LITHOFACIES ASSOCIATIONS AND DEPOSITIONAL-ENVIRONMENTS IN THE MIDDLE TRIASSIC DOIG FORMATION, BUICK CREEK FIELD, NORTHEASTERN BRITISH-COLUMBIA

Recent gas resource assessments for the Triassic of the Western Canada Sedimentary Basin suggest that one-half of reserves remain undiscover ed. The most promising play in this interval is the Halfway/Doig ''She lf'' in northeastem British Columbia, with estimated reserves of 4 tcf gas (112 x 10(9)m(3)). Most of the emphasis in this play has focused on the Halfway Formation. To our knowledge, no major study of a Doig r eservoir has been completed within this play. The Buick Creek Field in northeastern British Columbia represents the largest recognized Doig reservoir in the Fort St. John area, with 5 oil pools containing 20 mi llion bbls of oil (3.2 x 10(6)m(3)) and 12.5 bcf of associated gas (0. 35 x 10(9)m(3)). All pools lie on the same stratigraphic level and exh ibit depositional continuity. Twenty-two wells have core within the Do ig Formation in the Buick Creek Field area. Due to the abundance of co re available in the field (similar to 550 m), facies associations and depositional processes for the Doig interval can be determined directl y, based on observed physical characteristics. Nine sedimentary facies have been recognized and are grouped into three facies associations: (1) offshore/shelf, (2) shoreface, and (3) offshore transition. All pr oduction at Buick Creek is from facies association 2. This unit typica lly consists of fine-grained, massive to structureless sandstone and e rosively overlies facies association 1. This basal surface is interpre ted to be a regressive surface of marine erosion which developed durin g falling relative sea level. The sandstones are abruptly overlain by facies association 3 across a pronounced transgressive surface of eros ion marked by a coarse pebble lag. The sandstones of the Buick Creek F ield are interpreted to represent a lowstand shoreface. This character ization is a predictive depositional model which can be used to guide future hydrocarbon exploration.