Publication Name: PESA's Eastern Australasian Basin Symposium II
Authors: M. Lisk
Date Published: December 2004
Number of Pages: 30
Reference Type: Book Section
Abstract:The oil charge history of the Penola Trough has been described using fluid inclusion data from a selection of currently gas and water-bearing traps within reservoirs of the Pretty Hill Formation and Sawpit Sandstone. Grains with Oil Inclusions (GOI?) data integrated with information from conventional oil shows, fluid recoveries and geochemical analyses show that oil columns were once present in many traps from the Penola Trough, confirming the effective operation of a liquid petroleum system in this largely gas-prone basin.
Palaeo-oil columns are confidently identified in currently gas-bearing Pretty Hill Formation reservoirs in the
Haselgrove and Redman gas fields, the gas-bearing Eumeralla Formation in Katnook-1 and in water-bearing Pretty Hill Formation reservoir at Zema-1. The data are less conclusive in the gas and oil-bearing Sawpit Sandstone in Wynn-1 and the water-bearing Pretty Hill Formation reservoir at Pyrus-1, but nonetheless are consistent with higher palaeo-oil saturations than would be expected for oil migration pathways. The GOI data define palaeo-oil column heights that are much less than the current-day trap closure, indicating a significant degree ofunderfilling, with respect to oil. Whilst this could be the result of ineffective migration pathways, the relatively gas-prone organic matter typical of the region may point to an inadequate oil-prone source.
At a regional scale the underfilling with oil coupled with highly variable, but generally poor reservoir quality and
significant gas flushing and trap breach risks represent substantial impediments to finding economically viable oil columns elsewhere in the Penola Trough.