AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Petroleum Potential of a Triassic Carbonate Platform in the Whitehorse Trough Forearc Basin, Yukon, Canada
(1) Yukon Geological Survey, Whitehorse, YT, Canada.
Whitehorse Trough is a frontier basin in south-central Yukon with potential for natural gas that could be marketed locally (i.e., 'Energy for Yukon' initiative). Interpreted as an east-facing forearc basin, it consists of approximately 7000 m of sedimentary and volcanic rocks referred to as the Lewes River Group (Triassic), Laberge Group (Jurassic) and Tantalus Formation (Jura-Cretaceous). The uppermost part of the Lewes River Group (Hancock member) is an arc-fringing carbonate platform, 400 km long and 30 km wide, composed of numerous, discontinuous carbonate masses. These are elongate in plan view, approximately one kilometre wide and a few kilometres long, and up to several hundred metres thick. An east-to-west transect of the platform reveals the following lithofacies:
1) Transported carbonate breccia with outsized blocks (up to 3 m long in outcrop) occur in basin foreslope deposits to the east and mark the platform margin.
2) The interior of the platform is characterized by stacked, shallow-water, mixed matrix/skeleton-supported reefs (~130 m thick), consisting mainly of small patches (~2 m diameter) of calcareous sponges, spongiomorphs and corals, with associated bivalve, gastropod, ostracode, foraminifera, crinoid and algae reef-dwelling fauna, dispersed in skeletal sand sediment; shallow-water skeleton/matrix-supported reefs (~100 m thick), consisting of similar fauna that occurs mainly in larger core areas (~200 m long by 30 m thick) surrounded by skeletal sand sediment; and inter-reef carbonates representing locally derived accumulations of small disarticulated organisms and reef-derived debris.
3) Microbial laminated peritidal dolostone and organic-rich lagoonal carbonates occur along the western edge of the platform. Several conceptual plays (all dry gas due to the high thermal maturity of the strata) include: stratigraphic trapping in reef carbonate reservoirs charged by inter-reef carbonate source rocks; stratigraphic trapping in microbial laminated peritidal dolostone reservoirs charged insitu and by organic-rich lagoonal carbonate source rocks; and structural trapping (mainly thrusts and anticlines) in reef carbonate reservoirs charged by Laberge Group siliciclastic source rocks. Based on RISK(TM) modeling, potential gas pools are estimated to have a mean size of ~2 billion cubic metres (~70 Bcf).