Formation and flow behaviors of in-situ emulsions in heavy oil reservoirs

As important intermediates generated during surfactant flooding, emulsions are widely acknowledged to be beneficial for enhanced oil recovery. Formation and flow behaviors of W/O and O/W emulsions have been reported in detail. Nevertheless, flow behaviors of W/O/W emulsions have not been sufficiently investigated, which are the most common products during chemical flooding in heavy oil reservoirs. In this study, two surfactant systems with different emulsification tendencies were evaluated by both core flooding and microfluidic experiments. Core flooding experiments with strong emulsifying surfactant (SES) resulted in W/O/W emulsions, while those with weak emulsifying surfactant (WES) produced pure oil and brine. Furthermore, microfluidic experiments indicated the emulsification process of W/O/W emulsion to be time dependent. The W/O emulsions were generally formed at the contact interface of heavy oil and SES solution under the action of convection and diffusion. In addition, the W/O/W emulsions were formed by W/O emulsions under the shear action of porous media during the later period of SES flooding. The formed W/O emulsion with high viscosity and the W/O/W emulsion could divert the following aqueous phase and displace the bypassed oil phase, which contributed to an additional oil recovery.