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The AAPG/Datapages Combined Publications Database

CSPG Bulletin

Abstract


Bulletin of Canadian Petroleum Geology
Vol. 39 (1991), No. 2. (June), Pages 222-222

"Reservoir Development and Resource Emplacement in Selected Paleozoic Carbonates of Northeastern British Columbia and Northwestern Alberta [Abstract]"

Reimer, J.D.1, Teare, M.R.1

ABSTRACT

A significant natural gas resource occurs in selected Paleozoic carbonates of northeastern British Columbia and adjacent northwestern Alberta. Proven reservoirs include the Debolt, Jean Marie, Slave Point, Keg River, Pine Point, and Nahanni formations. We have observed that many of these reservoirs exhibit similar diagenetic fabrics, on the basis of evidence from in-house core studies and the literature. These fabrics include intense fracturing, leached pinpoint to locally cavernous porosity, saddle dolomite cement, occasional sulphide/sulphate mineralization, and the presence of bitumen. The widespread distribution of these fabrics suggests that a common diagenetic mechanism has affected these rocks on a regional scale. Thermochemical sulphate reduction (TSR), combined with active paleohydrogeological flow, is one possible mechanism. In our model, TSR reaction "furnaces" developed within pre-existing oil pools, and sulphate was supplied from various sources via groundwater transport. We envisage four main stages to this process:

  1. fracturing of the surrounding rock, due to a pressure increase from the hydrocarbon phase change, which opened new vertical and lateral conduits for fluid migration
  2. porosity enhancement in and around these conduits by thermal cooling and weak acid leaching from excess CO2
  3. precipitation of dolomite cement and sulphur minerals in the emerging void space
  4. concurrent infusion of methane and other byproducts

We conclude that the TSR process both created and was the source for its own reservoirs. Therefore, we predict the existence of economic pools in stable platform settings, liquid-rich fields peripheral to the main reaction sites, and additional resources in overlooked units. The challenge facing our industry is to develop these ideas into new exploration techniques for this expansive gas theatre.

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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES

1 Home Oil Company Ltd., Calgary, Alberta T2P 2Z5

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