ABSTRACT
The production of petroleum fluids from underground reservoirs involves the movement of fluid-fluid interfaces through the tortuous paths within the porous rocks. The movement of oil, brine and gas phases relative to one another depends on the nature of distribution of these fluids in the rock pores as well as on the strength of interaction between the fluids and the rock surface. While the distribution of the phases is largely governed by the spreading coefficient, which involves the interfacial tensions at the three interfaces (gas/oil/brine), the strength of rockfluids interactions depends on the dynamic (advancing and receding) contact angles subtended by the moving fluid-fluid interface with the rock surface. These interfacial phenomena of fluid-fluid spreading and the rock-fluids interactions have
generally been lumped into one parameter called wettability in petroleum engineering literature. Although yielding the advantage of a single global term for all the interactions, the term wettability has masked our understanding of the surface and interfacial phenomena, e.g., adhesion, spreading, and their influence on the dynamics of fluids in petroleum reservoirs. The situation is further complicated by the fact that the conventional techniques used to measure dynamic contact angles in solid-liquid-vapor (S-L-V) systems have failed to yield meaningful results when applied to solid-liquid-liquid (S-L-L) systems such as the rock-oil-brine system of interest in petroleum engineering. This has resulted in concerns and skepticism surrounding the applicability of the contact angle concept to S-L-L systems to characterize their wetting tendency. The presence of a thin wetting film of an immiscible liquid on the solid surface and the parameters governing the stability of the wetting film are factors that control the preferential wetting behavior in S-L-L systems. In addition to addressing these concerns, this paper highlights the recent developments related to techniques for making meaningful measurements of dynamic contact angles in crude oil-brine-rock systems at actual reservoir conditions of pressure and temperature in addition to utilizing these data to understand the role of interfacial interactions involved in adhesion, spreading and wettability in S-L-L systems.
