A method for restoring weak reflection waveform characteristics of thin sandstone under salt layer during earthquakes

Abstract

A method for recovering weak seismic reflection waveform characteristics in thin sandstone beneath salt layers is disclosed, relating to the field of oil and gas exploration and development. The method involves creating multi-well synthetic seismic records, calibrating the positions of the in-phase axes of strong seismic wave peaks corresponding to the bottom of each salt layer, and tracing these axes to obtain seismic data. The seismic data is then output after frequency extension processing. Geological models of the salt, mud, and sand layers are created, and parameters are filled in and forward modeling is performed to analyze the shielding effect of the salt layers and the resolution of the seismic data. Seismic stratigraphic interpretation is performed on the top and bottom interfaces of multiple strong reflection axes of the salt layers. Using a matched pursuit decomposition algorithm, combined with single-well lithology calibration results, the optimal parameter combination is selected for wavelet decomposition and reconstruction calculations on the frequency extension seismic data. This method for recovering weak seismic reflection waveform characteristics in thin sandstone reservoirs beneath salt layers achieves the goal of identifying weak seismic reflection characteristics by improving the resolution of seismic data and removing strong reflections from the salt layers.

Description

Technical Field

[0001] This application relates to the field of oil and gas exploration and development, and more specifically, to a method for restoring the weak reflection waveform characteristics of seismic rocks in thin sandstone beneath salt layers. Background Technology

[0002] The lithological composition of salt lake basins is very complex, mainly consisting of sandstone, argillaceous sandstone, mudstone, and salt rock. Vertically, it usually shows alternating layers of sand, mud, and salt. The salt lake sedimentary environment creates favorable conditions for the formation of lithologic oil reservoirs.

[0003] However, the difficulty in predicting lithologic reservoirs in saline lacustrine basins lies in the fact that salt layers are widely distributed and have many vertical strata. The strong amplitude reflection of the bottom interface of the salt layer forms a "shielding effect" on the reflection of intersalt sandstone reservoirs, resulting in weak reflection energy and low resolution of the thin sand layer under the salt, which makes identification difficult and poses a great obstacle to reservoir prediction. Summary of the Invention

[0004] The purpose of this application is to provide a method for restoring the weak seismic reflection waveform characteristics of thin sandstone reservoirs beneath salt layers. This method aims to identify the weak seismic reflection characteristics of thin sandstone reservoirs beneath salt layers by improving the resolution of seismic data and removing strong reflections from the salt layer.

[0005] This application is implemented as follows: This application provides a method for restoring the weak reflection waveform characteristics of seismic rocks in thin sandstone beneath salt layers, including the following steps: S1. Create multi-well composite seismic records, pinpoint the position of the reflection phase axis of the strong seismic wave peak corresponding to the bottom of each salt layer and track it to obtain seismic data; S2. Perform frequency diffing on the seismic data and output the frequency diffed high-resolution seismic data. S3. Create geological models of salt, mud, and sand layers, fill in parameters and perform forward modeling calculations on the geological models, and analyze the shielding effect of salt layers and the resolution of seismic data. S4. Seismic horizon tracking interpretation of the top and bottom interfaces of each salt layer's strong reflection axis; S5. Using the matching pursuit decomposition algorithm and combining the single-well lithology calibration results, the optimal parameter combination is selected to perform wavelet decomposition and reconstruction calculations on the frequency-spreading seismic data, and the wavelet decomposition and reconstruction seismic data are obtained.

[0006] In some alternative implementations, when locating and tracing the position of the seismic strong wave peak reflection phase axis corresponding to the bottom of each salt layer, for a target segment with multiple salt layers, it is necessary to locate the strong reflection interface of each salt layer and perform layer tracing.

[0007] In some alternative implementations, a hybrid phase wavelet deconvolution method is used when performing frequency topology processing on seismic data.

[0008] In some alternative implementations, the parameters of the geological model are populated based on the logging rate and logging density of multiple wells.

[0009] In some alternative implementations, the analysis of the shielding effect of the salt layer and the resolution of seismic data involves analyzing the reflection waveform characteristics and resolution of sand layers of different thicknesses under the strong reflection shielding of the salt layer.

[0010] In some alternative implementations, when interpreting the seismic horizon tracing of the top and bottom interfaces of each salt layer reflection axis, the complete waveform of each salt layer reflection axis from trough to crest to trough is included.

