A method for oil and gas geochemical research using gas logging data

Abstract

The application provides a method for oil and gas geochemical research by using gas logging data, and relates to the technical field of oil and gas exploration, which comprises the following steps: counting gas logging data of abnormal layers and layers available as oil and gas layers of all exploratory wells in a research area, counting gas logging values of known main hydrocarbon source rocks in the research area, determining oil and gas sources by superimposing the gas logging data of the oil and gas layers in the research area and the data of the hydrocarbon source rocks; counting gas logging total hydrocarbon component big data of the hydrocarbon source rocks in the research area, obtaining the starting depth of effective hydrocarbon source rocks according to the condition that high carbon components are detected; and counting the total hydrocarbon content of the hydrocarbon source rocks in the research area, and obtaining the burial depth of the effective hydrocarbon source rocks in the research area according to the characteristics that all the detected components are effective hydrocarbon source rocks. The method for geochemical research can improve the identification efficiency of the hydrocarbon source rocks so as to provide a reference for exploration decision-making.

Description

Technical Field

[0001] This application relates to the field of oil and gas exploration technology, and in particular to a method for conducting oil and gas geochemical research using gas logging data. Background Technology

[0002] The science of studying the origin, migration, accumulation, and evolution of petroleum using chemical principles, and applying this knowledge to the exploration and development of petroleum, natural gas, bitumen, and other resources, is called petroleum geochemistry.

[0003] In oil and gas exploration, the six elements of "source, reservoir, cap, migration, trap, and preservation" are often used to summarize oil and gas evaluation. Among these, petroleum geochemistry research covers four aspects: oil generation, migration, reservoir, and preservation. The comprehensive application of multiple geochemical indicator systems can effectively reflect the characteristics and distribution patterns of source layers within a basin, the correlation of oil and gas sources, the direction, pathway, and scale of oil and gas migration, the injection time and sequence of oil and gas accumulation, and the preservation conditions of oil and gas reservoirs. Petroleum geochemistry is involved in all aspects of oil and gas exploration, or runs through the entire exploration process.

[0004] Current oil and gas geochemical research relies on a large amount of geochemical experimental analysis and data. However, obtaining this geochemical experimental data is time-consuming and costly. Furthermore, for exploration blocks with relatively few wells, the number of core samples and geochemical analysis samples is also relatively small. The conclusions drawn from the analysis of geochemical data from a single well are bound to be generalized from a single point, making it difficult to efficiently guide the exploration direction. Summary of the Invention

[0005] This application provides a method for conducting petroleum geochemical research using gas logging data, which improves the efficiency of source rock identification and provides a reference for exploration decisions.

[0006] This application provides a method for conducting petroleum geochemical research using gas logging data, including: statistical analysis of gas logging anomaly layers and sections that can be used as petroleum and gas layers in all exploration wells in the study area; statistical analysis of gas logging values ​​of known main source rocks in the study area; and determination of petroleum and gas sources by superimposing gas logging data of petroleum and gas-bearing layers in the study area with data of source rocks.

[0007] Effective source rocks are identified based on the geochemical parameters of the source rocks corresponding to the oil and gas sources.

[0008] In some embodiments of this application, the statistical analysis of gas logging anomaly layers and intervals that can be used as oil and gas reservoirs in all exploration wells in the study area includes:

[0009] Statistical analysis was conducted on the gas logging anomaly layers and the iC4, nC4, iC5, and nC5 data of all exploration wells in the study area that could be used as oil and gas reservoirs. The iC4 / nC4 and iC5 / nC5 relationship charts were obtained, and the oil and gas reservoir segments were determined based on the iC4 / nC4 and iC5 / nC5 relationship charts.

[0010] In some embodiments of this application, determining the oil and gas source based on the iC4 / nC4 and iC5 / nC5 relationship diagrams includes:

[0011] If the iC4 / nC4 and iC5 / nC5 values ​​correspond to geochemical heterocarbon ratio parameters of the oil and gas reservoir with high heterocarbon ratios, then the oil and gas reservoir segment is an oil and gas reservoir generated from source rocks in an oxidizing environment.

