PETE311_06A_Class19_(Maggard)

PETE311_06A_Class19_(Maggard) - Boundary Tension and...

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Boundary Tension and Wettability
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Immiscible Phases • Earlier discussions have considered only a single fluid in the pores – porosity – permeability • Saturation : fraction of pore space occupied by a particular fluid (immiscible phases) –S w +S o +S g =1 • When more than a single phase is present, the fluids interact with the rock, and with each other
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DEFINITION OF INTERFACIAL TENSION Interfacial (boundary) tension is the energy per unit area (force per unit distance) at the surface between phases Commonly expressed in milli- Newtons/meter (also, dynes/cm)
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BOUNDARY (INTERFACIAL) TENSION Modified from PETE 311 Notes • Imbalanced molecular forces at phase boundaries • Boundary contracts to minimize size • Cohesive vs. adhesion forces LIQUID (dense phase) Molecular Interface (imbalance of forces) GAS SOLID LIQUID GAS θ OLID Cohesive force Adhesion force
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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
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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
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DEFINITION OF ADHESION TENSION Adhesion tension is expressed as the difference between two solid-fluid interfacial tensions. θ σ = σ σ = cos A ow ws os T A positive adhesion tension indicates that the denser phase (water) preferentially wets the solid surface (and vice versa ). An adhesion tension of “0” indicates that both phases have equal affinity for the solid surface
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CONTACT ANGLE The contact angle, θ , measured through the denser liquid phase, defines which fluid wets the solid surface. A T = adhesion tension, milli-Newtons/m or dynes/cm) θ = contact angle between the oil/water/solid interface measured through the water, degrees σ os = interfacial energy between the oil and solid, milli-Newtons/m or dynes/cm σ ws = interfacial energy between the water and solid, milli-Newtons/m or dynes/cm σ ow = interfacial energy (interfacial tension) between the oil and water, milli-Newtons/m or dynes/cm Solid Water Oil Oil Oil σ os ws ow θ os
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This note was uploaded on 12/03/2009 for the course PETE 311 taught by Professor Staff during the Spring '08 term at Texas A&M.

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PETE311_06A_Class19_(Maggard) - Boundary Tension and...

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