Source Rock Characterisation in the Gippsland Basin: An Analysis of Rock Eval Pyrolysis Data From 15 Wells in the Central Deep
Moriarty, Steven George
Geoscience Honours Degree, 2010
University of Adelaide
The Department of Primary Industries (Victoria) holds a large database of Rock-Eval pyrolysis results taken from the Gippsland Basin. Most of the interpretation of these results that is in the public domain is broad in scope and does not indicate whether the samples have been checked for oil contamination.
This study examines the data from fifteen wells in the Central Deep of the Gippsland Basin. This study characterises each sample in terms of hydrocarbon generating potential, hydrocarbon type produced, kerogen type and degree of thermal maturity. This study found that the most promising source rock zone was in the eastern part of the Central Deep.
Results were checked against some of the main factors which can skew interpretations such as oil contamination. This study found that approximately 25-50% of samples showed indications of oil contamination. This suggests that if this check is not made then significant overestimations will occur when using Rock Eval data to either identify potential or contribute to source rock volumetric calculations.
The spore-pollen zones intersected by the well were also characterised in terms of hydrocarbon potential, type and thermal maturity. T. lilliei and F. longus were found to be the zones hosting the most excellent hydrocarbon potential with little difference between them in trends and spread. The most significant difference was that indicators of oil contamination were 80% more likely in T. lilliei than F. longus. This suggests that oil migration pathways favour deeper depths in the eastern part of the Central Deep.
Work produced in this study now allows for more direct comparisons with Rock Eval studies from the Otway and Bass Basins. An element of the petroleum system is now available for input into the evolving Gippsland Basin 3 D model. Further, templates have now been developed that can be used to efficiently characterise the remaining Rock Eval pyrolysis data of the Gippsland Basin
This study shows that Rock-Eval pyrolysis is most successful at determining hydrocarbon potential and type and thermal maturity. However the determining of kerogen type using Rock-Eval pyrolysis is inadequate and misleading. Results from the Hydrogen and Oxygen Indices reflect the mix of kerogen and not the kerogen type and other tests such as pyrolysis gas chromatography are needed to identify kerogen types from kerogen blends.