Method for testing permeability of fragile core

Abstract

The invention discloses a fragile rock core permeability testing method which comprises the following steps: cutting and polishing a fragile rock sample into a regular cuboid rock core, and recording the size of the cuboid rock core; placing the cuboid rock core in a cylinder of a rock core pouring mold, pouring by using liquid epoxy resin glue, naturally curing after pouring, and demolding to obtain the plunger rock core for the test; and drying the plunger core for testing, and finally loading the plunger core for testing into a core holder of a gas permeability tester for testing the permeability. By adopting the method to prepare the fragile rock core for permeability test, the test requirement can be met, the test efficiency is improved, and the test period is shortened.

Description

Technical Field

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

[0002] In the field of experimental research on oil and gas resources, in order to understand the properties of underground reservoirs, coring operations are often carried out, and then the cores are subjected to indoor physical simulation experiments to obtain geological parameters. The core samples used in the simulation experiment have certain specifications, that is, they are 1-inch or 1.5-inch cylindrical; during the simulation experiment, qualified cores are placed in the core holder, and pressure sensors are connected to both ends of the core inlet and outlet. Since the experimental medium has an inlet pressure when entering the core, there will be pressure loss in the process of passing through the core, so the pressure sensors at both ends of the inlet and outlet will collect different values. These values ​​can be put into the relevant formula to calculate the physical parameters such as the core permeability.

[0003] The existing core preparation method is basically suitable for dense sandstone plunger drilling with a diameter of 25mm and 38mm. It is not completely applicable to the drilling and cutting of fragile cores such as shale, coal rock, and conglomerate. Since such samples are highly heterogeneous and have developed cracks, they are prone to breakage during the preparation process, making core sampling very difficult. A large number of rock samples are required to drill suitable cores, and the corresponding sampling time is also relatively long, which leads to a long time required for the entire permeability test, and even fails to meet the test requirements. Summary of the invention

[0004] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a method for testing the permeability of fragile cores.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for testing the permeability of a fragile core comprises the following steps:

[0007] S1. Cut and grind the fragile rock sample into a regular rectangular core;

[0008] S2, measure the size of the cuboid core;

[0009] S3, placing the rectangular core in a core casting mold;

[0010] S4, injecting epoxy resin glue into the core casting mold, evacuating the residual air inside the core casting mold, and naturally curing;

[0011] S5. After the curing is completed, demoulding is performed to obtain a plunger core for testing;

[0012] S6, plunger core for drying test;

[0013] S7. Place the dried test plunger core into the core holder of the gas permeability tester, perform a permeability test on the test plunger core, and record the test results.

[0014] In the above technical solution, the step S2 measures the size of the rectangular core using a vernier caliper, and the size includes the length, height and width of the rectangular core.

[0015] In the above technical solution, the minimum graduation value of the vernier caliper is 0.01 mm.

[0016] In the above technical solution, the length, width and height of the core casting mold are all greater than the rectangular core.

[0017] In the above technical solution, the inner diameter of the cylinder of the core casting mold is 1 inch or 1.5 inches.

[0018] In the above technical solution, the injection amount of the epoxy resin glue in step S4 is enough to cover the height of the rectangular core.

[0019] In the above technical solution, in step S4, a vacuum machine is used for evacuation, the evacuation time is 2 hours to 3 hours, and the natural curing time is 10 hours.

[0020] In the above technical solution, the rectangular core in the test plunger core of step S5 is tightly combined with the epoxy resin glue without gaps, and there are no concave and convex bubbles on the surface of the test plunger core; the test plunger core has a temperature resistance of 120°C and a compressive strength greater than 10MPa.

[0021] In the above technical solution, the drying temperature of step S6 is 90° C. and the drying time is 10 hours.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a method for testing the permeability of a fragile core. The method is used to prepare a fragile core for permeability testing, which can meet testing requirements, improve testing efficiency, and reduce testing cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of the method of the present invention;

[0025] Figure 2 It is a schematic diagram of the structure of the plunger core used in the test of the present invention;

[0026] Figure 3 It is a comparison chart of the permeability results of the test plunger core and the standard plunger core in Example 1 of the present invention.

[0027] in:

[0028] 1. Epoxy resin glue; 2. Core.

[0029] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0031] Example 1

[0032] like Figure 1 As shown, a method for testing the permeability of a fragile core comprises the following steps:

[0033] S1. Take a piece of fragile rock sample and cut and grind it into a regular rectangular core using a core cutting and grinding device;

[0034] S2. Use a vernier caliper to measure the length, height and width of the rectangular core and record the measured dimensions. The minimum graduation value of the vernier caliper is 0.01 mm.

