Binary function analysis approximate logging paleo-burial depth inversion method

Abstract

The invention relates to the field of oil exploration, and provides a binary function analysis approximate logging paleo-burial depth inversion method. And according to the burial time and the burial depth of the stratum and the shale content of the stratum, a calculation formula of the stratum sandstone ancient porosity and a calculation formula of the stratum mudstone ancient porosity are constructed respectively. And constructing a binary function analysis approximation formula of the thickness of the stratum framework according to the fact that the thickness of the stratum framework is not changed. And according to a logging layering method, the average shale content of the stratum is counted. And the stratum skeleton thickness is not changed, layer-by-layer stripping solution is carried out, and the paleo-burial depth of the stratum is deduced by using a binary function analysis approximation formula of the stratum skeleton thickness. And based on the paleo-burial depth data, research on paleo-structure recovery is subsequently carried out. In the process of solving the paleo-burial depth, two variables, namely the stratum burial depth and the stratum burial time, are set at the same time to accurately invert the paleo-burial depth.

Description

Technical Field

[0001] This invention belongs to the field of petroleum exploration technology, and in particular relates to a bivariate function analytical approximate well logging paleodepth inversion method. Background Technology

[0002] Currently, my country's oil and gas resource exploration is increasingly focused on deeper layers. However, the geological conditions in deep areas are often extremely complex, making exploration difficult. How to accurately predict the distribution of deep oil and gas reservoirs is a significant challenge and a pressing issue that needs to be addressed.

[0003] In the study of the evolutionary history of oil and gas basins, the thickness of sedimentary layers is an extremely important parameter, and the determination of paleoburial depth through well logging is crucial. Currently, commonly used methods for stratigraphic thickness analysis generally use the present-day stratigraphic thickness to represent the stratigraphic thickness of geological periods, which inevitably leads to various errors. However, the thickness of sedimentary layers in different geological periods is not a constant; it should gradually decrease with increasing burial depth.

[0004] Traditional methods for determining paleodepth assume a constant stratigraphic thickness and derive the paleodepth using formulas for stratigraphic thickness calculation. Furthermore, in determining stratigraphic thickness, it is assumed that paleoporosity is only related to burial depth. However, burial time also affects paleoporosity. Therefore, it is crucial to find a method that describes the relationship between paleoporosity, burial time, and burial depth to accurately invert paleodepth. This is of great significance for accurately reconstructing the evolutionary history of basins. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a bivariate function analytical approximate well logging paleodepth inversion method.

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

[0007] A bivariate function analytical approximate well logging paleodepth inversion method includes the following steps:

[0008] Based on the burial time and depth of the strata, and the mud content of the strata, calculation formulas for the paleoporosity of sandstone and mudstone of the strata are constructed respectively.

[0009] Based on the assumption that the thickness of the formation skeleton remains constant, a bivariate analytical approximation formula for the thickness of the formation skeleton is constructed.

[0010] The average clay content of the formation was statistically analyzed using well logging stratification methods.

[0011] With the stratigraphic skeleton thickness remaining constant, the solution is obtained by peeling off layers one by one, and the paleoburial depth of the strata is derived using the bivariate function analytical approximation formula of the stratigraphic skeleton thickness.

[0012] Based on the paleoburial depth data, subsequent research on paleotectonic reconstruction will be conducted.

[0013] Furthermore, in constructing the paleoporosity calculation formula for stratigraphic sandstone and mudstone, when the study area consists of sandstone and mudstone strata, the paleoporosity of the stratigraphic sandstone is constructed based on the burial time and depth of the strata. The calculation formula is:

[0014]

[0015] Constructing paleoporosity of stratigraphic mudstone The calculation formula is:

[0016]

[0017] in, These are the initial porosity of sandstone and mudstone, respectively; a s b s c s a m b m c m , where z is the empirical coefficient based on statistics from the study area; z is the burial depth of the strata; and t is the burial time of the strata.

