Experimental investigation on using CO2/H2O emulsion with high water cut in enhanced oil recovery

CO 2 emulsions used for EOR have received a lot of interest because of its good performance on CO 2 mobility reduction. However, most of them have been focusing on the high quality CO 2 emulsion (high CO 2 fraction), while CO 2 emulsion with high water cut has been rarely researched. In this paper, we carried out a comprehensive experimental study of using high water cut CO 2 /H 2 O emulsion for enhancing oil recovery. Firstly, a nonionic surfactant, alkyl glycosides (APG), was selected to stabilize CO 2 /H 2 O emulsion, and the corresponding morphology and stability were evaluated with a transparent PVT cell. Subsequently, plugging capacity and apparent viscosity of CO 2 /H 2 O emulsion were measured systematically by a sand pack displacement apparatus connected with a 1.95-m long capillary tube. Furthermore, a high water cut (40 vol%) CO 2 /H 2 O emulsion was selected for flooding experiments in a long sand pack and a core sample, and the oil recovery, the rate of oil recovery, and the pressure gradients were analyzed. The results indicated that APG had a good performance on emulsifying and stabilizing CO 2 emulsion. An inversion from H 2 O/CO 2 emulsion to CO 2 /H 2 O emulsion with the increase in water cut was confirmed. CO 2 /H 2 O emulsions with lower water cuts presented higher apparent viscosity, while the optimal plugging capacity of CO 2 /H 2 O emulsion occurred at a certain water cut. Eventually, the displacement using CO 2 /H 2 O emulsion provided 18.98% and 13.36% additional oil recovery than that using pure CO 2 in long sand pack and core tests, respectively. This work may provide guidelines for EOR using CO 2 emulsions with high water cut.