A paleogeomorphological restoration method based on shelf margin structural trend constraints

Abstract

A paleo-geomorphology restoration method based on the constraint of shelf edge structural trend, belonging to the field of oil and gas geological exploration technology, first, collect three-dimensional seismic data, well logging data, and foraminifera analysis and testing data in the study area; second, establish the second-third order sequence stratigraphic framework in the study area; third, determine the residual stratum thickness in the depth domain of the target layer in the study area; fourth, de-compact and correct the residual stratum thickness to obtain the original stratum deposition thickness; fifth, restore the vertical paleo-water depth at the well point; sixth, restore the planar paleo-water depth data of the target layer during deposition; seventh, superimpose the original stratum deposition thickness on the planar paleo-water depth to restore the paleo-geomorphology during deposition. This method solves the problem of the influence of stratum compaction on thickness, obtains the vertical paleo-water depth data of a single well with higher accuracy, quantifies the planar paleo-water depth distribution, and solves the problem of low accuracy in paleo-geomorphology restoration in the shelf edge-deepwater basin area.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas geological exploration technology, and in particular relates to a paleogeographic restoration method based on the structural trend constraints of the continental shelf margin. Background Technology

[0002] Paleogeomorphological reconstruction is an important part of paleoenvironmental research and sedimentary basin analysis. Paleogeomorphology can effectively reveal characteristics such as source areas, sediment transport channels, sedimentary zones, and the distribution patterns of sedimentary systems. Reconstructing paleogeomorphology, analyzing its impact on sedimentation, and determining its control over hydrocarbon accumulation have become important aspects of oil and gas exploration research.

[0003] Existing research includes patents CN111766630A and CN105425316A, which disclose a paleogeomorphological restoration method based on layer flattening. CN114994748A discloses a paleogeomorphological restoration method combining the imprinting method and the residual thickness method. CN113312695A discloses a paleogeomorphological restoration method combining the residual thickness method and trend surface analysis. CN107991714A discloses a quantitative method for lake basin paleotopographic restoration. CN105652341A discloses a rapid quantitative paleogeomorphological restoration method considering the influence of paleotectonic structures. Wang Xinyi et al., combining the correlation between shoreline trajectory migration patterns and sediment supply rates, quantitatively calculated the changes in paleowater depth in the Weinan Depression delta, ultimately accurately reconstructing the paleogeomorphology of the Weinan Depression delta flow over a period of time. In 2017, Volume 29, Issue 4, "Lithologic Oil and Gas Reservoirs," Wu Aijun et al., starting with sequence stratigraphic studies such as sequence boundary identification and systems tract division, combined with constraints such as compaction correction and paleowater depth correction, used quantitative stratigraphic stripping techniques to reconstruct the paleogeography of different systems tracts in the early stages of deposition. In 2022, Volume 38, Issue 5, "Frontiers in Marine Geology," Shu Liangfeng et al., based on shelf-slope sedimentary characteristics, used a sedimentary configuration technique combining fine seismic line drawing of sedimentary bodies within a third-order sequence framework and flattening of key base surfaces within systems tracts to semi-quantitatively calculate the vertical and planar paleowater depths of five key geological periods in the post-rift stage of the Baiyun Depression. In the process of reconstructing the Pliocene paleogeography of the Yinggehai Basin, Xiao Kunze et al., in Volume 42, Issue 2, 2020, discovered a significant positive correlation between stratigraphic thickness and paleowater depth. Therefore, by using stratigraphic thickness maps and the ratio coefficient between paleowater depth and stratigraphic thickness, combined with single-well data to determine local paleowater depth as a constraint, and applying the "proportional compensation" method, they predicted the distribution of paleowater depth in different periods of the entire region in order to reconstruct the Neogene paleotectonic geomorphology of the Yinggehai Basin.

