Page 432 - Enhanced Oil Recovery in Shale and Tight Reservoirs

400 Enhanced Oil Recovery in Shale and Tight Reservoirs

deionized water or the surfactant solution was not higher, because the capil-
lary pressure might be marginal compared with the injection pressure and
the surfactant concentration was too low. But the flow back volume of
the surfactant solution was higher than the deionized water because the sur-
factant changed the rock from strongly water-wet to intermediate-wet.