[0012] In some embodiments of this application, determining the oil and gas source based on the iC4 / nC4 and iC5 / nC5 relationship diagrams includes:

[0013] If iC4 / nC4 is less than 1 and iC5 / nC5 is constant around 1, then the oil and gas layer is an oil and gas layer generated from source rocks in a reducing environment.

[0014] In some embodiments of this application, the statistical analysis of gas measurements of known main source rocks in the study area includes:

[0015] The gas-gauge iC4 / nC4 and iC5 / nC5 values ​​of the known main source rocks in the study area were statistically analyzed to determine whether the overall iC4 / nC4 ratio of the measurement points was less than 1, and whether the overall iC5 / nC5 ratio of the measurement points was less than 1.5.

[0016] In some embodiments of this application, if the total number of iC4 / nC4 measurement points is less than 1 and the total number of iC5 / nC5 measurement points is less than 1.5, the gas measurement data of the oil and gas-bearing strata in the study area is superimposed with the data of the source rock to obtain the superposition result.

[0017] In some embodiments of this application, if the superposition results show that, except for the oil and gas showing wells in oxidizing environments, the other oil and gas showing wells all have a predetermined affinity with the gas geochemical characteristics of the known main source rocks, then the oil and gas in the other layers originate from the known main source rocks in the study area.

[0018] In some embodiments of this application, the sedimentary environment and maturity evaluation index of source rocks are determined by comparing the main source rocks in the known study area. The sedimentary environment and maturity evaluation index of source rocks are the isomeric carbon ratios iC4 / nC4 and iC5 / nC5.

[0019] In some embodiments of this application, the step of identifying effective source rocks based on geochemical parameters of the source rocks corresponding to the oil and gas sources includes:

[0020] Statistical analysis was performed on the total hydrocarbon composition data of the source rocks in the study area. The length and depth of the total hydrocarbon composition of each well were recorded. If no C4 or higher components were detected, it was considered a layer with incomplete total hydrocarbon composition. If C4 or higher components were detected, it was considered a layer with complete total hydrocarbon composition. Based on the condition that high carbon groups were detected, the layer was classified as an effective source rock, and the starting depth of the effective source rock was obtained.

[0021] In some embodiments of this application, the step of identifying effective source rocks based on the geochemical parameters of the source rocks corresponding to the oil and gas sources includes:

[0022] The total hydrocarbon content of source rocks in the study area was statistically analyzed. Based on the characteristic that all gas-detected components were effective source rocks, the burial depth of effective source rocks in the study area was determined.

[0023] This application has the following beneficial effects:

[0024] Compared to geochemical data of oil and gas or source rocks obtained in the laboratory, in-situ gas logging technology provides large volumes of data, while being inexpensive and timely. It can provide complete hydrocarbon and component data per meter, especially dense data and fully dehydrocarbon component data for gas logging anomaly sections. Besides quickly and intuitively identifying the source of oil and gas and the maturity depth of source rocks, thus providing decision-making references during drilling and exploration, it can also supplement oil and gas geochemical and source layer geochemical studies, enriching oil and gas geochemical research. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart illustrating the method for conducting petroleum geochemical research using gas logging data in the embodiments of this application.

[0027] Figure 2 This is a geochemical anisomorphic ratio parameter diagram of oil and gas reservoirs in the embodiments of this application;

[0028] Figure 3 This is a geochemical anisomorphic ratio parameter diagram of source rock and oil and gas reservoir in the embodiments of this application;

[0029] Figure 4 This is a schematic diagram of the conversion of organic matter into gas in the embodiments of this application;

[0030] Figure 5 This is a schematic diagram of hydrocarbon generation and expulsion in the source rock in the embodiments of this application;

[0031] Figure 6 This is a longitudinal distribution map of hydrocarbon source rock gas components in the embodiments of this application;

[0032] Figure 7 This is a graph showing the relationship between total hydrocarbon content and depth in source rock gas analysis in this application embodiment. Detailed Implementation

[0033] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The terminology used in the embodiments section of this application is only used to explain the specific embodiments of this application and is not intended to limit this application.

