A palaeocurrent recovery method and system based on palaeogeomorphology and minimum runoff gradient

Abstract

The application discloses a palaeocurrent recovery method and system based on palaeogeomorphology and minimum runoff gradient, relates to the technical field of palaeocurrent recovery, and comprises the following steps: obtaining stratum, structure and elevation basic data, correcting the basic data, and establishing a palaeotopography DEM; calculating the effective runoff gradient between a center grid and an adjacent downstream grid, and determining a palaeocurrent direction according to a minimum runoff resistance criterion; performing flow direction coding, confluence accumulation and water flow path analysis based on the palaeocurrent direction, extracting a palaeocurrent channel, a confluence area and a palaeochannel; combining known geological constraints to test and spatially screen the palaeocurrent path, and vectorizing the path and a dominant flow direction which meet the constraint conditions; compiling a palaeocurrent direction distribution map and a palaeodrainage system distribution map, recovering a main flow direction, a confluence relationship and a palaeodrainage system spatial pattern of a research area; and extending discrete palaeoflow direction data into a continuous palaeodrainage system network on a basin scale, and improving the spatial continuity and geological reliability of palaeocurrent recovery.

Description

Technical Field

[0001] This invention relates to the field of paleoflow restoration technology, and in particular to a method and system for paleoflow restoration based on paleogeography and minimum runoff gradient. Background Technology

[0002] The direction of paleocurrent is an important basic parameter for basin analysis, which is directly related to the identification of source areas, reconstruction of sedimentary system distribution, prediction of sand body transport paths, and paleoenvironmental reconstruction.

[0003] Traditional paleoflow reconstruction relies heavily on paleoflow direction indicators such as outcrop cross-bedding and channel patterns, or on sedimentary structures, heavy mineral assemblages, and detrital zircon provenance analysis from well cores. While these data have strong geological indicative significance, limitations in the number of outcrops and wells often only provide discrete locations or approximate provenance orientations, making it difficult to directly establish a continuous basin-scale drainage network. In actual basin studies, paleoflow direction is often simultaneously controlled by factors such as paleogeographic undulations, tectonic separation, provenance location, and variations in the sedimentary base level. Cross-bedding, channel patterns, and detrital components recorded by a single well or outcrop can only reflect local depositional periods and local hydrodynamic directions. When the study area is large, the well network is sparse, or the seismic data interpretation scale is coarse, significant spatial gaps often exist between discrete paleoflow direction evidence, making it difficult to directly determine the connectivity between different flow paths and the main and tributary levels.

[0004] On the other hand, paleogeographic surfaces are typically derived from the comprehensive processing of multiple data sources, including seismic stratigraphic interpretation, well calibration, residual thickness restoration, and erosion restoration. Different data sources vary in sampling density, vertical accuracy, and spatial continuity. After interpolation to generate a DEM, isolated low values, spikes, step-like elevation abrupt changes, or closed depressions are prone to appear. Without independent geological evidence for verification, relying solely on calculation results makes it difficult to distinguish the true paleoflow system framework from pseudo-paths caused by DEM errors, threshold settings, or tectonic elevation abrupt changes, thus reducing the continuity, interpretability, and geological reliability of paleoflow reconstruction. Summary of the Invention

[0005] This application provides a paleoflow restoration method and system based on paleogeography and minimum runoff gradient, which solves the problem in the prior art that paleoflow direction data is point-like and it is difficult to directly restore basin-scale planar paleoflow systems from a small number of well points or outcrops. It realizes the technical effect of expanding discrete paleoflow direction data into a continuous planar paleoflow system network at the basin scale, thereby improving the spatial continuity and geological reliability of paleoflow restoration.

[0006] This application provides a paleocurrent reconstruction method based on paleogeography and minimum runoff gradient, including: S1: Obtain the stratigraphic, structural, and elevation baseline data required for paleotopographic reconstruction and perform data correction. Based on the corrected paleotopographic elevation data, establish a paleotopographic DEM. S2: Determine the grid neighborhood based on the paleotopographic DEM, calculate the topographic tilt direction and slope characteristics of each grid unit; under the constraint of water flowing from high potential energy area to low potential energy area, calculate the elevation difference and horizontal distance between the central grid and the adjacent downstream grid to obtain the effective runoff gradient, and determine the paleorunoff direction based on the minimum runoff resistance criterion; each central grid corresponds to a paleorunoff direction. S3: Based on the paleorunoff direction, flow direction coding, confluence accumulation and flow path analysis are performed. Potential paleoflow channels, confluence areas and paleochannels are extracted based on the confluence accumulation value, and several paleoflow directions are determined. S4: Based on each ancient water flow direction, the corresponding ancient water flow path is obtained. Combined with ancient geomorphological elevation, slope, sedimentary geomorphology and known geological constraints, the obtained ancient water flow path is geologically rationalized and spatially screened. The ancient water flow path and dominant flow direction that meet the constraints are vectorized. S5: Based on ancient water flow direction vector data, ancient water flow direction distribution maps and ancient river system layout maps were compiled to restore the main direction of ancient water flow, confluence relationships and spatial pattern of ancient river system in the study area.

