Method for quantitatively recovering lake plane change based on coastal slope fracture trajectory

Abstract

The invention provides a method for quantitatively recovering lake plane change based on a coastal slope fracture trajectory. The method comprises the following steps: S1, constructing a sequence stratigraphic framework; s2, identifying a filling and finishing interface on the seismic section, performing layer leveling, identifying a lower super surface, taking a position with the maximum deposition thickness between the lower super surface and the filling and finishing interface as a basin center, taking a corresponding point of the basin center on the lower super surface as a reference point, and taking a horizontal plane corresponding to the reference point as a lower reference surface; s3, determining a coastal slope break point on the seismic section; s4, obtaining the thickness of a front lamination layer between each shoreside slope break point and the lower super surface; and S5, obtaining the stratum thickness between the projection point of each shoreside slope break point on the lower super surface and the lower reference surface, and summing the stratum thickness with the corresponding pre-lamination thickness to obtain relative lake plane depth data, thereby establishing a relative lake plane change curve. According to the method, the quantitative change curve of the lake plane can be obtained, the used data are easy to obtain, and the result accuracy is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of petroleum geology analysis, and relates to a method for quantitatively recovering lake level change based on shore slope break trajectory. BACKGROUND

[0002] The change of the paleo-lake level is an important basis for understanding the evolution of the past lacustrine basin, the change of the paleo-climate and the change of the paleo-environment, and has been a research hotspot in the field of sequence stratigraphy and sedimentary geology analysis. Compared with marine basins, the scale of a lake basin is generally smaller, and the response of the filling structure to the lake level change is more obvious. Meanwhile, the lake level change directly controls the type and distribution of lacustrine deposition, and is closely related to the spatial distribution of oil and gas reservoirs.

[0003] At present, it is still difficult to recover the lake level change in the geological history period, and the main methods include qualitative analysis and semi-quantitative-quantitative calculation. The qualitative analysis includes the methods of sedimentology, trace element ratio, paleo-fossils and Fischer diagram. The sedimentology mainly obtains the approximate range of the paleo-water depth according to the lithology, sedimentary structure and paleo-object data and basin denudation history stripping. The trace element ratio method can distinguish the sedimentary environment, but reflects the relative change of the water depth. The distribution range of the paleo-fossils changes greatly, and the uncertainty is high. The Fischer diagram obtains the relative lake level change curve, which also has no quantitative significance. The semi-quantitative-quantitative recovery mainly applies the cobalt element calculation. However, the method is greatly affected by the parameter value, and is limited by the difficulty in obtaining a large amount of test analysis data, so it is difficult to obtain a relatively continuous lake level change curve. SUMMARY

[0004] The purpose of the application is to provide a method for quantitatively recovering the lake level change based on the shore slope break trajectory, which can obtain the quantitative change curve of the lake level, and the data used is easy to obtain, thereby avoiding the influence of the parameter value on the calculation result in the process of the indirect calculation of multiple factors to a certain extent.

[0005] The application is implemented by the following technical scheme:

[0006] A method for quantitatively recovering the lake level change based on the shore slope break trajectory, comprising the following steps:

[0007] S1, constructing a sequence stratigraphic framework according to a seismic profile; or, constructing a sequence stratigraphic framework in combination with the seismic profile and drilling data of a drilled well;

[0008] S2, identifying a filling and filling interface on the seismic profile based on the sequence stratigraphic framework, layering the filling and filling interface, identifying a onlap surface, taking the position with the maximum sediment thickness between the onlap surface and the filling and filling interface as a basin center, taking the corresponding point of the basin center on the onlap surface as a reference point, and taking the horizontal plane corresponding to the reference point as a lower reference surface.

