"Four-element-dominated" prediction method and device for lacustrine high-quality source rocks in oil-rich depressions

Abstract

The present invention relates to a method and device for predicting high-quality lacustrine source rocks in an oil-rich depression dominated by four elements. The method comprises the following steps: determining whether a depression has "strong faulting" conditions based on analysis and judgment of the activity rate of faults controlling the depression and the basement rate; determining whether a depression has "moderate shielding" conditions based on analysis and judgment of the source-to-sag ratio, the depression subsidence rate and the sedimentation rate ratio, and the main development of muddy fine-grained sediments in the depression; determining whether a depression has "eutrophication" conditions based on analysis and judgment of the 4-methylsterane index and the average value of the total organic carbon (TOC) content; determining whether a depression has "thermal event" conditions based on analysis and judgment of the average terrestrial heat flow value in the depression area or the local terrestrial heat flow value in the depression; and evaluating high-quality lacustrine source rocks in the oil-rich depression based on a comprehensive evaluation of the four main controlling factors of "strong faulting, moderate shielding, eutrophication, and thermal events."

Description

Technical Field

[0001] The present invention relates to a "quaternary dominant" oil-rich depression lacustrine high-quality hydrocarbon source rock prediction method and device, belonging to the field of oil and natural gas exploration. Background Art

[0002] The "source control theory" in petroleum geology holds that the key to determining whether a basin will become an oil-rich sag lies in the presence of high-quality source rocks. Currently, prediction of high-quality lacustrine source rocks in oil-rich sags, both domestically and internationally, typically relies on a combined well-seismic approach. This approach combines drilling data with seismic data, calibrates the well-seismic data, and then extrapolates the data to the vicinity of the well site. In well-absent areas, source rock development is typically predicted by comparing seismic reflection characteristics with those in surrounding well-recorded areas. This well-seismic approach has some practical applications, but is significantly affected by seismic data and human factors. In recent years, with the integration of oil and gas exploration and computer technology, researchers have developed methods for source rock prediction using neural networks and other tools. However, these methods ultimately rely on well-seismic data and mathematical calculations, failing to understand the mechanisms of high-quality source rock development and predict its extent or potential to become an oil-rich sag. Summary of the Invention

[0003] In response to the above technical problems, the present invention provides a "four-element-dominant" method and device for predicting high-quality lacustrine source rocks in oil-rich depressions. This method is based on the analysis of the formation process and development characteristics of source rocks in confirmed oil-rich depressions, systematically summarizes and condenses the "four-element-dominant" (strong faulting-moderate obstruction-eutrophication-thermal events) formation mechanism of high-quality lacustrine source rocks in oil-rich depressions and establishes corresponding prediction indicators, providing a more scientific and effective method for predicting high-quality lacustrine source rocks in oil-rich depressions.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A "four-element-dominated" method for predicting high-quality lacustrine source rocks in oil-rich depressions includes the following steps:

[0006] Based on the analysis of the activity rate of the faults controlling the depression and the basement subsidence rate, it is determined whether the depression has the conditions for "strong fault depression";

[0007] Based on the source-sag ratio, the ratio of the sag subsidence rate to the sedimentation rate, and the analysis of the main development of muddy fine-grained sediments in the sag, it is concluded whether the sag has "moderate shielding" conditions;

[0008] Based on the analysis of the 4-methylsterane index and the average value of total organic carbon (TOC) content, it is determined whether the depression has "eutrophic" conditions;

[0009] Based on the analysis and judgment of the average terrestrial heat flow value in the depression area or the local terrestrial heat flow value in the depression, it is determined whether the depression has the conditions of a "thermal event";

[0010] Based on the comprehensive evaluation of the four main controlling factors of "strong faulting-moderate shielding-eutrophication-thermal events", the high-quality lacustrine source rocks in oil-rich depressions were evaluated.

[0011] The "four-element-dominated" method for predicting high-quality lacustrine source rocks in oil-rich depressions preferably determines whether the depression has "strong faulting" conditions by analyzing and judging that the activity rate of the depression-controlling fault is greater than 150m / Ma and the basement subsidence rate is greater than 200m / Ma.

[0012] The method for predicting high-quality lacustrine source rocks in the "quaternary-dominated" oil-rich depression preferably determines whether the depression has "moderate obstruction" conditions by analyzing and judging that the "source-to-sag ratio" is less than 2, the ratio of the depression subsidence rate to the deposition rate is greater than 1.02, and muddy fine-grained sediments are mainly developed in the depression.

