A substantial discovery of natural gas has been made at the Mangahewa gas condensate field in onshore Taranaki during new appraisal operations by Todd Energy.
Richard Tweedie, managing director of Todd Energy, said "a lot more gas" had been discovered following drilling of its Mangahewa-3 appraisal well earlier this year.
Mr Tweedie did not give any figures on the size of the discovery but he said that the Mangahewa field, which is 100% owned by Todd, is now one of the companies major assets.
"We see a big upside at Mangahewa," he said.
Mr Tweedie also said that Todd Energy sees potentially 2,000 petajoules (PJ) of new gas that Todd is currently actively evaluating in its fields.
He said this was additional to New Zealand's current gas reserves of 2,100 PJ.
Tweedie said this 2,000 PJ of new gas potential was made up not only of the Mangahewa field but of additional gas expected from the Pohokura gas field, which is 26% owned by Todd; from the Kapuni gas field (50% Todd) and from the company’s 100% owned undeveloped offshore Karewa field.
He believed New Zealand is going to get more of its future gas from 'nearfield' exploration and appraisal. Reservoir engineers who produce the estimates of reserves are often quite conservative in the early stages of a field, he said.
A good example was the Kapuni field which had estimated reserves of 250 PJ when discovered over 40 years ago. Total reserves have grown over four times to 1,100 PJ. Kapuni still has remaining reserves of 260 PJ.
Mr Tweedie said the Pohokura field, where the final offshore production wells are still being drilled, was likely to be not far behind Kapuni in size at about 1,000 PJ. "There's a lot of good signs coming from the Pohokura production wells drilled so far," he said. Pohokura reserves were listed as 900 PJ at 1 January 2007.
Todd Energy bought the neighboring Mangahewa and McKee fields from Shell in 2002. Initially Shell Todd Oil Services was contracted to operate the field before Todd took over operating on its own and began work on ways of increasing gas production from the field.
When the Mangahewa field was held by Fletcher Challenge Energy in the late 1990s, reports from the company suggested the formation could contain between 500 billion cubic feet and two trillion cubic feet of gas in a large structure going offshore into what is now the Pohokura field. Later seismic showed there were separate structures offshore from onshore.
The original 1997 Mangahewa-2 discovery-production well located some 20 m of hydrocarbon reservoirs over a number of different zones of "tight gas." Only three zones were hydraulically fractured and one zone was drawn on for flowing. When the field was commissioned in September 2001 with only one well, the reserves were listed as just over 100 bcf, considerably below earlier estimates.
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