A method for recovering exposed buried hill paleogeomorphology by combining forward and inversion techniques

Abstract

The application discloses a buried hill palaeogeomorphology recovery method combining forward and inversion techniques, and comprises the following steps: (i) performing fine geophysical data comprehensive interpretation; (ii) carrying out palaeogeomorphology inversion simulation in a sedimentary period with residual strata at present; (iii) carrying out inversion simulation result correction; (iv) carrying out forward simulation of palaeogeomorphology in a key structure period; (v) carrying out uplift amount comparison and correction; (vi) carrying out palaeogeomorphology inversion simulation in a sedimentary period without residual strata at present; and (vii) carrying out comparison and correction of palaeogeomorphology recovery results of forward simulation and inversion simulation. The method has strong operability and wide application, can recover buried hill palaeogeomorphology from multiple angles, and has accurate palaeogeomorphology recovery results.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development, and specifically relates to a method for restoring exposed buried hill paleogeographic features by combining forward and inverse modeling techniques. Background Technology

[0002] Paleogeomorphology is a crucial factor controlling the distribution of buried hill reservoirs. In the Bohai Bay Basin, buried hills are deeply burial and often undergo multiple tectonic movements, with significant differences in paleogeomorphic characteristics and paleostress distribution across each phase, further influencing fracture evolution and distribution. For large buried hill oil and gas fields, the prediction of dominant reservoirs and the study of fracture development patterns are key to efficient oil and gas field development. Controlled by paleogeomorphology, the intensity of weathering and tectonic activity in buried hills varies, thus affecting reservoir development. Therefore, based on tectonic evolution analysis, conducting detailed paleogeomorphic reconstruction using a combination of forward and inverse modeling techniques is the core work for predicting effective reservoirs in large and complex buried hills.

[0003] In recent years, the academic community both domestically and internationally has conducted extensive research on the restoration of paleogeography, and new methods and technologies are constantly emerging. Currently, research methods for paleogeography restoration can be broadly categorized into structural restoration and stratigraphic thickness restoration. Structural restoration typically employs methods such as the pagoda diagram, thickness map, balanced profile, echo analysis, sequence stratigraphy, and geophysical methods. Stratigraphic thickness restoration generally utilizes methods such as sandstone porosity, mudstone sonic transit time, paleothermal gradient, vitrinite reflectance, and sedimentary rate.

[0004] Traditional paleogeographic restoration techniques, such as the thickness compensation imprint method and the filling and leveling method, were widely used in early oil and gas exploration. However, due to low accuracy and large errors, they are no longer sufficient to meet the needs of refined paleogeographic restoration in the current development stage. In early paleogeographic restoration practices, researchers used various methods and techniques to reconstruct paleotopography, but unavoidable problems always existed. For example, geophysical methods are limited by objective conditions such as surface conditions and technical means, and are greatly affected by human factors; the imprint method is difficult to determine the reference surface, and stratigraphic decompaction correction is difficult; the residual thickness method cannot consider the influence of pre-depositional tectonic topography and erosion differences on sedimentary thickness, resulting in large mapping errors; the stratigraphic leveling method is difficult to select the filling and leveling reference surface, and decompaction correction is difficult to achieve. Currently, most of these methods are in the qualitative stage, and quantitative restoration methods and techniques are only capable of partial semi-quantitative research, leaving room for further exploration and development. Currently, no technical method has been found that can meet the needs of refined paleogeographic restoration of complex buried hills. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of previous studies, such as the difficulty of decompaction correction and the inability to consider the influence of pre-depositional tectonic topography and erosion on sediment thickness. It also addresses the current industry's problems of low accuracy and large errors in paleogeographic restoration methods, which cannot perform quantitative calculations. The purpose is to provide a method for restoring exposed buried hill paleogeographic features by combining forward and inverse modeling techniques.

[0006] This invention is achieved through the following technical solution:

[0007] A method for restoring paleogeographic features of exposed buried hills by combining forward and inverse modeling techniques includes the following steps:

[0008] (i) To conduct a comprehensive and detailed interpretation of geophysical data;

[0009] (ii) Conduct paleogeographic inversion simulations of sedimentary periods with existing residual strata;

[0010] (iii) Conduct inversion simulation result correction;

[0011] (iv) Conduct forward modeling of paleogeography during key tectonic periods;

[0012] (v) Conduct uplift volume comparison and correction;

[0013] (vi) Conduct paleogeographic inversion simulation of sedimentary periods where no residual strata remain today;

[0014] (vii) Conduct comparative correction of the paleogeographic restoration results of forward and inverse simulations.

[0015] In the above technical solution, the comprehensive interpretation of geophysical data is carried out using seismic data interpretation software. The interpretation includes stratigraphic interpretation and fault interpretation. Stratigraphic interpretation includes the tracking, closure, and densification of key tectonic phase interfaces. The faults being interpreted have the characteristics of cutting through multiple strata and having large fault displacements.

[0016] In the above technical solution, the interpretation derives two-dimensional and three-dimensional data; the two-dimensional data is exported in the form of seismic profile images and planar positions, and the three-dimensional data is exported in the form of X, Y, and Z coordinate points.

[0017] In the above technical solution, the inversion simulation in step (ii) is based on the comprehensive interpretation results of the geophysical data obtained in step (i). Starting from the existing data, the geomorphic features of different sedimentary periods are revealed by layer-by-layer stripping, and finally, three-dimensional paleogeomorphic morphology and two-dimensional geomorphic morphology profiles are obtained.