[0034] The study of the genesis, migration, accumulation, and evolution of petroleum using chemical principles, and the application of this knowledge to the exploration and development of petroleum, natural gas, bitumen, and other resources, is known as petroleum geochemistry. In oil and gas exploration, the six elements of "source, reservoir, cap, migration, trap, and preservation" are often used to summarize oil and gas evaluation. Petroleum geochemistry encompasses four aspects: source, migration, reservoir, and preservation. By comprehensively applying multiple geochemical indicator systems, it is possible to effectively reflect the characteristics and distribution patterns of source layers within a basin, the correlation of oil and gas sources, the direction, pathway, and scale of oil and gas migration, the injection time and sequence of oil and gas accumulation, and the preservation conditions of oil and gas reservoirs. Petroleum geochemistry involves all aspects of oil and gas exploration or runs through the entire exploration process.

[0035] Oil and gas are mainly composed of hydrocarbons, ranging from simple structures like methane to long-chain alkanes and complex structures like steranes, terpenes, and aromatics. Based on their form, oil and gas are classified as gaseous, liquid, and solid hydrocarbons. Gaseous hydrocarbons, due to their low carbon number and simple molecular structure, are primarily studied using carbon isotope analysis. Liquid hydrocarbons have medium molecular weights and relatively simple structures, with isomers increasing with the carbon number; therefore, their study primarily uses light hydrocarbon chromatography. Solid hydrocarbons have large molecular weights and very complex structures, such as n-alkanes and isoprene-like alkanes, which are analyzed using saturated hydrocarbon gas chromatography. Steanes, with their highly complex molecular structures, are analyzed using chromatography-mass spectrometry. Therefore, research on hydrocarbons with different carbon numbers should be given due attention. Gas logging data from drilling is mainly used for discovering oil and gas reservoirs; only in recent years has it been used for shale gas evaluation, but currently it is rarely used for geochemical research and evaluation of oil and gas and source rocks. In-situ gas logging technology can provide total hydrocarbon and component data per meter, especially dense data and complete hydrocarbon component data for gas logging anomaly sections. In addition to identifying oil and gas reservoirs, it can also be used to conduct geochemical and source geochemical studies on oil and gas, thus improving or supplementing oil and gas geochemical research.

[0036] However, based on current domestic and international research, systematic research on oil and gas geochemistry is relatively mature. The evaluation of source rocks and oil and gas reservoirs involves a combination of technologies. However, gaseous hydrocarbons, due to their low carbon number and simple molecular structure, are primarily studied using carbon isotope analysis, making the analytical techniques for gaseous hydrocarbons relatively limited. Currently, gas logging data from drilling is mainly used for oil and gas reservoir discovery and reservoir fluid properties research, and only recently has it been used for shale gas evaluation. However, the application of gas logging indicators for geochemical research and evaluation of oil, gas, and source rocks is rarely explored. Oil and gas geochemical research relies on extensive geochemical experimental analysis and data, but acquiring this data is time-consuming and costly. Furthermore, for exploration blocks with relatively few wells, the number of core samples and geochemical analysis samples is also relatively small. Conclusions drawn from single-well geochemical data analysis inevitably tend to be generalized, making it difficult to efficiently guide exploration direction.

