Controls on the Geometry of Large-Scale Clastic Injection Complexes Adjacent to Submarine Sope Channels; Upper Cretaceous, Offshore Norway

Jackson, Christopher Aiden-Lee¹, Gillian Barber¹, Mads Huuse² (1) Imperial College, London, United Kingdom (2) University of Aberdeen, Aberdeen, United Kingdom

Due to their potentially large volume and excellent reservoir properties, clastic injection complexes may represent attraction exploration targets. Determining the three-dimensional geometry of such complexes is problematic, however, due to spatially-limited outcrop exposures and insufficient seismic resolution and well coverage in the subsurface. 3D seismic from offshore Norway, allows the documentation of the geometry of seismic-scale clastic injection complexes emanating from submarine slope channels. Our analysis reveals that clastic dykes form planar to curvilinear sheets 0.5-5 km in length which parallel the channel margins, dip 20-25° and cross-cut up to 100 m of the overlying stratigraphy. The dykes are estimated to be 20-30 m thick and display highly complex three-dimensional geometries, locally passing upwards into sills or bifurcating at their upper tips and/or bifurcating laterally along-strike. Several factors may control the geometry of the clastic injection complexes. The vertical limit of the dykes may be due to them erupting onto the contemporaneous seafloor, blowing out in a shallow aquifer, or a mechanically resistant unit within the overburden which impedes upward dyke propagation, whereas the lateral extent of individual dykes may be related to mechanical interaction between adjacent dykes. It is noted that the orientation of the dykes appears not to be related to polygonal faults developed in the encasing mud-dominated strata. This study demonstrates that, (i) the seismic-scale geometries of clastic injection complexes are significantly more complex than previously documented, and (ii) the production of hydrocarbons housed in clastic injection complexes would be problematic and require unconventional field development models.