Sequence Stratigraphy in a Rift Basin: From Example from the Middle Jurassic Hugin Formation, Southern Viking Graben, North Sea

Atle Folkestad and Nicholas Satur
StatoilHydro, Bergen, Norway

The Jurassic Hugin Formation consists of shallow marine sandstones that belong to a significant hydrocarbon reservoir in the Sleipner Area in the North Sea. The formation encompasses coarsening-upward units of mouthbar and shoreface facies, interpreted as regression; and fining upward units with tidal channel, dune, and tidal flat facies interpreted as an estuary environment during transgression. The correlations reveal that the studied part of the Hugin Formation consists of 8 sequences, each with a transgressive and a regressive unit, representing the transgressive system tract and the highstand system tract respectively. The sequences are stacked landward, as a result of rapid tectonic subsidence due to rifting of the Viking Graben that led to an elongated shaped graben where tidal currents were amplified and wave-action damped. Lowstand and forced regressive system tracts are not identified as relative sea-level falls are suppressed in a rapidly subsiding basin as the basin subsidence rate outpaces any fall in eustatic sea level. Thus sequence stratigraphic architecture for subsiding basins can be very different than those sequence stratigraphic models proposed for passive margins. Through facies interpretation and sequence stratigraphic correlations between wells, these regressive and transgressive units show thickness trends in the form of sigmoidal shaped wedges stacked in an offset manner in a dip-direction. These thickness trends illustrate sediment partitioning within the sequences and are explained by the relationship between accommodation spaces versus the sediment supply. During regression the focus of sedimentation is pushed basinward, and during transgression it’s pushed landward as sediments are trapped there. The mapping of these sequence stratigraphic units serves as input to reservoir drainage management and to identify new exploration targets.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas