Wilson HTM says in its report that the greater Maari area, incorporating the Maari and Manaia prospects, has an updip potential that could increase the field's current reserves of 50 million barrels to about 87MMbbl.

The Australian investment group believes the upside potential from the M2A sands zone above the main Moki sands structure at Maari is about 12 million barrels.

It adds that the latest interpretation of the nearby Manaia prospect, about 10km southwest of Maari, indicates an upside potential of about 25MMbbl.

Both updip figures were calculated as a gross mean recoverable reserves potential, Wilson HTM said.

Its report also says studies of 3D seismic data show the original 1970 Manaia prospect discovery well, Maui-4, was drilled off-crest.

Maui-4 discovered an under-saturated oil accumulation in poor quality Mangahewa Formation sands that tested 575 barrels of oil per day. Two small Moki accumulations were also found in the Maui-4 well.

The partners, headed by operator Austrian firm OMV, are scheduled to use the jack-up Ensco Rig 107 to drill eight Maari development wells (five production and three water injection) later this year.

Wilson HTM said the Maari partners were also due to appraise the Manaia and M2A zones using the Ensco 107. Manaia had the potential as a subsea tie-back to the Maari production facilities of an unmanned platform and the floating, production storage and offtake (FPSO) vessel Raroa.

"AVO and inversion work also suggests that reservoir quality and/or hydrocarbon saturation may improve updip from Maui-4," Wilson HTM said.

OMV and partners approved the then $US360 million ($A399 million) development of Maari in late 2005, with first oil from the 50 million barrel field scheduled for March-April 2008 and a production plateau of about 35,000bopd achieved several months later.

Overall project costs have since increased to at least $US457 million ($A520 million).

Wilson HTM also said it would cost $US10-20 million (about $A11-22 million) for each additional well drilled, and that FPSO operating costs would be about $US250 million ($A277 million) over the first four years.

It would cost the partners $US50 million ($A55 million) to purchase the Raroa at the end of the initial four-year lease.

Total field production is expected to decline by about 25-30% per year.

The Maari partners are operator OMV NZ (69%), Horizon Oil (10%), Todd Petroleum Mining (16%) and Cue Energy Resources (5%).