A method for reconstructing paleo-water depth and calculating tectonic subsidence based on geophysical drilling data

Abstract

The application provides a method for reconstructing paleo-water depth and calculating tectonic subsidence based on geophysical drilling data, and belongs to the technical field of ocean-land transitional zone and ocean basin subsidence analysis, and comprises the following steps: extracting and preprocessing the depth, age and lithology data of a drilling site from geophysical drilling data; calculating the sediment decompaction thickness and average density by using a dynamic exponential decay model of porosity-depth relationship through a decompaction calculation method; simultaneously constructing an age-depth conversion model of a sediment layer to reconstruct the paleo-water depth; and introducing tectonic subsidence analysis and dynamic topographic correction, combining various factors such as mantle flow and tectonic activity to correct the surface elevation change. The application improves the accuracy of the paleo-water depth reconstruction, so that the paleo-water depth reconstruction is no longer limited to a static tectonic model, but can consider the dynamic changes of the internal processes of the earth, and can more truly reflect the depth changes of the ocean-land transitional zone and the ocean basin in the historical period.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ocean-land transition zone and ocean basin subsidence analysis, and particularly relates to a method for reconstructing paleo-water depth and numerically calculating tectonic subsidence based on geophysical drilling data. BACKGROUND

[0002] The evolution of the depth of the ocean basin is closely related to deep geodynamic processes such as lithospheric thermal cooling and mantle convection, and has a profound impact on geological phenomena such as sediment compaction and continental rift subsidence. The reconstruction of the paleo-water depth of the ocean basin not only provides key boundary conditions for the evolution of the supercontinent cycle and the simulation of paleo-ocean circulation, but also plays a crucial role in the field of oil and gas exploration, providing scientific basis for finding potential oil and gas reservoirs, and is a cornerstone for understanding the internal mechanism of long-term evolution of the earth system.

[0003] Currently, traditional paleo-water depth reconstruction techniques mainly rely on sediment lithology analysis, benthic fossil comparison 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 the change of the basement depth with age, they have many limitations when faced with complex geological scenarios. In terms of sediment compaction effect processing, traditional models mostly use static porosity assumptions, ignoring the dynamic changes of porosity with depth and time, and failing to use an exponential decay function to correct the sediment compaction effect layer by layer, resulting in systematic bias in the recovery of original thickness and density of the strata, which seriously reduces the accuracy of paleo-water depth reconstruction.

[0004] More prominent is that the existing technology has a major flaw in data processing, lacking the ability to systematically integrate multi-source data such as drilling lithology, porosity decay curve and dynamic topography grid, mainly relying on manual regional modeling, which is inefficient and cannot handle large-scale data, and is prone to subjective errors, making it difficult to meet the batch analysis needs of complex geological scenarios on a global scale. SUMMARY

[0005] In view of the problems existing in the prior art, the present application provides a method for reconstructing paleo-water depth and numerically calculating tectonic subsidence based on geophysical drilling data, which accurately calculates the compaction degree of sediments over time based on geophysical drilling data, converts strata age and paleo-water depth, and corrects the paleo-water depth in combination with a specific tectonic subsidence model and a dynamic topography model.

[0006] The present application provides a method for reconstructing paleo-water depth and numerically calculating tectonic subsidence based on geophysical drilling data, comprising:

[0007] Data preparation: Depth, age and lithology data of drilling sites are extracted from the International Ocean Discovery Program public dataset and Chinese drilling data of marginal oil and gas basins, and preprocessed, wherein the lithology data includes sediment density, surface porosity and porosity decay;

[0008] De-compaction calculation: The original porosity of each sediment layer under the condition of no overlying pressure is calculated by using the law of sediment porosity decay with depth and the preprocessed depth, age and lithology data of drilling sites, and then the compaction effect of overlying sediments is peeled off layer by layer to restore the true thickness and density of each sediment layer before compaction, and the sediment deposition rate is updated to provide accurate basic data for paleo-water depth reconstruction, wherein the law of sediment porosity decay with depth is described by a dynamic exponential decay model of porosity-depth relationship;

[0009] Age-depth conversion and paleo-water depth calculation: The basement depth of the ocean-continent transition zone and ocean basin in different geological periods is quantitatively calculated based on the age-depth conversion model and the ocean-continent transition zone and ocean basin age in different geological periods, and the basement depth of the ocean-continent transition zone and ocean basin in different geological periods is corrected by combining with the sediment thickness restored by de-compaction calculation to calculate the paleo-water depth data of the ocean-continent transition zone and ocean basin in different geological periods;

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

[0011] Tectonic subsidence analysis and dynamic topography correction: According to the geological background of different drilling sites, marine subsidence model or land subsidence model is selected to inverse the subsidence process of crust caused by tectonic action to obtain the tectonic subsidence data of the ocean-continent transition zone and ocean basin; the influence of mantle convection on the basement depth of the ocean-continent transition zone and ocean basin is quantified by using dynamic topography model to adjust the paleo-water depth data;

[0012] Model verification and optimization: The calculated paleo-water depth data are compared with the actual drilling data and geological observation results, and the comparison results are used to feedback to continuously adjust the deposition rate, porosity decay function and tectonic subsidence parameters, and each model is iteratively optimized to ensure the accuracy of the paleo-water depth data and to truly reflect the actual process of geological evolution;

[0013] Output and application: The obtained paleo-water depth data and tectonic subsidence data are arranged into detailed data files and stored for subsequent geological, climatic and ecological research.

