10 - Rock–Fluid Interactions

Abstract

This chapter presents the representation of rock–fluid interactions using physical parameters such as relative permeability and capillary pressure. Capillary pressure is the pressure difference across the curved interface formed by two immiscible fluids in a small capillary tube. Capillary pressure in reservoirs depends on the interfacial tension between two immiscible fluids, the contact angle between rock and fluid, and the pore radius of the rock. The contact angle is a function of wettability, and pore radius is a microscopic rock property. It depends on the history of the rock–fluid system. Capillary pressure is a function of saturation that depends on the direction of saturation change. The direction of saturation change depends on the historical events that led to the present distribution of fluids in the formation. Wettability can be inferred by examining relative permeability curves. The wettability indicators are not a substitute for laboratory measurements, but they can aid in the characterization of the fluid flow environment. One wettability indicator is the point of intersection on the saturation axis of two relative permeability curves.