--> --> Abstract: The Geochemistry of Montney and Lower Doig Tight Gas Reservoir, Northeastern British Columbia, Western Canada, by Edwin I. Egbobawaye, Murray Gingras, and John-Paul Zonneveld; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

The Geochemistry of Montney and Lower Doig Tight Gas Reservoir, Northeastern British Columbia, Western Canada

Edwin I. Egbobawaye1; Murray Gingras1; John-Paul Zonneveld1

(1) Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada.

Triassic Montney and Lower Doig strata in northeastern British Columbia and northwestern Alberta host substantial volumes of unconventional gas (est. 326.7 TCF). Despite the economic significance of these intervals the location and predictability of the best reservoir units remains conjectural: in large part because the lithologic variability, mineralogy, geochemistry and reservoir parameters of this succession has not been adequately characterized. This study aims to propose mechanisms of porosity / permeability development and preservation by establishing a petrogenetic framework for known reservoir intervals.

This study uses geochemistry coupled to sedimentology, petrography and mineralogical analyses to evaluate reservoir characteristics of the Montney (silty-shale) gas reservoir. In general, the succession is composed of siltstone with subordinate sandstone beds. The mineralogy comprises quartz, dolomite, feldspar and clay. Rock Eval data (Hydrogen Index and Oxygen Index) from the study area in northeastern British Columbia shows that the Montney and Lower Doig sediments contains mostly gas prone Type III / Type IV kerogen, TOC ranges from ~0.4 - 4.0 wt%, with rare spikes in the Doig interval of up to ~11 wt%. Vitrinite reflectance data indicates that hydrocarbon generation remains within the zone of ‘peak gas’ generation. Specimens imaged by SEM shows that Montney and Lower Doig samples analyzed in this study have variably abundant natural micro fractures (individual fractures approx. 2 microns in width and up to 7 microns in length). Lithological analyses and the presence of micro fractures provides two important pieces of information on reservoir intervals: (1) the natural brittleness of reservoir lithologies has allowed for enhanced reservoir fracturing; and (2) micro fractures that can serve as initial permeability conduits for gas flow are naturally present.