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Petrologic and Geochemical Evidence for Refluxing Brines in the Devonian Wabamun Group, West-Central Alberta*

By

Ihsan Al-Aasm1 and Samantha Raymus1

 

Search and Discovery Article #50046 (2007)

Posted July 30, 2007

 

*Adapted from oral presentation, AAPG Annual Convention (with SEPM), Long Beach, California, April 1-4, 2007

 

1University of Windsor, Windsor, Ontario, Canada ([email protected])

 

Abstract 

Recent sedimentological and geochemical investigations on several Devonian Crossfield reservoirs from Burnt Timber, Panther River, Moose Mountain, and Benjamin Ghost region west of the Crossfield trend, Alberta, provided new evidence for the role of reflux brines on the formation of pervasive fine-crystalline matrix dolomite and modification of porosity in these reservoirs. Other associated diagenetic processes that formed during early and late burial history include compaction, recrystallization of early matrix dolomite, precipitation of secondary anhydrite, blocky calcite, saddle dolomite and thermal sulphate reduction (TSR)-related diagenetic minerals. The evidence for density-driven refluxion from the Stettler brines for the formation of the fine-crystalline matrix dolomite include: (1) dolomitization occurs in sediments that are relatively uncompacted, and the degree of preservation of the original fabrics is quite significant in the dolomicrite and fine- to medium-crystalline matrix dolomite, (2) fabric-destructive stylolitization and the development of dissolution seams cross-cut dolomite matrix fabrics, (3) matrix dolomite is relatively fine- to medium-crystalline (<10 µm–200µm), planar-S to nonplanar, non-luminescent to very dully luminescent, (4) oxygen isotopic values range from -2.82 to -6.17 ‰ and carbon isotopic values from 0.22 to 1.47 ‰. These values are comparable to slightly more depleted than Famennian seawater isotopic signatures. The depletion is likely the result of recrystallization that has affected the matrix dolomite during subsequent burial and (5) 87Sr/86Sr ratios indicate that the dolomicrite and fine-crystalline dolomite precipitated from Famennian seawater. The associated primary evaporites show also values close to Famennian seawater, suggesting that the dolomicrite and fine-crystalline matrix dolomite precipitated from Famennian seawater.

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Selected Figures

 

Crossfield- Why Reflux of Upper Stettler Brines? 

  • Areal juxtaposition of dolomites and Stettler evaporites (decrease of dolomite to north and west)

  • Pervasive dolomitization (huge Mg-flux required)

  • Preservation of uncompacted fabrics, which therefore requires very early consolidation

  • Devonian seawater Sr87/Sr86 values

  • Calcian-rich (non-stochiometric) dolomites

  • Subtle gradient related to subsidence of Prophet Trough- enhances flow path for reflux brines

  • Presence of undolomitized/dolomitized intervals- “fingers”- edge of dolomitization front/periodic reflux

 

References 

Alberta Petroleum and Natural Gas Conservation, Board, 1956, Schedule of wells drilled for oil and gas in 1956, p. 12.

Andrichuk, J.M., 1960, Facies analysis of Upper Devonian Wabamun Group in west-central Alberta: AAPG Bulletin, v. 44, p. 1651-1681.

Belyea, H.R., and D.J. McLaren, 1962, Upper Devonian Formations, southern part of Northwest Alberta: Geological Survey of Canada, Paper 61-29, 72 p.

Bottrell, S.H., and R.J. Newton, 2006, Reconstruction of changes in global sulfur cycling from marine sulfate isotopes: Earth Science Reviews, v. 75, p. 59-83.

Claypool, G.E., C.N. Threlkeld, and L.B. Magoon, 1980, Biogenic and thermogenic origins of natural gas in Cook Inlet basin, Alaska: AAPG Bulletin, v. 64, p. 1131-1139.

deWit, R., and D.J. McLaren, 1950, Devonian Sections in the Rocky Mountains between Crowsnest Pass and Jasper, Alberta; Geological Survey of Canada, Paper 50-23.

