Interaction between Depositional and Post-Depositional Processes in the Cenozoic Northern North Sea and Implications for Understanding Basin-Scale Fluid Flow

Olobayo, Oluwatobi; Huuse, Mads; Jackson, Christopher A.

The North Sea Basin is a mature hydrocarbon province; it is covered by continuous 3-D seismic data and penetrated by thousands of boreholes. Numerous studies have demonstrated that the Cenozoic deepwater succession in the North Sea Basin is severely affected by post-depositional processes. This resulted in significant changes to geometry and connectivity of reservoir sandbodies and sealing mudstones, as well as wholesale injection and extrusion of sand through hundreds of metres of shale-dominated strata. An important implication of sand remobilization and injection is that crosscutting sandstones provide enhanced permeability and if sealed cause large-scale traps potentially hosting hundreds of millions of barrels. Although sand injectite complexes have been documented by numerous field-scale case studies, they have so far escaped a whole basin-scale analysis and their origins therefore remain poorly understood. Whilst sand injection appears to have enhanced prospectivity in the Cenozoic deep-water succession of the Central North Sea and South Viking Graben, this process appears to have compromised prospectivity in the North Viking Graben. This study focuses on the Northern North Sea and aims to document the interactions between depositional and post-depositional processes in the North Viking Graben, and the implications of these interactions for hydrocarbon prospectivity and for understanding basin-scale fluid flow processes.

Utilizing a 3-D seismic Mega Survey that covers c. 29,000 km2 and an extensive well log database for our study, key observations are: (1) presence of post-depositionally remobilized and injected sandstones from Cretaceous to Miocene differentiated from their non-remobilized deep-water sandstone counterparts, (2) multi-tier layer bound Polygonal Faults within Cretaceous to Miocene sediments, (3) silica diagenetic transformation in Paleocene to Oligocene sediments with the present day front manifested as a high amplitude reflection below the Oligocene injectites (4) pre-Tertiary fault systems morphology providing insight to deeper fluid pathway. We suggest a genetic relationship between these elements. We consider the stratigraphic position of the depositional and post-depositional facies; timing of emplacement of the sand injectites as well as the spatial and temporal occurrence of the processes (overpressure generation mechanisms) responsible for their formation in order to constrain their origin.

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