A multi-scale approach to dynamic processes at the oil-water interface in surfactant enhanced oil recovery

Abstract

Surfactant enhanced oil recovery (EOR) is used to increase production from oil reservoirs where, after conventional water-flooding processes, typically 60-70% of oil remains trapped by capillary forces. Enhanced recovery processes are important because of the reduction of easily accessible new reservoirs and increasing global demand for energy. This thesis describes studies on the visualisation of the oil-water interface during surfactant flooding enabling investigation of the underpinning mechanisms of surfactant EOR. The results will aid design systems for more efficient oil recovery and improve oil recovery models.
The thesis describes a multi-scale approach to the study of dynamic processes at the oil-water interface. The conventional approach to surfactant EOR depends upon equilibrium/continuum approach. However, behaviour at the interface depends on transport processes, local geometries, local concentrations, local oil-water ratio, and local wettability. These factors affect the local phase behaviour at the moving oil front, which in turn impacts oil mobilisation. Such factors cannot be described based on bulk analysis and equilibrium phase behaviour.
A pore-scale study demonstrated that the efficiency of a flood could be maintained at much reduced surfactant concentration, giving potential for substantial cost reduction. Furthermore, solubilisation of oil in a middle phase was shown not to be essential for complete oil desaturation from a pore network. Non-uniform adsorption at the oil-water interface in a hydrophilic pore network was suspected to be responsible for the mobilisation of oil blobs in the direction opposite to the flood direction. At the fracture scale, long-lasting self-induced convective flows were triggered by an interfacial tension gradient of less than 1% of the equilibrated interfacial tension. These two novel and captivating phenomena have not been reported previously. Finally, this thesis proposed a method development to monitor the formation of microemulsion at the oil-water interface by ellipsometry under convective and diffusive transport processes.