Microfluidic Pore-scale Analysis of Polymer Flooding Effects of Polymer Molecular Weight and Viscosity

Polymer flooding is a widely applied EOR method to increase oil recovery from heavy oil reservoirs by improving the mobility and conformance control of the displacement process. Core and sandpack floodings have been mostly applied to evaluate the polymer flooding performance for a given reservoir; but the associated pore-scale dynamics with varying polymer MW and chemistry remains unclear in these experiments. Hence, a synergistic approach of coreflood testing along with visual experiments can provide the detailed insight of polymer flow behavior and performance. Microfluidic experiments through accurate representation of reservoir rock properties and several sequences of EOR fluid injections can bridge this gap. In this study, a microfluidic chip analogus to Bentheimer sandstone outcrop was designed for all the injection experiments. Single viscosity injection tests with 2 different polymer MW resulted in improved mobility control and faster and higher ultimate oil recovery with higher viscosity slug compared to lower viscosity. Sequential injection tests of low and high viscosity resulted in higher ultimate oil recovery with lower MW polymer due to improved sweep efficiency. Optical analysis suggested higher residual oil in porous media due to significant pore plugging and fingering behavior with the higher MW polymer compared to lower MW polymer.