A method for dividing thermal evolution stages of hydrocarbon source rocks

Abstract

The application relates to a method for dividing the thermal evolution stage of a hydrocarbon source rock, and belongs to the technical field of oil and gas exploitation. The method comprises the following steps: obtaining the methane content percentage at different depths of a target area; obtaining a trend curve graph of depth and methane content percentage according to the methane content percentage and the depth corresponding to the methane content percentage; and dividing the thermal evolution stage of the target area according to the trend curve graph of depth and methane content percentage. The application uses the product proportion of different evolution stages to deduce the evolution stage, and only one deep exploration well is needed to accurately divide each evolution stage, so that the practical range is wide, and the problem that the evolution stage depth limit and evolution trend exist certain errors need to be deduced in combination with the trend and change rule in the deep part without coring or other data or in a new area with less data is solved.

Description

Technical Field

[0001] This application relates to the field of oil and gas extraction technology, and in particular to a method for dividing the thermal evolution stages of source rocks. Background Technology

[0002] In oil and gas surveys and assessments, especially in the initial stages, the evaluation of source rocks is paramount. The study of the thermal evolution of source rocks is a crucial component of this evaluation. Differences in the thermal evolution history of source rocks within a basin significantly impact the distribution of oil and gas within the basin, reflecting its genesis and development process. This is of great importance in guiding oil and gas exploration (Jin Chunshuang, "A Brief Discussion on the Significance of Basin Thermal History and Source Rock Thermal Evolution Research in China's Strategic Selection and Evaluation of Oil and Gas Resources"). During the development of sedimentary basins, primary organic matter, along with other minerals, is deposited. As burial depth increases and geothermal temperatures rise, organic matter gradually transforms into oil and gas under an oxygen-deficient reducing environment. Because various energy conditions exhibit different effects at different depths, the nature of the organic matter transformation reaction and its main products show significant differences, indicating that the transformation process from primary organic matter to oil and natural gas has distinct stages. Regarding the stages of organic matter thermal evolution, scholars both domestically and internationally have proposed many schemes. Zhang Houfu (1981) divided it into the biochemical gas generation stage, the thermocatalytic oil and gas generation stage, the thermal cracking condensate gas generation stage, and the deep high-temperature gas generation stage. Tissot and Wilt (1984) divided it into the diagenetic stage (methane), the plutonic stage (oil, wet gas), and the epigenetic stage (methane). Pan Zhongxiang (1986) divided it into the biogenic methane gas stage, the heavy-light oil stage, the condensate-wet gas stage, and the dry gas stage. The degree / stage of organic matter evolution is usually characterized by organic matter maturity. Typically, when the source rock maturity is approximately <0.5%, 0.5%-1.3%, 1.3%-2.0%, or >2.0%, the corresponding evolution stages are the immature stage (immature zone), the mature stage (oil zone), the highly mature stage (wet gas zone), and the over-mature stage (dry gas zone).

[0003] Currently, commonly used indicators of organic matter maturity both domestically and internationally include vitrinite reflectance, pollen carbonization degree, thermal distortion index, TTI value, n-alkane odd-even dominance ratio, and methane carbon isotopes. These indicators can help determine the depth and temperature at which organic matter begins to mature and generate large quantities of petroleum, wet gas, and dry gas. Obtaining maturity data requires extensive analytical testing, typically involving core sampling or oil and gas sampling. For deeper areas without core samples or other analytical data, it is necessary to combine trends and patterns of change to infer the depth limits corresponding to each evolutionary stage, and these evolutionary trends are subject to certain errors. Summary of the Invention

[0004] This application provides a method for dividing the thermal evolution stages of source rocks, in order to solve the problem that the current method requires core sampling or other analytical data to accurately divide the thermal evolution stages.

[0005] This application provides a method for dividing the thermal evolution stages of hydrocarbon source rocks, the method comprising:

[0006] The percentage of methane content at different depths in the target area was obtained;

[0007] Plot a curve based on the methane content percentage and the depth corresponding to the methane content percentage;

[0008] The target region is divided into thermal evolution stages based on the curve.

[0009] As an optional implementation, the step of dividing the target source rock into thermal evolution stages based on the curve specifically includes:

[0010] Based on the curve, the first approximate horizontal segment, the minimum point of methane content percentage, and the second approximate horizontal segment are divided along the direction of gradually increasing depth.

[0011] Based on the first approximate horizontal segment, the immature stage (immature zone) of the thermal evolution stage of the target area is obtained.

