Neodymium isotope stratigraphy of Gullfaks Oilfield

Abstract

Samples collected from over 500 m of stratigraphy from 4 wells, which represent the complete reservoir interval of Gullfaks Oilfield, have been analysed for Sm-Nd isotopic composition. The data are used to examine variations in the provenance of the various reservoir units, to assess the utility of the Sm-Nd method as a correlation tool and to illuminate paleaogeography. Provenance ages for the Rhaetian to Lower Jurassic Statfjord Formation vary between 2400 Ma and 1500 Ma with the higher ages tending to be concentrated in the lower section. The groupings of provenance ages between 1850 and 2400 Ma reflects an ancient source terrain which, it is postulated, lay in the Archaean shield to the west of Scotland. The Lower Jurassic Dunlin Group has fairly uniform provenance ages in the range 1500 to 1750 Ma and shows a slight tendency towards higher ages upwards through the section. Provenance ages in this range are not diagnostic and could represent several source areas in the hinterland of the northern North Sea. Correlation of Nd isotope characteristics can be observed at the within-field and between-field scales. It is concluded that Sm-Nd provenance ages have potential as a new correlation tool. -from Author