Modeling Elastic Stiffness Tensor in Transverse Isotropic Media
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Solution Overview
Problem
Current methods for calculating anisotropy parameters in subsurface imaging, such as Thomsen parameters, are expensive and require extensive laboratory data or well logs, making them impractical for widespread application in reservoir geophysics, especially in transverse isotropic (TI) media.
Innovation Solution
A rock physics workflow that utilizes conventional well-log suites to model the elastic stiffness tensor in TI media by downscaling and upsampling normal logs using the Backus model, integrating anisotropy information and allowing for the determination of Thomsen parameters (ε, δ, γ) without the need for extensive data, using a combination of rock physics modeling and well-log data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional methods using Thomsen parameters are used to calculate anisotropy effects, then measurement precision is improved, but device complexity and cost increase due to requirement of laboratory data or well logs in different directions
Solution Approach 1:
The patent extracts and utilizes only the vertical well log data (p-wave velocity, s-wave velocity, density) that is already available during drilling operations, eliminating the need to collect additional laboratory data or well logs in different directions. By taking out only the necessary data that is already present in conventional well logs, the method reduces data collection complexity while maintaining anisotropy calculation accuracy.
Solution Approach 2:
The patent creates a simplified model that copies the essential anisotropy information from complex multi-directional measurements into a single vertical well log framework. Through the Backus model and rock physics relationships, it reconstructs anisotropy parameters (ε, δ, γ) using only vertical well log data, effectively copying the information content from complex measurements into a simpler data structure.
2Measurement precision
If extensive laboratory data or multi-directional well logs are collected to determine anisotropy parameters, then measurement precision is improved, but loss of time and increased cost occur
Solution Approach 1:
The patent performs preliminary action by utilizing the vertical well log data that is already collected during the drilling process before any anisotropy analysis is needed. The method prepares and processes this pre-existing data through rock physics modeling and the Backus model to directly obtain anisotropy parameters, eliminating the need for subsequent time-consuming laboratory measurements or additional well log acquisitions.
Solution Approach 2:
The patent skips the time-consuming steps of collecting laboratory data or multi-directional well logs by directly processing existing vertical well log data through simplified rock physics relationships. It rushes through the data processing pipeline by using analytical models (Backus model, Thomsen parameter relationships) that convert vertical well log data into anisotropy parameters without intermediate measurement steps.
3Ease of operation
If conventional well-log suites are used without rock physics modeling, then ease of operation is improved, but measurement precision deteriorates due to inability to accurately model elastic stiffness tensor in TI media
Solution Approach 1:
The patent introduces rock physics modeling and the Backus model as intermediary steps between conventional well log data and anisotropy parameter determination. These intermediary models serve as mediators that transform simple vertical well log measurements into accurate elastic stiffness tensor representations and Thomsen parameters, bridging the gap between ease of data acquisition and modeling precision.
Solution Approach 2:
The patent applies parameter changes by transforming the elastic stiffness tensor components into Thomsen parameters (ε, δ, γ) through mathematical relationships. It changes the parameter representation from the complex elastic stiffness tensor to the more intuitive Thomsen parameters, which can be directly calculated from vertical well log data using the Backus model, improving both operational simplicity and modeling accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides a cost-effective and accurate estimation of anisotropy effects in TI subsurface media, enabling the determination of possible anisotropy ranges and improving subsurface characterization using conventional well-logs, which can be further refined with seismic or laboratory data.
Implementation Method 1
The workflow uses downscaling followed by upscaling of normal logs by the Backus model. The rock physics modelling is performed within the downscaling step.
Implementation Method 2
Velocity anisotropy, which is known as the directional dependency of velocities, is important in subsurface imaging and characterization.
Data Source
AI summary
Modeling an elastic stiffness tensor in a transverse isotropic subsurface medium acquires well log data for at least one well passing through the transverse isotropic subsurface medium. The transverse isotropic subsurface medium is divided into an effective anisotropic layer and an isotropic layer. The effective anisotropic layer elastic parameters are modeled, and the isotropic layer elastic parameters are modeled using the effective anisotropic layer elastic parameters and the acquired well log data. The modeled effective anisotropic layer elastic parameters and the modeled isotropic layer elastic parameters are used to upscale the effective anisotropic layer and the isotropic layer into the transverse isotropic subsurface medium comprising a single layer and to determine the five members of the elastic stiffness tensor for the transverse isotropic subsurface medium.