Abstract

Detailed examination of available core from a number of Middle Triassic Doig Formation sandstone reservoirs in the Fort St. John area of northeastern British Columbia (Buick Creek, Cache Creek, Fireweed and Stoddart-West) reveals a number of pronounced similarities with respect to sedimentologic characteristics, sandbody geometry and the nature of bounding surfaces. Sedimentary facies can be grouped into: 1) offshore/shelf, 2) shoreface and 3) offshore transition facies associations. The shoreface sandstones are narrow, linear sandbodies oriented with their depositional axes elongate parallel to the paleoshoreline; net sand distribution defines a pronounced linear pattern exceeding 20 km in strike length in the Buick Creek field. Dip dimensions are limited to less than 2.0 km. Facies changes are abrupt, both vertically and laterally; the shoreface sandstones abruptly overlie offshore siltstones and shales across an erosive contact and represent development of the shoreface during a lowstand of sea level. The base of the sandstone is interpreted as a regressive surface of marine erosion (RSME) reflecting a fall in relative sea level. The shoreface sandstones, where the upper contact has been cored, are erosionally truncated by a transgressive surface of erosion/ravinement surface (TSE) and are overlain by a discontinuous coarse lag deposit which is abruptly overlain by finer grained sediments of offshore to offshore-transition affinities. The TSE and RSME merge in a paleolandward direction, removing any evidence of subaerial exposure. Recognition of these characteristics and their interpretation within a sequence stratigraphic framework, provides a powerful tool to guide exploration and constrain development decisions in the Doig Formation of northeastern British Columbia. The depositional history and orientation of these sandstones implies that exploration should emphasize strike continuity. The abrupt fluctuations in relative sea level, evidenced by the nature of the bounding surfaces, results in a fortuitous juxtaposition of reservoir, seal and potential source.

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