A method for calculating the contribution ratio of coal-rock gas mixture at different maturity levels

Abstract

This invention discloses a method for calculating the contribution ratio of coal-rock gas mixtures at different maturity levels. The method comprises the following steps: S1, establishing a dynamic model for identifying the mixing ratio of mixed-source gas; S2, taking a specific natural gas extraction area as the research object, obtaining several coal-rock gas and mudstone gas samples, and measuring the methane and ethane carbon isotopes, as well as the aridity coefficient; S3, taking several unoxidized pure coal-rock and pure mudstone samples, and measuring the vitrinite reflectance; S4, performing correlation analysis based on the data obtained in steps S2 and S3 to derive regression equations for each parameter; S5, substituting the regression equations into the model formula and plotting a natural gas mixing ratio identification chart; S6, inputting the methane carbon isotope, ethane carbon isotope, and aridity coefficient data of the natural gas sample to the chart to obtain the coal-rock gas mixing contribution ratio. This method can calculate the contribution ratio of different types of source rocks at different maturity levels using methane carbon isotopes, ethane carbon isotopes, and the aridity coefficient.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, and in particular to a method for calculating the contribution ratio of coal-rock gas mixtures at different maturity levels. Background Technology

[0002] Natural gas is a mixture naturally occurring in geological formations, encompassing both hydrocarbon and non-hydrocarbon gases. Coal-rock gas, which is generated within the coal itself or transported from other gas sources, exists in both free and adsorbed states, with a high content of free gas. Through effective reservoir modification, it can rapidly produce gas, enabling industrial-scale extraction. Its essence is a hydrocarbon gas.

[0003] In the complex geological structure of coal-bearing strata, source rocks are not limited to coal. In fact, mudstones developed in the upper and lower strata also possess the ability to serve as source rocks and supply hydrocarbons. The carbon isotope composition of natural gas generated from the thermal cracking of organic matter is closely related to the degree of thermal evolution of the parent material. This correlation provides important clues for exploring the properties of source rocks and can reflect their characteristics to a certain extent.

[0004] In the field of natural gas research, methane and ethane carbon isotopes play a crucial role, often used to determine the maturity and genetic type of natural gas. Methane carbon isotopes are particularly significantly affected by maturity, and are therefore frequently used as an important indicator of natural gas maturity. Although natural gas carbon isotopes as a whole are affected by thermal evolution, the carbon isotopes of heavier hydrocarbons such as ethane are relatively stable and less affected by thermal maturity, instead primarily reflecting differences in the type of parent material. Therefore, ethane carbon isotopes have become an important indicator for identifying the genetic type of natural gas.

[0005] Coal-bearing and argillaceous source rocks produce natural gas with distinct characteristics due to their significantly different parent material types. However, both types of natural gas are humic, making it difficult to determine the mixing ratio using conventional methods. While precise ethane carbon isotope analysis can differentiate these two types of natural gas to some extent, it remains challenging to distinguish the contribution of different source rocks when identifying mixed-origin coal-bearing gas, especially the mixture of humic coal-bearing gas and humic mudstone gas. Currently, when determining the contribution ratio of different source rocks in mixed-origin coal-bearing gas of varying maturity, the distinction between coal-bearing and mudstone gas is often transformed into a distinction between humic and saprophytic natural gas, neglecting the influence of humic mudstone gas in this assessment. Furthermore, the common phenomenon of mixed hydrocarbon supply from different types of source rocks in coal-rock gas makes it impossible to simultaneously determine the maturity and genetic type of coal-rock gas. Moreover, the influence of thermal evolution on carbon isotopes is ignored, leading to significant errors in conventional methods for determining the maturity and genetic type of mixed-genetic coal-rock gas. In short, current techniques cannot accurately determine the contribution ratio of different source rocks in mixed-genetic coal-rock gas of varying maturity. Therefore, establishing a calculation method to directly identify the contribution ratio of different source rocks in mixed-genetic coal-rock gas (coal-rock gas and mudstone gas) is of great significance. Summary of the Invention

[0006] To address the problem that existing technologies cannot accurately determine the contribution ratio of different source rocks in mixed-origin coal-rock gas of different maturity levels, this invention provides a method for calculating the mixed contribution ratio of coal-rock gas of different maturity levels.

[0007] The method for calculating the contribution ratio of coal-rock gas mixture at different maturity levels provided by this invention includes the following steps:

[0008] S1. Establish a dynamic model for determining the mixing ratio of mixed-source gas. This model includes the following two formulas:

[0009] (1)

[0010] (2)

[0011] In the formula, It is a mixture of methane carbon isotopes from natural gas. It is a mixture of ethane carbon isotopes from natural gas. The mixing ratio of coal, shale gas, and natural gas. To calculate methane gas content using coal rock gas maturity; To calculate ethane gas content using coal gas maturity, For coal and rock gas maturity, To calculate methane carbon isotopes using coal gas maturity, To calculate ethane carbon isotopes using coal gas maturity, To calculate methane carbon isotopes using the coal rock gas drying coefficient, To calculate ethane carbon isotopes using the coal rock gas drying coefficient; To calculate methane gas content using mudstone gas maturity, To calculate ethane gas content using mudstone gas maturity, For mudstone gas maturity, To calculate methane carbon isotopes using mudstone gas maturity, To calculate ethane carbon isotopes using mudstone gas maturity, To calculate methane carbon isotopes using the mudstone gas drying factor, To calculate ethane carbon isotopes using the mudstone gas drying factor, The drying coefficient of coal gas. The drying coefficient of mudstone gas;

[0012] S2. Taking a specific natural gas extraction area as the research object, several coalbed methane and mudstone gas samples were obtained to determine the carbon isotopes of methane and ethane, as well as the drying coefficient. The coalbed methane and mudstone gas samples were obtained from pure mudstone and pure coalbed methane samples through hydrocarbon generation thermal simulation experiments.

[0013] S3. Take several unoxidized pure coal rock samples and pure mudstone samples to determine the vitrinite reflectance.

[0014] S4. Based on the data obtained in steps S2 and S3, perform correlation analysis to determine the correlation between the parameters involved in step S1 and... , ,or The relationship is obtained by formulating the regression equations for each parameter.

[0015] S5. Substitute the regression equation obtained in step S4 into formulas (1) and (2) and draw a natural gas mixing ratio identification chart. The specific method is as follows:

[0016] S51, respectively with δ 13 C1, δ 13 Establish a three-dimensional coordinate system using C and the aridity coefficient as coordinates;

[0017] S52. Using the hypothesis method, the regression equations of each parameter are... or This indicates the default. and The same value equals the natural gas maturity. ,use replace and Then, substitute the regression equations of each parameter into formulas (1) and (2), and... The value range is set to 0.4% to 4.4%, with different values ​​taken at equal intervals. The value, δ in the three-dimensional coordinate system 13 C1-δ 13 δ is drawn on the C2 plane. 13 C1 and δ 13 C2 intersection diagram;

[0018] S53. Using the assumption method, first... and Using the drying coefficient respectively and The expression is then used to transform the regression equations for each parameter into equations using the drying coefficient. and This indicates the default. and The values ​​are the same and equal to the natural gas drying factor. ,use replace and Then, substitute the regression equations of each parameter into formulas (1) and (2), and... The value range is set to 1.6~90.6, with different values ​​taken at equal intervals. The value, δ in the three-dimensional coordinate system 13 δ was obtained by plotting the C1-dryness coefficient plane. 13 C1 and aridity coefficient intersection diagram; δ in the three-dimensional coordinate system 13 δ was obtained by plotting the C2-dryness coefficient plane. 13 The C2 and dryness coefficient intersection diagram is used to ultimately form a natural gas mixing ratio identification chart.

[0019] S6. Input the data values ​​of methane carbon isotopes, ethane carbon isotopes, and dryness coefficient of the natural gas sample to be tested into the graph of step S5 and δ. 13 C1-δ 13 C2 plane, δ 13 C1-dryness coefficient plane and δ 13 Project the C2-dryness coefficient onto the plane and read the corresponding values ​​on the cross plot. Calculate the average of the read values, which is the contribution ratio of coal-rock gas mixture; the contribution ratio of mudstone gas mixture is equal to 100% minus the contribution ratio of coal-rock gas mixture.

