Distribution of porosity and facies in the Gay's River formation, south-side Antigonish Harbour: Implications as a possible hydrocarbon reservoir

Abstract

The Gays River Formation is a limestone unit located at the base of the Windsor Group, located adjacent to paleotopographical basement highs. It is in nonconformable contact with the underlying pre-Carboniferous basement rock, which, in the case of the south side Antigonish Harbour outcrop, is a granodiorite. Underlying organic-rich shales of the Horton Group, and overlying evaporite deposits of the Bridgeville Formation, combined with the natural upward slope of the underlying basement provide an ideal environment for a hydrocarbon trap to occur. In this study, the lithological constituents and porosity were examined in hand sample as well as thin section. Four facies were identified, bafflestone, wackestone, mudstone and a mixed wackestone-bafflestone. The porosities ranged from 10%-31 % and showed no apparent preference to facies-type. A representative cross-section of the area was made from the combination of measured sections from the field and the lab data, and from this the distribution of these facies and porosity, with respect to the basement rock was studied. The wackestone was found to be the most extensive facies, and the bafflestone was restricted to regions of immediate contact with the granodiorite basement. Porosity values combined with qualitative assessments of reservoir rocks suggest that the Gays River Formation shows good potential as a reservoir rock.