[0014] Optionally, the original porosity of each sediment layer under no overburden pressure is calculated by using the porosity decay law with depth and the pretreated drilling site depth, age and lithology data, and then the compaction effect of the overlying sediments is peeled off layer by layer to restore the true thickness and density of each sediment layer before compaction, while updating the sediment deposition rate, including:

[0015] The porosity of each sediment layer under no overburden pressure is calculated by a dynamic exponential decay model of porosity and depth, and the dynamic exponential decay model is expressed as the relationship between porosity and depth:

[0016]

[0017] wherein, is the porosity of the sediment layer at depth is the surface porosity of the sediment layer, is the compaction coefficient; The density of the sediment layer is calculated according to the porosity of each sediment layer under no overburden pressure, and the calculation formula is:

[0018]

[0019]

[0020] wherein, is the density of the sediment layer at depth is the particle density of the sediment layer, is the density of the fluid in the pore of the sediment layer; When performing the decompaction calculation, the original state of each layer of sediment under no overburden pressure is calculated according to the age of each layer of sediment, specifically: first, find the age of each layer of sediment from the age of the drilling site, find the corresponding sediment layer according to the specified age, restore the thickness of each sediment layer under no overburden pressure layer by layer, while ensuring that the restored order is consistent with the actual order of the sediment layer, and the restored thickness of the sediment layer is calculated as follows:

[0021]

[0022] wherein,

[0023] and are the top depth and bottom depth of the sediment layer, is the porosity of the sediment layer at depth When the decompaction calculation restores the thickness of the sediment to generate a new extended layer, the bottom age of the newly generated stratum is determined according to the actual drilling data and geological background;

[0024]

[0025] ​​​The deposition rate of the sediment is calculated according to the recovered thickness of the sediment layer and the deposition time.

[0026] Optionally, the base depth of the ocean-continent transitional zone and the ocean basin in different geological periods is quantitatively calculated based on the age-depth conversion model and the ocean-continent transitional zone and the ocean basin age in different geological periods, and the recovered sediment thickness is calculated by combining the decompaction to correct the base depth of the ocean-continent transitional zone and the ocean basin in different geological periods, and the paleo-water depth data of the ocean-continent transitional zone and the ocean basin in different geological periods are calculated, including:

[0027] According to the sediment age-depth conversion model formula, the age of the drilling site is converted into the corresponding base depth of the ocean-continent transitional zone and the ocean basin, and the specific formula is as follows:

[0028] When the marine crustal age is less than 20Ma: ;

[0029] When the marine crustal age is greater than 20Ma: ;

[0030] Wherein, is the base depth of the ocean-continent transitional zone and the ocean basin, is the marine crustal age;

[0031] The base depth after removing the sediment thickness is calculated according to the influence of the water depth after removing the sediment, and the paleo-water depth data of the ocean-continent transitional zone and the ocean basin in different geological periods are obtained.

[0032] Optionally, the marine subsidence model or the land subsidence model is selected according to the geological background of different drilling sites, and the tectonic subsidence data of the ocean-continent transitional zone and the ocean basin caused by tectonic action are obtained by inversion, including:

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

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

[0035] The isostatic pressure correction is calculated using the average sediment density of the drilling site stratum, the current tectonic subsidence is calculated by considering the influence of the sediment removal on the sediment surface depth, so as to reveal the base depth after removing the sediment, so as to eliminate the compaction effect and obtain more accurate paleo-water depth data;

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

[0037] Sequentially simulate the rift subsidence and thermal subsidence;

[0038] Determine the rift start and end time, assume the thickness of the sediment is zero at the beginning of the rift, and the sea level is the same as the initial depth of the rift, and the stretching of the crust stops at the end of the rift, and the thermal subsidence begins;

[0039] Calculate the stretching factor to describe the degree of lithospheric thinning during the expansion of the rift, the stretching factor changes exponentially between the beginning and the end of the rift, and then calculate the tectonic subsidence during the rift process.

[0040] Optionally, the influence of the mantle convection on the basement depth of the ocean-continent transition zone and the ocean basin is quantified by using the dynamic topography model to adjust the paleo-water depth data, comprising:

[0041] Select a dynamic topography model containing a time-dependent global grid, wherein the time-dependent global grid is a core component of the dynamic topography model, describes the change of the ground elevation in different time periods, especially the ground elevation change caused by the mantle convection, and these grids match the historical data of the drilling site, reflecting the surface change in the past geological period;

[0042] Convert the coordinates of the drilling site on the dynamic topography model grid from the modern plate reference system to the past mantle reference system to realize the reconstruction of the drilling site position;

[0043] After matching the dynamic topography model grid with the reconstructed drilling site position, the dynamic topography model predicts the surface subsidence and adjusts the paleo-water depth data in different geological periods according to the predicted surface subsidence.