[0013] The "quaternary-dominated" oil-rich depression lacustrine high-quality source rock prediction method preferably determines whether the depression has "eutrophic" conditions by analyzing and judging whether the 4-methylsterane index is greater than 0.1 and the average total organic carbon content is greater than 2%.

[0014] The method for predicting high-quality source rocks in lacustrine facies of oil-rich depressions with the “quaternary dominant” principle is preferably carried out by measuring the average terrestrial heat flow value of the depression area or the local terrestrial heat flow value in the depression>65mW / m 2 Through analysis and judgment, it can be concluded whether the depression has the conditions of "thermal event".

[0015] The "four-element-dominant" method for predicting high-quality lacustrine source rocks in oil-rich depressions preferably evaluates whether the oil-rich depression has the four factors of "strong faulting - moderate shielding - eutrophication - thermal events". When these four conditions are met, it is predicted that the lacustrine phase developed in the oil-rich depression is high-quality source rock.

[0016] The second aspect of the present invention provides a "quaternary-dominant" prediction device for high-quality lacustrine source rocks in oil-rich depressions, comprising:

[0017] The first processing unit is used to determine whether the depression has "strong fault depression" conditions based on the analysis and judgment of the activity rate of the fault controlling the depression and the basement subsidence rate;

[0018] The second processing unit is used to determine whether the sag has "moderate shielding" conditions based on the analysis of the source-sag ratio, the ratio of the sag subsidence rate to the deposition rate, and the main development of muddy fine-grained sediments in the sag;

[0019] The third processing unit is used to determine whether the depression has "eutrophic" conditions based on the analysis of the 4-methylsterane index and the average value of the total organic carbon (TOC) content;

[0020] The fourth processing unit is used to determine whether the depression has the "thermal event" condition based on the analysis of the average terrestrial heat flow value of the depression area or the local terrestrial heat flow value in the depression;

[0021] The fifth processing unit is used to evaluate the high-quality lacustrine source rocks in oil-rich depressions based on a comprehensive evaluation of the four main controlling factors: strong faulting, moderate shielding, eutrophication, and thermal events.

[0022] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the computer program implements the steps of the above-mentioned "quaternary-dominated" method for predicting high-quality lacustrine source rocks in oil-rich depressions.

[0023] The fourth aspect of the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned "quaternary-dominated" method for predicting high-quality lacustrine source rocks in oil-rich depressions when executing the computer program.

[0024] The present invention has the following advantages due to the adoption of the above technical solution:

[0025] 1. Based on seismic data, drilling data, and analytical data, this analysis method predicts the presence of high-quality lacustrine source rocks in the study area through a comprehensive qualitative and quantitative evaluation of the four key controlling factors: strong faulting, moderate obstruction, eutrophication, and thermal events. This provides a basis for selecting oil-rich sags, evaluating exploration potential, and deploying exploration within petroliferous basins.

[0026] 2. Based on the analysis of the formation process and development characteristics of source rocks in proven oil-rich depressions, the present invention systematically summarizes and condenses the "four-element dominant" (strong faulting - moderate obstruction - eutrophication - thermal events) formation mechanism of high-quality lacustrine source rocks in oil-rich depressions and establishes corresponding prediction indicators, providing a more scientific and effective method for predicting high-quality lacustrine source rocks in oil-rich depressions.

[0027] 3. The prediction method of the present invention is based on the formation mechanism of source rocks. It makes predictions from a mechanistic perspective and is more in-depth, more meaningful and more accurate than well-seismic combined extrapolation and seismic reflection analogy analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 An analysis roadmap for the "quaternary-dominated" lacustrine high-quality source rock prediction method provided by one embodiment of the present invention;

[0029] Figure 2 This is a comprehensive seismic-geological analysis map of the X20 Depression in the Pearl River Mouth Basin provided by this embodiment of the present invention. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by ordinary persons in this field based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] In view of the shortcomings of existing source rock prediction methods in the study of exploration potential of oil-rich depressions, this paper proposes a "four-element dominant" method for predicting high-quality lacustrine source rocks in oil-rich depressions. This method is based on seismic data, drilling data, analytical and test data, and makes a qualitative and quantitative comprehensive evaluation of the four main controlling factors of "four-element dominant" (strong fault depression, moderate shielding, eutrophication, and thermal events). Figure 1 ), to predict whether high-quality lacustrine source rocks are developed in the study area, and to provide a basis for selecting oil-rich depressions, evaluating exploration potential, and deploying exploration in oil and gas basins.