[0018] In the above technical solution, the specific steps of the inversion simulation in step (ii) include: loading geophysical data, establishing two-dimensional and three-dimensional models, tectonic inversion, and paleomorphological reconstruction.

[0019] In the above technical solution, the specific operation of correcting the inversion simulation results in step (iii) is as follows: the three-dimensional paleogeomorphic map obtained after interpolating the two-dimensional geomorphic profile obtained in step (ii) is compared with the three-dimensional geomorphic morphology obtained in step (ii). If the geomorphic morphology of the same depositional period is consistent, it indicates that the obtained paleogeomorphology of the depositional period with residual strata is relatively accurate; if the two are significantly different, it is necessary to correct the interpretation of faults and stratigraphic positions or increase the density of two-dimensional profile interpretation.

[0020] In the above technical solution, step (iv) forward modeling process includes multi-stage evolutionary structure analysis, multi-stage forward iterative numerical modeling, forward iterative modeling of the optimal parameter combination and the optimal model, data processing and paleogeographic reconstruction.

[0021] In the above technical solution, the specific operation of step (v) uplift amount comparison and correction is as follows: the uplift amount obtained by the forward modeling method in step (iv) after repeated iterative calculations is compared and corrected with the uplift amount obtained by the stratigraphic erosion amount calculation method from the tectonic geochronological test results; if the two results are consistent, it indicates that the obtained uplift amount data is accurate; if the two results differ significantly, the forward modeling parameters in step (iv) need to be modified and iterated again, or the experiment needs to be checked for improper operation that caused the error.

[0022] In the above technical solution, the corrected uplift amount obtained in step (v) is combined with the two-dimensional paleogeographic profile obtained in step (ii) in the inversion simulation to restore the paleogeography of the sedimentary period of the strata that are now completely eroded from the perspective of inversion.

[0023] In the above technical solution, the specific method for step (vii) correction is as follows: compare the paleomorphological restoration results of the inversion simulation in steps (ii) and (vii) with the paleomorphological restoration results of the forward simulation in step (iv). If the paleomorphological morphology restored in the same period by the forward simulation and the inversion simulation is consistent, it indicates that the restored paleomorphological morphology is accurate; if the two results are inconsistent, the parameters of the forward simulation or the inversion simulation for geomorphological restoration need to be modified.

[0024] The beneficial effects of this invention are:

[0025] This invention provides a method for restoring paleogeographic features of exposed buried hills by combining forward and inverse modeling techniques. Based on tectonic evolution research and constrained by tectonic chronology, it employs both forward and inverse modeling to restore paleogeographic features of exposed buried hills, combining quantitative and qualitative analysis. This method not only provides a powerful tool for fine-grained reservoir prediction in the Bohai Sea region but also offers a reference for paleogeographic feature restoration in other regions. The method is highly operable and widely applicable, capable of restoring paleogeographic features of buried hills from multiple perspectives, with accurate results. Attached Figure Description

[0026] Figure 1 This is a flowchart of a method for restoring exposed buried hill paleogeography that combines forward and inverse modeling techniques according to the present invention;

[0027] Figure 2 This is a detailed seismic profile of the target area and its planar location map in Embodiment 1 of the present invention (the planar location map is shown in the lower right corner);

[0028] Figure 3 The above is a three-dimensional paleogeographic map of the study area with residual strata obtained by inversion simulation in Embodiment 1 of the present invention (a is the geomorphology of the Guantao Formation during the deposition period; b is the geomorphology of the Dongying Formation during the deposition period; c is the geomorphology of the Paleogene during the deposition period; d is the geomorphology of the Mesozoic during the deposition period; e is the geomorphology of the Paleozoic during the deposition period).

[0029] Figure 4 This is a two-dimensional equilibrium profile of the study area with residual strata obtained by inversion simulation in Embodiment 1 of the present invention (a is the present; b is before the deposition of Minghuazhen Formation; c is before the deposition of Guantao Formation; d is before the deposition of Dongying Formation; e is before the deposition of Shahejie Formation + Kongdian Formation).

[0030] Figure 5 This is a planar projection coordinate transformation diagram of the data node on the cross section in Embodiment 1 of the present invention (a is the planar coordinate transformation diagram of the NW-SE section; b is a schematic diagram of the main cross section direction; c is the planar coordinate transformation diagram of the NE-SW section).

[0031] Figure 6 These are paleogeographic maps of the period with residual strata deposition obtained by two-dimensional and three-dimensional inversion simulation in Embodiment 1 of the present invention (a is the paleogeographic map obtained by interpolation of the paleogeographic morphology profile obtained by 2D module inversion simulation; b is the paleogeographic map obtained by 3D module inversion simulation).

[0032] Figure 7 This is a geometric modeling diagram based on geophysical interpretation profiles in Embodiment 1 of the present invention (a is a structural interpretation profile diagram; b is the corresponding numerical model diagram (black lines represent fracture structures); c is the finite element partitioning diagram of the numerical model).

[0033] Figure 8 The paleogeographic maps obtained based on forward numerical simulation in Embodiment 1 of the present invention are as follows: (a is a 3D map of the Indosinian period; b is a 2D map of the Indosinian period; c is a 3D map of the Yanshanian period; d is a 2D map of the Yanshanian period; e is a 3D map of the Himalayan period; f is a 2D map of the Himalayan period).

