Method for judging applicability of mudstone compaction extrapolation method based on sound wave and density logging

Abstract

The invention belongs to the technical field of basin simulation, and particularly relates to a mudstone compaction extrapolation method applicability discrimination method based on sound wave and density logging. The method comprises the following steps of: 1, selecting a continuous mudstone section to sample data points, valuing interval transit time delta tma of a rock skeleton, and drawing a plumbing relational graph; 2, identifying stratum interfaces with different interval transit time data convergence trends of upper and lower stratum mudstone sections according to the convergence trend of discrete distribution of data points; 3, obtaining a fitting straight line of each data point group segment or data point group segments above and below the target unconformity surface; 4, the difference between the buried depth corresponding to the baseline value delta t0 in the fitted curve and the buried depth corresponding to the researched unconformity surface is obtained, and the assumed stratum recovery denudation amount H is obtained; 5, obtaining the function relationship rho '(Z) of the density of the destination stratum group section with respect to the buried depth through logarithm fitting, and 6, calculating the recovery pressure Pb and the current pressure Px, and comparing the values of the recovery pressure Pb and the current pressure Px.

Description

Technical Field

[0001] This invention belongs to the field of basin simulation technology, specifically relating to a method for judging the applicability of mudstone compaction extrapolation based on sonic transit time logging and density logging. Background Technology

[0002] Formation erosion recovery is a crucial step in basin simulation, and mudstone compaction extrapolation is a commonly used method. This method estimates erosion volume by extrapolating and fitting a curve based on the relationship between mudstone sonic transit time and burial depth. However, in practical applications, due to factors such as formation complexity, variations in sedimentary environment, and logging data errors, the applicability of mudstone compaction extrapolation is often difficult to accurately determine, leading to significant deviations in erosion recovery results and affecting the accuracy of basin simulation and the reliability of oil and gas exploration. Summary of the Invention

[0003] To address the problems existing in the background technology, this invention provides a method for judging the applicability of mudstone compaction extrapolation based on acoustic and density logging. The purpose is to solve the problem that existing methods lack objective basis and are prone to misjudgment when judging the applicability of mudstone compaction extrapolation, thereby improving the accuracy and reliability of erosion recovery.

[0004] This invention adopts the following technical solution: a method for judging the applicability of mudstone compaction extrapolation based on acoustic and density logging, the method comprising the following steps:

[0005] Step 1: Using a single well point as the basic working unit, based on sonic transit time logging data, select continuous mudstone sections for data point sampling, and analyze the sonic transit time Δt of the rock skeleton. ma Values ​​were selected, and the relationship between burial depth and sonic transit time logging was plotted in Z-ln(Δt-Δt). ma A diagram showing the relationship between projected points in a coordinate system.

[0006] Step 2: Using stratigraphic units as the basic research unit, the acoustic transit time data of the mudstone section is segmented and marked according to the burial depth. Based on the convergence trend of the discrete distribution of data points, the stratigraphic interfaces with different convergence trends of acoustic transit time data of mudstone sections in upper and lower strata are identified, namely unconformities.

[0007] Step 3: Using the unconformity as the boundary, divide the data point into segments consisting of sonic transit time data points from single stratigraphic segments or multi-stratigraphic segments with conformable contact in mudstone formations. Obtain the fitted straight line for each data point segment or the data point segments above and below the target unconformity, Z-ln(Δt-Δt). ma Using a semi-logarithmic coordinate system, the mathematical model formula for the fitted line is as follows:

[0008] ln(Δt-Δt ma )=-CZ+ln(Δt0-Δt ma(1).

[0009] In the formula, Δt ma The time difference of acoustic waves in the rock skeleton is expressed in µs·m. -1 Δt0 represents the initial deposition acoustic time difference baseline value, in µs·m. -1 C represents the slope of the compaction trend line, in meters (m). -1 Z represents depth, measured in meters (m).