[0018] The evolution relationship of total paleoporosity of the strata with burial depth and burial time was constructed based on the paleoporosity of the sandstone and mudstone of the strata:

[0019]

[0020] in, S represents the total paleoporosity of the strata. h This refers to the mud content of the formation.

[0021] Furthermore, by separating the formation rock skeleton particles from the pore fluids, and keeping the volume of the formation rock skeleton particles constant, the changes in formation thickness can be characterized by the expansion and contraction of formation pores and pore fluids. A bivariate analytical approximation formula for the formation skeleton thickness can then be constructed as follows:

[0022]

[0023] In the process of obtaining the analytical approximate solution of the bivariate function approximation formula for the thickness of the formation skeleton, Taylor series expansions are performed on the burial depth z and burial time t respectively, and first-order approximations are made for both. Finally, the approximate solution for the thickness of the formation skeleton is obtained as follows:

[0024]

[0025] For the research area, the parameters and Ei1 is a constant, and Ei1 is an exponential integral function. Since the parameter... and If it is a constant, then and

[0026] It also becomes a constant that can be calculated.

[0027] In the process of statistically analyzing the average clay content of formations, outliers in the well logging clay content curves are removed. The well logging clay content curves are then standardized, and the average clay content within each stratum is statistically analyzed.

[0028] The thickness of the stratigraphic skeleton is obtained from the bivariate function analytical approximation formula for the thickness of the stratigraphic skeleton. The thickness of the stratigraphic skeleton within each layer segment is then calculated using the current stratigraphic layer depth and the corresponding burial depth.

[0029] Furthermore, removing the first layer of the aforementioned stratigraphic strata, the starting burial depth and burial time of the corresponding second layer are both set to 0. The formula for calculating an approximate solution to the stratigraphic skeleton thickness is iterated multiple times at depth intervals of dz. The process stops when the calculated value exceeds the stratigraphic skeleton thickness. Then, (n-0.5)*dz represents the paleoburial depth of the second layer during that geological period. This process is repeated to calculate the paleoburial depth corresponding to the strata for each geological period.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] In determining paleodepth, two variables—the burial depth of the strata and the burial time of the strata—are set to accurately invert the paleodepth, resulting in more precise paleodepth values. Assuming the volume of the stratigraphic rock skeleton particles remains constant, the expansion and contraction of pores and pore fluids are used to characterize changes in stratigraphic thickness, solving the problem of determining the thickness of the stratigraphic skeleton. Using the current stratigraphic layer depths and their corresponding burial depths, the thickness of the stratigraphic skeleton within each layer is calculated. Layer by layer, the paleodepth corresponding to each geological period is calculated.

[0032] The bivariate function analytical approximate well logging paleodepth inversion method of this invention fully considers the influence of tectonic movements on the paleodepth values ​​of strata in different historical periods, has good application value, and is of great significance to the study of the evolution history of oil and gas basins.

[0033] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A flowchart illustrating an embodiment of the present invention is shown;

[0036] Figure 2 The map shows the precise reconstruction of the ancient burial depth of section 81 of the reservoir in work area A, representing the base formation period. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Current methods for analyzing stratigraphic thickness generally use the present-day stratigraphic thickness to represent the thickness of stratigraphic layers from different geological periods, which inevitably leads to various errors. However, the thickness of sedimentary layers from different geological periods is not a constant; it should gradually decrease with increasing burial depth.

[0039] Traditional methods for determining paleodepth assume that the thickness of the stratigraphic framework remains constant and derive the paleodepth using the framework thickness calculation formula. Since burial time is related to paleoporosity, it is necessary to find a relationship that describes the relationship between paleoporosity, burial time, and burial depth in order to accurately invert the paleodepth.

[0040] like Figure 1 As shown, in the process of determining the paleoburial depth, only two variables were set: the burial depth of the stratum and the burial time of the stratum. All other values ​​used were measured constants to accurately invert the paleoburial depth.

