Method for evaluating early hydrocarbon generation potential of source rock in saline lake basin

Abstract

The present application belongs to the field of oil and gas geochemistry and petroleum geological exploration technology, and particularly relates to a method for evaluating early hydrocarbon generation potential of source rocks in a salinization lake basin, comprising the following steps: step S10, obtaining source rock samples of a target layer and measuring resin content, organic sulfur to organic carbon atomic ratio and gammacerane index of the source rock samples; step S20, respectively normalizing the resin content, organic sulfur to organic carbon atomic ratio and gammacerane index; step S30, calculating an early hydrocarbon generation potential comprehensive index based on the normalized parameters; and step S40, evaluating early hydrocarbon generation potential of the source rocks according to the calculated early hydrocarbon generation potential comprehensive index. The present application integrates three core geochemical parameters for characterizing early hydrocarbon generation precursors, hydrocarbon generation promotion mechanisms and salinization preservation environments, constructs a comprehensive evaluation model, and realizes accurate prediction and grade division of oil generation capacity of the source rocks at a low maturity stage.

Description

Technical Field

[0001] This invention relates to a method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins, belonging to the field of oil and gas geochemistry and petroleum geological exploration technology. Background Technology

[0002] Saline lacustrine basins are an important exploration area for continental oil and gas resources in my country. Compared with freshwater lacustrine basins, source rocks in saline lacustrine basins have unique hydrocarbon generation mechanisms, generally exhibiting characteristics of "low organic matter abundance, high conversion rate, and early hydrocarbon generation." Traditional source rock evaluation systems mainly rely on general parameters such as total organic carbon content (TOC), organic matter type index, and vitrinite reflectance (Ro). While these parameters can effectively evaluate the overall hydrocarbon generation capacity and maturity of source rocks, they have significant shortcomings: First, they cannot effectively distinguish and quantify the specific hydrocarbon generation potential of source rocks at the low maturity stage (Ro < 0.8%), i.e., the "early hydrocarbon generation" capacity; second, general indicators fail to fully consider the unique hydrocarbon generation promoting factors (such as the catalytic effect of sulfur-rich kerogen) and special hydrocarbon generation parent materials (such as resin bodies) in saline environments.

[0003] In the prior art, patent CN112179806A discloses a method for evaluating the hydrocarbon generation potential of source rocks, but its evaluation target is still "total hydrocarbon generation potential" and does not focus on "early hydrocarbon generation". Patent CN117514130A discloses a method, device and equipment for identifying sweet spots in shale oil in saline lacustrine basins. It involves the identification of sweet spots in shale oil in saline lacustrine basins, but it is mainly based on geophysical logging and seismic attributes and lacks a core model for quantitatively evaluating early hydrocarbon generation potential from the perspective of geochemical mechanisms.

[0004] Therefore, there is an urgent industrial need to develop an evaluation method that can closely integrate the hydrocarbon generation mechanism of saline lake basins, integrate key geochemical parameters, and achieve quantitative classification of early hydrocarbon generation potential, in order to accurately predict low-maturity oil resources and reduce exploration risks. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing a method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins. This method integrates three core geochemical parameters that characterize the early hydrocarbon generation parent material, hydrocarbon generation promotion mechanism, and saline preservation environment, and constructs a comprehensive evaluation model to achieve accurate prediction and classification of the oil generation capacity of source rocks in the low-maturity stage.

[0006] The technical solution provided by this invention to solve the above-mentioned technical problems is: a method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins, comprising the following steps: Step S10: Obtain source rock samples from the target stratum and measure the resin content, organic sulfur to organic carbon atom ratio, and gamma cerane index of the source rock samples. Step S20: Normalize the resin content, the ratio of organic sulfur to organic carbon atoms, and the gamma-cerane index respectively. Step S30: Calculate the comprehensive index of early hydrocarbon generation potential based on the normalized parameters; Step S40: Evaluate the early hydrocarbon generation potential of source rocks based on the calculated comprehensive index of early hydrocarbon generation potential.

[0007] A further technical solution is that the source rock sample is a source rock core or rock fragment sample.

[0008] A further technical solution is that the process for determining the resin content is as follows: the source rock sample is subjected to kerogen separation and purification, the micro-components are separated by zinc chloride heavy liquid density gradient centrifugation, and the volume percentage of the resin is identified and counted under reflected light and fluorescence microscopes.

[0009] A further technical solution is that the process for determining the ratio of organic sulfur to organic carbon atoms is as follows: the powder of the source rock sample is tested using a pyrolysis analyzer to directly obtain the total organic carbon content and organic sulfur content, and then converted into the S / C atomic ratio according to atomic weight.