[0010] Step 4: Take the initial depositional acoustic transit time Δt0 of the target stratigraphic segment below the target unconformity. Using extrapolation, extrapolate the fitted curve of the data point segment below the target unconformity to the initial depositional acoustic transit time value, i.e., Δt0. Then, use the burial depth H corresponding to the baseline value Δt0 in the fitted curve. Δt0 The burial depth H corresponding to the unconformity surface studied m The difference is used to obtain the assumed formation recovery erosion amount H, which is calculated using the following formula:

[0011]

[0012] Step 5: Set the initial density ρ0 of the target formation below the unconformity. Combining the known density logging curve of the target formation with the formation recovery erosion amount H assumed in Step 4, obtain the functional relationship ρ' of the density of the target formation with respect to the burial depth z through logarithmic fitting. (Z) The fitting formula is as follows:

[0013] ρ′ (Z) =f (Z) (3).

[0014] Step Six: Use the assumed formation to recover the erosion amount H and the functional relationship ρ' from Step Five. (Z) Calculate the assumed formation restoration erosion amount H and the resulting restoration pressure P on the target formation segment. b , restore pressure P b Take the absolute value; simultaneously utilize the known density logging curve ρ of the overlying strata on the target unconformity. (Z) Calculate the present pressure P exerted by the overlying strata on the target stratigraphic unit at the Z-depth of the target unconformity. x Current pressure P x Take the absolute value; and compare it with the recovery pressure P. b With current pressure P x The magnitude of P x <P b This indicates that the original sedimentary patterns of the strata have not been destroyed, and the amount of erosion can be recovered using the mudstone compaction extrapolation method. If P x <<P bThis indicates that the strata may be affected by complex factors. Before using the mudstone compaction extrapolation method to recover the amount of erosion, it is necessary to make a judgment and analysis. Otherwise, the mudstone compaction extrapolation method cannot be used.

[0015] Restoring pressure P b The calculation formula is as follows:

[0016]

[0017] In the formula, ρ' (Z) The set of continuous mudstone segments sampled from the target strata below the target unconformity is fitted together with the initial density-depth coordinate points (ρ0, ZH) composed of the initial density ρ0 of the target strata below the target unconformity and the assumed stratum recovery erosion amount H. This is used to characterize the function relationship between the density and depth of the assumed eroded strata.

[0018] Current pressure P x The calculation formula is as follows:

[0019]

[0020] In the formula, ρ (Z) The known density logging curves of the overlying strata on the current target unconformity are used to characterize the differential relationship between density and depth of the overlying strata on the actual target unconformity.

[0021] Furthermore, the density fitting function ρ' (z) Using the natural logarithmic form can better characterize the nonlinear characteristics of density variation with depth, thus improving the accuracy of pressure calculation.

[0022] Furthermore, in step six, the pressure integral uses the absolute unit Pa to ensure the objectivity and consistency of the pressure comparison.

[0023] The beneficial effects of this invention are as follows: It provides a method for determining the applicability of mudstone compaction extrapolation based on acoustic and density logging. By combining acoustic time-of-flight logging and density logging data, and utilizing the pressure comparison principle, the applicability of the mudstone compaction extrapolation method is objectively determined, avoiding subjective misjudgments and improving the accuracy of erosion recovery. The determination method has clear steps, is highly operable, and is applicable to complex formation conditions, providing reliable technical support for basin simulation and oil and gas exploration. Attached Figure Description

[0024] Figure 1 This is a flowchart of the method for judging the applicability of the mudstone compaction extrapolation method.

[0025] Figure 2 This is a curve showing the acoustic time difference pattern of well Nanbao 4-20 in the embodiment.

[0026] Figure 3This is a curve showing the density distribution of well Nanbao 4-20 in the embodiment. Detailed Implementation

[0027] 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, and 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.

[0028] Example 1

[0029] Taking well 4-20 in the Nanpu Depression as an example, such as Figure 1-3 As shown.