[0011] In some alternative implementations, when interpreting the seismic horizon tracing of the top and bottom interfaces of the strong reflection axes of each salt layer, a calculation time window is selected using the complete strong axis waveform as the standard.

[0012] In some alternative implementations, when performing wavelet decomposition and reconstruction calculations on the frequency-spread seismic data in step S2, the optimal parameter combination is selected by performing multiple calculations and comparing the calculation results with the drilled well indices.

[0013] The beneficial effects of this application are as follows: The method for restoring weak seismic reflection waveform characteristics in thin sandstone beneath salt layers provided in this application includes the following steps: generating multi-well synthetic seismic records, calibrating and tracing the positions of the in-phase axes of the strong seismic wave peaks corresponding to the bottom of each salt layer to obtain seismic data; performing frequency extension processing on the seismic data to output high-resolution seismic data after frequency extension; generating geological models of salt, mud, and sand layers, performing parameter filling and forward modeling calculations on the geological models, and analyzing the shielding effect of salt layers and the resolution of seismic data; interpreting the seismic horizon tracking at the top and bottom interfaces of the strong reflection axes of each salt layer, selecting a calculation time window based on including the complete strong axis waveform; and using a matching pursuit decomposition algorithm, combined with the lithology calibration results of a single well, selecting the optimal parameter combination to perform wavelet decomposition and reconstruction calculations on the frequency extension seismic data to obtain the seismic data after wavelet decomposition and reconstruction. The method for restoring weak seismic reflection waveform characteristics in thin sandstone beneath salt layers provided in this application achieves the purpose of identifying weak seismic reflection characteristics of thin sandstone reservoirs beneath salt layers by improving the resolution of seismic data and removing strong reflections from salt layers. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A schematic flowchart illustrating the method for restoring weak reflection waveform characteristics of thin sandstone under salt layers in earthquakes, as provided in this application embodiment; Figure 2 A schematic diagram of lithological calibration and wellbore indication in the single-well synthetic seismic record of the weak reflection waveform characteristic recovery method for thin sandstone under salt layer provided in the embodiments of this application; Figure 3 The method for restoring weak reflection waveform characteristics of thin sandstone under salt layer earthquakes provided in the embodiments of this application includes the sandstone and mudstone strata model and forward modeling response characteristics under salt layer shielding of the sandstone and mudstone strata. Figure 4 The method for restoring weak reflection waveform characteristics of thin sandstone under salt layer in seismic earthquakes provided in the embodiments of this application includes sandstone and mudstone strata models and forward modeling response characteristics without salt layer shielding; Figure 5 This is a cross-sectional view of the original earthquake before frequency spreading processing in the method for restoring weak reflection waveform characteristics of thin sandstone under salt layers provided in the embodiments of this application. Figure 6 This is a cross-sectional view of the original earthquake after frequency conversion processing in the method for restoring weak reflection waveform characteristics of thin sandstone under salt layers provided in the embodiments of this application. Figure 7 This is a seismic profile before seismic wavelet decomposition and reconstruction in the method for restoring weak reflection waveform characteristics of thin sandstone under salt layers provided in the embodiments of this application. Figure 8 Seismic profile after seismic wavelet decomposition and reconstruction in the method for restoring weak reflection waveform characteristics of thin sandstone under salt layers provided in the embodiments of this application; Figure 9 This is a waveform inversion profile of the original seismic data in the method for restoring weak reflection waveform characteristics of thin sandstone under salt layers provided in the embodiments of this application. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0017] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0018] The features and performance of the earthquake weak reflection waveform characteristic recovery method for thin sandstone under salt layer of this application are further described in detail below with reference to the embodiments.

