Oil Maturity, Families and Oil-Source Rock Correlations in the Danish North Sea Based On Biomarker Studies

Four main oil families and four subtypes have been defined in the Danish part of the North Sea based on multivariate analysis of data from 99 oil samples i.e. 43 sterane and hopanes biomarker ratios. The major oil families, and their subtypes, are correlated to the sequence stratigraphical framework established for the Jurassic. The compositionally resolved oil families turn out to have distinct geographical distributions suggesting that several kitchen areas contributed to the accumulated oils. 90% of the total known oil resource of 480 m.m3 oil was sourced by only two marine Upper Jurassic organofacies (subtypes 1A, 1D) while 50% of the known gas resource of 230 bn.Nm3 gas is related to a Middle-Upper Jurassic marine (terrestrially influenced) organofacies (oil family 2). A comprehensive sediment extract data set is used to calibrate 16 maturity-sensitive biomarker ratios to the sample depth (1000–4800 m) which provides regional oil maturity maps for the reservoired oils. The oil maturity increase from southern part of the North Sea and to the north and northwest, mainly reflecting the depth and thickness of the Upper Jurassic sequence. The identified key biomarkers and derived analytics thus form important calibration data or basin modelling and as tool for exploration.