Geologic and resource assessment of the Upper Devonian Grosmont and upper Ireton Formations, central Grosmont shelf complex, Alberta, Canada

Abstract

The Devonian Grosmont and upper Ireton (GUI) Formations of northeastern Alberta contain between 300 and 574 billion bbl of in situ bitumen. The GUI stratal succession shallows upward and is partitioned into five progradational, shallow marine sequences. Although matrix porosity is highest within intertidal deposits (commonly 20%–30%), matrix permeability is similar for subtidal and intertidal facies (commonly 10–3000 md). Reservoir zones are 29–98 ft (9–30 m) thick and from oldest to youngest include the A1, A2, B, C1, C2, D1, D2, D3, and upper Ireton. Because of truncation beneath the sub-Cretaceous unconformity, the GUI thins from 656 ft (200 m) within the western part of the study area to an erosional edge within the easternmost part. Intertidal facies most commonly underlie the sub-Cretaceous unconformity and are commonly karsted. Karst breccia and associated fractures occur within thin (3–20 ft [1–6 m]) intervals that are parallel to bedding and most abundant in proximity (164–328 ft [50–100 m]) to the unconformity. Within the study area bitumen is concentrated above 475 ft (145 m) above sea level, and in-place bitumen is estimated at 58 billion bbl (9.2 × 106 m3); the greatest in-place bitumen volume (66%) is associated with the D2, D3, and upper Ireton intervals. A proof-of-concept numerical model evaluates the potential effectiveness of steam-assisted gravity drainage enhanced oil recovery within the GUI. The model suggests bitumen recovery as high as 189,000 bbl over a 20-yr period with an injector–producer spacing between 33 and 41 ft (10 and 12 m).