[0034] Figure 9 This is a flowchart illustrating the calculation of the buried hill erosion rate and erosion amount in Embodiment 1 of the present invention;

[0035] Figure 10This is a flowchart of the geomorphological restoration method for a study area without sedimentary strata in Embodiment 1 of the present invention;

[0036] Figure 11 This is a process diagram of the geomorphological restoration method in the study area without sedimentary strata in Implementation Example 1 of this invention (a. Paleozoic strata thickness and pre-Indosinian fault location map; b. Pre-Indosinian fault morphology map; c. Forward modeling evolution profile morphology map; d. Paleomorphological undulation trend map; e. Schematic diagram of erosion rate and erosion amount calculated by age-elevation method; f. Paleozoic residual strata distribution plan map; g. Paleomorphological inversion simulation results of areas without residual sedimentary strata).

[0037] Figure 12 This is a comparison of paleogeographic maps obtained based on inversion simulation and forward simulation in Embodiment 1 of the present invention (a is the forward simulation paleogeographic map of the Indosinian period; b is the inversion simulation paleogeographic map of the Indosinian period; c is the forward simulation paleogeographic map of the Himalayan period; d is the forward simulation paleogeographic map of the Himalayan period).

[0038] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0039] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0040] A method for restoring paleogeographic features of exposed buried hills by combining forward and inverse modeling techniques includes the following steps:

[0041] (i) Conduct detailed comprehensive interpretation of geophysical data

[0042] Large-scale seismic data interpretation software was used to perform detailed interpretation of the stratigraphy and faults in the study area, and to export two-dimensional and three-dimensional data of the stratigraphy and two-dimensional data of the faults. The two-dimensional data was exported in the form of seismic profile images and planar locations, and the three-dimensional data was exported in the form of X, Y and Z coordinate points.

[0043] In the interpretation of stratigraphy and faults using seismic data interpretation software, stratigraphic interpretation in the study area includes tracing, closing, and densifying the interfaces of key tectonic periods; fault interpretation includes morphological delineation, and fault interpretation is only applied to faults in the study area that cut through at least two strata and have a large displacement; in the inversion simulation process, there is a step called "fault restoration", which is to eliminate the fault displacement and restore the state of the fault before the displacement was formed. For the accuracy of the results, any fault with displacement needs to be interpreted.

[0044] Identifying each layer is called tracking; comparing and correcting the interpretation results of each layer on the cross-section in each direction is called closure; and densification is called increasing the density of the interpretation of the two-dimensional cross-section lines.

[0045] The large-scale seismic data interpretation software can be any one of Landmark, GeoFrame, Geoeast, or Geological Magnifier. In addition to the above software, other commonly used seismic interpretation software can be applied to this step to perform detailed interpretation of the stratigraphy and faults in the study area.

[0046] (ii) Conduct paleogeographic inversion simulation of the sedimentary period of the present-day residual strata.

[0047] Based on the comprehensive interpretation results of geophysical data obtained in step (i) (two-dimensional and three-dimensional data of stratigraphy, two-dimensional data of faults), starting from existing data (present-day geological features), the geological conditions and geomorphological features of different sedimentary periods are revealed by layer-by-layer stripping, and finally, three-dimensional paleogeomorphological morphology and two-dimensional geomorphological profiles are obtained.

[0048] Back-stripping is based on the principle of sediment compaction. Starting from the known single-well stratification parameters, it removes the strata layer by layer in order of geological age from newest to oldest. The erosion recovery process takes into account geological factors such as sediment compaction, sedimentary discontinuity, and stratum erosion, until all strata are stripped away.

[0049] The specific steps of the inversion simulation include: loading geophysical data, establishing two-dimensional and three-dimensional models, tectonic inversion, and paleogeographic reconstruction; the above steps are the steps of the inversion simulation process using Move software.

[0050] When loading geophysical data, if simulation is performed using two-dimensional data, the profile needs to be loaded as an image, and the actual length, height, and starting coordinates of the profile in the image need to be set; if simulation is performed using three-dimensional data, the three-dimensional data only needs to be imported into the software as X, Y, and Z coordinate points.

[0051] The establishment of the two-dimensional model is specifically as follows: loading the cross-sectional view, then clearing the faults and layers in the cross-sectional view, and filling the blank areas between layers or faults with color. After completing the above operations, the model is established. Clearing includes drawing fault and layer lines, resampling line segments, and smoothing. The establishment of the three-dimensional model is specifically as follows: loading the coordinate data (x, y, z three-dimensional coordinates) of layers and faults, and then performing regional boundary editing, resampling, smoothing, and other processing on the data.

[0052] The structural inversion operation specifically involves sequentially performing de-compaction, fault restoration, and stratigraphic leveling operations. This process involves setting multiple parameters, which need to be analyzed and repeatedly modified based on the actual situation to obtain the optimal parameter combination.

[0053] The paleogeographic reconstruction operation is as follows: after the structural inversion parameters are set, the operations of decompaction, fault restoration and stratification are performed in sequence to obtain the three-dimensional paleogeographic and two-dimensional paleogeographic morphology of the study area with residual strata.

[0054] (iii) Conduct inversion simulation result correction

[0055] Compare the three-dimensional paleogeographic map obtained by interpolating the two-dimensional geomorphological profile obtained from the inversion simulation in step (ii) with the three-dimensional geomorphological map obtained from the inversion simulation in step (ii). If the geomorphological features are consistent for the same depositional period, it indicates that the obtained paleogeographic features for the depositional period with residual strata are relatively accurate. If the two are significantly different, it is necessary to correct the interpretation of faults and stratigraphic positions or increase the density of two-dimensional profile interpretation (density of stratigraphic interpretation).

[0056] The correction of faults includes: (1) whether the top and bottom interfaces of the strata on both sides of the fault are consistent at the same time; (2) whether the morphological interpretation of the fault is correct.

[0057] The correction of the stratigraphic position includes: (1) redefining the stratigraphic contact relationship in complex tectonic regions; (2) checking whether the interpretation of the stratigraphic interface features corresponding to the regional seismic reflection characteristics is correct; and (3) judging whether the tracking of the seismic reflection axis in the same direction is continuous and correct.

[0058] The above-mentioned methods for correcting faults and strata are conventional techniques well known to those skilled in the art, and they can choose how to correct them based on the actual situation.

[0059] The method for converting the two-dimensional landform profile into a three-dimensional landform in step (iii) is as follows:

[0060] Stratigraphic data of the two-dimensional paleogeomorphological profiles for each sedimentary period obtained from the inversion simulation were exported in the format L (actual distance from the profile start point / km) and Z (actual profile depth / m). The x-coordinate (X) and y-coordinate (Y) of the profile nodes were extracted, and the model coordinates were converted to the planar projection coordinates of the study area using trigonometric functions.

[0061] x1=x0+Lsin0

[0062] y1=y0+Lsinθ

[0063] (x1, y1) represent the planar projection coordinates of the study area; (x0, y0) represent the node coordinates on the profile; θ represents the orientation of the profile on the plan view; L represents the distance between the profile node and the profile start point in km. Finally, based on the x, y, and z values ​​on each profile, the Kriging method is used for interpolation to obtain a three-dimensional paleogeographic map obtained from the two-dimensional geomorphological profile interpolation.

[0064] (iv) Conduct forward modeling of paleogeography during key tectonic periods.

[0065] Based on multi-stage tectonic evolution profiles, numerical models for each tectonic deformation stage are constructed. Forward modeling is performed to reconstruct the paleogeography of the buried hill by tectonic stage. The forward modeling process includes: tectonic analysis of multi-stage evolution, modeling of multi-stage forward iterative numerical models, forward iterative modeling of the optimal parameter combination and the optimal model, data processing, and paleogeography reconstruction. Except for the "tectonic analysis of multi-stage evolution" step, all other steps are performed using software. The examples explain in detail how each parameter is determined and adjusted.

[0066] The multi-stage evolutionary tectonic analysis, starting from geophysical data, consists of the following steps: (1) analyzing the displacement of the main extensional or compressional faults to determine the extensional and compressional amounts of the profile; (2) identifying the main uplift and erosion areas in the study area; (3) determining the spatial distribution characteristics of the sedimentary strata in the study area; and (4) analyzing the erosion and subsidence amounts of the regional strata. The multi-stage evolutionary tectonic analysis provides a basis for the reconstruction of forward models (erosion and sedimentary models) for different stages, including analyzing the displacement of the main faults, the spatial distribution characteristics of the main uplift, erosion, or extensional sedimentary areas, defining the erosion amount in the compressional tectonic deformation stage, and the subsidence and sedimentary thickness in the extensional tectonic deformation stage.

[0067] For each tectonic deformation stage's interpretation profile, a corresponding forward iterative numerical model was established, including geometric modeling and mechanical model selection. The reconstruction of the geometric model for different stages considered the uplift, erosion, and sedimentary thickness of different phases. The model boundary conditions mainly considered the tectonic compression and extension amounts of different phases, i.e., the direction and magnitude of displacement at the model boundary. An elastoplastic model was selected for the mechanical model, considering the elastic and plastic deformation characteristics of the strata.

[0068] The parameters involved in the forward modeling process of the optimal parameter combination and the optimal model mainly include stratigraphic rock mechanics parameters, fault and basement strength parameters, model erosion and deposition parameters, and model boundary condition parameters. The optimal parameter combination was obtained through comprehensive analysis and calculation from multiple aspects, including referring to previous studies, repeated iterative calculations, geological characteristic analysis, and numerical quantitative simulation.

[0069] (v) Conduct uplift volume comparison and correction.

[0070] The uplift amount obtained through iterative calculations using the forward modeling method in step (iv) is compared and corrected with the uplift amount obtained from the tectonic geochronological test results using the stratigraphic erosion calculation method. If the two results are consistent, the obtained uplift data is accurate. If the two results differ significantly, it is necessary to modify the parameters involved in the forward modeling iteration process of the optimal parameter combination and the optimal model in step 4 and continue the iteration, or check whether any improper operation during the experiment caused errors.

[0071] The method for calculating the amount of erosion of the strata is the age-elevation method;

[0072] The tectonic geochronological test results are data obtained through apatite fission track and zircon (U-Th) / He tests;

[0073] Calculating uplift is a mature and existing technology; the main references are as follows:

[0074] [1]Wagner GA, Reimer G M.Fission track tectonics:The tectonic interpretation of fission track apatite ages[J].Earth&Planetary ScienceLetters,1972,14(2):263-268.DOI:10.1016 / 0012-821X(72)90018-0.

[0075] [2]Gleadow AJW, Fitzgerald P G.Uplift history and structure of theTransantarctic Mountains; new evidence from fission track dating of basementapatites in the Dry Valleys area,southern Victoria Land[J].Earth&PlanetaryScience Letters,1987,82(1-2):1-14.DOI:10.1016 / 0012-821X(87)90102-6.

[0076] [3]Benjamin MT, Johnson NM, Naeser C W.Recent rapid uplift in the Bolivian Andes: Evidence from fission-track dating[J].Geology,1987,15(7).DOI:10.1130 / 0091-7613(1987)152.0.CO; 2.

