A method for quantitatively restoring ancient water depth based on multi-method optimization

Abstract

This invention discloses a quantitative paleowater depth recovery method based on multi-method optimization, comprising the following steps: establishing a fine stratigraphic framework using seismic logging data; reconstructing paleomorphological features; calculating the paleowater depth of the sampling area; estimating the paleowater depth of the unsampled area; and performing sensitivity analysis and data optimization to obtain the final paleowater depth data. The beneficial effects of this invention are: by fusing and complementing multi-source data, it significantly improves the accuracy, reliability, and applicability of paleowater depth recovery in rift basins, providing more accurate data support for the prototype reconstruction of sedimentary basins, analysis of sedimentary evolution processes, and prediction of source-reservoir-seal distribution in oil and gas geological exploration.

Description

Technical Field

[0001] This invention relates to the field of oil and gas geological exploration technology, and in particular to a method for quantitative reconstruction of paleowater depth based on multi-method optimization. Background Technology

[0002] Paleowater depth reconstruction is a crucial step in oil and gas geological exploration, holding significant importance for reconstructing prototype basins, analyzing sedimentary evolution, and predicting source-reservoir-seal distribution in petroleum geology. Currently, numerous methods exist for paleowater depth research, including geochemical, paleontological and sedimentological, well logging, structural geology, and, in recent years, artificial intelligence methods. These methods can quantitatively or semi-quantitatively reconstruct paleowater depth values ​​from different periods, but they also have limitations. On the one hand, semi-quantitative analysis methods have strict requirements regarding paleomorphological features and accuracy; on the other hand, methods based on experimental test data lack accuracy in areas with sparse or missing test samples, making it difficult to achieve high-precision calculations across a wide region.

[0003] In recent years, quantitatively reconstructing paleowater depth has gradually become a crucial step in reconstructing the prototype of sedimentary basins. A Chinese patent application with publication number CN 114624775 A proposes a paleowater depth reconstruction method for deltaic sedimentary facies. This method involves reconstructing the shoreline, sampling within the reconstructed paleowater depth area, conducting trace element tests to obtain the Fe / Co ratio, and then mathematically fitting the semi-quantitative data to establish a mathematical relationship between the trace element ratio and the paleowater depth. While this method can reconstruct paleowater depth to some extent, it has limitations in terms of sedimentary facies type and is highly dependent on large sample data during the mathematical fitting process, potentially leading to errors in the fitting results. Furthermore, the method of reconstructing the shoreline using seismic profiles is only applicable to deep-water sedimentary environments and performs poorly in shallow-water environments and areas with poor seismic data quality.

[0004] Chinese patent application CN113674806A proposes a method for reconstructing paleowater depth in sedimentary lacustrine basins based on trace elements and paleontological differentiation. Before using this method, it is necessary to optimize the selection of the most suitable trace elements and verify it in conjunction with contemporaneous paleoclimatic factors to improve the rationality of the paleowater depth reconstruction. However, this method still faces the complexity and uncertainty of the trace element selection process in practical applications.

[0005] Chinese patent application CN 113970796 A proposes a method for accurately reconstructing paleowater depth in sedimentary basins. This method uses empirical formulas to calculate the compaction coefficients of sandstone and mudstone at the paleoburial depth, thereby calculating the thickness of the deltaic foreland layer during the depositional period and finally obtaining the paleowater depth. In this process, the influence of tectonic movement on paleowater depth is fully considered, but it depends on the applicability of empirical formulas and the accuracy of regional data.

[0006] Another method, "A Method for Reconstructing Paleowater Depth in Graben Basins," was proposed in Chinese Patent Application Publication No. CN114839674 A. This method employs structural geology, studying fault activity and utilizing the principle of area conservation to reconstruct paleoshorelines and thus obtain paleowater depth. While this method offers some simplicity, in complex paleogeomorphologies, differential subsidence during sedimentation can disrupt the relationship between accommodation space and sedimentary supply. Therefore, this method is only suitable for areas with relatively simple geometric features and may have limitations in accuracy.

