Areas V07-1, V07-2 and V07-3
Gippsland Basin
Release Area Geology
Area V07-1
The majority of Area V07-1 is located on the Northern Platform (Figure 2). According to seismic interpretations, the main play type is the stratigraphic pinch-out of the Latrobe Group (Figures 6, 7 and 8). North of the Lake Wellington Fault System, the Palaeozoic basement is at shallow depths and is overlain by a thin veneer of Early Cretaceous (Strzelecki Group) and the Paleocene (Kingfish Formation) sediments. The northernmost limit of the Latrobe Group and the ultimate pinch-out is interpreted to lie immediately north of Northright 1. Reservoir quality sandstones are known to exist on the platform; hydrocarbon charge would be derived from either mature Strzelecki Group source rocks on the Northern Platform or mature Latrobe Group source rocks along, or south of, the Rosedale Fault System.
The southwestern corner of this release area lies between the Rosedale and Lake Wellington fault systems and is part of the top-Latrobe play fairway (Figure 6), where top-Latrobe gas accumulations appear to have been sourced from the Strzelecki Group. High resolution seismic mapping can trace the continuation of these half-graben laterally and should delineate appropriate hanging wall inversion structures (similar to Sole) that may have received and preserved a gas-charge from the Strzelecki source system.
Area V07-2
Area V07-2 is dominated by shallow basement across its entire northern portion, and hence the only play that has been interpreted to exist within Area V07-2 is the Latrobe pinch-out play-type (Figure 6). On seismic data, the undulating basement surface is readily mappable (Figure 9), and hence multiple pinch-out features may be developed. The currently available data do not permit any comment about the presence and properties of the potential reservoir units. Recent work on the Southern Platform (Bernecker et al, 2006) highlighted the presence of an Oligocene sandstone unit above the Latrobe Unconformity. If equivalent sandstones exist on the Northern Platform, then hydrocarbon charge would potentially come from the mature Strzelecki Group source rocks in the Northern Graben (Figure 9).
Area V07-3
From a petroleum geological perspective, Area V07-3 is the most diverse of the 2007 Gippsland release areas as it covers the main four play-fairways (Figure 6) that have been mapped on the basis of extensive well control further west. Regional seismic lines across the area (Figures 8 and 10) outline the distribution of basement highs that are flanked by sediment-filled graben. Several basin-wide unconformities can be recognised and, if put into the regional context, allow the correlation between various basin-fill sequences.
Shallow basement in the northern part of Area V07-3 equates to the Latrobe pinch-out play fairway, highlighted on Figure 6. The nature of the top-Latrobe play fairway is less clear in the area, due to very limited seismic data, but would have to rely on the presence of a Strzelecki-Emperor filled rotated half graben, which are seen on Figures 8 and 10.
The Golden Beach-Emperor play fairway (Figure 6) is only a valid target in the western segment of the area, because submarine erosion associated with the development of the Bass Canyon removed parts of the deeper Latrobe Group. The easternmost part of Area V07-3 is crossed by the East Gippsland Rise, a basement high that represents the eastern boundary of the Gippsland Basin.
The intra-Latrobe play fairway is only present in the southwestern corner of Area V07-3. Access to the intra-Latrobe petroleum system (Volador Formation source and Golden Beach/intra-Volador reservoirs, intra-Volador seals) appears viable. However, lateral facies variations could possibly mean that the entire Volador section further east is dominantly marine in nature. This may translate to enhanced reservoir properties, while shaly sealing units may be less frequently developed. Moreover, water depths in this segment vary between 1,000 and 2,000 m, significantly increasing the potential drilling costs.