A method for dividing source rock sedimentary organic facies by using dibenzofuran and methylfluorene

Abstract

This invention relates to the field of oil and gas field exploration technology, specifically to a method for classifying the sedimentary organic facies of source rocks using dibenzofuran and methyl fluorene. The method uses the aromatic compounds dibenzofuran and methyl fluorene as indicators to classify the sedimentary organic facies of source rocks. The method is simple, highly accurate, and provides important evidence for source rock evaluation and fine oil source correlation.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field exploration technology, specifically to a method for classifying the organic phases of source rock sediments using dibenzofuran and methylfluorene. Background Technology

[0002] In recent years, organic facies have been increasingly used in oil and gas exploration and resource assessment. Sedimentary organic facies should encompass characteristics such as sedimentary environment, bioassortment, and redox conditions; that is, the same sedimentary organic facies should possess similar organic matter characteristics. When studying source rock organic facies, only by comprehensively considering its organic petrology, organic geochemistry, and sedimentology can its typical hydrocarbon generation conditions and spatial distribution characteristics be clearly identified. Therefore, expanding the concept of organic facies to include sedimentary organic facies can better reflect the genesis and distribution characteristics of organic matter in sedimentary strata.

[0003] Chinese invention patent CN110441813B discloses a method for predicting the development and distribution of high-quality lacustrine source rocks. In this method, the sedimentary organic facies types of each single well are divided based on the sedimentary environment, paleolaceous model, organic matter abundance, and organic matter type. The sedimentary organic facies are divided into five types: A, B, C, D, and E. Among them, type A sedimentary organic facies (referred to as A facies) and type B sedimentary organic facies (referred to as B facies) are the dominant facies zones for the development of high-quality source rocks. Among the five sedimentary organic phases (A, B, C, D, and E) identified, the average TOC content in phase A was 3.33%, the average S1+S2 content was 22.42 mg / g, and the average HI content was 580 mg / g; in phase B, the average TOC content was 1.92%, the average S1+S2 content was 9.07 mg / g, and the average HI content was 364 mg / g; in phase C, the average TOC content was 1.13%, the average S1+S2 content was 4.01 mg / g, and the average HI content was 236 mg / g; in phase D, the average TOC content was 3.64%, the average S1+S2 content was 14.42 mg / g, and the average HI content was 225 mg / g; and in phase E, the average TOC content was 0.42%, the average S1+S2 content was 0.61 mg / g, and the average HI content was 100 mg / g.

[0004] Because the classification of organic facies in source rock sediments involves numerous organic matter characteristics, each with different applicable conditions, existing methods are complex and do not adequately consider all the relevant organic matter characteristics. Therefore, a simple, effective, and comprehensive method for classifying organic facies in source rock sediments is needed. Summary of the Invention

[0005] The main objective of this invention is to provide a method for classifying the organic phases of source rocks using dibenzofuran and methyl fluorene. This method is simple, highly accurate, and takes into account various factors, providing an important basis for source rock evaluation and fine oil source correlation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for classifying the organic facies of source rocks using dibenzofuran and methyl fluorene, comprising the following steps: determining the main stratigraphic sequence of source rock development; determining the distribution range of source rocks; selecting source rock samples from the same stratigraphic sequence in the study area to determine the dibenzofuran index in aromatic compounds; selecting source rock samples from the same stratigraphic sequence in the study area to determine the methyl fluorene ratio in aromatic compounds; analyzing the variation patterns of dibenzofuran and methyl fluorene indices on the plane of the study area; compiling a lithofacies paleogeographic map of the study area; and combining the lithofacies paleogeographic map of the study area with the variation patterns of dibenzofuran and methyl fluorene indices to classify the organic facies of source rocks and identify favorable areas for the development of source rocks in each organic facies.

[0008] Furthermore, based on geochemical data of the study area, such as rock organic carbon, pyrolysis, and vitrinite reflectance, combined with geological condition analysis, the main stratigraphic layers for hydrocarbon source rock development were determined.

[0009] Furthermore, based on the development, sedimentary characteristics, and organic geochemical characteristics of mudstone and shale strata within depressions or basins, the distribution range of high-quality source rocks can be determined.

[0010] Furthermore, source rock samples from the same strata in the study area were selected for online aromatic hydrocarbon chromatography-mass spectrometry analysis of biomarkers, and the dibenzofuran index was calculated to reflect the characteristics of the biological assemblage in the sedimentary organic phase.

[0011] Furthermore, the formula for calculating the dibenzofuran index is as follows:

[0012] Dibenzofuran index = Dibenzofuran content / (Dibenzofuran content + 3-methylbiphenyl content + 4-methylbiphenyl content).

[0013] Furthermore, source rock samples from the same strata in the study area were selected for online aromatic hydrocarbon chromatography-mass spectrometry analysis of biomarkers, and the methyl fluorene ratio was calculated to reflect the characteristics of the diagenetic environment and redox conditions in the sedimentary organic phase.

