A MATURATION FRAMEWORK FOR JURASSIC SEDIMENTS IN THE STABLE SUBBASIN,OFFSHORE NOVA-SCOTIA

The Sable Subbasin, offshore Nova Scotia, contains significant accumul ations of hydrocarbons, chiefly natural gas, that have been sourced an d reservoired in a thick sequence of postrift Mesozoic sediments. A se quence of deltaic clastics (Jurassic-Cretaceous Mic Mac, Missisauga an d Verrill Canyon formations) with lipid poor, terrestrial Type III org anic matter, low in TOC, represents one of several source rock concept s that have been invoked to explain these hydrocarbon occurrences. We present an organic maturity framework for such a source concept with o rganic matter distributed in the upper Jurassic (152 Ma datum) Mic Mac and Verrill Canyon formations (lateral equivalents). Our maturity fra mework models result from an examination of the interplay between the subsidence, compaction and thermal histories of 24 wells. Illustrated with reference to the Eagle C-21 well location, the assumed source int erval entered into the gas generative zone at around 110 Ma. The full sensitivity of this timing to time variant thermal (heat flow) assumpt ions is examined. The maturation timing sensitivity due to heat flow a ssumptions is of the order of 25 Ma. The progressive maturity of the p resumed source datum throughout the basin is imaged and provides a pre liminary framework for hydrocarbon charge modelling studies within the basin.