[0012] Based on the minimum value of the methane content percentage in the first approximate horizontal segment, the mature stage (oil zone) of the thermal evolution stage of the target area is obtained.

[0013] Based on the minimum point of the methane content percentage and the second approximate level segment, the high maturity stage (humid zone) of the thermal evolution stage of the target area is obtained.

[0014] Based on the second approximate horizontal segment, the over-mature stage (dry gas zone) of the thermal evolution stage of the target area is obtained.

[0015] As an optional implementation, the step of dividing the target region into immature stages (immature zones) based on the first approximate horizontal segment specifically includes:

[0016] By dividing the strata into layers no deeper than the depth corresponding to the end point of the first approximate horizontal segment, the immature stage (immature zone) of the thermal evolution stage of the target area is obtained.

[0017] As an optional implementation, the step of dividing the target area into heated oil zones based on the minimum point of the first approximate horizontal segment and the percentage of methane content specifically includes:

[0018] By dividing the strata from the depth corresponding to the end point of the first approximate horizontal segment to the depth corresponding to the minimum value of the methane content percentage, the mature stage (oil zone) of the thermal evolution stage of the target area is obtained.

[0019] As an optional implementation, the step of dividing the target area into a high-maturity stage (humid zone) of thermal evolution based on the minimum point of the methane content percentage and the second approximate level segment specifically includes:

[0020] By dividing the strata from the depth corresponding to the minimum methane content percentage point to the depth corresponding to the starting point of the second approximate horizontal segment, the high-maturity stage (moisture zone) of the thermal evolution stage of the target area is obtained.

[0021] As an optional implementation, the step of dividing the target region into the over-mature stage (dry gas zone) of thermal evolution based on the second approximate horizontal segment specifically includes:

[0022] By dividing the strata at a depth corresponding to the starting point of the second approximate horizontal segment, the over-mature stage (dry gas zone) of the thermal evolution stage of the target area is obtained.

[0023] As an optional implementation, the percentage of methane content at different depths is obtained from well logging gas logging data.

[0024] As an optional implementation, the methane content percentage is calculated as follows:

[0025] [C1] / ([C1]+[C2]+[C3]+[C4]);

[0026] Wherein, [C1] represents the content of methane, [C2] represents the content of ethane, [C3] represents the content of propane, and [C4] represents the content of butane.

[0027] As an optional implementation, the target area is a quasi-continuously evolving sedimentary strata, and is in multiple evolutionary stages.

[0028] As an optional implementation, the step of plotting a curve based on the methane content percentage and the depth corresponding to the methane content percentage specifically includes:

[0029] Based on the methane content percentage and the corresponding depth, a curve is plotted with the methane content percentage as the vertical axis and the depth as the horizontal axis.

[0030] The technical solutions provided in this application have the following advantages compared with the prior art:

[0031] The method provided in this application innovatively uses the product ratio of different evolution stages to deduce the current evolution stage. Only one relatively deep exploration well is needed to accurately divide each evolution stage. It has a wide range of applications and solves the problem that in deep areas without coring or other data, or in new areas with little data, it is necessary to combine trends and change patterns to infer the depth limit of the evolution stage, and there is a certain error in the evolution trend. Attached Figure Description

[0032] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0033] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart illustrating the method provided in the embodiments of this application;

[0035] Figure 2 This application provides a map showing the different oil and gas occurrence states at different depths in region G.

[0036] Figure 3 This is a diagram showing the maturity and organic matter evolution stages of the L-shaped depression provided in the embodiments of this application. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0039] Definitions:

[0040] The immature stage (immature zone) – This stage extends from the sedimentary interface to depths of hundreds or even 1500 meters, with temperatures ranging from 10-60℃ and a maturity of <0.5%. It is dominated by bacterial activity and largely corresponds to the diagenetic stage of the sediments. In this reducing environment lacking free oxygen, anaerobic bacteria are highly active, and biologically derived sedimentary organic matter is selectively decomposed into lower molecular weight biochemical monomers (such as phenols, amino acids, monosaccharides, and fatty acids). Some organic matter is completely decomposed into simple molecules such as CO, CH4, NH3, H2S, and H2O. During this stage, these newly formed products interact to form complex geological polymers called "sapropelic mud" and "humus," both of which become precursors to kerogen. At this stage, the burial depth is shallow, and the temperature and pressure are low. Except for a small amount of high-molecular-weight liquid hydrocarbons (unripe oil) and volatile gases, most of the organic matter is converted into kerogen and preserved in the sedimentary rocks. Due to the biochemical degradation by bacteria, the products are mainly methane, lacking light (C4-C8) n-alkanes and aromatic hydrocarbons, with a methane content of over 95%.

