Large channels in the Glauconitic interval of southern Alberta have proved to be elusive exploration targets owing to the discontinuous nature of reservoir sands. In the Little Bow area, a 20 m deep channel has been cut through sandstones and shales of the Glauconitic interval and limestones and shales of the underlying Ostracod Zone. Mineralogy, texture, and geometry of the channel sands are distinctly different from those adjacent to the channels.
The montmorillonitic Bantry Shale of the Ostracod Zone is an excellent regional marker and is absent only where it has been cut out by a channel. Sediments of the Glauconitic interval, which conformably overlie the Bantry Shale, were deposited in a broad, shallow subtidal marine bar system. The marine bars are tabular sand bodies only a few meters thick, and are composed of low porosity fine to medium-grained, calcite and clay cemented chertarenites.
The incised channel system contains 20-m thick point bar accretion sets and shale plugs. Point bar sands are porous medium to coarse-grained sublitharenites with high angle cross-stratification. Sand bodies are discontinuous along the length of the channel, and the channel margins are abrupt.
Geologic exploration for these discontinuous channel sands is difficult and high resolution seismic data integrated with sound geologic modeling is critical for successful prospect delineation.