Mechanisms of Residual Oil Displacement by Steam Injection

Abstract

Summary In an attempt to isolate various thermal and hydrodynamic mechanisms, a model of one-dimensional (1D) steam displacement of residual oil has been developed. The quasisteady model considers capillary pressure gradients and gravity forces during the simultaneous flow of oil, water, and steam to be the dominant factors in oil-bank mobilization. It was shown that under most conditions, the Buckley-Leverett displacement velocity is significantly faster than the steam-condensation-front velocity. This feature dictates the use of the steam-condensation-front velocity as the characteristic velocity in the problem formulation. Semianalytical solutions of saturation and pressure distributions are presented. Experiments were conducted to examine steam displacement of volatile, partially volatile, and nonvolatile nonaqueous-phase liquids at a residual saturation of 2.5%. Complete displacement of all low-viscosity, partially volatile liquids was observed. Displacement of a high-viscosity, nonvolatile oil was not observed. These experiments and similar results from the literature were in reasonable agreement with the model. It is concluded that mass-transfer-limited evaporation of hydrocarbon components with significant vapor pressures is responsible for the observed low residual oil saturations (ROS’s) in the steam zone.