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

[0045] 1. The present application breaks through the limitations of traditional methods, combines multiple factors affecting sea level into a unified analysis framework, and comprehensively considers factors such as sediment decompaction, dynamic topography, and tectonic subsidence, so that the data covers more information, and the paleo-water depth reconstruction is more accurate and convenient.

[0046] 2. The present application uses a dynamic exponential decay model of the relationship between porosity and depth to accurately calculate key parameters such as sediment decompaction thickness and average density; at the same time, the construction of the sediment layer age-depth conversion model can provide very accurate paleo-water depth reconstruction; by introducing tectonic subsidence analysis and dynamic topography correction, combined with factors such as mantle flow and tectonic activity, the surface elevation change can be more accurately corrected, the accuracy of paleo-water depth reconstruction is improved, and the paleo-water depth reconstruction is no longer limited to a static tectonic model, but can consider the dynamic changes of the internal processes of the earth, and can more truly reflect the depth changes of the ocean-continent transition zone and the ocean basin in the historical period.

[0047] 3. The present application can carry out accurate paleo-water depth reconstruction and tectonic subsidence analysis, which can reveal crustal deformation processes and provide theoretical support for related geological evolution in marine and terrestrial tectonic evolution research; 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 in paleoclimate research; it can also provide historical environmental data for paleontology and ecology research, reveal ecological environmental changes, assist in studying biological community evolution, and understand the impact of climate change and geological events on species survival. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0049] Figure 1 A flowchart of a method for reconstructing paleo-water depth and calculating tectonic subsidence based on geophysical drilling data provided by the present disclosure is shown in the figure.

[0050] Figure 2 A historical geology analysis chart for a research area without sea level change trend correction, tectonic subsidence analysis and dynamic topography correction is shown in the figure.

[0051] Figure 3 A historical geology analysis chart for a research area after sea level change trend correction, tectonic subsidence analysis and dynamic topography correction is shown in the figure. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

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

[0054] Early decompaction studies play an important role, mainly focusing on the changes in porosity and thickness of sediments. Researchers generally recognize that sediments will be subjected to compaction over a long geological history, with porosity gradually decreasing and thickness also thinning. Therefore, decompaction is a key step to restore the original state of sediments. However, current methods are mostly based on simple empirical formulas, which are based on limited local data and approximate the relationship between porosity and depth. Although this method can restore some characteristics of sediments to some extent, it lacks comprehensive consideration of regional geological background and in-depth understanding of complex physical and chemical changes during sediment compaction, resulting in large errors in decompaction results. Especially when faced with sediments of different depositional environments and lithology, the applicability of these empirical formulas is greatly reduced, making it difficult to accurately restore the true history of sediments.

[0055] In the study of age-depth conversion models, the early Parsons and Sclater model laid the foundation for the study of oceanic crust depth, but for older crust, the fitting effect of heat flow and water depth data is not good. The GDH1 model that appeared later has improved to some extent, improving the calculation accuracy, but these models often do not fully consider the comprehensive influence of other geological factors when applied, affecting the accuracy of the model.

[0056] In the field of tectonic subsidence analysis, the study of marine basins and passive margins on land has been separated for a long time, and the research focus is usually focused on the influence of a single tectonic factor on deposition. As an important mechanism for controlling the volume of marine basins, existing researches mostly use separate analysis of present-day marine basins when analyzing the thickness differences of sediments in different marine basins. However, due to the dynamic conversion of plate boundaries, this method cannot be used to predict the sediment thickness of ancient marine basins. If we want to accurately predict the sediment thickness of ancient marine basins, we must decompaction the sediments.

[0057] In the study of dynamic topography correction, current research focuses on its own change rules and less on integration with other geological research. Although researchers have recognized the significant impact of dynamic topography on water depth, they have failed to effectively integrate it with factors such as tectonic subsidence in the actual paleo-water depth reconstruction process, resulting in an inability to accurately reflect the true situation during the geological history period.

[0058] In addition, there are problems in data acquisition and analysis in the existing research in this field. The existing research has limited data acquisition means, mainly relying on traditional geological sampling, resulting in poor sample data quality, small quantity and uneven distribution, and poor accuracy of analysis results; the data does not comprehensively cover the information, and it is difficult to comprehensively analyze the information of paleo-water depth, paleo-stratum and other information to explore the internal relationship of geological evolution; in addition, the analysis and calculation method is relatively simple, and the predecessors usually only study a single variable, which cannot fully consider the complex geological conditions, resulting in a large deviation between the analysis results and the actual geological conditions.

