DEVELOPMENT OF THE TARANAKI BASIN AND COMPARISONS WITH THE GIPPSLAND BASIN: IMPLICATIONS FOR DEEPWATER EXPLORATION

Abstract

Exploration of the Taranaki Basin entered a new phase in 2001 with Astrolabe, a 6,200 km high-quality 2D seismic survey acquired by TGS-NOPEC that has outlined a large depocentre containing up to 10 km of sedimentary fill. This new data has extended the previously-known Taranaki Basin into deeper water beyond the shelf edge. Subsequently, the New Zealand Government released an area of 42,000 km2 for competitive bidding to close in September 2003.

Sequence analysis shows that a major deltaic system, comparable to the Golden Beach and Emperor subgroups of the Gippsland Basin, built into a restricted seaway during the Late Cretaceous and culminated with deposition of the Rakopi Formation coal measure succession. The Rakopi Formation covers an area of at least 15,000 km2 of the study area and was followed by a transgression that continued until the Miocene.

Minor Eocene folding created broad structures with potential to trap large volumes of petroleum. Other potential trapping structures include drape across Cretaceous rift blocks and turbidite mounds of Miocene age.

Modelling shows that much of the Early Cretaceous delta is thermally mature and should be expelling petroleum today. Reservoir facies are present at many horizons, but the primary target is expected to be sandstones of the Rakopi Formation coal measures.

Many analogies can be drawn between the Taranaki and Gippsland basins. The deepwater Taranaki basin appears to be equivalent, however, to the offshore, oilprone part of Gippsland while the nearshore Taranaki and Great South basins together form an analogy for the more gas-prone nearshore part of Gippsland.