[0004] After analyzing the above-mentioned existing technologies, the following problems were found: (1) The stratigraphic thickness analysis methods such as the layer flattening method, the imprinting method, and the residual thickness method that have emerged in recent years are mainly used to restore the paleomorphology (including paleowater depth) of the corresponding sedimentary period based on the thickness of different strata. These methods are only applicable to terrestrial sedimentary basins; (2) For marine sedimentary basins, the paleotectonic landform is mainly controlled by the seawater depth. In the current paleowater depth restoration technology, it is easy to obtain the paleowater depth data of a single well in the vertical direction by using well logging and paleontological markers. However, the problem of the distribution of paleowater depth in the region has not been effectively solved; (3) The method of restoring paleowater depth by stratigraphic thickness is essentially to use the linear relationship between the initial stratigraphic thickness and the paleowater depth to quantitatively restore the paleowater depth. However, the stratigraphic thickness is affected by many factors such as differential subsidence. Therefore, the stratigraphic thickness can only reflect water depth information when the differential subsidence is negligible. This method lacks consideration of the influence of tectonics on paleowater depth. Summary of the Invention

[0005] The purpose of this invention is to provide a paleogeographic restoration method based on the constraints of tectonic trends at the shelf margin, thereby addressing the problem in existing technologies that cannot accurately and quantitatively restore paleogeography in the shelf margin-deep-water basin region. This method not only considers the impact of differential compaction on thickness but also quantitatively obtains vertical paleowater depth data from a single well by measuring the percentage of planktonic foraminifera. Most importantly, it quantifies the planar distribution of paleowater depth by utilizing the relationship between tectonic trends and paleowater depth, solving the problem of quantitative restoration of paleowater depth in the shelf margin-deep-water basin region. This achieves a shift from qualitative to quantitative methods in paleogeographic restoration of the shelf margin-deep-water basin region, making the restoration results more accurate and reliable.

[0006] The technical solution adopted in this invention is:

[0007] A paleogeomorphological restoration method based on shelf margin tectonic trend constraints includes the following steps:

[0008] Step 1: Collect 3D seismic data, well logging data, and foraminifera analysis and testing data from all wells in the study area;

[0009] Step 2: Detailed interpretation of 3D seismic data for the study area, and establishment of a second- to third-order sequence stratigraphic framework;

[0010] Step 3: Based on the establishment of the sequence stratigraphic framework, select marker beds and determine the residual stratigraphic thickness in the target depth domain of the study area;

[0011] Step 4: Perform decompaction correction on the residual stratum thickness in the target layer depth domain to obtain the original stratum deposition thickness;

[0012] Step 5: Select the percentage content data of planktonic foraminifera from the foraminifera analysis and test data, and reconstruct the vertical paleowater depth data at the well point based on the relationship between the percentage content of planktonic foraminifera and water depth.

[0013] Step 6: Establish the correspondence between paleowater depth and top structural interface depth to obtain the paleowater depth trend surface; and correct the paleowater depth trend surface based on the residual of paleowater depth at the well point to obtain planar paleowater depth data of the target layer deposition period in the study area.

[0014] Step 7: Overlay the original stratum thickness onto the plane paleowater depth to obtain a paleogeographic map of the target stratum during its deposition period.

[0015] Furthermore, in step two, the method for establishing a second- to third-order sequence stratigraphic framework is as follows: based on regional tectonic and stratigraphic development characteristics, and based on the results of single-well sequence stratigraphic analysis, single-well combined synthetic seismic records are produced. The main isochronous interfaces are identified, tracked, and closed through fine calibration of the synthetic seismic records and layer tracing interpretation techniques. The properties of each isochronous interface are determined, the level of each layer boundary is clarified, and a second- to third-order sequence stratigraphic framework is established.

[0016] Furthermore, in step three, the method for determining the residual stratum thickness in the target layer depth domain of the study area is as follows:

[0017] 1) Calculate the time-domain structural map of the top and bottom interfaces of the target layer: Based on the establishment of the sequence stratigraphic framework, select the in-phase axis on the seismic profile that shows strong amplitude, high frequency, good continuity and any of the phenomena of overshoot, undercut or truncation as the top and bottom interfaces of the target layer in the study area; use the Geometry algorithm to interpolate the selected and interpreted top and bottom interfaces to obtain the time-domain structural maps M1 and M2 of the top and bottom interfaces of the target layer.