[0032] like Figure 1 As shown, the first step of the prediction method of the present invention is to judge the first main controlling factor "strong fault" in the "four dominant factors". Structural geology and sequence stratigraphy theory show that in faulted lake basins, strong faults controlled by deep and large faults can provide sufficient accommodation space for the development of high-quality source rocks, which is conducive to the development of high-quality lacustrine source rocks. Based on the source positioning analysis of gravity and magnetic data and the analysis of medium and deep seismic data, it is revealed that during the heyday of the Eocene rifting in offshore basins, the offshore basins were affected by a strong tensile stress field. Many deep and large faults developed in the Bohai Sea, the northern depression zone of the Pearl River Mouth Basin, the Beibu Gulf Basin, etc., which controlled the substantial subsidence of some potential oil-rich depressions in the basins. Based on the statistical analysis of typical oil-rich depressions in offshore and eastern China, it is shown that the criteria for judging strong faults are the activity rate of the controlling faults greater than 150m / Ma and the basement subsidence rate greater than 200m / Ma. Deep depressions can be formed, which is conducive to the development of high-quality lacustrine source rocks.

[0033] The second step of the prediction method of the present invention determines the second main controlling factor of the "four dominant factors," "moderate obstruction." The sedimentological "source-sink" theory suggests that during the development of the main source rock, when the source material transported from the periphery of the sag into the sag is "moderately obstructed," it is conducive to the development of fine-grained sediments within the sag, forming high-quality source rocks. An analysis of proven oil-rich sags in offshore basins shows that moderate obstruction has four qualitative indicators: when the main provenance is moderately obstructed by "sand basins," fault troughs, and uplifts, the input of terrigenous coarse debris into the sag is limited; and one quantitative indicator: when the ratio of the water catchment area of the provenance area to the area of the sag ("source-sag ratio") is less than 2, and the ratio of the sag sedimentation rate to the sedimentation rate is greater than 1.02, indicating that the source supply capacity is limited, the sag mainly develops muddy fine-grained sediments, and is prone to the formation of high-quality source rocks.

[0034] The third step of the prediction method of the present invention is to judge the third main controlling factor "eutrophication" in the "four dominant factors". Geobiological and organic geochemical theories show that the degree of organic matter enrichment in lake-phase source rocks is the key to determining the scale of oil generation. Based on geochemical analysis and experiments, it is proposed that the "fertilization effect" of nutrient elements during the sedimentation period promotes the development of high-quality source rocks. During the formation of offshore oil-rich depression source rocks, hydrogen-rich fluids, volcanic ash, and rivers flowing through granite source areas in the deep earth are rich in nutrients such as C, N, P, Fe, and S. These are input into the lake basin water for nutrient supplementation, resulting in a "fertilization effect" and promoting the bloom of algae. The quantitative judgment criteria for eutrophication are that the 4-methylsterane index is greater than 0.1, the average total organic carbon (TOC) content of the main source layer is greater than 2%, and the formed source rocks are rich in organic matter, which increases the hydrocarbon generation potential.

[0035] The fourth step of the prediction method of the present invention is to judge the fourth main controlling factor "thermal event" in the "four dominant factors". Petroleum geology theory shows that high-quality source rocks need to have an appropriate degree of thermal evolution (vitrinite reflectance Ro>1.0%) to generate a large amount of oil and gas, and thermal events such as late magmatic activity and hydrothermal activity accelerate the thermal evolution of source rocks and large-scale oil production. Based on gravity and magnetic analysis, it is proposed that after the formation of source rocks, they are affected by thermal events such as late magmatic activity and deep faults. The geothermal gradient is higher than the average value, which accelerates the thermal evolution of source rocks. The heat flow statistics of China's offshore basins show that the criterion for distinguishing thermal events is the average or local terrestrial heat flow value of the depression>65mW / m 2 For local or intermittent thermal events, hydrocarbon expulsion thresholds are used to evaluate the occurrence of these events. In sags affected by thermal events, the hydrocarbon expulsion thresholds become shallower than normal. When the shallowing is greater than 300m, the resource potential of the sag can be significantly enhanced.