[0007] A paleoflow restoration system based on paleogeography and minimum runoff gradient is applied to the above method. The system includes: a paleogeography construction module, used to acquire the stratigraphic, structural and elevation basic data required for paleogeography restoration and to perform data correction, and to establish a paleotopographic DEM based on the corrected paleotopographic elevation data; The runoff gradient and flow direction calculation module is used to determine the grid neighborhood based on the paleotopographic DEM, calculate the topographic tilt direction and slope characteristics of each grid unit; under the constraint of water flowing from high potential energy area to low potential energy area, it calculates the elevation difference and horizontal distance between the central grid and the adjacent downstream grid to obtain the effective runoff gradient, and determines the paleorunoff direction based on the minimum runoff resistance criterion. The confluence network extraction module is used for flow direction coding, confluence accumulation, and flow path analysis based on paleorunoff direction. It extracts potential paleoflow channels, confluence areas, and paleochannels based on the confluence accumulation value, and determines several paleoflow directions. The geological constraint verification and vectorization module is used to obtain the corresponding paleoflow path based on each paleoflow direction. Combined with paleogeographic elevation, slope, sedimentary geomorphology and known geological constraints, the module performs geological rationality verification and spatial screening on the obtained paleoflow paths, and vectorizes the paleoflow paths and dominant flow directions that meet the constraints. The output module is used to compile ancient water flow direction distribution maps and ancient river system layout maps based on ancient water flow direction vector data, and to restore the main direction of ancient water flow, confluence relationship and spatial pattern of ancient river system in the study area.

[0008] One or more technical solutions provided in this application have at least the following technical effects or advantages: By employing the minimum runoff resistance criterion for grid flow direction optimization, and simultaneously incorporating elevation drop and grid center distance into the judgment, a unified and comparable scale is achieved between different neighborhood directions. This reduces the interference of local pseudo-depressions, abrupt changes in fault elevation, and interpolation noise on flow direction, enabling the expansion from discrete paleoflow direction data to continuous surface reconstruction at the basin scale, thus realizing the restoration of paleoflow direction from point to surface.

[0009] By combining flow topology with confluence accumulation, and by performing multi-level threshold calculations based on the study area scale, DEM resolution, paleogeographic relief, and target paleochannel level, the main channel, tributaries, and confluence areas of paleochannels can be identified simultaneously, forming a dendritic-convergent paleoriver network with upstream and downstream topological relationships, providing spatial constraints for the prediction of sediment transport paths and sand body distribution.

[0010] By introducing multiple independent geological evidence sources, such as core paleoflow direction, outcrop cross-bedding, heavy mineral provenance zoning, detrital zircon provenance analysis, and seismic sedimentary facies, as constraints, the geological rationality of the simulated water flow path is tested and spatially screened. This can eliminate spurious water flow paths and retain verified dominant flow directions, reduce model ambiguity, and improve the geological reliability of paleoflow reconstruction results. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of a paleoflow restoration method based on paleogeography and minimum runoff gradient in an embodiment of the present invention. Figure 2 This is a diagram illustrating the architecture of a paleoflow restoration system based on paleogeography and minimum runoff gradient in an embodiment of the present invention. Detailed Implementation

[0012] To facilitate understanding of the present invention, a more complete description of this application will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and complete understanding of the disclosure of the present invention.

[0013] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0014] The paleocurrent reconstruction method proposed in this application is applicable to study areas where basic geological data are unevenly distributed and traditional paleocurrent evidence is relatively discrete, but conditions for regional paleogeomorphological reconstruction are available. Through continuous grid flow direction and confluence topology, local paleocurrent evidence can be organized into a regional drainage framework. This framework is then gradually corrected using newly added well data or provenance results, forming an iteratively updatable paleocurrent interpretation model. In provenance analysis, the main paleocurrent direction can be used to verify the spatial correspondence between provenance zones; in sedimentary system reconstruction, potential sediment transport directions can be analyzed based on confluence centers and flow channels; and in sand body prediction, stable main channels can serve as planar references for favorable sand transport paths.