[0018] 2) Calculation of the depth domain structure map of the top and bottom interface of the target layer: Depth and time data from several wells within the study area were selected, and numerical fitting was performed using both linear and nonlinear methods. Based on the fitting results, the method with higher fitting accuracy was selected as the time-depth relationship. The linear and nonlinear relationships are as follows:

[0019] W=a1Q+a2

[0020] W=b1Q p +b2Q p-1 +b3Q p-2 +…+b p+1， Where p≥2,

[0021] In the formula: Q represents time, in milliseconds (ms); W represents depth, in meters (m); a1, a2, b1, b2, b3, ..., b p+1 These are undetermined coefficients, dimensionless;

[0022] Substituting the time-domain construction diagrams M1 and M2 of the top and bottom interfaces of the target layer into the time-depth relation (substituting the time-domain construction diagrams into the relation means substituting the construction depths T1 and T2 (time domain) of the top and bottom interfaces of the target layer M1 and M2 into the relation to obtain the depth-domain construction diagrams M3 and M4, with corresponding construction depths D1 and D2 (depth domain)), the depth-domain construction diagrams M3 and M4 corresponding to the top and bottom interfaces of the target layer are calculated.

[0023] 3) Calculate the residual formation thickness map of the target layer depth domain: Obtain the residual formation thickness D0 of the target layer depth domain by subtracting the depths of the top and bottom interfaces. The calculation formula is: D0 = D1 - D2, where D0 represents the residual formation thickness of the target layer depth domain, D1 represents the depth of the bottom interface of the target layer, and D2 represents the depth of the top interface of the target layer. The units of D0, D1, and D2 are all meters.

[0024] Furthermore, in step four, the method for determining the original stratum thickness is as follows:

[0025] 1) The porosity data from core analysis and well logging interpretation of different rock types in the study area were fitted using an exponential function distribution to obtain the relationship between burial depth (H) and porosity (Ф) for different lithologies:

[0026] ;

[0027] In the formula: Ф is the porosity at depth H, a decimal, dimensionless; C is the initial porosity of the earth's surface, a decimal, dimensionless; C is the compaction coefficient, with units of m. -1 H represents the burial depth of the strata, and its unit is meters (m).

[0028] 2) Solve for the compacted burial volume based on the integral equation of the rock skeleton:

[0029] ;

[0030] Where h1 is the current burial depth of the top surface of the strata, in meters; h2 is the current burial depth of the bottom surface of the strata, in meters; and h is the compacted burial volume, in meters.

[0031] Given the current top and bottom burial depths of the strata, the integral equation of the rock skeleton is calculated using Matlab software to determine the compaction burial volume h; then, the original stratum deposition thickness (referring to the stratum thickness that has just finished deposition and has not yet undergone compaction) H0 of each small layer of sand and mudstone in a single well is obtained according to the calculation formula H0=h2-h1+h.

[0032] Subsequently, based on the ratio of the original formation thickness to the current residual formation thickness, the compaction rate t of each sub-layer in a single well is calculated, where t = H0 / (h2 - h1).

[0033] The wellpoint compaction rate of all wells in the study area was calculated sequentially according to the methods in 1)~2). Then, the wellpoint compaction rate of all wells was interpolated using the Kriging algorithm with Petrel software to obtain the planar compaction rate k of the entire study area.

[0034] 3) Multiplying the planar compaction rate k by the current depth domain residual stratum thickness D0 yields the original stratum depositional thickness D of the study area; the calculation formula is as follows: Where k represents the plane compaction rate of the target layer, and D represents the original sedimentary thickness of the target layer, with the unit being m.

[0035] Furthermore, in step five, the method for determining the vertical paleowater depth at the well point is as follows:

[0036] The study found that the percentage of planktonic foraminifera, P, and water depth, d, have significantly different relationships between the shelf edge and deep-sea basin regions: for the shelf region with a water depth of less than 200m, the two satisfy a logarithmic relationship, while for the slope-deep-sea region with a water depth of more than 200m, the two satisfy a linear relationship.

