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Two seismic vessels make progress in Great South Basin
13 February 2008 - A large two-vessel seismic data acquisition programme underway in the Great South Basin is making good progress despite delays caused by poor weather and ocean swells.
OMV New Zealand, which holds three permits in the basin with partners Thai national oil company PTTEP Offshore Investment and the Japanese trading house subsidiary Mitsui E&P Australia, said it has completed 9,900 km or over 60% of the total 16,000 km of 2D seismic it plans.
The OMV-led partners in the PEP 50119, 50120 and 50121 permits, commenced on 3 November 2007 using the seismic vessel Discoverer-II.
In the southernmost of the Great South Basin permits PEP 50117, operator US-based ExxonMobil New Zealand (Exploration) Ltd and local partner Todd Exploration Ltd had completed by the end of January approximately 90% of its planned 960 km of 2D seismic lines.
However, collection of the 1,340 sq km of 3D seismic data was approximately 30% complete, ExxonMobil Australia’s senior issues and government relations adviser Rob Young said from Melbourne.
ExxonMobil are using the WesternGeco seismic vessel Western Trident which mobilised from Bluff at the end of November. PEP 50117 is centred about 200 km south of Bluff.
OMV said the Discoverer-II encountered unstable weather in November, but conditions improved in December. However weather standby increased to 23% during January.
Minor technical downtime has been experienced, and is to be expected due to the long lines, some over 200 km long, and the swells in the southern ocean, OMV said.
Line orientation has proved to be a major factor in susceptibility to swell noise, OMV said.
“Lines in the NW-SE direction are sub-parallel to the predominant swell, and are much quieter than lines in the SW-NE direction. This has allowed the Discoverer-II to continue acquisition in marginal conditions on NW-SE lines, whereas SW-NE lines would have been aborted in similar conditions due to swell noise.
Metocean conditions varied within the three permits, OMV said. The company has commissioned twice-daily metocean forecasting for 11 sites which enabled Discoverer-II to sequence acquisition to avoid exposed areas.
OMV said it expects to complete its survey by the end of April.
ExxonMobil said the weather up to late December on the ratio of seismic data collected vs standby time was as expected pre-survey. Weather conditions deteriorated in January.
Whilst the completion date of the survey is weather dependent, Exxon anticipates completion of the survey in March.
