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Line 17: + + + − The figure shows data for a set of oils from eight fields in the Norwegian sector of the North Sea. The left figure is concentration of sulfur in oil plotted against API gravity, showing a trend of decreasing sulfur content with increasing gravity. Note that the Ekofisk and Eldfisk field oils show only small ranges in sulfur content and gravity. The right figure shows ααα-20S/(20S+20R) ratios plotted for each of the eight fields. This wide range extends from a decidedly marginally mature oil (in Hod field) to oils in which this parameter has reached equilibrium.+ − − [[file:oiloil-and-oilsource-rock-correlations_fig8-46.png|thumb|{{figure number|8-46}}From Hughes et al.<ref name=ch08r20 />); reprinted with permission from Graham and Trotman.]]
Oil correlation case history: Norwegian sector, North Sea (view source)
Revision as of 21:16, 13 February 2014
, 21:16, 13 February 2014→Initial evidence suggests several oil families
==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.]]
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.
[[:file:oiloil-and-oilsource-rock-correlations_fig8-46.png|Figure 1]] shows data for a set of oils from eight fields in the Norwegian sector of the North Sea. The left figure is concentration of sulfur in oil plotted against API gravity, showing a trend of decreasing sulfur content with increasing gravity. Note that the Ekofisk and Eldfisk field oils show only small ranges in sulfur content and gravity. The right figure shows ααα-20S/(20S+20R) ratios plotted for each of the eight fields. This wide range extends from a decidedly marginally mature oil (in Hod field) to oils in which this parameter has reached equilibrium.
==Further evidence shows oils are similar==
==Further evidence shows oils are similar==