[0015] The paleoflow reconstruction described in this invention is not a direct simulation of modern surface hydrological processes. Instead, it reconstructs the paleogeographic energy field based on stratigraphic interface reconstruction, tectonic correction, and erosion reconstruction for a specific geological period. Then, it infers the possible migration paths of paleorunoff based on the relative elevation relationships between grids and the confluence topology. The objects processed can be continuous paleogeographic surfaces at the basin scale, or key study areas between local tectonic zones, sedimentary depressions, or source-sink areas. The results can serve as spatial constraint data for the interpretation of sedimentary systems and source analysis.

[0016] Example 1: As Figure 1 As shown, a paleocurrent reconstruction method based on paleogeography and minimum runoff gradient is proposed, the method comprising: S1: Obtain the stratigraphic, structural, and elevation baseline data required for paleotopographic reconstruction and perform data correction. Based on the corrected paleotopographic elevation data, establish a paleotopographic DEM.

[0017] In some embodiments, the basic data includes at least one of seismic interpretation stratigraphic data, well stratigraphic data, fault structure data, and stratigraphic erosion recovery results; stratigraphic interfaces are recovered according to the target stratigraphic level for the study period, and necessary corrections are made for erosion, tectonic subsidence or uplift, and fault displacement. The corrected paleotopographic elevations are gridded to establish a paleogeographic DEM for the study area; the data correction includes at least one of erosion correction, tectonic subsidence correction, uplift correction, and fault displacement correction.

[0018] Preferably, before performing paleogeographic elevation gridding, a unified coordinate system, a unified elevation datum, and unified stratigraphic constraints are applied to data from different sources. For well control points, well-seismic calibration results can be used as local elevation constraints; for fault-developed areas, interface restoration can be performed based on the relationship between the hanging wall and footwall of the fault to avoid elevation transitions that do not conform to the structural pattern caused by direct interpolation across faults. For erosion restoration results, the regional variation trend is preferentially preserved, and cross-checked with the current residual stratum thickness and structural interpretation results.

[0019] When constructing the DEM, the raster resolution is determined based on the data density of the study area and the target paleochannel scale. An excessively large raster scale will weaken local gully and slope break information, while an excessively small scale may amplify seismic interpretation errors and interpolation noise. Therefore, the optimal raster size is one that can represent the main paleogeographic undulations without being significantly smaller than the effective spatial resolution of the basic interpretation data. For areas without data and at the boundaries of the study area, a NoData mask is set to prevent the confluence algorithm from crossing areas without geological constraints and forming false flow connections.

[0020] S2: Determine the grid neighborhood based on the paleotopographic DEM, calculate the topographic tilt direction and slope characteristics of each grid cell; under the constraint of water flowing from high potential energy area to low potential energy area, calculate the elevation difference and horizontal distance between the central grid and the adjacent downstream grid to obtain the effective runoff gradient, and determine the paleorunoff direction based on the minimum runoff resistance criterion. Each central grid corresponds to one paleorunoff direction.

[0021] In some embodiments, the method further includes: performing depression filling and outlier processing on the paleotopographic DEM to eliminate pseudo-depressions without drainage outlets within the DEM and abnormal low points caused by data noise. The depression filling process prioritizes correcting closed low points that are small in area, shallow in depth, and lack tectonic or sedimentological evidence. For low-lying areas that may represent genuine paleolae basins, local fault depressions, or tectonic depressions, they should not be unconditionally leveled; instead, they should be preserved as runoff endpoints or internal catchment areas, depending on the research objectives. Outlier identification can be achieved through a combination of neighborhood elevation differences, local slope abrupt changes, and retrospective analysis of original seismic interpretation points, thereby avoiding misclassifying genuine slope break zones as noise.

[0022] The DEM undergoes depression filling, outlier identification, and necessary smoothing to eliminate geologically insignificant localized low points. Subsequently, slope and aspect are calculated to aid in identifying the overall gradient trend. Slope and aspect are used to check the overall tilt trend and local slope continuity of the reconstructed paleogeography, but do not directly replace the final paleoflow direction determination. By overlaying the slope and aspect results with the original paleogeographic elevation, non-geological features that may be generated by interpolation, such as abnormally steep slopes, isolated high points, and localized annular aspects, can be quickly identified. Necessary verification is performed before proceeding to the calculation of the neighboring flow direction. The method further includes: employing an eight-neighbor grid search approach, for the central grid i and each candidate adjacent grid j, when the elevation of the adjacent grid is less than the elevation of the central grid, the formula for calculating the effective runoff gradient is as follows: ;in, It is the effective runoff gradient; and These are the elevations of the center grid and the adjacent grid, respectively. The horizontal distance between the centers of two grid cells; orthogonal neighbor cells For the grid side length, diagonally to the neighboring cells The grid side length times.