[0037] Based on the location of each well in the study area and the percentage of planktonic foraminifera in the target layer, the corresponding formula can be selected and substituted to obtain the vertical paleowater depth data at each well point in the study area.

[0038] Furthermore, in step six, planar paleowater depth data for the depositional period of the target layer in the study area are obtained using the following method:

[0039] 1) On the target layer top interface depth domain structure map M3 in step three, select a total of n well points (n≥10) containing planktonic foraminifera percentage data from the shelf area, slope area to deep water basin area according to the structural trend from high to low.

[0040] 2) Read the structural depth and paleowater depth data corresponding to n well points, and fit the paleowater depth data and structural depth to obtain the fitting formula: In the formula: X is the tectonic depth, in meters; Y is the paleowater depth, in meters; c and f are undetermined coefficients, dimensionless;

[0041] Then, by substituting the structural depth M3 of the top interface of the target layer in step three, the paleowater depth trend surface S of the study area during this period can be obtained.

[0042] 3) Wellpoint paleodepth residual correction: Subtract the paleodepth data at n wellpoints on the paleodepth trend surface from the vertical paleodepth data at the wellpoints obtained in step five to obtain the paleodepth residual data CC at the n wellpoints. i ,

[0043] Its calculation formula is: CCi =S i -d i， Where i = 1, 2, 3, ..., n, and S i d represents the paleodepth data at the i-th well point on the paleodepth trend surface. i This represents the vertical paleowater depth data at the i-th well point obtained in step five.

[0044] 4) Planar paleodepth residual correction: First, the paleodepth residual data at the well points are interpolated using the Kriging algorithm to obtain the residual trend surface; then, the paleodepth trend surface is subtracted from the residual trend surface to obtain the final planar paleodepth data HH.

[0045] The calculation formula is: HH=S-CC, where S represents the paleodepth trend surface and CC represents the residual trend surface.

[0046] The present invention has the following beneficial effects:

[0047] This invention not only effectively utilizes the content of planktonic foraminifera in analytical data to quantitatively obtain vertical paleowater depth data for a single well; but also, building upon previous methods of reconstructing planar paleowater depth through stratigraphic thickness, considers the influence of paleotectonic structures on paleowater depth, constraining it using tectonic trends and resolving the distribution problem of planar paleowater depth; finally, by overlaying the original stratigraphic sedimentary thickness onto the reconstructed paleogeography, the final reconstructed paleomorphology can reflect relative micro-geomorphological features. This provides a framework for paleowater depth reconstruction in shelf margin-deep-water basins across various sedimentary periods and significantly improves the accuracy of paleogeographic reconstruction in marine basins. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a flowchart of the method of the present invention;

[0049] Figure 2 This is a schematic diagram of the isochronous stratigraphic grid of the present invention;

[0050] Figure 3 This is a schematic diagram of the porosity-depth relationship fitted to different lithologies in the decompaction correction of this invention;

[0051] Figure 4 This invention provides the structural model and compaction rate calculation for each single well sandstone and mudstone rock.

[0052] Figure 5 This invention provides a comprehensive paleowater depth bar chart for a single well, established using the relationship between the percentage content of planktonic foraminifera and the paleowater depth function.

[0053] Figure 6 This is a schematic diagram illustrating the selection of control points based on the top surface structural trend in this invention;

[0054] Figure 7This is a quantitative relationship diagram between the paleowater depth of the key well in the Lingshui Depression and the structural depth of the second member of the Meishan Formation in an embodiment of the present invention;

[0055] Figure 8 This is a predicted paleowater depth map of the Meishan Formation II in the Lingshui Depression during the depositional period, as described in this embodiment of the invention.

[0056] Figure 9 This is a paleowater depth residual trend diagram during the depositional period of the second member of the Meishan Formation in the Lingshui Depression, as described in this embodiment of the invention.

[0057] Figure 10 This is a paleowater depth prediction map of the final depositional period of the Meishan Formation II in the Lingshui Depression, as shown in this embodiment of the invention.

