McKee Mangahewa

The McKee oil field was discovered in 1980 by state-owned Petrocorp Exploration Ltd. Over the next four years a number of accumulations in adjoining fault blocks were discovered, Pouri, Pukemai, Tuhua and ToeToe. It soon became apparent that these compartments formed part of the overall McKee field.

The geologically complex McKee structure is a major thrust fault, with a north-east direction. The hydrocarbon accumulation occupies a steep south-easterly dipping (up to 60o) sandstone reservoir sequence truncated against a deep thrust fault 2000-2400m below sea level. The field is cut by a number of lesser reverse and normal faults. 

The oil was located in an oil rim, located on the flank of the structure, with a natural gas cap overlying this rim in the crestal part of the field. Due to compartmentalisation, the original fluid contacts varied from block to block.

The Mangahewa structure was recognised as a prospect in the early days of exploration in New Zealand, with the exploration well Mangahewa-01 drilled in 1961 by the Shell-BP-Todd Joint Venture. The well found traces of gas in the Kapuni Group (ca. 3500-3600m below sea level), and on testing produced water with a small, sub-economic amount of gas (1-2 mmscf/d). The well was subsequently plugged and abandoned.

Further exploration occurred in the mid-1990s, with Fletcher Challenge Energy drilling the Mangahewa-02 natural gas discovery well (1996/97) in this low relief anticline situated to the west of the McKee overthrust. This was followed by short and long term production testing of this well (1997), acquisition of 3D seismic (1997), and testing of the northern flank of the Mangahewa structure with Ohanga-2 well (1998).