Waterflood Performance Analyses for the Bhagyam Viscous Oil Reservoir

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Summary The Bhagyam field contains medium-gravity viscous crude oil. Notably, its waterflood performance has been substantially worse than projected in its initial field development plan (FDP) and poorer than in nearby analog fields and other viscous oil waterfloods from around the world. Early simulation models could not replicate Bhagyam waterflood performance without numerous major modifications. Poor performance was initially attributed to unforeseen severe heterogeneity. As data accumulated, conceptual simulations showed that an extreme level of heterogeneity was required to match observed performance, suggesting permeability heterogeneity alone could not explain results. Log data from later infill wells also showed that injected water was not confined to high-permeability streaks but was areally and vertically widespread. Two major changes drove significant improvements in waterflood simulation history matches. First, a new porosity/permeability model calibrated to pressure falloff (PFO) tests in the aquifer resulted in a higher degree of heterogeneity, which accelerated water production in updated simulation models. Second, a new oil/water relative permeability model that accounted for the hypothesized presence of a small, solid wax saturation reduced initial oil relative permeability and predicted oil rates, and further accelerated water production. Resulting simulation models showed excellent history matches and have continued to match performance during the past 2 years with only minor additional modifications.