Process-Based Modeling of the Brent Delta: Effects of the Oseberg Formation Pinch Out on the Wave-Dominated Brent Delta Early Progradation. North Sea Norwegian Sector — Huldra Gas Field

The stratigraphic and tectonic framework of the wave-dominated deltaic Brent Group (Early-Middle Jurassic), and their respective depositional environments, has been extensively studied and are well documented in the literature. Its early deposition occurred under high sediment supply rate outpacing the accommodation space created by basin subsidence under an overall sea level rise stage. Although the stratigraphy and facies distribution of the Brent’s deltaic sequences are considered to be governed by autogenic processes, there is still insufficient understanding of the detailed stratigraphic characteristics and facies development as response of the interaction between steady (fluvial, climatic, basinal) forcing with specific-local scale basin geometries (e.g. paleobathymetry, shoreline orientation).

In this study a process-based forward model (Delft3D) was used to recreate and understand autogenic stratigraphic responses of the early prograding Brent Delta at the Huldra area. At this location, the Brent delta was deposited over a particular paleobathymetry generated by the pinching out Oseberg Fm. composed of coarse sand-grained fan deltas with thicknesses up to 40m and an averaged foreset angle of 2°. The aim was to create a downscaled model of the Brent deltaic system in the Huldra area based on available pre-existing river-system attributes and on the paleobathymetry inferred from seismic surveys. The model was used to evaluate the geomorphological evolution, sediment partitioning and stratigraphic response for several scenarios considering (a) three different shoreline orientations with respect to the pinch out true dip and (b) two different levels of substrate erodability.

The numerical experiments produced extensive lobate sand-prone sediment wedges (25m thick), with no wave induced reworking of sand-grainsized sediments below 5m water depth. Changes in shoreline orientation impacted on wave spreading which affected the basinal-river forcing interplay and sediment partitioning resulting in different reservoir geometries. The erodability of the substrate controls the distributary channel’s geometry and resulted to be a limited extra source of sediment. This study has shownthe potential of a process-based model application in petroleum geosciences for the exploration or reservoir architecture and production geology problems related to fluvial, deltaic, and shallow marine reservoirs.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California