Abstract
Little oil is recovered from fractured oil-wet carbonate rocks by waterflooding. Surfactant treatments are being developed to enhance oil recovery from such formations. This work investigates the effect of temperature on such surfactant treatments. Anionic and nonionic surfactants have been identified for oil recovery from fractured low permeability carbonate rocks at high temperatures. For most of the surfactants studied, optimal salinity decreases slightly or remains unchanged with an increase in temperature. Contact angles on initially oil-wet calcite plates decrease on addition of most of the surfactants; the final contact angle decreases with the increase in temperature for all the surfactants in the current study. Oil recovery rate due to surfactant solution imbibition increases with temperature for all surfactants. At 90°C, high recovery (~60% OOIP in 30 days) was obtained for many surfactants at very low surfactant concentrations (<0.1 wt%) in tight (~15 md) carbonate cores. Surfactant brine imbibition was found to be a gravity driven process. Increase in temperature leads to reductions in viscosity and contact angle (which in turn increases oil relative permeability) which enhances the oil recovery rate.