[0010] A further technical solution is that the determination process of the gammacerane index is as follows: Soxhlet extraction and column chromatography are performed on the source rock sample to obtain the saturated hydrocarbon fraction. The gammacerane and C fraction are then integrated on a mass chromatogram at m / z 191 using gas chromatography-mass spectrometry. 30 Calculate the peak area of ​​hopane and its ratio.

[0011] A further technical solution is that the normalization formula in step S20 includes:

[0012]

[0013]

[0014] In the formula: Resin content; This serves as a reference threshold for resin content; Normalized resin content; The ratio of organic sulfur to organic carbon atoms; This is a reference threshold for the ratio of organic sulfur to organic carbon atoms; The normalized ratio of organic sulfur to organic carbon atoms; Gammacerane index; This serves as the reference threshold for the gammacerane index; The normalized gammacerane index.

[0015] A further technical solution is that the reference threshold for the resin content... =15%, the reference threshold for the ratio of organic sulfur to organic carbon atoms. =0.06, the reference threshold for the gammacerane index. =3.0.

[0016] A further technical solution is that the formula for calculating the comprehensive index of early hydrocarbon generation potential is as follows:

[0017] In the formula: This is a comprehensive index of early hydrocarbon generation potential; Normalized resin content; The normalized ratio of organic sulfur to organic carbon atoms; Normalized gammacerane index; , , All are weighting coefficients.

[0018] A further technical solution is that in step S30... =0.55, =0.30, =0.15.

[0019] A further technical solution is that, in step S40, the early hydrocarbon generation potential is classified according to the following criteria based on the calculated comprehensive index: Level I - High Potential: ≥0.70 indicates that the source rocks possess superior material basis and hydrocarbon generation conditions for forming large-scale low-maturity oil reservoirs, making them a priority target for exploration.

[0020] Level II - Medium Potential: 0.40≤ <0.70 indicates that the source rock has a certain early hydrocarbon generation capacity and may form local oil and gas accumulation.

[0021] Level III - Low Potential: <0.40 indicates that the early hydrocarbon generation capacity of the source rock was limited, and its exploration value was low.

[0022] The present invention has the following beneficial effects: 1. Mechanism-driven and highly targeted: It is the first to transform the three core mechanisms controlling early hydrocarbon generation in saline lake basins (hydrogen-rich mother material supply, sulfur catalysis to reduce activation energy, and preservation of saline-reducing environment) into quantifiable indicators and integrate them into the same evaluation model, thus solving the problem of insufficient targeting of general methods. 2. Quantification and Standardization: By using normalization thresholds and weighting coefficients based on large sample statistics, an objective and repeatable quantitative evaluation standard was established, realizing a leap from experience-based judgment to model calculation, which greatly improved the scientificity and comparability of the evaluation results. 3. Practice-oriented and highly applicable: The final output is a clear graded conclusion (high / medium / low), which can be directly applied to exploration deployment decisions, such as selecting favorable exploration zones, determining "sweet spot" layers, or assessing resource potential. The methodology is clear and easy to promote and apply in exploration units. 4. Thorough verification and high reliability: The parameter selection, weight calibration and threshold determination of this method are all based on actual data from multiple basins. Its effectiveness has been cross-verified by geological facts and oil and gas discoveries in several successful exploration basins such as Hetao and Junggar, and it has good universality. Attached Figure Description

[0023] Figure 1 This is a complete operation flowchart of the evaluation method described in this invention; Figure 2 This is a schematic diagram of a rapid evaluation board for early hydrocarbon generation potential constructed using the method of this invention. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] like Figure 1 As shown, the present invention provides a method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins, which specifically includes the following steps: Step 1: Obtain source rock samples from the target stratum; Step 2: Divide the source rock sample into three parts. Perform kerogen separation and purification on one part of the sample. Use zinc chloride heavy liquid density gradient centrifugation to separate micro-components. Identify and count the volume percentage of resin under reflected light and fluorescence microscopy to obtain the resin content of the sample. Another sample powder was tested using a Rock-Eval 7S pyrolysis analyzer with sulfur quantitative analysis capabilities to directly obtain the total organic carbon content (TOC, wt%) and organic sulfur content (wt%). (wt%), and converted to S / C atomic ratio according to atomic weight to obtain the organic sulfur to organic carbon atomic ratio of the sample; Finally, the third sample was subjected to Soxhlet extraction and column chromatography to obtain the saturated hydrocarbon fraction. The fraction was then analyzed by gas chromatography-mass spectrometry (GC-MS) at m / z 191, where gamma-ceramide and C2O2 were integrated. 30 The peak area of ​​hopane is calculated, and the ratio is used to obtain the gamma-cerane index of the sample. Step 3: To eliminate the influence of dimensions and ensure the model calculation is reasonable, the three original parameters are normalized. A reference threshold is set: =15%, =0.06, =3.0; and calculate the normalized value using the following formula;