[0036] If a potential oil-rich sag meets the four conditions of "strong faulting - moderate shielding - eutrophication - thermal events", it is predicted that the oil-rich sag will develop high-quality lacustrine source rocks.

[0037] The prediction method of the present invention will be further described below with reference to specific embodiments.

[0038] This example takes the prediction of high-quality lacustrine source rocks in the X20 sag of the Pearl River Mouth Basin as an example ( Figure 2 ).

[0039] The X20 sag in the Pearl River Mouth Basin is located in the northwest of the Zhuyi Depression, with an area of 300 km. 2 Based on the regional geological background and drilling conditions in adjacent areas, it is predicted that the main source rock in the depression is the high-quality lacustrine source rock of the Wenchang Formation.

[0040] 1) Based on the first controlling factor "strong faulting" among the "four dominant factors", the fault throw and activity period were calculated. The results show that the activity rate of the deep sag-controlling fault in the X20 sag during the deposition of the Wenchang Formation was 260 m / Ma, and the basement subsidence rate was 300 m / Ma. These meet the criteria of the first controlling factor "strong faulting", which requires a fault activity rate greater than 150 m / Ma and a basement subsidence rate greater than 200 m / Ma.

[0041] 2) Based on the second main controlling factor of "moderate shielding" in the "four dominant factors", qualitatively, the provenance of the X20 sag comes from the uplift area in the northern part of the basin. Seismic data identification shows that the X14 sag and other sags have been newly discovered in the north of the X20 sag, which can shield the provenance. Quantitatively, the "source-to-sag ratio" of the X20 sag is 0.4 after measuring and calculating the areas of the provenance and sag areas, which meets the criterion of a "source-to-sag ratio" less than 2 required by the second main controlling factor "moderate shielding".

[0042] 3) Based on the third controlling factor of "eutrophication" in the "quaternary dominance", the Wenchang Formation, the main source rock revealed by drilling in the X20 sag, has a 4-methylsterane index of 3.0 and an average total organic carbon (TOC) content of 2.5%, which meets the criteria of the third controlling factor "eutrophication": a 4-methylsterane index greater than 0.1 and an average total organic carbon (TOC) content greater than 2%.

[0043] 4) Based on the fourth controlling factor of the “four dominant factors”, “thermal events”, the heat flow value of the X20 sag is about 67.0 mW / m 2 , and there is a late magmatic activity thermal event after the deposition of the main source rock, which promotes the thermal evolution of the source rock, meeting the requirements of the fourth main controlling factor "thermal event" that the qualitative and average terrestrial heat flow value is >65mW / m 2 Quantitative judgment criteria.

[0044] 5) Based on a qualitative and quantitative comprehensive evaluation of the four main controlling factors (strong faulting, moderate shielding, eutrophication, and thermal events), the X20 sag in the Pearl River Mouth Basin developed high-quality lacustrine source rocks, making it a favorable oil-rich sag. Drilling revealed oil and gas fields in the sag, confirming the reliability of the method.

[0045] The second aspect of the present invention provides a "quaternary-dominant" prediction device for high-quality lacustrine source rocks in oil-rich depressions, comprising:

[0046] The first processing unit is used to determine whether the depression has "strong fault depression" conditions based on the analysis and judgment of the activity rate of the fault controlling the depression and the basement subsidence rate;

[0047] The second processing unit is used to determine whether the sag has "moderate shielding" conditions based on the analysis of the source-sag ratio, the ratio of the sag subsidence rate to the deposition rate, and the main development of muddy fine-grained sediments in the sag;

[0048] The third processing unit is used to determine whether the depression has "eutrophic" conditions based on the analysis of the 4-methylsterane index and the average value of the total organic carbon (TOC) content;

[0049] The fourth processing unit is used to determine whether the depression has the "thermal event" condition based on the analysis of the average terrestrial heat flow value of the depression area or the local terrestrial heat flow value in the depression;

[0050] The fifth processing unit is used to evaluate the high-quality lacustrine source rocks in oil-rich depressions based on a comprehensive evaluation of the four main controlling factors: strong faulting, moderate shielding, eutrophication, and thermal events.

[0051] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the computer program implements the steps of the above-mentioned "quaternary-dominated" method for predicting high-quality lacustrine source rocks in oil-rich depressions.

[0052] The fourth aspect of the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned "quaternary-dominated" method for predicting high-quality lacustrine source rocks in oil-rich depressions when executing the computer program.

