An Overview of the Geology of the Upper Devonian Grosmont Carbonate Bitumen Deposit, Northern Alberta, Canada

Abstract

The platform carbonates of the Upper Devonian Grosmont Formation hold an estimated 50 billion m3 of bitumen in place and therefore host a significant amount (one-sixth) of the total bitumen resources in northern Alberta. However, unlike the overlying Athabasca oil sands, the bitumen resource has not been tapped as yet. The present study is an overview and integration of recent subsurface studies, largely focused along the eastern subsurface erosional edge of the Winterburn Group in northern Alberta. The basis of the regional geologic framework includes a detailed study of 42 cores with an emphasis on facies description of both reservoir and nonreservoir facies, and the summary of a diagenetic sequence model to demonstrate the major influences on bitumen accumulation. The Grosmont Formation carbonates have been subject to various stages of diagenesis, including dolomitization and karstification with a profound effect on the distribution of porosity and permeability, which resulted in highly heterogeneous reservoirs. In addition, low effective permeabilities because of high bitumen saturation, the high viscosity of the heavily biodegraded bitumen, and the continuity and integrity of shales capping bitumen-bearing reservoir facies are further factors that must be considered in applying future in-situ recovery schemes to the Grosmont carbonate bitumen deposit.