THE DRUMMOND BASIN: LOW- COST EXPLORATION IN A HIGH- RISK AREA

Abstract

Shell was attracted to the potential of the northern Drummond Basin by large anticlinal structures, already evident from patchy outcrop and limited seismic data. An exploration strategy was developed to assess, in the most cost effective manner, the principal uncertainties associated with the play over a two- year period.

Initially a regional seismic program of 270 km was acquired. This provided sub- surface control essential for the subsequent corehole drilling program, and an outline of the regional structural framework. The drilling program of six 500 m coreholes, each overlapping slightly in terms of stratigraphy, was sited along one of Shell's seismic lines. A total of 2569 m of core was recovered, providing 2083 m of true stratigraphic coverage, thus facilitating detailed stratigraphic, reservoir, seal and geochemical studies.

The new seismic data have led to a revision of the tectonic model of the basin, which, despite a complex uplift history, remains at maturity levels compatible with hydrocarbon occurrence. Core studies have highlighted the major exploration risks as relatively poor reservoir quality, limited source- rock development and thin intra- formational seals.

Despite the disappointing outcome in terms of hydrocarbon prospectivity, significant advances have been made in the understanding of the geology of central Queensland, particularly relating to tectonics and burial history, which may be of regional significance.