Investigation of the microscopic displacement mechanisms and macroscopic behavior of alkaline flooding at different wettability conditions in shaly glass micromodels

Among various chemical methods, alkaline flooding has a great potential for enhancing heavy oil recovery, especially for reservoirs which contain acidic crude oil. However, fundamental understanding about microscopic displacement mechanisms and macroscopic behavior during alkaline floods at different wettabilities is not well understood, especially in five-spot shaly models. In this work several alkaline floods are performed on a glass micromodel containing randomly distributed shale streaks at different wettability conditions. Various mechanisms responsible for enhancing heavy oil recovery during alkaline flooding are investigated at different wettability conditions. These mechanisms include IFT reduction, deformation of residual oil, pore wall transportation, inter-pore and intra-pore bridging of oil and alkaline solution, the flow of long thin oil strings, production of W/O emulsion at the front, formation of high non-uniform pressure gradient, production of O/W emulsion in the swept regions that leads to emulsification and entrainment and emulsification and entrapment, and wettability reversal (from oil-wet to water-wet and water-wet to oil-wet). The macroscopic investigation of the experiments shows that alkaline injection improves sweep efficiency via formation of W/O emulsion at the front. It also modifies the fingering pattern so that the displacing fluid penetrates and sweeps the oil from around and between the shales. It lingers the breakthrough and reduces the amount of bypassed oil so that a considerable increase in oil recovery factor is observed.