Pohokura gas field is located offshore the north-east of New Plymouth in the Taranaki Basin, close to the Methanex Motunui site near Waitara. It lies in 35m water depth in Block PMP 38154.
The field is operated by Shell Todd Oil Services (STOS) and is owned by OMV (26%), Shell Exploration NZ (30%), Shell (Petroleum Mining) (18%) and Todd Pohokura (26%).
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Geology
The Taranaki Basin includes reservoirs ranging from Paleocene to Pliocene. The gas-condensate field is on a low-relief anticline. The 16km-long and 5km-wide area, at about 3,600m depth, extends offshore north-west from the coast.
Gas-condensate and oil are encountered in reservoirs of Paleogene age. The Middle to Late Eocene Mangahewa Formation consists of hydrocarbons.
Discovery and drilling
The field was discovered in March 2000 by Fletcher Challenge Energy. The first offshore well Pohokura-1 penetrated a 130m gas column and found 17.6mmscf/d of gas.
The Pohokura-2 well was drilled in the central part of the structure located 5km away from the discovery well. The well penetrated a 115m gas column and flowed 35.3mmscf/d during drill stem test.
The Pohokura South-1 onshore well was drilled in March 2001. Two appraisal wells Pohokura-03 and Pohokura South-01B were drilled between September 2002 and January 2003.
Pohokura South-1B was drilled in 2001 between the Pohokura and Mangahewa field structures.
It encountered poor quality of sand in the reservoir segment and no movable hydrocarbons in the Mangahewa Formation.
Shell acquired the assets of Fletcher Challenge Energy in 2001 and drilled three wells from the onshore site located at Motunui and five from an offshore platform.
Reserves
The Pohokura field is estimated to contain reserves of 884PJ of natural gas and 44mmbbls of condensate.
As one of the largest gas condensate fields in New Zealand, Pohokura will contribute about 40% of the nation’s natural gas production.
Field development
The $1bn Pohokura development project was completed in June 2008. The offshore wells feed the onshore production station located on the Motonui coast. The field was developed in two stages.
Three development wells in the first stage were drilled from onshore into the southern end of the field using a large onshore rig. Drilling activities were completed in August 2006. The first gas was fed into the North Island network in September 2006.
Initially six wells were planned to be drilled, but later it was decided that five wells would be sufficient to take out the reserves. The offshore section development was carried out in the second stage using an Ensco-56 jack-up rig having placed the offshore platform and topsides in place.
The offshore platform and the onshore production station will be remotely controlled from the New Plymouth offices of Shell.
In December 2004, Technip signed a contract with STOS to supply and install flexible lines, umbilicals and the wellhead platform for the field. Technip engaged AME to provide engineering designs, draft and site personnel during the execution of the project.
Technip contracted AME to provide engineering design, drafting and site personnel during the execution of the Pohokura field development. AME provided assistance in flowline installation, jacket and topsides installation, and self drilling piles.
Field infrastructure
The Pohokura field development infrastructure includes a wellhead platform, a subsea pipeline connecting the wellhead platform and the coast, and an onshore gas plant.
Technip is responsible for the supply and installation of a 7.25km-long 11.5in diameter flexible pipeline and a 9.2km-long umbilical and service line, and the wellhead platform.
Umbilicals are manufactured by Duco, Technip’s subsidiary based in Newcastle, UK, while flexible lines are made at Le Trait in France.
Production
The first commercial gas was produced from three onshore extended reach drilling (ERD) wells in September 2006. The gas and condensate flowed from the first of five offshore wells in March 2007.
The field produced 4.3mmbbl of oil and condensate, and gas of 58.5bcf in 2009. The cumulative production to date includes 14.5mmbbl of oil and condensate, and 190bcf of gas.
Export
Natural gas from Pohokura is transferred via the North Island gas network.
The condensate is separated from the gas flow at the production station and supplied through a pipeline owned by Todd Energy and Shell / OMV, to storage tanks installed at Omata near New Plymouth for transporting to refineries.
