Low Salinity Waterflood at Reduced Capillarity

Abstract

Abstract A new generation EOR methods comes from combining techniques to make the overall process more efficient and minimize the retention or loss of chemicals. One of the hybrid EOR methods we are investigating combines low salinity brine and reduced capillarity by surfactants, which has potential to increase EOR oil and cost efficiency. It is well documented that low salinity waterflooding may give improved recovery. Judging from published data, it is likely that more than one mechanism is contributing to the observed oil recovery. We have summarized that two of the main effects are destabilization and mobilization of oil layers, and fines migration due to destabilization of clays. The latter is believed to contribute to increased oil recovery by pore blocking and microscopic diversion. If capillary forces are high, the oil mobilized by either of these two mechanisms is easily re-trapped. However if the capillary forces are lowered by adding surfactant, re-trapping may be avoided. The effect of decreasing interfacial tension was investigated in a series of constant rate, low salinity floods performed on crude oil aged Berea sandstone cores. The purpose is to explore the added benefit of the low salinity surfactant process over low salinity brine injection, and to investigate to which extent the capillary forces needs to be reduced to take advantage of the incremental recovery that may be obtained by combining the two processes. The results show that reduction of interfacial tension in low salinity waterfloods gives an increase in oil recovery which exceeds the expected performance of injecting a solution with the same reduction in interfacial tension but without the low salinity contribution. The combined effect of low salinity brine and surfactant injection may have the potential to improve the economy of EOR operations. The desalination cost and logistic involved may in some cases limit the possibility for low salinity waterflood, but enhanced oil recovery by simultaneous lowering of interfacial tension giving a much higher additional oil recovery may improve the overall economy.