Changes

==Initial evidence suggests several oil families==

==Initial evidence suggests several oil families==

[[file:oiloil-and-oilsource-rock-correlations_fig8-46.png|thumb|{{figure number|1}}From Hughes et al.<ref name=ch08r20 />); reprinted with permission from Graham and Trotman.]]

[[file:oiloil-and-oilsource-rock-correlations_fig8-46.png|thumb|300px|{{figure number|1}}Data for a set of oils from eight fields in the Norwegian sector of the North Sea. From Hughes et al.<ref name=ch08r20 />); reprinted with permission from Graham and Trotman.]]

The eight fields are in the Central Graben of the North Sea, where the oils occur in Cretaceous and Jurassic reservoirs at 2800–3500 m true vertical depth. The source is presumed to be Upper Jurassic mudstones, based on a correlation of Ekofisk oil to Kimmeridgian [[source rocks]].<ref name=ch08r55>van den Bark, E., Thomas, O., D., 1980, Ekofisk: first of the giant oil fields in western Europe, in Halbouty, M., T., ed., Giant Oil and Gas Fields of the Decade 1968–1978: AAPG Memoir 30, p. 195–224.</ref> Initial examination of bulk geochemical parameters in the 30 oils indicated wide compositional variation, as illustrated in the percent sulfur vs. API gravity plot below. Similar variability exists in the nitrogen concentrations and in the distribution of saturated hydrocarbons, aromatic hydrocarbons, NSO, and asphaltene fractions (not shown). Using these data alone, we might conclude that several source-distinctive families exist.

The eight fields are in the Central Graben of the North Sea, where the oils occur in Cretaceous and Jurassic reservoirs at 2800–3500 m true vertical depth. The source is presumed to be Upper Jurassic mudstones, based on a correlation of Ekofisk oil to Kimmeridgian [[source rocks]].<ref name=ch08r55>van den Bark, E., Thomas, O., D., 1980, Ekofisk: first of the giant oil fields in western Europe, in Halbouty, M., T., ed., Giant Oil and Gas Fields of the Decade 1968–1978: AAPG Memoir 30, p. 195–224.</ref> Initial examination of bulk geochemical parameters in the 30 oils indicated wide compositional variation, as illustrated in the percent sulfur vs. API gravity plot below. Similar variability exists in the nitrogen concentrations and in the distribution of saturated hydrocarbons, aromatic hydrocarbons, NSO, and asphaltene fractions (not shown). Using these data alone, we might conclude that several source-distinctive families exist.