Paleowater depth reconstruction and tectonic settlement numerical calculation method based on geophysical drilling data

Abstract

The invention provides a paleo-water depth reconstruction and tectonic settlement numerical calculation method based on geophysical drilling data, and belongs to the technical field of ocean-land transition zone and ocean basin settlement analysis. The paleo-water depth reconstruction and tectonic settlement numerical calculation method comprises the steps that the depth, age and lithology data of a drilling site are extracted from the geophysical drilling data and preprocessed; calculating the decompaction thickness and average density of the sediment by using a dynamic exponential decay model of the porosity and depth relationship through a decompaction calculation method; meanwhile, a sedimentary layer age-depth conversion model is constructed for paleo-water depth reconstruction; by introducing tectonic settlement analysis and dynamic terrain correction and combining various factors such as mantle flow, tectonic activity and the like, the surface elevation change is corrected. According to the method, the precision of paleo-water depth reconstruction is improved, the paleo-water depth reconstruction is not limited to a static structure model any more, the dynamic change of the internal process of the earth can be considered, and the ocean-land transition zone and ocean basin depth change in the historical period can be reflected more truly.

Description

Technical Field

[0001] The present invention relates to the technical field of ocean-continent transition zone and ocean basin subsidence analysis, and in particular to a method for paleo-water depth reconstruction and tectonic subsidence numerical calculation based on geophysical drilling data. Background Art

[0002] The evolution of ocean basin depths is closely linked to deep geodynamic processes such as lithospheric thermal cooling and mantle convection, and has profound implications for geological phenomena such as sediment compaction and continental rifting. Paleobathymological reconstructions of ocean basins not only provide key boundary conditions for supercontinental cycle evolution and paleoocean circulation simulations, but also play a crucial role in oil and gas exploration, providing a scientific basis for the search for potential oil and gas reservoirs and laying the foundation for understanding the underlying mechanisms of the long-term evolution of the Earth system.

[0003] Currently, traditional paleowater depth reconstruction techniques mainly rely on sediment lithology analysis, comparison of benthic fossils, and empirical age-depth models, such as the plate cooling model proposed by Parsons and Sclater. Although these methods can outline the general trend of basement depth changes with age, they have many limitations when faced with complex geological scenarios. In terms of dealing with sediment compaction effects, traditional models mostly use static porosity assumptions, ignoring the dynamic changes of porosity with depth and time, and fail to use exponential decay functions to correct the sediment compaction effects layer by layer, resulting in systematic deviations in the recovery of the original thickness and density of the strata, which seriously reduces the accuracy of paleowater depth reconstruction.

[0004] What is more prominent is that the existing technology has major defects in data processing. It lacks the ability to systematically integrate multi-source data such as borehole lithology, porosity attenuation curves, and dynamic terrain grids. It mainly relies on manual regional modeling, which is inefficient, unable to process large-scale data, and easily introduces subjective errors. It is difficult to adapt to the batch analysis needs of complex geological scenarios at the global scale. Summary of the Invention

[0005] In response to the problems existing in the existing technology, the present invention provides a method for paleowater depth reconstruction and tectonic subsidence numerical calculation based on geophysical drilling data. The method accurately calculates the degree of compaction of sediments over time based on geophysical drilling data, converts the stratigraphic age and paleowater depth, and corrects the paleowater depth by combining a specific tectonic subsidence model and a dynamic terrain model.

[0006] The present invention provides a method for paleo-water depth reconstruction and tectonic subsidence numerical calculation based on geophysical drilling data, comprising:

[0007] Data preparation: Extract and preprocess the depth, age, and lithology data of the drilling sites from the International Ocean Drilling Program public dataset and drilling data from China's marginal oil and gas basins. The lithology data includes sediment density, surface porosity, and porosity decay.

[0008] Decompaction calculation: Utilizing the law of sediment porosity decay with depth and pre-processed drilling site depth, age, and lithology data, the original porosity of each sedimentary layer before overburden pressure is calculated. The compaction effect of the overlying sediments is then removed layer by layer, restoring the true thickness and density of each sedimentary layer before compaction. Simultaneously, the sediment deposition rate is updated, providing accurate basic data for paleowater depth reconstruction. The law of sediment porosity decay with depth is described by a dynamic exponential decay model of the porosity-depth relationship.

[0009] Age-depth conversion and paleowater depth calculation: Based on the age-depth conversion model and the ages of the ocean-continental transition zone and oceanic crust in different geological periods, the basement depths of the ocean-continental transition zone and ocean basins in different geological periods are quantitatively estimated. At the same time, the basement depths of the ocean-continental transition zone and ocean basins in different geological periods are corrected by combining the sediment thickness restored by decompaction calculation, and the paleowater depth data of the ocean-continental transition zone and ocean basins in different geological periods are calculated;

[0010] Sea level trend correction: The paleo-water depth data of the ocean-continent transition zone and ocean basins are corrected by introducing the sea level trend;

[0011] Tectonic subsidence analysis and dynamic topography correction: Based on the geological background of different drilling sites, oceanic or terrestrial subsidence models are selected to invert the crustal subsidence process caused by tectonic action to obtain tectonic subsidence data for the ocean-continent transition zone and ocean basins. Dynamic topography models are used to quantify the impact of mantle convection on the basement depth of the ocean-continent transition zone and ocean basins, and to adjust paleo-water depth data.

[0012] Model validation and optimization: Compare the calculated paleo-water depth data with actual drilling data and geological observations. Use the comparison results as feedback to continuously adjust the sedimentation rate, porosity attenuation function, and tectonic subsidence parameters, and iteratively optimize each model to ensure the accuracy of the paleo-water depth data and truly reflect the actual process of geological evolution.

