1998 EXPLORATION REVIEW—GEOLOGICAL SIGNIFICANCE OF NEW DISCOVERIES AND DEVELOPMENTS

Abstract

A record level of offshore exploration activity was achieved during 1998, despite a significant fall in the oil price. Seventyfour offshore wells were drilled, far exceeding the previous record of 64 wells achieved in 1990. Conversely, only 94 onshore exploration wells were drilled during the year, 25 fewer than in 1997, resulting in a slight reduction in the total exploration wells drilled from 176 in 1997 to 168 in 1998, following what had been a steady increase since 1992. Seismic acquisition in 1998 was also at a record level, twice that recorded in 1997. In contrast, the final quarter of 1998 may reflect the reduced activity forecast by industry, with less exploration wells spudded and almost 10,000 line-km fewer than that shot during the 1997 December quarter.

This increased offshore exploration activity was rewarded with several discoveries and appraisal successes. The Carnarvon Basin was again the most successful area for offshore exploration in 1998, with 35 wells spudded during the year. The discoveries included Gipsy–1, Rose–1, Lee–1, John Brookes–1, Vincent–1, Caribou–1, Legendre South–1 and Mutineer–IB. In addition, significant successful appraisal drilling included two Gorgon wells, Egret–2, Dockrell–2 and Woollybutt–2A ST1.

The Cooper/Eromanga Basin continued to be the focus of onshore exploration in Australia. Fifty-two exploration wells were spudded during the year. Discoveries were heavily weighted toward gas, with only one oil discovery in the basin, Chilla–1. The most significant gas discoveries included Verona–1 and Cabernet–1.

Other important oil and gas discoveries and appraisal successes occurred in the Bonaparte Basin, at Sunset West–1, Sunrise–2 and Evans Shoal–2; in the Browse Basin, at Caspar–IA and two of the Cornea wells; in the Otway Basin, at Killanoola–l/DWl; in the Bass Basin, at White Ibis–1; in the Bowen Basin, at Yandina–2; and in the Surat Basin, at Digger–1 and West Noorindoo–1. Three significant appraisal wells were drilled in Papua New Guinea during 1998: Hides–4 proved continuity of the Hides Field over a distance of 12.6 km, Moran–4X extended the Moran Field to the northwest and Moran- 5X constrained the southeastern extent of the field. There were also significant discoveries in two New Zealand basins and these are covered in greater detail in Plume (1999).

The lower oil price presents a challenge for the industry to maintain these high levels of exploration activity. New technology and better data quality have allowed re- interpretation of previously uneconomic or sub- commercial discoveries to successfully confirm the existence of economic fields. Several of the recent commercial discoveries followed up uncommercial discoveries drilled as much as 30 years earlier and have highlighted the fact that potential still exists in these areas. Improved subsurface imaging through 3D seismic acquisition, high-resolution processing, pre-stack depth migration and advanced time-to-depth conversion together with improved geological understanding has contributed to many of the successful wells drilled in 1998.