[0077] (vi) Conduct paleogeographic inversion simulation of sedimentary periods where no residual strata remain.

[0078] By combining the corrected uplift obtained in step (v) with the two-dimensional paleogeographic profile obtained from the inversion simulation in step (ii), the paleogeography of the sedimentary period of the now completely eroded strata can be restored from the perspective of inversion.

[0079] Step (vi) in the paleogeographic reconstruction of the sedimentary period where no residual strata remain today requires combining the morphology and location of residual faults, the planar distribution characteristics of residual strata, the corrected uplift, the forward-modeled geomorphic undulations, and the geomorphic undulations during the Paleogene sedimentary period for analysis. Specifically:

[0080] The Paleozoic strata residual thickness map obtained in step (ii) and the regional Paleozoic sedimentary thickness summarized from the literature review are used to constrain the Paleozoic strata sedimentary characteristics of different study areas; the two-dimensional equilibrium profile obtained in step (ii) is used to determine the development location, fault morphology and geomorphic undulation characteristics of the main faults; and the uplift characteristics of different study areas are determined by referring to the forward modeling in step (v) and the uplift data obtained by tectonic chronology testing.

[0081] Finally, this result is combined with the paleogeographic inversion simulation results of sedimentary periods with residual strata obtained in step (ii) to obtain paleogeographic maps of the study area from the perspective of inversion for each sedimentary period.

[0082] (vii) Conduct comparative correction of the paleogeographic restoration results of forward and inverse simulations.

[0083] Compare the paleogeomorphological reconstruction results obtained by combining steps (ii) and (vi) with the paleogeomorphological reconstruction results obtained by forward simulation in step (iv). If the paleogeomorphological features reconstructed by the forward and inversion simulations for the same period are consistent, it indicates that the reconstructed paleogeomorphological features are accurate. If the two results are inconsistent, the parameters of the forward or inversion simulation geogeomorphological reconstruction need to be modified.

[0084] If the paleogeographic reconstruction results from steps (ii) and (vi) are correct in parameter selection and accurate in seismic interpretation, the two results should be basically consistent. If one of them is consistent with the correct paleogeographic morphology, the situation needs to be considered. If the forward modeling result is incorrect, the main change is to modify the parameters; if the inversion result is incorrect, the main change is to modify the seismic interpretation.

[0085] When the paleogeomorphological reconstruction results from steps (ii) and (vi) are inconsistent with those from the forward simulation in step (iv), the fault and basement strength parameters are corrected first. This mainly involves adjusting the friction coefficients of the major faults through repeated iterations. The change in the friction coefficient is the most significant factor affecting the overall profile morphology.

[0086] Example 1

[0087] This implementation example provides a novel method for restoring paleogeographic features of exposed buried hills using a combination of forward and inverse modeling techniques of this invention (technical process reference). Figure 1 Taking the Bozhong 19-6 exposed buried hill tectonic belt as an example, the method for accurate paleogeographic reconstruction of buried hills is as follows:

[0088] (i) Detailed interpretation of geophysical data. The seismic data interpretation software Geoframe was used to perform detailed interpretation of the stratigraphy and faults in the study area. The interpreted stratigraphy included Tg8 (Archaeological-Paleozoic boundary), Tg2 (Paleozoic-Mesozoic boundary), T8 (Mesozoic-Paleogene boundary), T3 (Shahejie Formation-Dongying Formation boundary), T2 (Dongying Formation-Guantao Formation boundary), and T0 (Guantao Formation-Minghuazhen Formation boundary). The stratigraphic interpretation density was 50*50. Faults that cut through multiple strata and had large displacements were selected for morphological delineation. Finally, three-dimensional and two-dimensional data of the stratigraphy and faults were exported. The two-dimensional data were exported in the form of seismic profile images and their planar locations. Figure 2 The three-dimensional data is exported in the form of X, Y and Z coordinate points.

[0089] (ii) Conduct paleogeomorphological inversion simulations of existing strata from different sedimentary periods. Starting from existing data, a layer-by-layer stripping method is used to reveal the geological conditions and geomorphological features of different sedimentary periods. This step utilizes the 2D and 3D functions of Move software to strip back the existing strata with residual layers. The steps for restoring the paleogeomorphology of buried hills with existing residual strata using inversion simulation methods include: loading geophysical data, establishing two-dimensional and three-dimensional models, tectonic inversion, and paleogeomorphological reconstruction.

[0090] Regarding the loading of geophysical data, if using Move software's 2D function for simulation, the profile needs to be loaded as an image, and the actual length, height, and starting coordinates of the profile in the image need to be set. If using Move software's 3D function for simulation, simply import the 3D data into the software as X, Y, and Z coordinate points.

[0091] The steps for creating 2D and 3D models differ. In Move software, the 3D model creation only requires editing the region boundaries, resampling, and smoothing of the imported strata and fault coordinate data (x, y, z 3D coordinates). However, the 2D model creation is more complex. After loading the cross-section, the faults and strata in the image need to be cleared (drawing fault and stratum lines, resampling line segments, and smoothing). At the same time, the blank areas between strata or faults need to be filled with color. After completing the above operations, the model creation is complete.

