DEFINITION OF INTERFACIAL TENSION•Interfacial (boundary) tensionis the energy per unit area (force per unit distance) at the surface between phases–Commonly expressed as mN/m (also, dynes/cm)DEFINITION OF WETTABILITY•Wettabilityis the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids.•Wettability refers to interaction between fluid and solid phases.•Reservoir rocks (sandstone, limestone, dolomite, etc.) are the solid surfaces •Oil, water, and/or gas are the fluids WHY STUDY WETTABILITY?•Understand physical and chemical interactions between•Individual fluids and reservoir rocks•Different fluids with in a reservoir•Individual fluids and reservoir rocks when multiple fluids are present•Petroleum reservoirs commonly have 2 – 3 fluids (multiphase systems)•When 2 or more fluids are present, there are at least 3 sets of forces acting on the fluids and affecting HC recovery
DEFINITION OF ADHESION TENSION•Adhesion tensionis expressed as the difference between two solid-fluid. interfacial tensions.•A positive adhesion tension indicates that the denser phase (water) preferentially wets the solid surface (and vice versa).•An adhesion tension of zero indicates that both phases have equal affinity forthe solid surfaceWETTING PHASE FLUID•Wetting phasefluid preferentially wets the solid rock surface.•Attractive forces between rock and fluid draw the wetting phase into small pores.•Wetting phase fluid often has low mobile.wowoswsoTAcos
•Attractive forces limit reduction in wetting phase saturation to an irreduciblevalue (irreducible wetting phase saturation).•Many hydrocarbon reservoirs are either totally or partially water-wet.NONWETTING PHASE FLUID •Nonwetting phasedoes not preferentially wet the solid rock surface•Repulsive forces between rock and fluid cause nonwetting phase to occupy largest pores•Nonwetting phase fluid is often the most mobile fluid, especially at large nonwetting phase saturations•Natural gas is never the wetting phase in hydrocarbon reservoirsWATER-WET RESERVOIR ROCK•Reservoir rock is water - wet if water preferentially wets the rock surfaces•The rock is water- wet under the following conditions:•so > sw•AT > 0 (i.e., the adhesion tension is positive)•0<<90If is close to 0, the rock is considered to be “strongly water-wet”•0<q<90•Interfacial tension between the rock surface and water is less than between the rock surface and oil.SolidWaterOilsoswwo
OIL-WET RESERVOIR ROCK•90<q<180•The interfacial tension between the rock surface and oil is less than between the rock surface and water.
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- Surface tension, capillary pressure, Capillary pressure data