[0058] Figure 11 This is a paleogeographic reconstruction map of the second member of the Meishan Formation in the Lingshui Depression during the depositional period, as described in this embodiment of the invention. Detailed Implementation

[0059] In this example, through systematic analysis of 3D seismic data from the Lingshui Depression in the Qiongdongnan Basin, seismic profiles and paleontological fossils since the Middle Miocene clearly record the location of the shelf slope break. Comparison with current seawater depths and seafloor structural maps reveals a significant positive correlation between seafloor structure and seawater depth: areas with greater paleowater depths have lower structural locations, and the distribution of paleowater depths in the basin largely matches the distribution of seafloor structures. Therefore, based on the determination of vertical paleowater depths from a single well, this invention proposes using the top structural interface of each depositional period as a constraint. The relationship between paleowater depth and the depth of the top structural interface is used to reconstruct the paleowater depth of the Meishan Formation II in the study area for different depositional periods, thereby accurately reconstructing the paleogeography of the Meishan Formation II before deposition.

[0060] The recovery process is as follows Figure 1 As shown, it specifically includes the following seven steps:

[0061] Step 1: Collect 3D seismic data, well logging data, and foraminifera analysis data from all wells in the target block of the Lingshui Depression in the southeastern Qiongzhou Basin.

[0062] Step 2: Based on the characteristics of second- to third-order seismic sequence interfaces, using a combination of well and seismic data, identify and trace the main seismic reflection interfaces such as T40, T41, and T50, and establish a second- to third-order sequence stratigraphic framework for the Lingshui Depression based on this. (See...) Figure 2 As shown;

[0063] Step 3: Based on the establishment of the sequence stratigraphic framework, select marker beds and determine the research...

[0064] The specific method for determining the residual stratum thickness in the target layer depth area is as follows:

[0065] 1) Calculate the time-domain structural map of the top and bottom interfaces of the target layer: Based on the establishment of the sequence stratigraphic framework, select the in-phase axes T41 and T50 on the seismic profile that exhibit strong amplitude, high frequency, good continuity, and any phenomenon such as overshoot, undercut, or truncation as the top and bottom interfaces of the target layer in the study area; use the Geometry algorithm to interpolate the selected and interpreted top and bottom interfaces to obtain the time-domain structural maps M1 and M2 of the top and bottom interfaces of the target layer;

[0066] 2) Calculation of the depth domain structure map of the top and bottom interface of the target layer: Linear numerical fitting was performed on the depth and time data of three wells in the study area to obtain the time-depth relationship curve: W=1.6602Q-1118.2, where: Q is time in ms; W is depth in m; Based on the time-depth relationship, the time domain structure maps M1 and M2 of the top and bottom interface of the target layer were substituted into the calculation to obtain the depth domain structure maps M3 and M4 corresponding to the top and bottom interface of the target layer.

[0067] 3) Calculate the residual formation thickness map of the target layer depth domain: Obtain the residual formation thickness D0 of the target layer depth domain by subtracting the top and bottom interfaces. The calculation formula is: D0=D1-D2, where D0 represents the residual formation thickness of the target layer depth domain, D1 represents the depth of the bottom interface of the target layer, and D2 represents the depth of the top interface of the target layer; the units of D0, D1, and D2 are all m.

[0068] Step 4: Decompact and correct the residual strata thickness in the target layer depth region to obtain the original strata deposition thickness. Specific procedures are as follows:

[0069] 1) The second member of the Meishan Formation in the Lingshui Depression mainly consists of silty mudstone, silty mudstone, and mudstone. Through statistical analysis of core porosity and well logging interpretation data for these three different rock types, porosity-depth relationship curves for these three lithologies were established. (See...) Figure 3 As shown;

[0070] (1)

[0071] (2)

[0072] (3)

[0073] In the formula: Ф is the porosity at depth H, a decimal, dimensionless; H is the burial depth of the stratum, in meters (m).

