The Egret Member, a Prolific Kimmeridgian Source Rock from Offshore Eastern Canada

  • M. G. Fowler
  • K. D. McAlpine
Part of the Casebooks in Earth Sciences book series (CASEBOOKS)

Abstract

The Jeanne d’Arc basin is situated in the northeastern part of the Grand Banks, off the east coast of Newfoundland. Several large oil and gas fields have been discovered in this basin, the largest of which is the giant Hibernia field. The principle source rock for most of the oils in the Jeanne d’Arc basin is the Kimmeridgian-aged Egret Member of the Rankin Formation. This interval is easily identified on downhole and geochemical logs, principally because of its higher TOC content compared to surrounding units. The Egret Member ranges in thickness from 55 m to in excess of 200 m. Based on the analysis of cutting samples (no core has yet been taken of this unit), it shows average TOC contents up to 4.58%, and average hydrogen index values of immature samples in the 500–700 range. The organic matter is predominately amorphous in appearance, with terrestrial-derived material significant only in some wells on the eastern side of the basin.

Most Egret Member extracts have hydrocarbon distributions that show the characteristics of marine-derived organic matter deposited under reducing conditions. These include pristane/phytane ratios of usually less than one, high abundance of 4-methylsteranes derived from dinosterol, a predominance of C27 over C29 regular steranes, a low abundance of tricyclic terpanes relative to hopanes, and a smooth distribution of C31–C35 17α(H)-hopanes. Some wells on the eastern side of the basin (e.g., Archer K-19 and Fortune G-57) show biomarker characteristics that suggest a greater contribution from terrestrially-derived organic matter in this area. The depositional environment for the Egret Member is interpreted to be a silled marine basin with high (periodic?) primary productivity, especially from dinoflagellates. The bottom waters were suboxic to anoxic. The primary organic matter was extensively reworked by anaerobic bacteria.

Quantitative geochemical techniques show the Egret Member to be a prolific oil source rock and suggest that perhaps as little as 15% of Jeanne d’Arc basin recoverable oil reserves may presently be discovered.

Keywords

Foam Petroleum Drilling Cretaceous Dolomite 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1995

Authors and Affiliations

  • M. G. Fowler
    • 1
  • K. D. McAlpine
    • 2
  1. 1.Institute of Sedimentary and Petroleum GeologyCalgary, AlbertaCanada
  2. 2.Atlantic Geoscience CentreBedford Institute of OceanographyDartmouthCanada

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