[0007] In summary, existing paleowater depth reconstruction methods face challenges in terms of regional adaptability, data dependence, and computational accuracy during application. How to improve the accuracy and reliability of paleowater depth reconstruction under different sedimentary environments remains an important research topic in the field of oil and gas geological exploration. Summary of the Invention

[0008] To address the shortcomings of relying on single methods for estimating paleowater depth, such as strong dependence on a single method, poor adaptability, and insufficient computational accuracy, this invention provides a quantitative paleowater depth recovery method based on multi-method optimization, applicable to rift basins. The method of this invention estimates paleowater depth regionally using three methods—elemental chemistry, paleogeography, and sedimentary thickness—based on a detailed stratigraphic framework. This overcomes the limitations of single methods in different sedimentary environments and improves the accuracy of regional paleowater depth prediction.

[0009] To achieve the above-mentioned objectives, this invention provides a method for quantitative reconstruction of paleowater depth based on multiple optimization methods, comprising the following steps: S1: Establishing a detailed stratigraphic framework using seismic logging data: S2: Reconstruct ancient landforms; S3: Calculate the paleowater depth of the sampling area; S4: Estimate the paleowater depth in unsampled areas; S5: Sensitivity analysis and data optimization are conducted to obtain the final paleowater depth data.

[0010] Specifically, S1 involves: identifying sequence stratigraphic boundary marker layers based on seismic data and well logging curves, interpreting fault locations, determining sequence boundaries, and establishing a fine stratigraphic framework. Specifically, S2 is: S201: For the apparent thickness of the formation obtained from drilling data, the dip angle correction formula is used to calculate the true thickness. The calculation formula is: True thickness = Apparent thickness × cosα, where α is the dip angle of the formation. S202: Reconstructing the local stratigraphic thickness of the erosion zone using stratigraphic correlation and tectonic trend methods; S203: Establish the compaction coefficient-depth relationship curve using empirical formulas, fit the compaction curve equation, and obtain the paleogeographic morphology during the depositional period.

[0011] Specifically, S3 involves: calculating paleowater depth based on sensitive chemical element ratios and paleontological pollen data, and using paleosalinity and paleoclimate obtained from analysis to correct the results of geochemical methods; wherein, the sensitive chemical element ratio indicators include: The Sr / Cu ratio is used to determine the humidity of paleoclimate. The Sr / Ba ratio is used to analyze paleosalinity. The Fe / Mn ratio is used to estimate the depth of a lake basin. In step S4, for unsampled areas, the relationship between the original sedimentary thickness and paleowater depth is established using data from the sampled areas to estimate the paleowater depth. Specifically: Using wellbore data, establish the relationship between the compaction coefficient and depth of the target basin; Restore the original deposition thickness of the target layer; Establish the relationship between paleowater depth and original sediment thickness using data from the sampling area; Calculate the ancient water depth.

[0012] In addition, the paleowater depth in unsampled areas can also be estimated using the following method, specifically: Based on the restored paleogeography and fault activity, the location of the ancient shoreline is calculated; Calculate the horizontal distance from the ancient shoreline based on its location. Restoring the ancient slope; The ancient water depth was estimated by combining the horizontal distance from the ancient shoreline and the ancient slope angle.

[0013] The sensitivity analysis in S5 uses error screening to select the sample points with the smallest error range for difference calculation.

[0014] The beneficial effects of this invention are: by fusing and complementing multi-source data, this invention significantly improves the accuracy, reliability, and applicability of paleowater depth reconstruction in rift basins, providing more accurate data support for the reconstruction of sedimentary basin prototypes, analysis of sedimentary evolution processes, and prediction of source-reservoir-seal distribution in oil and gas geological exploration. Specifically: 1. By adopting scientific calculation methods, the ancient water depth can be calculated relatively simply, with high operational efficiency and ease of application.