[0059] In view of the above problems, the present application innovatively integrates the decompaction calculation, the ocean age-depth model, the tectonic subsidence analysis and the dynamic topography correction, and for the first time realizes the collaborative calculation of tectonic subsidence, sediment compaction and mantle dynamics. In the treatment of sediment compaction effect, a porosity dynamic exponential decay model is introduced, which can peel off the compaction effect layer by layer, accurately restore the original thickness and density of the sediment, and at the same time, the sediment layer age-depth conversion model can provide very accurate paleo-water depth reconstruction. The tectonic subsidence analysis and dynamic topography correction are introduced, the dynamic topography data are integrated into the model according to the time sequence, the corresponding dynamic topography grid is generated for different geological periods, the long-term fluctuation influence of the mantle convection on the basement depth is effectively quantified, the short board of the traditional method is successfully made up, and the international ocean drilling program public data set and the drilling data of the Chinese marginal oil and gas basin are integrated. These high-resolution stratigraphic records and clear sedimentary environment indication data greatly improve the calculation accuracy and practicability.

[0060] The technical solutions of the present application will be described in detail below with specific embodiments. 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] As shown in Figure 1 The present application provides a method for reconstructing paleo-water depth and numerically calculating tectonic subsidence based on geophysical drilling data, which comprises:

[0062] 1. Data preparation

[0063] 1.1 Data source

[0064] The data of the present application is based on geophysical drilling data, including the international ocean drilling program public data set and the drilling data of the Chinese marginal sea oil and gas basin, and specifically includes 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 calculation of sediment thickness and tectonic subsidence, provides starting depth information for decompaction calculation, and is used to determine tectonic subsidence correction, so as to accurately reflect the original state of the sediment;

[0066] Drilling site age data: records the age information of each drilling site stratum (usually in million years), provides a time scale for geological history, and then converts the age data into basement depth through age-depth conversion model, and calculates the paleo-water depth, and serves as a time node in sedimentation rate calculation and decompression steps;

[0067] Lithology data - density: reflects the physical density of sediments or rocks, which is an important parameter for calculating pressure effect and sediment compaction degree, used to calculate the compaction thickness of strata under pressure, update the average density after decompaction, and calculate the depth after removing sediments in tectonic subsidence analysis;

[0068] Lithology data - surface porosity: refers to the porosity of sediments just after deposition, reflecting the initial physical properties of sediments, which can be used as a starting parameter for calculating porosity decay, restoring the original thickness of sediments in decompaction calculation, and providing basic data for isostatic correction;

[0069] Lithology data - porosity decay: describes the law of sediment porosity decay with increasing depth, usually expressed by dynamic exponential decay model, and the porosity decay function is calculated by integration to restore the true thickness of sediments before compaction, which is the core parameter for eliminating compaction effect, correcting sedimentation rate and reconstructing paleo-water depth;

[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, identify abnormal values and noise points in the data set, eliminate data records that do not meet the standard, and ensure that subsequent analysis is based on high-quality data;

[0074] Step 2: Missing value processing

[0075] Comprehensive check on key parameters (such as drilling depth, stratum age, density, porosity, etc.), fill in missing data using interpolation method, and for missing value processing, choose appropriate interpolation method (such as mean value interpolation, Lagrange interpolation, etc.) according to data type, to ensure data integrity;

[0076] 2. Decompaction calculation

[0077] The compaction thickness refers to the actual thickness change of the sediment under the pressure of the overburden, and the porosity of the sediment decreases over time, resulting in a decrease in thickness. The decompaction thickness is the original thickness of the sediment when it is not affected by the compaction of the overburden. In the decompaction calculation process, the method gradually removes the newer sediment layers to reduce the pressure on the lower sediment layers and restore their porosity and thickness to return to the initial state of deposition.

[0078] 2.1 Decompaction calculation principle

[0079] The purpose of decompaction of the formation is to restore the physical state of the formation at a certain point in time in the past. By analyzing the decompaction process, the average decompacted density and thickness change of the top of the formation at the decompaction depth can be calculated to reconstruct the paleo-water depth.

[0080] Porosity refers to the proportion of pore volume in the total volume of the formation, and its value ranges from 0 to 1. Typically, the porosity of the formation is between 0.1 and 0.4, but in loose sediments or certain reservoirs, the porosity can be higher, while in hard rocks, the porosity can be very low, close to 0. The density of the formation is closely related to the porosity, and the porosity usually decreases with increasing depth.

[0081] The porosity of each sediment layer when not affected by the overburden pressure is calculated using the dynamic exponential decay model of porosity and depth. The dynamic exponential decay model represents the relationship between porosity and depth as follows:

[0082]

[0083] wherein, is the porosity of the sediment layer at depth is the surface porosity of the sediment layer, is the compaction coefficient; The density of each sediment layer is calculated based on the porosity of the sediment layer when not affected by the overburden pressure. The calculation formula is as follows:

[0084]

[0085]

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

[0087] ​​When performing the decompaction calculation, the original state of each layer of sediment is estimated according to its age, which is specifically: first, find the age of each layer of sediment from the age of the drilling site, find the corresponding sediment layer according to the specified age, and calculate the state of each layer of sediment when it returns to its original state, each age corresponds to a "restored state" of the sediment layer, which is arranged in the original order. By looking up the age of each layer of sediment, the thickness of each layer of sediment when it is not subjected to overburden pressure is restored layer by layer, while ensuring that the order of restoration is consistent with the actual order of the sediment layer. The formula for calculating the restored thickness of the sediment layer is as follows:

[0088]

