WETTING OF QUARTZ BY OLEIC AQUEOUS LIQUIDS AND ADSORPTION FROM CRUDE-OIL/

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 wetti ng of quartz by oil and brine. Changes in wetting of the quartz plate from a completely water-wet state were induced by adsorption from crud e oil or de-asphalted crude oil (maltenes). Other variables included b rine composition, pH, aging temperature and time, the solvent used to remove excess crude oil from the plate, and the temperature of measure ment. The effect of plate speed and allowing an equilibration time dur ing the course of measurement were also investigated. Force-distance r elationships 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-r eceding force-distance curves sometimes exhibited small-scale fluctuat ions for receding contact angles in the range of about 62-100 degrees. These were ascribed to heterogeneity of wetting. Two modes of contact angle transition, pinning and slippage, were observed. Experimental r esults were compared with predicted force-distance relationships given by interface pinning during transitions from receding to advancing co ntact angles. Slippage during contact angle transitions was usually ob served for receding angles in the range of 30 degrees to about 60 degr ees with associated advancing angles in the range of 65-165 degrees, S lippage was eliminated by allowing an equilibration time of about 30-6 0 min prior to reversing the direction of movement of the plate; exper imental results were then in close agreement with theory. (C) 1998 Els evier Science B.V.