[0074] 2) Solve for the compacted burial volume based on the integral equation of the rock skeleton:

[0075] (4)

[0076] Where h1 is the current burial depth of the top surface of the strata (m), h2 is the current burial depth of the bottom surface of the strata (m), and h is the compacted burial volume (m). Given the current burial depths of the top and bottom surfaces of the strata, the compacted burial volume h is calculated using the above integral equation via Matlab software, thus obtaining the original stratum thickness H0 of the sandstone and mudstone of the second member of the Meishan Formation in a single well. Then, based on the ratio of the original stratum thickness to the current residual stratum thickness, the compaction rate t of each sub-layer in the single well is calculated. The calculated compaction rate of a single well is generally between 1.1 and 1.15. Finally, using the wellpoint compaction rate of all wells in the study area as a reference, the planar compaction rate of the entire study area is obtained by interpolation using the Kriging algorithm. Figure 4 As shown;

[0077] 3) By multiplying the plane compaction rate by the current depth domain residual stratum thickness, the original stratum depositional thickness of the study area can be obtained;

[0078] Step 5: Select the percentage of planktonic foraminifera from the foraminifera analysis data, and reconstruct the vertical paleowater depth at the well point based on the relationship between the percentage of planktonic foraminifera and water depth. Specific procedures are as follows:

[0079] The study found that the percentage of planktonic foraminifera (P) and water depth (d) have significantly different relationships between the shelf margin and the deep-sea basin; for shelf areas with water depths less than 200m, the two follow a logarithmic relationship.

[0080] P = 46.89lnd - 150.38 (5)

[0081] In the continental slope-deep-sea region where the water depth is greater than 200m, the two satisfy a linear relationship:

[0082] P = -0.0019d + 99.03 (6)

[0083] In the formula, P is the percentage of planktonic foraminifera, and its unit is %, and d is the water depth, and its unit is m;

[0084] The Meishan Formation II in the Lingshui Depression is generally a shallow-marine to semi-deep-marine sedimentary environment. The study area is located in the shelf area above the slope break zone, with a water depth of less than 200m, making it suitable for using equation (5) to reconstruct paleowater depth. Substituting the percentage of planktonic foraminifera in the analytical data of 10 wells in the Meishan Formation II of the study area into equation (5), the vertical paleowater depth data at each well point of the 10 wells were calculated. See Figure 5 As shown;

[0085] Step Six: Establish the correspondence between paleowater depth and the top structural interface depth to obtain the paleowater depth trend surface; and correct the paleowater depth trend surface based on the residual paleowater depth at the well point to obtain planar paleowater depth data for the depositional period of the target layer in the study area. Specific procedures are as follows:

[0086] 1) On the structural map M3 of the target layer top interface depth domain in step three, a total of 10 well points containing data on the percentage content of planktonic foraminifera were selected from the shelf area, slope area to deep-water basin area according to the structural trend from high to low. See Figure 6 As shown;

[0087] 2) Read the structural depth and paleowater depth data corresponding to 10 well points, and fit the paleowater depth data and structural depth to obtain the fitting formula: Y=116.61e 0.0001X In the formula: X is the tectonic depth, in meters; Y is the paleowater depth, in meters. (See [reference needed]). Figure 7 As shown;

[0088] Then, substituting the structural depth M3 of the top interface of the target layer in step three into the equation yields the paleowater depth trend surface S of the study area during this period. (See...) Figure 8 As shown;

[0089] 3) Wellpoint paleodepth residual correction: The paleodepth data at 10 wellpoints on the paleodepth trend surface are subtracted from the paleodepth data in the vertical direction of each wellpoint obtained in step five to obtain the paleodepth residual data CC at the 10 wellpoints. i ,See Figure 9 As shown, its calculation formula is: CC i =S i -d i， Where i = 1, 2, 3, ... 10, and S i d represents the paleodepth data at the i-th well point on the paleodepth trend surface. i This represents the vertical paleowater depth data at the i-th well point obtained in step five.

[0090] 4) Planar paleodepth residual correction: First, the paleodepth residual data at the well points are interpolated using the Kriging algorithm to obtain the residual trend surface; then, the paleodepth trend surface is subtracted from the residual trend surface to obtain the final planar paleodepth data HH, calculated as: HH = S - CC, where S represents the paleodepth trend surface and CC represents the residual trend surface. (See...) Figure 10 As shown.