[0023] If the elevation of a neighboring cell is not lower than that of the central grid, it will not participate in the selection process in this round. When there are no neighboring cells lower than the central grid, they are marked as flat areas to be processed or local low points. A secondary judgment is made in combination with the results of filling depressions, the continuous slope of the neighborhood, and the relationship with the upstream water flow. This can avoid forcibly generating random flow directions when there is no obvious elevation advantage, which is conducive to maintaining the continuity of the main water flow path.

[0024] In some embodiments, the runoff resistance is defined as the reciprocal of the effective runoff gradient. The minimum runoff resistance criterion selects the direction with the minimum runoff resistance from candidate neighbors whose adjacent grid elevations are less than the central grid elevation as the paleorunoff direction of the central grid. When multiple candidate neighbors have the same runoff resistance, priority is determined by combining slope continuity and upstream water direction. Slope continuity refers to the slope azimuth angle between the candidate neighbor and the central grid; the smaller the azimuth angle, the higher the priority. The upstream water direction refers to the angle between the candidate neighbor and the upstream grid flow direction; the smaller the angle, the higher the priority, maintaining the continuity of the confluence channel and the inertial effect of the flow.

[0025] For example, when the difference in runoff resistance between two or more candidate neighbors of the central grid is less than a preset tolerance, these directions are considered equivalent in terms of topographic driving. In this case, disambiguation is performed by combining slope aspect continuity and upstream water direction: Suppose that the candidate neighbors of the central grid include east-facing neighbors and southeast-facing neighbors, whose effective runoff gradients are close and whose runoff resistance difference is less than the tolerance. If the overall slope aspect of the region points southeast, then the slope aspect azimuth of the east-facing neighbor is greater than that of the southeast-facing neighbor, and the southeast direction is preferentially selected based on slope aspect continuity; if the upstream grid already has a clear flow direction pointing towards the central grid and the water direction comes from the northwest, then the angle between the southeast direction and the upstream water direction is smaller, which can maintain the water flow inertia, so the southeast direction is preferentially selected as the paleorunoff direction of the central grid. The above tolerance is used to handle numerical parallelism caused by DEM elevation rounding, interpolation smoothing, or local near-horizontal terrain. Its setting principle is to not change the obviously dominant direction, but only to provide stable decision rules among multiple approximately equivalent paths. The theoretical basis of this disambiguation rule is the inertial effect of water flow and the continuity of the confluence channel: the energy required for water flow to continue along the existing channel is minimal, and the smaller the angle between the slope azimuth and the upstream water direction, the more it conforms to the real runoff process, which can avoid local flow oscillation and checkerboard bidirectional flow.

[0026] S3: Based on paleorunoff direction, flow direction coding, confluence accumulation, and flow path analysis are performed. Potential paleoflow channels, confluence areas, and paleochannels are extracted based on the confluence accumulation values, and several paleoflow directions are determined. Each adjacent grid corresponds to one paleoflow direction, and eight neighborhoods correspond to eight paleoflow directions.

[0027] In some embodiments, the confluence accumulation value is calculated according to the flow direction coding results, and the confluence accumulation threshold is determined based on the study area scale, DEM resolution, paleogeographic relief, and target paleochannel level; grids with confluence accumulation values ​​not less than the confluence accumulation threshold are identified as paleochannel candidate units.

[0028] For the same study area, a set of candidate thresholds from high to low were set to extract the river network, and the changes in the location of the main channel, the number of tributaries, the location of the confluence point, and the river network density were compared under different thresholds. If a certain flow line persists within a wide threshold range, it indicates that it is strongly controlled by the regional paleogeography and can be given priority for preservation as a stable paleoflow channel.

[0029] During the river network extraction process, short-distance isolated line segments, radial flow lines controlled only by a single anomalous low point, and connections that clearly cross watersheds are marked. These marked paths are not directly deleted, but rather used as key targets for geological verification to distinguish algorithmic noise from potentially geologically significant local tectonic drainage phenomena.

