DEFINITION OF INTERFACIAL TENSION • Interfacial (boundary) tension is 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 • Wettability is 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 tension is 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 for the solid surface WETTING PHASE FLUID • Wetting phase fluid 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. wo wo sw so T A cos
NONWETTING PHASE FLUID • Nonwetting phase does 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 reservoirs WATER-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 < < 90 If 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. Solid Water Oi l so sw wo
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. WATER-WET OIL-WET Solid Water Oil wo Ayers, 2001 FREE WATER GRAIN SOLID (ROCK) WATER OIL SOLID (ROCK) WATER OIL GRAIN BOUND WATER F R E E W A T E R OIL OIL RIM < 90 > 90 WATER Oi l Ai r WATER
WETTABILITY IS AFFECTED BY: • Composition of pore-lining minerals • Composition of the fluids • Saturation history (hysteresis effects
You've reached the end of your free preview.
Want to read all 21 pages?
- Fall '13
- Surface tension, capillary pressure, Capillary pressure data