[0091] Step 7: By superimposing the original stratigraphic thickness onto the planar paleowater depth, the paleogeography of the Meishan Formation II in the Lingshui Depression of the Qiongdongnan Basin during its depositional period can be obtained. (See...) Figure 11 As shown.

Claims

1. A paleo-geomorphology restoration method based on shelf edge structural trend constraints, characterized in that: The following steps are involved: Step 1: Collect 3D seismic data, well logging data, and foraminifera analysis data from all wells in the study area; Step 2: Finely interpret the 3D seismic data in the study area and establish the second- and third-order sequence stratigraphic framework; Step 3: Based on the established sequence stratigraphic framework, select the marker layer and determine the residual stratigraphic thickness in the depth domain of the target layer in the study area; Step 4: decompact and correct the residual formation thickness in the depth domain of the target layer to obtain the original formation deposition thickness; Step 5: Select the planktonic foraminifera percentage data in the foraminifera analysis test data, and restore the vertical paleo-water depth data at the well point based on the relationship between the planktonic foraminifera percentage and the water depth; Step 6: Establish the corresponding relationship between the paleo-water depth and the depth of the top structural interface to obtain the paleo-water depth trend surface; and correct the paleo-water depth trend surface according to the residual of the paleo-water depth at the well point to obtain the planar paleo-water depth data of the target layer in the study area during the deposition period. The method used is: S601: On the depth domain structural map M3 of the top interface of the target layer in step 3, a total of n well points containing planktonic foraminifera percentage data are selected from the shelf area, the slope area to the deep water basin area according to the structural trend from high to low; S602: Read the structural depth and paleo-water depth data corresponding to n well points, and fit the paleo-water depth data and structural depth to obtain the fitting formula: Y = c * e fX , where: X is the structural depth, its unit is m; Y is the paleo-water depth, its unit is m; c and f are the unknown coefficients, dimensionless; Then substitute the structural depth M3 of the top interface of the target layer in step 3 to obtain the paleo-water depth trend surface S of the study area during this period; S603: Well point paleo-depth residual correction: The paleo-depth data at n well points on the paleo-depth trend surface are subtracted from the paleo-depth data at the well points in the vertical direction obtained in step 5 to obtain the paleo-depth residual data CC at n well points. i , the calculation formula is: CC i =S i -d i (i=1,2,3,…,n), where S i represents the paleo-water depth data at the i-th well point on the paleo-water depth trend surface, d i represents the vertical paleo-water depth data at the i-th well point calculated in step 5; S604: Plane paleo-water depth residual correction: First, the paleo-water depth residual data at the well point are interpolated using the Kriging algorithm to obtain a residual trend surface; then the paleo-water depth trend surface is subtracted from the residual trend surface to obtain the final planar paleo-water depth data HH, and the calculation formula is: HH = S-CC, where S represents the paleo-water depth trend surface and CC represents the residual trend surface; Step 7: Superimpose the original stratum sedimentary thickness on the planar paleo-water depth to obtain the paleo-geomorphological map of the target layer during its deposition period.

2. A paleo-geomorphology restoration method based on shelf edge structural trend constraints as claimed in claim 1, characterized in that: In step 2, the method for establishing a secondary to tertiary sequence stratigraphic framework is as follows: based on the regional structural and stratigraphic development characteristics and the results of single-well sequence stratigraphic analysis, a single-well synthetic seismic record is produced, and the main isochronous interfaces are identified, tracked and closed through fine calibration of synthetic seismic records and stratigraphic tracing interpretation technology, the properties of each isochronous interface are determined, the level of each layer boundary is clarified, and a secondary to tertiary sequence stratigraphic framework is established.

