Fractured Source Rock Characterization for Stress-Dependent Permeability
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Solution Overview
Problem
Existing models for fracture permeability in unconventional reservoirs do not adequately account for stress-dependent permeability changes due to elastic and plastic deformations, which significantly impact hydrocarbon production rates.
Innovation Solution
A method involving a core holder system with pressure and flow control mechanisms to measure effective stress and permeability pairs, allowing determination of parameters such as initial permeability (ki), stress sensitivity parameters (αE and αP) for elastic and plastic deformations, respectively, to predict hydrocarbon production rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If previous elastic deformation models are used, then the model complexity is low, but the prediction accuracy for stress-dependent permeability is insufficient
Solution Approach 1:
The patent transforms the permeability-stress relationship from a simple exponential model to a piecewise function with distinct elastic and plastic deformation regimes. By introducing a transition stress parameter and separate sensitivity coefficients (αE for elastic, αP for plastic), the model captures complex rock mechanical behavior while maintaining computational tractability through parameter calibration from laboratory tests.
Solution Approach 2:
The model dynamically adapts its behavior based on the current stress state relative to the transition stress. When effective stress is below the transition point, the elastic regime applies; when above, the plastic regime takes over. This dynamic switching allows the model to respond appropriately to varying production conditions without requiring a completely complex theoretical framework.
2Measurement precision
If more stress and permeability data points are collected, then the parameter determination accuracy improves, but the testing time and operational complexity increase
Solution Approach 1:
The patent requires a minimum of four stress-permeability data points to calibrate the five model parameters (ki, αE, αP, σtrans, and Bi), which is sufficient to achieve accurate parameter determination without requiring excessive testing time. This partial action approach balances data sufficiency with operational efficiency.
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 enables accurate prediction of hydrocarbon production rates by considering the stress-dependent permeability changes in unconventional reservoirs, thereby improving the estimation of stimulated reservoir volume and overall production efficiency.
Implementation Method 1
obtain at least four pairs of effective stress and permeability values for the sample rock
Implementation Method 2
The pore pressure change can result in complex behavior of the stress-dependent permeability associated with a combination of rock elastic and plastic deformations
Implementation Method 3
The pore pressure change can result in complex behavior of the stress-dependent permeability associated with a combination of rock elastic and plastic deformations
Data Source
AI summary
Systems, methods, and apparatus for characterizing reservoirs are discussed. As an example, a method for characterizing a reservoir is discussed that includes determining a ki parameter, a αE parameter, and a αP parameter based at least in part on the at least four pairs of effective stress and permeability; and predicting a hydrocarbon production rate from reservoir represented by the sample rock based at least in part on the ki parameter, the αE parameter, and the αP parameter.