[0013] Output and application: The obtained paleowater depth data and tectonic subsidence data are organized into detailed data files and stored for subsequent geological, climate and ecological research.

[0014] Optionally, the method utilizes the law of sediment porosity decay with depth and the pre-processed depth, age, and lithology data of the drilling site to calculate the original porosity of each sedimentary layer before being subjected to overlying pressure, and then gradually removes the compaction effect of the overlying sediments to restore the true thickness and density of each sedimentary layer before compaction, and simultaneously updates the sediment deposition rate, including:

[0015] The porosity of each sedimentary layer when not subjected to overburden pressure is calculated using the dynamic exponential decay model of the porosity-depth relationship. The dynamic exponential decay model is expressed as the relationship between porosity and depth:

[0016]

[0017] in, is depth The porosity of the sediment layer at is the surface porosity of the sediment layer, is the compaction coefficient;

[0018] The density of the sedimentary layer is calculated based on the porosity of each sedimentary layer when it is not subjected to overburden pressure. The calculation formula is:

[0019]

[0020] in, is depth The density of the sediment layer at is the particle density of the sediment layer, is the density of the fluid in the pores of the sediment layer;

[0021] When performing decompaction calculations, the age of each sediment layer is used to infer its original state before overburden pressure. Specifically, the age of each sediment layer is found from the age of the drilling site. The corresponding sediment layer is found according to the specified age, and the thickness of each sediment layer before overburden pressure is restored layer by layer. At the same time, the order of restoration is consistent with the actual order of the sediment layers. The restored thickness of the sediment layer is calculated as follows:

[0022]

[0023] in, and are the top and bottom depths of the sedimentary layer, is depth The porosity of the sediment layer at

[0024] When decompaction calculations are performed to recover the thickness of the sediments to generate a new extension layer, the bottom age of the newly generated stratum is determined based on actual drilling data and geological background;

[0025] The sediment deposition rate is calculated based on the recovered thickness of the sediment layer and the deposition time.

[0026] Optionally, the basement depths of the ocean-continental transition zone and ocean basins in different geological periods are quantitatively estimated based on the age-depth conversion model and the ages of the ocean-continental transition zone and oceanic crust in different geological periods, and the basement depths of the ocean-continental transition zone and ocean basins in different geological periods are corrected in combination with the sediment thickness restored by decompaction calculation, to estimate paleowater depth data of the ocean-continental transition zone and ocean basins in different geological periods, including:

[0027] According to the sediment age-depth conversion model formula, the age of the drilling site is converted into the basement depth of the corresponding ocean-continental transition zone and ocean basin. The specific formula is as follows:

[0028] When the oceanic crust is younger than 20 Ma: ;

[0029] When the oceanic crust is older than 20 Ma: ;

[0030] in, It is the basement depth of the ocean-continent transition zone and ocean basins. is the age of the oceanic crust;

[0031] Based on the impact of sediment removal on water depth, the basement depth after removing the sediment thickness was calculated, and the paleowater depth data of the ocean-continental transition zone and ocean basins in different geological periods were obtained.

[0032] Optionally, the method of selecting an ocean subsidence model or a land subsidence model according to the geological background of different drilling sites, and inverting the subsidence process of the crust caused by tectonic action to obtain tectonic subsidence data of the ocean-continent transition zone and the ocean basin includes:

[0033] If the drilling site is located on the ocean crust, the ocean subsidence model is selected to invert the subsidence process of the ocean crust caused by tectonic action, as follows:

[0034] The depth of the sediment surface is obtained using the bathymetric grid;

[0035] Isostatic pressure correction is calculated using the average sediment density of the formation at the drilling site. By considering the impact of sediment removal on the depth of the sediment surface, the current tectonic subsidence is calculated, thereby revealing the basement depth after sediment removal, eliminating the compaction effect and obtaining more accurate paleowater depth data.

[0036] If the drilling site is located on the crust of a passive land margin, the land subsidence model is used to invert the subsidence process of the land crust caused by tectonic action, as follows:

[0037] Simulate rift valley subsidence and thermal subsidence in sequence;

[0038] Determine the start and end times of rifting. When rifting begins, the sediment thickness is assumed to be zero and the sea level is the same as the initial depth of the rift. When rifting ends, the stretching of the crust stops and thermal subsidence begins.

[0039] The stretch factor is calculated to describe the degree of lithosphere thinning during rift propagation. The stretch factor changes exponentially between the beginning and end of the rift, thereby calculating the tectonic subsidence during the rift process.

[0040] Optionally, the use of a dynamic topography model to quantify the effect of mantle convection on the basement depth of the ocean-continent transition zone and ocean basins and adjust paleo-water depth data includes:

[0041] Selecting a dynamic terrain model that includes a time-dependent global grid, wherein the time-dependent global grid is a core component of the dynamic terrain model and describes the changes in surface elevation over time, especially the rise and fall of the surface due to mantle convection. These grids are matched to historical data from the drilling site and reflect surface changes in past geological periods.

[0042] The coordinates of the drill sites on the dynamic terrain model grid are converted from the modern plate reference system to the past mantle reference system to achieve the reconstruction of the drill site positions;

[0043] After matching the dynamic terrain model grid with the reconstructed drilling site locations, the dynamic terrain model predicts surface subsidence and adjusts paleowater depth data for different geological periods based on the predicted surface subsidence.

[0044] After adopting the above technical solution, the present invention has at least the following beneficial effects:

[0045] 1. This invention breaks through the limitations of traditional methods by combining multiple factors affecting sea level into a unified analytical framework, and comprehensively considers factors such as sediment decompaction process, dynamic topography, and tectonic subsidence, so that the data covers more comprehensive information and the reconstruction of paleowater depth is more accurate and convenient.

