Abstract

Several hydrocarbon discoveries have been made recently within the Mesozoic syn-rift/drift sediments of the Birds' Head of Irian Jaya (Figure 1). Notably, the Roabiba-1 well (Figure 3) tested 23.6MMCFGPD from Early to Mid-Jurassic sands. This well represents the most significant discovery of Mesozoic hydrocarbon exploration in Irian Jaya to date.

This relatively stable portion of the Australoid (see Figure 2) continental margin has a demonstrably different geological history from other sections of this emerging oil and gas province. The West Irian Micro-continent (WIMC) and its structural controls are redefined.

The previous Mesozoic stratigraphic nomenclature (Figure 4) is revised, in accordance with the individuality of the WIMC's stratigraphy and a new scheme is presented (Figure 6). Recently published high-resolution biostratigraphy, combined with electro facies and sequence stratigraphy, enables an updated dynamic stratigraphic picture of the Mesozoic of the WIMC to emerge.

A series of major unconformities are recognised within the Jurassic, bounding individually recognisable "Polysequences". The latter is a new term introduced to describe the rock packages recorded from 12 study wells in the area (Figure 5).

The Mesozoic sediments discussed in this paper contain source, reservoir and seal rocks, and therefore constitute the principal attributes of the area's Petroleum System.

Compressional tectonic overprinting during the Tertiaryhas significantly complicated our understanding of hydrocarbon exploration in the WIMC. Guidelines are provided for further exploration of the Mesozoic of the area, including petroleum systems' attributes, regional analogues and new play concepts.