[0041] Maturation Stage (Oil Zone) – As sediment burial depth exceeds 1500-2500m, maturity reaches 0.5%-1.3%, entering the early stage of epigenetic processes. The temperature experienced by organic matter rises to 60-180℃, and the most active factor promoting organic matter transformation is thermocatalysis. With increasing depth, diagenesis intensifies, and the adsorption capacity of clay minerals increases, leading to continuous redistribution based on the adsorption properties of material components. The catalytic effect of clay minerals can lower the maturation temperature of organic matter, promoting petroleum formation. Due to the catalytic effect of clay minerals, not only are long-chain hydrocarbons broken down into smaller molecules, but the content of olefins also relatively decreases, while the content of isomeric hydrocarbons, cycloalkanes, and aromatic hydrocarbons relatively increases. Under the catalytic effect of clay minerals, the maturation threshold can be reached without excessively high temperatures. Kerogen undergoes thermal degradation, and the bonds of heteroatoms (O, N, S) break, releasing volatile substances such as carbon dioxide, water, ammonia, and hydrogen sulfide, while simultaneously yielding large amounts of low-molecular-weight liquid and gaseous hydrocarbons.

[0042] High-maturity stage (humid zone) – When the sediment burial depth exceeds 3500-4000m, the maturity is 1.3%-2.0%, and the ground temperature reaches 180-250℃, it enters the late stage of epigenetic processes. At this time, the ground temperature exceeds the critical temperature of hydrocarbons. In addition to continuing to break heteroatom functional groups and side chains, generating small amounts of water, carbon dioxide, and hydrogen, the main reaction is the breakage of a large number of C25 chains, including the ring opening and rupture of cycloalkanes, resulting in a sharp decrease in liquid hydrocarbons. The content of high molecular weight n-alkanes with more than C25 gradually approaches zero, with only a small amount of low-carbon cycloalkanes and aromatic hydrocarbons; conversely, low molecular weight n-alkanes increase dramatically, mainly methane and its gaseous homologues. Deep underground, they are in a gaseous state, but when extracted to the surface, as the temperature and pressure decrease, they condense into liquid light petroleum, i.e., condensate oil, accompanied by moisture, indicating the high-maturity stage. At this stage, the nature of hydrocarbon reactions can be divided into two processes: petroleum thermal cracking and petroleum thermal coking. Petroleum thermal cracking refers to the breaking down of aliphatic structures into smaller molecules at high temperatures, transforming them into methane and its gaseous homologues, and concentrating the aromatic hydrocarbons contained in petroleum. Petroleum thermal coking refers to the condensation reaction of hydrogen-poor petroleum (generally composed mainly of aromatic hydrocarbons containing heteroatoms) at high temperatures, mainly forming solid residues, and relatively increasing the aliphatic content and decreasing the heteroatoms in the petroleum. These two reactions can occur in parallel or overlap.

[0043] The mature stage (dry gas zone) – when the depth exceeds 6000-7000m, the sediments have entered the metamorphic stage, reaching the final stage of organic matter transformation. Temperatures exceed 250℃, characterized by high temperature and pressure. The formed liquid hydrocarbons and heavy gaseous hydrocarbons undergo intense cracking, transforming into the thermodynamically most stable form of methane. After releasing methane, the kerogen residues further condense, reducing the H / C atomic ratio to 0.45-0.3, close to the minimum limit for methane formation. Therefore, this stage produces the final products of the thermal evolution of all sedimentary organic matter: dry gas methane and carbon bitumen or sub-graphite. This phenomenon has been confirmed in laboratory, field observations, and deep well drilling results: the Institute of Geochemistry, Chinese Academy of Sciences, conducted high-temperature and high-pressure experiments on petroleum and found that when the pressure remained constant, petroleum differentiated significantly towards two extremes as the temperature increased, eventually forming gas and solid bitumen. The evolution process is: petroleum → oil + gas → oil + gas + solid bitumen + liquid bitumen → gas + solid bitumen. (Zhang Houfu, *Petroleum Geology*). For different basins, due to factors such as subsidence history, geothermal history, and the type of original organic matter, the hydrocarbon conversion process may not necessarily go through four stages, and the depth and temperature boundaries of each stage vary. Defining the stages of hydrocarbon generation and evolution is one of the fundamental tasks for conducting depression geological research and hydrocarbon exploration. It determines the type of exploration target (oil or gas) and the direction of subsequent exploration. If the organic matter in a basin is in an immature evolution stage, it does not have hydrocarbon exploration value or is mainly for biogas exploration. If the organic matter in a basin is in an overmature evolution stage, the main focus is on finding natural gas exploration targets. In many basins, the organic matter at different depths is in different evolution stages, which also determines the differences in the types of exploration targets at different depths.