[0030] The runoff accumulation value is calculated based on the flow direction coding results. The flow direction coding result refers to the integer grid formed by converting the flow direction of each grid into a numerical code. Each valid grid obtains a corresponding flow direction coding value. The eight neighborhood directions of the central grid are assigned specific integer values ​​(such as powers of 1, 2, 4, 8, 16, 32, 64, 128, etc.) to form a flow direction coded grid. The entire grid forms a directed topological relationship with grid cells as nodes and flow direction as the direction. The calculation of the runoff accumulation value follows the water balance principle, that is, the runoff accumulation of each grid cell is equal to the sum of its own initial water volume and the water volume of all upstream grid cells that directly or indirectly flow into the grid. Specifically, by default, each grid cell carries one unit of water volume as the initial value. If there are spatial differences in rainfall, runoff coefficient, or source-sink supply intensity data in the study area, corresponding initial weight values ​​can also be assigned to different grids for weighted runoff accumulation.

[0031] The in-degree of each grid is counted based on the flow direction coding grid, i.e., the number of upstream grids pointing to that grid. Grids with an in-degree of zero are identified as source grids (i.e., watersheds or the starting point of the flow) and used as the starting node for calculation. Grids are traversed and accumulated one by one in topological order from upstream to downstream. The specific process is as follows: For an outflow grid with a known cumulative value, the corresponding downstream inflow grid is found based on its flow direction coding. The cumulative value of the outflow grid is transferred and added to the cumulative value of the downstream grid. The accumulation process is repeated until all grids with valid flow direction codes in the entire area have been traversed. During the accumulation and transfer, if the downstream grid is an undefined grid, the water transfer for the corresponding path is terminated, and the undefined grid is retained as a local confluence endpoint. Undefined grids are confluence endpoints and do not transfer water downstream.

[0032] After the accumulation process is completed, each effective grid in the entire area obtains an integer or floating-point cumulative runoff value, which is used to quantitatively characterize the number of upstream grids (or the corresponding equivalent catchment area) that each grid receives.

[0033] A grid with a larger accumulation value indicates a stronger water collection capacity and a greater likelihood of forming surface runoff and paleochannels.

[0034] Based on this, a set of multi-level candidate thresholds, from high to low, was pre-set and tested according to the study area, DEM resolution, paleogeographic undulation, and target paleochannel level. Grids with confluence accumulation values ​​not less than the current threshold were identified as paleochannel candidate units; when lowering the threshold caused the tributary density to significantly exceed the interpretable range at the paleogeographic scale, further threshold reduction was stopped. Thus, a dendritic-convergent paleoporosis candidate network with hierarchical characteristics, consistent with paleogeographic undulation, was finally obtained for subsequent steps to verify geological rationality and for vectorization output. The threshold determination employed a multi-level threshold trial algorithm, extracting the river network from the confluence accumulation grid using multi-level candidate thresholds from high to low, and comparing the changes in main channel location, tributary number, confluence node location, and river network density under different thresholds. Threshold reduction was stopped when the tributary density significantly exceeded the interpretable range at the paleogeographic scale. Discharge lines whose positions remained essentially unchanged within a relatively wide threshold range were identified as stable main channels.

[0035] Study area scale refers to the spatial extent (area) of the study area, which is directly determined by the boundary of the study area; DEM resolution is the actual ground size corresponding to the raster pixels, which is determined by the pixel size of the DEM data itself; paleotopographic relief is the variation range of paleotopographic elevation (degree of difference in elevation), which is statistically derived from the paleotopographic DEM established in step S1 (the difference between the maximum and minimum elevations); target paleochannel level is the scale level of the main channel or secondary tributary to be extracted, which is determined by the research objectives and geological understanding (main channels correspond to higher thresholds, and secondary tributaries correspond to lower thresholds).

[0036] S4: Based on each ancient water flow direction, the corresponding ancient water flow path is obtained. Combined with ancient geomorphological elevation, slope, sedimentary geomorphology and known geological constraints, the obtained ancient water flow paths are geologically rationalized and spatially screened. The ancient water flow paths that meet the constraints and the dominant flow direction are vectorized.

[0037] In some embodiments, the known geological constraints include at least one of the following: well core paleocurrent data, outcrop cross-bedding occurrence, heavy mineral provenance zoning, detrital zircon provenance analysis results, and seismic sedimentary facies interpretation results. False flow paths are eliminated by verifying the consistency between the simulated flow direction and the known geological constraints. The geological rationality test is divided into three levels: (1) Topographical accessibility: checking whether the path generally extends from high-altitude areas to low-altitude areas, and whether it cuts through paleogeographic highlands without basis. (2) Directional consistency: comparing the simulated flow direction with independent evidence such as the core paleocurrent direction, outcrop cross-bedding occurrence, heavy mineral provenance zoning, and detrital zircon provenance analysis results to assess the degree of consistency. (3) Sedimentary response rationality: checking whether the main confluence zone has a spatial correspondence with the interpreted valley, deltaic progradation direction, or sand body distribution trend.

