Paleozoic and Mesozoic Petroleum Systems in the Timor and Arafura Seas, Eastern Indonesia

Abstract

Abstract The Timor and Arafura Seas extend over a substantial portion of the northern Australian continental margin. Exploration commenced in Australian waters in 1971, resulting in the discovery of the Greater Sunrise discovery and Evans Shoals gas accumulations, while the first significant discovery in Indonesian waters was the Abadi-1 gas discovery in 2000. The subject of this paper is the interpretation of a new seismic survey, the Matahari MC2D seismic survey, which links the Australian gas discoveries of Greater Sunrise and Evans Shoal with the Abadi accumulation and extends into open acreage within Indonesian waters to the north and east of Abadi. Abadi and earlier Australian discoveries including Greater Sunrise, Evans Shoal and Lynedoch lie on the Sahul Platform, a peri-rift basement high, separated from the Australian craton by a failed Jurassic to Early Cretaceous rift. This rift is identified as the Malita Graben which extends east into the Calder Graben, providing key depocentres and an effective charge kitchen from mature Early to Middle Jurassic Plover Formation source rocks (mixed Type 2 to Type 3 kerogens), which are regarded as the origin of these gas-condensate accumulations. The latter are reservoired in Plover Formation paralic and shelfal sandstones. To the north and northeast of the Abadi discovery, in open acreage, new seismic interpretation has revealed the existence of hitherto untested Paleozoic basins, especially on the southeastern margin of the Tanimbar Trough. Based on analogues with the Bonaparte Basin and Goulburn Graben of northern Australia, these Paleozoic Basins could contain high quality and mature oil-prone source rocks of Cambrian, Devonian and Carboniferous age. In addition, deeply buried Early Cretaceous source rocks may exist along the flanks of the Tanimbar Trough, with similar attributes to excellent quality Echuca Shoals Formation source rocks in the northern Bonaparte Basin, which charged oil discoveries such as the Elang Field in the East Timor Joint Development Area.