Recognizing Facies Heterogeneities Key to Managing Reservoir Uncertainties: Recent Trends

Mohamed N. Bushara
Nimr Petroleum Engineering, Petroleum Development Oman, Muscat, Oman

Facies are rock units with particular characteristics contained in sedimentary strata of different depositional environments. They vary in scale from microscopic, core to outcrop, & may contain drastically contrasting reservoir properties. Realistic facies characterization provides constraining rules for establishing recognition criteria of heterogeneities affecting reservoir productivity & reserves. It is observed that even though well data is faithfully honored, as are trends in 3D seismic, most facies models lack geological realism. The spatial arrangements of facies appear barren of sensible depositional morphology.

Recent facies work has been focusing on describing intricate reservoir heterogeneities affecting production. Therefore, new forward modeling techniques are developed particularly in fluvial shallow marine environments to better characterize heterogeneities. Centimeter-scale mini-models are built to describe high-order lithofacies variance that is carried through pseudo functions to a FFM. Flumy, SBed, & Geochron are some of emerging process-based modeling techniques aimed at bringing real understanding of reservoir heterogeneity. These techniques utilize modern rules related to channel dynamics & associated physical processes by taking in parameters such as accommodation, floodplain slope, frequency of avulsion, channel migration to simulate facies.

These efforts underscore the importance of building robust facies architecture that leads to improvement in understanding of oil recovery methods. In all fronts, exploration, appraisal, or development, geoscientist must have a conceptual depositional model in mind prior to making inferences about sand distribution. Greater geologic realism is obtained when deterministic methods are used combining seismic, logs & analog data. Two case studies are presented to elucidate these methods.

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