Method for quantitatively evaluating diffusivity of gas in rock

Abstract

The invention relates to the technical field of geological survey, and provides a method for quantitatively evaluating the diffusivity of gas in rock, which comprises the following steps: under the conditions of target temperature and pressure, introducing a gas a with a preset molar weight into a first diffusion chamber positioned on one side of a rock sample, introducing a gas b with a preset molar weight into a second diffusion chamber positioned on the other side of the rock sample, at least one of the gas a and the gas b is gas to be detected; detecting the molar weight of the gas b diffused into the first diffusion chamber and the molar weight of the gas a diffused into the second diffusion chamber at set time intervals; and determining the diffusion index of the to-be-detected gas based on a pre-constructed diffusion index model and the molar concentration change condition of the gas a and the gas b between the first diffusion chamber and the second diffusion chamber. According to the technical scheme, the diffusivity of the gas in the rock can be more objectively, scientifically and quantitatively represented, and reliable geological theoretical data is provided for the sealing performance of a cover layer in a resource gas reservoir and gas storage medium evaluation.

Description

Technical Field

[0001] The invention relates to the technical field of geological survey, and in particular to a method for quantitatively evaluating the diffusion capacity of gas in rocks. Background Art

[0002] Whether it is traditional natural gas, green and low-carbon natural hydrogen resources, or rare helium resources, they are all energy resources that have accumulated in underground rock formations over a long geological history. In the process of searching for such resources, it is necessary to evaluate the rocks that seal these gases. Quantitative characterization of the diffusion capacity of gases in the formation is an important parameter for evaluating the sealing performance of gas reservoir caprocks, gas preservation conditions, and gas resource potential.

[0003] At present, the evaluation of the diffusion capacity of gas in rocks at home and abroad is to obtain the diffusion coefficient of the gas by using the change in the volume content of gas diffusion in the isobaric diffusion experiment, that is, using a gas chromatograph to measure the volume concentration of the gas to be tested in two diffusion chambers, and using the measured concentration combined with Fick's law to calculate.

[0004] However, using the above-mentioned related technology, no matter which two gases are diffused at equal pressure, the gas diffusion coefficients obtained by this method are equal. Such calculation results cannot truly reflect the diffusion capacity of the gas, thereby affecting the evaluation results.

[0005] Therefore, how to objectively and scientifically quantitatively characterize the gas diffusion capacity is an important issue that needs to be solved urgently. Summary of the invention

[0006] The present invention provides a method for quantitatively evaluating the diffusion capacity of gas in rock, which is used to solve the problem of inaccurate gas diffusion coefficient measured by isobaric diffusion experiment in the prior art, and can quantitatively characterize the diffusion capacity of gas in rock more objectively and scientifically.

[0007] The present invention provides a method for quantitatively evaluating the diffusion capacity of gas in rock, which is characterized by comprising the following steps: Under target temperature and pressure conditions, a preset molar amount of gas a is introduced into a first diffusion chamber located on one side of the rock sample, and a preset molar amount of gas b is introduced into a second diffusion chamber located on the other side, wherein at least one of gas a and gas b is the gas to be tested; At every set time interval, detecting the molar amount of gas b diffused into the first diffusion chamber and the molar amount of gas a diffused into the second diffusion chamber; The diffusion index I of the gas to be measured is determined based on a pre-constructed diffusion index model and the change in molar concentration of gas a and gas b between the first diffusion chamber and the second diffusion chamber.

[0008] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, the diffusion index model is constructed based on the mass flux and molar concentration gradient of the gas to be measured and combined with Fick's first law.

[0009] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, the diffusion index model is: ; in, is the molar concentration difference of the gas to be measured between the first diffusion chamber and the second diffusion chamber at the initial moment; The first diffusion chamber and the second diffusion chamber are The molar concentration difference of the gas to be measured at each moment; is the volume of the first diffusion chamber; is the volume of the second diffusion chamber; is the initial moment; S is the cross-sectional area of ​​the rock sample to be tested; H is the length of the rock sample to be tested.

[0010] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, in the diffusion index model, the volume of the first diffusion chamber is and the volume of the second diffusion chamber Is a fixed value.