[0020] In step S6, if the projection point of a certain plane does not fall within the cross plot, the value cannot be read, and the average of the readings from the other two planes is used as the coal-rock-gas mixing contribution ratio; if the projection points of two certain planes do not fall within the cross plot, the value cannot be read, and the reading from the other plane is directly used as the coal-rock-gas mixing contribution ratio; if the projection points of all three planes do not fall within the cross plot, it means that the plot is not suitable for testing the sample, and a new plot needs to be made according to the methods in steps S2-S5.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] (1) The calculation method of the present invention is applicable to coal gas of mixed origin at various maturity levels, and the accuracy of calculating the contribution ratio of different source rocks of coal gas of mixed origin of coal-series source rocks and argillaceous source rocks is relatively high.

[0023] (2) For different natural gas extraction areas, the method of the present invention can be used to draw a natural gas mixing ratio identification chart applicable to the area, which can then be used to determine the coal-rock gas mixing contribution ratio of all samples to be tested in the area.

[0024] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0025] Figure 1 The results obtained from the analysis in the examples and The relationship curve between them.

[0026] Figure 2 This is a diagram illustrating the natural gas mixing ratio in the example. Detailed Implementation

[0027] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0028] This invention provides a method for calculating the mixed contribution ratio of coal-gas at different maturity levels based on methane carbon isotopes, ethane carbon isotopes, and aridity coefficient. Methane carbon isotopes become heavier with increasing thermal evolution. The parent material sources of coal and mudstone differ significantly. During the gas generation process from source rocks, the carbon isotopes of kerogen are inherited. Therefore, under the same or similar thermal evolution conditions, coal-gas from coal-bearing source rocks has a heavier carbon isotope composition than mudstone gas from argillaceous source rocks. Based on geochemical data analysis of coal-gas samples, the coal-gas is generally dominated by methane, with most methane contents exceeding 80%, and methane carbon isotope values ​​mainly distributed in the range of -45‰ to -25‰. Ethane carbon isotopes are divided into two categories: coal-bearing source rocks and argillaceous source rocks. The ethane carbon isotopes of natural gas generated from coal-bearing source rocks are relatively heavy, mainly distributed in the range of -22‰ to -16‰; the ethane carbon isotopes of natural gas generated from argillaceous source rocks are relatively light, mainly distributed in the range of -29‰ to -22‰.

[0029] Studies have revealed significant differences between traditional methods for identifying the mixing ratio of coal-rock gas and mudstone gas, and those for identifying humic and saprophytic natural gas. Traditional methods rely on methane and ethane carbon isotopes, which are insufficient for identifying coal-rock gas and mudstone gas. Both coal-rock gas and mudstone gas are supplied by humic kerogen, making judgment based solely on methane and ethane carbon isotopes prone to error. Therefore, this invention, in addition to methane and ethane carbon isotopes, also analyzes extensive hydrocarbon generation thermal simulation experimental data, revealing a difference in the drying coefficients of coal-rock gas and mudstone gas. Under the same maturity conditions, the drying coefficient of mudstone gas is significantly lower than that of coal-rock gas, and the drying coefficient can be used to assist in determining the mixing ratio of mudstone gas and coal-rock gas.

[0030] Based on this, the method of the present invention calculates the contribution ratio of coal-rock gas mixing at different maturity levels using methane carbon isotopes, ethane carbon isotopes, and drying coefficients.

[0031] The following describes the calculation method for the contribution ratio of coal-rock gas mixtures at different maturity levels, using a natural gas extraction area in a basin as an example. The specific steps are as follows:

[0032] S1. Establish a dynamic model for identifying the mixing ratio of mixed-source gas.

[0033] It can reflect the maturity of natural gas. These parameters can reflect the type of natural gas source material, but in practice, it is difficult to determine the type based solely on these two parameters; in addition to and In addition, it is necessary to select a parameter to establish a hybrid equation, and to work with different parameters... and By fitting the data, it was found that the drying coefficient was related to... and The dryness coefficient showed a good correlation (see Table 1), so it was chosen as the third parameter.

[0034] Table 1. Correlation coefficients between carbon isotopes and dryness coefficient

[0035]

[0036] Based on the definition of isotopes and the principle of mass balance, precise formulas can be derived for the carbon isotope ratios of mixed-source gases and end-member gases, as well as the mixing ratio, which can be approximated as a weighted average of the end-member gases. Using an end-member gas geochemical model to replace the static parameters, a dynamic model for identifying the mixing ratio of mixed-source gases is obtained. The model includes the following two formulas:

[0037] (1)

[0038] (2)

[0039] The meanings of each parameter in the formula are explained in Table 2.

[0040] Table 2 Explanation of the meaning of relevant parameters

[0041]

[0042] S2. Obtain several coalbed methane and mudstone gas samples from the study area, and determine the methane and ethane carbon isotopes, as well as the drying coefficient, for each sample. The coalbed methane and mudstone gas samples were obtained from pure mudstone and pure coalbed methane samples through hydrocarbon generation thermal simulation experiments.

[0043] The methods for determining the carbon isotopes of methane and ethane are as follows:

[0044] (1) Take 3 ml of coal rock gas or mudstone gas sample and inject it into an Agilent 6890N gas chromatograph equipped with a flame ionization detector, and separate the gas through a capillary column (filled with alumina, 50 m × 0.53 mm);

[0045] (2) Set the temperature program of the gas chromatograph as follows: initial temperature is 40℃, hold temperature for 7 min, then increase temperature to 180℃ at 10℃ / min, hold temperature for 15 min, carrier gas is helium, flow rate is 13 ml / min.

[0046] (3) Collect the separated hydrocarbon compounds, including methane gas and ethane gas, by chromatographic separation;

[0047] (4) The separated methane gas is reacted with oxygen in a high-temperature reaction tube at a reaction temperature of 1000℃. The resulting reaction gas is then passed through a liquid nitrogen cold trap and an alcohol cold trap in sequence to achieve the separation of carbon dioxide gas from water and helium.

[0048] (5) The obtained carbon dioxide gas was detected in a Thermo Delta V mass spectrometer equipped with an Agilent 6890N gas chromatograph to obtain the values ​​of methane carbon isotopes in natural gas;

[0049] (6) The separated ethane gas is reacted with oxygen in a high-temperature reaction tube at a reaction temperature of 900°C. The resulting reaction gas is then passed through a liquid nitrogen cold trap and an alcohol cold trap in sequence to achieve the separation of carbon dioxide gas from water and nitrogen.

[0050] (7) The obtained carbon dioxide gas was detected in a Thermo Delta V mass spectrometer equipped with an Agilent 6890N gas chromatograph to obtain the values ​​of ethane carbon isotopes in natural gas.

[0051] The method for determining the drying coefficient is as follows:

[0052] (1) Use stainless steel high-pressure sampling bottles with a dual-valve design and passivation treatment; maintain pipeline pressure (≥5MPa) to avoid volatilization of light components; keep the temperature consistent with the ambient temperature to avoid condensation effect; flush the pipeline with the gas to be tested more than three times before sampling to reduce air pollution. Analyze within 24 hours after sampling, or store the sample in a low-temperature (-20℃) environment to inhibit component changes.

[0053] (2) A chromatograph equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD) was used; a Porapak Q pre-column was used to separate interfering substances such as CO2 and H2S; an HP-PLOT Al2O3 (50m×0.53mm×15μm) main column was used for the separation of C1-C6 hydrocarbons; high-purity helium was used as the carrier gas at a flow rate of 1.5mL / min. The injection port temperature was set to 200℃ and the split ratio was 50:1; the initial column temperature was set to 40℃ and held for 5min, then increased to 180℃ at a rate of 10℃ / min and held for 10min; the detector temperatures were set to FID 250℃ and TCD 200℃; the injection volume was 1μL (through a six-way valve quantitative loop).

[0054] (3) Use GC-MS to characterize complex components (such as sulfur-containing compounds) to avoid interference from overlapping chromatographic peaks.

