Role of viscous cross-flow and emulsification in recovery of bypassed oil during foam injection in a microfluidic matrix-fracture system

Role of viscous cross-flow and emulsification on foam displacement process, has been experimentally studied in a microfluidic device (consists of homogeneous matrix pattern and a fracture in one side) by changing the injectant type (gas/foam/aqueous solution of surfactant/water) and foam quality and presence of connate water. Two distinct regions have been identified during foam displacement: 1) A dynamic region where gas and foam saturation is low and it mostly consists of aqueous phase. Emulsions of oil phase is generated at the front of dynamic region. 2) A static region where foam saturation is high and fluids' mobility is low. The discussion has been also supported by analysis of calculated oil recovery variation versus foam quality with a bell-shaped trend, matched with foam rheology reported in standard quality scan tests. Foam injection tests and gas injection ones as the case of no viscous cross-flow have been contrasted and the results confirmed the proposed role of viscous drives. Proper condition of emulsification has been discussed in foam injection tests and it has been shown that lack of such conditions in surfactant injection leads to weak emulsification. Moreover, foam generation mechanisms which have been observed during the experiments are snap-off and pinch-off.