Oil seepage onshore West Greenland: evidence of multiple source rocks and oil mixing

Abstract

Widespread oil seepage and staining are observed in lavas and hyaloclastites in the lower part of the volcanic succession on northwestern Disko and western Nuussuaq, central West Greenland. Chemical analyses suggest the existence of several petroleum systems in the underlying Cretaceous and Paleocene fluvio–deltaic to marine sediments. Seepage and staining commonly occur within vesicular lava flow tops, and are often associated with mineral veins (mostly carbonates) in major fracture systems.Organic geochemical analyses suggest the existence of at least five distinct oil types: (1) a waxy oil which, on the basis of the presence of abundant angiosperm biological markers, is interpreted as generated from Paleocene mudstones (the ‘Marraat type’); (2) a waxy oil, probably generated from coals and shales of the Cretaceous Atane Formation (the ‘Kuugannguaq type’); (3) a low to moderately waxy oil containing 28,30-bisnorhopane, and abundant C27-diasteranes and regular steranes (the ‘Itilli type’), possibly generated from presently unknown Cenomanian–Turonian marine mudstones; (4) a low wax oil of marine, possibly lagoonal/saline lacustrine origin, containing ring-A methylated steranes and a previously unknown series of extended 28-norhopanes (the ‘Eqalulik type’); (5) a waxy oil with biological marker characteristics different from both the Kuugannguaq and Marraat oil types (the ‘Niaqornaarsuk type’), probably generated from Campanian mudstones.The presence of widespread seepage and staining originating from several source rocks is encouraging for exploration in basins both on- and offshore western Greenland, where the existence of prolific source rocks has previously been the main exploration risk.