[0026]

[0027]

[0028] In the formula: Resin content; This serves as a reference threshold for resin content; Normalized resin content; The ratio of organic sulfur to organic carbon atoms; This is a reference threshold for the ratio of organic sulfur to organic carbon atoms; The normalized ratio of organic sulfur to organic carbon atoms; Gammacerane index; This serves as the reference threshold for the gammacerane index; Normalized gammacerane index; When the calculated value is greater than 1, it is counted as 1. Step 4: Calculate the comprehensive index of early hydrocarbon generation potential based on the normalized parameters;

[0029] In the formula: This is a comprehensive index of early hydrocarbon generation potential; Normalized resin content; The normalized ratio of organic sulfur to organic carbon atoms; Normalized gammacerane index; , , All are weighting coefficients; Among them, the weighting coefficient + + =1, and the specific preferred value range is: =0.5~0.6, =0.25~0.35, =0.15~0.25. The optimal solution is =0.55, =0.30, =0.15, this combination has the highest distinguishability of early hydrocarbon generation characteristics.

[0030] Step 5: Based on the calculated comprehensive index of early hydrocarbon generation potential, classify the projects according to the following criteria: Level I - High Potential: ≥0.70 indicates that the source rocks possess superior material basis and hydrocarbon generation conditions for forming large-scale low-maturity oil reservoirs, making them a priority target for exploration.

[0031] Level II - Medium Potential: 0.40≤ <0.70 indicates that the source rock has a certain early hydrocarbon generation capacity and may form local oil and gas accumulation.

[0032] Level III - Low Potential: <0.40 indicates that the early hydrocarbon generation capacity of the source rock was limited, and its exploration value was low.

[0033] Example 1 Evaluation of high-potential source rocks (taking the Linhe Formation of the Xinglong tectonic belt in the Linhe Depression of the Hetao Basin as an example) Samples and tests: Core sample XH12-2 (depth 5236.73m, dark gray gypsum-bearing mudstone) was selected.

[0034] Parameter acquisition: Micro-component analysis was obtained =8.5%.

[0035] Rock-Eval 7S analysis showed TOC = 1.8%. =1.2%, calculated as follows Atomic ratio = 0.04.

[0036] Gammacerane index determined by GC-MS analysis =1.24.

[0037] Parameter normalization: =8.5 / 15=0.57; =0.04 / 0.06=0.67; =1.24 / 3.0=0.41; calculate : Use the optimal weighting coefficient ( =0.55, =0.30, =0.15).

[0038] =0.55×0.57+0.30×0.67+0.15×0.41=0.314+0.201+0.062=0.58; Potential assessment: =0.58, which, according to the grading standard, belongs to Level II (medium potential). This evaluation result is consistent with the actual exploration situation in the layer where the sample is located, where industrial oil flows have been obtained but the production is moderate, indicating that the evaluation method is accurate.

[0039] Example 2: Evaluation of low-potential hydrocarbon source rocks (comparative sample) Samples and tests: Sample NG-1 (delta front, gray mudstone) was selected from the same basin but different sedimentary facies zones.

[0040] Parameter acquisition: =1.2%; Atomic ratio = 0.01; =0.25; Parameter normalization: =1.2 / 15=0.08; =0.01 / 0.06=0.17; =0.25 / 3.0=0.08; calculate : =0.55×0.08+0.30×0.17+0.15×0.08=0.044+0.051+0.012=0.11; Potential assessment: =0.11, belonging to Level III (low potential). No oil or gas shows were observed in the drilling area where this sample was located, which proves the method's ability to screen unfavorable areas.

[0041] Example 3 Method universality verification across basins (taking the Lucaogou Formation in the Jimsar Depression of the Junggar Basin as an example). Background and Objective: To verify the applicability of the method of this invention to different saline lacustrine basins, a retrospective evaluation was conducted on known samples of Permian Lucaogou Formation source rocks in the Jimsar Depression of the Junggar Basin. This source rock suite is currently the main stratigraphic unit for shale oil exploration, and its early hydrocarbon generation characteristics have been widely confirmed.

[0042] Samples and tests: Three core samples with clear geochemical backgrounds were selected (J1, J2, J3).

[0043] Parameter acquisition and calculation: Sample J1 (premium segment): =10.2%, =0.048, =2.8. The normalized result is: =0.68, =0.80, =0.93, =0.72, rated as Level I (high potential).

[0044] Sample J2 (medium layer): =5.5%, =0.025, =1.5. The normalized result is: =0.37, =0.42, =0.50, =0.45, rated as Level II (medium potential).

[0045] Sample J3 (poor section): =1.8%, =0.008, =0.6. The normalized result is: =0.12, =0.13, =0.20, =0.18, rated as Level III (low potential).

