Understanding exploration success and failure in the Cooper and Eromanga Basins, South Australia

Exploration well analysis is a multidisciplinary process aimed at understanding exploration success and failure, whereby data collated and lessons learned inform decision-making going forward. Looking back at the Cooper and Eromanga open-file well and production data provides an historical account of success and failure. Incorporating external non-geological forces such as oil price and political events broadens the scope of learnings beyond the subsurface. Prior to the 1999 expiry of the 30-year-old Cooper and Eromanga Basin Petroleum Exploration Licences 5 and 6, some 386 exploration wells were drilled in South Australia, resulting in 59 oil and 131 gas discoveries. Post-expiry some 415 exploration wells were drilled, yielding an additional 102 oil and 66 gas discoveries. Of the 415 wells, 348 or 84% were drilled by new-to-the-basin operators. While gas success rates remained consistent post-expiry, oil success rates more than doubled and produced oil volumes increased fivefold. Convention dictates that the large fields are discovered early, and this is (still) the case for Cooper Basin gas, but not for Eromanga Basin oil. The discovery of oil in the Western Flank quickly followed the arrival of new operators via the grant of new exploration licences. Despite the basins’ maturity in years, areas remain underexplored in terms of well density and seismic coverage. For example, the Nappamerri Trough, comparable in area to the Western Flank, has no dedicated oil exploration wells. This highlights the importance of regular acreage releases that result in land turnover and competition in realising overlooked potential.