The Wabiskaw D Member, Clearwater Formation: a World Class Oil Sands Reservoir Hosted in from Incised Valley Complex
The Canadian Athabasca Oil Sands Deposit (north-eastern Alberta) contains vast quantities of bitumen emplaced in the Lower Cretaceous (Albian - Aptian) sandstones of the Clearwater - McMurray succession. The Wabiskaw D, a member of this succession, is preserved intermittently throughout the Athabasca Region and within the Kirby Project Area (T75, R9W4 - R8W4) this unit constitutes a high quality oil sands reservoir. Historically, the Region has produced bitumen predominantly from the stratigraphically lower McMurray Formation; in contrast, this paper introduces the Wabiskaw D as an emerging yet under-studied oil sands reservoir.
At Kirby, the Wabiskaw D can be subdivided into two backstepping depositional successions representing a transgressive continuum of tidally influenced channel fill (FA1) overlain by high energy bay fill deposits (FA2). FA1 consists of massive to cross bedded fine grained quartzose sands interbedded with rare brecciated and toe-set intervals. FA2 is composed of flaser to wavy bedded hummocky cross stratified sands and muds. The highest quality reservoir resides in FA1. The sediment contained within the Wabiskaw D was largely cannibalized from the Upper McMurray and while it can be difficult to differentiate these two units, some indicative criteria do exist. The Wabiskaw D can be distinguished mineralogically by the occurrence (up to 6%) of tripolitic chert, in addition to the presence of diagnostic blue-gray mudstones. The most robust method for valley-fill recognition remains via the correlation of truncated Upper McMurray markers.
Following McMurray time, a relative drop in sea level resulted in the incision of a NE - SW elongate valley through the Kirby Project Area. During the subsequent transgression this valley was backfilled with Wabiskaw D (valley-fill) sediment. This valley-fill was deposited under outer estuarine conditions and as such represents a marked shift in depositional environment from the fluvial / inner estuarine dominated McMurray Formation. This fundamental shift results in the Wabiskaw D manifesting a homogeneous and laterally continuous sandbar geometry; a significant departure from the inclined heterolithically stratified (IHS) point bar deposits which characterize much of the McMurray. The increased continuity inherent to the Wabiskaw D significantly reduces geological risk, particularly for in-situ production schemes such as steam assisted gravity drainage (SAGD).
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009