An Investigation into Free-Imbibition of Sessile Drop when Measuring Contact Angle on Porous Substrates

Contact angle measurements play an important role in determination of liquid wettability and hence, recovery from hydrocarbon reservoirs. When a liquid sessile drop is placed on a surface the balance of dominant forces affects its spreading rate and the equilibrium state for the shape of the liquid drop. On a porous surface, the capillary forces of the pores play an important role on the droplet equilibrium state. In this study, the impact of the capillary-driven imbibition on air-liquid contact angle data has been investigated. In each test, contact angle, droplet volume, droplet height and base diameter have been measured versus time for various liquids using a well-equipped automatic drop shape analyzer. The experimental results show that the rate of imbibition depends on the properties of fluids (i.e. surface tension and viscosity) and porous rock (i.e. permeability and wetting tendency). Based on the experimental observations, a conceptual model has been proposed to describe the free imbibition rate into the porous substrate when the spreading rate of the liquid drop on the surface is negligible.