Predicted and measured petrophysical and geochemical characteristics of the Egret Member oil source rock, Jeanne d'Arc Basin, offshore eastern Canada

Abstract

The Δ log R wireline log technique has been used to predict high vertical resolution geochemical profiles for 17 well penetrations of the Upper Jurassic Egret Member source rock of the Jeanne d'Arc Basin, offshore Newfoundland. The predictions are compared with Rock-Eval data obtained from the same interval. High resolution comparison of the computed total organic carbon (TOC) curves with gamma ray logs implies that the source rock layers in the Egret Member are mainly shale/claystone and the non-source rock layers are limestone/marl (to the south) and siltstone/sandstone (to the north). These comparisons also indicate that in the mature area some coarse-grained non-source rock layers are filled with hydrocarbons, implying primary migration of oil/gas. Using the average computed TOC value, the thickness of the Egret Member and the average formation density, the mass of organic carbon was calculated at 19 well locations and regional variations examined. Areas with a great mass of organic carbon were identified. The present mass of organic carbon is primarily related to the amount of organic matter being deposited and preserved, but the expulsion of oil/gas may also exert a control. Using 1 wt.% as the lower limit for a source rock, it was observed that the percentage of non-source rock in the Egret Member is generally higher in immature wells (LOM ⩽ 7) than in mature wells, probably as a result of hydrocarbon migration/expulsion after maturation.