The Diamond Offshore Drilling rig has arrived on location, 12 km off the Motunui coast, and is rigging up to drill the vertical Pohokura-3 well, which will help define the northern extent of the 1tcf-plus gas-condensate field.

Pohokura-3 will target the Mangahewa sandstones within the Kapuni formation and be drilled to a target depth of 3800m. Total drilling time is expected to be about 45 days, with any testing likely to take another 15 days.

Onshore the Parker Drilling Rig 188 is over 2003m down towards its 5447m target depth at the Pohokura South-01 well site near the Methanex Motunui complex. Pohokura South-01 will help define the southern extent of the Pohokura field and will extend about 2.6 km off the coast in a northwesterly direction under the sea.

Meanwhile, Pohokura operator Shell Todd Oil Services has released more details on the proposed $NZ900 million Pohokura gas field development, including a possible three-year drilling program.

Pohokura project manager Nigel Dee has told a resource consents hearing in New Plymouth this week that as many as 24 production wells might be drilled off the north Taranaki coast during the $NZ900 million development project.

Up to 3 wellhead platforms may be developed and each of these may have up to eight wells drilled from them by a jack-up rig that will also install the wellhead platform. Fabrication of each of the wellhead platforms will take up to six months and the platforms will be installed once constructed.

The first four wells will start immediately after the installation of the first platform and be completed within six months. After those wells have been drilled they will be connected to a subsea pipeline to shore so commercial hydrocarbon production can start. Drilling of the next batch of wells will then continue simultaneously with production from the first four wells.

No processing facilities will be located on the normally unmanned wellhead platforms. There will be up to four pipelines and a services umbilical will be installed in association with the offshore platforms.

The pipeline to bring product ashore will be a 600mm-diameter steel pipe with external concrete coating. A 250mm-diameter gas re-injection pipeline steel pipe, with external concrete coating, will convey dry gas from onshore back out to the platforms, to be re-injected into the reservoir to help maintain formation pressure and the production of liquid hydrocarbons.

Services pipelines will be 75mm diameter and will convey glycol and corrosion inhibitors from the shore to the platforms. They will be attached to the main 600 mm diameter gas pipeline so that all three can be installed as one.

A temporary jetty structure will be erected, from above the shoreline to approximately 800m offshore to the 5m water depth, to provide a platform from which to carry out the pipeline trench excavation.

The pipelines will be laid in 5km maximum lengths using a tug, barge or winch system. They will be pulled from onshore (where the 500m sections will be welded together as the pipeline is towed out), then 'bottom' or mid-water towed offshore to their final position.

It is proposed to lay the pipelines in an excavated trench for the first 800m (up to 5m water depth) and thereafter to lay them on the seabed.