[0044] Gas logging is one of the most commonly used projects in the drilling process. In the geological exploration of oil and gas, gas logging technology is the most important logging technique. Gas logging obtains the composition (mainly methane C1, ethane C2, propane C3, butane C4, etc.) and content of the gas carried by the drilling fluid returning from the bottom of the well during oil and gas drilling. Further analysis based on this data determines whether the formation contains oil and gas and whether oil and gas production is possible. It provides a basis for identifying and evaluating oil, gas, and water layers, as well as for oil and gas testing. It has the advantages of continuity and sensitivity, and is the main logging method for discovering and evaluating various oil and gas layers (Wang Yan, "Application Research of Gas Logging Technology in Deep Gas Layer Evaluation"). Through literature and patent searches, the most widespread application of gas logging is the identification of reservoir fluids: ① Discovering oil and gas layers. ① Oil-bearing reservoirs have higher heavy hydrocarbon content than gas-bearing reservoirs and contain hydrocarbons with components greater than propane; gas-bearing reservoirs have lower heavy hydrocarbon content, and the heavy hydrocarbon components only include ethane, propane, etc., without large molecular weight hydrocarbons; ② Preliminary identification of oil, gas, and water layers. Hydrocarbon gases are poorly soluble in water, but some water layers still contain small amounts of dissolved gas, which will also appear on the gas logging curve. The appearance of water layers on the gas logging curve is much lower than that of oil layers; ③ Preliminary identification of heavy or light oil layers. Since the solubility of hydrocarbon gases in petroleum increases with increasing relative molecular mass, the content of heavy hydrocarbons is not entirely the same in oil layers of different properties. Light oil has a higher heavy hydrocarbon content than heavy oil, so the anomaly of heavy hydrocarbons in oil layers containing light oil is obvious, while the anomaly of heavy hydrocarbons in oil layers containing heavy oil is far less obvious than that in oil layers containing light oil. In recent years, gas logging has been gradually applied to the evaluation of new fields such as deep gas and shale gas, but it has never deviated from the scope of identifying and evaluating oil and gas layers.

[0045] During the invention process, the applicant discovered that the evolutionary stage of organic matter can be deduced by observing the products and their content changes at different evolutionary stages. Immature source rock strata often contain dispersed methane or biogenic methane gas, with a methane content of almost 100%. As the burial depth increases, the source rock begins to generate hydrocarbons, the heavy hydrocarbon component begins to increase, and the methane proportion decreases. Entering the highly mature stage, some crude oil begins to pyrolyze, and the methane proportion begins to rise again. Entering the over-mature stage, dry gas is the main component, and the methane content is even higher.

[0046] Therefore, by using gas logging to obtain percentage content maps of C1, C2, C3, and C4 at different depths, and by using the trend of C1 percentage content at different depths, the evolution stage can be deduced.

[0047] This application provides a method for dividing the thermal evolution stages of hydrocarbon source rocks, the method comprising:

[0048] S1. Obtain the percentage of methane content at different depths in the target area;

[0049] In this embodiment, the percentage of methane content at different depths is obtained based on well logging gas measurement data.

[0050] It should be noted that the premise for using gas logging to quickly divide the thermal evolution stages is: (1) the source rock is a quasi-continuous evolutionary sedimentary stratum; (2) the stratum is thick and is in multiple evolutionary stages.

[0051] In this embodiment, well logging data C1 (methane), C2 (ethane), C3 (propane), and C4 (butane) are obtained during the drilling process of a certain well.

[0052] S2. Based on the percentage of methane content at different depths from the well logging gas data, obtain a trend curve of depth and percentage of methane content;

[0053] Specifically, obtaining a trend curve of depth versus methane content percentage based on the methane content percentage and the depth corresponding to the methane content percentage includes:

[0054] Based on the methane content percentage and the corresponding depth, a trend curve of depth and methane content percentage is obtained with the methane content percentage as the vertical axis and depth as the horizontal axis.

