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Gravity Driven Collapse Systems on Passive Margins: A Previous HitFieldNext Hit Study in Seismic

Abstract

Gravity driven collapse systems occur on most of the world's passive continental margins and are becoming an increasingly attractive target for hydrocarbon exploration. Existing models that assume a balanced up-dip extension coupled to a down-dip toe thrust system have recently been called into question because of a growing consensus that there is commonly a mis-balance with an excess of extensional strain. Previous studies have focussed on seismic or experimental Previous HitdataNext Hit partially due to the lack of onshore Previous HitfieldNext Hit Previous HitexamplesNext Hit on which sub-seismic features can be observed; this has left a gap in our understanding of their temporal and spatial evolution. In this study we consider Previous HitfieldNext Hit Previous HitexamplesNext Hit of a shale detachment gravity driven systems in Northern Spain, in which we observed multiple smaller scale compressive features. These structures are contained within the extensional portion of the collapse system imply considerable internal compaction prior to the formation of a down dip compressional domain. We use these Previous HitfieldNext Hit observations to re-interpret seismic Previous HitexamplesNext Hit of multiple shale driven collapses in the Orange Basin, offshore Namibia and South Africa. These seismic Previous HitexamplesNext Hit show considerable variations in style and complexity including; multiple detachment horizons lines containing only extensional features and numerous reactivations. We undertake multiple restorations of both Previous HitfieldNext Hit and seismic Previous HitexamplesNext Hit to estimate the effect of smaller scale deformation on measurements of extension versus compression. Our results suggest that this sub-seismic scale strain can account for up to 10% of previously unrecognized compression. By applying our observations from the Previous HitfieldNext Hit to seismic Previous HitexamplesNext Hit we are able to interpret structures close to seismic resolution and make predictions about the likely effects of sub-seismic features on reservoir prospectivity, hazard prediction, permeability and porosity