[0030] The applicability assessment method for mudstone compaction extrapolation based on acoustic and density logging includes the following steps:

[0031] Step 1: Using a single well point as the basic working unit, based on sonic transit time logging data, select continuous mudstone sections for data point sampling, and analyze the sonic transit time Δt of the rock skeleton. ma Values ​​were taken. In well Nanpu 4-20, a continuous mudstone section within the Ed1 layer was sampled, and the burial depth and sonic transit time were plotted within the range of Z-ln(Δt-Δt). ma Projection point relationship diagram in coordinate system ( Figure 2 ), where Δt ma The value is 180 μs·m -1 .

[0032] Step 2: Using stratigraphic units as the basic research unit, the sonic transit data of the mudstone section is segmented and marked according to the burial depth to identify unconformities. In well Nanbao 4-20, an unconformity was identified at a burial depth of 2336m at the top of the Ed1 section.

[0033] Step 3: Using the unconformity as the boundary, obtain the fitted straight line for the data point segment below the unconformity, Z-ln(Δt-Δt). ma Using a semi-logarithmic coordinate system, the mathematical model formula for the fitted line is as follows:

[0034] ln(Δt-Δt ma )=-CZ+ln(Δt0-Δt ma (1).

[0035] Δt0 is taken as 600 μs·m -1 C represents the slope of the compaction trend line.

[0036] Step 4: Using the extrapolation method, extrapolate the fitting curve of the data point group below the unconformity surface to the initial sedimentary acoustic time difference baseline value Δt0 to obtain the hypothetical formation restoration erosion amount H. In Well Nanpu 4-20, the extrapolated hypothetical erosion thickness H = 1285 m.

[0037] Step 5: Set the initial density ρ0 of the target formation section below the target unconformity surface to 1.3 g·cm-3. Combine the known density logging curve and the hypothetical erosion thickness H1, and obtain the function relationship ρ' of density with depth through logarithmic fitting. (Z) .

[0038] ρ′ (Z) = 0.39·ln(z + 92.53) - 0.46 (3).

[0039] Step 6: Use the hypothetical erosion thickness H and the density function ρ' (Z) to calculate the restored pressure Pb, and at the same time use the density logging curve ρ of the overlying formation of the unconformity (Z) to calculate the current pressure Px.

[0040]

[0041] Compare Pb and Px. Pb < Px, which does not meet the applicable condition of Px < Pb, indicating that the original formation sedimentation law has been destroyed and the acoustic time difference method is not applicable to restore the erosion thickness.

[0042] The erosion surface burial depth of the Ed1 section in Well Nanpu 4-20 is relatively deep, and Px > Pb, indicating that the phenomenon of "law erasure" has occurred in the formation. The erosion thickness of 1285 m restored by the acoustic time difference method is a false result and has no geological significance.

[0043] The above embodiments show the actual application process of the method of the present invention in Well Nanpu 4-20. Through the combination of acoustic time difference and density logging data, the quantitative discrimination of the applicability of the shale compaction extrapolation method is realized, providing a reliable technical basis for the erosion amount restoration work under similar geological conditions.