[0019] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Figure 9 As shown in the figure, this application provides a method for restoring the weak reflection waveform characteristics of seismic rocks in thin sandstone beneath salt layers, including the following steps: S1. Construct multi-well synthetic seismic records, pinpoint the positions of the seismic peak reflection phase axes corresponding to the bottom of each salt layer, and trace them to obtain seismic data; for target segments with multiple salt layers, it is necessary to pinpoint the strong reflection interfaces of each salt layer and perform stratigraphic tracing. S2. Use the hybrid phase wavelet deconvolution method to perform frequency upsetting processing on the seismic data and output the frequency-upset high-resolution seismic data. S3. Create geological models of salt, mud, and sand layers. Based on the logging rate and density of multiple wells, fill in the parameters of the geological models and perform forward modeling calculations. Analyze the shielding effect of salt layers and the resolution of seismic data. Specifically, analyze the reflection waveform characteristics and resolution of sand layers of different thicknesses under the strong reflection shielding of salt layers. S4. Perform seismic horizon tracking interpretation on the top and bottom interfaces of each salt layer's strong reflection axis, and select the calculation time window based on the inclusion of the complete strong axis waveform. The selected calculation time window includes the complete waveform of each salt layer's strong reflection axis from trough to peak to trough. A time window that is too large or too small is not suitable. S5. Using the matching pursuit decomposition algorithm and combining the lithology calibration results of a single well, the optimal parameter combination is selected to perform wavelet decomposition and reconstruction calculations on the post-frequency seismic data, resulting in the reconstructed seismic data. The parameters include the type of seismic wavelet, the number of decomposition atoms, and the reconstructed wavelet components. Multiple calculations are required, and the results are compared with the indicators of the drilled wells to select the optimal parameter combination.

[0020] This application provides a method for restoring the weak seismic reflection waveform characteristics of thin sandstone beneath salt layers. Addressing the issues of weak reflection energy and low identification accuracy in sandstone reservoirs beneath salt layers, mud layers, and sand layers in saline lacustrine basins, this method, through multi-well calibration and forward modeling quality control, improves the vertical resolution of seismic data, making it more suitable for thin-layer identification. By eliminating the influence of strong reflection axes from salt layers, it solves the problems of insufficient seismic resolution and strong reflection shielding from salt layers, restoring the seismic reflection waveform characteristics of thin sandstone beneath salt layers. Post-stack target processing significantly reduces the overall processing time, offering advantages such as flexibility, speed, and reliability, laying the foundation for subsequent high-precision reservoir prediction.

[0021] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for recovering the seismic weak reflection waveform features of sub-salt thin sandstone, characterized in that, Includes the following steps: S1. Create multi-well composite seismic records, pinpoint the position of the reflection phase axis of the strong seismic wave peak corresponding to the bottom of each salt layer and track it to obtain seismic data; S2. Perform frequency diffing on the seismic data and output the frequency diffed high-resolution seismic data. S3. Create geological models of salt, mud, and sand layers, fill in parameters and perform forward modeling calculations on the geological models, and analyze the shielding effect of salt layers and the resolution of seismic data. S4. Seismic horizon tracking interpretation of the top and bottom interfaces of each salt layer's strong reflection axis; S5. Using the matching pursuit decomposition algorithm and combining the single-well lithology calibration results, the optimal parameter combination is selected to perform wavelet decomposition and reconstruction calculations on the frequency-spreading seismic data, and the wavelet decomposition and reconstruction seismic data are obtained.

2. The method according to claim 1, characterized in that, When calibrating and tracing the position of the seismic strong wave peak reflection phase axis corresponding to the bottom of each salt layer, for the target segment with multiple salt layers, it is necessary to calibrate the strong reflection interface of each salt layer and perform layer tracing.

3. The method according to claim 1, characterized in that, Hybrid phase wavelet deconvolution is used when performing frequency topology processing on seismic data.

4. The method according to claim 1, characterized in that, When filling parameters into the geological model, the logging rate and logging density of multiple wells should be considered.

5. The method of recovering the seismic weak reflection waveform features of the sub-salt thin sandstone of claim 1, characterized in that, The analysis of the shielding effect of salt layers and the resolution of seismic data involves analyzing the reflection waveform characteristics and resolution of sand layers of different thicknesses under the strong reflection shielding of salt layers.

6. The method of recovering the seismic weak reflection waveform features of sub-salt thin sandstone according to claim 1, characterized in that, When interpreting the seismic horizon tracing of the top and bottom interfaces of each salt layer's strong reflection axis, the complete waveform of each salt layer's strong reflection axis from trough to peak to trough is included.

7. The method of recovering the seismic weak reflection waveform features of sub-salt thin sandstone according to claim 1, characterized in that, When interpreting the seismic horizon tracing of the top and bottom interfaces of the strong reflection axes of each salt layer, the calculation time window is selected based on the complete strong axis waveform.

8. The method for restoring weak reflection waveform characteristics of thin sandstone under salt layers during earthquakes according to claim 1, characterized in that, When performing wavelet decomposition and reconstruction calculations on the frequency-spread seismic data, the optimal parameter combination is selected by performing multiple calculations and comparing the calculation results with the drilled well indices.

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