Petrographic, chemical, and isotopic studies
of the Mississippian (Visean) upper Debolt Formation in the Blueberry field,
British Columbia, Canada, reveal that dolomitization was the result of
several diagenetic events and that neomorphic alteration of these dolomites
significantly modified their original chemical signatures. These studies
also demonstrate how tectonics play an important role in controlling and
modifying reservoir dolomites in the area. Petrographic investigations
have documented two early dolomite phases, (1) early matrix dolomite and
(2) pervasive dolomite, and two later generations, (3) coarse cement and
(4) pseudomorphic replacement of crinoids.
Early matrix dolomite occurs as small (average
25 µm) subhedral to euhedral crystals that replace the matrix of
carbonate mudstones, wackestones, and packstones. Petrographic evidence
suggests that early matrix dolomite had a relatively early, precompaction
origin, possibly from marine fluids. However, geochemical evidence indicates
that later fluids have altered their original geochemical signatures.
©Copyright
1997. The American Association of Petroleum Geologists. All rights reserved.
1Manuscript
received February 1, 1996; revised manuscript received August 16, 1996;
final acceptance January 19, 1997.
2Department
of Earth Sciences, University of Windsor, Windsor, Ontario, Canada N9B
3P4. Present address: Chauvco Resources, Ltd., 2900, 255-5th Avenue S.W.,
Calgary, Alberta T2P 3G6 Canada.
3Department
of Earth Sciences, University of Windsor, Windsor, Ontario, Canada N9B
3P4.
This
research was supported by individual operating grants from Canada's Natural
Sciences and Engineering Research Council (NSERC) awarded to I. S. Al-Aasm
and additional funding from PanCanadian Petroleum Resources Limited, and
Suncor Inc. S. Durocher acknowledges support from an Ontario Graduate Scholarship.
S. Brame (Talisman Energy), L. Williams (Phillips Petroleum Resources,
Ltd.), G. Burrowes and I. Mcllreath (PanCanadian Petroleum Ltd.), and J.
Packard (Rhomb Carbonate Consulting Ltd.) are thanked for the valuable
information, insights, and ideas for tackling the complexities of the Blueberry
field. Thanks are also due to J. Veizer (University of Bochum and University
of Ottawa) for strontium isotope analysis. An earlier version of this paper
benefited from critical reviews by M. Malone (Texas A&M University),
C. Viau (Shell Canada, Ltd), S. Schutter, J. Dravis (Dravis Interest Inc.),
and an anonymous reviewer.
