Evaluation of organic maturity and hydrocarbon source potential of the Ringnes Formation, Sverdrup Basin, Arctic Canada

Abstract

Organic-rich shales are common in the Ringens Formation/Member, an Oxfordian-Kimmeridgian argillaceous unit which is widespread in the Sverdrup Basin of the Canadian Arctic Archipelago. The shales and siltstones of the Ringnes are laminated to burrowed and are interpreted to have been deposited under sub-oxic conditions in a mid to outer shelf setting. The organic matter (OM), which is up to 11 wt%, has relatively low H1 and OI values. Rock-Eval/TOC data, organic petrography and the environment of deposition of the Ringnes, are interpreted to infer that the organic matter in basin margin samples is mainly of terrestrial origin, with a variable but minor marine component. In the axial region of the basin, the OM appears to be of a mixed marine and terrestrial origin and has been partially oxidized. The high organic content is attributed to sedimentation rates high enough to bury the organic-rich sediments before complete destruction by aerobic bacteria and benthic scavengers. The organic content and HI values increase towards the axis of the basin. The thermal maturity of the Ringnes shales varies from immature on the basin margins to mature along the basin axis. In the eastern and central portions of the basin, however, the Ringnes shales are overmature at many localities due to the presence of diabase sills and dykes which were intruded in Early Cretaceous. By contrast, the maturity of the Ringnes is anomalously low over the crests of large salt-cored structures. Rock-Eval/TOC data and petrographic evidence indicate that the Ringnes shales have potential to generate significant amounts of thermogenic gas at low levels of thermal maturity.