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Stratigraphic Control on Oil Field Performance in Clastic Reservoirs of the Norwegian Continental Shelf


Adequate knowledge of reservoir architecture is key in the placement of injector wells, pressure maintenance, and secondary recovery which in turn can contribute to reserve growth. The main aim of this study is to determine the impact of depositional environment and primary facies architecture on reservoir performance. Fields from the Norwegian Sea, the Norwegian North Sea and the Barents Sea were used to build a database of 91 fields all with more than 11 million barrels of oil in place. A total of 76 clastic reservoirs were classified into three gross depositional environments: continental, paralic/shallow marine and deep marine. 61% of the reservoirs are paralic/shallow marine, 11% are continental and 28% are deep marine. Reservoirs were further classified into eight sub-environment to capture depositional complexity. Representative reservoirs from each sub-environment were analyzed at architectural element scale using logs and core to determine reservoir heterogeneity. Principal component analysis (PCA) was utilised to identify the importance of stratigraphically dependent variables in the dataset, and to determine the key parameters that have strong effects on the overall variability of the data. PCA reveals that gross depositional environment and sedimentological related parameters dominate the first four principal components . Fluid properties such as API and water saturation are unexpectedly among the less important parameters. A simple box plot of reservoir depositional sub-environment against recovery factor for reservoirs produced via pressure depletion and those supported through water injection reveals weakening recovery with increasing stratigraphic heterogeneity. Delta front, wave-dominated shoreface, tidal non-delta, stacked multistorey fluvial and deep marine reservoirs have relatively good recovery, whereas, offshore/transition zone reservoirs and isolated meandering fluvial channel deposits have low recovery.