[0009] S3, determining a shoreface break point on the seismic profile;

[0010] S4, obtaining progradation layer thickness between each shoreface break point and the onlap surface;

[0011] S5, obtaining stratum thickness between the projection point of each shoreface break point on the onlap surface and the base level, summing up with the corresponding progradation layer thickness to obtain relative lake level depth data, establishing a relative lake level change curve with stratigraphic sequence as the horizontal coordinate and relative lake level depth data as the vertical coordinate.

[0012] Preferably, in S1, if there is logging data, then a sequence stratigraphic framework is constructed in combination with the seismic profile through the well and the well logging data, otherwise, a sequence stratigraphic framework is constructed according to the seismic profile.

[0013] Preferably, in S1, a sequence stratigraphic framework is constructed in combination with the seismic profile through the well and the well logging data, specifically: selecting the seismic profile through the well, carrying out single-well sequence boundary division on the well to identify the flooding surface; carrying out well-to-seismic calibration to determine the corresponding positions of each flooding surface on the seismic profile, carrying out sequence stratigraphic correlation interpretation based on well-to-seismic calibration to construct a high-precision sequence stratigraphic framework.

[0014] Preferably, in S1, if there is dating data constraint, then the development time limit of the stratigraphic unit in the sequence stratigraphic framework is determined.

[0015] Preferably, in S3, if there is well logging data, then the shoreface break point is determined in combination with the well logging data and the seismic profile, otherwise, the shoreface break point is determined according to the seismic profile.

[0016] Further, the shoreface break point is determined in combination with the well logging data and the seismic profile, specifically: according to the well logging data, taking the conversion position of the distributary channel and the river mouth bar as the shoreface break point, and taking the topset layer on the upper part of the progradation reflection interface and the progradation layer slope mutation point on the seismic profile as the shoreface break point.

[0017] Further, the shoreface break point is determined according to the seismic profile, specifically: taking the topset layer on the upper part of the progradation reflection interface and the progradation layer slope mutation point on the seismic profile as the shoreface break point.

[0018] Preferably, S4 further comprises: obtaining bottomset layer thickness between the lowest part of the flooding surface where each shoreface break point is located and the onlap surface;

[0019] S5 further comprises: subtracting the corresponding bottomset layer thickness from the relative lake level depth data to obtain maximum paleo-water depth data, establishing a maximum paleo-water depth change curve with stratigraphic sequence as the horizontal coordinate and maximum paleo-water depth data as the vertical coordinate.

[0020] Further, the thickness of the bottom-accumulation layer between the lowest part of the lake flooding surface where the coastal slope break point is located and the downlap surface is obtained, specifically: the thickness of the sedimentary stratum between the lowest part of the lake flooding surface where the coastal slope break point is located and the downlap surface is counted, and the decompaction correction is performed to obtain the thickness of the bottom-accumulation layer.

[0021] Preferably, S4 is specifically: the thickness of the sedimentary stratum between the coastal slope break point and the downlap surface is counted, and the decompaction correction is performed to obtain the thickness of the progradation layer.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] In recent years, with the progress and wide application of two-dimensional and three-dimensional seismic acquisition technology, new progress has been made in seismic stratigraphy and sequence stratigraphy, especially with the continuous improvement of the resolution capability of high-quality three-dimensional seismic, which provides a basis for the establishment of high-precision isochronous stratigraphic framework, which also makes it possible to reconstruct the lake level change by using the response of the lake basin stratum filling structure. Therefore, the present application proposes a quantitative recovery method of lake level change under the joint constraint of the coastal slope break trajectory and the stratum structure. According to the progradation layer structure in the lake basin, the present application establishes a quantitative recovery method of lake level change based on the migration characteristics of the coastal slope break point and considering the position of the basin center reference point. The advantage of the method is that the basic data is relatively easy to obtain, and to some extent, the influence of the key parameter value in the fitting formula or empirical relationship on the result is reduced, and by determining the reference point, the influence of the change of the ancient bottom shape of the lake basin in different regions on the water depth recovery is avoided, thereby improving the accuracy of the quantitative calculation of the lake level. Compared with the methods of biology, sedimentology and geochemistry, the required drilling and seismic data are easy to obtain, and the calculation is based on the geometric structure characteristics of the stratum, which to some extent avoids the great influence of the parameter value on the calculation result in the indirect calculation process of multiple factors.