3. A paleo-geomorphology restoration method based on shelf edge structural trend constraints as claimed in claim 1, characterized in that: In step 3, the method for determining the residual stratum thickness in the depth domain of the target layer in the study area is: S301: Calculate the time domain structural map of the top and bottom interfaces of the target layer: On the basis of the establishment of the sequence stratigraphic framework, select the event axis with strong amplitude, high frequency, good continuity and any of the phenomena of onlap, downcut or truncation on the seismic section as the top and bottom interfaces of the target layer in the study area; use the Geometry algorithm to interpolate the selected interpreted top and bottom interfaces to obtain the time domain structural maps M1 and M2 of the top and bottom interfaces of the target layer; S302: Calculate the depth domain structural map of the top and bottom interfaces of the target layer: Select the bathymetric and time data of several wells in the study area, perform numerical fitting in linear and nonlinear forms, and then select the form with higher fitting accuracy as the time-depth relationship based on the fitting results. The linear and nonlinear relationship are respectively: W=a1Q+a2 W=b1Q p +b2Q p-1 +b3Q p-2 +…+b p+1 (p≥2) Where: Q is time, its unit is ms; W is depth, its unit is m; a1, a2, b1, b2, b3, ..., b p+1 are the unknown coefficients, dimensionless; Substitute the time domain structural diagrams M1 and M2 of the top and bottom interfaces of the target layer into the time-depth relationship to calculate the depth domain structural diagrams M3 and M4 corresponding to the top and bottom interfaces of the target layer; S303: Calculate the residual formation thickness map of the target layer depth domain: obtain the residual formation thickness D0 of the target layer depth domain by subtracting the top and bottom interface depths. The calculation formula is: D0=D1-D2, where D0 represents the residual formation thickness of the target layer depth domain, D1 represents the depth of the bottom interface of the target layer, and D2 represents the depth of the top interface of the target layer.

4. A paleo-geomorphology restoration method based on shelf edge structural trend constraints as claimed in claim 1, characterized in that: In step 4, the method for determining the original stratum sediment thickness is: S401: The porosity of core analysis of different rock types in the study area and the porosity data interpreted by logging are fitted according to the exponential function distribution to obtain the relationship between burial depth and porosity of different lithologies: Ф=Ф0exp(-C*H) Where: Ф is the porosity at depth H, in decimal; Ф0 is the initial porosity at the surface, in decimal; C is the compaction coefficient, in m -1 ; H is the burial depth of the formation, its unit is m; S402: Solve the compaction burial volume based on the rock skeleton integral equation: Among them, h1 is the top burial depth of the current stratum, the unit is m, h2 is the bottom burial depth of the current stratum, the unit is m, and h is the compacted burial volume, the unit is m; When the top and bottom burial depths of the current strata are known, the rock skeleton integral equation is calculated to find the compacted burial volume h; then the original stratum deposition thickness H0 of each small layer of sand and mudstone in a single well is obtained according to the calculation formula H0=h2-h1+h; Then, the compaction rate t of each small layer in a single well is calculated based on the ratio of the original formation thickness to the current residual formation thickness, where t = H0 / (h2-h1); According to the methods of S401 to S402, the well point compaction rates of all wells in the study area are calculated in sequence, and then the well point compaction rates of all wells are interpolated using the Kriging algorithm using the Petrel software to obtain the plane compaction rate k of the entire study area; S403: By multiplying the plane compaction rate k with the residual stratum thickness D0 in the current depth domain, the original stratum deposition thickness D of the study area can be obtained; the calculation formula is: D=D0*k, where k represents the plane compaction rate of the target layer, and D represents the original stratum deposition thickness of the target layer, and its unit is m.

5. The paleo-geomorphology restoration method based on shelf edge structural trend constraint according to claim 1, characterized in that: In step 5, the method for determining the vertical ancient water depth at the well point is: The percentage of planktonic foraminifera P and water depth d have significantly different relationships between the shelf edge and deep sea basin areas: for the shelf area with a water depth of less than 200m, the two satisfy a logarithmic relationship, and for the slope-deep sea area with a water depth of more than 200m, the two satisfy a linear relationship; According to the location of each well in the study area and the percentage of planktonic foraminifera in the target layer, the corresponding relationship can be selected to obtain the vertical paleo-water depth data at each well point in the study area.

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