TIRRAWARRA AND MOORARI ENHANCED OIL RECOVERY PROJECTS—‘GETTING MORE OIL OUT FROM DOWN UNDER’

Abstract

The Tirrawarra and Moorari oilfields are located in the South Australian portion of the Cooper Basin. Production to date in the fields has been maintained primarily by infill drilling, with individual wells showing substantial declines in productivity. In the absence of an active aquifer, some form of pressure maintenance was required to arrest this productivity decline and increase recovery. The miscibility characteristics of the reservoir oil, the low rock permeability, and the availability of miscible injection gases made miscible gas flooding the preferred improved recovery process.

In 1984 pilot gas injection floods were initiated in both the Tirrawarra and Moorari fields to test the effectiveness of pressure maintenance and the miscible process in the Tirrawarra Sandstone. Injection was initiated using the Tirrawarra Field non-associated Patchawarra Formation separator gas to defer the high facility costs associated with alternative injection gases.

The results of the pilot injection programs have been most promising. Production has improved in most offset producing wells with no sign of early injection gas breakthrough. In 1986, expansion of the Tirrawarra pilot will complete development of a major portion of the Tirrawarra Field on inverted seven spot injection patterns. Ultimate development of the field for full scale injection may involve infill drilling and well conversions resulting in skewed five spot patterns. Three alternative injection gases are being considered: Patchawarra separator gas, carbon dioxide, and ethane, each of which show favourable miscibility characteristics with the Tirrawarra oil. The incremental oil recovery expected from the full development is 23 million stock tank barrels oil.