Micro-Scale Experiment and CFD Modeling of Viscoelastic Polymer; Trapped Oil Displacement and Deformation at the Dead-End

Abstract

Abstract Polymers are used in enhanced oil recovery (EOR) to control the mobility ratio between displaced fluid (oil) and displacing fluids (water). Polymer improves sweep efficiency by overcoming gravity overriding, viscous fingering, and channeling. For many years, improving sweep efficiency was considered the only significant mechanism to increase the oil recovery in polymer-flooding. But recently, experimental and field data suggest that viscoelastic polymers such as hydrolyzed polyacrylamide (HPAM) improve displacement efficiency as well and reduce the residual oil saturation. One of the hypotheses is that the elasticity of polymer triggers the pulling-effect on the trapped oil at the dead ends, thus leading to the mobilization of the trapped oil. In this study, micro-scale experiments were done to prove or disprove the hypothesis of viscoelasticity pulling-effect. Then, steady-state (static) CFD modeling was performed in the dead ends of the porous medium to analyze the flow characteristics of viscoelastic polymer. The streamlines, velocity contours, and normal stress contours are discussed here. Both, experimental work and steady-state simulation results show that the oil can be barely mobilized in normal reservoir condition mimicked by the micro-scale experiments. Additionally, transient (dynamic) CFD modeling was carried out for a better understanding of oil droplet movement and deformation at dead-end geometry. The Arbitrary Lagrangian-Eulerian (ALE) finite-element formulation is used to keep track of interface between oil and the displacing fluid. The dynamic simulation results are in agreement with static simulation and experimental results. This study shows that with normally used viscoelastic polymers, the pulling-effect is not the main mechanism resulting in reduced residual oil saturation. However, ways increasing of the Deborah number through potential means, such as using polymer with higher relaxation time, may result in a more significant pulling effect and thereby recover residual oil.