[0046] 2. The present invention uses an original decompaction calculation method and a dynamic exponential decay model of the porosity-depth relationship to accurately calculate key parameters such as sediment decompaction thickness and average density. Simultaneously, a sedimentary layer age-depth conversion model is constructed to provide highly accurate paleowater depth reconstruction. By introducing tectonic subsidence analysis and dynamic topography corrections, combined with multiple factors such as mantle flow and tectonic activity, more precise corrections can be made to surface elevation changes, thereby improving the accuracy of paleowater depth reconstruction. This makes paleowater depth reconstruction no longer limited to static tectonic models, but can take into account the dynamic changes in the Earth's internal processes, and can more realistically reflect the depth changes of the ocean-continent transition zone and ocean basins in historical periods.

[0047] 3. The present invention can accurately reconstruct paleowater depths and analyze tectonic subsidence. In the study of marine and terrestrial tectonic evolution, it can reveal processes such as crustal deformation, providing theoretical support for related geological evolution. In the field of sea level change simulation and climate research, it can reconstruct water depth changes, reveal the relationship between sea level rise and fall and climate change, and assist paleoclimate research. It can also provide historical environmental data for paleontological and ecological research, revealing changes in the ecological environment, assisting in the study of biological community evolution, and understanding the impact of climate change and geological events on species survival. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0049] Figure 1 A flow chart of a method for paleo-water depth reconstruction and tectonic subsidence numerical calculation based on geophysical drilling data provided in an embodiment of the present disclosure;

[0050] Figure 2 This is a geohistorical analysis map of the study area without correction for sea level trend, tectonic subsidence analysis, and dynamic topography.

[0051] Figure 3 This is a geohistorical analysis map of the study area after correction of sea level change trend, tectonic subsidence analysis and dynamic topography. DETAILED DESCRIPTION

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] In the field of traditional paleowater depth reconstruction research, decompaction research, age-depth conversion models, tectonic subsidence analysis and dynamic terrain correction have always been important research directions. With the gradual deepening of research, these fields have accumulated rich results. However, the long-term independent research model has also exposed many problems.

[0054] Early decompaction research occupied an important position, mainly focusing on the changes in sediment porosity and thickness. Researchers generally recognize that sediments will be compacted during the long geological history, the porosity will gradually decrease, and the thickness will also become thinner. Therefore, decompaction becomes a key link in restoring the original state of the sediments. However, most of the current methods are based on simple empirical formulas, which approximate the relationship between porosity and depth based on limited local data. Although this method can restore some characteristics of the sediments to a certain extent, due to the lack of comprehensive consideration of the regional geological background and in-depth understanding of the complex physical and chemical changes during the sediment compaction process, there are large errors in the decompaction results. Especially when facing sediments with different sedimentary environments and lithologies, the applicability of these empirical formulas is greatly reduced, and it is difficult to accurately restore the true history of the sediments.

[0055] In the study of age-depth conversion models, the early Parsons and Sclater model laid the foundation for the study of ocean crust depth, but for older crust, its heat flow and water depth data did not fit well. Although the subsequent GDH1 model has been improved and the calculation accuracy has been improved to a certain extent, these models often fail to fully consider the combined influence of other geological factors when applied, affecting the accuracy of the model.

[0056] In the field of tectonic subsidence analysis, research on ocean basins and passive terrestrial margins has long been separated, and the research focus is usually on the impact of a single tectonic factor on sedimentation. Sedimentation is an important mechanism controlling the volume of ocean basins. Existing studies have mostly used the method of analyzing present-day ocean basins separately when analyzing the differences in sediment thickness in different ocean basins. However, due to the dynamic transformation of plate margins, this method cannot be used to predict the sediment thickness of ancient ocean basins. If the sediment thickness of ancient ocean basins is to be accurately predicted, the sediments must be decompacted.

[0057] In terms of research on dynamic topography correction, current research focuses on its own changing laws and has little integration with other geological studies. Although researchers have recognized that dynamic topography has a significant impact on water depth, in the actual process of paleo-water depth reconstruction, it has not been effectively integrated with factors such as tectonic subsidence, resulting in the inability to accurately reflect the actual situation in the geological history period.

[0058] Furthermore, existing research in this field faces challenges with data acquisition and analysis. Existing research methods are limited, relying primarily on traditional geological sampling. This results in poor quality, small quantities, and uneven distribution of sample data, leading to inaccurate analytical results. The data also lack comprehensive information, making it difficult to comprehensively analyze information such as paleowater depths and paleostrata to explore the inherent connections between geological evolution. Furthermore, analytical methods are relatively simplistic, often focusing on a single variable and failing to fully consider complex geological conditions. This results in significant deviations from actual geological conditions.

[0059] To address the above problems, the present invention innovatively integrates decompaction calculation, ocean age-depth model, tectonic subsidence analysis and dynamic topography correction, and realizes the coordinated calculation of tectonic subsidence, sedimentary compaction and mantle dynamics for the first time. In the treatment of sediment compaction effect, the porosity dynamic exponential decay model is introduced, which can peel off the compaction influence layer by layer and accurately restore the original thickness and density of the sediment. At the same time, the construction of the sediment layer age-depth conversion model can provide very accurate paleowater depth reconstruction. The introduction of tectonic subsidence analysis and dynamic topography correction integrates dynamic topography data into the model in time series, and generates corresponding dynamic topography grids for different geological periods, effectively quantifying the long-term fluctuation effect of mantle convection on basement depth, successfully making up for the shortcomings of traditional methods, and integrating the public data set of the International Ocean Drilling Program and drilling data of China's marginal oil and gas basins. These high-resolution stratigraphic records and clear sedimentary environment indicator data greatly improve the calculation accuracy and practicality.