[0037] like Figures 1 to 7 As shown, to solve at least one of the above-mentioned technical problems in the prior art, an embodiment of this application provides a method for conducting oil and gas geochemical research using gas logging data, comprising:

[0038] 1. Oil source identification

[0039] Based on the aforementioned principles, gas-produced hydrocarbons are C1-C5 gaseous hydrocarbons with simple molecular structures. Compared to other hydrocarbons, their geochemical characteristics are much simpler and clearer, and their geochemical significance should also be relatively clear. Under reducing conditions, organic matter exhibits low heterocarbon ratios (iC4 / nC4 and iC5 / nC5) during thermal evolution and hydrocarbon generation; under oxidizing conditions, organic matter exhibits high heterocarbon ratios (iC4 / nC4 and iC5 / nC5) during thermal evolution and hydrocarbon generation. Statistical analysis of iC4, nC4, iC5, and nC5 data from gas-produced anomaly layers and oil / gas reservoirs in all wells within a study area yielded a graph showing the relationship between iC4 / nC4 and iC5 / nC5. Figure 2As can be seen from the geochemical isocarbon ratio parameters of each oil and gas layer, the iC4 / nC4 and iC5 / nC5 values ​​are clearly divided into two regions: the upper right oil and gas layer has a high isocarbon ratio, indicating an oil and gas layer produced by source rocks from an oxidizing environment; the lower layer has iC4 / nC4 less than 1 and iC5 / nC5 stabilizing around 1, indicating an oil and gas layer produced by source rocks from a reducing environment. These two regions of oil and gas layers reflect source rocks from different sedimentary environments. The same applies to the hydrocarbon content of source rocks in gas logging. If the total hydrocarbon content is dominated by methane, the sedimentary environment of the source rock is relatively oxidizing, and its main cracking products are mainly isoalkanes, exhibiting high iC4 / nC4 and iC5 / nC5 ratios; while source rocks dominated by lacustrine reduction produce gases with low iC4 / nC4 and iC5 / nC5 ratios. Gas logging data from source rocks possesses natural origin; simultaneously, source rock well sections are relatively long, resulting in good continuity of gas logging data. Furthermore, gas logging data from different depths within the basin or depression can be obtained. Statistical analysis of the gas logging iC4 / nC4 and iC5 / nC5 values ​​for known primary source rocks in a study area shows that the overall iC4 / nC4 ratio is less than 1, and the overall iC5 / nC5 ratio is less than 1.5. Overlaying the gas logging data of oil and gas-bearing strata with source rock data reveals that, except for oil and gas-showing well sections in oxidizing environments, other oil and gas-showing well sections show a good affinity with the gas logging geochemical characteristics of known primary source rocks, confirming that the oil and gas in other strata originate from the known primary source rocks in this study area.

[0040] Furthermore, by comparing the main source rocks in the known study areas, it can be concluded that the isomeric carbon ratios iC4 / nC4 and iC5 / nC5 can be used as evaluation indicators of the sedimentary environment and maturity of source rocks. That is, in the same environment, the iC4 / nC4 value is lower than the iC5 / nC5 value and the low values ​​of iC4 / nC4 and iC5 / nC5 (less than 1) indicate mature source rocks.

[0041] 2. Identification of effective source rocks

[0042] The thermal evolution process of organic matter transforming into gaseous hydrocarbons is also traceable. Figure 4 The principle behind this is that hydrocarbon expulsion is a process from generation to adsorption "saturation," and then to hydrocarbon expulsion. The hydrocarbon expulsion effect preferentially expels small molecule hydrocarbons (C1-C3), followed by the relatively heavier C4 and C5 hydrocarbons. Figure 5 Low-temperature, shallowly buried reservoirs have low hydrocarbon generation, with the main components being C1 and C2. +The components are present in very low concentrations, making it difficult for instruments to detect high-carbon components. Only after thermal evolution to a certain degree can high-carbon components be generated, at which point the source rock can be considered an effective source rock. Based on this theory, the gas logging data of the source rocks in the study area were statistically analyzed. The length and depth of the gas logging data for each well were recorded. The absence of C4 or higher components indicates incomplete hydrocarbon composition in the stratigraphic units, while the presence of C4 or higher components indicates complete hydrocarbon composition in the stratigraphic units. Figure 6 Based on the condition that high-carbon arrays are detected as effective source rocks, the starting depth of effective source rocks can be obtained.