[0024] Further, if there is drilling data, the coastal slope break point is determined in combination with the drilling data and the seismic profile, so that the position of the determined coastal slope break point is more accurate, and the accuracy of the result of the present application can be improved.

[0025] Further, the method of the present application can obtain the quantitative change curves of the lake level and the maximum ancient water depth at the same time, and the two are comprehensive, which provides a basis support for the research on the filling evolution process and mechanism of the continental lake basin.

[0026] Further, the decompaction correction is performed on the thickness of the sedimentary stratum between the coastal slope break point and the downlap surface, so that the thickness of the progradation layer obtained is closer to the original thickness of the progradation layer, thereby making the result obtained by the present application more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0027] 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 in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0028] Figure 1 Sequence interface division and well-seismic calibration schematic diagram;

[0029] Figure 2 Seismic filling and reference point position leveling schematic diagram;

[0030] Figure 3 Drilling sedimentary facies microfacies identification and shore slope break point position schematic diagram;

[0031] Figure 4 Sedimentary filling structure and various parameter change schematic diagram;

[0032] Figure 5 Relative lake level and maximum paleo-water depth recovery schematic diagram. DETAILED DESCRIPTION

[0033] The present application will be described in more detail by the following specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. The present application can also be implemented or applied by different specific embodiments, and various modifications or changes can be made to the details in the specification without departing from the spirit of the present application.

[0034] It should be noted that the process equipment or device not specifically mentioned in the following examples is the conventional equipment or device in the art.

[0035] It should be noted that the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not a limitation on the arrangement order of each method step or a limitation on the scope of the present application. Changes or adjustments of the relative relationship, without substantial changes in technical content, are also considered as the scope of the present application.

[0036] The method for quantitatively recovering lake level change based on shore slope break trajectory according to the present application comprises the following steps:

[0037] (1) Establishing a sequence stratigraphic framework

[0038] The sequence stratigraphic framework is constructed according to a seismic profile, or in combination with a seismic profile and drilling data of a drilled well.

[0039] If there is logging data, the sequence stratigraphic framework is constructed in combination with a seismic profile and drilling data of a drilled well, otherwise, the sequence stratigraphic framework is constructed according to a seismic profile.

[0040] The sequence stratigraphic framework is constructed in combination with a seismic profile and drilling data of a drilled well, specifically: a seismic profile of the drilled well is selected, single-well sequence boundary division is carried out on the well, and the position of a lake flooding surface or a water flooding surface is identified; on the basis of the single-well sequence boundary division and the lake flooding surface identification, well-seismic calibration is carried out, the corresponding positions of each lake flooding surface on the seismic profile are determined, sequence stratigraphic correlation interpretation based on well-seismic calibration is carried out, a high-precision sequence stratigraphic framework is constructed, and if there is dating data constraint, the development time limit of a stratigraphic unit in the sequence stratigraphic framework can be further determined.

[0041] (2) Determining a datum point

[0042] Based on the sequence stratigraphic framework, a fill-up and make-up boundary surface is identified on the seismic profile, the fill-up and make-up boundary surface is layer-flattened, an onlap surface is identified, the position with the maximum sedimentary thickness between the onlap surface and the fill-up and make-up boundary surface is taken as a basin center, and the corresponding point of the basin center on the onlap surface is taken as a datum point. The horizontal plane corresponding to the datum point is a lower datum plane.

[0043] (3) Depiction of shoreface slope break migration trajectory

[0044] According to the drilling data, the conversion position of a distributary channel and a river mouth bar is taken as a shoreface slope break point, the topset layer and the slope break point of the foreset layer on the topset reflection boundary surface on the seismic profile are taken as the shoreface slope break point, the positions of different period shoreface slope break points in different stratigraphic units are determined through comprehensive analysis of the drilling and seismic data and are marked on the seismic profile, and the shoreface slope break points are connected to form a shoreface slope break migration trajectory.

