Rock Sample Permeability Testing Under Constant Differential Pressure
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Solution Overview
Problem
Measuring permeability and effective stress dependence in unconventional source rocks is challenging due to hysteresis effects caused by soft components like total organic carbon and clays, leading to inaccurate parameter extraction.
Innovation Solution
Perform multiple series of permeability measurements with increasing confining and pore pressures, maintaining a constant differential pressure to ensure non-negative effective stress, and use a selected Biot coefficient between 0 and 1 to reduce hysteresis, determining the actual Biot coefficient through curve fitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional permeability measurement methods are used on unconventional source rocks, then measurement can be performed, but hysteresis effects caused by soft components lead to grossly inaccurate parameter extraction
Solution Approach 1:
The patent transforms the permeability measurement approach by changing the parameter control strategy: instead of controlling stress conditions and measuring permeability, it controls permeability (via constant differential pressure) and measures stress conditions. This parameter transformation eliminates hysteresis effects and enables accurate determination of Biot coefficient and effective stress dependence.
2Measurement precision
If multiple permeability measurements are performed at different stress conditions, then permeability evolution can be captured, but hysteresis causes the measured permeability to differ significantly between loading and unloading cycles
Solution Approach 1:
The patent inverts the traditional measurement approach: rather than applying stress cycles and measuring permeability changes, it maintains constant differential pressure (inverting the control variable) and measures the resulting stress conditions and flow properties. This inversion eliminates the hysteresis problem entirely.
3Measurement precision
If traditional effective stress dependence measurement is performed, then stress effects can be quantified, but soft components cause partial loss of elasticity resulting in hysteresis and inaccurate coefficients
Solution Approach 1:
The patent extracts the harmful hysteresis effect by separating the measurement into two independent parts: (1) determining Biot coefficient from permeability measurements at constant differential pressure, and (2) determining effective stress dependence from the relationship between measured permeability and effective stress. This extraction eliminates the coupling that causes hysteresis.
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
Accurately determines Biot coefficient and effective stress dependence, reducing hysteresis effects, and provides better permeability evolution estimation with pore pressure changes, enhancing hydrocarbon production prediction and economic evaluation.
Implementation Method 1
performing a plurality of series of permeability measurements of a rock sample with a permeability test assembly to derive a plurality of permeability values
Implementation Method 2
the presence of soft components, such as total organic carbon (TOC) and clays, which cause the partial loss of elasticity of the rock samples, thus resulting in the phenomenon called hysteresis
Data Source
AI summary
Techniques for determining properties of a rock sample include performing a plurality of series of permeability measurements of a rock sample with a permeability test assembly to derive permeability values, where each series includes permeability measurements of the rock sample at a respective, constant differential pressure between a particular confining pressure and a particular pore pressure; for each series of the plurality of series, performing a curve fit operation to determine a slope and an intercept of a curve associated with a selected Biot coefficient, the permeability values, and the particular pore pressures to generate a plurality of slope values and a plurality of intercept values; determining an effective stress coefficient of the rock sample; and determining an actual Biot coefficient of the rock sample.