RIVOLI-1 GAS DISCOVERY — EXMOUTH SUB-BASIN, WESTERN AUSTRALIA

Abstract

Offshore exploration in the Exmouth Gulf commenced with seismic surveys during the early 1960s and resulted in the first well Bundegi-1 being drilled in 1978. This well, situated on the Rivoli-Bundegi Trend, encountered an interpreted residual hydrocarbon zone in the Birdrong Sandstone, an 18 m untested hydrocarbon zone in the Learmonth Formation, and tight, possibly gas bearing sandstones in the Mungaroo Formation.Modern shallow-water marine seismic data acquired by the EP 325 Joint Venture during surveys in 1987 and 1988 allowed accurate mapping of the basal Cretaceous section and the distribution of the Birdrong Sandstone. Complex structuring in the Jurassic and Triassic section was also resolved with the modern data.The Rivoli gas discovery, approximately 4.5 km northeast of Bundegi-1, was made in August 1989, with the intersection of a 10.5 m hydrocarbon column consisting mainly of gas but with a very thin oil leg (0.2 m). The Birdrong Sandstone reservoir comprises 10 m of fluvial sandstones overlain by 7 m of marginal marine sandstones and provides an important calibration point for depositional environments in this unit. The Rivoli gas pool occurs in a simple, downthrown anticline sealed by Winning Group shales. Geochemical analysis of oil extracted from core, suggests an earlier charge of 'Rough Range-type' oil, possibly generated from pre-Jurassic source rocks.Several prospects and a variety of play types are recognised and considerable exploration potential remains to be tested along the Rivoli-Bundegi Trend.