Study of wettability and spreading impact in three-phase gas injection by cryo-scanning electron microscopy

Much has been already done and written on the effect of wettability and spreading in three-phase displacement properties and efficiency. However, a direct visualization of the impact of these parameters in the distribution of the three fluids (water–oil–gas) within the pore space and consequently on the recovery mechanisms has been lacking. The objective of this paper is to obtain at the pore scale the necessary information to interpret the macroscopic behavior and to predict ultimate oil recovery for well controlled wetting and spreading conditions. To this end cryo-scanning electron microscopy (cryo-SEM) observations are performed in water-wet and oil-wet Fontainebleau sandstone plugs for spreading and non-spreading conditions. It is demonstrated that cryo-SEM can be used as a tool to study at the pore scale the fluid distributions and efficiency of oil recovery processes involving three phases. It is also proved that in a real porous medium both wettability and spreading affect gas injection efficiency by controlling three-phase distributions at the pore level and phase connectivity.