Stress-Sensitive Single-Phase Permeability for Navajo Sandstone Coupling Experimental Testing and Numerical Simulation

Abstract:

Understanding the role of pore fluid flow and the associated fluid properties is vital for generating representative reservoir models. In reservoir simulations it is presumed that pore fluid flow and the accompanying rock permeability are not affected by principle stress or pore pressure changes. However, when elastoplasticity occurs, changes in rock permeability must be taken into account. As a result, reservoir simulations for both fluid production and injection scenarios must include reservoir rock pore deformation.

This study investigates the role of effect stress on permeability measurements for single-phase fluid flow using three distinct pore fluids: nitrogen, supercritical CO₂, and brine. A single outcrop Navajo Sandstone sample from southern Utah was used to remove discrepancies in experimental results for the three fluids. Each of the pore fluids was evaluated using the same effective stress testing matrix to measure the corresponding permeability values and rock deformation. The compiled results show the role of pore fluid type and effective stress on elastoplasticity for the Navajo Sandstone. The core sample properties and experimental data were then used to develop a constitutive model using a finite element simulation package to replicate the laboratory results in the simulator. Both experimental and simulation findings demonstrate the dissimilar rock responses to the different pore fluids and varying effective stresses. Using these findings, a more accurate porous media simulation was generated for each fluid type under changing effective stress conditions. It is anticipated that the findings will clarify permeability concerns associated with changes in effective stress for varying fluid production or injection scenarios that may not have been previously accounted for or considered.