[0043] As the underlying sedimentary layers increase in depth, geothermal temperature rises, and maturity increases, the organic matter content in source rocks continuously increases during the evolution of organic matter, regardless of whether it is liquid or gaseous hydrocarbons. Correspondingly, the total hydrocarbon content also increases sequentially. The total hydrocarbon composition changes from undetectable high-carbon components (C4, C5) to detectable high-carbon components (C4, C5) with increasing depth. By statistically analyzing the total hydrocarbon content of source rocks in the study area, and based on the characteristic that all gaseous samples are from effective source rocks, the burial depth of effective source rocks in the study area can be determined. Figure 7 As shown in the figure, geochemical studies of the gaseous environment indicate that the effective hydrocarbon source has a depth of 3000m and a total hydrocarbon content greater than 0.1%.

[0044] The gas logging data used in this embodiment is geochemical data obtained during drilling. Currently, the gas logging data recorded in field drilling is a large volume of data compared to the geochemical data of oil and gas or source rocks obtained in the laboratory, while also being inexpensive and timely. In-situ gas logging technology can provide total hydrocarbon and component data per meter, especially the densified data and complete hydrocarbon component data of gas logging anomaly sections. In addition to quickly and intuitively identifying the oil and gas source and the maturity depth of the source rock, thus providing decision-making reference during drilling exploration, it can also be used to conduct geochemical and source layer geochemical studies of oil and gas, supplementing the research on oil and gas geochemistry.

[0045] The working principle of this embodiment is as follows:

[0046] (1) Under acidic catalytic conditions, organic matter undergoes significant carbon skeleton rearrangement, resulting in diversified organic matter products. This catalytic cracking can break down long-chain alkanes into a large number of low-molecular-weight isoalkanes. Under acidic conditions, hydrocarbons are mainly cracked by carbon cations, with isoalkanes being the main products, exhibiting a high isocarbon ratio. Under neutral conditions, free radical cracking is the main process, with n-alkanes being the main products, exhibiting a low isocarbon ratio. Corresponding to the formation conditions, oxidizing conditions are considered to be acidic media, while reducing conditions are considered to be neutral to alkaline media. That is to say, organic matter under reducing conditions has a low isocarbon ratio during thermal evolution and hydrocarbon generation, while organic matter under oxidizing conditions has a high isocarbon ratio during thermal evolution and hydrocarbon generation. The geochemical parameters of this correlated gas logging anomaly layer can be used to determine the oil and gas and the sedimentary environment of source rocks in different layers and wells through the isocarbon ratio, thereby determining the source of oil and gas.

[0047] (2) As the overlying sedimentary strata increase, the burial depth increases, the geothermal temperature rises, and the maturity of organic matter in source rocks increases, the hydrocarbon content continuously increases and the molecular composition of hydrocarbons continuously decreases during the process of organic matter changing from solid to liquid or gaseous state. In other words, the content and composition of gaseous hydrocarbons in source rocks also change with the thermal evolution of organic matter. The total hydrocarbon content increases with depth, and at the same time, the composition of gaseous hydrocarbons changes from incomplete to complete. The depth at which the composition begins to become complete is the depth of source rock maturity.

[0048] This embodiment uses the "positive-isomeric carbon ratio" in gas sampling components to identify oil and gas sources and uses the total hydrocarbon component content to identify effective source rocks. It can obtain geochemical data of oil and gas sources and source rocks in the first time during the drilling process, providing a reference for exploration decisions.

