Methods for quantitatively restoring the gammacerane index of highly mature crude oil

Abstract

The present invention belongs to the field of organic geochemistry, and relates to a method for quantitatively recovering the gammacerane index in high-maturity crude oil. The method comprises the following steps: selecting crude oil samples of different maturity from the same set of source rocks; performing sample component separation and chromatography-mass spectrometry analysis; calculating the concentration of the target compound, calculating the methylphenanthrene index and equivalent maturity of each sample; performing data fitting to obtain the original gammacerane index. The method of the present invention provides a method for quantitatively recovering gammacerane in high-maturity crude oil for the first time, and the obtained result has high accuracy; the method of the present invention is of great significance for expanding the application scope of the gammacerane index, accurately judging the sedimentary environment of source rocks, and correctly classifying the genetic type of crude oil.

Description

Technical Field

[0001] The invention belongs to the field of organic geochemistry and relates to a method for quantitatively recovering the gammacerane index in high-maturity crude oil. Background Art

[0002] Gammacerane is a common pentacyclic triterpenoid compound in source rock extracts and crude oil. It is believed to be formed by dehydration and hydrogenation of tetrahymenol. It is commonly found in samples from oil and gas basins, especially in marine and terrestrial sediments with high salinity and their hydrocarbon products. Therefore, it is widely used as an indicator of high salinity of sedimentary water or water stratification.

[0003] In practical applications, the gamma cerane index (gamma cerane content / C 30 The gammacerane index is used as a characterization parameter to identify the sedimentary water environment. This index is widely used in the analysis of source rock sedimentary environment, determination of crude oil genesis, and tracing of crude oil sources. However, with the increase of thermal evolution, especially when it reaches a high maturity stage, the gammacerane and C 30 Hopanes will undergo cracking, resulting in a significant decrease in their content, and the two types of compounds have different cracking ranges with increasing maturity, so the gammacerane index undergoes complex changes and cannot reflect the original characteristics, limiting the application of this parameter in high-maturity crude oil. Regular sterane isomerization parameters, hopane isomerization parameters, methylphenanthrene index, etc. are commonly used parameters to characterize the maturity of source rocks and crude oil. Among them, the methylphenanthrene index has a high equilibrium value and a wide range of maturity, and is still applicable to high-maturity samples.

[0004] For highly mature samples, how to establish the relationship between maturity and gammacerane, C 30 The quantitative restoration of the original gammacerane index of high-maturity samples is of great significance for expanding the application scope of the gammacerane index, accurately judging the sedimentary environment of source rocks, and correctly classifying the genetic type of crude oil. At present, there is no report on the quantitative restoration of the original gammacerane index of high-maturity samples. Summary of the invention

[0005] In order to solve the problems that the gammacerane index in high-maturity samples cannot be used, the sedimentary environment of source rocks is difficult to identify, and the origin analysis of crude oil is limited, the present invention provides a new method for quantitatively recovering the gammacerane index.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for quantitatively recovering the gammacerane index in high-maturity crude oil, which comprises the following steps: selecting crude oil samples with different maturity from the same set of source rocks; separating sample components and performing chromatography-mass spectrometry analysis; calculating the concentration of target compounds, calculating the methylphenanthrene index and equivalent maturity of each sample; and performing data fitting to obtain the original gammacerane index.

[0008] Furthermore, the method for separating sample components is as follows: adding each crude oil sample to n-hexane for precipitation, collecting the supernatant by centrifugation, concentrating the supernatant by evaporation, analyzing it with a silica gel / alumina column, and eluting with n-hexane and toluene in turn to obtain saturated hydrocarbon and aromatic hydrocarbon components.

[0009] In a further step, when performing chromatography-mass spectrometry analysis, an internal standard is added to each sample for absolute quantitative analysis.

[0010] Furthermore, the absolute concentration of the target compound was calculated.

[0011] Furthermore, the target compound includes gammacerane, C 30 Hopane, phenanthrene and methylphenanthrene series compounds. The methylphenanthrene series compounds include 1-methylphenanthrene, 2-methylphenanthrene, 3-methylphenanthrene and 9-methylphenanthrene.

