Norwegian Sea deepwater basin overview, play types and remaining prospectivity
|Location||International Geological Congress,oslo 2008|
|Author||Seger, Mark; Ravnهs, Rodmar; Norton, Mike|
|Holding Date||08 September 2008|
The Norwegian-Greenland Sea was subject to prolonged rifting from the ?Permian leading to break-up and drifting in the Eocene. A proper understanding and assessment of 1) the geological evolution, 2) the play types present in the basin and their potential as well as 3) the remaining prospectivity of the mid-Norway deepwater areas, can only be fully achieved using a holistic approach with the basin placed into the context of its conjugate margins.
Sixteen exploration wells has been drilled since the acreage was opened for exploration 12 years ago - all targeting Upper Cretaceous or Lower Paleogene plays. Exploration success rate is high with seven discoveries, although currently only one, the 13tcf Ormen Lange Field, has been large enough to be developed. Failures are ascribed to either lack of viable reservoirs or to problems with trap integrity.
Thus, evaluation of the various play types and identification of the more prospective plays and areas rely on solid geological knowledge and integration of various ’geodisciplines’. In particular, the integration of structuring history of the basin and its margins with the sediment infill patterns is crucial in order to understand reservoir, seal and source rock distribution. Furthermore, source rock maturation and charge/retention potential rely heavily on the late (late Cretaceous to early Paleogene) rift history and the post-break up (post Eocene) fault reactivation, inversion and the basin’s subsidence/uplift history.
The late Cretaceous to early Paleogene rift history of the Norwegian-Greenland Sea rift was characterized by continued extension from the Coniacian, culminating with successful rifting and break-up in the early Eocene. The late Cretaceous rifting was characterized by temporal variations in stretching velocity resulting in a series of distinct rift maxima, of which the late Coniacian - Campanian and the late Maastrichtian were the most significant. Rift phases were dominated by a clayey infill whereas the proto-rift and intervening syn-rift intervals of relative tectonic quiescence was characterized by sandy deepwater reservoir deposition. Sandy systems were supplied axially into the basin from uplifted areas to the north, as well as laterally from the opposing Greenland and Norwegian margins.
During the Paleocene, rifting was accompanied by thermal uplift of the central rift-area, or the present sub-basalt area, complicating the relatively simple tectono-stratigraphic relationship observed in the Upper Cretaceous basin-fill. Thermal uplift of the central rift-area led to shut off coarse supply to parts of some sub-basins and established new intra-basinal provenance areas for other sub-basins. Thus an understanding of the integrated thermal, tectonic and volcanic history of the Paleocene is a prerequisite to properly predict Paleocene reservoir distribution and quality.