Exploration on the Scotian Shelf has so far resulted in eight gas and oil-condensate discoveries, all within halokinetically deformed Jurassic and Cretaceous sand and chalk reservoirs. The paper sums up the geology as determined from 55 wells drilled prior to 1976, and the geochemistry from 13 of these wells.
The post-Drift sequence consists of a Jurassic platform with bank-edge carbonates and a basinal facies, overlain by a Lower Cretaceous clastic deltaic development, followed by an Upper Cretaceous deltaic and littoral marine sand facies and terminating with deep marine shales and a chalky sequence of the latest Cretaceous. Shallow occurring Tertiary shales and silts lack significant hydrocarbon potential.
The content of source organic matter in the Jurassic and Lower Cretaceous is generally poor to average, and of the gas prone-woody type. In the Upper Cretaceous, it is average in grade and of the gas prone woody and mainly oil prone-amorphous types. The poor to average gas-prone source within the Jurassic and Lower Cretaceous reaches marginal maturation only in the outer-central Shelf.
Therefore, deep objectives in the outer-central Shelf (generally in deep waters), remain as the most interesting targets for future exploration in the offshore Nova Scotia.
The Scotian Shelf is defined as that portion of the Canadian Atlantic continental shelf bounded by the Laurentian Channel to the northward and the Northeast Channel to the southwest. It is a 75-100 mile (120-l60 km) wide and 450 mile (725 km) long platform that covers approximately 45,000 square miles (115,000 sq. km). The area contains over 20,000 feet of post Lower Jurassic sediments in the main depo-centre, in the central part of the Shelf around Sable Island.
A total of 64 wells have been drilled on the Scotian Shelf at some 41 locations since 1967. The exploration activity, largely restricted to water depths shallower than 200 m has resulted in 8 gas and condensate discoveries. Most wells tested structural closures related to block faulting or salt diapirism. The distribution of wells is illustrated in Figure 1.
The present paper summarizes and evaluates the pre-1976 drilling and examines it with regard to reservoir development and geochemical source and maturation. In this paper, the geochemical evaluation is preceded by a brief description of the stratigraphic section and regional geology.
The geological history of the Scotian Shelf is closely related to the opening of the Atlantic and the drifting apart of North America from Northwest Africa. This drifting was initiated in the Middle Jurassic. Figure 2 portrays the stratigraphic column and Figure 3 a schematic cross section across the Shelf.
The structural map on top of the Western Bank Group (Figure 4) which approximates the top of Jurassic, gives an idea of the present depth to the Jurassic sediments and also the thickness of the post-Jurassic sequence on the Shelf.
