Method for identifying algal bloom oil shales based on carbon isotopes and biomarkers

Abstract

The present invention discloses a method for identifying algae-forming oil shale based on carbon isotopes and biomarkers, which belongs to the field of testing or analyzing materials by measuring the chemical or physical properties of materials. The method comprises the following steps: first, Soxhlet extraction is performed on a cleaned, dried and pulverized sample to obtain soluble organic matter and residual rock powder; then, the soluble organic matter components are separated to obtain saturated hydrocarbon and aromatic hydrocarbon components; then, kerogen is extracted from the residual rock powder and carbon isotope analysis is performed; and based on the biomarker data of the saturated hydrocarbon and aromatic hydrocarbon components by gas chromatography-mass spectrometry, the 4-methylsterane index, C 30 Tetracyclic polyisoprene and C 27 The method analyzes the correlation between these parameters, demarcates the parameter boundaries for different lithologic sampling areas, and establishes a quantitative identification standard for algal bloom-type oil shales based on carbon isotopes and biomarkers. This method enables scientific, accurate, and reliable identification of algal bloom-type oil shales.

Description

Technical Field

[0001] The present invention belongs to the field of testing or analyzing materials by means of measuring the chemical or physical properties of the materials, and specifically relates to a method for identifying algal bloom oil shale based on carbon isotopes and biomarkers. Background Art

[0002] Currently, algal bloom oil shales, as the primary source rock in crude oil exploration and production areas, are primarily characterized by high organic carbon (TOC) content and 4-methylsterane, an indicator of algal biogenic input. However, a clear distinction between algal bloom oil shales and mudstones has not yet been established. Furthermore, the recent widespread use of oil-based drilling muds has led to widespread contamination of rock samples. TOC is easily affected by the oil-based mud, resulting in distorted TOC data and inability to accurately identify algal bloom oil shales, further complicating oil shale identification. Therefore, a new indicator system is urgently needed to accurately identify algal bloom oil shales. Summary of the Invention

[0003] The present invention is proposed to solve the problem in the existing technology that the organic carbon content (TOC) and the molecular geochemical indicator 4-methylsterane index can qualitatively identify oil shale and mudstone, but due to the contamination of the source rock sample by drilling mud, the TOC data is distorted, and it is difficult to accurately identify algae-type oil shale based solely on 4-methylsterane. Its purpose is to provide a method for identifying algae-type oil shale based on carbon isotopes and biomarkers.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for identifying algal bloom oil shale based on carbon isotopes and biomarkers comprises the following steps:

[0006] (I) Sample pretreatment

[0007] Typical oil shale and mudstone core samples from the study area were taken, the surface mud of the samples was cleaned, and then they were dried at 40℃ for 4 hours, and then crushed to obtain powder core samples with a particle size greater than 80 mesh.

[0008] Refer to the Petroleum and Natural Gas Industry Standard SY / T 5118-2021 of the People's Republic of China for processing;

[0009] (II) performing Soxhlet extraction on the powdered core sample obtained in step (I) using a solvent to separate soluble organic matter and residual rock powder after extraction;

[0010] (III) separating the soluble organic matter obtained in step (II) into group components, and analyzing the separated saturated hydrocarbon and aromatic hydrocarbon components;

[0011] (IV) Extracting kerogen from the residual rock powder obtained in step (II), analyzing the carbon isotope composition of the extracted kerogen, and obtaining the carbon isotope content of the kerogen (δ 13 C 干酪根 );

[0012] (V) Obtain biomarker data by gas chromatography-mass spectrometry analysis of saturated hydrocarbon and aromatic hydrocarbon components according to step (III), call the mass chromatogram of saturated hydrocarbon m / z 217, and analyze C 29 Steranes and C 30 The 4-methyl sterane series compounds were integrated (the peak areas of the corresponding compounds were integrated) and the 4-methyl sterane index was calculated;

[0013] (VI) Obtain biomarker data by gas chromatography-mass spectrometry analysis of saturated hydrocarbon components according to step (III), call the mass chromatogram of saturated hydrocarbon m / z 259, and analyze C 30 Tetracyclic polyisoprene and C 27 Integrate the rearranged sterane series compounds (integrate the peak areas of the corresponding compounds) and calculate C 30 Tetracyclic polyisoprene and C 27 ratio of rearranged steranes;

[0014] (VII) Obtaining biomarker data according to the gas chromatography-mass spectrometry analysis of the aromatic hydrocarbon components in step (III), calling the total ion chromatogram of the aromatic hydrocarbon gas chromatography-mass spectrometry, integrating the C0-C3 naphthalene series compounds and the C0-C3 phenanthrene series compounds (integrating the peak areas of the corresponding compounds), and calculating the ratio of the phenanthrene series to the naphthalene series;

[0015] (VIII) Fitting of kerogen 13 C isotope, C 30 Tetracyclic polyisoprene and C 27 The correlation between the ratio of rearranged steranes, the ratio of phenanthrene series / naphthalene series and the 4-methylsterane index is used to divide the parameter boundaries of the sampling areas of different lithologic samples, and to establish a quantitative identification standard for algal bloom oil shale based on carbon isotopes and biomarkers.

