A permeability testing method suitable for soft coal samples

Abstract

This invention discloses a permeability testing method suitable for soft coal samples, comprising the following steps: (1) scanning the soft coal sample to be prepared into a digital model on a computer, and measuring the maximum length Lmax and the minimum cross-sectional area Amin of the vertical soft coal sample model; (2) placing the soft coal sample into a cylindrical inner hole mold using a rope; (3) pouring transparent casting material into the cylindrical inner hole of the mold; (4) removing the prepared columnar coal sample; (5) measuring the effective seepage length L of the coal sample, calculating the tilt angle α of the soft coal sample using L and Lmax, and calculating the minimum effective seepage cross-sectional area A using angle α and the minimum cross-sectional area Amin; (6) opening holes at the top and bottom of the prepared columnar coal sample to the soft coal sample, placing the columnar coal sample into a triaxial seepage test system, and measuring the permeability; (7) calculating the permeability of the coal sample based on the experimental parameters; this method can effectively test the permeability of soft coal samples.

Description

Technical Field

[0001] This invention relates to the field of permeability testing of coal samples, and more specifically to a permeability testing method suitable for soft coal samples. Background Technology

[0002] To measure the mechanical and permeability parameters of coal, specialized instruments are required. These instruments can only work with columnar coal samples, especially those that require the application of confining pressure, such as the existing triaxial flow test system.

[0003] Current methods for preparing columnar coal samples generally involve selecting large coal samples with fewer fissures and relatively intact structure, then sending them into a coal sampling chamber for drilling using a vertical coring machine. During drilling, the coal sample is usually fixed in place, and the rotation speed must be strictly controlled to ensure uniform drilling by the drill bit and maintain the integrity of the coal core. After coring, an automatic double-sided rock grinder is used to cut the cored coal sample into columnar sections and polish them smooth, ensuring that both ends are parallel. The standard height-to-diameter ratio of a columnar coal sample is 2:1.

[0004] However, there are also many soft coal bodies in coal mines. Due to the action of tectonic stress, the original structure and texture of these coals are severely damaged by cracks, resulting in structural changes such as fragmentation, wrinkling, and polishing. This makes the existing core-taking columnar coal sample preparation method unusable here, and it cannot effectively test the permeability of soft media. Therefore, there is an urgent need to provide a permeability testing method suitable for soft coal samples. Summary of the Invention

[0005] In view of the above-mentioned technical deficiencies, the purpose of this invention is to provide a permeability testing method suitable for soft coal samples.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a permeability testing method suitable for soft coal samples, comprising the following steps:

[0008] (1) Use a 3D scanner to scan the soft coal sample to be made into a digital model on the computer, import it into CAD software and measure the maximum length Lmax of the vertical soft coal sample model and the area Amin of its minimum cross section.

[0009] (2) Use a rope to attach the top of the soft coal sample from step (1), and use the rope to put the soft coal sample into the mold with the cylindrical inner hole.

[0010] (3) Pour transparent casting material that is not adsorbed by the coal sample and does not react with it into the cylindrical inner hole of the mold in step (2);

[0011] (4) After the transparent material poured in step (3) has cooled, open the mold and take out the completed columnar coal sample containing the transparent poured material.

[0012] (5) Use a laser rangefinder to measure the effective seepage length L of the soft coal sample inside the columnar coal sample prepared in step (4). Record the upper and lower limits where the laser cannot penetrate the columnar coal body. The distance between the two points is the effective seepage length L. Calculate the inclination angle α of the soft coal sample using L and Lmax, and calculate the minimum effective seepage cross-sectional area A using angle α and the minimum cross-sectional area Amin. The calculation formula is as follows:

[0013]

[0014] (6) Make holes at the top and bottom of the columnar coal sample prepared in step (4) to the soft coal sample to obtain a columnar coal sample for analyzing mechanical and permeability parameters; put the columnar coal sample into the triaxial flow test system, introduce gas flow at the opening position, put on heat shrink tubing, and measure the permeability.

