Viscous oil recovery and in-situ deasphalting in fractured reservoirs – Part 2: Effect of solvent type and temperature

Abstract

This paper advances the understanding of the solvent-based EOR methods from our previous work by investigating the effect of solvent type and temperature on the recovery of viscous oil by liquid extraction using sandstone cores with an artificial fracture. The production mechanisms were identified through the analysis of oil production rate, ultimate recovery, and in-situ deasphalting in different sections of the core. The use of dichloromethane (DCM) was introduced as the reference to study the production without in-situ deasphalting whereas n-pentane injection was compared to that of n-butane injection to study the effect of paraffin length on production with in-situ deasphalting. Sustained high production rates, which deviate from the behavior of typical gravity drainage processes, were observed in the cases with in-situ deasphalting. This discrepancy was attributed to the enhanced convection in the matrix due to the alteration of fracture aperture by asphaltene precipitation and deposition. Temperature has a significant impact on oil production through its effect on mass diffusivity as well as asphaltene rheology. The result of this work indicates that solvent selection is a key factor in the optimizing solvent EOR process and potential asphaltene deposition should be taken into consideration.