[0016] In the above technical solution, the solvent in step (II) is dichloromethane; and the Soxhlet extraction time in step (II) is 72 hours.

[0017] In the above technical solution, the separation of soluble organic matter components in step (III) is carried out according to the industry standard SY / T5119-2016;

[0018] The analysis of saturated hydrocarbon and aromatic hydrocarbon components in step (III) was performed using an Agilent 7890 / 5975 gas chromatography-mass spectrometry system. The specific chromatographic conditions were as follows: the chromatographic column was an HP-5MS capillary column (60 m×0.25 mm×0.25 μm); the inlet temperature was 300°C, the carrier gas was 99.999% helium, and the flow rate was 1.0 mL / min; the initial temperature of the temperature program was 40°C, which was retained for 2 min, then increased to 100°C at a rate of 10°C / min, and then increased to 300°C at a rate of 3°C / min, and maintained at this temperature for 30 min; the detection method was full scan ion detection.

[0019] In the above technical solution, the extraction of kerogen in step (IV) is carried out in accordance with the national standard GB / T 19144-2010;

[0020] The carbon isotope analysis in step (IV) was performed using a Thermo Fisher Scientific MAT253 stable isotope mass spectrometer. The carbon isotope analysis was calibrated using the laboratory standard GBW4407 (-22.43‰), δ 13 C 干酪根 The values ​​were calculated relative to the American Pee Dee Belemnite Standard (VPDB) based on repeated measurements, δ 13 C 干酪根 The analytical accuracy is better than ±0.2‰.

[0021] In the above technical solution, the calculation formula of the 4-methylsterane index in step (V) is:

[0022] 4-MSI=C 30 4-Methylsterane / C 29 steranes

[0023] Where: 4-MSI is 4-methylsterane index, C 30 4-Methylsterane is C 30 The integrated area of ​​4-methylsterane; C 29 Steranes are C 29 The integrated area of ​​steranes.

[0024] In the above technical solution, the quantitative identification criteria for algal bloom oil shale based on carbon isotopes and biomarkers in step (VIII) are specifically:

[0025] When kerogen carbon isotopes (δ 13 C 干酪根 )>-24.5‰, 4-methylsterane index (4-MSI)>1.4, C 30 Tetracyclic polyisoprene / C 27 The rearranged sterane ratio is greater than 1.5 and the phenanthrene series / naphthalene series ratio is greater than 3, indicating that the oil shale type is a strong algae-type oil shale;

[0026] When the kerogen carbon isotope is between -26‰ and -24.5‰ and the 4-methylsterane index is between 0.8 and 1.4, C 30 Tetracyclic polyisoprene / C 27 The rearranged sterane ratio is between 0.8 and 1.5, and the phenanthrene series / naphthalene series ratio (Phs / Nas) is between 2 and 3, indicating that the oil shale type is weak algae bloom type oil shale.

[0027] When the kerogen carbon isotope is less than -26‰, the 4-methylsterane index is less than 0.8, C 30 Tetracyclic polyisoprene / C 27 The rearranged sterane ratio is <0.8 and the phenanthrene series / naphthalene series ratio is <2, indicating that the oil shale type is algae-free bloom type oil shale.

[0028] The beneficial effects of the present invention are:

[0029] The present invention provides a method for identifying algal bloom oil shale based on carbon isotopes and biomarkers, which can realize scientific, accurate and reliable identification of algal bloom oil shale. In addition to the 4-methylsterane index, the present invention also newly establishes kerogen carbon isotopes, C 30 Tetracyclic polyisoprene / C 27 The ratios of rearranged steranes and phenanthrene / naphthalene series are both good indicators of algal blooms and can accurately and effectively distinguish algal bloom-type oil shales from mudstones. Moreover, regardless of the degree of oil-based mud contamination, kerogen carbon isotopes are almost unaffected because the contaminated soluble organic matter has been completely removed before analytical testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an intersection diagram of the 4-methylsterane index and kerogen carbon isotope value of the oil shale and mudstone samples of Example 1 of the present invention;

[0031] Figure 2 The 4-methylsterane index and C of the oil shale and mudstone samples in Example 1 of the present invention are 30 Tetracyclic polyisoprene / C 27 Rearranged sterane value intersection diagram;

[0032] Figure 3 This is an intersection diagram of the 4-methylsterane index and the phenanthrene series / naphthalene series values ​​of the oil shale and mudstone samples of Example 1 of the present invention;

[0033] Figure 4 This is the mass chromatogram of saturated hydrocarbons m / z 217 and m / z 259 of the oil shale and mudstone samples in Example 1 of the present invention;

[0034] Figure 5This is a gas chromatography-mass spectrometry total ion current (TIC) graph of aromatic hydrocarbons of oil shale and mudstone samples in Example 1 of the present invention.

