oa PETROLEUM SYSTEM OF DUVA OIL AND GAS FIELD IN NORTHERN NORTH SEA, NORWAY

The Duva oil and gas field is located at ca. 5 km northeast of the Gjøa field in the Northern North Sea. The reservoir contains oil and gas in a turbiditic sandstone of the Early Cretaceous Agat formation. Highly waxy oils were collected, and its geochemical characteristics were investigated by GC and GC-MS analyses. We performed position-specific isotope analysis (PSIA) on a gas sample from the Duva field to identify the effective source rock of the gas. 2-dimensional basin modelling was conducted to understand the petroleum system including complex migration and accumulation processes of the Duva field. The abnormally waxy oil in the Duva field possibly formed by the large input of terrestrial organic matter into the Upper Jurassic marine source rocks and/or the evaporative migration fractionation based on the biomarkers and carbon isotopic compositions. Intramolecular carbon isotopic compositions of propane in the gas sample suggested that the gas in the Duva field was generated from coals in the Middle Jurassic or older. A late charge of the gas derived from the coaly source rock into an initial oil accumulation may have caused the evaporative fractionation resulting in the formation of the waxy oil in the Duva field.