Summary
In 2004, the large Mangala, Aishwariya, and Bhagyam oil-fields were discovered in the remote Barmer basin of Rajasthan, India. The fields contain light, paraffinic crude oils with wax-appearance temperatures only 5°C less than reservoir temperatures and in situ viscosities that range from 8 to 250 cp. As these were the first significant hydrocarbon discoveries in this part of India, there were few analog performance data available. Development plans for the fields are based on hot waterflooding to prevent problems with in-situ wax deposition, with production startup expected in 2009.
This article presents some waterflood results from viscous-oil fields around the world, benchmarks the expected performance of the newly discovered Rajasthan fields to this database, and discusses several issues associated with waterflooding viscous oils. Given that the Rajasthan oils have some properties that might be considered "unusual" and potentially troublesome for waterflooding and that there are no long-term production data or a history match of waterflood performance in hand, these benchmarks were considered important reality checks. In fact, fields with similar or much higher viscosities are waterflooded routinely with excellent recoveries in Canada, the USA, and elsewhere.
Introduction
Waterflooding is sometimes dismissed as an ineffective process for a viscous-oil field, with development plans focused on more-exotic and -expensive recovery mechanisms such as chemical or thermal processes. However, basic application of Darcy's law and fractional flow theory, combined with operations that focus on production at very high water cuts, clearly shows that viscous-oil fields can yield reasonably good ultimate recoveries under waterflood.