Propagation and Entrapment of Hydrocarbons in Porous Media under Capillarity Controlled Phase-Alteration Conditions: A Visual Microfluidics Analysis.

The displacement characteristics of gas-liquid systems in capillary media under nonisothermal and nonisobaric conditions are controlled by capillarity as phase alteration (specifically vaporization) starts earlier in smaller (nano)capillaries compared to the larger ones. For an accurate modeling of these types of natural and engineered processes, this thermodynamically dictated displacement process should be well understood. With this aim, the capillarity effect on phase change and the displacement dynamics of hydrocarbon liquids in homogeneous and heterogenous silicate microfluidics chips was studied. It was observed that the boiling temperatures of pentane, a pentane-heptane mixture, and a pentane-heptane-octane mixture were 1.6-6.9% lower than bulk measurements due to confinement effects, and the early vaporization had a significant influence on the vapor displacement process. In homogeneous (uniform capillary pressure distribution) porous media, the consistency of capillary pressure resulted in a uniform and quicker propagation/displacement of vapor. However, in the media with variable capillary pressure (heterogeneous pore structure), the vapor's flow tended to take place nonuniformly along the system, thus leading to a major gas fingering and gas-flow restriction. The presence of other-heavier-components (liquid phase) in the porous medium developed an excessive barrier against the vapor's flow throughout the pore channels that was specifically caused by the viscous forces of the liquids. Moreover, it was observed that the existence of liquids with high boiling points contribute to slowing the vapor propagation of the lighter components, and the gas displacement becomes slower as the density and viscosity of the liquid-phase components increases.