Dynamic CFD Modeling of Viscoelastic Polymer; Trapped Oil Displacement and Deformation at the Pore-Level
Ali Afsharpoor and Matthew T. Balhoff
Petroleum and Geosystems Engineering, University of Texas at Austin, 1 University Station C0300 Austin, TX 78712-0228
Polymers are used in enhanced oil recovery (EOR) for the purpose of increasing sweep efficiency, but recent experimental and field data suggest that viscoelastic polymers such as hydrolyzed polyacrylamide (HPAM) can reduce the residual oil saturation as well; thus improving the recovery by an additional 20%. This contradicts decades of belief that polymer improves the sweep efficiency with mobility reduction mechanism, but does not have any effect on residual oil saturation.
We perform dynamic CFD modeling around oil threads in geometries representative of pore throats. The oil thread stability in porous media has been studied to prove the hypothesis that the oil thread is more stable against snap-off in viscoelastic flow than for non-elastic flow. As a result, the oil threads remains connected in successive pores and are therefore more easily displaced. In comparison, using purely-viscous polymer leads to an oil phase that becomes disconnected and a high capillary pressure required to mobilize the trapped oil droplets. We show that the polymer elasticity helps to defer snap-off mechanism and this effect increases with Deborah number as the fluid elasticity be more pronounced. This work studies viscoelastic polymers during both secondary and tertiary recovery, and explains the physics behind the recent observations in laboratory and oil fields. The experiments and field data show residual oil saturation is reduced in secondary recovery, but not tertiary recovery when viscoelastic polymer is used.
AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013