EXPLORATION IN THE EAST COAST BASIN, NEW ZEALAND

Abstract

Numerous oil and gas seeps have been known in the East Coast Basin of New Zealand since the last century; however, no commercial discovery has been made in the region. Although a number of wells was drilled earlier, the present phase of systematic geological and geophysical exploration was begun by BP Shell Todd Petroleum Development Limited in 1957 and by 1970 had resulted in the drilling of five wells. These wells indicated the presence of thick marine mudstones and siltstones of Cretaceous through Tertiary age, but failed to find any suitable reservoir beds. This, plus complex geological structure and rugged topography are major problems of the region, particularly in the northern portion.

Beaver Exploration subsequently became interested in the area because of the presence of a porous Pliocene coquina limestone (known as the Te Aute Beds) cropping out in the Southern Hawke's Bay region. This unit was considered to be a good drilling target if it occurred adequately sealed in the deeper parts of the basin. In an effort to determine this, Beaver conducted a Seismic Survey with the object of tracing the limestone from outcrop into the subsurface, where hopefully it would be found structurally closed.

The survey was successful and three drill sites were chosen. In two of these the drill penetrated the Te Aute Beds which had excellent porosity and permeability but were water filled; in the third well the reservoir was missing. Correlations between the seismic and the drilling results indicated that the Te Aute Beds are probably mappable at least over some parts of the Southern Hawke's Bay region. The problem now is to find these beds in areas where they are less likely to be water flushed.