[0046] Verification results: The evaluation results are in perfect agreement with the actual production data of the three appraisal wells (J1 corresponds to a high-yield well, J2 to a medium-yield well, and J3 to a low-yield / non-yield well). This proves that the method of the present invention can effectively distinguish the differences in hydrocarbon generation potential within the same set of source rocks, has cross-basin universality and reliability, and can be directly used to guide the selection of exploration targets in areas with similar geological backgrounds.

[0047] Application scenario expansion This method is not only applicable to the macroscopic evaluation of source rock formations in the early stages of basin-level exploration, but can also be further applied to: Fine identification of shale oil / tight oil "sweet spot": By applying this method to intensive vertical sampling within the confirmed source rock strata, the micro-strata with the highest early hydrocarbon generation potential can be identified, guiding the design of horizontal well trajectories and the selection of fracturing strata.

[0048] Assessment of immature to low-maturity oil resource potential: In resource calculation, this method is used to classify source rocks, which can assign differentiated hydrocarbon production rate parameters to source rocks of different potential levels, thereby more accurately estimating the amount of immature to low-maturity oil resources.

[0049] Re-evaluation of the exploration potential of old areas: Reapplying this method to saline lacustrine strata in mature exploration areas that have been overlooked due to low TOC may uncover new, hidden resources with early hydrocarbon generation potential.

[0050] The above description is not intended to limit the present invention in any way. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins, characterized in that, Includes the following steps: Step S10: Obtain source rock samples from the target stratum and measure the resin content, organic sulfur to organic carbon atom ratio, and gamma cerane index of the source rock samples. Step S20: Normalize the resin content, the ratio of organic sulfur to organic carbon atoms, and the gamma-cerane index respectively. Step S30: Calculate the comprehensive index of early hydrocarbon generation potential based on the normalized parameters; Step S40: Evaluate the early hydrocarbon generation potential of source rocks based on the calculated comprehensive index of early hydrocarbon generation potential.

2. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 1, characterized in that, The source rock sample is a source rock core or rock fragment sample.

3. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 1, characterized in that, The process for determining the resin content is as follows: the source rock sample is subjected to kerogen separation and purification, the micro-components are separated by zinc chloride heavy liquid density gradient centrifugation, and the volume percentage of resin is identified and counted under reflected light and fluorescence microscopes.

4. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 1, characterized in that, The determination process for the organic sulfur to organic carbon atomic ratio is as follows: the powder of the source rock sample is tested using a pyrolysis analyzer to directly obtain the total organic carbon content and organic sulfur content, and then converted into the S / C atomic ratio according to atomic weight.

5. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 1, characterized in that, The determination process of the gammacerane index is as follows: Soxhlet extraction and column chromatography separation are performed on the source rock sample to obtain the saturated hydrocarbon fraction. The gammacerane and C fraction are then integrated on the m / z 191 mass chromatogram using gas chromatography-mass spectrometry. 30 Calculate the peak area of ​​hopane and its ratio.

6. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 1, characterized in that, The normalization formula in step S20 include: In the formula: Resin content; This serves as a reference threshold for resin content; Normalized resin content; The ratio of organic sulfur to organic carbon atoms; This is a reference threshold for the ratio of organic sulfur to organic carbon atoms; The normalized ratio of organic sulfur to organic carbon atoms; Gammacerane index; This serves as the reference threshold for the gammacerane index; The normalized gammacerane index.

7. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 6, characterized in that, The reference threshold for the resin content =15%, the reference threshold for the ratio of organic sulfur to organic carbon atoms. =0.06, the reference threshold for the gammacerane index. =3.

0.

8. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 1, characterized in that, The formula for calculating the comprehensive index of early hydrocarbon generation potential is as follows: In the formula: This is a comprehensive index of early hydrocarbon generation potential; Normalized resin content; The normalized ratio of organic sulfur to organic carbon atoms; Normalized gammacerane index; , , All are weighting coefficients.

9. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 8, characterized in that, In step S30 =0.55, =0.30, =0.

15.

10. The method for evaluating the early hydrocarbon generation potential of source rocks in saline lacustrine basins according to claim 1, characterized in that, In step S40, the early hydrocarbon generation potential is classified according to the following criteria based on the calculated comprehensive index: Level I - High Potential: ≥0.70 indicates that the source rocks possess superior material basis and hydrocarbon generation conditions for forming large-scale low-maturity oil reservoirs, making them a priority target for exploration. Level II - Medium Potential: 0.40≤ <0.70 indicates that the source rock has a certain early hydrocarbon generation capacity and may form local oil and gas accumulation. Level III - Low Potential: <0.40 indicates that the early hydrocarbon generation capacity of the source rock was limited, and its exploration value was low.

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