[0055] (4) Data processing

[0056] The peak areas are normalized, and the peak areas of each component are integrated, combined with a correction factor. The correction factor needs to be calibrated in advance using a standard gas, i.e., multi-point calibration using NIST SRM standard gas (such as SRM 2614a).

[0057] Dryness coefficient calculation:

[0058] (3)

[0059] A is the peak area, and f is the correction factor for each component.

[0060] (5) Error control and quality control

[0061] Repeatability: Three parallel determinations, relative standard deviation (RSD) ≤ 1%;

[0062] Standard addition method: Add a known concentration of C2H6 standard gas to the sample, and the recovery rate needs to be between 90% and 102%;

[0063] Blank experiment: Use high-purity helium to verify the system background.

[0064] (6) Auxiliary analysis methods (cross-validation)

[0065] Dew point determination method: A cold mirror dew point meter (Michelson interferometer) was used to determine the dew point of gaseous water and hydrocarbons; the dryness coefficient is negatively correlated with the hydrocarbon dew point and is used to verify the GC results.

[0066] FTIR (Full-Time Infrared Spectroscopy): Detection of characteristic absorption peaks of CH4 and C2H6 (CH4: 3018 cm⁻¹) -1 C2H6: 2975cm -1 ), supplementing quantitative analysis.

[0067] S3. Measure the reflectance of vitrinite;

[0068] Several unoxidized pure coal rock samples and pure mudstone samples were taken and their vitrinite reflectance was measured. The measurement method is as follows:

[0069] (1) Select unoxidized pure coal rock samples or pure coal rock samples, seal and store them in an argon atmosphere to avoid photothermal decomposition; use epoxy resin for vacuum impregnation (curing at 40℃ for 24h) to avoid changes in the organic structure caused by high temperature; use silicon carbide sandpaper to grind from 400 to 1200 mesh in stages, and then use diamond suspension (3μm to 0.25μm) to polish the surface to a roughness R. a ≤0.02μm, ensuring no scratches interfere with reflectivity measurement.

[0070] (2) A polarized light system equipped with a halogen lamp (546nm monochromatic light, color temperature 3200K) was used. The objective lens was a 50× oil immersion objective lens (NA=0.85), with an oil refractive index n=1.518 (calibrated at 23℃). The detector was a photomultiplier tube (PMT) or a high dynamic range CCD (signal-to-noise ratio ≥10). 6 :1) A microphotometer system; and using synthetic sapphire (R o=0.58%) or YAG crystal (R o Calibrate using a value of 0.89%, with a daily calibration deviation ≤0.02%.

[0071] (3) Identify homogeneous vitrinite under transmitted light, and exclude detrital vitrinite or oxidized regions (oxidized regions show blue light in fluorescence mode); measure each particle 10 times under rotated polarized light to eliminate the influence of anisotropy, randomly select no less than 50 particles (particle size ≥ 5 μm), and record the maximum reflectance (R0). o,max ) and random reflectance (R o,ran ).

[0072] (4) Remove outliers using the Grubbs test to achieve a confidence level of 95%; calculate the mean R. o,mean Using standard error (SE), histograms were plotted to analyze maturity distribution patterns.

[0073] (5) Error control and quality control

[0074] Repeated experiments should ensure that the deviation between different operators for the same sample is ≤0.05%. A standard sample (SARM 20, Ro=0.58%) should be inserted in each batch, and the measured value should be within ±0.03%. The laboratory temperature should be controlled at 23±1℃, and the humidity <40% to avoid thermal drift and sample moisture absorption.

[0075] S4. Based on the large amount of data measured in steps S2 and S3, perform correlation analysis between the parameters to determine the correlation between the parameters involved in step S1 and... , ,or The relationship is obtained by formulating the regression equations for each parameter.

[0076] To analyze and Let's take the relationship between them as an example to illustrate. For example... Figure 1 As shown, based on the methane carbon isotope and aridity coefficient data of several coal shale gases measured in step S2, using... x-axis Using the ordinate as the vertical axis, plot the graph in a plane coordinate system, and fit the graph to obtain the fitted curve and the corresponding fitting formula. This formula is... and The relational expression derived in this embodiment is as follows: .