[0038] The dominant flow direction refers to the dominant flow direction identified at a specific confluence node or river segment after verification using multi-source geological data (core paleoflow direction, outcrop cross-bedding, heavy mineral provenance zoning, etc.). It represents the flow direction with the highest credibility after verification by independent geological evidence. A paleoflow path may have different dominant flow directions in different segments (e.g., river bends, changes in direction after confluence), but for a specific river segment or confluence node, there is only one dominant flow direction. The entire paleoflow network is composed of several paths with their own dominant flow directions, forming a complete upstream-downstream topology. Vectorization includes converting paleochannel candidate rasters into line features, connecting and smoothing line segments according to the confluence topology, and assigning flow direction, confluence cumulative value, order, and geological verification status attributes to the line features.

[0039] For paths with consistent evidence from multiple sources, a high level of geological confidence is assigned; for paths supported only by topography but lacking independent evidence, they are retained as flow lines awaiting verification; for paths that simultaneously exhibit reverse slopes, cross watersheds, and significantly conflict with multiple types of geological data, their upstream DEMs and threshold settings are reviewed before a decision is made on whether to remove them. This tiered approach avoids the excessive deletion of potentially plausible paleoflow channels due to the lack of a single piece of evidence.

[0040] Vectorization preserves the upstream and downstream topology of the raster river network, converts continuous candidate rasters into line features, and segments them at confluence nodes. Each line feature can record attributes such as start point, end point, main stream direction, confluence cumulative value, channel order, source threshold, and geological verification status, so as to facilitate subsequent querying, hierarchical display, and spatial overlay analysis with sedimentary facies, sand bodies, or provenance data in the GIS platform.

[0041] S5: Based on ancient water flow direction vector data, ancient water flow direction distribution maps and ancient river system layout maps were compiled to restore the main direction of ancient water flow, confluence relationships and spatial pattern of ancient river system in the study area.

[0042] Preferably, in addition to planar maps, the output can also save intermediate data such as flow direction grids, confluence accumulation grids, candidate river network grids, and the final vector river network. By retaining process data, recalculation can be quickly performed when adding new wells, updating seismic interpretations, or adjusting paleogeomorphological restoration schemes, without having to repeat all data preparation work from scratch. For applications requiring sedimentary system analysis, the length proportions of paleoflow lines in different directional intervals, the locations of major confluence centers, and the spatial relationships between main drainage systems and target sand bodies can be further statistically analyzed, providing quantitative planar constraints for source orientation identification, sedimentary channel tracking, and favorable sand body prediction.

[0043] Example 2: Figure 2 As shown, based on the method in Embodiment 1, this application also provides a paleocurrent reconstruction system based on paleogeography and minimum runoff gradient, the system comprising: The paleogeographic construction module is used to acquire the stratigraphic, structural, and elevation baseline data required for paleogeographic reconstruction and to perform data correction. Based on the corrected paleogeographic elevation data, a paleogeographic DEM is built.

[0044] The runoff gradient and flow direction calculation module is used to determine the grid neighborhood based on the paleotopographic DEM, calculate the topographic tilt direction and slope characteristics of each grid cell; under the constraint of water flowing from high potential energy area to low potential energy area, it calculates the elevation difference and horizontal distance between the central grid and the adjacent downstream grid to obtain the effective runoff gradient, and determines the paleorunoff direction based on the minimum runoff resistance criterion.

[0045] The confluence network extraction module is used for flow direction coding, confluence accumulation, and flow path analysis based on paleorunoff direction. It extracts potential paleoflow channels, confluence areas, and paleochannels based on the confluence accumulation value, and determines several paleoflow directions.

[0046] The geological constraint verification and vectorization module is used to obtain the corresponding paleoflow path based on each paleoflow direction. Combining paleogeographic elevation, slope, sedimentary geomorphology and known geological constraints, it performs geological rationality verification and spatial screening on the obtained paleoflow paths, and vectorizes the paleoflow paths and dominant flow directions that meet the constraints.

[0047] The output module is used to compile ancient water flow direction distribution maps and ancient river system layout maps based on ancient water flow direction vector data, and to restore the main direction of ancient water flow, confluence relationship and spatial pattern of ancient river system in the study area.