[0035] S3, placing the measured rectangular core in the cylinder of the core casting mold, and the length, width and height of the rectangular core are all smaller than the size of the cylinder of the core casting mold, and fixing the mold cover of the core casting mold to the cylinder of the core casting mold; the size of the cylinder of the core casting mold is 1 inch;

[0036] S4, prepare the liquid epoxy resin AB glue according to the weight ratio of A:B=3:1, and then inject the prepared liquid epoxy resin AB glue into the mold tube from the pouring port on the mold cover by using an injector until the epoxy resin glue covers the height of the core sample, and use a vacuum machine to extract the residual air inside the mold tube. The vacuum machine runs for 3 hours, and then naturally cures for 10 hours;

[0037] S5. After the solidification is completed, the cast plunger core is demoulded to obtain the plunger core for the test. Figure 2 As shown, the cuboid core in the test plunger core is tightly combined with the epoxy resin glue without gaps, and there are no concave and convex bubbles on the surface of the test plunger core. The temperature resistance of the test plunger core can reach 120°C, and the compressive strength is greater than 10MPa.

[0038] S6. Before performing gas permeability testing, remove the moisture contained in the test plunger core, and specifically use a drying oven to dry the moisture inside the test plunger core;

[0039] S7. Place the dried test plunger core into the core holder of the gas permeability tester, perform a permeability test on the test plunger core, and record the test results.

[0040] Permeability indicates the ability of porous media to transmit fluid. When gas flows in porous media, the formula for calculating gas permeability can be obtained from Darcy's law of one-dimensional stable flow of gas as follows:

[0041]

[0042] Where: K g is the gas permeability, in μm 2 ; Q0 is the gas flow rate, in cm 3 / s;

[0043] 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 length of the rock sample, in cm; A is the cross-sectional area of ​​the rock sample, in cm 2 ; P1 is the upstream pressure, unit is Psi; P2 is the downstream pressure, unit is Psi.

[0044] Ten coal cores from the same layer and the same depth were selected and prepared into 38*40mm plugs by sand wire cutting technology to obtain standard plug cores. The plug core permeability test was completed according to the standard. Then, the tested standard plug cores were prepared into rectangular cores with a cross-sectional area of ​​25*25mm. The rectangular cores were then plunged using a special core casting mold to cast into 38*40mm test plug cores. The permeability test was performed again according to the standard, and then the secondary permeability test data were compared and analyzed. The results are shown in Table 1.

[0045] Table 1: Comparison of permeability test data between plug core and cuboid core

[0046]

[0047] It can be seen from the data in Table 1 that the relative error of the permeability of the test plunger core (cast plunger core) of the present invention and the standard plunger core is between 3.8% and 20.3%, with an average error of 8.9%; while the error of the permeability of individual cores is relatively large, and the reason for the difference in permeability between the two types of cores is mainly due to the heterogeneity of the samples. Figure 3It can be seen that the correlation coefficient of the permeability of the experimental plunger core and the plunger-shaped core reached 0.9824, indicating that the permeabilities tested by the two methods have a high linear correlation. Therefore, the method of the present invention can be used to prepare fragile cores for permeability testing, which can meet the test requirements, improve test efficiency, and reduce the test cycle.

[0048] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for testing the permeability of fragile cores, characterized in that: The following steps are involved: S1. Cut and grind the fragile rock sample into a regular rectangular core; S2, measure the size of the cuboid core; S3, placing the rectangular core in a core casting mold; S4, injecting epoxy resin glue into the core casting mold, evacuating the residual air inside the core casting mold, and naturally curing; S5. After the curing is completed, demoulding is performed to obtain a plunger core for testing; S6. Use a drying box to dry the moisture inside the core; S7. Place the dried test plunger core into the core holder of the gas permeability tester, perform a permeability test on the test plunger core, and record the test results.

2. The fragile core permeability testing method according to claim 1, characterized in that: The step S2 measures the size of the rectangular core using a vernier caliper, and the size includes the length, height and width of the rectangular core.

3. The fragile core permeability testing method according to claim 1, characterized in that: The minimum graduation value of the vernier caliper is 0.01 mm.

4. The fragile core permeability testing method according to claim 1, characterized in that: The length, width and height of the core casting mold are all greater than the rectangular core.

5. The fragile core permeability testing method according to claim 1, characterized in that: The inner diameter of the cylinder of the core casting mold is 1 inch or 1.5 inches.

6. The fragile core permeability testing method according to claim 1, characterized in that: The injection amount of the epoxy resin glue in step S4 is enough to cover the height of the rectangular parallelepiped rock core.

7. The fragile core permeability testing method according to claim 1, characterized in that: In step S4, a vacuum machine is used for evacuation, the evacuation time is 2 to 3 hours, and the natural curing time is 10 hours.

8. The fragile core permeability testing method according to claim 1, characterized in that: The rectangular parallelepiped core in the test plunger core of step S5 is tightly combined with the epoxy resin glue without gaps, and there are no concave and convex bubbles on the surface of the test plunger core; the test plunger core has a temperature resistance of 120° C. and a compressive strength greater than 10 MPa.

9. The fragile core permeability testing method according to claim 1, characterized in that: The drying temperature in step S6 is 90° C. and the drying time is 10 hours.

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