[0092] The steps and parameter settings for the inversion simulation are the same regardless of whether the 3D or 2D functions of Move software are used. Each step involves setting multiple parameters. First, during the de-compaction process, the initial porosity is set to 0.56 and the depth coefficient is set to 0.39 km. 1 The grain density is 2680 kg / m³. 3 First, the compaction curve should be set to the "Sclater-Christie" option. Second, the fault restoration process is relatively simple; select the Simple Shear mode in the restoration mode. Finally, layer flattening is a crucial step in the structural inversion simulation process. For the datum selection, use "Unfold to Datum" and set the datum to 0, so the elevation of the flattened layer is 0. After setting the above parameters, perform the de-compaction, fault restoration, and layer flattening operations sequentially to obtain the three-dimensional paleogeography of the study area during the depositional period when residual strata still exist. Figure 3 ) and two-dimensional paleogeographic features ( Figure 4 ).

[0093] (iii) Correct the inversion simulation results. Export the stratigraphic data of the two-dimensional paleogeomorphological profiles of each sedimentary period obtained using the 2D function of Move software. The export format is L (actual distance from the profile start point / km) and Z (actual profile depth / m). Extract the x-coordinate and y-coordinate of the profile nodes, and convert the model coordinates into the plane projection coordinates of the study area using trigonometric functions.

[0094] x1=x0+Lsinθ

[0095] y1=y0+Lsinθ

[0096] (x1, y1) are the planar projection coordinates of the study area; (x0, y0) are the coordinates of the nodes on the profile; θ is the orientation of the profile on the plan view; L is the distance between the profile node and the profile start point (km). Figure 5 Finally, based on the x, y, and z values ​​on each profile, the Kriging method is used for interpolation to obtain a three-dimensional paleogeographic map derived from the two-dimensional geomorphological profile interpolation. This map is then compared and corrected with the geomorphological map obtained from the 3D inversion function of Move software. If the geomorphological features of the same depositional period are consistent, it indicates that the obtained paleogeographic map of the depositional period with residual strata is relatively accurate. Figure 6 ).

[0097] (iv) Conducting forward modeling simulations of paleogeomorphology during key tectonic periods. The Abaqus software was used to conduct forward modeling simulations of buried hill paleogeomorphology. This method involves constructing numerical models for each tectonic deformation stage based on multi-stage tectonic evolution profiles and performing forward modeling simulations in stages. Each numerical model uses different parameter combinations and undergoes iterative simulations. The simulation results are compared and verified with actual tectonic analysis results to obtain the optimal parameter combination and the best model. This yields quantitative results of tectonic uplift and subsidence in the entire region, providing data for paleogeomorphological reconstruction. The workflow of multi-stage forward modeling simulation includes several steps: tectonic analysis of multiple evolution stages, multi-stage forward modeling numerical model building, forward modeling iteration of the optimal parameter combination and the best model, data processing, and paleogeomorphological reconstruction.

[0098] Multi-stage tectonic analysis is based on geophysical interpretation profiles to obtain the displacement, main uplift and erosion areas of the main faults, or the spatial distribution characteristics of extensional sedimentary areas. This defines the erosion elevation and amount in the compressional tectonic deformation stage, and the subsidence and sedimentary thickness in the extensional tectonic deformation stage, providing a basis for the reconstruction of forward models (erosion and sedimentary models) for different stages. For each tectonic deformation stage interpretation profile, a corresponding forward iterative numerical model is established. The numerical modeling includes geometric modeling (…). Figure 7 The selection of the mechanical model is as follows: The reconstruction of the geometric model for different stages considers the uplift, erosion, and sedimentary thickness of different periods. The model boundary conditions mainly consider the tectonic compression and extension amounts of different periods, i.e., the direction and amount of displacement of the model boundary. An elastoplastic model is selected for the mechanical model, considering the elastic and plastic deformation characteristics of the strata. A nonlinear contact model is used for fault structures and basement slip. Specifically, the Indosinian period uses a compression model, with strata thickness mainly considering Archean and Paleozoic strata; the Yanshanian period uses a compression model, with strata thickness mainly considering Archean and Mesozoic strata; and the Himalayan period uses an extension model, with strata mainly considering Archean, Mesozoic, and Cenozoic strata.

[0099] The parameters involved in the forward modeling process for the optimal parameter combination and the optimal model mainly include formation rock mechanics parameters, fault and basement strength parameters, model erosion and deposition parameters, and model boundary condition parameters. Among these, the rock mechanics parameters mainly include density (kg·m³). -3 The rock mechanical parameters for different stratigraphic levels are: elastic modulus (GPa), Poisson's ratio, and plastic yield strength (MPa). The stratigraphy of the study area is divided into nine units, from oldest to youngest: Archean, Cambrian-Ordovician, Carboniferous-Permian, Upper-Middle Jurassic, Late Jurassic-Early Cretaceous, Paleogene Kongdian-Shahejie Formation, Paleogene Dongying Formation, Neogene Guantao Formation, and Neogene Minghuazhen Formation. The rock mechanical parameters for different stratigraphic levels are set as follows:

[0100] Table 1. Rock mechanical parameters of different strata in the BZ19-6 structural zone.

[0101]

[0102]

[0103] The determination of fault and basement strength parameters requires iterative calculations using different parameter combinations for each initial numerical model. The results of each iteration are then compared and verified with the analytical results of the cross-sectional structure. Based on the analysis of the fault system of the Bozhong 19-6 structural belt and combined with previous research, the initial friction coefficient parameter combination for faults in the forward model is mainly selected between 0.1 and 0.3, with the iterative parameters for individual faults ranging from 0.05 to 0.5. The basement strength friction coefficient is selected as 0.1.

