detection by the test gas.

[0061] Step S4 is specifically as follows:

[0062] 1. Measurement conditions:

[0063] Gas source: Helium cylinder 200psig (for testing), air / nitrogen cylinder 100psig (for operating pneumatic valves);

[0064] Power supply: 90~250VAC, 50~60Hz;

[0065] Ambient temperature: 25°C, fluctuation should be less than 1°C;

[0066] Stable test principle parameters: 3sec, 0.01psi.

[0067] 2. Operation steps:

[0068] (1) Set the helium pressure to 200 psig and the air / nitrogen pressure to 90 psig to ensure that there is no pressure loss along the entire line; select 5 calibration blocks for testing; test each calibration block in turn to generate a test baseline;

[0069] (2) Enter the sample block number and its dry weight, effective seepage length L, effective seepage cross-sectional area A and other information in the rock sample information area, and test each sample block in turn.

[0070] 3. After the test is completed, calculate the volume of the core sample based on L and A, then calculate the pore volume, and record the test results.

[0071] The correction factor F1 is determined by the following formula:

[0072] ;

[0073] Wherein, D is the total average thickness of the protective layer of the sample block, in cm; B is the inner diameter of the sample tank, in cm.

[0074] Permeability indicates the ability of porous media to transmit fluid. When gas flows in porous media, according to Darcy's law of one-dimensional steady flow, the corrected gas permeability is determined by the following formula:

[0075] ;

[0076] Where: is the corrected gas permeability, in μm 2 ; Kg is the gas permeability, unit is μm 2 ; Q0 is the gas flow rate, unit is cm 3 / s;P o is atmospheric pressure, in Psi; μ gis the viscosity of the gas under atmospheric pressure and test temperature, in mPa·s; L is the effective seepage length of the core sample, in cm; A is the effective seepage cross-sectional area of the core sample, in cm 2 ; P1 is the upstream pressure, unit is Psi; P2 is the downstream pressure, unit is Psi.

[0077] The corrected gas permeability of this embodiment is Kg'=Kg×F1=9.47×10 -9 ×0.885=8.38×10 -9 μm 2 .

[0078] The same salt rock block sample to be tested in this embodiment was drilled and cut using the existing method using a vertical core drill. The core was then polished into a standard cylindrical core sample and placed directly into the sample tank. The same test conditions as in this embodiment were used to test the sample. The gas permeability of the sample was calculated and obtained as Kg = 8.52 × 10 -9 μm 2 .

[0079] The error between Kg' in this embodiment and Kg obtained from the same sample source without a protective layer is: (8.52-8.38)×100% / 8.52=1.64%, which is relatively small.

[0080] Example 2

[0081] The permeability testing method for a salt rock core sample in this embodiment is the same as that in Example 1, except that the structural conditions of the salt rock block sample to be tested in this embodiment are poor. Step S1 also includes polishing a flat portion at the center of each end of the core sample. This portion is used to connect to the sample mold and to receive or output test gas during subsequent testing.

[0082] The areas of the end faces at both ends of the core sample are equal, the areas of the flat parts at both ends are also equal, and the ratio of the area of the flat parts to the area of the end faces of the core sample is 0.5:1.

[0083] In step S2, if Figure 2 As shown, the center of the bottom of the sample mold is provided with an upwardly protruding lower support platform 4, and the center of the lower surface of the cover is provided with a downwardly protruding upper support platform 3;

[0084] The lower support platform is in the shape of an inverted truncated cone, with a top diameter larger than a bottom diameter. The top surface of the lower support platform is used to contact and support the flat portion at the center of the bottom end of the core sample.

[0085] The upper support platform is in a truncated cone shape, with a top diameter smaller than a bottom diameter. The bottom surface of the upper support platform is used to contact and support the flat portion at the top center of the core sample.

