Phase Behaviors of Gas Condensate at Pore Scale: Direct Visualization via Microfluidics and In-Situ CT Scanning

Abstract

Summary Gas condensate is stored in multiscale pores, fractures, and vugs within geological formations. Confinement within these structures significantly influences the phase behavior of gas condensate, rendering it challenging to characterize through conventional bulk pressure/volume/temperature (PVT) measurements. In this study, we used microfluidics and in-situ computed tomography (CT) scanning to directly measure the upper dewpoint of gas condensate and the gas/oil ratio in porous media during depressurization. We used two microfluidic chips with different pore sizes to investigate the confinement effects on gas condensate phase behavior at various scales, including pores as small as 50 nm. Our results revealed a significant increase in the upper dewpoint within the pores compared to bulk PVT measurements, with a more pronounced deviation at smaller pore sizes. Additionally, the proportion of condensate oil in porous media exceeded that observed in bulk PVT measurements at the same pressure. To validate our microfluidic findings, we conducted in-situ CT scanning experiments using a porous media model created by packing quartz particles. CT scans revealed pores ranging from a few micrometers to over 100 micrometers. Consistently, we observed an increase in the upper dewpoint and liquid ratio within these pores. Our study provides crucial experimental evidence indicating that the phase behavior of gas condensate in porous media deviates from bulk PVT measurements. The observed increase in the upper dewpoint, even within micrometer-sized pores, has important implications for phase equilibrium calculations.