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Maja (B.E.) Buschkuehle1, Hans G. Machel1
(1) University of Alberta, Edmonton, AB

Abstract: Diagenesis of the Southesk-Cairn carbonate complex with implications for paleo fluid flow - Upper Devonian, Western Canada Sedimentary Basin

The Southesk-Cairn Carbonate Complex (SCCC)is located in West-Central Alberta, it crops out in the Rocky Mountains along several thrust sheets and continues into the subsurface of the Alberta basin into depths of 3000m to 5000m. In this area the complex contains some of the deepest hydrocarbon pools in the Alberta basin, which makes exploration and exploitation risky and expensive. A better understanding of the diagenesis and basin development can therefore provide valuable information for the petroleum industry.

The subsurface part of the carbonate complex consists of four carbonate platforms with associated reefs, which are separated by shales, marls, and evaporites. The SCCC encloses the Wild River Basin, which consists of marls and carbonates, as well as shales.

Diagenesis played an important role in the enhancement and destruction of reservoir quality. Pervasive dolomitization increased porosity and permeability, whereas cementation clogged porosity and decreased permeability. Stable and radiogenic isotope investigations of matrix dolomites, late diagenetic dolomite cements and calcite cements reveal that the pore fluids underwent a complex history from late Devonian seawater to tectonically expelled brines in the Early Tertiary. The most important and partially unexpected finding is that hydrothermal/metamorphic fluids appear to have been injected into some sour gas reservoirs during thermochemical sulfate reduction. The migration pathways are under further investigation and it seems that some fluids have been pushed in directions other than those presently established and/or recognized.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana