Mineralogy and Geochemical Trapping of Acid Gas in Northeastern British Columbia, Canada

Beate E. Buschkuehle¹ and Kyle Durocher^2
1 Alberta Energy and Utilities Board - Alberta Geological Survey, Edmonton, AB
² Alberta Research Council, Edmonton, AB

Geologically sequestered acid gas (CO₂, H₂S) can be contained within the subsurface by a number of processes. This study discusses the mineralogy and geochemical trapping possibilities at acid-gas injection sites in northeastern British-Columbia. The injection horizons consist of Mississippian to Triassic carbonates and sandstones. The carbonates consist of porous dolostone of the Carboniferous Debolt Formation (87% dolomite, 10% calcite and minor opaque minerals) and the Triassic Baldonnel Formation (94% very fine-grained dolomite, with minor amounts of anhydrite and quartz), which are sealed by shales of the Montney Formation and Fernie Group, respectively. Clastic injection horizons include the Permian Belloy Formation (78% Quartz, 10% Chert, 5% Glauconite, 5% opaque minerals, 1% carbonate and minor amounts of feldspar, mica and apatite) and the Triassic Halfway Formation (79% Quartz, 10% Chert, 5% glauconite, minor carbonate, feldspar, muscovite and apatite), which are vertically confined by shales of the Montney Formation and by evaporites of the Charlie Lake Formation, respectively. Using a geochemical mass transfer program, the potential reactions between the formation mineralogy, the formation waters and the injected gas were evaluated. In the carbonate units, the majority of the acid gas trapping is through solubility trapping, which may be augmented by the buffering reactions with the reservoir mineralogy. In the clastic units, mineralogical trapping of CO2 is significant over a long-term time span, and is the result of reactions between the calcium silicate minerals and the fluids.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005