[0077] Using the same method, other parameters were analyzed and... , ,or The relationship is given in the following equations. The regression equations for each parameter obtained in this embodiment are shown in equations (4)-(16). The correlation coefficients of the regression equations are shown in Table 3.

[0078] (4)

[0079] (5)

[0080] (6)

[0081] (7)

[0082] (8)

[0083] (9)

[0084] (10)

[0085] (11)

[0086] (12)

[0087] (13)

[0088] (14)

[0089] (15)

[0090] (16)

[0091] Table 3. Correlation coefficients of regression equations

[0092]

[0093] S5. Draw a natural gas mixing ratio identification chart. The specific method is as follows:

[0094] S51, respectively with δ 13 C1, δ 13 Establish a three-dimensional coordinate system using C and the aridity coefficient as coordinates;

[0095] S52. Using the hypothesis method, the regression equations (4)-(16) of each parameter are expressed as follows: or Indicate, then default and The values ​​are the same and equal to the natural gas maturity. ,use Replace the regression equation formula and Then, substitute the regression equations of each parameter into formulas (1) and (2); The value range is set to 0.4% to 4.4%, with different values ​​taken at equal intervals (0.2% intervals). The value, δ in the three-dimensional coordinate system 13 C1-δ 13 δ is drawn on the C2 plane. 13 C1 and δ 13 C2 intersection chart, see details. Figure 2 Black and white background.

[0096] S53. Using the assumption method, first... and Using the drying coefficient respectively and The expression is then used to transform the regression equations for each parameter into equations using the drying coefficient. and This indicates the default. and The values ​​are the same and equal to the natural gas drying factor. ,use Replace the regression equation formula and Then substitute the regression equations of each parameter into formulas (1) and (2); The value range is set to 1.6~90.6, with different values ​​taken at equal intervals (interval 1). The value, δ in the three-dimensional coordinate system 13 δ was obtained by plotting the C1-dryness coefficient plane. 13 The cross-plot of C1 and aridity coefficient can be found in [link to chart]. Figure 2 The red panel in the center. In the three-dimensional coordinate system, δ... 13 δ was obtained by plotting the C2-dryness coefficient plane. 13 For the C2 vs. aridity coefficient cross-section diagram, please see [link / details]. Figure 2 Medium blue plate. Final form Figure 2 The diagram shown illustrates the identification of natural gas mixing ratios.

[0097] S6. For the natural gas sample to be tested, first determine the specific values ​​of the methane carbon isotopes, ethane carbon isotopes, and dryness coefficient of the natural gas sample, using the same testing method as described in step S2, replacing the test sample with the natural gas sample at this location. Then, substitute the measured specific values ​​of the methane carbon isotopes, ethane carbon isotopes, and dryness coefficient of the natural gas sample into... Figure 2 The diagram is in δ 13 C1-δ 13 C2 plane, δ 13 C1-dryness coefficient plane and δ 13 Projecting the C2-dryness coefficient onto the plane and reading the corresponding values ​​on the cross-plot, then averaging the read values, yields the coal-rock gas mixing contribution ratio. The mudstone gas mixing contribution ratio is equal to 100% minus the coal-rock gas mixing contribution ratio.

[0098] To verify the accuracy of the calculation method of the present invention, the geochemical parameters of the artificially mixed gas mixture were substituted into the identification chart and compared with the actual mixing ratio. The results are shown in Tables 4 and 5.

[0099] Table 4 Comparison of Calculated and Actual Proportions

[0100]

[0101] Table 5 Predicted Results

[0102]

