Orthotropic Rock Physics Model for In-Situ Stress Determination
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Solution Overview
Problem
Current methods for determining in-situ stress in orthotropic rocks, particularly in complex geomechanical environments like shale, lack accuracy and efficiency due to the rock's significant orthotropic characteristics and developed bedding and fissures.
Innovation Solution
A method and system that determine multiple physical parameters of orthotropic rocks through well logging, mud logging, and indoor testing, constructing an orthotropic rock physics model to calculate stiffness coefficients and dynamic elastic parameters, and subsequently determining in-situ stresses using specific formulas and models like Hashin-Shtrikman bounds, anisotropic self-consistent approximation, and the Brown-Korringa model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional isotropic rock models are used for stress determination, then the method is simple, but the accuracy is low due to ignoring orthotropic characteristics
Solution Approach 1:
The patent changes the fundamental parameter assumption from isotropic to orthotropic rock physics models, introducing direction-dependent elastic parameters (c11, c33, c44, c66) to accurately represent the anisotropic nature of shale rocks with bedding and fissures, thereby improving stress determination accuracy
Solution Approach 2:
The patent employs a composite rock physics model that combines dry rock matrix properties with fluid saturation effects, integrating multiple material components (minerals, pores, formation fluids) to represent the complex orthotropic rock structure and enhance measurement precision
2Measurement precision
If comprehensive physical parameters are measured through well logging and indoor testing, then the model accuracy improves, but the time and cost increase
Solution Approach 1:
The patent performs preliminary determination of orthotropic elastic parameters (c11, c33, c44, c66) and mineral compositions through well logging and indoor testing before stress calculation, establishing the rock physics model in advance to enable efficient subsequent stress determinations
Solution Approach 2:
The patent introduces an intermediary orthotropic rock physics model that bridges the gap between measured physical parameters (density, acoustic velocity, mineral composition) and final stress calculations, allowing indirect but accurate stress determination through stiffness coefficients and Biot coefficients
Data Source
AI summary
The present disclosure provides systems and methods for determining in-situ stresses based on an orthotropic rock physics model. The method may include obtaining multiple physical parameters of a rock; constructing an orthotropic rock physics model based at least in part on the multiple physical parameters; determining multiple stiffness coefficients based on the orthotropic rock physics model; and determining one or more in-situ stresses of the orthotropic rock based on the multiple stiffness coefficients.