The source-rock potential and thermal maturity of the sedimentary succession in the Drake and Hecla hydrocarbon fields, Melville Island, Canadian Arctic Archipelago

Abstract

The thermal maturity and source-rock potential of the Mesozoic succession in the Drake and Hecla hydrocarbon fields, Melville Island, Arctic Canada were studied using optical microscopy and Rock-Eval pyrolysis. Vitrinite reflectance in Cretaceous sediments ranges from Ro = 0.35 to 0.55%; in Jurassic sediments it ranges from 0.50 to 0.70% and in Triassic sediments from Ro = 0.57 to 0.74%. Reflectance shows an overall increase with increasing depth of burial with some variations, caused mainly due to bitumen impregnation (staining), mineral matrix (lithology) and presence of hydrogen-rich (perhydrous) vitrinite of marine origin. Organic matter in the Triassic Schei Point Group is dominated by algae (Tasmanites), dinoflagellates and amorphous fluorescing matrix bituminite. Sporinite, cutinite, resinite, Botryococcus and liptodetrinite are the dominant components in the Lower to Middle Jurassic Jameson Bay, and in the Upper Jurassic Ringnes Formation. The Cape Richards and the Eden Bay Members of the Hoyle Bay Formation have TOC content of up to 5.0 wt.%, HI between 400 and 700 mg HC/g Corg and Tmax of 428-433°C in the Drake hydrocarbon field. The Cape Caledonia Member of the Murray Harbour Formation is less rich (TOC up to 4.0 wt.%), HI up to 550 mg HC/g Corg and Tmax is 433°C in the same field, reflecting differences in the level of thermal maturity and possibly less anoxic conditions in the depositional environment of the latter. The Eden Bay Member is also rich in the Hecla field (TOC up to 4.0 wt.%) and HI as high as 550 mg HC/g Corg. The carbon isotopic composition of the gases found in the Drake field is generally indicative of gas generated from marine source rocks in the peak of oil generation. In addition, residual oil present in the Hecla field has been degraded, possibly due to a combination of bacterial activity and water-washing. Alberta Research Council, Contribution No. 2100.