Some Investigations on the role of microparticles on the low salinity process

Abstract

Several papers dealing with laboratory experiments or field operations confirm that, in some circumstances, low salinity waterflooding improves oil recovery. However, the basic mechanisms explaining the oil recovery improvement are not clearly established. The literature points out several hypotheses, among them is the role of clay particles detachment and migration. Experiments using an intermediate-wet clayey sandstone were first performed showing an oil recovery increment when the injected brine salinity was reduced. SEM observations on native and flushed cores show the differences of pore surfaces before and after the low salinity waterflooding and the peculiar role of clay particles. Following this trail, in a second set of experiments we investigated the role of microparticles on the formation and stability of brine/oil emulsions when the salinity is changed. For that, we used calibrated latex particles negatively charged and several oils (mineral, crude and a blend of the two). Emulsion samples were observed using an optical microscope to determine their droplet size distributions and interface structures. The macroscopic stability of the emulsions was also investigated. The results show that the particle wettability, which is related to its surface charge and brine salinity, plays a central role. For high salinity the particles are hydrophobic and migrate toward the brine/oil interface forming a stable emulsion known as “Pickering emulsion”. For low salinity the particles are hydrophilic and the emulsion is not stable. In a third step the same latex particles were deposited in an artificial consolidated porous medium prior to two phase flow experiments. Our results show that even if no recovery improvement is observed, colloidal particles are recovered at the outlet when low salinity waterflooding is performed. The additional oil recovery during a low salinity brine injection is not a direct consequence of the particles mobilization but involves several mechanisms such as rock and brine composition, particle and oil nature, wettability, …. A thorough analysis of all these mechanisms calls upon further studies.