4D Seismic work will begin shortly on the Maui gas field offshore New Zealand. "The last time a major seismic survey was conducted over the Maui field was in 1991. Now we are going to survey exactly the same lines again, and fresh techniques and sophisticated equipment will tell us what has happened down there over those 11 years," said Shell Todd Oil Services general manager Chris Beath. While one reason for the survey is to assist in proper management of the Maui field as it headed towards eventual depletion, it is also hoped that pockets of bypass gas -- gas that had been missed by the wells drilled so far -- will be found.
The 4D survey technique has been developed over the past two or three years, but so far it has targeted oil, which is easier to locate. When the survey begins, the seismic vessel will tow behind it six streamers, each with equipment that will record seismic data bouncing back from the underground geology. The sound source will be compressed air, which will be fired as the vessel travels every 18 meters. The survey should last approximately two months.