Contribution of feldspar minerals to pH during Smart Water EOR processes in sandstones

It has previously been suggested that a local pH increase at pore surfaces is responsible for desorption of polar oil components and wettability alteration in sandstone reservoirs, leading to increased oil recovery during Smart Water or Low salinity injection. The pH increase can be a result of cation exchanges at clay surfaces or at other mineral surfaces present in sandstone reservoirs, such as feldspars, which is the topic of this paper. In this study, static batch tests and dynamic sandpack flooding tests have been performed to investigate the pH development in the brine phase in contact with three common feldspars, Ab-feldspar (albite), An-feldspar (anorthite) and Or-feldspar (microcline). Temperature was varied between 23 and 130°C, and brine salinity varied from 0 ppm (de-ionized water) to 100 000 ppm NaCl in batch tests. The sandpacks were composed of 10 wt% feldspar and 90 wt% quartz, and flooded with 100 000 ppm and 1000 ppm brines. In all tests, equilibrated brine pH was monitored to study cati...