Carboniferous, Hydrocarbon-Bearing Evaporite Sequence from Nova Scotia

D. C. Carter, P. G. McMahon

The Maritimes basin of eastern Canada represents a postorogenic, successor-type basin which accumulated essentially nonmarine molassic sediments, with one identifiable marine incursion, from Late Devonian to Early Permian time. Situated in the northeastern Appalachians, the basin extends from the southeastern edge of the Laurentian platform to the western edge of the Newfoundland platform. Present distribution represents the erosional remnants of a complex series of interconnected subbasin and arch or uplifts structures which controlled, and to some extent were controlled by, the sedimentary fill.

The basal sediments are referred to as Horton or Anquille Groups and comprise alluvial, fluvial-deltaic, and lacustrine lithofacies. The overlying Windsor or Codroy Group is a cyclic marine clastic-carbonate-evaporate sequence. Major units within these groups are correlatable across the basin. The only producing oil and gas field in eastern Canada, the Stoney Creek field in southeastern New Brunswick, is located stratigraphically within the Horton Group.

Recent diamond drilling to examine the evaporite sequence in the Shubenacadie basin of central Nova Scotia encountered a significant, overpressured flow of natural gas from within the basal halite and basal anhydrite units of the Windsor Group and resulted in the termination of the drill hole at 683.05 m. The gas flow, volume, and pressure were evaluated, within the limitations of the wireline drilling equipment, and gas samples were collected. Flow volume averaged 3,750 ft³/day at a pressure in excess of 1,500 psi from an undeveloped hole with two rod strings and coring assembly in place.

Horton Group rocks are only exposed along the faulted northwest margin and, therefore, are not well defined in the Shubenacadie basin. Thickness estimates range from 500 to 1,000 m. Windsor Group evaporites are well documented based on extensive diamond drilling. The basin is virtually unexplored in terms of hydrocarbon potential. Based on the known structure, stratigraphy, and presence of gas in the evaporites, that potential appears to be significant.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.