CO₂ emulsions used for EOR have received a lot of interest because of its good performance on CO₂ mobility reduction. However, most of them have been focusing on the high quality CO₂ emulsion (high CO₂ fraction), while CO₂ emulsion with high water cut has been rarely researched. In this paper, we carried out a comprehensive experimental study of using high water cut CO₂/H₂O emulsion for enhancing oil recovery. Firstly, a nonionic surfactant, alkyl glycosides (APG), was selected to stabilize CO₂/H₂O emulsion, and the corresponding morphology and stability were evaluated with a transparent PVT cell. Subsequently, plugging capacity and apparent viscosity of CO₂/H₂O 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%) CO₂/H₂O 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 CO₂ emulsion. An inversion from H₂O/CO₂ emulsion to CO₂/H₂O emulsion with the increase in water cut was confirmed. CO₂/H₂O emulsions with lower water cuts presented higher apparent viscosity, while the optimal plugging capacity of CO₂/H₂O emulsion occurred at a certain water cut. Eventually, the displacement using CO₂/H₂O emulsion provided 18.98% and 13.36% additional oil recovery than that using pure CO₂ in long sand pack and core tests, respectively. This work may provide guidelines for EOR using CO₂ emulsions with high water cut.

The development of environmental friendly low dose hydrate inhibitors like kinetic hydrate inhibitors (KHIs) is of great significance for the flow assurance in oil & gas production and transportation. In this work, a combined molecular dynamic simulation and experimental verification approach was adopted to increase the efficiency of KHIs development. The inhibition effect of a series of copolymers (N-vinylpyrrolidone and N-acrylate) on hydrate growth was studied by using both molecular dynamics simulation and experimental approaches. The simulation results demonstrated that introduction of hydrophobic ester and butyl group in PVP is beneficial for the inhibition. The length of the alkyl chain of ester group played an important role in improving inhibition performance. PVP-A, the one being introduced butyl ester group into PVP gets the best inhibition effect. In addition, inhibitors can restrict methane bubbles to re-dissolve into the liquid phase, thereby inhibiting the growth of methane hydrate. Increasing the interaction between KHIs and methane can also improve the inhibitory effect of KHIs. The experimental results confirm the reliability of the molecular dynamics simulation.