[0060] The following specific embodiments are used to describe the technical solution of the present invention in detail. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0061] like Figure 1 As shown, the embodiment of the present disclosure provides a method for paleo-water depth reconstruction and numerical calculation of tectonic subsidence based on geophysical drilling data, including:

[0062] 1. Data Preparation

[0063] 1.1 Data Source

[0064] The data in this paper are based on geophysical drilling data, including the public data set of the International Ocean Drilling Program and drilling data of oil and gas basins in China's marginal seas, specifically including the collection of the following data:

[0065] Drilling site depth data: records the actual burial depth of each drilling site, which is the basic data for subsequent calculations of sediment thickness and tectonic settlement. It provides starting depth information for decompaction calculations and is used to determine tectonic settlement corrections, thereby accurately reflecting the original state of the sediments.

[0066] Drilling site age data: records the age of the strata at each drilling site (usually in millions of years), providing a time scale for geological history. The age data is subsequently converted to basement depth using an age-depth conversion model, allowing paleowater depth to be estimated. This data also serves as a time point in sedimentation rate calculations and decompression steps.

[0067] Lithological data - density: reflects the physical density of sediment or rock. It is an important parameter for calculating pressure effects and sediment compaction. It is used to calculate the compacted thickness of the stratum under pressure, update the average density after decompaction, and estimate the depth after sediment removal in tectonic settlement analysis.

[0068] Lithological data - surface porosity: refers to the porosity of sediments immediately after deposition, reflecting the initial physical properties of the sediments. It can be used as a starting parameter for calculating porosity decay, used to restore the original thickness of sediments in decompaction calculations, and provides basic data for isostatic pressure correction.

[0069] Lithologic data—porosity decay: This describes the gradual decay of sediment porosity with increasing depth, typically expressed using a dynamic exponential decay model. By integrating the porosity decay function, the true thickness of the sediment before compaction is restored. This is a key parameter for eliminating compaction effects, correcting sedimentation rates, and reconstructing paleowater depths.

[0070] 1.2 Data Preprocessing

[0071] The data preprocessing process can be divided into the following steps:

[0072] Step 1: Data cleaning

[0073] Through statistical analysis, outliers and noise points in the data set are identified, and data records that do not meet the standards are eliminated to ensure that subsequent analysis is based on high-quality data;

[0074] Step 2: Missing Value Handling

[0075] Comprehensively check key parameters (such as drilling depth, formation age, density, porosity, etc.) and use interpolation methods to fill missing data. For missing values, select appropriate interpolation methods (such as mean interpolation and Lagrange interpolation) based on the data type to ensure data integrity;

[0076] 2. Decompaction calculation

[0077] Compaction thickness refers to the actual thickness change of sediment under the pressure of the overlying layer. Over time, the porosity of the sediment decreases, resulting in a thinning of the thickness. The decompaction thickness is to restore the sediment to its original thickness before the compaction of the overlying layer. During the decompaction calculation process, this method gradually removes the newer sediment layers, reduces the pressure on the underlying sediments, and restores their porosity and thickness, thereby returning to the initial state of deposition.

[0078] 2.1 Decompaction Calculation Principle

[0079] The purpose of stratum decompaction is to restore the physical state of the stratum at a certain point in the past. By analyzing the decompaction process, the average post-decompression density and thickness changes of the top of the stratum at the decompression depth can be calculated to reconstruct paleowater depth.

[0080] Porosity refers to the ratio of pore volume to total volume in a formation, and its value ranges from 0 to 1. Usually, the porosity of a formation is between 0.1 and 0.4. However, in loose sediments or certain reservoirs, the porosity may be higher, while in hard rocks, the porosity may be very low, close to 0. The density of the formation is closely related to the porosity. With increasing depth, the porosity generally decreases.

[0081] The porosity of each sedimentary layer when not subjected to overburden pressure is calculated using the dynamic exponential decay model of the porosity-depth relationship. The dynamic exponential decay model is expressed as the relationship between porosity and depth:

[0082]

[0083] in, is depth The porosity of the sediment layer at is the surface porosity of the sediment layer, is the compaction coefficient;

[0084] The density of the sedimentary layer is calculated based on the porosity of each sedimentary layer when it is not subjected to overburden pressure. The calculation formula is:

[0085]

[0086] in, is depth The density of the sediment layer at is the particle density of the sediment layer, is the density of the fluid in the pores of the sediment layer;

[0087] When performing decompaction calculations, the age of each sediment layer is used to infer its original state before the overburden pressure. Specifically, the age of each sediment layer is found from the age of the drilling site. The corresponding sediment layer is found according to the specified age and the recovery to the original state is calculated. Each sediment layer corresponding to the age will have a "recovered state". These states are arranged in the original order. By finding the age of each sediment layer, the thickness of each sediment layer before the overburden pressure is restored layer by layer, while ensuring that the recovery order is consistent with the actual order of the sediment layer. The recovery thickness calculation formula of the sediment layer is as follows:

[0088]

[0089] in, and are the top and bottom depths of the sedimentary layer, is depth The porosity of the sediment layer at

[0090] When the decompaction calculation restores the thickness of the sediment to generate a new extension layer, in order to determine the bottom age of these newly generated strata, the bottom age of the newly generated strata is determined based on the actual drilling data and geological background. For example, if the drilling site is located on the continental crust (especially in the rift zone), the bottom age of these new strata will be set to the age when the rift began;

