Understanding Deep Water Depositional Environments Offshore Nova Scotia

Brenton Smith and Mark Deptuck
CNSOPB, Halifax, NS, Canada

The Sable subbasin, on Nova Scotia’s outer continental shelf, contains at least 12 km of Early Jurassic to Late Cretaceous sand-rich sediments rapidly deposited by the Sable delta complex. The subbasin contains an estimated 6.7 Tcf recoverable gas with over 1.3 Tcf produced to date from five gas fields. Given the large volume of Jurassic and Cretaceous fluvial-deltaic sediments deposited in this subbasin, coarse clastics are expected to have been transported from shelf complexes down the slope into deeper water during periods of low sea level.

The present day deep water slope area offshore Nova Scotia encompasses 80,000km². Prior to 1986, only four wells were drilled in this area. Since 2001, six additional wells were completed involving 7 major companies. Although a working petroleum system has been confirmed, with one well encountering 27m of net gas pay over several turbidite zones, the limited success with encountering sand indicates that the sand trapping mechanisms on the slope are poorly understood.

Seven wells were targeting deep water equivalents to the Sable delta sands. Although drilling has occurred in water depths up to 2090 m, paleoenvironmental determinations from biostratigraphic studies indicate that only outer shelf to upper slope environments were encountered in the Cretaceous succession. An updated model of the depositional history of the slope is clearly required.

In this talk we will discuss some of the key learnings from recent drilling results on the slope with emphasis on improvements in the understanding of the turbidite systems afforded by 32,000 km² of 3-D and 150,000 km of 2-D seismic data acquired since 1998.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery