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Influence of Rift Tectonics on Halokinesis and Deposition of Net-Transgressive Shallow Marine Sandstone Reservoirs: Upper Jurassic, Cod Terrace, Norwegian North Sea

Mannie, Aruna; Jackson, Christopher A.; Hampson, Gary J.

Many of the world's hydrocarbon basins are influenced by salt tectonics (e.g. Gulf of Mexico, Central North Sea and circum-South Atlantic basins). In these basins, the need to understand the influence of halokinesis on structural evolution and the distribution of syn-tectonic reservoirs is important for evaluating exploration potential. This study is focussed on understanding accommodation creation, and its influence on depositional style, preservation potential, geometry and continuity of net-transgressive shallow marine sandstone reservoirs. We present a case study from the Upper Jurassic, Cod Terrace, Norwegian North Sea where we interpret rifting to have resulted in the rise and fall of salt diapirs, and the formation of two generations of minibasins. Previous interpretations have been: (i) unnecessarily complex, and implied that transpressional tectonics was the key control on salt mobility and basin structure; or (ii) were oversimplified and implied that passive diapirism, resulting from differential loading, was the dominant control on basin structure and the resultant sedimentation patterns.

3-D seismic reflection, biostratigraphic, wireline log and core data are used to construct a structural framework to characterize the stratigraphic architecture of the Upper Jurassic reservoir intervals, and to develop an integrated tectono-stratigraphic model for the Cod Terrace. Our analysis indicates that halokinesis started in the Early Triassic in response to regional, basement-involved extension. Passive diapir growth during the Middle-to-Late Triassic resulted in the development of Triassic minibasins prior to exhaustion of the salt source layer. After a period of regional uplift and erosion in the Early-to-Middle Jurassic, subsequent regional extension in the Middle-to-Late Jurassic resulted in the fall of diapirs, and development of minibasins above former diapir crests; these became sites for deposition and preservation of thick (up to 400 m), net-transgressive shallow-marine sandstone reservoirs. The results of this study provide an alternative interpretation for the structural and stratigraphic framework of the Cod Terrace, which takes into account the impact of regional tectonics on halokinesis and its influence on accommodation creation and reservoir distribution. The resulting model predicts Middle-to-Late Jurassic reservoir presence and thickness in the area.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013