Considerable hydrocarbon reserves are associated with heterogeneous stratified reservoirs. Many of these reservoirs demonstrate poor recovery efficiency, due to the low vertical and lateral sweep, if produced traditionally by depletion or waterflooding. Modern Improved Oil Recovery (IOR) methods have significant potential for such formations.
A Norwegian sandstone field was evaluated in this study. This field is characterized by extreme contrasts in reservoir properties. Horizontal permeability in the formation varies from 2 - 20 mD in the lower reservoir to more than 2000 mD in the upper reservoir. The sweep is accordingly very low in the lower reservoir, which contains 60-70% of oil in place.
A 3D model of the formation was constructed in order to investigate, in detail, potential IOR processes. The selection of the model area was conducted by a cross-discipline team. It was decided that a full field model was too resource intensive and a generic model would be too simplistic. A third alternative called, average pattern approach, was utilized. The cross-discipline team looked over the field and made a group decision to choose a specific area. A portion of the field that had average properties and well completion history was modelled. The area was large enough to capture different development schemes. The reservoir model reflects the main characteristics of the formation and, in particular, the high permeability contrast between the upper and lower reservoirs, interlayer communication and presence of faults. Actual operational and reservoir information was available for the selected pattern. This approach gives validity to predictions and evaluation of IOR processes and also minimizes the resources and time required for modelling.