AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Stratigraphy of the Eagle Plain Basin, Northern Yukon Territory: Reservoir Facies Distribution and New Play Opportunities in Middle to Upper Cretaceous Strata
(1) Geoscience, University of Calgary, Calgary, AB, Canada.
(2) Geological Survey of Canada, Calgary, AB, Canada.
Eagle Plain is a relatively unexplored sedimentary basin with recognized hydrocarbon potential located in northern Yukon Territory, straddling the Arctic Circle. A previous hydrocarbon assessment (Osadetz et al., 2005) estimated resources of 108 MMbbls of crude oil and 350 Bcf of natural gas within the Cretaceous succession, which is commonly considered a secondary target to Upper Palaeozoic strata. Of 35 wells drilled in the basin, 32 were drilled prior to 1978; wells are concentrated in south-east Eagle Plain where access is easiest and the most significant hydrocarbon shows were targeted in Laramide-related anticline and fault traps.
Coarse-grained clastic facies are observed throughout the Middle to Upper Cretaceous succession. The Cenomanian Parkin Formation consists of a basal transgressive pebbly sandstone member with high-quality reservoir characteristics, and a middle sandstone member with clean shoreface sandstones up to 20m thick in outcrop. The Parkin upper shale member is overlain by cycles of deltaic sandstones of the Turonian Fishing Branch Formation which have tested significant volumes of gas, with rates up to 3 300 mcf/day. Recent fieldwork discovered large outcrops in western Eagle Plain of convoluted interbedded sandstone and shales, interpreted as mass-transport deposits, which indicate the presence of a shelf-slope break in the Cretaceous basin with shelf-to-basin floor relief of >100m.
Previous hydrocarbon assessments of the Parkin and Fishing Branch Formations are based on lithostratigraphic correlation which interpret deposition in a broad marine shelf setting (Dixon, 1992), and greatly underestimate the potential for significant gas charge in large stratigraphic traps. Changing sedimentological parameters at the shelf-slope transition allow accommodation for thick sand units, and thereby produce a variety of new play opportunities, e.g., shelf-margin delta and turbidite fan sandstones. Such plays are host to very large gas reservoirs within world-class basins. Thus, a new comprehensive sequence stratigraphic model is vital to determine the distribution of reservoir facies within the Cretaceous strata of Eagle Plain. The relatively shallow depth of the Cretaceous succession adds to its economic viability as an exploration target. Petroleum systems in the basin are the subject of an ongoing study incorporating outcrop, well logs, and core, supplemented by reprocessed seismic data optimized for shallower intervals of the basin.