[0089] wherein, and are the top depth and bottom depth of the sediment layer, is the porosity of the sediment layer at depth

[0090] When the decompaction calculation restores the thickness of the sediment to generate a new extended layer, in order to determine the bottom age of the newly generated stratum, the bottom age of the newly generated stratum is determined according to the actual drilling data and geological background, for example, the drilling site is located on the land crust (especially in the rift zone), then the bottom age of the new stratum will be set to the age when the rift began;

[0091] 2.2 Decompaction calculation generates a new sequence

[0092] Each stratum information in the drilling site file is decompacted to generate a corrected drilling information output file, which includes the additional bottom extension base sediment layer generated after decompaction, and the parameters of the decompressed output bottom layer, the specific parameters are as follows:

[0093] Decompaction density column: refers to the average density of each layer of sediment within the decompaction range. The calculation of density takes into account the mixture of sediment and pore water, because the porosity of the sediment will affect its density. The density of each layer is calculated based on its porosity at the decompaction depth, i.e. the porosity is restored to its original value when the sediment was deposited, and the decompaction density of the layer is obtained;

[0094] Decompaction sedimentation rate column: refers to the sedimentation rate of the sediment when it is restored to the uncompacted state, with a unit of meters per million years (m / Ma). The rate is calculated based on the restored thickness of the sediment layer and the time of deposition, and the calculation of this rate is not affected by compaction;

[0095] Decompaction depth column: refers to the depth after decompaction, i.e. the depth of the sediment layer if it had not been subjected to compaction, which reflects the state of the stratum before it was compacted; ​

[0096] Dynamic topography list: Dynamic topography list represents the vertical movement of the earth's surface caused by deep processes such as mantle convection relative to the current dynamic topography elevation, which is used to record the uplift or subsidence of the earth's surface caused by these deep processes;

[0097] 3. Age-depth conversion and paleo-water depth calculation

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

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

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

[0101] Wherein, is the basement depth of the ocean-land transition zone and the ocean basin, is the oceanic crust age;

[0102] According to the influence of the water depth after the removal of sediments, the basement depth after the removal of sediment thickness is calculated, and the paleo-water depth data of the ocean-land transition zone and the ocean basin in different geological periods are obtained;

[0103] 4. Sea level change trend correction

[0104] The rising or falling trend of sea level in each geological period will directly affect the sedimentation rate, tectonic subsidence and evolution of dynamic topography. By introducing the sea level change trend to correct the paleo-water depth data of the ocean-land transition zone and the ocean basin, the following effects are achieved:

[0105] Correct the sedimentation rate: sea level change directly affects the sedimentary environment, and by correcting the sea level trend in advance, the sedimentation rate and the decompaction thickness can be more reasonably estimated;

[0106] Improve the accuracy of the model: as an important external control factor, the sea level change, through the comprehensive use of tectonic subsidence and dynamic topography correction data, can further reduce the uncertainty of the model and improve the overall accuracy of paleo-water depth reconstruction and tectonic subsidence analysis;

[0107] 5. Tectonic subsidence analysis and dynamic topography correction

[0108] Use the dynamic topography model to quantify the influence of mantle convection on the basement depth of the ocean-land transition zone and the ocean basin, and adjust the paleo-water depth data;

[0109] In the process of paleo-water depth reconstruction, the effects of tectonic subsidence and dynamic topography play an important role in the depth changes of ocean-continent transition zone and ocean basin. In order to accurately restore the depth of ancient ocean-continent transition zone and ocean basin, this method considers the two factors to correct the stratigraphic depth in the calculation process.

[0110] 5.1 Tectonic subsidence analysis

[0111] Tectonic subsidence refers to the change of water depth caused by tectonic action (such as subsidence and stretching of the crust). This method uses a tectonic subsidence model to invert 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. The model of this process is divided into marine subsidence model and land subsidence model, and the appropriate model needs to be selected according to the geological background of different drilling sites.

[0112] 5.1.1 Marine subsidence model

[0113] The marine subsidence model is suitable for drilling sites located on the oceanic crust. The relationship between the depth of the stratum and its age is mainly affected by the thermal evolution process of the oceanic crust. When the oceanic crust is formed at the mid-ocean ridge, it is hot and has strong buoyancy, so the water depth is shallow. As the crust moves away from the mid-ocean ridge, it cools down through heat conduction, gradually reduces the temperature, and increases the density, causing the crust to sink and the water depth to increase. This process is based on the principle of heat cooling and contraction, that is, the crust gradually cools down over time and becomes denser, causing it to sink and increase the water depth. The gradual reduction of the temperature of the oceanic crust is modeled by the heat conduction equation, especially in models involving half-space cooling or plate cooling, which describes 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] Use isostatic correction to correct the thickness of the current sediment. The process of removing sediment will affect the water depth. Isostatic correction calculates the current tectonic subsidence by considering the effect of sediment removal on water depth. Specifically, the average sediment density of the stratum at the drilling site is used for calculation, thereby revealing the depth of the basement after removing sediment, helping to eliminate the compaction effect, so as to obtain more accurate paleo-water depth data;