[0012] Furthermore, the methylphenanthrene index calculation formula is:

[0013] Methylphenanthrene index = 1.5 × (3-methylphenanthrene + 2-methylphenanthrene) / (phenanthrene + 9-methylphenanthrene + 1-methylphenanthrene);

[0014] The calculation formula for equivalent maturity is: equivalent maturity = 0.6 × methylphenanthrene index + 0.4.

[0015] Further, the gammacerane content, C 30 The data of hopane content and equivalent maturity were fitted to determine the relationship between the two and equivalent maturity.

[0016] Furthermore, taking the maturity of 0.5% as the low maturity boundary, the gammacerane and C 30 Hopane content.

[0017] Further, the original gammacerane index is equal to the ratio of the gammacerane content to the C30 hopane content at a maturity of 0.5%.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The method of the present invention provides a method for quantitatively recovering gammacerane of high-maturity crude oil for the first time. Based on the separation of sample components, the method of the present invention adds internal standard substances to perform chromatography-mass spectrometry analysis on saturated hydrocarbon and aromatic hydrocarbon components, quantitatively determines the absolute concentration of gammacerane and other compounds in the sample, determines the equivalent maturity of the sample by the methylphenanthrene index, and determines the relationship between maturity and gammacerane, C 30 The correlation between gammacerane and C 30 The content of hopane can be determined, thereby achieving quantitative recovery of the original gammacerane index of high maturity samples; the results obtained are highly accurate.

[0020] The method of the present invention is of great significance for expanding the application scope of the gammacerane index, accurately judging the sedimentary environment of source rocks, and correctly classifying the genetic type of crude oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] Figure 1 This is a flow chart of the method for quantitatively recovering the gamma cerane index of highly mature crude oil described in Example 1 of the present invention.

[0023] Figure 2 The relationship between gammacerane content and equivalent maturity was determined by fitting the data described in Example 1.

[0024] Figure 3 C is determined by fitting the data described in Example 1 30 Relationship between hopane content and equivalent maturity. DETAILED DESCRIPTION

[0025] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0027] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0028] Example 1

[0029] like Figure 1 As shown, the method for quantitatively recovering the gamma cerane index in high-maturity crude oil comprises the following steps:

[0030] Step 1. Sample selection: select crude oil samples of different maturity from the same set of source rocks in a certain study area;

[0031] Step 2. Perform sample component separation and chromatography-mass spectrometry analysis:

[0032] The sample was separated into group components to obtain saturated hydrocarbon and aromatic hydrocarbon components: a certain mass of crude oil sample was selected and precipitated with n-hexane, centrifuged at 3500r / min, the supernatant after centrifugation was concentrated by rotary evaporation, and then analyzed with a silica gel / alumina column, and eluted with n-hexane and toluene in turn to obtain saturated hydrocarbon and aromatic hydrocarbon components.

[0033] Chromatography-mass spectrometry analysis: A certain volume of 5α-androstane and D10-anthracene with known concentrations were added to the saturated hydrocarbon and aromatic hydrocarbon components of each sample as internal standards for GC-MS analysis to achieve absolute quantification of saturated hydrocarbon biomarkers and aromatic compounds in the sample. The GC-MS instrument selected was Agilent6890GC / 5975iMS. The GC carrier gas was helium with a purity of 99.99% and a flow rate of 1 mL / min. The chromatographic column selected was Agilent HP-5MS (60m×0.25mm×0.25μm). The initial GC temperature was 50°C, maintained for 1 min, then heated to 220°C at a heating rate of 8°C / min, and then heated to 300°C at 2°C / min, and kept at a constant temperature for 25 min. The MS ion source temperature was 230°C, the ionization energy was 70 eV, and the data acquisition mode was full scan / multiple ions.

[0034] Step 3. Calculate the concentration of target compounds, methylphenanthrene index and equivalent maturity of each sample:

[0035] Manual integration was used to obtain the target compounds in all samples: gammacerane, C 30 The peak area data of hopane, phenanthrene and methylphenanthrene series compounds were assumed to have a response coefficient of 1 for all compounds to the internal standard. The absolute concentration of the target compound was calculated based on the peak area of ​​the compound, the peak area of ​​the internal standard and the concentration of the internal standard.

