Influence of Large-Scale Remobilisations on Deepwater Reservoir Architecture: An Example from the Britannia Field, North Sea

Teloni, Riccardo; McCaffrey, William D.; Haughton, Peter; Patacci, Marco; Eggenhuisen, Joris T.; Butler, Robert

The interactions between mass failure and turbidite sedimentation are an important cause of deep-water reservoir heterogeneity at multiple scales, affecting both the geometry and connectivity of the producing sandstones. The characterization, quantification, or prediction of such heterogeneities is important for the optimization of oil and gas production. The Aptian deep-water Britannia Sandstone Formation, Outer Witch Ground Graben, UK North Sea hosts the extensively cored Britannia gas-condensate field. During deposition of the lower and middle reservoir zones, large-scale slope failures interrupted the deposition of broadly tabular deposits, with gross isopach variations reflecting compensation of younger deposits into the relict topography left by the mass failure. The immediate aim of this work is to study in detail the interaction between large-scale remobilisation and sand infill. A secondary aim is to characterise the architectural heterogeneity at the system scale induced by episodic slope failure.

Mapping of the densely-cored platform area shows that the topography of the sea floor was excavated by large-scale failures that transected and modified pre-failure sand-bodies via incision and substrate deformation. Well mixed debrites, probably sourced from further upslope, partially heal the accommodation space left by large-scale remobilisations. The balance of the accommodation space has been filled by younger turbidite sandstones, characterised by both banded and massive facies, whose variation highlights the change in the nature of the flows influenced by sediment routing patterns through the rugosity of the seafloor.

This study can be combined with earlier work to show that the Britannia stratigraphy is characterised by a series of failure-infill cycles, particularly evident in the lower and the middle reservoir section. The infill deposits can form good reservoir, but have spatially restricted distributions, whereas tabular, post-healing deposits form a framework of through-going carrier beds. The key challenge in the Britannia Field has been to identify key facies for recognising the processes of slope failure, associated debrite emplacement, turbidite sand infill and restoration of locally smooth sediment distribution pathways, in order to characterise the larger scale architectural variability. The insights thus gained are likely generic, and should be applicable elsewhere.

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