Effect of Temperature and Salinity on Wettability: Microscoscale Study

摘要

It is well known that thermal EOR improves recovery by lowering the oil viscosity and so is usually performed in heavy oil reservoirs. Wettability alteration may also occur during thermal EOR in which case it may also affect production rates in light oil reservoirs. The interaction between crude oil-brine on different rock surfaces as a function of temperature is not well defined. For example, for silicate surfaces some authors reported a complete reversal of wettability, from a predominantly water-wet system at lower temperature to a predominantly oil-wet system at higher temperature, while others found that the degree of water wetness increased with temperature. In this study, the microscopic behavior, by direct observation, of oil and brine on silicate surfaces at different temperatures up to 60°C was studied. Wetting preference of silica as a function of brine salinity, oil type and temperature has been studied during long time interaction (aging) tests. Four light crude oils of different asphaltene contents and brines of different composition have been used in this work. The study shows that as the temperature increases, the silicate wettability becomes more oil-wet as the asphaltene content of the crude oil decreases. When asphaltene is removed from a crude oil, the degree of oil-wetness is reduced. Regarding the brine effect, in acidic-lower salinity (NaCl brine) where oil adhesion occurs readily, hysteresis between advancing- receding contact angles is larger than for a neutral pH with high salinity brine. The consequence of these observations in flat surfaces is validated by flowing oil and water through glass micromodels, which provide wettability alteration evidence for lower salinity brine and as temperatures increases.