Anisotropic Rock Physics Model for Seismic Response Simulation
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Solution Overview
Problem
Current rock physics models for fractured rocks are limited in simulating seismic anisotropy due to assumptions of isolated fractures, inability to handle mixed anisotropy types, and computational expense, and fail to accurately model fluid communication and mixed geological environments.
Innovation Solution
A method for developing an anisotropic rock physics model that simulates seismic anisotropy by considering preferred orientations of clay-related pores, fracture anisotropy, and stress-induced anisotropy, using an upscaled 1D layered earth model to generate synthetic seismic responses, capable of handling orthorhombic anisotropy and calibrating parameters for accurate fluid flow and mass transport prediction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If inclusion-based effective medium theories (DEM and SC) are used to model fractured rocks, then the model can handle higher fracture porosity without dilute pore concentration assumption, but the model assumes isolated fractures which does not allow fluid communication between fractures and matrix pores, giving high-frequency response that is not suitable for simulating low-frequency seismic responses
Solution Approach 1:
The patent changes the frequency parameter to simulate different seismic conditions. By performing simulations at multiple frequencies (low-frequency limit and high-frequency limit), the model captures the transition between fluid communication regimes, allowing accurate representation of both connected and isolated fracture behaviors across different seismic frequency ranges
Solution Approach 2:
The patent introduces dynamic frequency dependence into the effective medium model. The model transitions from static assumptions about fracture connectivity to a dynamic framework where fluid communication behavior changes with seismic frequency, enabling the same model structure to represent both low-frequency (connected) and high-frequency (isolated) regimes
2Adaptability or versatility
If DEM or SC theory is used to model anisotropic elastic properties of fractured rocks, then the model can handle various fracture configurations, but the computational cost becomes extremely expensive, making it impractical for well log analysis
Solution Approach 1:
The patent changes the mathematical formulation parameters by introducing simplified mixing rules that approximate the complex DEM/SC theory results. By transforming the iterative computational parameters into direct calculation formulas, the model maintains versatility in handling different fracture configurations while reducing computational complexity to levels suitable for well log analysis
Solution Approach 2:
The patent replaces the computationally expensive iterative DEM/SC theory with a simpler, faster-to-calculate effective medium model. This 'cheaper' computational approach sacrifices some iterative refinement but provides sufficient accuracy for practical applications, enabling rapid processing of well log data without requiring supercomputing resources
3Adaptability or versatility
If Backus averaging is used to upscale elastic properties of layered media, then the model can handle VTI anisotropy, but the model is unable to handle mixed anisotropy types such as orthorhombic anisotropy from intersecting fractures
Solution Approach 1:
The patent creates a universal upscaling model that performs multiple functions: it can handle VTI anisotropy like Backus averaging, but also extends to orthorhombic and other mixed anisotropy types. The single framework accommodates different fracture configurations (single set, multiple orthogonal sets, intersecting sets) without requiring separate modeling approaches, making the model multi-functional and broadly applicable
4Measurement precision
If existing fracture models are used to estimate elastic properties of fractured rocks, then the model can provide seismic anisotropy characterization, but the model fails to handle rock columns with mixed anisotropy types (shale anisotropy and layering anisotropy mixed with fracture anisotropy)
Solution Approach 1:
The patent merges multiple anisotropy sources (shale anisotropy, layering anisotropy, and fracture anisotropy) into a single integrated effective medium model. By combining the effects of different anisotropic components using generalized mixing rules, the model simultaneously characterizes mixed geological factors and provides comprehensive seismic anisotropy prediction for complex rock columns containing multiple anisotropy types
Data Source
AI summary
Method for modeling anisotropic elastic properties of a subsurface region comprising mixed fractured rocks and other geological bodies. P-wave and fast and slow S-wave logs are obtained, and an anisotropic rock physics model of the subsurface region is developed (21). P- and fast and slow S-wave logs at the well direction are calculated using a rock physics model capable of handling fractures and other geological factors (22). Calculated values are compared to measured values in an iterative model updating process (23). An upscaled ID model is developed by averaging elastic properties in each layer using an upscaling theory capable of handling at least orthorhombic anisotropy (24). The ID model may be used to generate synthetic seismic response for well ties or AVO modeling (25). Further, a method is disclosed for estimating anisotropy parameters from P- and fast/slow S-wave logs from one or more deviated wells.