[0011] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, the initial time is set to 0, and the molar amount of the gas to be measured in the diffusion chamber on the other side at the initial time is set to 0, then the diffusion index model is: ; in, is the initial molar amount of the gas to be measured; The gas to be tested is The molar amount diffused at any given moment.

[0012] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, in the diffusion index model, the volume of the first diffusion chamber is and the volume of the second diffusion chamber equal.

[0013] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, the diffusion index model is: ; Wherein, V is the volume of the first diffusion chamber and the second diffusion chamber.

[0014] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, the diffusion index of the gas to be tested is determined based on a pre-constructed diffusion index model and the changes in the molar concentrations of gas a and gas b in the first diffusion chamber and the second diffusion chamber, comprising: Based on the molar amount of the gas to be measured at different times and the diffusion index model, the linear relationship between C and t is determined; The final diffusion index I was obtained by fitting based on the linear relationship between C and t.

[0015] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, the molar amount of the gas to be measured is obtained by measuring the volume fraction of the gas to be measured by a gas chromatograph.

[0016] According to a method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, under rational gas conditions, the volume fraction and the solvometric value satisfy the following relationship: ; in, for The volume fraction of gas a in the first diffusion chamber at a certain moment; for The volume fraction of gas a in the second diffusion chamber at the moment; is the molar amount of gas a in the first diffusion chamber at the initial moment; for The molar amount of gas a diffused into the second diffusion chamber at time instant; is the molar amount of gas b in the second diffusion chamber at the initial moment; for The molar amount of gas b diffused into the first diffusion chamber at time t

[0017] The method for quantitatively evaluating the diffusion capacity of gas in rock provided by the present invention, compared with volume concentration, molar concentration, as a dimensioned physical quantity, can more intuitively and accurately reflect the diffusion flux of gas in rock, thereby being able to quantitatively characterize the diffusion capacity of gas in rock more objectively and scientifically, and providing reliable geological theoretical data for the sealing property of caprocks in resource gas reservoirs and the evaluation of gas storage media, which is of great significance to the study of the reservoir-forming mechanism of resource gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a schematic flow chart of a method for quantitatively evaluating the diffusion capacity of gas in rock provided by an embodiment of the present invention.

[0020] Figure 2 It is a scatter plot of C and time t in the hydrogen and argon diffusion experiment provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In order to facilitate understanding of the method provided by the present invention for quantitatively evaluating the diffusion ability of gas in rocks, its application background is first introduced. For gas resources such as natural gas, natural hydrogen and helium stored in formations, quantitative characterization of the diffusion ability of gas in formations is an important parameter for evaluating the sealing performance of gas reservoir caprocks, gas preservation conditions and gas resource potential.

[0023] In the related technology, the evaluation of the diffusion capacity of gas in rocks at home and abroad is to obtain the diffusion coefficient of the gas by utilizing the change in volume content of gas diffusion in isobaric diffusion experiments (for details, please refer to the current industry standard "SY / T6129-2016, Determination of Diffusion Coefficient of Hydrocarbon Gas in Rocks").

[0024] In the experiment, a diffusion chamber is set in the isobaric gas device, and the rock to be tested divides the diffusion chamber into two air chambers. and , at a specific temperature and pressure, Gas a, such as methane, hydrogen, etc., is introduced into the gas chamber. A gas b, such as nitrogen or argon, is introduced into the gas, and the gas diffused to the The volume concentration of gas b and its diffusion to The volume concentration of gas a in the sample is calculated, and the diffusion coefficient of the gas to be measured is obtained based on the volume concentration change and combined with Fick's first law.

[0025] However, in actual experiments, the inventors found that using the above test method, no matter which two gases are used for isobaric diffusion and the gas diffusion coefficients obtained by this method are equal, it is set at the initial moment, the gas chamber The volume content of gas a in the gas chamber is 100%. The volume content of gas b in the gas chamber is 100%. At a certain moment, the gas chamber is measured by chromatograph. The content of gas b in the gas chamber is x%. If the content of gas a in the air chamber is y%, then The content of gas a in the gas chamber is (100-x)%. The content of gas b in the gas chamber is (100-y)%. At this time, the concentration difference of gas a in the two gas chambers is calculated to be (100-xy)%, and the concentration difference of gas b is (100-xy)%. The concentration differences of gas a and gas b between the two gas chambers are equal.

