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

Abstract

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.

Phase behavior of single and multi-component liquid hydrocarbons in real reservoir rocks

“…8 a,b). On the other hand, with multicomponent solvents, the liquid phase of heavier components with higher boiling temperatures restricts the movement of the vapour phase of lighter components as observed in our previous study 20 in silicate glass microfluidic chips. The delay of vapour bubbles to appear on the rock surface results in reduction of the temperature deviations specifically at the atmospheric pressure.…”

“…All these parameters affect the phase distribution and entrapment of generated gas, which eventually results in different phase behavior in multi-component systems. In situations where a single-component solvent exists, at the phase-change stage, a large percentage of the vapour phase does not get interrupted or trapped by the liquid phase from the same fluid 20 . This phenomenon explains the cause of noticeable temperature deviations of pure solvents from their normal boiling points (Fig.…”

“…As a result, shifted vaporization pressures of propane, heptane, and octane were noticed in the permeable rocks, including the tight rocks (shale and tight sandstone) at which a high percentage of their pore diameters are in nanoscale (< 100 nm). This paper is a continuation of our previous works [5][6][7]18,20 , and it investigates the vaporization temperature of pure-component hydrocarbon solvents, binary mixtures, and ternary mixtures in different reservoir rocks and under various pressures. Experimental data and evidences are provided as to the effect of confined environment (nano-pores and high capillary pressures) on the phase behavior (vaporization) of solvents.…”