Mechanistic Investigation of in-situ W/O Emulsion Formation During Heavy Oil Waterflooding

In-situ water-in-oil (W/O) emulsion formation is considered as a non-negligible and unwanted issue during heavy oil waterflooding. Low ultimate oil recovery, oil viscosity increase, formation damage, abnormal pressure spikes during the production period and further separation difficulties are known as the major drawbacks of in-situ W/O emulsion formation. In order to overcome the foregoing complications, a precise survey about the mechanisms of in-situ W/O emulsion formation is required. In this work, a series of pore- or micro-scale waterfloodings at room condition along with high pressure and temperature coreflood experiment have been performed to investigate the associated mechanisms of in-situ W/O emulsion emergence in porous media and subsequent formation damage. The outcomes indicate that in-situ W/O emulations formation during high salinity waterflooding in heavy oil reservoirs causes unstable displacement process which yields early breakthrough of injected water at core-scale and low sweep efficiency. More investigations at pore-scale show that the snap-off, water shortcut and emulsion division are leading mechanisms causing viscous emulsion formation. Heterogeneity of porous media plays a key role in intensifying the consecutive W/O emulsion. These emulsions are stable during flooding period which could be ascribed to the natural surface-active components, such as asphaltenes that act as natural emulsifiers.