[0086] The correction factor F1 is 0.885. The corrected gas permeability of this embodiment is Kg'=Kg×F1=12.60×10 -9 ×0.885=11.15×10 -9 μm 2 .

[0087] The same salt rock block sample to be tested in this embodiment was drilled and cut using the existing method using a vertical drilling and coring machine. The core was then polished into a standard cylindrical core sample and placed directly into the sample tank. The same test conditions as in this embodiment were used to test the sample. The gas permeability of the sample was calculated and obtained as Kg = 10.67 × 10 -9 μm 2 .

[0088] The error between the Kg' of this embodiment and the Kg obtained from the same sample source without a protective layer is: (11.15-10.67)×100% / 10.67=4.50%.

[0089] Example 3

[0090] The permeability testing method of a salt rock core sample in this embodiment is the same as that in Example 2, except that the ratio of the area of the flat parts at both ends of the core sample to the area of the end surface of the core sample is 0.8:1.

[0091] The correction factor F1 is 0.885. The corrected gas permeability of this embodiment is Kg'=Kg×F1=12.45×10 -9 ×0.885=11.02×10 -9 μm 2 .

[0092] The error between the Kg' of this embodiment and the Kg obtained from the same sample source without a protective layer is: (11.02-10.67)×100% / 10.67=3.28%.

[0093] Example 4

[0094] The permeability testing method of a salt rock core sample in this embodiment is the same as that in Example 2, except that the ratio of the area of the flat parts at both ends of the core sample to the area of the end surface of the core sample is 0.4:1.

[0095] The correction factor F1 is 0.885. The corrected gas permeability of this embodiment is Kg'=Kg×F1=12.70×10 -9 ×0.885=11.24×10 -9 μm 2 .

[0096] The error between the Kg' of this embodiment and the Kg obtained from the same sample source without a protective layer is: (11.24-10.67)×100% / 10.67=5.34%.

[0097] Example 5

[0098] The permeability testing method for a salt rock core sample in this embodiment is the same as that in Example 2, except that the upper support platform and the lower support platform of the sample mold are both cylindrical, so that the openings at both ends of the sample block are cylindrical.

[0099] The correction factor F1 is 0.885. The corrected gas permeability of this embodiment is Kg'=Kg×F1=12.84×10 -9 ×0.885=11.36×10 -9 μm 2 .

[0100] The error between the Kg' of this embodiment and the Kg obtained from the same sample source without a protective layer is: (11.36-10.67)×100% / 10.67=6.47%.

[0101] Table 1 Comparison of gas permeability errors after correction in the examples

[0102] .

Claims

1. A method for testing the permeability of a salt rock core sample, characterized in that: include: S1: Use a core drill to drill and coring machine to obtain core samples from massive salt rock; S2: Using 3D printing technology, print a hollow sample mold according to the inner dimensions of the sample tank of the permeability test instrument, so that the inner dimensions of the sample mold are equal to the inner dimensions of the sample tank; S3: Place the core sample in the center of the sample mold and inject castable material between the core sample and the inner wall of the sample mold; after the castable material solidifies, a protective layer is formed on the outside of the core sample; Removing the sample mold, and then removing all or part of the protective layers at both ends of the core sample facing the test gas input pipe and output pipe, respectively, to obtain a sample block; S4: Place the sample block into the sample slot of the permeability test instrument, and input and output the test gas from the exposed parts at both ends of the core sample to perform the permeability test; The test error caused by the thickness of the protective layer is classified as the correction factor and is determined by the following formula: ； Wherein, D is the total average thickness of the protective layer of the sample block, in cm; B is the inner diameter of the sample tank, in cm; The corrected gas permeability is then determined by the following formula: ； Where: is the corrected gas permeability, in μm 2 ; Kg is the gas permeability, unit is μm 2 ; Q0 is the gas flow rate, unit is cm 3 / s; P0 is atmospheric pressure, unit is Psi; μ g is the viscosity of the gas under atmospheric pressure and test temperature, in mPa·s; L is the effective seepage length of the core sample, in cm; A is the effective seepage cross-sectional area of the core sample, in cm 2 ; P1 is the upstream pressure, in Psi; P2 is the downstream pressure, in Psi.