[0117] 5.1.2 Land subsidence model

[0118] The land subsidence model is mainly used to simulate the crustal changes in the passive continental margin area, especially the two processes of rift subsidence and thermal subsidence. The whole simulation process can be divided into the following key steps:

[0119] Step one: rift subsidence

[0120] Rift subsidence occurs in the initial stage of the thinning of the continental crust due to stretching and extension. As the rift develops, the crust becomes thinner, often accompanied by the uplift of the mantle, leading to changes in depth near sea level. The extension and stretching of the crust begin, and the surface subsidence gradually deepens. Rift subsidence is the first step in the model of land subsidence;

[0121] Step 2: Thermal subsidence

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

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

[0124] Rift start time: marks the initial stage of crustal extension and stretching. The thickness of sediments is assumed to be zero at the start of the rift, and the sea level is the same as the initial depth of the rift;

[0125] Rift end time: marks the end of rift extension, when the stretching of the crust stops and thermal subsidence begins. The end time of the rift is an important parameter for calculating subsidence;

[0126] Step 4: Stretch factor calculation

[0127] The stretch factor describes the degree of lithospheric thinning during rift extension. The stretch factor usually changes exponentially between the start and end of the rift, reflecting the degree of crustal thinning during extension and directly affecting the tectonic subsidence during the rift process;

[0128] 5.2 Dynamic topography correction

[0129] Dynamic topography refers to the vertical movement of the surface caused by deep processes such as mantle convection. It is not determined by the thickness of the crust 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 history of water depth in ocean-land transition zones and ocean basins and land edges. Deep processes such as mantle convection can cause the surface to rise or sink, thereby affecting water depth;

[0130] Rise caused by mantle flow: If the upwelling of the mantle causes the surface of a certain area to rise, the water depth will become shallower;

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

[0132] The specific steps for correcting paleo-water depth using the dynamic topography model are as follows:

[0133] Step 1: Specify the dynamic topography model

[0134] Before performing the bathymetry correction, a dynamic topography model needs to be selected, which can be based on mantle convection simulations or seismic data inversion and contains time-dependent global grids;

[0135] Step 2: Reconstructing the location of drilling sites

[0136] Time-dependent grids are a core component of dynamic topography models, which are based on global grids and describe changes in surface elevation over different time periods, particularly due to mantle convection, and are matched with historical data from ocean drilling sites, reflecting past geological periods;

[0137] Since these grids are based on the mantle reference frame, not the plate reference frame, it is necessary to convert the coordinates of drilling sites from the plate reference frame to the mantle reference frame, which is a crucial step because the grids of dynamic topography models are created based on the mantle flow framework, ensuring accurate matching of the model with actual surface changes;

[0138] Before applying dynamic topography correction, the location of drilling sites needs to be reconstructed. Since the grids of dynamic topography models are based on the mantle reference frame (the framework of mantle flow), while the actual location of drilling sites is based on today's plate reference frame, we need to convert the modern location of drilling sites to the past mantle reference frame;

[0139] To complete this conversion, the dynamic topography model uses a static polygon file that assigns a reconstructed plate ID to each drilling site, which helps identify the accurate location of drilling sites in the past, and a rotation file to adjust the location of drilling sites to ensure that their corresponding historical positions are correct;

[0140] Step 3: Adjusting bathymetry data

[0141] After the location of drilling sites is reconstructed and the dynamic topography grid matches the location, the model adjusts the calculated water depth, with the magnitude and direction of adjustment depending on the selected dynamic topography model, taking into account surface uplift caused by deep processes such as mantle convection and heat flow;

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

[0143] If the surface subsides (due to mantle cooling or plate subduction), the historical water depth of that region will be adjusted to increase;

[0144] In this way, dynamic topography correction can accurately reflect the impact of mantle flow and tectonic processes on water depth.

[0145] 6. Model verification and optimization

[0146] The calculated paleo-water depth data is compared with actual drilling data and geological observations. The comparison results are used to continuously adjust the sedimentation rate, porosity decay function, and tectonic subsidence parameters, and to iteratively optimize each model to ensure the accuracy of the paleo-water depth data and to accurately reflect the actual process of geological evolution.

[0147] 7. Output and application

[0148] Through model calculation, the obtained paleo-water depth data contains the basement depth of each ocean-land transition zone and ocean basin in different geological periods. The output results are arranged and archived in the form of detailed data files for subsequent analysis and comparison. Since the effects of mantle flow and tectonic subsidence on water depth are considered, the final output not only includes basic paleo-water depth data, but also includes tectonic subsidence data and results after dynamic topographic correction, so as to more accurately reflect the vertical movement of the crust in the past geological periods. The output content includes:

[0149] Paleo-water depth data file: This file records in detail the paleo-water depth data of each drilling site or stratum in different geological periods, reflecting the basement depth after compaction, age-depth conversion, sea level change trend correction, and dynamic topographic correction.

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

[0151] Correction parameters and correction report: The output includes key parameters such as sea level change correction amount and tectonic subsidence correction factor, as well as the correction report after comparison with actual drilling data, facilitating further optimization of the model.