[0026] Specifically, taking methane and nitrogen as examples, the test results of "SY / T6129-2016, Determination of Diffusion Coefficient of Hydrocarbon Gas in Rocks" are shown in the following table: Table 1, diffusion coefficient test report one;

[0027] Table 2, Diffusion coefficient test report 2;

[0028] It can be seen from the above two sets of test results that at any time, the concentration difference of the two gases in the two diffusion chambers is equal. Therefore, according to "SY / T6129-2016, Determination of Diffusion Coefficient of Hydrocarbon Gas in Rocks", the diffusion coefficients of the two gases calculated are equal. However, there are two completely different gases in the two diffusion chambers. It is obviously unreasonable to say that the diffusion coefficients of any two completely different gases in the rock sample are equal. In other words, the above experimental method will only be accurate when the diffusion coefficients of the two gases in the rock sample are equal or very close. However, obviously, the diffusion coefficients of the two gases in the rock sample are unknown.

[0029] In addition, in actual tests, since the gases to be tested (such as methane, hydrogen, helium, etc.) are resource gases actually stored underground, the main purpose of the experiment is to evaluate the rocks that seal these gases. Therefore, researchers generally only focus on the concentration difference and diffusion coefficient of the gases to be tested, thereby measuring the diffusion capacity of the resource gases in the sealing rock formation. The concentration difference, diffusion coefficient and the relationship between the diffusion coefficient of the other gas used as an auxiliary gas and the diffusion coefficient of the gas to be tested are often ignored, resulting in the calculation results not being able to truly reflect the diffusion capacity of the gas, which in turn affects the evaluation results.

[0030] Therefore, how to objectively and scientifically quantitatively characterize the gas diffusion capacity is an important issue that needs to be solved urgently.

[0031] Based on the above technical problems and discoveries, the present invention provides a method for quantitatively evaluating the diffusion ability of gas in rocks, which can quantitatively characterize the diffusion ability of gas in rocks more objectively and scientifically, and provide reliable geological theoretical data for the sealing of cap rocks in resource gas reservoirs and the evaluation of gas storage media, which is of great significance to the study of the resource gas accumulation mechanism.

[0032] Combine the following Figure 1-Figure 2 The method of the present invention for quantitatively evaluating the diffusion capacity of gas in rock is described.

[0033] Reference Figure 1 , a method for quantitatively evaluating the diffusion capacity of gas in rock, comprising the following steps: Step 101. Under target temperature and pressure conditions, a preset molar amount of gas a is introduced into a first diffusion chamber on one side of a rock sample, and a preset molar amount of gas b is introduced into a second diffusion chamber on the other side, and at least one of gas a and gas b is the gas to be tested.

[0034] Step 102 : Detecting the molar amount of gas b diffused into the first diffusion chamber and the molar amount of gas a diffused into the second diffusion chamber at every set time interval.

[0035] Step 103: Determine the diffusion index of the gas to be measured based on the pre-constructed diffusion index model and the change in molar concentration of gas a and gas b between the first diffusion chamber and the second diffusion chamber.

[0036] Specifically, when the test is actually carried out, the rock sample is placed in the diffusion chamber of the isobaric gas device. The rock sample divides the diffusion chamber of the isobaric gas device into the above-mentioned first diffusion chamber and the second diffusion chamber. Gas a, such as hydrogen, methane, helium and other resource gases, is introduced into the first diffusion chamber, and gas b, such as nitrogen, argon and other chemically stable gases, is introduced into the diffusion chamber on the other side. At preset time intervals, the molar amount of gas b diffused into the first diffusion chamber and the molar amount of gas a diffused into the second diffusion chamber are detected, and the diffusion index is obtained based on the molar concentration gradient of gas a and gas b between the first diffusion chamber and the second diffusion chamber and a pre-constructed diffusion index model.