[0103] The data in the table demonstrates that the calculation method for the contribution ratio of coal-rock gas mixture at different maturity levels in this invention yields highly accurate results.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for calculating the contribution ratio of different maturity coal rock gas, characterized in that, The method comprises the following steps: S1, establishing a mixed-source gas mixing ratio identification dynamic model, which comprises the following two formulas: （1） （2） wherein, is the mixed natural gas methane carbon isotope, is the mixed natural gas ethane carbon isotope, is the coal rock gas natural gas mixing ratio, is the methane gas content calculated using coal rock gas maturity; is the ethane gas content calculated using coal rock gas maturity, is the coal rock gas maturity, is the methane carbon isotope calculated using coal rock gas maturity, is the ethane carbon isotope calculated using coal rock gas maturity, is the methane carbon isotope calculated using coal rock gas dryness coefficient, is the ethane carbon isotope calculated using coal rock gas dryness coefficient; is the methane gas content calculated using mud rock gas maturity, is the ethane gas content calculated using mud rock gas maturity, is the mud rock gas maturity, is the methane carbon isotope calculated using mud rock gas maturity, is the ethane carbon isotope calculated using mud rock gas maturity, is the methane carbon isotope calculated using mud rock gas dryness coefficient, is the ethane carbon isotope calculated using mud rock gas dryness coefficient, is the coal rock gas dryness coefficient, is the mud rock gas dryness coefficient; S2, taking a certain natural gas exploitation area as a research object, obtaining a plurality of coal rock gas and mudstone gas samples to measure methane carbon isotope and ethane carbon isotope, and a dry coefficient; S3, taking a plurality of pure coal rock samples and pure mudstone samples which are not oxidized to measure vitrinite reflectance; S4, correlation analysis is made on the data measured according to steps S2 and S3, and a relationship between each parameter involved in step S1 and , , or is obtained, i.e., a regression equation of each parameter is obtained; S5, substituting the regression equation obtained in step S4 into formulas (1) and (2) and drawing a natural gas mixing ratio identification chart; the specific method is as follows: S51, respectively, with δ 13 C1, δ 13 C and the dry coefficient of a three-dimensional coordinate system; S52, by the assumption method, the regression equation of each parameter is represented by or The value of default and is the same as the maturity of natural gas , replace and with , then substitute the regression equation of each parameter into formula (1) and (2), and set the value range of to 0.4~4.4%, take different values at equal intervals, draw the intersection graph of 13 C1-δ 13 C2 on the δ 13 C1 and δ 13 C2 plane in three-dimensional coordinate system; S53, by hypothesis method, first and respectively with dry coefficient and Indicated, then the regression equation of each parameter is transformed into the dry coefficient and The value of default and Is the same as the dry coefficient of natural gas , replace , and , and then substitute the regression equation of each parameter into formula (1) and (2), and The value range of Is set to 1.6~90.6, and different Values are taken at equal intervals, and 13 C1-dry coefficient plane in three-dimensional coordinate system is drawn to obtain 13 C1 and dry coefficient intersection diagram; in three-dimensional coordinate system of 13 C2-dry coefficient plane is drawn to obtain 13 C2 and dry coefficient intersection diagram; finally form natural gas mixed proportion identification chart; S6, the data values of the methane carbon isotope, ethane carbon isotope and dry coefficient of the natural gas sample to be tested are brought into the graph of step S5 and the corresponding value on the intersection graph is read out through projection of the C1-δ 13 C1-δ 13 C2 plane, δ 13 C1-dry coefficient plane and δ 13 C2-dry coefficient plane is projected and the corresponding value on the intersection graph is read out, and the average value of the read-out values is the contribution proportion of the coal rock gas mixture.

2. The method for calculating the contribution ratio of coal-rock gas mixtures at different maturity levels as described in claim 1, characterized in that, In step S6, if the projection point on a certain plane does not fall within the intersection chart, the value cannot be read, and the average value of the read values of the other two planes is taken as the coal rock gas mixing contribution ratio; if the projection point on two planes does not fall within the intersection chart, the value cannot be read, and the read value of the other plane is directly taken as the coal rock gas mixing contribution ratio; if the projection points on three planes do not fall within the intersection chart, it is indicated that the chart is not suitable for testing of the sample, and a new chart needs to be made according to the method of steps S2-S5.

3. The method for calculating the contribution ratio of coal-rock gas mixtures at different maturity levels as described in claim 1, characterized in that, In step S2, the coal rock gas and mudstone gas samples are obtained by hydrocarbon generation thermal simulation experiment on pure mudstone and pure coal rock samples.

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