Hydrocarbon source rocks, reservoir rocks and migration in the Orcadian Basin

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Abstract
Synopsis: Rock-Eval pyrolysis data shows that the ORS is a viable source rock for hydrocarbons in the Orcadian Basin, and that generally the sequence is not highly mature at present. Solvent-extracted pyrolysis data indicate that migrated hydrocarbons only form a significant proportion of the total organic carbon content where this content is less than 1.5 %. Hydrocarbons occur widely in mineral veins and fluviatile/aeolian sandstones. Hydrocarbon shows in sandstones are often adjacent to major faults, along which they may have migrated. Much porosity in the sandstone is secondary after calcite dissolution which may have been related to Permian deep weathering. Small volumes of hydrocarbons were generated by a late Permian intrusive igneous suite, but peak generation had probably occurred prior to this event.