[0015] 2. The data used are all commonly used data that are easy to obtain in conventional geological exploration, without relying on a large amount of analytical or paleontological data, which reduces the complexity of data preparation.

[0016] 3. It can provide high calculation accuracy for complex paleowater depths at the depression level, ensuring the reliability and scientific validity of the restoration results.

[0017] 4. It has good applicability to the reconstruction of paleowater depth in rift basins, providing strong support for the study of complex sedimentary geomorphological features.

[0018] 5. The method of this invention is efficient and accurate, providing precise data for sedimentary evolution analysis and source-reservoir-seal distribution prediction in the field of oil and gas exploration, and has broad application prospects. Attached Figure Description

[0019] Figure 1 This is a flowchart of Embodiment 3 of the present invention.

[0020] Figure 2 To establish a refined three-level grid for step 1 of embodiment 3 of the present invention.

[0021] Figure 3 This is for the restoration of the regional sedimentary paleogeography reconstructed in step 2 of embodiment 3 of the present invention.

[0022] Figure 4 This is a reference diagram for the qualitative correction of pollen fossils in step 3 of embodiment 3 of the present invention.

[0023] Figure 5 The result is the paleowater depth calculation result of step 3 of embodiment 3 of the present invention using the trace element method.

[0024] Figure 6 The result of paleowater depth calculation by sediment thickness method in step 4 of embodiment 3 of the present invention.

[0025] Figure 7 The result of step 4 in embodiment 3 of the present invention is the calculation result of estimating paleowater depth using paleogeography.

[0026] Figure 8 This is the final result of paleowater depth restoration in step 5 of embodiment 3 of the present invention. Detailed Implementation

[0027] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution.

[0028] Example 1 This invention provides a method for quantitative reconstruction of paleowater depth based on multi-method optimization, comprising the following steps: S1: Establishing a fine stratigraphic framework using seismic logging data: Specifically, based on seismic data and logging curves, identify sequence stratigraphic boundary markers, interpret fault locations, determine sequence boundaries, and establish a fine stratigraphic framework. S2: Reconstructing ancient landforms; specifically: S201: For the apparent thickness of the formation obtained from drilling data, the dip angle correction formula is used to calculate the true thickness. The dip angle correction formula is: True thickness = Apparent thickness × cosα, where α is the dip angle of the formation. S202: Reconstructing the local stratigraphic thickness of the erosion zone using stratigraphic correlation and tectonic trend methods; S203: Establish the compaction coefficient-depth relationship curve using empirical formulas, fit the compaction curve equation, and obtain the paleogeographic morphology during the depositional period.

[0029] S3: Calculate the paleowater depth of the sampling area; specifically: calculate the paleowater depth based on sensitive chemical element ratios and paleontological pollen data, and use paleosalinity and paleoclimate obtained from analysis to correct the results of the geochemical method. The sensitive chemical element ratios include: The Sr / Cu ratio is used to determine the humidity of paleoclimate. The Sr / Ba ratio is used to analyze paleosalinity. The Fe / Mn ratio is used to estimate the depth of a lake basin. S4: The paleowater depth of unsampled areas is estimated based on the proportional relationship between sand body thickness and paleowater depth, including: Using wellbore data, establish the relationship between the compaction coefficient and depth of the target basin; Restore the original deposition thickness of the target layer; Establish the relationship between paleowater depth and original sediment thickness using data from the sampling area; Calculate ancient water depth; S5: Sensitivity analysis and data optimization are adopted to obtain the final paleowater depth data. In the sensitivity analysis, the sample points with the smallest error range are selected for difference calculation through error screening.

