The Otway Basin is one of the more actively explored basins along the southern margin of mainland Australia, yet the onshore western portion of the Otway Basin remains relatively underexplored.
Eight commercial gas fields have been discovered in the western Otway Basin. These fields to date have produced approximately 70 Bcf of gas. The Katnook complex, comprising the Katnook, Haselgrove, Haselgrove South, and Redman gas fields produced gas and condensate from the Katnook processing facilities between 1991 and 2011.
Oil discoveries in the western Otway Basin include Killanoola-1 (1998), Jacaranda Ridge-1 (1999), Killanoola South East-1 (2011) and Jacaranda Ridge-2 (2011). Oil flow rates from these discoveries have ranged from 25 to over 400 barrels of oil per day (bopd) on test.
The western region of the Otway Basin in South Australia has recently seen an upsurge in exploration. This is being driven by forecast domestic gas supply shortages for the east of coast of Australia and the revised 2017 South Australia State Energy Plan, which through the Plan for Accelerating Exploration (PACE) initiative, is funding the exploration and production of new gas supply into the SA market as a means of securing energy supply for the State.
The PEL 155 Rawson-Vintage JV was awarded $4.95 million in December 2017 from the PACE Gas Grant Program to drill the Nangwarry prospect, a proven top Pretty Hill reservoir target, analogous to the nearby Katnook, Ladbroke Grove and Haselgrove gas fields.
Conventional Exploration: The most important established conventional reservoirs in the western Otway Basin are within the Pretty Hill Formation, which contains the Katnook complex gas fields. The formation comprises the Pretty Hill and Sawpit sandstones as well as other undifferentiated sandstones. The Windmere Sandstone and the Waarre Sandstones are also important reservoirs, particularly in the eastern Otway Basin, but also have significant potential in the western Otway Basin.
Unconventional Exploration: The primary targets for shale exploration within the western Otway Basin are the thick non-marine Sawpit and Casterton shales. They have good shale oil and gas potential in the deeper parts of the basin, including the Robe, Penola, Rivoli and St Clair troughs. There is also tight gas potential in the Pretty Hill Formation.