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Surface - Subsurface Gamma-Ray Correlation of Fluvio-Lacustrine Strata in the Region of the Mccully Gas Field, Moncton Basin, New Brunswick, Canada

Keighley, Dave 1; Yang, Chunlei 1
1 University of New Brunswick, Fredericton, NB, Canada.

Production from the McCully gas field, in the west of the Moncton Basin, is from tight sandstone in the upper Albert Formation of the Horton Group (Tournaisian, Mississippian). Road-cuts less than 50km to the west of the field expose strata also assigned to the same formation, and which are considered the correlatives of some of the source and reservoir rocks in the gas field. In total, four successions, detailing lithofacies and spectral gamma-ray response, have been measured ranging from 60m to over 200m vertical thickness.

The general lithofacies interpretation of the upper Albert Formation has fluvio-floodplain deposits interfingering and progressively prograding over a wave-dominated lake shoreface and offshore lacustrine strata. These lithofacies are identified in outcrop and each also has an associated characteristic spectral gamma-ray profile. Offshore lacustrine shale typically displays low potassium:uranium (K:U) ratios interpreted to reflect quiet (likely deep water) lacustrine deposition of abundant organic detritus, the decay of which involved the sequestering of uranium from pore waters. In contrast, shoreface and fluvial sandstone predominantly shows high total K values and high K:U ratios, with floodplain shale even higher values and ratios. This is considered to be a result of deposition of sand and mud consisting of volumetrically abundant K-bearing minerals (K-feldspar and mica).

The outcrop gamma-ray logs variably mimic log suites from the McCully field, including a particularly good fit for the producing "C" sand that, based on the outcrop interpretation is considered a shoaling upward, relatively high energy, shoreface sandbody.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009