[0030] Example 2 This invention provides a method for quantitative reconstruction of paleowater depth based on multi-method optimization, comprising the following steps: S1: Establishing a fine stratigraphic framework using seismic logging data: Specifically, based on seismic data and logging curves, identify sequence stratigraphic boundary markers, interpret fault locations, determine sequence boundaries, and establish a fine stratigraphic framework. S2: Reconstructing ancient landforms; specifically: S201: For the apparent thickness of the formation obtained from drilling data, the dip angle correction formula is used to calculate the true thickness. The dip angle correction formula is: True thickness = Apparent thickness × cosα, where α is the dip angle of the formation. S202: Reconstructing the local stratigraphic thickness of the erosion zone using stratigraphic correlation and tectonic trend methods; S203: Establish the compaction coefficient-depth relationship curve using empirical formulas, fit the compaction curve equation, and obtain the paleogeographic morphology during the depositional period.

[0031] S3: Calculate the paleowater depth of the sampling area; specifically: calculate the paleowater depth based on sensitive chemical element ratios and paleontological pollen data, and use paleosalinity and paleoclimate obtained from analysis to correct the results of the geochemical method. The sensitive chemical element ratios include: The Sr / Cu ratio is used to determine the humidity of paleoclimate. The Sr / Ba ratio is used to analyze paleosalinity. The Fe / Mn ratio is used to estimate the depth of a lake basin. S4: Estimating the paleowater depth in the unsampled area, specifically: Based on the restored paleogeography and fault activity, the location of the ancient shoreline is calculated; Calculate the horizontal distance from the ancient shoreline based on its location. Restoring the ancient slope; By combining the horizontal distance from the ancient shoreline and the ancient slope angle, the ancient water depth was estimated using the principle of accommodative space. S5: Sensitivity analysis and data optimization are adopted to obtain the final paleowater depth data. In the sensitivity analysis, the sample points with the smallest error range are selected for difference calculation through error screening.

[0032] Example 3 See Figure 1 This invention provides a method for fine-grained reconstruction of paleowater depth in rift basins, specifically including the following steps: Step 1: Establish an accurate stratigraphic framework using seismic logging data; Utilizing seismic data, detailed stratigraphic interpretation is performed to identify major faults. Key tectonic phase boundaries are traced, closed, and densified to determine fault locations and displacements. Unconformities are also traced. Combined with well logging characteristics, sequence stratigraphic boundary marker beds are identified, thus completing the determination of sequence stratigraphic boundaries. Finally, a detailed three-order sequence stratigraphic framework (such as...) is established. Figure 2 (As shown).

[0033] Step 2: Reconstruct paleomorphology through dip correction, tectonic correction, and sedimentary correction; Drilling data is used to obtain the apparent thickness of the formation. The true thickness is then calculated using the formula: True Thickness = Apparent Thickness × cosα (where α is the dip angle). Dip correction is applied to determine the true thickness. The erosion thickness is then reconstructed using stratigraphic correlation and tectonic trend methods. A compaction coefficient-depth relationship is established: k = b - alnH (where k is the compaction coefficient, a and b are constants, and H is the burial depth; for mudstone and shale, a = 0.1, b = 1.46; for sandstone, a = 0.08, b = 1.37), to reconstruct the original sedimentary thickness. Finally, the regional sedimentary paleogeographic morphology (e.g., ...) is reconstructed. Figure 3 (As shown).

[0034] Step 3: Calculate paleowater depth in the area where the chemical and paleontological data samples are located; During sediment transport, manganese (Mn) is more stable than iron (Fe), therefore the Fe / Mn ratio decreases with increasing water depth. Paleowater depth is estimated by measuring the Fe / Mn trace element ratio in rock samples. Paleoclimate and paleosalinity are then determined using the Sr / Cu ratio, pollen index, and Sr / Ba ratio. The estimated paleowater depth data points are then corrected (e.g.,...). Figure 4 (As shown). The results of reconstructing paleowater depth using chemical methods are as follows: Figure 5 As shown.

