Waterflood Performance Analyses for the Bhagyam Viscous Oil Reservoir

摘要

Bhagyam is a large oil field in the Barmer Basin of Rajasthan, India. The major producing intervals are shallow Paleocene-aged Fatehgarh sandstones. The paraffinic oil is viscous (20-500 cP) with wax appearance temperature (WAT) only 2-3°C lower than the average reservoir temperature of ~53°C. Bhagyam has been developed with 153 wells in an edge linedrive waterflood and has been producing since 2012. However, performance has been less than projected in the initial field development plan (FDP): not as good as the nearby Mangala and Aishwariya Fatehgarh waterfloods and at the lower-end of that seen in worldwide viscous oil waterflood analogues. Key contributors to Bhagyam's performance were lower than expected initial well productivity and a more rapid rise in water cut than projected. The lower initial well productivities were surprising when compared with experience from Mangala, where initial well productivity was closely aligned with expectations. Simulation models could not replicate Bhagyam performance without numerous major local modifications; hence long-term model predictions were not sufficiently reliable for business planning. Reservoir behaviour was initially attributed to severe heterogeneity and early models used high permeability streaks to match performance. However, saturation logs and selective zonal flow back of a few wells showed that injected water was not confined to select high permeability streaks but was widespread both areally and vertically. The more diffuse nature of water movement suggested a fundamental disconnect between field dynamics and the simulation model description and physics.