A Rich Middle Triassic Source Rock in the Barents Sea Area

Abstract

ABSTRACT The scope of the work presented in this paper is an evaluation of the petroleum potential of the source rock which shows most promise for the Barents Sea area. The evaluation is based on analysis of a large number of samples from a Middle Triassic black shale deposit on the various islands of the Svalbard Archipelago. This investigation has shown that the shale is an oil-prone source rock. Analysis of samples taken from areas in the Barents Sea, indicates that this shale sequence has similar potential as a source rock throughout the area south of Svalbard. Integration of this data with the available geophysical and geologica1 data allows us to propose that the rich, oilprone Middle Triassic shale sequence also has a widespread distribution throughout the Norwegian Arctic. The results of the geochemical analysis undertaken on Mesozoic deposits of Svalbard and from subsea outcrops in the Barents Sea area will be presented. In addition the significant geological data for the region will be included. The geochemical data to be discussed includes; total organic carbon content, Rock-Eval pyrolysis values, vitrinite reflectance and kerogen analysis in transmitted light. In addition some data on the amount and composition of extractable organic matter in the Triassic shales will be mentioned. Traditionally the Upper Jurassic shales have been regarded as the major source rocks on the Norwegian Continental Shelf. In addition to Jurassic source rocks there are some probable source rocks of Triassic age, particularly of Mid-Triassic age. Any oil and gas exploration in the Norwegian Arctic must take into account other possible source rocks from the Triassic, as well as those of Jurassic age which are regarded as the main source rocks in the North Sea. The presence of additional source rocks in the Barents Sea area increases the possibilities of oil and gas discoveries in this area. INTRODUCTION During the early stages of exploration for oil in the North Sea region there were lengthy discussions concerning the probable source rocks for the oil and gas, especially in the Northern North Sea. The geochemical techniques used in the late sixties and early seventies were rather crude and the errors introduced by this, at least in part, led to the conclusion that Paleocene shales were the source rock for the Ekofisk oi1 it was 1ater estab1ished that Ekofisk oil, as with other hydrocarbon accumulations found in the Central Graben (Fig. I), was sourced from the Upper Jurassic - Lower Cretaceous Kimmeridge Clay Formation. The situation in the Viking Graben (Fig. 1) is far more complex. It is generally accepted that most of the oil and gas found in the Norwegian sector of the North Sea has been sourced from shales of Jurassic age. Potential source rocks have been identified in shales from Upper, Middle and Lower Jurassic. In some areas potential source rocks have been identified in shales of Cretaceous and Lower Tertiary age, but it is believed that these are of minor importance.