[0037] At the initial moment, the molar concentration of gas a in the first diffusion chamber is ,in, is the molar amount of gas a, is the volume of the first diffusion chamber; the molar concentration of gas b in the second diffusion chamber is ,in, is the molar amount of gas b, is the volume of the second diffusion chamber.

[0038] At a certain moment, the molar amount of gas a diffused from the first diffusion chamber to the second diffusion chamber is x, and the molar amount of gas b diffused from the second diffusion chamber to the first diffusion chamber is y. Then the molar concentration of gas a in the first diffusion chamber is , the molar concentration of gas a in the second diffusion chamber is , the molar concentration of gas b in the second diffusion chamber is , the molar concentration of gas b in the first diffusion chamber is , the molar concentration difference of gas a between the first diffusion chamber and the second diffusion chamber is - , and the molar concentration difference of gas b between the first diffusion chamber and the second diffusion chamber is , the diffusion index is obtained according to the change in molar concentration and the diffusion index model.

[0039] Compared with volume concentration, molar concentration, as a dimensioned physical quantity, can more intuitively and accurately reflect the diffusion flux of gas in rocks, and thus can more objectively and scientifically quantitatively characterize the diffusion capacity of gas in rocks, providing reliable geological theoretical data for the sealing of cap rocks in resource-type gas reservoirs and the evaluation of gas storage media, which is of great significance to the study of the reservoir-forming mechanism of resource-type gas.

[0040] In one embodiment of the present invention, the diffusion index model is constructed based on the mass flux and molar concentration gradient of the gas to be measured in combination with Fick's first law.

[0041] Specifically, the construction of the diffusion index model includes the following steps.

[0042] The rock sample is cut into a cylinder with a bottom cross-sectional area of ​​S and a height of H. The gas diffusion amount passing through the rock sample within a certain period of time is measured in two diffusion chambers, and then the gas diffusion index is calculated based on these measured values ​​according to Fick's first law. According to Fick's first law, the flux from the high concentration area to the low concentration area is proportional to the concentration gradient. For one-dimensional diffusion, it can be regarded that the amount of material flux in the x direction (that is, the height direction of the rock to be measured) is proportional to the concentration gradient at that location. The specific formula is as follows (it should be noted that the units in the formula are determined according to the actual experimental situation):

[0043] Where N is the amount of diffused gas, mol; S is the bottom cross-sectional area of ​​the rock sample, cm 3 ; t is the duration of the diffusion test, s; I is the gas diffusion index, cm 2 / s; is the molar concentration difference of the diffused gas, mol / ml; H is the height of the rock sample, that is, the diffusion distance of the diffused gas, cm.

[0044] The volume of the first diffusion chamber is set to , the volume of the second diffusion chamber is , then after diffusion for time t, the molar concentrations of the gas to be measured in the first diffusion chamber and the second diffusion chamber are and , that is, .

[0045] According to the principle of conservation of mass, ; Substituting and simplifying, we can get:

[0046] At the initial moment, the molar concentration difference of the gas to be measured between the first diffusion chamber and the second diffusion chamber is ,go through After time diffusion, the molar concentration difference of the gas to be measured between the first diffusion chamber and the second diffusion chamber is , integrating the above formula yields: ,but .

[0047] The relationship between the change in molar concentration of the gas to be measured between the two diffusion chambers and the test time can be measured through the above diffusion index model.

[0048] In one embodiment of the present invention, in a diffusion test, the pressure between the first diffusion chamber and the second diffusion chamber is equal under ideal conditions. However, due to the different diffusion capabilities of gas a and gas b, a slight pressure difference will inevitably occur in the first diffusion chamber and the second diffusion chamber as the experiment proceeds. Therefore, under ideal conditions, the volumes of the first diffusion chamber and the second diffusion chamber can be adjusted as the experiment proceeds to ensure that the diffusion chambers on both sides are in an isobaric state.

[0049] However, the above method will undoubtedly increase the difficulty of the experiment. Considering that the pressure difference between the two diffusion chambers is very small and has limited influence on the results of the diffusion experiment, in the diffusion exponential model, the volume of the first diffusion chamber is and the volume of the second diffusion chamber Is a fixed value.

