Exploratory Drilling on the Canadian Continental Shelf, Labrador Sea

Abstract

The ice pack, icebergs, and meteorology are among the factors making exploratory drilling in the Labrador Sea difficult. After an unsuccessful attempt at operations with a conventionally anchored vessel, a technolog-ical breakthrough occured with the use of a dynamically positioned drillship. Introduction The continental shelf in the Labrador Sea comprises an area in excess of 50,000,000 acres. It is tightly covered by federal oil and gas permits granted to 24 single companies and joint-holder combines. The Labrador shelf's northern and southern boundaries are, respectively, the 61 degrees parallel (corresponding to the latitude of Hudson Strait) and the 52 degrees parallel (corresponding to the Strait of Belle Isle). parallel (corresponding to the Strait of Belle Isle). It is bounded on the west by the Labrador Marginal Channel, fringing the mainland made by the Canadian Precambrian Shield. On the east the 1,500-ft bathymetric contour line may be used as a practical limit. Because of this particular situation between the channel and the continental slope, there is neither shallow water nor gradual descent of the bottom from land toward the ocean depths. The "backbone" of the shelf is constituted of a succession of banks with an average water depth of 600 ft, separated by transverse topographical troughs and saddles (Fig. 1). These banks, running from north to south, are the Saglek Bank, Nain Bank, Harrison Bank, and the North and South Domino Banks. Their area varies from about 3,000,000 to 6,000,000 acres. The Eastcan Group holds titles to about one-half the shelf, including almost the entire area of the banks. Geophysical surveys and reconnaissance seismic work were begun as early as 1966; 50,000 miles have been shot in the area since then. As a result, it can be concluded that the shelf is underlain by a basin in which sediments in excess of 30,000 ft at some places have been deposited. The maximum thickness is encountered in the north (Saglek Bank), whereas the central and southern parts range from 5,000 to 20,000 ft. The exploratory targets are block faults related to rifting movements that took place when Labrador and Greenland drifted apart during Jurassic and Cretaceous times. There are a number of well defined structures yet to be drilled, and the stratigraphic objectives range in age from the Paleozoic up to the Tertiary. The Labrador shelf is in a very early stage of exploratory drilling. Among three wells drilled in 1973 and 1974, two were located on banks (the Leif and Bjarni Banks) and one was located in a saddle (Gudrid). To put the matter in a more regional perspective, it is interesting to note that the most active exploratory area of Eastern Canada so far has been the Grand Banks of Newfoundland to the east and south of the island and the Scotian shelf south of the peninsula of Nova Scotia. This area has reached a more mature stage of knowledge as compared with Labrador; the more than 100 wells drilled there have resulted in the discovery of oil and gas at Sable Island, some shows, and many dry wells. The level of activity is decreasing somewhat, and no final decision has been made regarding commercial exploitation of the discovery. JPT P. 372