[0035] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0036] 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 will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0037] Example 1

[0038] A method for identifying algal bloom oil shale based on carbon isotopes and biomarkers comprises the following steps:

[0039] (I) Take typical oil shale and mudstone core samples from the study area, clean the surface mud, dry and crush them for later use.

[0040] (II) Soxhlet extraction of the rock powder sample using dichloromethane for 72 hours to obtain soluble organic matter and residual rock powder after extraction;

[0041] (III) Soluble organic matter was separated into group components according to the industry standard SY / T 5119-2016. The separated saturated hydrocarbon and aromatic hydrocarbon components were analyzed using an Agilent 7890 / 5975 gas chromatograph-mass spectrometer.

[0042] (IV) The residual powder after extraction was used to extract kerogen according to the national standard GB / T 19144-2010. The carbon isotope composition of the extracted kerogen was analyzed using a Thermo Fisher Scientific MAT253 stable isotope mass spectrometer.

[0043] (V) Obtain biomarker data based on saturated hydrocarbon and aromatic hydrocarbon gas chromatography-mass spectrometry analysis, and call the mass chromatogram of saturated hydrocarbon m / z 217 ( Figure 4 ), for C 29 Steranes and C 30 The 4-methylsterane series compounds were integrated and the 4-methylsterane index (4-MSI = C 30 4-Methylsterane / C 29 steranes);

[0044] (VI) Call the mass chromatogram of saturated hydrocarbon m / z 259 ( Figure 4 ), for C 30 Tetracyclic polyisoprene and C 27 Integrate the rearranged sterane series compounds and calculate C 30 Tetracyclic polyisoprene / C 27 Rearranged sterane ratio (C30 TPP / D 27 St);

[0045] (VII) Calling the total ion current of aromatic hydrocarbon gas chromatography-mass spectrometry ( Figure 5 ), integrate the naphthalene series compounds of C0-C3 and the phenanthrene series compounds of C0-C3, and calculate the phenanthrene series / naphthalene series ratio (Phs / Nas).

[0046] (VIII) Fitting δ 13 C 干酪根 、C 30 TPP / D 27 The correlation between St, Phs / Nas and 4-MSI was used to demarcate the parameter boundaries of the sampling areas of different lithologic types, and a quantitative identification standard for algal bloom oil shale based on carbon isotopes and biomarkers was established. The quantitative identification standard is shown in Table 1.

[0047] Table 1: Quantitative identification criteria for algal bloom oil shales based on kerogen carbon isotopes and biomarkers

[0048]

[0049] The 4-methylsterane index (4-MSI) and kerogen carbon isotope (δ 13 C 干酪根 )、C 30 Tetracyclic polyisoprene / C 27 Rearranged sterane (C 30 TPP / D 27 St), phenanthrene series / naphthalene series (Phs / Nas) ratios have a very good linear relationship (see Appendix Figures 1-3 ), which can effectively distinguish source rocks of different lithologies.

[0050] As shown in Table 1, the present invention establishes a quantitative identification standard for algal bloom oil shale based on kerogen carbon isotopes and biomarkers; 13 C 干酪根 ,4-MSI,C 30 TPP / D 27 The St and Phs / Nas values ​​are greater than -26‰, 0.8, 0.8, and 2, respectively, while the indicators of mudstone are less than the above values.

[0051] Oil shale can be further divided into strong algae-type and weak algae-type oil shales. The δ 13 C 干酪根 ,4-MSI,C 30 TPP / D 27The St and Phs / Nas values ​​are greater than -24.5‰, 1.4, 1.5 and 3, respectively, while the indicators of weak algae bloom oil shale are less than the above values.

[0052] The quantitative index system established in the present invention is based on the results obtained from the corresponding analysis and testing of cleaned core samples, eliminating the impact of drilling mud contamination on the data; at the same time, it combines carbon isotopes with saturated hydrocarbon and aromatic hydrocarbon biomarkers to quantitatively identify algae-forming oil shales, making the identification results more accurate and convincing, and providing an effective method for accurately identifying algae-forming oil shales in the study area.

