Magmatic Plumbing Systems within the Faroe-Shetland Basin: Structure, Flow Pathways and Igneous Comparmentlization

Schofield, Nick¹; Jolley, David²; Holford, Simon P.³
¹Earth Sciences, University of Birmingham, Birmingham, United Kingdom.
²Geology and Petroleum Geology, University of Aberdeen, Aberdeen, United Kingdom.
³Australian School of Petroleum, Centre for Tectonics, Resources and Exploration (TRaX), Adelaide, SA, Australia.

As hydrocarbon exploration increasingly moves into frontier basins containing intrusive volcanics, the issue of compartmentalization of host rock strata by sills and dykes may become a significant risk to both source and reservoir rocks. At the basin scale, intrusions could also act as permeability barriers to hydrocarbon/fluid migration. Therefore understanding the structure of intrusions from a seismic to sub-seismic (outcrop scale) is essential to understanding the impact of intrusions on a petroleum system.

The Faroe-Shetland basin contains an extensive set of sill complexes over a large aerial extent, occurring both beneath the lava-pile and the non-basalt covered areas of the basin. The sills form a complex array of intrusions, with magma input points into the sedimentary basin often being controlled by existing basin structure. The intrusions often preferentially exploit faults of the pre-rift sequences and then when entering the main basin fill, appear to propagate laterally, often over distances of 10's km's. The magma preferentially exploited certain sequences within the basin, in particular the more shale to mud rich horizons of Cretaceous to Palaeogene age.

Due to the preferential exploitation of certain sedimentary sequences within the Faroe-Shetland basin by intrusions, igneous compartmentalization could be a major issue. In the extreme, compartmentalization could lead to the total isolation of a prospective source rock from a prospective reservoir, by trapping hydrocarbons at or near to the source. In a lesser case, the intrusive complex may act to create ‘barriers and baffles' to fluid/hydrocarbon flow, effecting hydrocarbon migration pathways and possibly preventing the filling/charging of prospective reservoirs by hydrocarbons. Therefore understanding sill structure in 3D across the basin is essential in understanding the interaction that intrusions may have with the hydrocarbon system within the Faroe-Shetland Basin.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012