STRATIGRAPHY AND PETROLEUM POTENTIAL OF THE ONSHORE CARPENTARIA BASIN, QUEENSLAND

Abstract

Over the past four years Comalco in joint venture with Bridge Oil have undertaken extensive exploration within the Carpentaria Basin. Over 3000 km of multifold reflection seismic data has been acquired and four petroleum exploration wells were drilled. In addition, the Queensland Department of Mines (GSQ) has drilled four cored full-section stratigraphic wells in the deeper parts of the basin.

Analysis of the work to date indicates that the basin is not as structurally simple as first thought. Four sub- basins are recognised based on the composition and timing of Mesozoic sedimentary fill. These are the Weipa, Western Gulf, Staaten and Boomarra sub-basins. The Boomarra Sub-basin contains a Middle Triassic red-bed sequence which is 250 m thick in drill hole GSQ Dobbyn- 1. Thick, Middle Jurassic-Lower Cretaceous, basal fluvial and marine sandstone sequences are restricted to the Weipa and Staaten sub-basins, where they are confined principally to the palaeotopographic valleys. The Western Gulf Sub-basin is believed to contain minimal basal Mesozoic sandstone.

Although sedimentary depositional environments exhibit widespread continuity throughout the Carpentaria Basin, variations in lithology and provenance as well as diachronism can be demonstrated between the various sub-basins. Most notably the late Neocomian marine transgression began earlier at Weipa than in the southern sub-basins. A basin-wide stratigraphy has been developed from deep drill hole correlations and mapping of outcrop sections around the margin of the basin in the Olive River, Gregory Range and Melish Park areas thus enabling the petroleum reservoir character of the basin to be determined.