[0053] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection 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 fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for identifying algal bloom oil shale based on carbon isotopes and biomarkers, characterized by: The following steps are involved: (I) Take typical oil shale and mudstone core samples from the study area, clean the surface mud of the samples, and then dry and crush them to obtain powder core samples; (II) performing Soxhlet extraction on the powdered core sample obtained in step (I) using a solvent to separate soluble organic matter and residual rock powder after extraction; (III) separating the soluble organic matter obtained in step (II) into group components, and analyzing the separated saturated hydrocarbon and aromatic hydrocarbon components; (IV) extracting kerogen from the residual rock powder obtained in step (II), analyzing the carbon isotope composition of the extracted kerogen, and obtaining the carbon isotope content of the kerogen; (V) Obtain biomarker data by gas chromatography-mass spectrometry analysis of saturated hydrocarbon and aromatic hydrocarbon components according to step (III), call the mass chromatogram of saturated hydrocarbon m / z 217, and analyze C 29 Steranes and C 30 The 4-methylsterane series compounds were integrated and the 4-methylsterane index was calculated; The calculation formula of the 4-methylsterane index is: 4-MSI=C 30 4-Methylsterane / C 29 steranes Where: 4-MSI is 4-methylsterane index, C 30 4-Methylsterane is C 30 The integrated area of ​​4-methylsterane; C 29 Steranes are C 29 integrated area of ​​steranes; (VI) Obtain biomarker data by gas chromatography-mass spectrometry analysis of saturated hydrocarbon components according to step (III), call the mass chromatogram of saturated hydrocarbon m / z 259, and analyze C 30 Tetracyclic polyisoprene and C 27 Integrate the rearranged sterane series compounds and calculate C 30 Tetracyclic polyisoprene and C 27 ratio of rearranged steranes; (VII) obtaining biomarker data by gas chromatography-mass spectrometry analysis of aromatic hydrocarbon components according to step (III), calling the total ion chromatogram of the aromatic hydrocarbon gas chromatography-mass spectrometry, integrating the C0-C3 naphthalene series compounds and the C0-C3 phenanthrene series compounds, and calculating the ratio of the phenanthrene series to the naphthalene series; (VIII) Fitting of kerogen 13 C isotope, C 30 Tetracyclic polyisoprene and C 27 The correlation between the ratio of rearranged steranes, the ratio of phenanthrene series to naphthalene series, and the 4-methylsterane index is used to define the parameter boundaries of the sampling areas of different lithologic types, and to establish a quantitative identification standard for algal bloom oil shales based on carbon isotopes and biomarkers. The quantitative identification standard for algal bloom oil shale based on carbon isotopes and biomarkers is specifically: When the kerogen carbon isotope is greater than -24.5‰, the 4-methylsterane index is greater than 1.4, C 30 Tetracyclic polyisoprene / C 27 The rearranged sterane ratio is greater than 1.5 and the phenanthrene series / naphthalene series ratio is greater than 3, indicating that the oil shale type is a strong algae-type oil shale; When the kerogen carbon isotope is between -26‰ and -24.5‰ and the 4-methylsterane index is between 0.8 and 1.4, C 30 Tetracyclic polyisoprene / C 27 The rearranged sterane ratio is between 0.8 and 1.5, and the phenanthrene series / naphthalene series ratio is between 2 and 3. The oil shale type is weak algae bloom type oil shale. When the kerogen carbon isotope is less than -26‰, the 4-methylsterane index is less than 0.8, C 30 Tetracyclic polyisoprene / C 27 The rearranged sterane ratio is <0.8 and the phenanthrene series / naphthalene series ratio is <2, indicating that the oil shale type is algae-free bloom type oil shale.

2. The method for identifying algal bloom oil shale based on carbon isotopes and biomarkers according to claim 1, characterized in that: The solvent in step (II) is dichloromethane; the Soxhlet extraction time in step (II) is 72 hours.

3. The method for identifying algal bloom oil shale based on carbon isotopes and biomarkers according to claim 1, characterized in that: The separation of soluble organic matter components in step (III) is carried out according to the industry standard SY / T 5119-2016; The analysis of saturated hydrocarbon and aromatic hydrocarbon components in step (III) was performed using Agilent 7890 / 5975 gas chromatography-mass spectrometry.

4. The method for identifying algal bloom oil shale based on carbon isotopes and biomarkers according to claim 1, characterized in that: The extraction of kerogen in step (IV) is carried out in accordance with the national standard GB / T 19144-2010; The carbon isotope analysis in step (IV) was performed using a Thermo Fisher Scientific MAT253 stable isotope mass spectrometer.

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