EXPLORATION POTENTIAL OF THE TIMOR GAP ZONE OF CO-OPERATION

Abstract

The area covered by the Zone of Co-operation (ZOC) in the eastern Timor Sea represents the last large area of sparsely explored continental shelf around Australia that has obvious potential for significant hydrocarbon accumulations.

Extravagant claims about the assumed exploration potential of the area have been widely published in Australia and Indonesia. The low level of exploration within the Zone does not allow confident prediction of potential at this time. Only five wells and less than 20 000 km of seismic are present in the ZOC. A similar level of exploration had been reached in the Ashmore-Cartier area in the western Timor Sea by 1972. With such a small data base, extrapolation of conclusions drawn from exploration of adjacent areas is fundamental to the present evaluation.

Many technical comparisons can be made between the ZOC and the heavily explored Ashmore-Cartier area. Evaluation of data within the ZOC and extrapolation of important information from other parts of the Timor Sea indicates that all the prerequisites for hydrocarbon accumulations exist within the area.

Jurassic reservoirs sealed by the Cretaceous Bathurst Island Formation provide the primary reservoir objectives in all areas of the ZOC away from the Malita Graben. Oil recovered in wells situated on the Londonderry High has been correlated with mature source rocks of the Jurassic Plover Formation in the Sahul Syncline. This depocentre is concluded to have the capacity of generating both oil and gas for potential accumulations in the southern and western part of the ZOC. The capacity of the Malita Graben to source major volumes of hydrocarbons from potential source rocks of the Flamingo Group is still to be established. Insufficient information is available to reliably predict the distribution of oil and gas in the ZOC.

Play types similar to those seen in the Ashmore-Cartier area are present in the ZOC. Fault-controlled horst plays, typified by the Jabiru Field, are prevalent on the Sahul Platform. Upper Cretaceous sandstone plays dominate the southern part of the ZOC where reservoir objectives in the Jurassic Plover Formation and Flamingo Group are considered to be too deep for economic exploration.

Application of some of the exploration lessons learnt in the western Timor Sea is essential to future activities in the ZOC in order to minimise possible discovery costs.