[0049] The above embodiments are merely explanations of this application and are not intended to limit it. After reading this specification, those skilled in the art can make modifications to the implementation methods of this application without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for conducting petroleum geochemical research using gas logging data, characterized in that, include: Gas logging data of gas-prone layers and oil-gas-bearing zones in all exploration wells in the study area were statistically analyzed. Gas logging values ​​of known main source rocks in the study area were also statistically analyzed. Oil and gas sources were determined by superimposing gas logging data of oil-gas-bearing layers in the study area with source rock data. Identify effective source rocks based on the geochemical parameters of the source rocks corresponding to the oil and gas sources; The statistical analysis of gas measurement values ​​of the known main source rocks in the study area includes: The gas-gauge iC4 / nC4 and iC5 / nC5 values ​​of the known main source rocks in the study area were statistically analyzed to determine whether the overall iC4 / nC4 ratio of the measurement points was less than 1, and whether the overall iC5 / nC5 ratio of the measurement points was less than 1.

5. If the total number of measuring points iC4 / nC4 is less than 1 and the total number of measuring points iC5 / nC5 is less than 1.5, then the gas measurement data of the oil and gas-bearing reservoirs in the study area will be overlaid with the data of the source rocks to obtain the overlay results. If the superposition results show that, except for the oil and gas showing wells in oxidizing environments, the other oil and gas showing wells all have a pre-defined affinity with the gas geochemical characteristics of the known main source rocks, then the oil and gas in the other intervals originate from the known main source rocks in the study area.

2. The method for conducting petroleum geochemical research using gas logging data according to claim 1, characterized in that, The statistical analysis of gas logging anomaly layers and intervals that can be used as oil and gas reservoirs in all exploration wells in the study area includes: Statistical analysis was conducted on the gas logging anomaly layers and the iC4, nC4, iC5, and nC5 data of all exploration wells in the study area that could be used as oil and gas reservoirs. The iC4 / nC4 and iC5 / nC5 relationship charts were obtained, and the oil and gas reservoir segments were determined based on the iC4 / nC4 and iC5 / nC5 relationship charts.

3. The method for conducting petroleum geochemical research using gas logging data according to claim 2, characterized in that, The determination of oil and gas sources based on the iC4 / nC4 and iC5 / nC5 relationship charts includes: If the iC4 / nC4 and iC5 / nC5 values ​​correspond to geochemical heterocarbon ratio parameters of the oil and gas reservoir with high heterocarbon ratios, then the oil and gas reservoir segment is an oil and gas reservoir generated from source rocks in an oxidizing environment.

4. The method for conducting petroleum geochemical research using gas logging data according to claim 2, characterized in that, The determination of oil and gas sources based on the iC4 / nC4 and iC5 / nC5 relationship charts includes: If iC4 / nC4 is less than 1 and iC5 / nC5 is constant around 1, then the oil and gas layer is an oil and gas layer generated from source rocks in a reducing environment.

5. The method for conducting petroleum geochemical research using gas logging data according to claim 1, characterized in that, The sedimentary environment and maturity evaluation indicators of source rocks were determined by comparing the known main source rocks in the study area. The sedimentary environment and maturity evaluation indicators of source rocks are the isomeric carbon ratios iC4 / nC4 and iC5 / nC5.

6. The method for conducting petroleum geochemical research using gas logging data according to any one of claims 1 to 5, characterized in that, The identification of effective source rocks based on the geochemical parameters of the source rocks corresponding to the oil and gas sources includes: Statistical analysis was performed on the total hydrocarbon composition data of the source rocks in the study area. The length and depth of the total hydrocarbon composition of each well were recorded. If no C4 or higher components were detected, it was considered a layer with incomplete total hydrocarbon composition. If C4 or higher components were detected, it was considered a layer with complete total hydrocarbon composition. Based on the condition that high carbon groups were detected, the layer was classified as an effective source rock, and the starting depth of the effective source rock was obtained.

7. The method for conducting petroleum geochemical research using gas logging data according to claim 6, characterized in that, The identification of effective source rocks based on the geochemical parameters of the source rocks corresponding to the oil and gas sources includes: The total hydrocarbon content of source rocks in the study area was statistically analyzed. Based on the characteristic that all gas-detected components were effective source rocks, the burial depth of effective source rocks in the study area was determined.

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