[0055] In some embodiments, the methane content is a volume content.

[0056] Specifically, the formula for calculating the percentage of methane content is:

[0057] [C1] / ([C1]+[C2]+[C3]+[C4]);

[0058] Wherein, [C1] represents the content of methane, [C2] represents the content of ethane, [C3] represents the content of propane, and [C4] represents the content of butane.

[0059] In this embodiment, gas measurement data was used to obtain percentage content maps of C1 (methane), C2 (ethane), C3 (propane), and C4 (butane) at different depths.

[0060] S3. Divide the target area into thermal evolution stages based on the trend curves of depth and methane content percentage.

[0061] In some embodiments, the step of dividing the target region into thermal evolution stages based on the trend curve of depth and methane content percentage specifically includes:

[0062] Based on the trend curve of depth and methane content percentage, the first approximate horizontal segment, the minimum point of methane content percentage, and the second approximate horizontal segment are obtained along the direction of gradually increasing depth.

[0063] Based on the first approximate horizontal segment, the minimum point of methane content percentage, and the second approximate horizontal segment, the thermal evolution stages of the target area are divided into an immature zone, an oil zone, a humid zone, and a dry zone.

[0064] Specifically, the division of the immature zone includes:

[0065] The strata at depths no greater than the end point of the first approximate horizontal segment are designated as immature zones in the thermal evolution stage.

[0066] The division of the oil band specifically includes:

[0067] The strata corresponding to the depth from the end point of the first approximate horizontal segment to the depth corresponding to the minimum methane content percentage are defined as oil zones in the thermal evolution stage.

[0068] The division of the moisture zone specifically includes:

[0069] The strata corresponding to the depth from the minimum point of the methane content percentage to the depth corresponding to the starting point of the second approximate horizontal segment are the humid zone of the thermal evolution stage.

[0070] The division of the dry air zone specifically includes:

[0071] The strata at depths corresponding to the starting points of the second approximate horizontal segment are defined as the dry gas zone of the thermal evolution stage.

[0072] In other words, by utilizing the C1 percentage content trends at different depths, four trends can be obtained: approximately horizontal, decreasing, increasing, and approximately horizontal again. The intersection of the approximately horizontal and decreasing trends corresponds to the depth of the boundary between the immature zone and the mature oil zone; the intersection of the decreasing and increasing trends corresponds to the depth of the boundary between the mature oil zone and the humid zone; and the intersection of the increasing and approximately horizontal trends corresponds to the depth of the boundary between the humid zone and the dry gas zone. The depths corresponding to the intersection points of these four trends represent the depth boundaries of the four evolutionary stages: the immature zone (including biogenic gas), the oil zone, the humid zone, and the dry gas zone.

[0073] This method differs from previous methods that used maturity to classify organic matter evolution stages. Instead, it innovatively uses the proportion of products from different evolution stages to infer the current evolution stage, representing a novel methodological system. It is convenient and fast. Gas logging is the most commonly used project in drilling, and gas logging data can be obtained during the drilling process, unlike previous methods that required separate sampling and analysis to obtain results, saving both time and cost. For deep areas without coring or other data, or new areas with limited data, it is necessary to combine trends and change patterns to infer the depth boundaries of evolution stages. Existing methods have certain errors in evolution trends, while this method only requires a relatively deep exploration well to accurately classify each evolution stage, making it widely applicable.

[0074] Taking the G region of the L-depression as an example, the evolutionary stages are divided as follows:

[0075] The operation of this method includes the following steps:

[0076] S1: Select well Y, which has a relatively deep drilling depth and is mainly composed of mudstone and shale, to obtain detailed gas logging data (C1 (methane), C2 (ethane), C3 (propane), and C4 (butane) at different depths).

[0077] S2: Obtain percentage content maps of C1, C2, C3, and C4 at different depths using gas chromatography data (e.g., Figure 2 (As shown).

[0078] S3: By utilizing the C1 percentage content trends at different depths (excluding the influence of hydrocarbon accumulation and other anomalous peaks between 3530-3930m), four trends can be obtained: approximately horizontal, decreasing, increasing, and approximately horizontal again. The depths corresponding to the intersection points of these four trends represent the depth boundaries of four thermal evolution stages: immature stage (immature zone), mature stage (oil zone), highly mature stage (humid zone), and over-mature stage (dry zone). The intersection point of the approximately horizontal trend and the decreasing trend, corresponding to a depth of 2600m, marks the boundary between the immature and mature stages. The intersection point of the decreasing trend and the increasing trend, corresponding to a depth of 4200m, marks the boundary between the mature and highly mature stages. The intersection point of the increasing trend and the approximately horizontal trend, corresponding to a depth of 4750m, marks the boundary between the highly mature and over-mature stages.

