High mobility-ration-waterflood performance prediction: Challenges and new insights

This paper presents the results of a comprehensive study to improve our understanding of high-mobility-ratio waterfloods (HMRWFs) and to improve performance prediction. Published data on heavy-oil water-injection field projects are limited. Several successful HMRWF projects have been reported, and they show significant oil recovery at high water cut. However, the range of reported recovery is large-waterflood (WF) recoveries of approximately 1-or-2% to 20% of original oil in place (OOIP) have been reported for similar reservoirs. Higher viscosities result in lower recovery. Mechanistic studies using fine-scale simulations show that the viscosity (or mobility) ratio primarily controls oil-recovery response, and that the recovery is lower at higher viscosity ratios. Further, viscous fingers dominate high-viscosity-ratio floods, and mobile water can reduce recovery significantly. Field-scale simulation results indicate that heterogeneity plays a more important role for an HMRWF than for conventional waterfloods. The amount of primary production before the start of the waterflood has a larger effect on incremental oil recovery for high-mobility-ratio floods. Furthermore, highly correlated thin, thief zones reduce recovery of HMRWFs more severely, and rock wettability (relative permeabilties) strongly influences oil recovery. These results indicate that, in addition to reservoir geology, accurate viscosity and relative permeability measurements are essential for a reliable performance prediction.