[0045] When there is no logging data, the positions of the shoreface slope break points can be determined only according to the seismic profile.

[0046] (4) Restoration of sedimentary stratigraphic thicknesses at different positions

[0047] The sedimentary stratigraphic thicknesses (i.e. present topset layer thicknesses) between each shoreface slope break point and the onlap surface are respectively counted, and are corrected for compaction to obtain the original topset layer thicknesses (h 1-1 , h 2-1 , h 3-1 …) of the original sedimentary period.

[0048] Meanwhile, the thickness of the sedimentary strata between the lowest point of the lake flooding surface and the downlap surface at each coastal slope break point (i.e. the present bottomset bed thickness) is counted and decompacted to obtain the original bottomset bed thickness (d 1-1 , d 2-1 , d 3-1 …) corresponding to each stratum unit.

[0049] Of course, the decompaction correction of the present progradational bed thickness and the present bottomset bed thickness is not a necessary process. However, the decompaction correction of the present progradational bed thickness and the present bottomset bed thickness is more preferred because it can improve the accuracy of the final result.

[0050] (5) Calculate the relative lake level and the maximum paleo-water depth

[0051] The thickness of the strata between the projection point of each coastal slope break point on the downlap surface and the downbase surface (h 1-2 , h 2-2 , h 3-2 …) is counted and summed with the above decompacted original progradational bed thickness (h 1-1 , h 2-1 , h 3-1 …) to obtain the relative lake level depth data (H1, H2, H3…). Then, the relative lake level depth data is subtracted by the corresponding original bottomset bed thickness to obtain the maximum paleo-water depth data (D1, D2, D3…). The above age data (if there is dating data) or stratum sequence (i.e. the stratum sequence in the sequence stratigraphic framework) is taken as the horizontal coordinate, and the relative lake level depth data and the maximum paleo-water depth data are taken as the vertical coordinate to establish the relative lake level and the maximum paleo-water depth change curve.

[0052] Embodiment

[0053] The method for quantitatively recovering the lake level change based on the coastal slope break trajectory according to the present application specifically comprises the following steps:

[0054] (1) Establish the sequence stratigraphic framework

[0055] The typical seismic profile in the source direction, across the basin or large area is preferred, while the seismic profile passes through the well as much as possible, and can better identify the obvious progradation layer reflection structure. Then the wells on the seismic profile are carried out single well sequence interface division, and the position of the lake flooding surface (or water flooding surface) is identified. The lake flooding surface refers to the weak compensation or under-compensation sedimentary interface formed by the lake area expansion and the maximum lake water level rise when the base level rises to the highest position, mainly dominated by shale deposition. Because the interface is widely distributed and the output horizon is very stable, it has strong isochronous. There are different levels of lake flooding surfaces, and the division accuracy is determined according to the research precision. The lake flooding surface with a thickness greater than 10m is generally selected in the Yanchang Formation, which generally shows high natural gamma (GR value greater than 140) and high acoustic time difference (AC value greater than 280) on the well logging.

[0056] On the basis of single well sequence interface division and lake flooding surface identification, well-to-seismic calibration is carried out to determine the corresponding position of each lake flooding surface on the seismic profile Figure 1 ), on the basis of which, sequence stratigraphic correlation interpretation is carried out based on well-to-seismic calibration, and a high-precision sequence stratigraphic framework is constructed. If there are dating data constraints, the development time limit of the stratigraphic unit can be further determined.

[0057] (2) Determine the reference point

[0058] Based on the sequence stratigraphic framework, the filling and filling interface is identified on the seismic profile. Across the filling and filling interface, the seismic reflection structure changes obviously, generally with sub-parallel-parallel characteristics. The filling and filling interface is flattened, combined with the filling structure characteristics of the progradation strata below, the downlap surface where the reflection phase axis terminates downward is identified, and the position with the maximum sedimentary thickness between the downlap surface and the filling and filling interface is taken as the basin center. The corresponding point of the basin center on the downlap surface is taken as the reference point, and the horizontal plane corresponding to the reference point is taken as the lower base level Figure 2 ).

[0059] (3) Shoreline slope break migration trajectory description

[0060] In siliceous clastic sedimentary basins, the position of the sedimentary shoreline slope break zone is roughly consistent with the position of the delta mouth bar to the lake. On the well, the sedimentary facies analysis is carried out through core and logging characteristics, and the transition position of the distributary channel and the mouth bar is taken as the shore slope break point Figure 3 ). The topset layer on the progradation reflection interface and the progradation layer slope break point on the seismic profile can be used as the position of the shore slope break point. Through the comprehensive analysis of the well and the seismic, the positions of the shore slope break points in different stratigraphic units and different periods are determined, and they are connected to form the shore slope break migration trajectory.

[0061] (4) Restore the thickness of sedimentary strata at different positions

[0062] The sedimentary stratum thicknesses (△h 1-1 , △h 2-1 , △h 3-1 …) between each coastal slope break point and the onlap surface are respectively counted. Figure 4 The above sedimentary stratum thicknesses are respectively subjected to decompaction correction, and the calculation formula is as follows:

[0063] h i-1 =△h i-1 ×(1+K)

[0064] K=φ 泥岩 ×K 泥岩 +φ 砂岩 ×K 砂岩

[0065] Wherein: △h i-1 is the present progradation layer thickness; h i-1 is the original progradation layer thickness recovered after decompaction correction; K is the stratum compaction rate; φ 泥岩 is the mud ratio, which is the thickness of mudstone to the thickness of stratum ratio multiplied by 100%, and can be obtained from drilling data; φ 泥岩 is the sand ratio, which is the thickness of sandstone to the thickness of stratum ratio multiplied by 100%, or obtained through calculation of φ 砂岩 =100%-φ 泥岩 ; K 泥岩 and K 砂岩 represent the compaction rates of mudstone and sandstone respectively, and the final compaction rate of pure sandstone is 0.2, and the final compaction rate of pure mudstone is 0.6-0.7.

[0066] Through the above calculation, the progradation layer thicknesses (h 1-1 , h 2-1 , h 3-1 …) of the original deposition period are obtained. In the same way, the sedimentary stratum thicknesses (△d 1-1 , △d 2-1 , △d 3-1 …) between the lowest part of the lake flooding surface where each coastal slope break point is located and the onlap surface, and the bottomset layer thicknesses (d 1-1 , d 2-1 , d 3-1 …) of the original deposition period after decompaction correction are obtained.

[0067] (5) Calculation of relative lake level and maximum paleo-water depth

[0068] The stratum thicknesses (h 1-2 , h 2-2 , h 3-2 …) between the projection points of each coastal slope break point on the onlap surface and the lower base level are counted, and compared with the original progradation layer thicknesses (h 1-1, h 2-1 , h 3-1 …), the relative lake level depth data (H1, H2, H3…) is obtained by summation, and the calculation formula is as follows: Figure 5

[0069] H i = h i-1 + h i-2

[0070] The relative lake level depth data is subtracted by the corresponding original bottomset thickness, and the maximum paleo-water depth data (D1, D2, D3…) is obtained, and the calculation formula is as follows:

[0071] D i = H i - d i-1

[0072] The relative lake level and maximum paleo-water depth change curves are established by taking the age data or stratigraphic sequence as the horizontal coordinate and taking the relative lake level depth data and the maximum paleo-water depth data as the vertical coordinate.

