"It's definitely not looking like a one tcf field now," said one industry commentator recently.
The new mean reserves estimate (P50) was now likely to be 500-600 bcf of gas, compared to the last official Fletcher Challenge Energy figure of 964 bcf.
"Even if these new figures prove true, Pohokura will still be a significant field by New Zealand standards and worth developing," he said.
Former Fletcher Challenge Energy chief operating officer and now Shell New Zealand chairman, Lloyd Taylor, told the 2000 NZ Petroleum Conference that recoverable reserves of about 200 bcf should be the breakeven point for any Pohokura development.
However, a significant downgrading of proven and probable Pohokura reserves will just intensify the competition between big users for Pohokura gas and probably hasten the departure of the biggest user Methanex from New Zealand as it will not be able to outbid electricity generators for long-term supplies of Pohokura gas.
The Parker Drilling 188 rig reached the 5032m along-hole target depth of the Pohokura South-1B sidetrack well reached earlier this month and operator Shell Todd Oil Services is now setting drill pipe before running tubing completion and installing a Christmas tree.
The Parker rig will then move south from the onshore Motunui site to drill the first appraisal well for years in the Kapuni field. Kapuni-16 is being drilled to appraise and develop the productive K1 reservoirs on the eastern flank of the field and has the potential to add substantial new gas-condensate bookable reserves for field owners Shell NZ and Todd Energy.
It is understood STOS will long-term production test that section of the Mangahewa reservoir accessed by the Pohokura South-1B well. This testing may last for up to a year, with off-spec test gas going to the nearby Methanex Motunui methanol complex.
This happened in the late 1990s, with then-owner FCE testing the Mangahewa-2 well for a year or so and sending that test gas to the Motunui complex for use in non-critical methanol manufacturing processes.
Although STOS has not released any test results from the Pohokura-3 well, it is believed the partners were satisfied with that program and the production testing of the lower premium sands, not the whole producing interval, within the northern part Mangahewa reservoir.
However, it is the more southern part of the Pohokura field, situated off the Methanex Motunui complex, which may be posing problems for the partners.
The southern reservoir sands are quite different from those further north and present a "tight" reservoir picture.
"They have not got another Maui; Pohokura has lower overall porosity and permeability and is quite a complex field," said the commentator.
STOS still has about a year's work of computer modelling to do before deciding on a preferred development option. It will want to do a thorough job and not jeopardise the integrity of the whole project by overstating (or understating) the size and numbers of platforms required to maximise hydrocarbon recovery from the field.
As estimates of ultimate hydrocarbon recovery can change several times throughout the life of a field, it is understood STOS is still working on scenarios involving the field lasting 10-20 years.
Under these scenarios, production would be coming onstream from late 2005 to early 2006 with rates varying from 60bcf-120bcf per annum from up to three unmanned mini-platforms in each of the near-shore, middle and northern limits of the field.
