Source Potential Of The Early Cretaceous Laira Formation, Western Otway Basin.
Honours Degree, 1992
University of Adelaide
Petroleum exploration within the Otway Basin to date has focussed on potential reservoirs of the Early Cretaceous Eumeralla Formation, Pretty Hill, Katnook and Windermere Sandstones. Recent drilling success within the Penola Trough and renewed interest in the offshore Chama Terrace area have stimulated investigations into the hydrocarbon generation of nearby source intervals, particularly the Laira Formation.
In this study 14 wells from the western Otway Basin, located in the Robe, Penola and St Clair Troughs, Chama Terrace and Crayfish Platform, were studied for TOC, Rock-Eval pyrolysis and vitrinite reflectance properties. Source richness, quality and maturity were determined and the generative potential, migration influence, kerogen type and palaeoenvironmetal aspects from these wells were examined. Source rock data were entered on burial history software with two additional wells sampled and analysed to complete information for the database. A section of Laira Formation core was logged and checked for the presence of fluorescence.
Maturity profiles from vitrinite reflectance data show good source rock potential within the Laira and Eumeralla Formations. The hydrocarbon window threshold (VR> 0.6%) is in many areas either reached or exceeded. Organic richness, generative potential and maturity is particularly encouraging within the Penola Trough, and Chama Terrace. The algal species present are consistent with organic richness and hydrocarbon potential.
Burial history analysis indicates that the Laira Formation entered the oil window at the end of the Late Cretaceous by which time suitable seals and structural traps were in place. Organic richness levels were found to be higher at the basin margins and this has implications for further studies involving mapping wireline log correlations with algal blooms within the Laira Formation across the basin.
These encouraging signs dictate that the Laira Formation should be an important explorational focus in the Otway Basin.