SHELL'S OFFSHORE VENTURE, IN SOUTH AUSTRALIA

Abstract

Offshore South Australia permit O.E.L. 38 was granted to Shell Development (Aust.) Pty. Ltd. on 1st January 1966. An aeromagnetic survey of 10,300 km, three seismic surveys totalling 10,300 km and five man months of coastal field work were carried out before the permit was reissued at the end of 1968 as three separate permits SA-5, SA-6 and SA-7 under the newly enacted joint offshore legislation. At that time Shell also secured two adjoining deep Water permits SA-10 and SA-11.

In the period 1969-70 two seismic surveys totalling some 11,750 km were shot. Given geophysical results, a six well drilling programme was planned to commence early 1972. Two dry wells, Platypus-1 and Echidna-1 were drilled in early 1972 in SA-6 and SA-7, with Platypus-1 providing some geological encouragement.

Several more prospects were found in SA-6 and SA-7 by the 1973 and 1974 seismic surveys, but these were so small that further work could not be economically justified. SA-6 and SA-7 were surrendered in late 1975 without further wells being drilled. Potoroo-1 was drilled in early 1975 in SA-5. It severely downgraded the prospectivity of that permit, leading to early relinquishment later in 1975, but provided vital geological information relevant to permits SA-10 and SA-11 where drilling was due to commence in 1978. A detail seismic survey in the latter two permits was shot in 1976. Prior to 1976, the main incentive for exploration of the deepwater play had been the apparent presence of a very large anticlinal trend in the central part of SA-10. Interpretation of the 1976 survey showed this trend to be non-prospective, and as a result SA-10 and SA-11 were relinquished in April, 1977. This ended a venture in which three wells were drilled and 24,546 km of seismic data recorded for a total expenditure of $15,837,000.