[0104] The reconstruction of erosion and sedimentary parameters in the model is based on the residual stratum thickness and the displacement of the main fault to constrain the erosion amount in the compressional tectonic deformation stage and the sedimentary thickness in the extensional tectonic deformation stage of the forward model. The next stage of the forward model is reconstructed based on the deformation results of the earlier stage. The Indosinian period represents a compressional tectonic deformation stage, requiring stratigraphic erosion processing of the forward model calculation results to reconstruct the next stage of the forward model iteration. The stratigraphic erosion thickness is mainly estimated based on the residual stratum thickness and the uplift and erosion amounts obtained from tectonic analysis. The Yanshanian tectonic deformation forward model is based on the Indosinian calculation results with stratigraphic erosion reconstruction. The Himalayan tectonic forward model is based on the Yanshanian calculation results with stratigraphic sedimentary compensation and reconstruction. The stratigraphic erosion thickness in the Indosinian period is mainly 500–1700 m, in the Yanshanian period it is mainly 199–860 m, and in the Himalayan period it is 370–1160 m.

[0105] The model boundary conditions include the displacement direction and magnitude of the model boundaries. The boundary displacement direction of the forward modeling for each tectonic deformation stage considers both tectonic compression and extensional backgrounds, as well as the dynamic source. The model boundary displacement magnitude considers the shortening rate during compressional tectonic deformation and the elongation rate during extensional tectonic deformation. Based on the equilibrium profile restoration results, the shortening rates of the Indosinian and Yanshanian compressional models are set to 8%–10% and 2%–10%, respectively, while the elongation rate for the Himalayan stage is set to 4%–8%.

[0106] Finally, based on the results of the forward modeling simulation, node data from the optimal profile of each forward modeling iteration are extracted, and three-dimensional data interpolation is performed to restore and reconstruct the paleogeography at different stages. Figure 8 ).

[0107] (v) Conduct uplift volume comparison and correction. The uplift volumes for the Yanshanian and Indosinian periods obtained through iterative calculations using the forward modeling method in step four are compared and corrected with the uplift history and volume calculated using the age-elevation method based on tectonic geochronological testing results. The age-elevation method is the stratigraphic erosion volume calculation method used in this study. Figure 9 This method uses vertical topographic profiles to approximate the bedrock exposure differences within the Earth's crust, simplifying rock mass exposure into a one-dimensional movement process. It quantitatively inverts the bedrock exposure (elevation difference) and time (age difference) information by using samples at different elevations on the vertical profile and their thermal ages. The calculation formula is as follows:

[0108] Erosion rate = ΔE / Δt

[0109] Erosion amount = Erosion rate * Erosion time

[0110] E represents the depth from the ground surface to the elevation baseline; △E represents the elevation difference; △t represents the age difference measured; · represents the age measured.

[0111] This study used zircon fission track data from two closely located wells, BZ19-6-2Sa and BZ19-6-4, at different depths to investigate the erosion rate and amount in the Bozhong 19-6 buried hill area. Data processing yielded an average depth of 4090 m for the BZ19-6-2Sa sample and a zircon fission track age of 84.1 ± 3.2 Ma; and an average depth of 4625 m for the BZ19-6-4 sample and a zircon fission track age of 165 ± 16 Ma. The calculated erosion rate (erosion rate = elevation difference / time difference after sealing temperature) was approximately 8.8 m / Ma, and the erosion rate of the Bozhong 19-6 buried hill was approximately 8.8 m / Ma. The erosion amount during the middle to late Yanshanian period (165–84 Ma) was approximately 800 m. Based on this, the erosion amount of the Indosinian / Yanshanian "bald" buried hill was inferred to be 1800 ± 300 m.

[0112] The geological model provided by the forward modeling method, after repeated iterative calculations, yields an average surface uplift of 300–500 m during the Indosinian period, with a maximum uplift of 500–1700 m. The maximum uplift reaches 1628.4 m. During the Yanshanian tectonic compression deformation period, the average surface uplift is generally 50–510 m, with a maximum uplift of 200–860 m. The maximum uplift reaches 858.1 m. The uplift values ​​obtained by the two methods show little difference and are in good agreement.

[0113] (vi) Conduct paleogeographic inversion simulation of sedimentary periods in strata without residual sedimentation. Combine the corrected uplift obtained in step 5 with the equilibrium profile obtained from the 2D functional inversion simulation of Move software in step 2 to reconstruct the paleogeography of the sedimentary periods in strata that are now completely eroded from the perspective of inversion. Figure 10 This simulation process requires a thorough integration of the results from the previous steps, including evolution profiles of the surrounding sedimentary zone and the target unsedimented zone, the morphology of residual faults, the stratigraphic undulations of key tectonic periods, and uplift amounts. First, refer to the Paleozoic stratigraphic residual thickness map obtained in the second step (…). Figure 11 f) and the regional pre-Indosinian sedimentary thickness summarized from consulted materials ( Figure 11 a) This is used to constrain the Paleozoic stratigraphic sedimentary characteristics of different study areas. Secondly, the two-dimensional equilibrium profile obtained in the second step is used to determine the development location of the main faults. Figure 11 a) Fault morphology Figure 11 b) and the characteristics of landform undulation ( Figure 11 d). Finally, the uplift characteristics of different study areas were determined by referring to the forward modeling in step 5 and the uplift data obtained by tectonic geochronological testing. Figure 11 e). Of particular note is the need to reconstruct the topographic relief characteristics of the buried mountain summit interface using fault data from the Paleogene sedimentary period, eliminate stratigraphic deformation caused by extensional stress fields, and compare the topographic relief changes obtained from forward modeling. Figure 11 c) Compare and correct several steps. After this operation, a two-dimensional paleogeographic profile of the sedimentary period of the strata without residual sediments can be obtained. Following the interpolation calculation methods in steps two and four above, a three-dimensional paleogeographic profile of the sedimentary period of the present-day strata without residual sediments can be obtained. Figure 11 g).