[0036] Calculate the methylphenanthrene index and equivalent maturity of each sample:

[0037] The formula for calculating the methylphenanthrene index is:

[0038] Methylphenanthrene index = 1.5 × (3-methylphenanthrene + 2-methylphenanthrene) / (phenanthrene + 9-methylphenanthrene + 1-methylphenanthrene);

[0039] The calculation formula for equivalent maturity is: equivalent maturity = 0.6 × methylphenanthrene index + 0.4.

[0040] The absolute concentration of the target compound of each sample, the methylphenanthrene index and the equivalent maturity are shown in Table 1 below.

[0041] Table 1 Absolute concentrations of target compounds and related parameters in the study area

[0042]

[0043] Step 4. Perform data fitting to obtain the original gammacerane index:

[0044] The gamma cerane content, C 30 The hopane content was fitted with the equivalent maturity to determine the relationship between the two and the equivalent maturity. The gammacerane content (y1) and the equivalent maturity (x) were linearly related, as shown in Figure 2. Figure 2 As shown, y1 = -1200x + 1702.6, C 30 The hopane content (y2) and equivalent maturity (x) are exponentially related, such as Figure 3 As shown, y2 = 30217e -3.837x , taking the maturity of 0.5% as the low maturity boundary, calculate the gammacerane and C 30 The hopane contents were 1102.2 ppm and 4436.7 ppm respectively. 30 The gammacerane index is calculated by comparing the hopane content with the hopane content, which is 0.25. That is, the original gammacerane index of this series of high maturity crude oil samples is 0.25.

[0045] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for quantitatively recovering the gamma cerane index in highly mature crude oil, characterized in that: The following steps are involved: Select crude oil samples of different maturity from the same set of source rocks; Separate sample components and perform chromatography-mass spectrometry analysis; Calculate the concentration of target compounds, the methylphenanthrene index and equivalent maturity of each sample; calculate the gamma cerane content, C 30 The data of hopane content and equivalent maturity were fitted to determine the relationship between the two and equivalent maturity. Among them, the relationship between gammacerane content and equivalent maturity was linear. 30 The relationship between hopane content and equivalent maturity is exponential; taking maturity equal to 0.5% as the low maturity boundary, the gammacerane and C 30 Hopane content, gammacerane content and C 30 The gammacerane index was calculated by comparing the hopane content.

2. The method according to claim 1, characterized in that: The method for separating the sample components is as follows: adding each crude oil sample to n-hexane for precipitation, collecting the supernatant by centrifugation, concentrating the supernatant by evaporation, analyzing it with a silica gel / alumina column, and eluting with n-hexane and toluene in turn to obtain saturated hydrocarbon and aromatic hydrocarbon components.

3. The method according to claim 1, characterized in that: When performing chromatography-mass spectrometry analysis, an internal standard is added to each sample for absolute quantitative analysis.

4. The method according to claim 1, characterized in that: Calculate the absolute concentration of the target compound.

5. The method according to claim 1 or 4, characterized in that: The target compounds include gammacerane, C 30 Hopane, phenanthrene and methylphenanthrene series compounds.

6. The method according to claim 1, characterized in that The formula for calculating the methylphenanthrene index is: Methylphenanthrene index = 1.5 × (3-methylphenanthrene + 2-methylphenanthrene) / (phenanthrene + 9-methylphenanthrene + 1-methylphenanthrene); The calculation formula for equivalent maturity is: equivalent maturity = 0.6 × methylphenanthrene index + 0.

4.

7. The method according to claim 1, characterized in that The gamma cerane content, C 30 The data of hopane content and equivalent maturity were fitted respectively to determine the relationship between the two and equivalent maturity.

8. The method according to claim 7, characterized in that Taking the maturity of 0.5% as the low maturity boundary, calculate the gammacerane and C 30 Hopane content.

9. The method according to claim 1, characterized in that: The original gammacerane index is equal to the gammacerane content and C at a maturity of 0.5%. 30 The ratio of hopane content.

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