Abstract

This chapter dissects the petroleum systems of the South Viking Graben, and, in as far as data allow, starts with a discussion of the oils and gas-condensates in terms of their expulsion maturity spectra based on bulk, molecular, and isotopic properties of four molecular weight fractions (gas, gasoline, mid, and heavy) of the major accumulations. The Upper Jurassic source rocks are characterized in terms of the amount (total organic carbon), kerogen type (kinetics), and yield properties, the latter in units of million barrels of oil per square kilometers of mature source rock. Depth trends for temperature and maturity parameters are used, together with 1-D modeling, to derive an asymmetric basin-wide geothermal model based on variation of heat flow. This is generalized using 3-D modeling of seismic surfaces to define the source rock kitchens, the expelled volumes, the migration paths, and the hydrocarbon charges to major groups of traps. Charge volumes predicted by modeling are compared with reported in-place petroleum. The Brae member fan sands of the U.K. margin are the “closed” (close-coupled) end-member example of the generally “open” petroleum systems of the North Sea. While the Upper Jurassic Kimmeridge Clay–Draupne Formation source rocks explain the observed volumes and properties of oils, uncertainty remains on the properties and origin(s) of gas(es) required to explain the observed gas/oil ratios, gas compositions, and isotope profiles.