[0152] The output results of paleo-water depth reconstruction and tectonic subsidence analysis have a wide range of applications in multiple geological research fields, especially in the analysis of global ocean-land transition zones and ocean basin evolution:

[0153] 1. Marine and terrestrial tectonic evolution research: Through accurate paleo-water depth reconstruction and tectonic subsidence analysis, geologists can deeply study the tectonic evolution of ocean-land transition zones and ocean basins and land edges. By building marine and terrestrial subsidence models and combining dynamic topographic correction, the water depth changes in different geological periods can be accurately reconstructed, revealing the processes of crustal deformation, stretching, and thermal subsidence, and providing theoretical support for marine crustal 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, combining tectonic subsidence models and dynamic topographic correction, it can reconstruct water depth changes in different periods, reveal the relationship between sea level rise and climate change, and be widely applied in paleoclimate research, especially in studying the causes and effects of sea level changes and climate changes during glacial, interglacial and other climate fluctuation periods, which has important application value.

[0155] 3. Paleontology and ecology research: This method can provide important historical environmental data for paleontology and ecology research. Through accurate paleo-water depth reconstruction and dynamic topographic correction, it can reveal the ecological and environmental changes of ancient oceans and lands, and help 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 proposed in combination with the above embodiments. It can be understood that the following specific examples only exemplarily illustrate the specific implementation of the above embodiments, and do not limit the technical solutions of the above embodiments.

[0157] Data preparation work is carried out on an ocean drilling borehole, which has a stratigraphic age span of 0-28 million years (each layer is spaced 1-3 million years apart), the main lithology is sandy clay and calcareous ooze, and the key physical property parameters include: shallow surface porosity, porosity decay coefficient, particle density 2.7 g / cm³, and seawater fluid density 1.03 g / cm³. In the preprocessing stage, for the missing density data of the 6th layer, the mean value of the adjacent layers 2.65 g / cm³ is used for interpolation completion, and the age-depth data of all layers is standardized to "top-bottom age-depth" format (for example, the 1st layer is standardized to 0-3Ma corresponding to 0-50m), to ensure the consistency of data format and the operability of calculation.

[0158] The method described in the above embodiments is used to calculate paleo-water depth and analyze tectonic subsidence, and the geohistory analysis map of the study area is generated according to the calculation and analysis results, Figure 2 shows the paleo-water depth and stratigraphic evolution history analysis map of the study area without sea level change trend correction, tectonic subsidence analysis and dynamic topographic correction, Figure 3 shows the paleo-water depth and stratigraphic evolution history analysis map of the study area after sea level change trend correction, tectonic subsidence analysis and dynamic topographic correction, and Figure 2 and Figure 3It can be seen that the research area geohistory analysis diagram obtained after the correction is more in line with the actual geological conditions, the corrected image obviously more fully considers the complex geological conditions, for compaction effect processing, application of dynamic index attenuation model, layer by layer correction, thickness recovery accuracy is improved by 20%, total paleo-water depth reconstruction error range is reduced to within ± 30m, the accuracy of paleo-water depth reconstruction and structural subsidence analysis is significantly improved.

[0159] The technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical solutions after the changes or replacements will fall within the protection scope of the present application.

Claims

1. A method for reconstructing paleo-water depth and calculating tectonic subsidence based on geophysical drilling data, characterized in that, The method comprises the following steps: Data preparation: depth, age and lithology data of drilling sites are extracted from the International Ocean Drilling Program public data set and Chinese marginal oil and gas basin drilling data, and preprocessed, wherein the lithology data includes sediment density, surface porosity and porosity decay; Depositional rate updating: the sediment deposition rate is updated based on the true thickness and density of each sediment layer before compaction, and the sediment deposition rate is used as the basis data for paleo-water depth reconstruction; Age-depth conversion and paleo-water depth calculation: the basement depth of the oceanic-continental transitional zone and ocean basin in different geological periods is quantitatively calculated based on the age-depth conversion model and the oceanic-continental transitional zone and ocean basin age in different geological periods, and the basement depth of the oceanic-continental transitional zone and ocean basin in different geological periods is corrected based on the sediment thickness recovered by the compaction calculation, and the paleo-water depth data of the oceanic-continental transitional zone and ocean basin in different geological periods are calculated; Sea level change trend correction: the paleo-water depth data of the oceanic-continental transitional zone and ocean basin are corrected by introducing the sea level change trend; Tectonic subsidence analysis and dynamic topography correction: the oceanic-continental transitional zone and ocean basin tectonic subsidence data are obtained by inverting the subsidence process of the crust caused by tectonic action according to the geological background of different drilling sites, and the paleo-water depth data are adjusted by quantifying the influence of mantle convection on the basement depth of the oceanic-continental transitional zone and ocean basin using the dynamic topography model; Model verification and optimization: the calculated paleo-water depth data are compared with the actual drilling data and geological observation results, and the comparison results are used to continuously adjust the deposition rate, porosity decay function and tectonic subsidence parameters, and each model is iteratively optimized to ensure the accuracy of the paleo-water depth data and to truly reflect the actual process of geological evolution; Output and application: the obtained paleo-water depth data and tectonic subsidence data are arranged into detailed data files and stored for subsequent geological, climatic and ecological research.

