Changes

==Oil preservation pattern==

==Oil preservation pattern==

The figure below shows whole oil chromatograms of crude oils from two reservoirs in the East Breaks 160-161 field. Oil 1 is from the HB-2 reservoir; oil 2 is from the ''Glob alt'' GA-3 reservoir. Both are interpreted as biodegraded and mixed with fresh oil, suggesting multiple pulses of accumulation.

[[file:sedimentary-basin-analysis_fig4-52.png|thumb|{{figure number|1}}After Dow et al.<ref name=ch04r29 />). Copyright: Gulf Coast SEPM.]]

[[file:sedimentary-basin-analysis_fig4-51.png|thumb|{{figure number|4-51}}. Copyright: Dow et al. (1990); courtesy Gulf Coast SEPM.]]

The oil preservation pattern is attributed to the history of generation, expulsion, secondary migration, and accumulation.<ref name=ch04r29 /> The better preserved C₁₀ to C₃₀ alkanes in the GA-3 oil occur where the reservoir temperature is about [[temperature::160&deg;F]] ([[temperature::71&deg;C]]). The more poorly preserved alkanes in the HB-2 oil occur where the reservoir temperature is about [[temperature::130&deg;F]] ([[:file:sedimentary-basin-analysis_fig4-52.png|Figure 1]]). Microbial activity responsible for biodegradation occurs at temperatures below [[temperature::140&deg;F]] ([[temperature::60&deg;C]]). The earliest migration fluids would have been the least mature and potentially most biodegraded due to the shallow level of accumulation. With increasing burial of the [[source rock]], more mature oil and condensate would have been generated and better preserved in deeper reservoirs below the depth of microbial activity. These observations suggest sequential expulsion and migration of progressively more mature products as the source(s) passed through the oil window. Alternative interpretations are offered in Dow et al.<ref name=ch04r29 />).

[[file:sedimentary-basin-analysis_fig4-52.png|thumb|{{figure number|4-52}}After Dow et al.<ref name=ch04r29 />). Copyright: Gulf Coast SEPM.]]

[[file:sedimentary-basin-analysis_fig4-51.png|thumb|{{figure number|2}}. Copyright: Dow et al. (1990); courtesy Gulf Coast SEPM.]]

 

==See also==

==See also==