De-trending AVO via Effective Stress Chi Angles
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Solution Overview
Problem
Conventional seismic data processing methods struggle to provide accurate and consistent seismic interpretations across varying effective stress conditions, leading to difficulties in distinguishing hydrocarbons from other subsurface features, as constant Chi angles fail to account for spatial changes in rock compaction and properties.
Innovation Solution
The method involves determining Chi angles as a spatially varying function of effective stress, allowing for the generation of seismic projections that are invariant laterally and vertically, using a formula Proj=A cos(Chi[ES])+B sin(Chi[ES]), where Chi varies with effective stress, optimizing feature representation and de-emphasizing non-hydrocarbon fluids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If constant Chi angles are used in seismic projection, then the processing method is simple and consistent, but the interpretation accuracy varies across different effective stress conditions and spatial locations
Solution Approach 1:
The patent applies the dynamics principle by transitioning from static constant Chi angles to dynamic spatially-varying Chi angles that adapt to local effective stress conditions. The Chi angle becomes a function of position and effective stress (Chi(x,y,z,ES)), allowing the projection method to dynamically adjust to varying subsurface conditions throughout the seismic volume, thereby maintaining interpretation accuracy across different stress regimes without requiring manual intervention for each zone.
Solution Approach 2:
The patent implements parameter changes by modifying the Chi angle parameter from a constant value to a variable parameter that changes based on effective stress. This is achieved by calculating Chi as a function of effective stress (Chi=arctan((1-2ν)/(2ν)) where ν is Poisson's ratio derived from effective stress), allowing the projection to adapt to varying rock mechanics conditions while maintaining a systematic and reproducible approach.
2Stability of the object's composition
If spatially-varying Chi angles as a function of effective stress are used, then interpretation consistency across the volume is improved, but the processing complexity and computational requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating the effective stress distribution throughout the seismic volume before performing the AVO projection. The effective stress volume is computed in advance using gravity and pore pressure models, and this pre-computed stress information is then used to determine the spatially-varying Chi angles. This preliminary preparation ensures that when the projection is performed, the consistent interpretation results are achieved without requiring complex real-time calculations during the projection step itself.
Solution Approach 2:
The patent uses effective stress as an intermediary parameter that bridges the gap between raw seismic data and meaningful interpretation. By introducing effective stress as a mediating variable, the system can translate varying subsurface mechanical conditions into appropriate Chi angle adjustments, thereby achieving interpretation consistency across different geological settings without directly complexifying the projection algorithm itself.
3Measurement precision
If constant Chi projection is applied locally to optimize specific features, then those features are enhanced, but the projection becomes counter-productive for other regions with different effective stress conditions
Solution Approach 1:
The patent implements local quality by allowing different Chi angles to be applied to different spatial locations based on their local effective stress conditions. Each voxel in the seismic volume receives a Chi angle optimized for its specific stress regime, enabling local feature enhancement while maintaining global consistency. This is achieved through the spatially-varying Chi function that automatically adapts to local conditions without requiring manual zone-by-zone optimization.
Solution Approach 2:
The patent achieves universality by creating a single projection methodology that works across all regions of the seismic volume regardless of effective stress variations. The spatially-varying Chi angle function serves multiple purposes simultaneously: it optimizes for local features in each region while maintaining consistency across the entire volume, eliminating the need for separate local optimizations and making the projection universally applicable throughout the subsurface volume.
Data Source
AI summary
A method including: obtaining intercept and gradient stacks and an effective stress volume that correspond to seismic data for a subsurface region; determining Chi angles as a function of effective stress; and generating a seismic volume with the Chi angles that vary as a function of effective stress.