Basins bounty sought

February 1, 2013

As oil and natural gas production continues to fluctuate at a level well below demand, John Mueller looks at New Zealand’s growing need to aggressively explore the nation’s vast and extensive offshore sedimentary basins.

Taranaki Basin, located along the west coast of New Zealand’s North Island, has been the principal focus of oil & gas exploration and production. It commenced with the large gas and condensate discoveries made in 1969 with the onshore Kapuni and offshore Maui fields, and continuing throughout this on and offshore petroleum province.

Other significant hydrocarbon finds include the offshore Tui and Maari oil fields and Kupe and Pohokura gas fields.

The Maui field, formerly the premier deposit, has been in sharp decline.

The Maari and Pohokura fields contain about 49% of remaining oil and condensate reserves, Pohokura accounting for 45% of natural gas with the balance distributed over 17 other fields.

Exploration is being conducted in other basins, subcommercial discoveries achieved in the East Coast Basin of North Island and in the Canterbury and Great South basins offshore South Island.

More than 400 wells have been drilled in the 330,000 sq km Taranaki Basin, but none beyond the marine shelf edge. New discoveries have been made at a steady rate, and new play types are still being found.

Elsewhere in New Zealand, frontier basins have yielded discoveries confirming viable petroleum systems, with many untested structures having closures greater than the Maui field.

Concerted geophysical data gathering since the mid2000s, coupled with advancing deepwater drilling and production technology, has shifted exploration further offshore in anticipation of larger oil and gas accumulations. Sections of five offshore frontier basins: Great South, Canterbury, Raukumara, Deepwater Taranaki and Reinga, are currently licensed to major international companies.

The increasing acquisition of seismic data has prompted frontier basin exploratory efforts that have yielded several significant, albeit non-commercial deposits. These included two off the east coast of South Island in the Great South Basin, where Kawau-1A in 1977 flowed 6.8mmcf/d of gas with estimated reserves of 461bcf and in the Canterbury Basin well Galleon-1 produced 10mmcf/d of gas and 2300b/d of condensate in 1985.

There are multiple sedimentary basins with known or potential hydrocarbons onshore and underlying the extensive continental shelf of New Zealand, as well as several deepwater basins within its Exclusive Economic Zone where sovereign rights extend over more than 5.7 million sq km of seabed, a region more than 22 times greater than the land area.

Commercial and sub-commercial discoveries, abundant potential source rocks, thick Cretaceous-Cenozoic sediments, and numerous hydrocarbon seeps and shows in exploration wells indicate widespread petroleum generation and migration.

Block awards

The tender in 4Q 2012 involved 23 blocks including 40,200sq km offshore. Five offshore exploration permits were awarded, with the remainder likely to be included in the this year’s block offer.

Oil output has varied widely over the past 15 years, rising and falling year to year, from approximately 22,000b/d in 1997 to around 7000b/d in 2006 and then to around 16,500b/d in 2011, primarily from the Pohokura, Tui and Maari fields – Maui only producing about 1500b/d that year.

Gas production in 2011 averaged 395mmcf/d, mainly from Pohokura, Kapuni and Maui, all of it consumed domestically.

Proved hydrocarbon reserves are relatively modest, estimated at around 113 million barrels and about 1.2tcf of natural gas in 2011.

Hydrocarbon consumption in 2011, according to the BP Statistical Review of World Energy, was 148,000b/d of oil and 377mmcf/d of gas, each a decline from 2010.

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