Analysis Of Cainozoic Deformation In The Penola Trough Of The Western Otway Basin.
Honours Degree, 1996
University of Adelaide
The aim of the study was to determine the timing and orientation of faulting in the Cainozoic rocks in the Penola Trough of the western Otway Basin. Three main phases of deformation have been generally recognised in the Otway Basin. The first two were extensional, related to the separation of Australia and Antarctica during the Cretaceous. The third, during the Tertiary, was compressional. The effect of this later phase on the hydrocarbon potential of the trough is of particular interest, as it may have breached the seal of some traps, and allowed carbon dioxide dilution in others.
To study these deformations, post-1985 2D seismic reflection data were interpreted over an area of 260km in the Penola Trough which included the Katnook and Haselgrove Gas Fields and the Laira and Zema wells. The interpretation was conducted using Geoquest software. Five horizons were interpreted, spanning the Late Cretaceous to Middle Eocene.
The study suggests that Late Cretaceous and Tertiary faulting is controlled in part by pre-existing Late Jurassic and Early Cretaceous faults and structural trends. The Late Cretaceous extensional regime was orientated N-S in the study area. It is likely that a NE-SW extensional regime, related to an increase in the rate of sea-floor spreading, became active in the Tertiary. A NW-SE compressional regime has had an effect upon the overall structure in the trough since the Eocene.
The commercial Katnook and Haselgrove Gas Fields are situated beneath a significant, E-W-trending, Late Cretaceous-Tertiary rollover anticline, which has a level of structural integrity absent from other prospects. The Ladbroke Grove accumulation, which contains a significant proportion of carbon dioxide, is situated in an area of Late Cretaceous and Tertiary antithetic faulting. The dry Laira and Zema wells are located in a zone of persistent NW-SE faults, which, as a result of extension and compression, were active throughout the Tertiary.