An integrated sedimentological and organic geochemical study of the Terra Nova Field and selected wells in the Jeanne d'Arc Basin, Grand Banks, Newfoundland
The proven hydrocarbon-bearing province, the Jeanne d'Arc Basin, located some 300km offshore SE Newfoundland, contains a relatively continuous Triassic to Tertiary rock record. This comprises evaporites, volcanics, mudrocks and sandstones, the latter two with source and reservoir potential respectively. Three extensional tectonic rift episodes helped produce structural traps for the migrating hydrocarbons. The Terra Nova Field which forms the main focus of this work is located within the Jeanne d'Arc Basin and is estimated to contain in excess of 160 million m3 original oil in place. The main reservoir units have been extensively cored with over 400m cut from six wells. 281m of core have been studied and are described and correlated on the basis of detailed sedimentological and depositional analyses. The prime reservoir sequence is the Upper Jurassic Jeanne d'Arc Formation, comprising braided fluvial deposits within which five distinctive facies patterns are identified. Organic GC-MS analysis of alkanes, hopanes and steranes, together with TOC and sulphur data from 27 samples from two wells have been combined with the sedimentological and palynological study. The purpose of these studies is to investigate the depositional environment for the Beothuk and Gandalf Members within the Jeanne d'Arc Formation, testing the validity of the freshwater lacustrine environment proposed by previous workers and establishing the palaeoenvironments of other members in the formation. Facies represented are axial braided fluvial, in-channel cross-stratified sandstones, bar-top immature palaeosols; channel abandonment fills with channel re-activation together with some overbank floodplain mudrocks; transverse fan delta sandstones, conglomerates and primarily river-dominated deltaic mudrocks. No evidence, either sedimentological or organic-geochemical, has been found to corroborate the suggested lacustrine palaeoenvironments. A detailed palaeoenvironmental model is presented.