2. The method for testing the permeability of a salt rock core sample according to claim 1, wherein: In step S2, the sample mold is cylindrical and has a removable cover on the top, and all inner walls of the sample mold are smooth; there is at least one through hole on the cover for injecting castable into the sample mold, and the position of the through hole corresponds to the space between the core sample and the inner wall of the sample mold.

3. The permeability testing method of salt rock core sample according to claim 2, characterized in that: In step S3, the core sample is placed in the sample mold, and the lid is closed, with the upper and lower ends of the core sample respectively resting against the bottom surface of the sample mold and the lower surface of the lid to fix the core sample; Seal the lid to prevent the castable from overflowing; inject the castable through the through hole on the lid; then evacuate the remaining air in the sample mold, and then allow the castable to solidify naturally to obtain a sample block.

4. The method for testing the permeability of a salt rock core sample according to claim 3, wherein: For samples with better structural conditions, both ends of the core sample are polished into flat surfaces. The two ends of the core sample are flat and fit against the bottom surface of the sample mold and the lower surface of the lid respectively. The sides of the core sample are wrapped with castables, and the end faces at both ends are not covered with a protective layer, or are covered with only a thin layer of protective layer. Before testing, the protective layers on both end faces of the core sample are peeled off to expose the salt rock end faces to facilitate the reception or output of test gas.

5. The method for testing the permeability of a salt rock core sample according to claim 3, wherein: For samples with poor structural conditions, step S1 also includes grinding out a flat portion at the center of both ends of the core sample. This portion is used to connect with the sample mold and to receive or output the test gas during subsequent testing.

6. The method for testing the permeability of a salt rock core sample according to claim 5, wherein: The areas of the end faces at both ends of the core sample are equal, the areas of the flat parts at both ends are also equal, and the ratio of the area of the flat parts to the area of the end faces of the core sample is not less than 0.

5.

7. The method for testing the permeability of a salt rock core sample according to claim 5, wherein: In step S2, a lower support platform protruding upward is provided at the center of the bottom of the sample mold, and an upper support platform protruding downward is provided at the center of the lower surface of the cover; The lower support platform is in the shape of an inverted truncated cone, with a top diameter larger than a bottom diameter. The top surface of the lower support platform is used to contact and support the flat portion at the center of the bottom end of the core sample. The upper support platform is in a truncated cone shape, with a top diameter smaller than a bottom diameter. The bottom surface of the upper support platform is used to contact and support the flat portion at the top center of the core sample.

8. The method for testing the permeability of a salt rock core sample according to claim 1, wherein: Between step S1 and step S2, there is also a step of measuring the structure and size of the core sample. Specifically, the core sample is scanned using a laser and / or a 3D scanner to obtain three-dimensional size data of the core sample; then, CAD software is used to obtain the relationship between the cross-sectional area in the direction of fluid flow in the core sample and the corresponding position.

9. The method for testing the permeability of a salt rock core sample according to claim 8, wherein: Import the three-dimensional dimension data of the core sample into the CAD software and measure the maximum length L of the core sample along the central axis. max , and the minimum cross-sectional area A min ; For core samples with regular shapes, L max and A min It can be calculated by combining the three-dimensional size data with common formulas, L max is the effective seepage length, A min is the effective seepage cross-sectional area; For irregularly shaped core samples, L max is the distance between the upper and lower limits of the core sample, L is the effective seepage length of the core sample, and the inclination angle α of the irregularly shaped core sample is determined by the following formula: cosα=L / L max The effective seepage cross-sectional area A of the irregularly shaped core sample is determined by the inclination angle α and A min Determined using the following formula: A=A min / cosα。

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