[0014] Furthermore, the formula for calculating the methylfluorene ratio is as follows:

[0015] Methylfluorene ratio = 3-methylfluorene content / (2-methylfluorene content + 1-methylfluorene content + 4-methylfluorene content).

[0016] Furthermore, by statistically analyzing the sandstone thickness and sand-to-land ratio data of the main source rock strata, and combining this with geological structures, a lithofacies paleogeographic map was drawn.

[0017] Furthermore, based on the variation patterns of dibenzofuran and methylfluorene in the plane, relevant standards for the division of sedimentary organic phases were established.

[0018] When the dibenzofuran index is <0.1 and the methyl fluorene ratio is >0.5, the organic facies of the source rock sediments is a slightly brackish terrestrial-aquatic facies.

[0019] When the dibenzofuran index is 0.1-0.2 and the methyl fluorene ratio is <0.5, the organic phase of the source rock sediment is a brackish water mixed-source phase;

[0020] When the dibenzofuran index is 0.2-0.6 and the methyl fluorene ratio is <0.5, the organic facies of the source rock sediments is a brackish deep lacustrine facies.

[0021] When the dibenzofuran index is >0.6 and the methylfluorene ratio is >0.5, the organic phase of the source rock sediment is a slightly brackish mixed source phase.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] This invention offers a simple and highly accurate method for classifying hydrocarbon sources. The use of dibenzofuran and methyl fluorene, two aromatic hydrocarbon indices, is highly innovative and has been largely unused in the past, yet they have proven very effective in this study. Furthermore, these two indices comprehensively consider numerous factors, including sedimentary environment, bioassemblage characteristics, sedimentary diagenetic environment, and redox conditions, demonstrating a high degree of comprehensiveness. Based on the dibenzofuran and methyl fluorene indices, brackish water-terrestrial facies, brackish water mixed-source facies, brackish water deep lacustrine facies, and brackish water mixed-source facies can be classified. This invention provides an important basis for hydrocarbon source rock evaluation and refined oil source correlation. Attached Figure Description

[0024] Figure 1 This is a flowchart of the method for dividing the organic phases of source rock sediments using dibenzofuran and methylfluorene, as described in Example 1 of the present invention.

[0025] Table 1 shows the correspondence between sedimentary organic phases and identification indicators;

[0026] Figure 2 A planar feature diagram showing the differences in dibenzofuran index characteristics in a certain depression;

[0027] Figure 3 This is a planar feature diagram showing the difference in the methylfluorene ratio of a certain depression. Detailed Implementation

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0030] 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 described in detail below with reference to specific embodiments.

[0031] Example 1

[0032] like Figure 1 As shown, Figure 1 This is a flowchart of a specific embodiment of the method of dividing source rock sedimentary organic phases using dibenzofuran and methylfluorene according to the present invention.

[0033] Step 101: Based on geochemical data such as organic carbon, pyrolysis, and vitrinite reflectance, combined with geological condition analysis, determine the main stratigraphic sequence for hydrocarbon source rock development. Proceed to Step 102.

[0034] Step 102: Based on the development, sedimentary characteristics, and organic geochemical characteristics of mudstone and shale strata within the depression or basin, determine the distribution range of high-quality source rocks. The process then proceeds to step 103.

[0035] Step 103: Uniformly select source rock sample points within the study area and perform online aromatic hydrocarbon chromatography-mass spectrometry analysis of biomarkers to calculate the dibenzofuran index and methyl fluorene ratio. Dibenzofuran index = dibenzofuran / (dibenzofuran + 3-methylbiphenyl + 4-methylbiphenyl); Methyl fluorene ratio = 3-methyl fluorene / (1-methyl fluorene + 2-methyl fluorene + 4-methyl fluorene). The dibenzofuran index characterizes the sedimentary environment and bioassemblage characteristics, while the methyl fluorene ratio characterizes the sedimentary diagenetic environment and redox environment. Proceed to step 104.

[0036] Step 104: Statistical analysis of the dibenzofuran index and methyl fluorene ratio of high-quality source rock samples in the study area is performed, and a planar distribution bar chart of these two aromatic hydrocarbon indicators in the study area is generated, summarizing the variation patterns. The process then proceeds to step 105.

[0037] Step 105: Statistical analysis of sandstone thickness and sand-to-soil ratio data for the main source rock strata is performed. Combined with geological structural information, a lithofacies paleogeographic map is drawn, and sedimentary facies are zoned according to different sedimentary environments. The process then proceeds to step 106.

[0038] In step 106, based on the different sedimentary environments of the study area and the variation patterns of the dibenzofuran index and methyl fluorene ratio on the plane, the differences between each adjacent unit are identified, the final division of the organic facies of the source rock sediments is carried out, and favorable areas for the development of source rocks are identified.

[0039] Taking a certain depression in a basin as an example, by adopting the principle of comprehensive classification and naming based on sedimentary environment and organic matter source, and combining the differences in sedimentary facies and geochemical characteristics, four types of sedimentary organic facies were summarized in a certain depression: slightly brackish water-terrestrial facies, brackish water mixed-source facies, brackish water deep lacustrine facies, and slightly brackish water mixed-source facies.

