Characterization of a Giant Heavy Oil Reservoir Hosted in Carbonates – The Devonian Grosmont Reservoir, Alberta, Canada

Borrero, Mary Luz¹; Machel, Hans G.; and Schreiber, B. Charlotte
¹[email protected]

Advances in thermal recovery technologies and a worldwide decrease in conventional oil reserves have made the unconventional resources in the Grosmont reservoir a focus of interest over the past few years. The Grosmont platform, which includes the Grosmont Formation and interbedded Hondo evaporites, is part of the Woodbend Group, a Devonian succession considered the world’s largest heavy oil deposit hosted in carbonates with an estimated 318 to 406 billion barrels of oil in place. The reservoir is located in east-central Alberta, Canada, at depths of ~250 m to 1200 m close to the updip-pinchout of the Devonian Woodbend Group subjacent to the well-known Athabasca oil (tar) sands deposit.

A study to understand the reservoir architecture was undertaken using detailed log interpretation, core examination; facies and diagenetic analyses, including strontium, sulphur, carbon and oxygen isotope data. Diagenetic processes changed the original fabrics, their component compositions, and the petrophysical characteristics of both the carbonates and the evaporites. The main processes that affected these formations include dolomitization, multiple phases of karstification, anhydritization, chemical compaction/stylolitization and fracturing, dolomite cementation, calcite cementation, oil migration, gypsification, and extensive biodegradation. In addition, several fracture systems have been identified.

This study reveals the complexity when evaluating a heavy oil reservoir hosted in a pervasive diagenetic altered carbonate succession. The Grosmont reservoir is extremely complex; hydrocarbon trapping and geometry in the Grosmont Formation is a combination of facies distribution, dissolution features, and stratigraphic position. A valuable model of the methodology is presented here on how to evaluate the many facets of this complex heavy oil reservoir.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013