[0050] In one embodiment of the present invention, the initial time is set to 0, and the molar amount of the gas to be measured in the diffusion chamber on the other side at the initial time is 0, then the diffusion index model is: .

[0051] in, is the initial molar amount of the gas to be measured, The gas to be tested is The molar amount diffused at any given moment.

[0052] Through the above diffusion index model, the relationship between the change in the molar amount of the gas to be measured between the two diffusion chambers and the test time can be measured.

[0053] In one embodiment of the present invention, in order to further improve the convenience of the experiment, in the above diffusion index model, the volume of the first diffusion chamber is The volume of the second diffusion chamber If they are equal, then the diffusion exponential model is:

[0054] Where V is the volume of the first diffusion chamber and the second diffusion chamber, and C is .

[0055] By measuring The molar amount of the gas to be measured at any moment can be obtained The value of the gas C to be measured at the moment.

[0056] In one embodiment of the present invention, step 103 includes the following steps: Step S1: Determine the linear relationship between C and t based on the molar amount of the gas to be measured diffused at different times and the diffusion index model.

[0057] Step S2: obtaining the final diffusion index through fitting based on the linear relationship between C and t.

[0058] Specifically, by measuring different The molar amount of the gas to be measured at each moment can be used to obtain the corresponding The value of C of the gas to be measured at the moment is used to fit the data using the least squares method to obtain the linear relationship between C and t, and the slope is the final diffusion index.

[0059] The following will take hydrogen and argon as specific examples, conduct isobaric diffusion experiments under the conditions of 3MPa and 25°C, and take the calculation of hydrogen diffusion index as an example. Substitute the collected data into the formula and obtain the following table through calculation.

[0060] Table 3, Diffusion index test report of hydrogen and argon.

[0061]

[0062] Reference Figure 2 , make a scatter plot of time t and C, and use the least squares method to perform linear fitting to get the slope =3.78683E-05(cm 2 / s), determination coefficient =0.9771.

[0063] In one embodiment of the present invention, the molar amount of the gas to be measured is obtained by measuring the volume fraction of the gas to be measured by a gas chromatograph.

[0064] At the initial moment, the molar amount of gas a in the first diffusion chamber is , the molar amount of gas b in the second diffusion chamber is , suppose after After diffusion of time, the molar amount of gas a entering the second diffusion chamber from the first diffusion chamber is , the molar amount of gas b entering the first diffusion chamber from the second diffusion chamber is The volume fraction of gas a in the first diffusion chamber is measured by gas chromatograph. , the volume fraction of gas a in the second diffusion chamber is , then under ideal conditions, the molar amount and volume fraction satisfy the following relationship:

[0065] Finally, the molar amount of gas a diffusion is obtained as: ; The molar amount of gas b diffused is: .

[0066] By adopting the above scheme, the molar amount of the gas to be measured can be measured by using a gas chromatograph.

[0067] It is to be understood that, without mutual contradiction, those skilled in the art may combine and combine the different embodiments or examples and the features of the different embodiments or examples described in this specification.

[0068] According to the method for quantitatively evaluating the diffusion capacity of gas in rock provided by the embodiment of the present invention, at the initial moment, the molar concentration of gas a in the first diffusion chamber is ,in, is the molar amount of gas a, is the volume of the first diffusion chamber; the molar concentration of gas b in the second diffusion chamber is ,in, is the molar amount of gas b, is the volume of the second diffusion chamber.