[0040] The organic facies of source rock sediments were divided using the method described in Example 1. The variation patterns of dibenzofuran index and methyl fluorene ratio on the plane were as follows: The brackish terrestrial facies was mainly composed of lacustrine and nearshore underwater fan sediments. The organic matter originated from lower aquatic organisms mixed with terrestrial higher plants carried by rivers. The dibenzofuran index was very low, while the methyl fluorene ratio was relatively high. Figure 2 , Figure 3 The first half-brackish water facies, characterized by high terrigenous clastic content, low carbonate content, and an oxidizing environment, indicates a high-salinity environment. The second half-brackish water facies, dominated by lacustrine and alluvial fan deposits, features parent material composed of lower aquatic organisms mixed with higher terrigenous plants. Terrigenous deposition is evident, with low dibenzofuran indices and methyl fluorene ratios, indicating high terrigenous clastic content, low carbonate content, and a high-salinity reducing environment. The third half-brackish deep-lacustrine facies is dominated by lower lacustrine aquatic organisms, with well-developed mudstone and limestone sedimentary assemblages. High dibenzofuran indices and low methyl fluorene ratios indicate low terrigenous clastic content, high carbonate content, and a stratified water environment with halocline. The fourth half-brackish water facies, characterized by slump turbidite fan deposits, features parent material composed of a mixture of lower aquatic organisms and higher terrigenous plants. High dibenzofuran indices and high methyl fluorene ratios indicate a low carbonate content and a slightly reducing environment. Based on the results of the index analysis, the parameter ranges for each sedimentary organic phase are given (Table 1).

[0041] Table 1. Correspondence between sedimentary organic phases and aromatic compound parameters in a certain depression.

[0042]

[0043] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for classifying organic facies of source rocks using dibenzofuran and methylfluorene, characterized in that, Includes the following steps: Identify the main stratigraphic layers in the development of hydrocarbon source rocks; Determine the distribution range of source rocks; Hydrocarbon source rock samples from the same stratigraphic strata in the study area were selected for determination of the dibenzofuran index in aromatic compounds, including: Hydrocarbon source rock samples from the same stratigraphic layer in the study area were selected for online aromatic hydrocarbon chromatography-mass spectrometry analysis of biomarkers, and the dibenzofuran index was calculated to reflect the characteristics of the biological assemblage in the sedimentary organic phase. The formula for calculating the dibenzofuran index is as follows: Dibenzofuran index = Dibenzofuran content / (Dibenzofuran content + 3-methylbiphenyl content + 4-methylbiphenyl content); The determination of the methyl fluorene ratio in aromatic compounds was carried out on source rock samples from the same stratum in the study area. This included: online aromatic hydrocarbon chromatography-mass spectrometry analysis of biomarkers was performed on source rock samples from the same stratum in the study area, and the methyl fluorene ratio was calculated to reflect the characteristics of the diagenetic environment and redox conditions in the sedimentary organic phase. The formula for calculating the methylfluorene ratio is as follows: Methylfluorene ratio = 3-methylfluorene content / (1-methylfluorene content + 2-methylfluorene content + 4-methylfluorene content); Analyze the variation patterns of dibenzofuran and methylfluorene in the study area; A lithofacies paleogeographic map of the study area was compiled; Based on the lithofacies paleogeographic map of the study area and the variation patterns of dibenzofuran and methylfluorene, the organic facies of the source rocks were divided, and favorable areas for the development of source rocks of each organic facies were identified, including: Based on the planar variation patterns of dibenzofuran and methylfluorene, relevant criteria for the division of sedimentary organic phases were established: When the dibenzofuran index is <0.1 and the methyl fluorene ratio is >0.5, the organic facies of the source rock sediments is a slightly brackish terrestrial-aquatic facies. When the dibenzofuran index is 0.1-0.2 and the methyl fluorene ratio is <0.5, the organic phase of the source rock sediment is a brackish water mixed-source phase; When the dibenzofuran index is 0.2-0.6 and the methyl fluorene ratio is <0.5, the organic facies of the source rock sediments is a brackish deep lacustrine facies. When the dibenzofuran index is >0.6 and the methylfluorene ratio is >0.5, the organic phase of the source rock sediment is a slightly brackish mixed source phase.

2. The method of claim 1, wherein, Based on geochemical data of the study area and geological condition analysis, the main stratigraphic layers for hydrocarbon source rock development were determined.

3. The method of claim 1, wherein, The distribution range of high-quality source rocks can be determined based on the development, sedimentary characteristics, and organic geochemical characteristics of mudstone and shale strata within depressions or basins.

4. The method of claim 1, wherein, By statistically analyzing the sandstone thickness and sand-to-land ratio data of the main source rock strata, and combining this with geological structures, a lithofacies paleogeographic map was drawn.

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