[0091] 2.2 Decompacting the calculation to generate a new sequence

[0092] Each stratigraphic layer in the input drill site file is decompacted to generate a modified drill information output file, which contains an additional bottom extended base sediment layer generated after decompaction, and contains the parameters of the decompressed output bottom layer. The specific parameters are as follows:

[0093] Uncompacted density column: refers to the average density of each sediment layer within the uncompacted range. The density calculation takes into account the mixture of sediment and pore water. Because the porosity in the sediment affects its density, the density of each layer is calculated based on its porosity at the uncompacted depth, that is, the porosity is restored to the original value at the time of deposition to obtain the uncompacted density of the layer;

[0094] Decompaction Sedimentation Rate: This is the sedimentation rate when the sediment is restored to an uncompacted state. The unit is meters per million years (m / Ma). This rate is calculated based on the thickness of the sediment layer and the time of deposition. The calculation of this rate is not affected by compaction.

[0095] Decompaction Depth Column: refers to the depth after decompaction, that is, the depth when the sediment layer is assumed to be not compacted. It reflects the depth that the stratum would have been if it had not been subjected to sedimentary pressure, that is, the state of the stratum before compaction.

[0096] Dynamic topography column: The dynamic topography column represents the elevation relative to the current dynamic topography. Dynamic topography is the vertical movement of the surface caused by deep processes such as mantle convection. This column is used to record the surface uplift or subsidence caused by these deep processes.

[0097] 3. Age-depth conversion and paleowater depth calculation

[0098] According to the sediment age-depth conversion model formula, the age of the drilling site is converted into the basement depth of the corresponding ocean-continental transition zone and ocean basin. The specific formula is as follows:

[0099] When the oceanic crust is younger than 20 Ma: ;

[0100] When the oceanic crust is older than 20 Ma: ;

[0101] in, It is the basement depth of the ocean-continent transition zone and ocean basins. is the age of the oceanic crust;

[0102] Based on the effect of sediment removal on water depth, the basement depth after sediment removal was calculated, and paleo-water depth data of the ocean-continental transition zone and ocean basins in different geological periods were obtained.

[0103] 4. Correction of sea level change trend

[0104] The rising or falling trend of sea level in various geological periods will directly affect the sediment deposition rate, tectonic subsidence, and the evolution of dynamic topography. By introducing the sea level change trend to correct the paleo-water depth data of the ocean-continent transition zone and ocean basins, the following effects can be achieved:

[0105] Correcting sedimentation rate: Sea level changes directly affect the sedimentary environment. By correcting the sea level trend in advance, more reasonable estimates of sedimentation rate and decompaction thickness can be made;

[0106] Improve model accuracy: Sea level change, as an important external control factor, can be combined with tectonic subsidence and dynamic topography correction data to further reduce model uncertainty and improve the overall accuracy of paleobathymetry reconstruction and tectonic subsidence analysis.

[0107] 5. Tectonic Subsidence Analysis and Dynamic Terrain Correction

[0108] Use dynamic topographic models to quantify the impact of mantle convection on the basement depth of the ocean-continent transition zone and ocean basins, and adjust paleo-bathymetry data;

[0109] In the process of paleo-depth reconstruction, the influence of tectonic subsidence and dynamic topography plays an important role in the depth variation of the ocean-continental transition zone and ocean basins. In order to accurately restore the depth of the ancient ocean-continental transition zone and ocean basins, this method takes these two factors into account during the calculation process to correct the stratigraphic depth.

[0110] 5.1 Tectonic Subsidence Analysis

[0111] Tectonic subsidence refers to changes in water depth caused by tectonic forces (such as the sinking and stretching of the Earth's crust). This method uses a tectonic subsidence model to invert the subsidence process of the Earth's crust caused by tectonic forces to obtain tectonic subsidence data for the ocean-continent transition zone and ocean basins. The models for this process are divided into ocean subsidence models and land subsidence models. The appropriate model needs to be selected according to the geological background of different drilling sites.

[0112] 5.1.1 Ocean sedimentation model

[0113] Ocean subsidence models are applicable to drilling sites located on oceanic crust. The relationship between the depth of the formation and its age is primarily influenced by the thermal evolution of the oceanic crust. When the oceanic crust forms at mid-ocean ridges, it is hot and buoyant, resulting in shallow water depths. As the crust moves away from the ridge, it cools by conduction, gradually decreasing in temperature and increasing in density, which causes the crust to sink and, in turn, increase in water depth. This process is based on the principle of thermal cooling and contraction, where the crust gradually cools over time and becomes denser, causing it to sink and increase in water depth. The gradual decrease in the temperature of the oceanic crust is modeled using heat conduction equations, particularly when models involve half-space cooling or plate cooling, which describe the depth changes of the oceanic crust at different ages.

[0114] The specific steps are as follows:

[0115] Use the water depth grid to obtain the current water depth, that is, the depth of the sediment surface;

[0116] Isostatic pressure correction is used to correct for current sediment thickness. The process of sediment removal affects water depth. Isostatic pressure correction calculates current tectonic subsidence by taking into account the effect of sediment removal on water depth. Specifically, the average sediment density of the formation at the drilling site is used for calculation. This reveals the basement depth after sediment removal and helps eliminate compaction effects, resulting in more accurate paleowater depth data.

