The Cambrian Deadwood Formation and Lower Palaeozoic Winnipeg Formation, a New Petroleum System Within the Williston Basin, or Not!?

Stephen Bend¹, Mauri Smith², Christopher Seibel³, Scott Rainville⁴, and Bingli Lu¹. (1) Department of Geology, University of Regina, Regina, SK S4S 0A2, Canada, phone: (306) 565-4147, Stephen.Bend@uregina.ca, (2) Shell Canada Limited, 400 - 4th Avenue S.W, Calgary, AB T2P 0J4, (3) Nexen Inc, 801-7th Avenue S.W, Calgary, AB T2P 3P7, Canada, (4) Department of Geology, The University of Regina, Regina, SK S4S 0A2, Canada

The Cambrian Deadwood Formation and Lower Palaeozoic Winnipeg Formation, a new petroleum system within the Williston Basin, or not!?

The geochemical composition of Cambrian and Winnipeg Formation oils, determined using GC and GCMS suggests that the oils originate from a source as yet not defined in the basin. This paper examines the geochemical signature of the Cambrian Deadwood and Winnipeg Ordovician Formation oils and potential sources within the Cambrian and Ordovician within the Williston Basin. Winnipeg oil is characterised by a high abundance of methylhexanes, significant differences in C7 Mango parameters and a unique biomarker distribution. The Winnipeg oil has a regular sterane distribution that is C27>C28C29, in contrast to the stratigraphically adjacent Red River oil (C29 regular sterane predominance) and the Deadwood oil (C27>C28>C29 sterane abundance). The Middle Ordovician Icebox Member (Winnipeg Formation) has been identified as having source potential and has been characterised in Saskatchewan using an organofacies framework. Five organofacies have been petrographically defined and range from a ‘platformal' type, containing G.prisca, through to a ‘basinally' derived organically lean organofacies. The organofacies have also been analysed by RockEval, GC and GCMS, indicating the greatest generative potential (i.e. highest TOC's and S2) typifies Organofacies 1, which is dominated by G.prisca. However, thermal maturities are too low within Saskatchewan and recent research has focused on equivalent formations within North Dakota, seeking to extend the organofacies beyond the Saskatchewan portion of the Williston Basin. Attempts to match the geochemical signature of the Cambrian and Winnipeg oils to their source have met with mixed success, although there are indications that the Winnipeg Formation oil is not a small localised phenomenon.

Petroleum Systems of Canada
2005 AAPG Annual Convention (June 19-22, 2005) Technical Program