[0069] At a certain moment, the molar amount of gas a diffused from the first diffusion chamber to the second diffusion chamber is x, and the molar amount of gas b diffused from the second diffusion chamber to the first diffusion chamber is y. Then the molar concentration of gas a in the first diffusion chamber is , the molar concentration of gas a in the second diffusion chamber is , the molar concentration of gas b in the second diffusion chamber is , the molar concentration of gas b in the first diffusion chamber is , the molar concentration difference of gas a between the first diffusion chamber and the second diffusion chamber is - , and the molar concentration difference of gas b between the first diffusion chamber and the second diffusion chamber is The diffusion index is obtained according to the change in molar concentration and the diffusion index model. Compared with volume concentration, molar concentration, as a dimensioned physical quantity, can more intuitively and accurately reflect the diffusion flux of gas in rocks, thereby being able to quantitatively characterize the diffusion capacity of gas in rocks more objectively and scientifically, providing reliable geological theoretical data for the sealing of caprocks in resource-type gas reservoirs and the evaluation of gas storage media, which is of great significance for the study of the reservoir-forming mechanism of resource-type gas.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for quantitatively evaluating the diffusion capacity of gas in rock, characterized in that: The following steps are involved: Under target temperature and pressure conditions, a preset molar amount of gas a is introduced into a first diffusion chamber located on one side of the rock sample, and a preset molar amount of gas b is introduced into a second diffusion chamber located on the other side, wherein at least one of gas a and gas b is the gas to be tested; At every set time interval, detecting the molar amount of gas b diffused into the first diffusion chamber and the molar amount of gas a diffused into the second diffusion chamber; The diffusion index I of the gas to be measured is determined based on a pre-constructed diffusion index model and the change in molar concentration of gas a and gas b between the first diffusion chamber and the second diffusion chamber.

2. The method for quantitatively evaluating the diffusion capacity of gas in rock according to claim 1, characterized in that: The diffusion index model is constructed based on the mass flux and molar concentration gradient of the gas to be measured and combined with Fick's first law.

3. The method for quantitatively evaluating the diffusion capacity of gas in rock according to claim 2, characterized in that: The diffusion index model is: ； in, is the molar concentration difference of the gas to be measured between the first diffusion chamber and the second diffusion chamber at the initial moment; The molar concentration difference of the gas to be measured between the first diffusion chamber and the second diffusion chamber at time instant; is the volume of the first diffusion chamber; is the volume of the second diffusion chamber; is the initial moment; S is the cross-sectional area of ​​the rock sample to be tested; H is the length of the rock sample to be tested.

4. The method for quantitatively evaluating the diffusion capacity of gas in rock according to claim 3, characterized in that: In the diffusion exponential model, the volume of the first diffusion chamber is and the volume of the second diffusion chamber Is a fixed value.

5. The method for quantitatively evaluating the diffusion capacity of gas in rock according to claim 4, characterized in that: The initial time is set to 0, and the molar amount of the gas to be measured in the diffusion chamber on the other side at the initial time is set to 0, then the diffusion index model is: ； in, is the initial molar amount of the gas to be measured; The gas to be tested is The molar amount diffused at any given moment.

6. The method for quantitatively evaluating the diffusion capacity of gas in rock according to claim 5, characterized in that: In the diffusion exponential model, the volume of the first diffusion chamber is and the volume of the second diffusion chamber equal.

7. The method for quantitatively evaluating the diffusion capacity of gas in rock according to claim 6, characterized in that: The diffusion index model is: ； Wherein, V is the volume of the first diffusion chamber and the second diffusion chamber; C is .

8. The method for quantitatively evaluating the diffusion capacity of gas in rock according to claim 7, characterized in that: The method of determining the diffusion index of the gas to be measured based on the pre-constructed diffusion index model and the molar concentration changes of the gas a and the gas b in the first diffusion chamber and the second diffusion chamber includes: Based on the molar amount of the gas to be measured at different times and the diffusion index model, the linear relationship between C and t is determined; The final diffusion index I was obtained by fitting based on the linear relationship between C and t.

9. The method for quantitatively evaluating the diffusion capacity of gas in rock according to any one of claims 1 to 8, characterized in that: The molar amount of the gas to be measured is obtained by measuring the volume fraction of the gas to be measured by a gas chromatograph.

10. The method for quantitatively evaluating the diffusion capacity of gas in rock according to claim 9, characterized in that: Under rational gas conditions, the volume fraction and the molar amount satisfy the following relationship: ； in, for The volume fraction of gas a in the first diffusion chamber at a certain moment; for The volume fraction of gas a in the second diffusion chamber at the moment; is the molar amount of gas a in the first diffusion chamber at the initial moment; for The molar amount of gas a diffused into the second diffusion chamber at time instant; is the molar amount of gas b in the second diffusion chamber at the initial moment; for The molar amount of gas b diffused into the first diffusion chamber at time t

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