Detection of petroleum heterogeneity in Eldfisk and satellite fields using thermal extraction, pyrolysis-GC, GC-MS and isotope techniques

Eldfisk Field is one of several oil-producing chalk fields of the North Sea. Analysis was performed on core samples from 11 wells from the Palaeocene/Cretaceous Chalk reservoir. Analyses performed on cores included various pyrolysis techniques. Conventional GC-MS, was performed on 27 oils from the 2/7 block. Stable carbon isotope analysis was performed on bulk and n-alkane fractions of the oils. Pyrolysis data could be used to detect the main producing section of the reservoir and show that there appear to be sections of the reservoir rich in waxes. Biomarker and pyrolysis data indicate that there are differences in maturity of the petroleum of Eldfisk Alpha and Bravo structures and that there are lateral and vertical variations in composition within each structure. Based on both biomarker and isotopic data, there is evidence for at least two phases of reservoir filling.