Geologic Reservoir Model for the Triassic Doig Formation, Northeast British Columbia, Canada

MOSLOW, THOMAS F., University of Alberta, Edmonton, Alberta, Canada, and HUGH D. MUNROE, International Geoscience Consulting Ltd., Calgary, Alberta, Canada

A subsurface investigation of the mid-Triassic Doig formation in northeastern British Columbia documented two main reservoir facies. Both are a product of mass movement and sediment gravity flow processes on a progradational, tectonically active continental shelf margin. Substrate instability was likely a product of sediment loading, perhaps in concert with seismic activity. Sedimentary facies and reservoir parameters were determined from analysis of approximately 150 cores and 900 well logs.

Laterally discontinuous Doig sandstones are up to 60 m thick and trend northeasterly within the study area. The main reservoir facies are incised density flow deposits and laterally extensive slump deposits. Reservoir quality within these sands is extremely variable with porosity ranging from less than 5% to 15%. In core, these deposits consist of moderately well sorted, very fine grained sandstones with no vertical grain size variation. The sandstone is generally massive but contains intervals of oversteepened bedding, disturbed clay laminae, fragmented shell material, and rip-up clasts of fine-grained shelf sediments. These deposits have a sharp basal contact and a blocky gamma ray signature, very similar to fluvial channel fill sequences. The channelized density flow deposits form hick but laterally restricted reservoirs. The best production to date is in the Buick Creek field with initial flows of 346 BOPD. The slump deposits are thinner and tend to be more elongate parallel to paleoshoreline. These sands were subject to some wave or current reworking. Modern analogs where similar processes and products of deposition are known to occur include the Gulf of Alaska continental shelf and the Fraser River Delta slope.

Doig sandstones usually are enclosed in fine-grained shelf deposits that provide a good stratigraphic trapping mechanism.

Successful development of Doig reservoirs must incorporate geologic models that assist in understanding the complex and highly variable reservoir quality of sandstone units.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)