Viscosity ratio effects on fluid displacement pattern and recovery efficiency on porous media

The injection of a fluid to displace another fluid is a very common process used to enhance the recovery factor in oil reservoirs. In circumstances where gravitational segregation and inertial forces are negligible and the capillarity number is high, the viscosity ratio is the only parameter that governs the flow. The main contribution of this study is the verification of the applicability of a simple equation to predict the effects of viscosity ratio on the residual oil mass that is kept trapped into the porous media, also called lost mass. The experiments, together with data from the literature, allowed us to evaluate the accuracy of the proposed equation. The simulations use an homogeneous representation of the porous media, since the heterogeneous representation is usually limited to micro-scale problems due to its high computational cost. Despite the limitations of the homogeneous model, it succeeded in predicting the flow patterns and the lost mass values for all the viscosity range evaluated except for viscosity ratio values smaller than one because, for this condition, the flow tends to the stable displacement pattern and, in this case, the adhesive forces of the oil with the grains that comprise the porous media must be considered.