Modeling and Managing Large Mature Carbonate Fields: Examples from the Cretaceous of North Oman

Malcolm Dransfield, Joachim E. Amthor, Nada Al Kindy, Hassan Behairy, Anthony Brooks, Richard Chia, Huw Davies, Philippe Gauthier, Jeremey Harris, Patrick Hogarty, Mohamed Al Mughairy, Robbert Nieuwenhuijs, and Daniel Rayes
Petroleum Development Oman, Muscat, Oman

The remaining potential of two contrasting, large, mature carbonate fields from North Oman is realized through a combination of reservoir modelling and reservoir management techniques, ranging from pragmatic analytical methods to full field simulation models. Both fields produce from fractured carbonates of the Cretaceous Shuaiba Formation. In one field, the reservoir consists of homogeneous basin-floor carbonate mudstones and has been developed by one of the world's largest waterflood. In the other, the reservoir is a complex rudist reef accumulation developed on primary depletion with a waterflood pilot just commencing. Both fields have some 35 years of production history and hundreds of well penetrations. Full-field static and dynamic models have been built for both fields. A base case with sensitivities was chosen for the less heterogeneous reservoir. For the complex rudist reef accumulation, a multi-scenario approach was taken: low, base and high case models were built and history matched to capture the full range of uncertainty. Permeability is a key uncertainty parameter for both fields and different modelling approaches have been taken. In addition to the full-field models, traditional well reviews are used extensively and form the basis of a healthy portfolio of optimisation activities. 3D visualisation is used as well as more traditional map and cross-section displays, not just for well data and static model realisations, but also for dynamic model pressure and saturation arrays. Analytical reservoir engineering (pattern analysis, voidage calculations, and decline curve analysis) is used in conjunction with the model results for reviewing the fields and forecasting the results of new activities.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005