Core Permeability Estimation via Mobile Continuum Porosity
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Solution Overview
Problem
Current methods for measuring shale matrix permeability in source rock reservoirs are inaccurate due to their reliance on total porosity, which fails to account for the dual-continuum system in shale cores, leading to inefficient permeability estimation in pulse-decay experiments.
Innovation Solution
A method and system that estimate the porosity of the mobile continuum within the dual-continuum system, using a pulse-decay setup with controlled confining pressure and nitrogen saturation, to accurately calculate core permeability by monitoring pressure changes in upstream and downstream reservoirs and applying a pressure pulse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If total porosity is used in permeability calculation for shale core, then the measurement process is simple, but the permeability estimation accuracy deteriorates
Solution Approach 1:
The patent segments the porosity parameter into two distinct components: mobile continuum porosity (Φf) and immobile continuum porosity. This segmentation allows the measurement process to specifically target and measure only the mobile continuum porosity using nitrogen saturation and pressure pulse decay methods, thereby resolving the contradiction between measurement simplicity and accuracy by eliminating the need to measure and differentiate all pore types while maintaining procedural straightforwardness.
2Reliability
If steady state flow method is used for permeability measurement, then the measurement is reliable, but the measurement time increases significantly
Solution Approach 1:
The patent employs periodic action through the pressure pulse decay method, where a pressure pulse is applied to the core sample and the resulting pressure decay is monitored over time. This transient measurement approach captures the necessary flow information in a short time frame, eliminating the need for prolonged steady-state conditions while maintaining measurement reliability through the characteristic decay curve analysis.
Solution Approach 2:
The patent changes the measurement parameter from steady-state flow rate to transient pressure decay behavior. By monitoring how pressure changes over time during a pulse decay experiment and using the mobile continuum porosity (Φf) in the analysis, the method achieves reliable permeability measurements without requiring the extended time periods needed for steady-state methods.
3Loss of time
If pressure decay method on crushed rock is used, then the measurement time is reduced, but the measurement reliability deteriorates due to sensitivity to particle size and unconfined stress condition
Solution Approach 1:
The patent applies preliminary action by saturating the core sample with nitrogen before conducting the pressure pulse decay measurement. This saturation step ensures that all mobile continuum pores are filled with nitrogen, providing a consistent and reliable starting condition that eliminates sensitivity to particle size variations and stress conditions, thereby maintaining measurement reliability while keeping the process rapid.
Solution Approach 2:
The patent applies local quality by focusing the measurement on the mobile continuum phase specifically, rather than treating the crushed rock as a homogeneous material. By using nitrogen saturation to selectively access and measure only the mobile continuum porosity and applying confining pressure to maintain realistic stress conditions, the method achieves both speed and reliability that crushed rock methods cannot provide.
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 significantly improves permeability estimation accuracy, reducing relative differences with steady-state flow methods to within ±10%, and provides a practical technique for determining core permeability in pulse decay experiments.
Implementation Method 1
saturating the sample holder and the core sample with nitrogen at a saturation pressure, P saturation
Implementation Method 2
applying a pressure pulse, P pulse , to one end of the sample holder... determining core permeability using the porosity of mobile continuum when the pressure in the upstream reservoir, the downstream reservoir, and the mobile continuum is in equilibrium
Data Source
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AI summary
Methods and systems method for determining core permeability of a subsurface formation. The method includes connecting an upstream reservoir to one end of a sample holder comprising a core sample of a subsurface formation, connecting a downstream reservoir to another end of the sample holder, providing a constant confining pressure within the sample holder, saturating the sample holder and the core sample with nitrogen at a saturation pressure, applying a pressure pulse to one end of the sample holder, and determining core permeability using the porosity of the mobile continuum when the pressure in the upstream reservoir, the downstream reservoir, and the mobile continuum is in equilibrium.