Experimental investigation on using CO 2 /H 2 O 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 con firmed. 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. (c) 2023 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).