Wetting of quartz by oleic/aqueous liquids and adsorption from crude oil

Abstract

Contact angles for crude oil and brine on smooth quartz are sometimes used to assess the wettability of sandstone reservoirs. In this paper, the dynamic Wilhelmy plate technique is applied to the study of wetting of quartz by oil and brine. Changes in wetting of the quartz plate from a completely water-wet state were induced by adsorption from crude oil or de-asphalted crude oil (maltenes). Other variables included brine composition, pH, aging temperature and time, the solvent used to remove excess crude oil from the plate, and the temperature of measurement. The effect of plate speed and allowing an equilibration time during the course of measurement were also investigated. Force–distance relationships for a quartz plate passing through an oil–brine interface were used to obtain water-receding and water-advancing contact angles under dynamic conditions. Wetting states ranged from completely water-wet through hybrid-wet (very large contact angle hysteresis) to very strongly oil-wet. Contact angle hysteresis was often observed. Water-receding force–distance curves sometimes exhibited small-scale fluctuations for receding contact angles in the range of about 62–100°. These were ascribed to heterogeneity of wetting. Two modes of contact angle transition, pinning and slippage, were observed. Experimental results were compared with predicted force–distance relationships given by interface pinning during transitions from receding to advancing contact angles. Slippage during contact angle transitions was usually observed for receding angles in the range of 30° to about 60° with associated advancing angles in the range of 65–165°. Slippage was eliminated by allowing an equilibration time of about 30–60 min prior to reversing the direction of movement of the plate; experimental results were then in close agreement with theory.