Halbertsma, H.L., and N.C. Meijer-Dress, 1987, Wabamun limestone sequences in north-central Alberta, in Devonian lithofacies and reservoir styles in Alberta, F.F. Krause and O.G. Burrows, eds., 13th Core Conference Guide, Alberta Society of Canadian Petroleum Previous HitGeologistsNext Hit, Calgary, Alberta, p. 21-37.

Majid, A.H. 1989, Regional geology and hydrocarbon occurrences in the Wabamun Group, west-central Alberta, Canada, in Current Research, Part D, Geological Survey of Canada, Paper 89-1D, p. 25-33.

Martindale, W., J.J. Packard, and Ihsam Al-Aasm, 2004, The Wabamun Crossfield Member in Southern Alberta (est. 4.9 Tcfe resource) – an example of reflux dolomitization of peritidal carbonates, in Dolomites: The Spectrum: Mechanisms, Models, Reservoir Development: CSPG seminor and ocre conference, January 13-15, 2004, Calgary, Alberta (CD-ROM).

Packard, J.J., 1992, The Dunvegan Field, NW Alberta, Canada: Dolomitization and porosity preservation in Mississippian sabkha and contiguous subtidal sediments (abs.): AAPG Bulletin, v. 76, no. 13 (annual mtg).

Packard, J., and G. J. Pellegrin, 1989, Diagenesis and dolomitization associated with hydrothermal karst in Famennian Upper Wabamun ramp sediments, northwestern Alberta, in G. Bloy and M. Hadley, eds., The development of porosity in carbonate reservoirs: Canadian Society of Petroleum Previous HitGeologistsNext Hit Short Course, p. 9-1-9-19.

Packard, J.J., G.J. Pellegrin, I.S. Al-Aasm, I. Samson, and J. Gagnon, 1990, Diagenesis and dolomitization associated with hydrothermal karst in Famennian Upper Wabamun ramp sediments, northwestern Alberta, in G. Bloy and M. Hadley, eds., The development of porosity in carbonate reservoirs: Canadian Society of Petroleum Previous HitGeologistsNext Hit Short Course, p. 9-1 - 9-27.

Packard, J.J., P. Churcher, Ihsan S. Al-Aasm, Iain Samson, Ronald Spencer, A. Hamid Majid, and J.G. Sen Gupta, 1992, Hydrothermal karstification and dolomitization of Upper Devonian(Wabamun Formation) medial ramp limestones: North-central Alberta, Canada: AAPG Bulletin, v. 76, no. 13 (annual mtg), p. 100 – 101.

Packard, J.J., Ihsan Al-Aasm, Iain Samson,  Zeev Berger, and Jim Davies, 2001, A Devonian hydrothermal chert reservoir: the 225 bcf Parkland field, British Columbia, Canada: AAPG Bulletin, v. 85, p. 51-84.

Reinson, G.E., P.J. Lee, W. Waters, K.G. Osadetz, L.L. Bell, P.R. Price, F. Trollope,  R.I. Campbell, and J.E. Barclay, 1993, Devonian gas resources of the Western Canada Sedimentary Basin: Geological Survey of Canada, Bulletin 452, 157 p.

Saller and Yaremko, 1994, Dolomitization and porosity development in the middle and upper Wabamun Group, Southeast Peach River arch, Alberta, Canada: AAPG Bulletin, v. 78, p. 1406-1430.

Wonfor, J.S., and J.M. Andrichuk, 1956,. The Wabamun Group in the Stettler area, Alberta: Journal of the Alberta Society of Petroleum Previous HitGeologistsTop, v. 4, p. 99-111.

Workum, R. H., 1991, Peace River arch Wabamun dolomite, tectonic or subaerial karst: Bulletin of Canadian Petroleum Geology, v. 39, p. 54-56.

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