[0041] Specifically, such as Figure 1 As shown, the bivariate function analytical approximate well logging paleodepth inversion method is characterized by including:

[0042] S101: Based on the burial time and depth of the strata and the mud content of the strata, respectively construct the paleoporosity calculation formulas for sandstone and mudstone.

[0043] S102: Construct the formula for the thickness of the formation skeleton based on the fact that the thickness of the formation skeleton remains constant;

[0044] S103: Calculate the average clay content of the formation according to the well logging stratification method;

[0045] S104: The thickness of the stratigraphic skeleton remains constant. The solution is obtained by peeling off each layer and the paleoburial depth of the strata is derived using the stratigraphic skeleton thickness formula.

[0046] S105: Based on the paleoburial depth data, subsequent research on paleotectonic reconstruction will be carried out.

[0047] In S101, the study area consists of sandstone and mudstone strata. Paleoporosity of the sandstone strata is constructed by simultaneously considering the burial time and depth of the strata. The calculation formula is:

[0048]

[0049] Constructing paleoporosity of stratigraphic mudstone The calculation formula is:

[0050]

[0051] in, These are the initial porosity of sandstone and mudstone, respectively; a s b s c s a m b m c m , where z is the empirical coefficient based on statistics from the study area; z is the burial depth of the strata; and t is the burial time of the strata.

[0052] The evolution relationship between total paleoporosity of strata and burial depth and time can be constructed from the paleoporosity of sandstone and mudstone strata as follows:

[0053]

[0054] in, S represents the total paleoporosity of the strata. h This refers to the mud content of the formation.

[0055] In S102, assuming that the formation rock skeleton particles and pore fluids are separable, and further assuming that the volume of the formation rock skeleton particles remains essentially constant, then the variation in formation thickness is mainly characterized by the expansion and contraction of formation pores and pore fluids. The formation skeleton thickness h can be constructed. s The formula is:

[0056]

[0057] Determining the thickness h of the formation skeletons In the process of analyzing the approximate solution of the formula, Taylor series expansions are performed on z and t respectively, and first-order approximations are made for both, which finally yields h. s The analytical approximate solution is:

[0058]

[0059] For a specific research area, the parameters and Ei1 is a constant, and Ei1 is an exponential integral function. Since the parameter... and If it is a constant, then and This also becomes a constant that can be calculated. Assuming that the formation rock skeleton particles and pore fluids can be separated, and further assuming that the volume of the formation rock skeleton particles remains basically unchanged, then the change in formation thickness is mainly characterized by the expansion and contraction of formation pores and pore fluids, and the formation skeleton thickness can be further solved.

[0060] In S103, outliers in the logging clay content curve are removed and standardized. Then, the average clay content value within each stratum is statistically analyzed according to the S103 interval. h .

[0061] The stratigraphic skeleton thickness formula (5) obtained in step S102 is used to calculate the stratigraphic skeleton thickness within each layer segment using the current stratigraphic layer depth and corresponding burial depth. Then, the first layer is removed, and the starting burial depth and burial time of the corresponding second layer are both set to 0. The formula is iterated n times with a depth interval of dz to obtain h. s The analytical approximation solution stops when the calculated value exceeds the thickness of the stratigraphic framework. Therefore, (n-0.5)*dz represents the paleoburial depth of the second layer during that geological period. This process can be repeated to calculate the paleoburial depth of strata for each geological period.

[0062] Applying this invention to work area A, and using the method of this invention to invert the paleoburial depth of well logging, the main steps are as follows:

[0063] 1. Remove outliers from the well logging clay content curve and standardize it. Then, calculate the average clay content within each layer according to the stratification.

[0064] 2. Based on the assumption that the thickness of the stratigraphic skeleton remains constant, the layers are peeled off one by one, and the ancient burial depth of the strata is derived using the skeleton thickness calculation formula.

[0065] Figure 2 The ancient burial depth map of the bottom of section 81 in work area A, which was accurately restored, shows the topographic features of two high points and one depression, and the consistency with the current oil wells has been greatly improved.

Claims

1. A dual function analytical approximation well log paleoburial depth inversion method characterized by, The dual-element function analytical approximation logging paleo-burial depth inversion method comprises the following steps: According to the burial time and burial depth of the stratum, and the shale content of the stratum, a stratum sandstone paleo-porosity calculation formula and a stratum shale paleo-porosity calculation formula are respectively constructed; According to the invariable stratum framework thickness, a dual-element function analytical approximation formula of the stratum framework thickness is constructed; According to a logging layering method, the average shale content of the stratum is counted; The stratum framework thickness is invariable, and the paleo-burial depth of the stratum is derived layer by layer by using the dual-element function analytical approximation formula of the stratum framework thickness; Based on the paleo-burial depth data, subsequent research on paleo-tectonic restoration is carried out.

2. The dual-element function analytical approximation logging paleo-burial depth inversion method according to claim 1, characterized in that, In the formula for calculating the paleo-porosity of sandstone and mudstone, in the case of sandstone and mudstone in the study area, according to the burial time and burial depth of the stratum, the formula for calculating the paleo-porosity of sandstone and mudstone is constructed as follows: Paleo-porosity of sandstone = 0.5 × (Paleo-porosity of mudstone) Constructing paleoporosity of mudstone The calculation formula is: wherein, φi, φ2are initial porosities of sandstone and mudstone, respectively; a s , b s , c s , a m , b m , c m are empirical coefficients according to statistics of the study area; z is the burial depth of the formation, and t is the burial time of the formation.

3. The dual-element function analytical approximation logging paleo-burial depth inversion method according to claim 2, characterized in that, An evolution relationship of the total paleo-porosity of the stratum with the burial depth and the burial time is constructed according to the stratum sandstone paleo-porosity and the stratum shale paleo-porosity: wherein, S is the total formation porosity; and h S is the formation shale content.

4. The dual-element function analytical approximation logging paleo-burial depth inversion method according to claim 3, characterized in that, The stratum rock framework particles and the pore fluid are separated, the volume of the stratum rock framework particles remains unchanged, the stretching and contraction changes of the stratum pores and the pore fluid are used to represent the changes of the stratum thickness, and a dual-element function analytical approximation formula of the stratum framework thickness is constructed as:

5. The dual-element function analytical approximation logging paleo-burial depth inversion method according to claim 4, characterized in that, In the process of obtaining the analytical approximation solution of the dual-element function analytical approximation formula of the stratum framework thickness, Taylor series expansion is performed on the burial depth z and the burial time t respectively, and first-order approximation is performed on both, and finally the approximate solution of the stratum framework thickness is obtained as: where the parameters and are constant for the study area, Ei1is an exponential integral function, and since the parameters and are constant, then and also become determinable constants.

6. The dual-element function analytical approximation logging paleo-burial depth inversion method according to claim 5, characterized in that, In the process of counting the average shale content of the stratum, the logging shale content curve is de-abnormal value; And the logging shale content curve is standardized, and then the average shale content value in the layer section is counted according to layering.

7. The dual function analytical approximation well depth of burial inversion method of claim 6, wherein , The stratum framework thickness is obtained in the dual-element function analytical approximation formula of the stratum framework thickness, and the stratum framework thickness in each layer section is obtained according to the present stratum layering depth and the corresponding burial depth.

8. The dual function analytical approximation well depth of burial inversion method of claim 7, wherein , The first layer of the stratum layering is removed, the starting burial depth and the burial time of the corresponding second layer are both from 0, and the approximate solution formula of the stratum framework thickness is calculated by iteration for multiple times with dz as the depth interval, when the calculated value is greater than the stratum framework thickness, the calculation is stopped, and (n-0.5)*dz is the paleo-burial depth of the second layer in the current geohistory period; The corresponding paleo-burial depths of the stratum in each geohistory period are calculated in turn.

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