[0079] Therefore, the conclusion of this method is that the source rocks below 2600m are immature, the main oil-forming zone is between 2600m and 4200m, the wet gas zone is between 4200m and 4750m, and the dry gas zone is above 4750m. This also determines that the exploration of secondary oil and gas reservoirs is mainly conducted below 2600m, and the exploration of primary cracked gas is mainly conducted above 4750m, which guides the exploration direction in the region.

[0080] Meanwhile, taking the G region of the L depression as an example, the evolutionary stages are divided as follows:

[0081] The test was performed using conventional core analysis, and the results are as follows: Figure 3 As shown in the figure, the maturity level Ro at 2700m is 0.5%, reaching the maturity limit, and the maturity level Ro at 4300m is 1.3%, reaching the high maturity limit.

[0082] This shows that the conclusions of this method are basically consistent with those of conventional core analysis, and can meet the actual requirements of geological research and exploration deployment.

[0083] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0084] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0085] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for dividing the thermal evolution stages of source rocks, characterized in that, The method includes: Obtain well logging gas logging data at different depths in quasi-continuously evolving sedimentary strata in the target area. The well logging gas logging data includes the contents of methane, ethane, propane, and butane. The target area is in multiple evolutionary stages. Based on the well logging gas data, the percentage of methane content at different depths is calculated, where the percentage of methane content is the ratio of methane content to the total content of methane, ethane, propane, and butane. Based on the methane content percentage and the depth corresponding to the methane content percentage, a trend curve of depth versus methane content percentage is obtained; The target region is divided into thermal evolution stages based on the curve diagram. The step of dividing the target region into thermal evolution stages based on the curve specifically includes: Based on the curve, the first approximate horizontal segment, the minimum point of methane content percentage, and the second approximate horizontal segment are divided along the direction of gradually increasing depth. Based on the first approximate horizontal segment, the immature stage of the thermal evolution of the target area is obtained; Based on the minimum point of the first approximate horizontal segment and the percentage of methane content, the mature stage of the thermal evolution of the target area is obtained; Based on the minimum point of the methane content percentage and the second approximate level segment, the high maturity stage of the thermal evolution stage of the target area is obtained; Based on the second approximate horizontal segment, the over-mature stage of the thermal evolution of the target region is obtained.

2. The method for dividing the thermal evolution stages of source rocks according to claim 1, characterized in that, The step of dividing the target area into immature zones based on the first approximate horizontal segment specifically includes: By dividing the strata into layers with a depth no greater than the end point of the first approximate horizontal segment, the immature stage of the thermal evolution of the target area is obtained.

3. The method for dividing the thermal evolution stages of source rocks according to claim 1, characterized in that, The mature stage of the source rock thermal evolution is determined by dividing the first approximate horizontal segment and the minimum point of methane content percentage, specifically including: By dividing the strata from the depth corresponding to the end point of the first approximate horizontal segment to the depth corresponding to the minimum value of the methane content percentage, the mature stage of the thermal evolution of the target area is obtained.

4. The method for dividing the thermal evolution stages of source rocks according to claim 1, characterized in that, The high-maturity stage of the thermal evolution of the target area is determined by dividing the target area into stages based on the minimum point of the methane content percentage and the second approximate level segment, specifically including: By dividing the strata from the depth corresponding to the minimum methane content percentage point to the depth corresponding to the starting point of the second approximate horizontal segment, the high-maturity stage of the thermal evolution of the target area is obtained.

5. The method for dividing the thermal evolution stages of source rocks according to claim 1, characterized in that, The step of dividing the target region's thermal evolution stage into an over-mature stage based on the second approximate horizontal segment specifically includes: By dividing the strata into layers at depths not less than the starting point of the second approximate horizontal segment, the over-mature stage of the thermal evolution of the target area is obtained.

6. The method for dividing the thermal evolution stages of source rocks according to claim 1, characterized in that, The step of plotting a curve based on the methane content percentage and the depth corresponding to the methane content percentage specifically includes: Based on the methane content percentage and the corresponding depth, a curve is plotted with the methane content percentage as the vertical axis and the depth as the horizontal axis.

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