LAUSR

Abstract We evaluated the performance of microemulsions for a heavy oil reservoir with respect to the geochemistry inherent. Two microemulsion (ME) formulations were prepared from Gemini surfactant, heavy oil (API 16.6°) and saline water and further injected in a Berea sandstone. Monitoring the ionic composition of the effluent water showed that the emulsion cut and the sludge deposition were both subsequent to the degradation of the formulation, owing to the dissolution of feldspar due to the water acidity. As per the modeling study, a weak and reversible cation exchange between sodium (Na+) and calcium (Ca2+) was highlighted. Herein was shown that Na+ could prevent and/or mitigate the heightened adsorption of ME to the rock surface. A mildly basic pH for controllable anorthite and albite precipitation plus silica cementation due to sludge formation. We hypothesized that feldspar alteration has an antagonistic effect on the oil expulsion efficiency and ME adsorption. Anhydrite alteration affects CEOR negatively due to high divalent ions causing high ME degradation due to adsorption. Whereas, albite, anorthite and silicate precipitation promotes high recovery and less ME adsorption, due to high Na+ and K+ ions. Silica cementation was proven to increase formation rock wettability. Hence, to achieve high oil recovery and minimal surfactant loss due to adsorption, we propose a high and stable Na+ presence. Graphical Abstract