[0117] 5.1.2 Land Subsidence Model

[0118] The land subsidence model is mainly used to simulate crustal changes in passive land margins, especially rift valley subsidence and thermal subsidence. The entire simulation process can be divided into the following key steps:

[0119] Step 1: Rift Valley Subsidence

[0120] Rift valley subsidence occurs in the early stages of thinning of the continental crust due to stretching and expansion. As rift valleys form, the crust becomes thinner, usually accompanied by the rise of the mantle, resulting in changes in depth near sea level. The expansion and stretching of the crust begin, and surface subsidence gradually deepens. Rift valley subsidence is the first step in the continental subsidence model.

[0121] Step 2: Heat Subsidence

[0122] Thermal subsidence occurs after the rift valley extension ends, when the crust temperature decreases and the density increases, leading to thermal subsidence. This process usually occurs over a long period of time after the rift valley extension and continues to affect surface subsidence in the model.

[0123] Step 3: Determine the start and end time of the rift

[0124] Rift onset: marks the beginning of crustal extension and stretching. When the rift begins, it is assumed that the thickness of the sediment is zero and the sea level is the same as the initial depth of the rift.

[0125] Rift end time: marks the end of rift extension, the cessation of crustal stretching, and the beginning of thermal subsidence. Rift end time is an important parameter for calculating subsidence;

[0126] Step 4: Calculate the stretch factor

[0127] The stretch factor describes the extent of lithosphere thinning during rift extension. The stretch factor usually changes exponentially between the beginning and end of a rift, reflecting the extent of crust thinning during extension and directly affecting tectonic subsidence during rifting.

[0128] 5.2 Dynamic Terrain Correction

[0129] Dynamic topography refers to vertical surface movement caused by deep processes such as mantle convection. It is not determined by crustal thickness or the age of the oceanic crust, but is driven by deep processes such as mantle flow. Dynamic topography has a significant impact on water depth when studying the historical water depths of the ocean-continent transition zone, ocean basins, and continental margins. Deep processes such as mantle convection can cause surface uplift or subsidence, thereby affecting water depth.

[0130] Upwelling caused by mantle flow: If the surface of a region rises due to upwelling of the mantle, the water depth will become shallower;

[0131] Subsidence caused by mantle flow: If mantle flow causes the crust in a region to sink, the water depth will increase;

[0132] The specific steps for correcting paleowater depth using the dynamic terrain model are as follows:

[0133] Step 1: Specify the dynamic terrain model

[0134] Before performing water depth correction, it is necessary to first select a dynamic terrain model, which can be based on mantle convection simulations or inversion of seismic data and contains a global grid that varies with time;

[0135] Step 2: Reconstruct the location of the drilling site

[0136] Time-dependent grids are a core component of dynamic terrain models. They are based on global grids and describe changes in surface elevation over time, particularly the rise and fall of the surface due to mantle convection. These grids are matched with historical data from marine drilling sites, reflecting surface changes over past geological periods.

[0137] Since these grids are constructed based on the mantle reference system rather than the plate reference system, the coordinates of the drilling sites need to be converted from the plate reference system to the mantle reference system. This conversion step is very important because the grid of the dynamic terrain model is created based on the mantle flow framework, ensuring that the model accurately matches the actual surface changes;

[0138] Before applying the dynamic terrain correction, the positions of the drill sites need to be reconstructed. Since the dynamic terrain model grid is based on the mantle reference frame (the framework for mantle flow), and the actual positions of the drill sites are based on today's plate reference frame, we need to transform the modern positions of the drill sites to the past mantle reference frame.

[0139] To accomplish this conversion, the dynamic terrain model uses a static polygon file that assigns a reconstruction plate ID to each drill site. This ID helps identify the drill site's exact location in the past. The model also uses a rotation file to adjust the drill sites to ensure they are correct relative to their historical locations.

[0140] Step 3: Adjust water depth data

[0141] Once the drilling site is re-established and the dynamic topography grid is matched to that location, the model will adjust the calculated water depth. The magnitude and direction of the adjustment depend on the dynamic topography model selected, and will take into account surface rise and fall caused by deep processes such as mantle convection and heat flow.

[0142] If a dynamic terrain model predicts surface uplift in a region (due to mantle upwelling), the historical water depth in that region will be adjusted to be shallower;

[0143] If the surface is sinking (mantle cooling or plate subduction), the historical water depth in the region will be adjusted to increase;

[0144] In this way, dynamic topography corrections can accurately reflect the effects of mantle flow and tectonics on water depth.

[0145] 6. Model Validation and Optimization

[0146] The calculated paleowater depth data are compared with actual drilling data and geological observations. The sedimentation rate, porosity attenuation function, and tectonic subsidence parameters are continuously adjusted using the feedback from the comparison results. Each model is iteratively optimized to ensure the accuracy of the paleowater depth data and to truly reflect the actual process of geological evolution.

[0147] 7. Output and Application

[0148] The paleo-bathymetric data obtained through model calculations include the basement depths of various ocean-continental transition zones and ocean basins in different geological periods. The data output will be organized and archived in the form of detailed data files to facilitate subsequent analysis and comparison. Since the influence of factors such as mantle flow and tectonic subsidence on water depth is taken into account, the final output includes not only basic paleo-bathymetric data, but also tectonic subsidence data and results after dynamic topography correction to more accurately reflect the vertical movement of the crust in past geological periods. The output content includes:

[0149] Paleobathymetric data file: This file records the paleobathymetric data of each drilling site or formation in different geological periods in detail, reflecting the basement depth after decompaction, age-depth conversion, sea level trend correction, and dynamic topography correction;

[0150] Tectonic subsidence data: Contains the tectonic subsidence of each region calculated based on the tectonic subsidence model, providing a quantitative basis for regional geological evolution;

[0151] Correction parameters and correction reports: Output includes key parameters such as sea level change correction, tectonic subsidence correction factor, and correction reports compared with actual drilling data to facilitate further optimization of the model;

[0152] The output of paleo-bathymetric reconstruction and tectonic subsidence analysis has wide applications in multiple geological research fields, especially in the analysis of the evolution of global ocean-continent transition zones and ocean basins:

[0153] 1. Research on the tectonic evolution of oceans and continents: Through precise paleo-bathymetric reconstruction and tectonic subsidence analysis, geologists can conduct in-depth research on the tectonic evolution of the ocean-continent transition zone, ocean basins, and continental margins. By constructing ocean and continental subsidence models and combining them with dynamic topography corrections, they can accurately reconstruct changes in water depth over different geological periods, revealing processes such as crustal deformation, stretching, and thermal subsidence, thereby providing theoretical support for oceanic crust evolution and rift formation.