[0073] The above content is only for describing the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the present application.​

Claims

1. A method for quantitatively recovering lake level changes based on shoreline slope break trajectories, characterized in that, Includes the following steps: S1, construct a sequence stratigraphic framework based on seismic profiles; or, construct a sequence stratigraphic framework by combining seismic profiles and well data obtained from drilling. S2, based on the sequence stratigraphic framework, the fill-in interface is identified on the seismic profile, the fill-in interface is flattened by layering, the lower surface is identified, the location with the largest depositional thickness between the lower surface and the fill-in interface is taken as the basin center, the corresponding point of the basin center on the lower surface is taken as the reference point, and the horizontal plane corresponding to the reference point is taken as the lower reference plane. S3, determine the break point of the shoreline slope on the seismic profile; S4, obtain the thickness of the pre-aggregate layer between each shoreline slope inflection point and the lower superface; S5. Obtain the stratigraphic thickness between the projection point of each shore slope inflection point on the lower supersurface and the lower reference surface, and sum it with the corresponding pre-accretion layer thickness to obtain the relative lake level depth data. With the stratigraphic sequence as the abscissa and the relative lake level depth data as the ordinate, establish the relative lake level change curve.

2. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 1, characterized in that, In S1, if well logging data exists, a sequence stratigraphic framework is constructed by combining the seismic profiles of the drilled wells with the drilling data; otherwise, a sequence stratigraphic framework is constructed based on the seismic profiles.

3. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 1, characterized in that, In S1, a sequence stratigraphic framework is constructed by combining the seismic profiles and drilling data from the drilled wells. Specifically, the seismic profiles from the drilled wells are selected, and single-well sequence boundaries are delineated to identify floodplains. Well-seismic calibration is performed to determine the corresponding positions of each floodplain on the seismic profile. Seismic stratigraphic correlation interpretation based on well-seismic calibration is then performed to construct a high-precision sequence stratigraphic framework.

4. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 1, characterized in that, In S1, if there are dating data constraints, the development time limit of stratigraphic units in the sequence stratigraphic framework should be clearly defined.

5. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 1, characterized in that, In S3, if drilling data exists, the break point of the shore slope is determined by combining the drilling data and the seismic profile; otherwise, the break point of the shore slope is determined based on the seismic profile.

6. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 5, characterized in that, The method of determining the shore slope inflection point by combining drilling data and seismic profiles is as follows: based on drilling data, the transition position between the distributary channel and the mouth bar is taken as the shore slope inflection point, and the abrupt change in slope between the top sedimentary layer and the foreseary layer above the foreseary reflection interface is taken as the shore slope inflection point.

7. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 5, characterized in that, The method of determining the shore slope inflection point based on the seismic profile is as follows: the point where the slope of the top accumulation layer and the foreaccumulation layer changes abruptly above the foreaccumulation reflection interface on the seismic profile is taken as the shore slope inflection point.

8. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 1, characterized in that, S4 also includes: obtaining the thickness of the subsurface layer between the lowest point of the floodplain where each shore slope inflection point is located and the subsurface; S5 also includes: using the relative lake level depth data to subtract the corresponding subsurface thickness to obtain the maximum paleowater depth data, and using the stratigraphic sequence as the abscissa and the maximum paleowater depth data as the ordinate to establish the maximum paleowater depth variation curve.

9. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 8, characterized in that, To obtain the thickness of the basement layer between the lowest point of the lacustrine flooding surface and the lower surface at each shore slope inflection point, specifically: the thickness of the sedimentary strata between the lowest point of the lacustrine flooding surface and the lower surface at each shore slope inflection point is calculated and decompaction correction is performed to obtain the basement layer thickness.

10. The method for quantitatively recovering lake level changes based on shoreline slope break trajectories according to claim 1, characterized in that, S4 specifically involves: calculating the thickness of sedimentary strata between each shoreline slope inflection point and the lower surface, and performing decompaction correction to obtain the thickness of the pre-sedimentary layer.

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