Using Biodegradation to Date Hydrocarbon Entry Into Reservoirs: Examples From the Cooper/Eromanga Basin, Australia

Abstract

This study identifies common biodegradation of Cooper/Eromanga Basin (CEB) oils and condensates from changes to the n-alkane and isoprenoid whole oil gas chromatograph (WOGC) hydrocarbon profiles, which because of their generally mild degradation has not been previously identified or has been ignored. Three hydrocarbon families are recognised on the basis of their level of biodegradation (biodegraded, biodegraded with fresh charge and essentially non biodegraded). A review of biodegradation processes suggests that these families can be related to different reservoir entry temperatures and a scale relating biodegradation to reservoir entry temperature is proposed. The WOGC biodegradation profiles from the CEB oil Families allow a better understanding of reservoir fill history and provide a guide to the approximate temperature range during liquid hydrocarbon reservoir fill in the CEB. Combining the hydrocarbon fill temperature data provided by biodegradation with maturity and temperature data from the basin can help constrain the hydrocarbon charge history of the CEB, and the principles presented can be applied to other basins. The development of a better understanding of reservoir fill timing can then be combined with conventional basin modelling to provide constraints on hydrocarbon expulsion timing.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015