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Stratigraphic Forward Modelling for Aeolian Reservoir Prediction: Norphlet (EGOM)

Abstract

Reservoirs in the Norphlet Fm. (US Gulf of Mexico) are composed by aeolian sandstones deposited in a large erg system (Late Jurassic), which interfinger with non-reservoir fluvial fan and sabkha environments of deposition. Norphlet hydrocarbon discoveries in the deepwater areas of the US Gulf of Mexico are located around specific areas surrounding the Middle Ground Arch basement high (MGA). Seismic resolution provides ambiguous results for identification of other areas with similar erg systems around the MGA.

To understand processes controlling erg development and make first-order predictions on subregional trends on reservoir presence in uncalibrated areas, three-dimensional stratigraphic forward models were built. The numerical models simulate the main geological processes controlling erg accumulation at exploration scale (grid cells in the order of 1km by 1km and a simulated duration of several millions of years). The numerical models start from an initial topography and simulate regional subsidence, sediment loading into underlying Louann salt, base-level fluctuations and the effective average wind velocity patterns due to the interaction of multiple wind with topography. Sedimentation is simulated using a rule-based approach incorporating fuzzy logic capable of distinguishing between lake, sabkha, alluvial fan and erg facies associations.

Multiple scenarios were obtained constrained by the existing well information. The models demonstrate that thick erg accumulation occurs preferentially in areas in which there is an optimum combination of: a) accommodation due to salt withdrawal related to sediment loading, b) low or decreasing effective wind velocities, and c) relatively far from areas dominated by alluvial fans. This provides scenarios of erg distribution around the MGA yielding potential areas that could be interesting for exploration from a reservoir-presence perspective. Synthetic seismic computed from the stratigraphic forward models also suggests the presence of subtle seismic geometries characteristic of the erg accumulations to guide seismic interpretation.