[0053] The present invention is described in terms of flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to specific embodiments. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as a combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0054] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0055] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 The steps for the function specified in one or more boxes.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A "quaternary-dominated" method for predicting high-quality lacustrine source rocks in oil-rich depressions, characterized by: The steps include: Based on the analysis and judgment of the activity rate of the sag-controlling faults and the basement subsidence rate, it is determined whether the sag has the conditions for "strong fault depression". By analyzing and judging whether the activity rate of the sag-controlling faults is greater than 150m / Ma and the basement subsidence rate is greater than 200m / Ma, it is determined whether the sag has the conditions for "strong fault depression". Based on the source-sag ratio, the ratio of sag subsidence rate to deposition rate, and the analysis of the main development of muddy fine-grained sediments in the sag, it is determined whether the sag has "moderate shielding" conditions. By analyzing and judging the "source-sag ratio" less than 2, the ratio of sag subsidence rate to deposition rate greater than 1.02, and the main development of muddy fine-grained sediments in the sag, it is determined whether the sag has "moderate shielding" conditions. Based on the analysis and judgment of the 4-methylsterane index and the average total organic carbon content, it is determined whether the depression has "eutrophic" conditions; by analyzing and judging whether the 4-methylsterane index is greater than 0.1 and the average total organic carbon content is greater than 2%, it is determined whether the depression has "eutrophic" conditions; Based on the analysis and judgment of the average terrestrial heat flow value in the depression area or the local terrestrial heat flow value in the depression, it is concluded whether the depression has the "thermal event" conditions; by the average terrestrial heat flow value in the depression area or the local terrestrial heat flow value in the depression>65mW / m 2 The analysis and judgment can determine whether the depression has the "thermal event" conditions; Based on the comprehensive evaluation of the four main controlling factors of "strong faulting, moderate shielding, eutrophication, and thermal events", the high-quality lacustrine source rocks in oil-rich depressions were evaluated.

2. The "quaternary-dominated" method for predicting high-quality lacustrine source rocks in oil-rich depressions according to claim 1 is characterized in that: The oil-rich sag is judged to determine whether it has the four factors of "strong faulting, moderate shielding, eutrophication, and thermal events". If these four conditions are met, it is predicted that the lacustrine facies developed in the oil-rich sag is high-quality source rock.

3. A "quaternary-dominant" prediction device for high-quality source rocks in oil-rich depressions, characterized by: include: The first processing unit is used to determine whether the sag has "strong faulting" conditions based on the analysis and judgment of the activity rate of the sag-controlling fault and the basement subsidence rate. The first processing unit is used to determine whether the sag has "strong faulting" conditions based on the analysis and judgment of the activity rate of the sag-controlling fault greater than 150m / Ma and the basement subsidence rate greater than 200m / Ma. The second processing unit is used to determine whether the sag has "moderate shielding" conditions based on the source-sag ratio, the ratio of the sag subsidence rate to the deposition rate, and the predominance of fine-grained mud sediments in the sag. The determination of "moderate shielding" conditions is made by analyzing the conditions where the "source-sag ratio" is less than 2, the ratio of the sag subsidence rate to the deposition rate is greater than 1.02, and the predominance of fine-grained mud sediments in the sag. The third processing unit is configured to determine whether the depression has "eutrophic" conditions based on analysis and judgment of the 4-methylsterane index and the average total organic carbon content; whether the depression has "eutrophic" conditions is determined by analyzing and judging whether the 4-methylsterane index is greater than 0.1 and the average total organic carbon content is greater than 2%. The fourth processing unit is used to determine whether the depression has the "thermal event" condition based on the analysis of the average terrestrial heat flow value of the depression area or the local terrestrial heat flow value in the depression; the average terrestrial heat flow value of the depression area or the local terrestrial heat flow value in the depression is greater than 65mW / m 2 The analysis and judgment can determine whether the depression has the "thermal event" conditions; The fifth processing unit is used to evaluate high-quality lacustrine source rocks in oil-rich depressions based on a comprehensive evaluation of the four main controlling factors: strong faulting, moderate shielding, eutrophication, and thermal events.

4. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the "quaternary-dominated" oil-rich depression lacustrine high-quality source rock prediction method according to claim 1 or 2 are implemented.

5. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the "quaternary-dominated" oil-rich depression lacustrine high-quality source rock prediction method according to claim 1 or 2 are implemented.

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