The 363.1 km Central Subsystem comprises the 14 in. diameter Kapuni – Huntly pipeline, which was built by McConnell Dowell along a similar route as the Maui pipeline. Currently the pipeline is the only access to northern gas markets for non-Maui gas and is therefore well utilised, although its capacity is less than one tenth of that of the Maui pipeline
(11 PJ/a compared with Maui’s 125 PJ/a).
The growth of gas and major expansions of the North Island system
In the early 1980s, gas consumption trebled from about 32.9 PJ in 1980 to 105.1 PJ in 1984. In order to meet increasing demand, a number of major pipelines and extensions were built.
In 1984, the Huntly – Gisborne pipeline was built, which served demand on the west coast of the North Island from four large consumers (the Hospital, Watties, Gisborne Refrigeration and Advanced Meats). The pipeline and its laterals to Taupo, Tauranga and Rotorua comprise the Bay of Plenty subsystem and extends for 608.3 km.
In 1986, the 373.7 km Kapuni – Huntly pipeline was lengthened to transport gas to Auckland and eventually Whangarei and Kauri in the far north of the North Island. The 14 in. diameter pipeline was aptly-named by pipeline owner Natural Gas Corporation as the North Subsystem.
The Frankley Road pipeline is owned by NGC and runs from the Maui pipeline at Frankley Road to the Kapuni treatment statement, a distance of 47 km. The 20 in. pipeline carries specification gas and is able to carry Maui gas to the South Subsystem. In September 2005, upgrades to the pipeline have added bidirectional capacity, allowing it to carry gas from the southern Taranaki fields like Kapuni, Rimu and Kauri to the Maui pipeline.
The Pohokura gas field
The decline of the Maui field has prompted a flurry of exploration, but few successful discoveries. The major exception is the Pohokura Basin, which is located in the Taranaki Basin. The Pohokura Basin is the country’s third-largest gas producing field, producing some 8.6 per cent of the country’s gas production and has estimated recoverable reserves of about 700 Bcf.
Development of the field has involved the drilling of three wells from a land-based site at Motunui and six from an offshore platform located 8 km off the coast. First commercial gas flowed in September 2006 from three onshore extended reach drilling wells in the southern part of the field tied to the unmanned platform, a 12 in. diameter 8 km subsea gas pipeline.
The other parts of the project include an onshore processing plant at Motunui, a gas export pipeline that ties in to the Maui line at Bertrand Road, and a 34 km condensate pipeline to the Westgate Port at New Plymouth for export of liquids. The 7 km onshore pipeline has been installed by New Zealand engineering firm BTW, which connects the existing Todd pipeline network to the Pohokura production station.
In March last year, gas and condensate flowed from the first of six planned offshore wells. Natural gas from the Pohokura field is fed into the North Island gas network, and the condensate is piped to storage tanks at Omata near New Plymouth for shipping to refineries.
While the Pohokura field is likely to fuel New Zealand’s gas requirements in the near term, there are a number of other developments that have spurred pipeline development, as in the case of the Kupe field, or have the potential in the future.
The Kupe gas field
The Kupe gas field is one of New Zealand’s largest undeveloped gas fields and is located 30 km off the New Zealand coast, south of Taranaki Basin. The field, which is being developed by a joint venture between Origin Energy, New Zealand Oil and Gas, Genesis Power and Mitsui E & P, contains proved and probable (2P) reserves of over 230 PJ of sales gas plus considerable condensate and LPG, with additional reserves potential.