[0154] 2. Sea-level change simulation and climate research: This method helps simulate historical sea-level changes. By restoring paleo-water depth data and combining it with tectonic subsidence models and dynamic topography corrections, it can reconstruct water depth changes over different periods and reveal the relationship between sea-level rise and fall and climate change. It can be widely used in paleoclimate research, especially in studying sea-level changes during glacial and interglacial periods, as well as the causes and impacts of climate change.

[0155] 3. Paleontological and ecological research: This method can provide important historical environmental data for paleontological and ecological research. Through accurate paleo-bathymetric reconstruction and dynamic topography correction, it can reveal the ecological and environmental changes in ancient oceans and land, thereby helping to study the evolution, extinction and migration patterns of different biological communities, and understand the impact of climate change and geological events on species survival.

[0156] The following specific examples are provided in conjunction with the above embodiments. It can be understood that the following specific examples are merely illustrative of the specific implementation of the above embodiments, and are not intended to limit the technical solutions of the above embodiments.

[0157] Data preparation was conducted using a borehole from the Ocean Drilling Project as an example. The stratigraphic ages for this borehole range from 0 to 28 million years (with intervals ranging from 1 to 3 million years). The primary lithologies are sandy clay and calcareous mud. Key physical properties include shallow surface porosity, porosity attenuation coefficient, particle density of 2.7 g / cm³, and seawater density of 1.03 g / cm³. During preprocessing, missing density data for layer 6 were interpolated using the mean value of 2.65 g / cm³ from adjacent layers. Furthermore, age-depth data for all layers were standardized to a "top-bottom age-depth" format (for example, layer 1 was standardized as 0-3 Ma corresponding to 0-50 m) to ensure data format consistency and computational operability.

[0158] The method described in the above embodiment is used to calculate paleo-water depth and analyze tectonic subsidence, and a geohistorical analysis map of the study area is generated based on the calculation and analysis results. Figure 2 The analysis diagram of paleo-water depth and stratigraphic evolution history of the study area without correction of sea level change trend, structural subsidence analysis and dynamic topography is shown. Figure 3 The paleo-water depth and stratigraphic evolution history analysis of the study area after correction of sea level change trend, structural subsidence analysis and dynamic topography are shown. Figure 2 and Figure 3It can be seen that the corrected geohistorical analysis map of the study area is more consistent with the actual geological conditions. The corrected image obviously takes into account the complex geological conditions more fully. For the compaction effect processing, the dynamic exponential decay model is applied, and layer-by-layer correction is performed. The thickness recovery accuracy is improved by 20%, and the error range of the total paleowater depth reconstruction is reduced to within ±30m, which significantly improves the accuracy of paleowater depth reconstruction and tectonic subsidence analysis.

[0159] The embodiments of the present invention have so far described the technical solutions of the present invention in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A method for paleo-water depth reconstruction and numerical calculation of tectonic subsidence based on geophysical drilling data, characterized in that: include: Data preparation: Extract and preprocess the depth, age, and lithology data of the drilling sites from the International Ocean Drilling Program public dataset and drilling data from China's marginal oil and gas basins. The lithology data includes sediment density, surface porosity, and porosity decay. Decompaction calculation: Utilizing the law of sediment porosity decay with depth and pre-processed drilling site depth, age, and lithology data, the original porosity of each sedimentary layer before overburden pressure is calculated. The compaction effect of the overlying sediments is then removed layer by layer, restoring the true thickness and density of each sedimentary layer before compaction. Simultaneously, the sediment deposition rate is updated, providing accurate basic data for paleowater depth reconstruction. The law of sediment porosity decay with depth is described by a dynamic exponential decay model of the porosity-depth relationship. Age-depth conversion and paleowater depth calculation: Based on the age-depth conversion model and the ages of the ocean-continental transition zone and oceanic crust in different geological periods, the basement depths of the ocean-continental transition zone and ocean basins in different geological periods are quantitatively estimated. At the same time, the basement depths of the ocean-continental transition zone and ocean basins in different geological periods are corrected by combining the sediment thickness restored by decompaction calculation, and the paleowater depth data of the ocean-continental transition zone and ocean basins in different geological periods are calculated; Sea level trend correction: The paleo-water depth data of the ocean-continent transition zone and ocean basins are corrected by introducing the sea level trend; Tectonic subsidence analysis and dynamic topography correction: Based on the geological background of different drilling sites, oceanic or terrestrial subsidence models are selected to invert the crustal subsidence process caused by tectonic action to obtain tectonic subsidence data for the ocean-continent transition zone and ocean basins. Dynamic topography models are used to quantify the impact of mantle convection on the basement depth of the ocean-continent transition zone and ocean basins, and to adjust paleo-water depth data. Model validation and optimization: Compare the calculated paleo-water depth data with actual drilling data and geological observations. Use the comparison results as feedback to continuously adjust the sedimentation rate, porosity attenuation function, and tectonic subsidence parameters, and iteratively optimize each model to ensure the accuracy of the paleo-water depth data and truly reflect the actual process of geological evolution. Output and application: The obtained paleowater depth data and tectonic subsidence data are organized into detailed data files and stored for subsequent geological, climate and ecological research.