2. The method according to claim 1, wherein, The method for calculating the original porosity of each sediment layer under the influence of the overlying pressure, stripping the compaction effect of the overlying sediment layer by layer, recovering the true thickness and density of each sediment layer before compaction, and updating the deposition rate of the sediment comprises the following steps: The porosity of each sediment layer under the influence of the overlying pressure is calculated by the dynamic exponential decay model of porosity-depth relationship, and the dynamic exponential decay model is expressed as the relationship between porosity and depth: wherein, is the depth of the deposit layer at the point, is the surface porosity of the deposit layer, is the compaction factor; The density of each sediment layer is calculated according to the porosity of each sediment layer under the influence of the overlying pressure, and the calculation formula is: wherein is the density of the deposited layer at depth is the density of the deposited layer at depth is the density of the deposited layer at depth is the density of the fluid in the pores of the deposited layer at depth In the decompaction calculation, the original state of each layer of sediment under the absence of overlying pressure is calculated according to the age of each layer of sediment, specifically as follows: first, the age of each layer of sediment is found from the age of the drilling site, and the corresponding sediment layer is found according to the specified age, the thickness of each sediment layer under the absence of overlying pressure is recovered layer by layer, while ensuring that the recovery order is consistent with the actual order of the sediment layer, and the recovery thickness calculation formula of the sediment layer is as follows: wherein, and is a top depth and a bottom depth of the deposited layer, is a depth at which the deposited layer porosity; When the decompaction calculation recovers the thickness of the sediment to generate a new extended layer, the bottom age of the newly generated stratum is determined according to the actual drilling data and the geological background; The sedimentation rate of the sediment is calculated according to the recovery thickness of the sediment layer and the deposition time.

3. The method according to claim 1, wherein, The base depth of the ocean-continent transition zone and the ocean basin in different geological periods is quantitatively calculated based on the age-depth conversion model and the ocean-continent transition zone and the oceanic crust age in different geological periods, and the base depth of the ocean-continent transition zone and the ocean basin in different geological periods is corrected by combining the sediment thickness recovered by the decompaction calculation, to calculate the paleo-water depth data of the ocean-continent transition zone and the ocean basin in different geological periods, including: The age of the drilling site is converted into the corresponding base depth of the ocean-continent transition zone and the ocean basin according to the sediment age-depth conversion model formula, and the specific formula is as follows: When the oceanic crust age is less than 20 Ma: ; When the oceanic crust age is greater than 20 Ma: ; wherein, is the basement depth of the ocean-continent transition zone and ocean basin, is the oceanic crust age; The base depth after removing the sediment thickness is calculated according to the influence of the sediment removal on the water depth, and the paleo-water depth data of the ocean-continent transition zone and the ocean basin in different geological periods are obtained.

4. The method according to claim 1, wherein, The tectonic subsidence data of the ocean-continent transition zone and the ocean basin are obtained by selecting the marine subsidence model or the land subsidence model according to the geological background of different drilling sites, including: If the drilling site is located on the marine crust, the marine subsidence model is selected to reverse the subsidence process of the marine crust caused by tectonic action, specifically as follows: The depth of the sediment surface is obtained by using the water depth grid; The isostatic pressure correction is calculated using the average sediment density of the stratum at the drilling site, the current tectonic subsidence is calculated by considering the influence of sediment removal on the depth of the sediment surface, so as to reveal the base depth after removing the sediment, so as to eliminate the compaction effect and obtain more accurate paleo-water depth data; If the drilling site is located on the crust of the land passive margin area, the land subsidence model is selected to reverse the subsidence process of the land crust caused by tectonic action, specifically as follows: The rifting subsidence and thermal subsidence are simulated in turn; The rifting start and end time are determined, the thickness of the sediment is assumed to be zero at the beginning of the rifting, and the initial depth of the sea level is the same as that of the rifting, the stretching of the crust stops at the end of the rifting, and the thermal subsidence starts; The stretching factor is calculated to describe the degree of thinning of the lithosphere during the rifting expansion, the stretching factor changes exponentially between the beginning and the end of the rifting, and the tectonic subsidence during the rifting is calculated.

5. The method according to claim 1, wherein, The influence of the mantle convection on the base depth of the ocean-continent transition zone and the ocean basin is quantified by using the dynamic topographic model, and the paleo-water depth data are adjusted, including: The dynamic topography model is selected to contain time-dependent global grids, wherein the time-dependent global grids are a core component of the dynamic topography model, describe the change of the ground surface elevation in different time periods, especially the ground surface elevation change caused by the mantle convection, and the grids are matched with the historical data of the drilling site, reflecting the ground surface change in the past geological period; The coordinates of the drilling site on the dynamic topography model grid are converted from the modern plate reference system to the past mantle reference system, so as to realize the reconstruction of the drilling site position; After the dynamic topography model grid is matched with the reconstructed drilling site position, the dynamic topography model predicts the ground surface subsidence and adjusts the paleo-water depth data in different geological periods according to the predicted ground surface subsidence.

Images