[0048] In one implementation, data is transferred between modules through a unified raster spatial reference and attribute fields: after the paleogeomorphology construction module outputs a standard DEM, the runoff gradient and flow direction calculation module generates a flow direction raster; the confluence network extraction module calculates confluence accumulation based on the flow direction raster and forms a candidate river network; the geological constraint verification and vectorization module loads the geological constraint layer and writes verification attributes, and finally, the output module generates maps and GIS data packages. The system can set parameter log files to save information such as raster resolution, depression filling settings, threshold sequences, flow direction disambiguation rules, and geological verification status. After updating paleogeomorphology or adding geological data, users can call existing parameters to rerun specified modules, enabling rapid comparison between different interpretation schemes for the same study area. Each module can be implemented as an independent software unit or combined into a GIS model tool, script tool, or desktop application; the processor executes the corresponding computer program to complete the above steps.

[0049] To make the technical solution of the present invention clearer, the above specific embodiments may involve several specific numerical values, thresholds, parameters, formulas, and examples. Those skilled in the art should understand that these specific contents are merely exemplary descriptions given for ease of implementation and are not essential technical features necessary for realizing the present invention, nor do they constitute a limitation on the scope of protection of the present invention. The mathematical formulas, parameter values, model structures, calculation rules, constraints, and data acquisition methods described in the specific embodiments section of this application are preferred examples for realizing the technical concept of the present invention, not the only implementation methods. Based on the core logic and inventive concept disclosed in this application, those skilled in the art can make reasonable equivalent substitutions, parameter adjustments, or logical optimizations to the parameters, formulas, and algorithm models according to actual conditions, industry standards, or conventional experimental methods, without producing substantial differences. Any changes that do not depart from the inventive concept of this application fall within the scope of this application. All mathematical expressions in this application should ensure that their physical meaning is clear when applied; parameters such as weights and thresholds can be calibrated using statistical or machine learning methods known in the art.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A paleocurrent reconstruction method based on paleogeography and minimum runoff gradient, characterized in that, include: S1: Obtain the stratigraphic, structural, and elevation baseline data required for paleotopographic reconstruction and perform data correction. Based on the corrected paleotopographic elevation data, establish a paleotopographic DEM. S2: Determine the grid neighborhood based on the paleotopographic DEM, calculate the topographic tilt direction and slope characteristics of each grid unit; under the constraint of water flowing from high potential energy area to low potential energy area, calculate the elevation difference and horizontal distance between the central grid and the adjacent downstream grid to obtain the effective runoff gradient, and determine the paleorunoff direction based on the minimum runoff resistance criterion; each central grid corresponds to a paleorunoff direction. S3: Based on the paleorunoff direction, flow direction coding, confluence accumulation and flow path analysis are performed. Potential paleoflow channels, confluence areas and paleochannels are extracted based on the confluence accumulation value, and several paleoflow directions are determined. S4: Based on each ancient water flow direction, the corresponding ancient water flow path is obtained. Combined with ancient geomorphological elevation, slope, sedimentary geomorphology and known geological constraints, the obtained ancient water flow path is geologically rationalized and spatially screened. The ancient water flow path and dominant flow direction that meet the constraints are vectorized. S5: Based on ancient water flow direction vector data, ancient water flow direction distribution maps and ancient river system layout maps were compiled to restore the main direction of ancient water flow, confluence relationships and spatial pattern of ancient river system in the study area.

2. The paleocurrent reconstruction method based on paleogeography and minimum runoff gradient according to claim 1, characterized in that, The basic data includes at least one of seismic interpretation stratigraphic data, well stratigraphic data, fault structure data, and formation erosion recovery results; the data correction includes at least one of erosion correction, tectonic subsidence correction, uplift correction, and fault displacement correction.

3. The paleocurrent reconstruction method based on paleogeography and minimum runoff gradient according to claim 1, characterized in that, In step S2, the method further includes: performing depression filling and outlier processing on the paleotopographic DEM to eliminate pseudo depressions without drainage outlets and abnormal low points caused by data noise.

4. The paleocurrent reconstruction method based on paleogeography and minimum runoff gradient according to claim 1, characterized in that, In step S2, the method further includes: using an eight-neighbor grid search method, for the central grid i and each candidate neighboring grid j, when the elevation of the neighboring grid is less than the elevation of the central grid, the formula for calculating the effective runoff gradient is as follows: ;in, It is the effective runoff gradient; and These are the elevations of the center grid and the adjacent grid, respectively. The horizontal distance between the centers of two grid cells; orthogonal neighbor cells For the grid side length, diagonally to the neighboring cells The grid side length times.

