Shale Gas TOC Prediction via Direct Velocity Ratio Inversion
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Solution Overview
Problem
Existing TOC prediction methods for shale gas reservoirs face errors due to indirect calculation of primary-to-shear wave velocity ratio using pre-stack elastic wave impedance inversion, leading to inaccurate inversion results.
Innovation Solution
A method involving well-seismic calibration, noise elimination, spectral shaping, and simultaneous pre-stack inversion combined with support vector machine-based post-stack inversion to directly predict TOC content, using well data and seismic data to establish a fitting relationship and reduce multiple solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pre-stack elastic wave impedance inversion method is used, then TOC content can be predicted, but the inversion results cannot be directly analyzed with TOC content and require indirect calculation of primary-to-shear wave velocity ratio, increasing error probability
Solution Approach 1:
The patent extracts and directly inverts the primary-to-shear wave velocity ratio from pre-stack seismic data, separating this critical parameter from the traditional impedance inversion process. By directly obtaining this ratio and using it to calculate TOC content through established relationships, the method eliminates the need for indirect calculations through multiple intermediate steps, thereby reducing error accumulation while maintaining manageable process complexity
Solution Approach 2:
The patent introduces the primary-to-shear wave velocity ratio as an intermediary parameter that directly connects seismic data to TOC content. Instead of the traditional path of impedance inversion followed by indirect ratio calculation, this intermediary enables a more direct and accurate determination of TOC content, improving measurement precision while streamlining the overall inversion workflow
2Measurement precision
If indirect calculation of primary-to-shear wave velocity ratio is used, then TOC content can be obtained, but the probability of error in inversion increases
Solution Approach 1:
The patent segments the inversion process into distinct, optimized components: direct primary-to-shear wave velocity ratio inversion, wavelet extraction, and TOC content calculation. By separating these functions and optimizing each independently, the method reduces cumulative errors that occur in integrated indirect calculation approaches, thereby improving both accuracy and reliability
Solution Approach 2:
The patent inverts the traditional approach by directly solving for the primary-to-shear wave velocity ratio from pre-stack seismic data rather than deriving it indirectly from impedance results. This inverted methodology reduces the number of calculation steps and intermediate transformations, thereby minimizing error propagation and enhancing inversion reliability
Data Source
AI summary
The present disclosure provides a TOC prediction method for shale gas reservoirs, including: determining by well-seismic calibration a top interface Ttop and a bottom interface Tbottom of the shale gas reservoirs, and performing layer tracking in the entire area; converting the pre-stack CRP gather into angle gather seismic data; performing spectral shaping processing on the pre-stack migration pure wave seismic data; establishing an initial model, and then performing pre-stack simultaneous inversion to obtain P-wave impedance, S-wave impedance, primary-to-shear wave velocity ratio and density data volume; obtaining a TOC inversion volume A through a post-stack inversion; obtaining a TOC inversion volume B by calculation; then adding the well data for correction, and finally determining a planar distribution law of TOC content. The method can eliminate the multiple solutions of pre-stack inversion and improve the accuracy of TOC content prediction of shale.