Effect of water injection on subsequent polymer floods in viscous oil reservoirs

Abstract

Waterfloods (WF) in viscous oil reservoirs (>100 cp) are unstable and usually bypass a large amount of oil. Polymer floods (PF) often follow waterfloods and improve oil recovery through improved sweep efficiency. This study examines the effect of prior waterflood on the subsequent polymer flooding. The displacement of a viscous oil by water and polymer solution is studied in a custom-built 2D porous medium. Floods are conducted at the interstitial velocity of 1 ft/day with the oil viscosity (μo) of 390 cp at 25 °C. The extent of waterflood beyond the water breakthrough (WBT) is varied from 0 to 0.5 injected pore volume (PV). Polymer injection after the waterflood displaces the oil which further pushes the brine in the established water fingers and is reflected in a decrease in the water cut down to 0–0.3. After dewatering of the fingers, the polymer solution displaces the oil across the whole cross-section. The final recoveries range from 73 to 83 % of the original oil in place (OOIP). Injecting the viscous solution at earlier stages results in earlier production, higher crest of oil cut (fo) and slightly higher cumulative oil production (NpD). This work can help engineers optimize the strategy of polymer flooding in viscous oil reservoirs.