Sediment Transport from Shelf to Slope Offshore Nova Scotia

Brenton Smith
CNSOPB, Halifax, NS, Canada

The Sable subbasin, offshore Nova Scotia, is a sand-rich, productive delta system formed during the Jurassic and Cretaceous. This subbasin contains an estimated 6.7 Tcf recoverable gas with over 1 Tcf produced to date, from five gas fields. The upper part of the Early Cretaceous Missisauga formation’s seaward depositional edge is interpreted as a shelf margin delta complex. It is believed that given the large volume of Jurassic and Cretaceous sediments deposited in the subbasin and evidence of rapid sedimentation, coarse clastics should have been transported from shelf complexes down slope into deeper water during lowstand periods.

The deep water slope area offshore Nova Scotia encompasses 80,000km2. There were 4 wells drilled into this area pre-1986, and 6 wells post-2001 in a drilling effort involving 7 major companies. Although a working petroleum system has been confirmed, with one well encountering 27m of net gas pay over several zones, the overall lack of sand has been disappointing.

The age and depth of the slope sediments makes it very difficult to identify gas sands using seismic attributes. This stresses the importance of constructing Jurassic and Cretaceous paleogeographic maps to identify potential sand prone areas. The search for evidence of sands being transported into deeper water has been frustrated by extensive reworking of outer self sediments during Jurassic and Cretaceous sea level changes, heavy incision of the modern slope morphology, and by salt movement. This presentation will illustrate some of the ongoing work mapping numerous Tertiary and Upper Cretaceous channels that will contribute to our understanding of the processes during the Cretaceous and Jurassic periods and hopefully assist in determining the location of potential deep water reservoir sands.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas