Landmark Regional Discoveries
In basin and petroleum system modeling, the spatial resolution of models is too coarse to cover all of the relevant geologic processes that occur in reservoirs. Reservoir models are built on a static (time invariant) grid and cannot cover the charge history of a field or processes related to changing geologic structures through time. A new method to combine regional-scale petroleum system models and local reservoir- or prospect-scale models was developed and applied to an oil field in Kuwait. In the field, heavy oil zones occur at the original oil-water contact and also in stratigraphic and structural positions above it. Heavy oil occurs in the highly permeable Fourth Sand and Middle Third Sand of the Burgan Formation in the field. This study demonstrates that the heavy oil distribution in those layers can be explained by the petroleum charge history. An early charge from the Cretaceous Makhul Formation was replenished by the Cretaceous Kazhdumi Formation, the stratigraphic equivalent of the Burgan Sands. These sediments were deposited in the area of the Dezful Embayment of the Zargos Fold Belt. No Jurassic charge, breaking through the Gotnia evaporites, is needed to fill the structures of the Cretaceous Burgan reservoirs in the field. Well data and the results of the high-resolution petroleum system model covering the area of the oil field and describing the distribution of charge from the regional model to the field scale lead to the conclusion that the heavy oil zones are mainly the result of gravity segregation, although some influence of water washing cannot be excluded.