[0114] (vii) Conduct comparative corrections between forward and inverse simulations of paleogeomorphological reconstruction results. Compare the Indosinian paleogeomorphological reconstruction results from the second and sixth steps of the inverse simulation with the Indosinian paleogeomorphological reconstruction results from the fourth step of the forward simulation. Figure 12 If the paleomorphological features restored by forward and inverse simulations are consistent for the same period, it indicates that the restored paleomorphological features are accurate and can serve as an important basis for oil and gas exploration and reservoir prediction.

[0115] Based on tectonic evolution research and constrained by tectonic chronology, this invention combines forward and inverse simulations, fully considering stratigraphic compaction, stratigraphic erosion thickness, residual stratigraphic thickness, and strain characteristics of key tectonic phases. Through a combination of quantitative calculation and qualitative analysis, and after multiple comparisons and corrections of calculation and simulation results, accurate paleogeomorphology of each key tectonic phase in exposed buried hills is obtained. The buried hill geomorphology restoration technology system based on tectonic evolution-tectonic chronology constraints-forward and inverse modeling feedback constructed in this invention provides a basis for carrying out effective reservoir prediction work in buried hill areas.

[0116] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for restoring paleogeographic features of exposed buried hills by combining forward and inverse modeling techniques, characterized in that: Includes the following steps: (i) To conduct a comprehensive and detailed interpretation of geophysical data; The interpretation includes stratigraphic interpretation and fault interpretation; stratigraphic interpretation includes tracing, closing, and refining the boundaries of key tectonic phases; fault interpretation includes morphological delineation; the faults used for interpretation are characterized by cutting through multiple strata and having large displacements. (ii) Conduct paleogeographic inversion simulations of sedimentary periods with existing residual strata; The inversion simulation is based on the comprehensive interpretation results of the geophysical data obtained in step (i). Starting from the existing data, it adopts the method of layer-by-layer stripping to reveal the geomorphic features of different sedimentary periods, and finally obtains three-dimensional paleogeomorphic morphology and two-dimensional geomorphic morphology profiles. (iii) Conduct inversion simulation result correction; The specific operation for correcting the inversion simulation results is as follows: the three-dimensional paleogeographic map obtained after interpolating the two-dimensional geomorphic profile obtained by the inversion simulation in step (ii) is compared with the three-dimensional geomorphic morphology obtained by the inversion simulation in step (ii). If the geomorphic morphology of the same depositional period is consistent, it indicates that the obtained paleogeographic morphology of the depositional period with residual strata is relatively accurate. If the two differ significantly, the interpretation of faults and horizons needs to be revised or the density of two-dimensional profile interpretation needs to be increased. (iv) Conduct forward modeling of paleogeography during key tectonic periods; Based on multi-stage tectonic evolution profiles, numerical models for each tectonic deformation stage are constructed, and forward modeling is performed to reconstruct the paleogeography of the buried hill by tectonic stage. The forward modeling process includes multi-stage evolutionary structure analysis, multi-stage forward iterative numerical modeling, forward iterative modeling of the optimal parameter combination and the optimal model, data processing, and paleogeographic reconstruction. (v) Conduct uplift volume comparison and correction; The specific operation of the uplift amount comparison and correction is as follows: the uplift amount obtained by the forward modeling method in step (iv) after repeated iterations is compared and corrected with the uplift amount obtained by the stratigraphic erosion amount calculation method from the tectonic geochronological test results; if the two results are consistent, it indicates that the obtained uplift amount data is accurate; if the two results differ significantly, the forward modeling parameters in step (iv) need to be modified and iterations continued or the experiment needs to be checked for any improper operation that caused the error. (vi) Conduct paleogeographic inversion simulations of sedimentary periods where no residual strata remain today; In the inversion simulation, the corrected uplift amount obtained in step (v) is combined with the two-dimensional paleogeographic profile obtained in step (ii) to restore the paleogeography of the sedimentary period of the strata that are now completely eroded from the perspective of inversion. (vii) Conduct comparative correction of the paleogeographic restoration results of forward and inverse simulations; The specific method for correction is as follows: compare the paleomorphological restoration results of the inversion simulation in steps (ii) and (vi) with the paleomorphological restoration results of the forward simulation in step (iv). If the paleomorphological morphology restored in the same period by the forward simulation and the inversion simulation is consistent, it indicates that the restored paleomorphological morphology is accurate; if the two results are inconsistent, the parameters of the forward simulation or the inversion simulation for geomorphological restoration need to be modified.

2. The method for restoring exposed buried hill paleogeography by combining forward and inversion techniques according to claim 1, characterized in that: The comprehensive interpretation of the geophysical data was performed using seismic data interpretation software.

3. The method for restoring exposed buried hill paleogeography by combining forward and inversion techniques according to claim 2, characterized in that: The interpretation derives two-dimensional and three-dimensional data; the two-dimensional data is exported as seismic profile images and planar locations, while the three-dimensional data is exported as X, Y, and Z coordinate points.

4. The method for restoring exposed buried hill paleogeography by combining forward and inversion techniques according to claim 1, characterized in that: The specific steps of the inversion simulation in step (ii) include: loading geophysical data, establishing two-dimensional and three-dimensional models, tectonic inversion, and paleogeographic reconstruction.

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