DISCOVERY AND EXPLOITATION OF NEW OILFIELDS IN THE COOPER-EROMANGA BASINS

Abstract

Since 1975 the level of petroleum exploration in the Cooper-Eromanga basins has undergone an unprecedented expansion due to the discovery and development of an increasing number of oil reservoirs, largely in the Eromanga Basin sequence. The commercial incentive provided by the Commonwealth Government's Import Parity Pricing and excise arrangements have been instrumental in the lead up to and continuation of this series of discoveries.Three types of oil discovery in the Eromanga Basin sequence are evident; firstly, shallow pools above Cooper Basin gas fields; secondly, separate single-field discoveries in areas of limited exploration; and thirdly, as multifield discoveries along major structural trends. Exploitation of the Eromanga Basin oil discoveries has been made possible by a combination of rapid appraisal and development drilling and early commencement of production.The initial Eromanga Basin oil discoveries overlie major Cooper Basin gas fields and were located during appraisal and development drilling of deeper Cooper Basin gas reservoirs. Wildcat and appraisal drilling on Eromanga Basin prospects, such as Wancoocha and Narcoonowie, has upgraded the prospectivity of the Eromanga Basin sequence in the southern Cooper Basin—an area where earlier exploration for Cooper Basin gas was unsuccessful. Significant oil discoveries in Bodalla South 1 and Tintaburra 1, in the Queensland sector of the Eromanga Basin, have extended the range of exploration success and generated considerable interest in lesser known parts of the Eromanga Basin.Three successive phases of Cooper-Eromanga exploration have led to the present high level of success. Early exploration, before 1969, led to the initial discovery and development of Cooper Basin gas fields and was largely supported by the Petroleum Search Subsidy Acts (19571974). The results of the second phase, between 1970 and 1975, provided little encouragement to operators to extend exploration beyond the limits of the then known gas accumulations. In the decade since 1975, the oil potential of the Eromanga and parts of the Cooper Basin sequences has become a major factor in the exploration and development activity of the region. Since 1975, the favourable commercial conditions prevailing under the Import Parity Pricing scheme and the concessional crude oil excise arrangments for production from 'newly discovered' oilfields provided a significant incentive for development and exploitation of the post-1975 oil discoveries.