Direct visualization of pore-scale fines migration and formation damage during low-salinity waterflooding

Abstract

Formation damage due to fines migration results, potentially, in significant decreases in reservoir permeability and, hence, the recoverability of crude oil from reservoirs. On the other hand, low salinity brine injection is a promising technique for increasing oil recovery from clay-rich sandstones in an economic manner. Clay detachment at low salinity conditions, however, drastically alters fluid flow. In this work, clay-functionalized etched-silicon micromodels are used to visualize directly the mobilization of clay at low salinity conditions in (i) the absence of oil, and (ii) the presence of oil. Study results include clay mobilization and pore plugging in the absence and presence of oil visualized by saturating the clay-functionalized micromodel with high salinity brine followed by injections of reduced salinity brines. Clay detachment and migration was observed in oil-free systems for 4000 ppm NaCl low salinity injection brine. The extent of fines detachment was quantified to determine the types of clay structures affected. Furthermore, fines migration, flocculation, and re-deposition were visualized directly. The types of structures formed (i.e., pore-plugging, pore-lining, etc.) by the re-deposited clay particles are characterized to determine their impact on formation damage. Clay detachment in the presence of oil was also visualized. Initial conditions analogous to clastic reservoirs were established by allowing the crude oil, brine, and solids to interact (i.e., age). Clay detachment occurred during 4000 ppm NaCl low salinity oil recovery. Real-time, pore-level visualization revealed significant mechanisms during oil recovery processes and their influence on multiphase flow. Specifically, pore plugging particles in water-filled pores obstructed preferential flow paths and diverted injection fluid to unswept regions thereby increasing oil production.