[0035] Step 4: For areas where samples are missing, measurements can be taken using sedimentary facies type or structural slope; In some areas where rock samples are missing, the paleowater depth cannot be determined using the trace element method. In such cases, it can be estimated using stratigraphic thickness. The specific steps are as follows: using wellbore data, establish the relationship between the compaction coefficient and depth of the target basin; reconstruct the original sedimentary thickness of the target layer; use sampling area data to establish the relationship between paleowater depth and original sedimentary thickness; calculate the paleowater depth. Specific results are shown below. Figure 6 As shown.

[0036] Secondly, estimations can be made using reconstructed paleogeography. Fault location can be reconstructed by analyzing fault activity, and the paleoshoreline can be reconstructed based on the principle of area conservation. The paleoslope angle can then be calculated, and the paleowater depth can be calculated from the horizontal distance between the paleoslope angle and the shoreline. Specific results are as follows: Figure 7 As shown.

[0037] Step 5: Finally, sensitivity analysis is performed to select the best paleowater depths recovered by multiple methods, and the final paleowater depth data is obtained. Based on the paleodepth data recovered by the three methods, the optimal data points from each method were selected, as shown in Table 1. By combining the data points and using interpolation, a more detailed paleodepth map of the rift basin was obtained. Specific results are shown below. Figure 8 As shown.

[0038] Table 1. Optimal selection of paleowater depth data points in rift basins

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for quantitatively reconstructing paleowater depth based on multi-method optimization, characterized in that, Includes the following steps: S1: Establish a detailed stratigraphic framework using seismic logging data; S2: Reconstruct ancient landforms; S3: Calculate the paleowater depth of the sampling area; S4: Estimate the paleowater depth in unsampled areas; S5: Sensitivity analysis and data optimization are conducted to obtain the final paleowater depth data.

2. The method according to claim 1, characterized in that, Specifically, S1 involves identifying sequence stratigraphic boundary marker layers based on seismic data and well logging curves, interpreting fault locations, determining sequence boundaries, and establishing a fine stratigraphic framework.

3. The method according to claim 1, characterized in that, Specifically, S2 is: S201: The true thickness is calculated using the dip angle correction formula based on the apparent thickness of the formation obtained from drilling data; S202: Reconstructing the local stratigraphic thickness of the erosion zone using stratigraphic correlation and tectonic trend methods; S203: Establish the compaction coefficient-depth relationship curve using empirical formulas, fit the compaction curve equation, and obtain the paleogeographic morphology during the depositional period.

4. The method according to claim 3, characterized in that, The dip correction formula in S201 is: true thickness = apparent thickness × cosα, where α is the dip angle of the formation.

5. The method according to claim 1, characterized in that, Specifically, S3 involves: calculating paleowater depth based on sensitive chemical element ratios and paleontological pollen data, and using paleosalinity and paleoclimate obtained from the analysis to correct the results of the geochemical method.

6. The method according to claim 5, characterized in that, The ratio of the sensitive chemical elements includes: The Sr / Cu ratio is used to determine the humidity of paleoclimate. The Sr / Ba ratio is used to analyze paleosalinity. The Fe / Mn ratio is used to estimate the depth of a lake basin.

7. The method according to claim 1, characterized in that, In step S4, for unsampled areas, the relationship between the original sediment thickness and the paleowater depth is established using the data from the sampled areas, and the paleowater depth is estimated.

8. The method according to claim 1, characterized in that, In S4, the paleowater depth of the unsampled area is estimated as follows: Based on the restored paleogeography and fault activity, the location of the ancient shoreline is calculated; Calculate the horizontal distance from the ancient shoreline based on its location. Restoring the ancient slope; The ancient water depth was estimated by combining the horizontal distance from the ancient shoreline and the ancient slope angle.

9. The method according to claim 1, characterized in that, The sensitivity analysis in S5 uses error screening to select the sample points with the smallest error range for difference calculation.

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