2. The method for paleo-water depth reconstruction and numerical calculation of tectonic subsidence based on geophysical drilling data according to claim 1 is characterized in that: The method uses the law of sediment porosity decay with depth and the pre-processed depth, age and lithology data of the drilling site to calculate the original porosity of each sedimentary layer before being subjected to overlying pressure, and then gradually removes the compaction effect of the overlying sediments to restore the true thickness and density of each sedimentary layer before compaction, and simultaneously updates the sediment deposition rate, including: The porosity of each sedimentary layer when not subjected to overburden pressure is calculated using the dynamic exponential decay model of the porosity-depth relationship. The dynamic exponential decay model is expressed as the relationship between porosity and depth: in, is depth The porosity of the sediment layer at is the surface porosity of the sediment layer, is the compaction coefficient; The density of the sedimentary layer is calculated based on the porosity of each sedimentary layer when it is not subjected to overburden pressure. The calculation formula is: in, is depth The density of the sediment layer at is the particle density of the sediment layer, is the density of the fluid in the pores of the sediment layer; When performing decompaction calculations, the age of each sediment layer is used to infer its original state before overburden pressure. Specifically, the age of each sediment layer is found from the age of the drilling site. The corresponding sediment layer is found according to the specified age, and the thickness of each sediment layer before overburden pressure is restored layer by layer. At the same time, the order of restoration is consistent with the actual order of the sediment layers. The restored thickness of the sediment layer is calculated as follows: in, and are the top and bottom depths of the sedimentary layer, is depth The porosity of the sediment layer at When decompaction calculations are performed to recover the thickness of the sediments to generate a new extension layer, the bottom age of the newly generated stratum is determined based on actual drilling data and geological background; The sediment deposition rate is calculated based on the recovered thickness of the sediment layer and the deposition time.

3. The method for paleo-water depth reconstruction and tectonic subsidence numerical calculation based on geophysical drilling data according to claim 1 is characterized in that: The basement depths of the ocean-continental transition zone and ocean basins in different geological periods are quantitatively estimated based on the age-depth conversion model and the ages of the ocean-continental transition zone and oceanic crust in different geological periods. At the same time, the basement depths of the ocean-continental transition zone and ocean basins in different geological periods are corrected in combination with the sediment thickness restored by decompaction calculation. The paleowater depth data of the ocean-continental transition zone and ocean basins in different geological periods are estimated, including: According to the sediment age-depth conversion model formula, the age of the drilling site is converted into the basement depth of the corresponding ocean-continental transition zone and ocean basin. The specific formula is as follows: When the oceanic crust is younger than 20 Ma: ; When the oceanic crust is older than 20 Ma: ; in, It is the basement depth of the ocean-continent transition zone and ocean basins. is the age of the oceanic crust; Based on the impact of sediment removal on water depth, the basement depth after removing the sediment thickness was calculated, and the paleowater depth data of the ocean-continental transition zone and ocean basins in different geological periods were obtained.

4. The method for paleo-water depth reconstruction and tectonic subsidence numerical calculation based on geophysical drilling data according to claim 1 is characterized in that: The method of selecting an ocean subsidence model or a land subsidence model according to the geological background of different drilling sites, and inverting the subsidence process of the crust caused by tectonic action to obtain tectonic subsidence data of the ocean-continent transition zone and ocean basins includes: If the drilling site is located on the ocean crust, the ocean subsidence model is selected to invert the subsidence process of the ocean crust caused by tectonic action, as follows: The depth of the sediment surface is obtained using the bathymetric grid; Isostatic pressure correction is calculated using the average sediment density of the formation at the drilling site. By considering the impact of sediment removal on the depth of the sediment surface, the current tectonic subsidence is calculated, thereby revealing the basement depth after sediment removal, eliminating the compaction effect and obtaining more accurate paleowater depth data. If the drilling site is located on the crust of a passive land margin, the land subsidence model is used to invert the subsidence process of the land crust caused by tectonic action, as follows: Simulate rift valley subsidence and thermal subsidence in sequence; Determine the start and end times of rifting. When rifting begins, the sediment thickness is assumed to be zero and the sea level is the same as the initial depth of the rift. When rifting ends, the stretching of the crust stops and thermal subsidence begins. The stretch factor is calculated to describe the degree of lithosphere thinning during rift propagation. The stretch factor changes exponentially between the beginning and end of the rift, thereby calculating the tectonic subsidence during the rift process.

5. The method for paleo-water depth reconstruction and tectonic subsidence numerical calculation based on geophysical drilling data according to claim 1 is characterized in that: The use of a dynamic terrain model to quantify the impact of mantle convection on the basement depth of the ocean-continent transition zone and ocean basins and adjust paleo-water depth data includes: Selecting a dynamic terrain model that includes a time-dependent global grid, wherein the time-dependent global grid is a core component of the dynamic terrain model and describes the changes in surface elevation over time, especially the rise and fall of the surface due to mantle convection. These grids are matched to historical data from the drilling site and reflect surface changes in past geological periods. The coordinates of the drill sites on the dynamic terrain model grid are converted from the modern plate reference system to the past mantle reference system to achieve the reconstruction of the drill site positions; After matching the dynamic terrain model grid with the reconstructed drilling site locations, the dynamic terrain model predicts surface subsidence and adjusts paleowater depth data for different geological periods based on the predicted surface subsidence.

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