Exploratory Drilling on the Canadian Continental Shelf,Labrador Sea

Abstract

ABSTRACT The Labrador Shelf is still at a very early stage of exploration. The various factors which make exploratory drilling particularly difficult and shorten the operating season, like ice-pack, icebergs, meteorology, are discussed. After a first unsuccessful attempt in 1971 whith a conventional anchored-type vessel, the technological breakthrough occurred when PELICAN, a dynamically positioned drillship, was successfully used in 1973 and 1974, which resulted in two gas discoveries out of three wells drilled. A description of this operation is presented as well as possible applications to other areas. 1. INTRODUCTION AND GENERALITIES The Labrador Shelf 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. Its northern and southern boundaries are respectively the 61° parallel (which corresponds to the latitude of Hudson Strait), and the 52° parallel (Strait of Belle Isle). It is bound to the West by the Labrador Marginal Channel, fringing the mainland made up by the Canadian Precambrian Shield. To the East one can take the 1500' bathymetric contour line as a practical limit. Due to this particular situation between a channel and the continental slope there is neither shallow water nor gradual descent of the bottom from the Continent towards the oceanic depths. The "backbone" of the shelf is constituted by a succession of banks with an average water depth of 600 feet, separated by transverse topographical troughs and saddles (Figure 1). These banks are from North to South : Saglek Bank, Nain Bank, Harrison Bank, North and South Domino Banks. Their area varies from approximately 3,000,000 to 6,000,000 acres. The Eastcan Group (1) holds titles over approximately half of the Shelf, including almost the entire area of the banks. Various geophysical surveys and reconnaissance seismic work began as early as 1966 and 50,000 miles have been shot in the area since. As a result one can conclude that the Shelf is underlain by a basin in which sediments in excess of 30,000 feet at some places, have deposited. The maximum thickness is to be encountered in the North (Saglek), whereas the central and southern parts range from 5,000 to 20,000 feet. The exploratory targets are blockfaults related to rifting movements which took place when Labrador and Greenland drifted apart during Jurassic and Cretaceous times. There are a number of well-defined structures to be drilled in the years to come and the stratigraphic objectives range in age from the Paleozoic up to the Tertiary. The Labrador Shelf is at a very early stage of exploration drilling. Among three wells drilled so far, two were located on banks (Leif and Bjarni) and one in a saddle (Gudrid). To put the matter in a more regional perspective, it is interesting to recall 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.