[0044] If there are other embodiments, any modifications, equivalent replacements or improvements made within the principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for judging the applicability of mudstone compaction extrapolation based on acoustic and density logging, characterized in that, The discrimination method includes the following steps: Step 1: Using a single well point as the basic working unit, based on sonic transit time logging data, select continuous mudstone sections for data point sampling, and analyze the sonic transit time Δt of the rock skeleton. ma Values ​​were selected, and the relationship between burial depth and sonic transit time logging was plotted in Z-ln(Δt-Δt). ma A diagram showing the relationship between projected points in a coordinate system; Step 2: Using stratigraphic units as the basic research unit, the acoustic transit time data of the mudstone section is segmented and marked according to the burial depth. Based on the convergence trend of the discrete distribution of data points, the stratigraphic interfaces with different convergence trends of acoustic transit time data of mudstone sections in upper and lower strata are identified, namely unconformities. Step 3: Using the unconformity as the boundary, divide the data point into segments consisting of sonic transit time data points from single stratigraphic segments or multi-stratigraphic segments with conformable contact in mudstone formations. Obtain the fitted straight line for each data point segment or the data point segments above and below the target unconformity, Z-ln(Δt-Δt). ma Using a semi-logarithmic coordinate system, the mathematical model formula for the fitted line is as follows: ln(Δt-Δt ma )=-CZ+ln(Δt0-Δt ma ) (1); In the formula, Δt ma The time difference of acoustic waves in the rock skeleton is expressed in µs·m. -1 Δt0 represents the initial deposition acoustic time difference baseline value, in µs·m. -1 C represents the slope of the compaction trend line, in meters (m). -1 Z represents depth, in meters (m). Step 4: Take the initial depositional acoustic transit time Δt0 of the target stratigraphic segment below the target unconformity. Using extrapolation, extrapolate the fitted curve of the data point segment below the target unconformity to the initial depositional acoustic transit time value, i.e., Δt0. Then, use the burial depth H corresponding to the baseline value Δt0 in the fitted curve. Δt0 The burial depth H corresponding to the unconformity surface studied m The difference is used to obtain the assumed formation recovery erosion amount H, which is calculated using the following formula: Step 5: Set the initial density ρ0 of the target formation below the unconformity. Combining the known density logging curve of the target formation with the formation recovery erosion amount H assumed in Step 4, obtain the functional relationship ρ' of the density of the target formation with respect to the burial depth z through logarithmic fitting. (Z) The fitting formula is as follows: ρ′(Z)=f(Z) (3); Step Six: Use the assumed formation to recover the erosion amount H and the functional relationship ρ' from Step Five. (Z) Calculate the assumed formation restoration erosion amount H and the resulting restoration pressure P on the target formation segment. b , restore pressure P b Take the absolute value; simultaneously utilize the known density logging curve ρ of the overlying strata on the target unconformity. (Z) Calculate the present pressure P exerted by the overlying strata on the target stratigraphic unit at the Z-depth of the target unconformity. x Current pressure P x Take the absolute value; and compare it with the recovery pressure P. b With current pressure P x The magnitude of P x <P b This indicates that the original stratigraphic depositional pattern has not been destroyed, if P x <<P b This indicates that the strata may be affected by complex factors; Restoring pressure P b The calculation formula is as follows: In the formula, ρ' (Z) The data point set of continuous mudstone segments obtained by sampling the target strata below the target unconformity is used to characterize the density of the hypothetical eroded strata as a function of depth. Current pressure P x The calculation formula is as follows: In the formula, ρ (Z) The known density logging curves of the overlying strata on the current target unconformity are used to characterize the differential relationship between density and depth of the overlying strata on the actual target unconformity.

2. The applicability judgment method for mudstone compaction extrapolation based on acoustic and density logging according to claim 1, characterized in that, In step five, the density fitting function ρ′ (z) It is expressed in the form of a natural logarithm.

3. The applicability judgment method for mudstone compaction extrapolation based on acoustic wave and density logging according to claim 1, characterized in that, In step six, the pressure integral is expressed in absolute unit Pa.

4. The applicability judgment method for mudstone compaction extrapolation based on acoustic and density logging as described in claim 1, characterized in that, In step six, ρ' (Z) The initial density-depth coordinates (ρ0, ZH) are obtained by fitting the initial density ρ0 of the target stratigraphic segment below the set target unconformity surface and the assumed formation recovery erosion amount H together.

5. The applicability judgment method for mudstone compaction extrapolation based on acoustic and density logging according to claim 1, characterized in that, In step six, if P x <P b This indicates that the original stratigraphic depositional pattern has not been destroyed, if P x <<P b This indicates that the strata may be affected by complex factors.

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