ABSTRACT

Geophysical data have indicated that sediments in excess of 30,000 ft (9150 m) have been deposited under conditions of extension tectonics on the Labrador Shelf, east of the Canadian Precambrian Shield.

Three wells drilled in the Labrador Shelf--Tenneco et al. Leif E-38, which was abandoned at 3567 ft (1088 m), in sediments tentatively classed as Oligocene, because of adverse weather in the fall of 1971; Eastcan et al. Leif M-48 and Bjarni H-81, drilled in 1973 to 6165 and 8252 ft (1880 and 2517 m) respectively, terminating in Early Cretaceous volcanic rocks--are described herein.

Persistent stratigraphic units, seismic markers and unconformities on this shelf allow correlation of the two deeper wells.

Regional correlations with the better-known Grand Banks and Nova Scotia Shelf sections are attempted, rather than the definition of new formations from two wells 135 miles apart.

The section is approximately as follows:

Pleistocene glacial boulder beds, 72 and 172 ft (22 and 53 m) thick in Leif M-48 and Bjarni H-81 respectively, are part of a veneer spread over the shelf to a depth of 1000 ft (305 m). Sparker and airgun surveys show an erosional unconformity at their base.

Upper Tertiary arkosic, pebbly sands occur in all wells and are 1639 ft (500 m) thick in Bjarni H-81 and approximately 827 ft (252 m) thick in Leif M-48.

Miocene-Oligocene lutites, 2510 and 1998 ft (765 and 607 m) thick in Leif M-48 and Bjarni H-81 respectively, underlie the arkoses with a transitional boundary.

Eocene-Paleocene shale, sandstone, limestone sequence about 2000 ft (610 m) thick; has an abrupt but conformable upper contact with the overlying beds. The base of this unit is abrupt and appears to be a disconformity with a hiatus in early Paleocene.

Upper Cretaceous indurated shale, 196 and 570 ft (60 and 174 m) thick in Leif M-48 and Bjarni H-81 respectively rests unconformably on a Lower Cretaceous arkosic sandstone reservoir unit in Bjarni H-81 and Lower Cretaceous basaltic lava in Leif M-48.

This Tertiary-Cretaceous sedimentary wedge, known as the Coastal Plain Sequence, is underlain by an angular unconformity often associated with lavas. The unconformity has been ruptured by extension faults, which may have acted locally as feeders for the lava flows.

An open-hole drillstem test of the arkosic sandstone between 7050 and 7400 ft (2150 and 2257 m) (the top of the lavas) in Bjarni H-81 yielded 0.675 specific gravity gas at a rate of 13 MMCFPD with a little 55° API condensate, from about 160 ft (49 m) of effective porosity.

Source beds with a favourable maturation history for hydrocarbon generation, seal and reservoir beds are associated with large structures in drape and pinchout traps, and a number of down-faulted blocks of pre-Cretaceous sediments are seen in the reflection sections.

End_Page 361------------------------

Regional geology and location map (about 11,000,000:1).

End_Page 362------------------------