Fundamentals of Fluid Flow in Porous Media
Multi-phase Saturated Rock Properties:
Wettability: Contact Angle Hysteresis
According to the definition ‘hysteresis’ occurs when a measured variable depends on the direction of change of an independent variable. Some factors that may contribute to contact angle hysteresis are as follows:
- Surface roughness,
- Solid surface heterogeneity and differential adsorption of wettability aerating compounds,
- Surface immobility which prevents fluid motion that is necessary for the system to reach a three-phase contact point equilibrium. For example, a surfactant desorbing from the solid-liquid interface into the bulk liquid, and the solid film at the oil-water interface,
- Components in different phases equilibrate among the phases. This can occur when surfactants have solubility in oil and water and adsorb at both interfaces.
- The solid phase contains soluble components and/or when oil contains compounds that adsorb onto solids. The adsorption of oil components is slow and the contact angle changes over hours or months; systems that are initially water-wet may change to oil-wet.
Figure 2‑38 shows the significant effect of rock-fluid-fluid interactions on the contact angle measurement.
Figure 2-38: Rock-Fluid Interactions Effect on the Contact Angle