Abstract

Canned sample cuttings from 12 exploratory wells drilled on the Labrador Shelf and East Newfoundland Shelf were analyzed and the data were used to determine the quality of source rocks, diagenesis of organic matter, and the potential of rocks to produce oil and gas.

The results of this study indicate that the Cenozoic-Mesozoic rocks contain high concentrations of organic carbon derived mainly from a terrestrial source, which is usually gas prone. Consequently, many thick sections in several wells, particularly those located on the northern part of the Labrador Shelf, contain large concentrations of gaseous hydrocarbons. However, the concentrations of heavy hydrocarbons in relation to organic carbon in many of these wells are below the threshold levels for oil occurrences. Thus their rating for oil is poor.

The poor oil rating is generally attributed to the organic matter type, which is largely terrestrial, and to insufficient time and temperature for thermal maturation. A few maturity indicators suggest that the organic facies of Cretaceous sediments in the northern Labrador Shelf wells (Herjolf, Snorri and Karlsefni) have attained maturity at a depth of about 3 000-3 500 m. A marginally mature zone was encountered in the Bonavista, Leif and Bjarni wells; whereas the organic facies of the remaining wells are still immature.