[0015] (7) Based on the experimental parameters from step (6), the permeability of the coal sample is calculated using the following formula:

[0016]

[0017] In the formula, K is the coal permeability under each gas pressure, in meters. 2 p2 is the inlet pressure, MPa; p1 is the outlet pressure, MPa; p0 is atmospheric pressure, taken as 0.1 MPa; q is the gas flow rate, m³ / s. 3 / s; μ is the dynamic viscosity of the gas at the measurement temperature, MPa·s; L is the effective seepage length of the coal sample, m; A is the effective seepage cross-sectional area of ​​the coal sample, m². 2 .

[0018] Preferably, the mold in step (2) includes a left mold and a right mold, which are fastened together by bolts.

[0019] Preferably, the ratio of the inner diameter to the height of the cylindrical inner hole in step (2) is less than 1:2.

[0020] Preferably, in step (2), when placing the soft coal sample into the cylindrical inner hole, the center of the soft coal sample is placed at half the height of the cylindrical inner hole.

[0021] Preferably, the transparent casting material in step (3) is liquid polyvinyl chloride.

[0022] The beneficial effects of this invention are as follows:

[0023] This invention can prepare columnar coal samples from soft coal samples for permeability testing without altering the properties of the soft coal samples themselves. This invention can effectively test the permeability of soft coal samples. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the mold structure according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the arrangement of the columnar coal sample and the aeration path during permeability testing according to an embodiment of the present invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1. Soft coal sample; 2. Aeration path. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This embodiment provides a permeability testing method suitable for soft coal samples, including the following steps:

[0031] (1) Use a 3D scanner to scan the soft coal sample to be made into a digital model on the computer, import it into CAD software and measure the maximum length Lmax of the vertical soft coal sample model and the area Amin of its minimum cross section.

[0032] (2) Use a rope to attach the top of the soft coal sample from step (1), and use the rope to put the soft coal sample into the mold with the cylindrical inner hole.

[0033] (3) Pour transparent casting material that is not adsorbed by the coal sample and does not react with it into the cylindrical inner hole of the mold in step (2);

[0034] (4) After the transparent material poured in step (3) has cooled, open the mold and take out the completed columnar coal sample containing the transparent poured material.

[0035] (5) Use a laser rangefinder to measure the effective seepage length L of the soft coal sample inside the columnar coal sample prepared in step (4). Record the upper and lower limits where the laser cannot penetrate the columnar coal body. The distance between the two points is the effective seepage length L. Calculate the inclination angle α of the soft coal sample using L and Lmax, and calculate the minimum effective seepage cross-sectional area A using angle α and the minimum cross-sectional area Amin. The calculation formula is as follows:

[0036]

[0037] (6) Make holes at the top and bottom of the columnar coal sample prepared in step (4) to the soft coal sample to obtain a columnar coal sample for analyzing mechanical and permeability parameters; put the columnar coal sample into the triaxial flow test system, introduce gas flow at the opening position, put on heat shrink tubing, and measure the permeability.

[0038] (7) Based on the experimental parameters from step (6), the permeability of the coal sample is calculated using the following formula:

[0039]

[0040] In the formula, K is the coal permeability under each gas pressure, in meters. 2 p2 is the inlet pressure, MPa; p1 is the outlet pressure, MPa; p0 is atmospheric pressure, taken as 0.1 MPa; q is the gas flow rate, m³ / s. 3 / s; μ is the dynamic viscosity of the gas at the measurement temperature, MPa·s; L is the effective seepage length of the coal sample, m; A is the effective seepage cross-sectional area of ​​the coal sample, m². 2 .

[0041] like Figure 1 As shown, the mold in step (2) includes a left mold and a right mold. The left mold and the right mold are fastened by bolts. The ratio of the inner diameter to the height of the cylindrical inner hole in step (2) is less than 1:2, so that when testing the permeability later, the height can be changed by cutting the two ends of the column to make a columnar coal sample with an inner diameter to height ratio of 1:2.

[0042] The mold used in this embodiment is a mold with openings at both ends, which is well known to those skilled in the art and will not be described in detail here.

[0043] Step (2) When placing the soft coal sample into the cylindrical inner hole, place the center of the soft coal sample at half the height of the cylindrical inner hole. In specific operation, fix the end of the rope away from the coal sample to a support that can be erected on the upper part of the mold, which is well known to those skilled in the art. First, try to release the soft coal sample outside the mold. After the center of the soft coal sample reaches the center position of the mold's central hole, mark the rope and fix the marked position of the rope to the support. Then place the support on the mold. In this embodiment, the center of the soft coal sample refers to the center of the soft coal sample in vertical height after the rope is vertically suspended.

[0044] The transparent casting material in step (3) is liquid polyvinyl chloride.

[0045] like Figure 2 The diagram shows the arrangement of the columnar coal sample and the gas passage during permeability testing in this embodiment. In this embodiment, the outlet pressure p1 is fixed at 2 MPa, the experimental temperature is 30℃, the dynamic viscosity of methane at this temperature is 11.175 × 10⁻⁶ MPa·s, the atmospheric pressure is 0.1 MPa, the effective seepage length L is 0.072 m, and the effective seepage cross-sectional area A is 1.018 × 10⁻⁶ m. -3 m 2 .

[0046] The specific test results are shown in the table below:

[0047] <![CDATA[Downstream pressure p2 / MPa]]> <![CDATA[Gas flow rate q / (m 3 / s)]]> <![CDATA[Permeability K / m 2 > 7.7199 31 <![CDATA[8.814×10 -5 ]]> 8.0297 32.6 <![CDATA[8.521×10 -5 ]]> 8.2896 33.8 <![CDATA[8.256×10 -5 ]]> 8.3960 34.1 <![CDATA[8.107×10 -5 ]]> 8.4343 34.5 <![CDATA[8.123×10 -5 ]]>

[0048] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A permeability testing method suitable for soft coal samples, characterized in that, Includes the following steps: (1) Use a 3D scanner to scan the soft coal sample to be made into a digital model on the computer, import it into CAD software and measure the maximum length Lmax of the vertical soft coal sample model and the area Amin of its minimum cross section. (2) Use a rope to attach the top of the soft coal sample from step (1), and use the rope to put the soft coal sample into the mold with the cylindrical inner hole. (3) Pour transparent casting material that is not adsorbed by the coal sample and does not react with it into the cylindrical inner hole of the mold in step (2); (4) After the transparent material poured in step (3) has cooled, open the mold and take out the completed columnar coal sample containing the transparent poured material. (5) Use a laser rangefinder to measure the effective seepage length L of the soft coal sample inside the columnar coal sample prepared in step (4). Record the upper and lower limits where the laser cannot penetrate the columnar coal body. The distance between the two points is the effective seepage length L. Calculate the inclination angle α of the soft coal sample using L and Lmax, and calculate the minimum effective seepage cross-sectional area A using angle α and the minimum cross-sectional area Amin. The calculation formula is as follows: (6) Make holes at the top and bottom of the columnar coal sample prepared in step (4) to the soft coal sample to obtain a columnar coal sample for analyzing mechanical and permeability parameters; put the columnar coal sample into the triaxial flow test system, introduce gas flow at the opening position, put on heat shrink tubing, and measure the permeability. (7) Based on the experimental parameters from step (6), the permeability of the coal sample is calculated using the following formula: In the formula, K is the coal permeability under each gas pressure, in meters. 2 p2 is the inlet pressure, MPa; p1 is the outlet pressure, MPa; p0 is atmospheric pressure, taken as 0.1 MPa; q is the gas flow rate, m³ / s. 3 / s; μ is the dynamic viscosity of the gas at the measurement temperature, MPa·s; L is the effective seepage length of the coal sample, m; A is the effective seepage cross-sectional area of ​​the coal sample, m². 2 .

2. The permeability testing method for soft coal samples as described in claim 1, characterized in that, The mold in step (2) includes a left mold and a right mold, which are fastened together by bolts.

3. The permeability testing method for soft coal samples as described in claim 1, characterized in that, The ratio of the inner diameter to the height of the cylindrical inner hole in step (2) is less than 1:

2.

4. The permeability testing method for soft coal samples as described in claim 1, characterized in that, Step (2) When placing the soft coal sample into the cylindrical inner hole, place the center of the soft coal sample at half the height of the cylindrical inner hole.

5. The permeability testing method for soft coal samples as described in claim 1, characterized in that, The transparent casting material in step (3) is liquid polyvinyl chloride.

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