Experimental Study of Two-Phase Fluid Flow and Relative Permeability in Low-Permeability Rocks

Abstract The key characteristics of unconventional reservoirs include high heterogeneity of the porous space, low permeability resulting from the nanosized pores, and the presence of solid insoluble organic compounds in the rock. These factors complicate the application of existing physical and mathematical flow models with sufficient accuracy and cause challenges in estimating the recoverable hydrocarbon reserves of unconventional formations. To enhance the characterization of the gas flow in low-porosity and low- permeability media, a detailed study of mass transfer is essential. In current study, we attempt to fill this gap by proposing the NMR- based method for characterizing the fluid flow with accurate saturation measurement in low-permeable rocks. The goal of this research is to study the physicochemical specifics of gas flow and determine the water-gas and oil-gas relative permeability in low-permeability rocks using low-field NMR and X-ray CT assisted core flooding experiments. Both techniques enable the quick and accurate monitoring of fluid saturation in tight rocks under high-pressure conditions. As result, an experimental workflow for determining the relative permeability in two-phase low-permeability systems using NMR was proposed. The impact of the different fluid flow rate is demonstrated in steady-state and unsteady-state core flooding tests for carbonate and tight sandstone core samples. NMR-defined relative permeability is in good agreement with the one determined by X-ray scanning for the same core model.