How does the presence of an oleic phase influence salt transport during polymer-enhanced low-salinity waterflooding?

Abstract

Our preceding single-phase experiments demonstrated that polymer enhanced low-salinity waterflooding (PELS) can significantly reduce salt dispersion and improves low-salinity waterflooding (LSWF) performance. In this paper, we extended the research to two-phase fluid flow conditions in the presence of an oleic phase. To assess this quantitatively, a series of two-phase coreflooding experiments using artificial cores were conducted. To eliminate the impact of fluid–fluid and rock–fluid interactions associated with LSWF on salt dispersion, a model, non-polar oleic phase was chosen. The salinity breakthrough results of two-phase corefloods were interpreted using a non-Fickian model based on the Mobile-Immobile Model to infer salt dispersion coefficient. The impact of Partially-Hydrolyzed Polyacrylamide (HPAM) concentration, injection rate, salinity difference, and flooding mode (secondary or tertiary) on salt transport and dispersion through porous media were studied. The results revealed an increase in the salt dispersion coefficient under two-phase conditions by as much as sixfold; taking significantly larger times to displace the high salinity brine. Thus, the optimal HPAM concentration required to effectively suppress mixing was found to be twice (∼400 ppm) as much under the single-phase flow. Reduction of salinity difference also resulted in the reduction of the salt dispersion coefficient by 32%. Moreover, it was observed that in tertiary mode injection where the starting water saturation of the core is higher due to a prior high salinity flooding, the salt dispersion can be increased by more than 21%. These new two-phase results and insights support the possibility of mixing-control under two-phase condition by using PELS and provides a solution to facilitate field implementation.