5. The paleocurrent reconstruction method based on paleogeography and minimum runoff gradient according to claim 1, characterized in that, The minimum runoff resistance criterion selects the direction with the minimum runoff resistance from candidate neighboring cells where the elevation of adjacent cells is less than that of the central cell, and uses this direction as the paleorunoff direction of the central cell. When multiple candidate neighboring cells have the same runoff resistance, priority is determined by combining slope continuity and upstream water direction; the slope continuity refers to the slope azimuth angle between the candidate neighboring cell and the central grid; the upstream water direction refers to the angle between the candidate neighboring cell and the upstream grid's flow direction. The runoff resistance is defined as the reciprocal of the effective runoff gradient.

6. The paleocurrent reconstruction method based on paleogeography and minimum runoff gradient according to claim 1, characterized in that, In step S3, the confluence accumulation value is calculated according to the flow direction coding results, and the confluence accumulation threshold is determined based on the study area scale, DEM resolution, paleogeographic relief, and target paleochannel level. Rasteres with a confluence accumulation value not less than the confluence accumulation threshold are identified as paleochannel candidate units.

7. The paleocurrent reconstruction method based on paleogeography and minimum runoff gradient according to claim 1, characterized in that, The known geological constraints include at least one of the following: paleocurrent data from well cores, cross-bedding occurrence of outcrops, heavy mineral provenance zoning, detrital zircon provenance analysis results, and seismic sedimentary facies interpretation results. False flow paths are eliminated by simulating the consistency between the flow direction and the known geological constraints.

8. The paleocurrent reconstruction method based on paleogeography and minimum runoff gradient according to claim 6, characterized in that, The flow accumulation value is calculated based on the flow direction coding result. The flow direction coding result refers to the integer grid formed by converting the flow direction of each grid into a numerical code. The eight neighborhood directions of the center grid are assigned specific integer values, and each valid grid obtains a corresponding flow direction coding value to form a flow direction coding grid. The entire grid forms a directed topology with grid cells as nodes and flow direction as the direction. The calculation of the cumulative flow value follows the water balance principle, that is, the cumulative flow of each grid cell is equal to the sum of its own initial water volume and the water volume of all upstream grid cells flowing into the grid. The in-degree of each grid is counted based on the flow direction coding grid. Grids with an in-degree of zero are identified as source grids and used as the starting node for calculation. The grids are traversed and accumulated one by one in the topological order from upstream to downstream. The accumulation process is repeated until all grids with valid flow direction codes in the entire area have been traversed. When accumulating and transferring, if the downstream grid is an undefined grid, the water transfer of the corresponding path is terminated. The undefined grid is retained as a local confluence endpoint. As a confluence endpoint, the undefined grid does not transfer water downstream. After the accumulation process is completed, each valid grid cell in the entire area will receive a cumulative value.

9. The paleocurrent reconstruction method based on paleogeography and minimum runoff gradient according to claim 1, characterized in that, The vectorization includes converting ancient river channel candidate rasters into line features, connecting and smoothing line segments according to confluence topology, and assigning flow direction, confluence cumulative value, order, and geological verification status attributes to the line features.

10. A paleocurrent reconstruction system based on paleogeography and minimum runoff gradient, applied to the paleocurrent reconstruction method based on paleogeography and minimum runoff gradient as described in any one of claims 1 to 8, characterized in that, The system includes: a paleogeographic construction module, used to acquire the stratigraphic, structural and elevation basic data required for paleogeographic restoration and perform data correction, and to establish a paleogeographic DEM based on the corrected paleogeographic elevation data; The runoff gradient and flow direction calculation module is used to determine the grid neighborhood based on the paleotopographic DEM, calculate the topographic tilt direction and slope characteristics of each grid unit; under the constraint of water flowing from high potential energy area to low potential energy area, it calculates the elevation difference and horizontal distance between the central grid and the adjacent downstream grid to obtain the effective runoff gradient, and determines the paleorunoff direction based on the minimum runoff resistance criterion. The confluence network extraction module is used for flow direction coding, confluence accumulation, and flow path analysis based on paleorunoff direction. It extracts potential paleoflow channels, confluence areas, and paleochannels based on the confluence accumulation value, and determines several paleoflow directions. The geological constraint verification and vectorization module is used to obtain the corresponding paleoflow path based on each paleoflow direction. Combined with paleogeographic elevation, slope, sedimentary geomorphology and known geological constraints, the module performs geological rationality verification and spatial screening on the obtained paleoflow paths, and vectorizes the paleoflow paths and dominant flow directions that meet the constraints. The output module is used to compile ancient water flow direction distribution maps and ancient river system layout maps based on ancient water flow direction vector data, and to restore the main direction of ancient water flow, confluence relationship and spatial pattern of ancient river system in the study area.

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