Bulletin of the Geological Society of Malaysia, Volume 22, Dec. 1988; pp. 209 – 227
Sarawak Shell Berhad, Lutong, Sarawak
Abstracts: 3D seismic surveys with exploration, appraisal and development objectives have been acquired in Shell-operated offshore Sarawak acreage since 1984. In all, 10 surveys have been performed covering an area of almost 1500 sq. km. 3D surveys offer improved structural delineation and reduce the risk of an inconclusive well, particularly in geologically complicated areas. In the case of success, 3D surveys allow follow-up appraisal plans to be matured quickly since further infill shooting should not be required (as happens with 2D seismic surveys).
The very significant effect of 3D seismic acquisition and processing is illustrated by a comparison using a conventional 2D seismic line extracted from a 3D survey and a 3D processed section along the same subsurface trajectory. Contour maps using 3D seismic data have been proved by drilling to be more accurate than maps constructed using only 2D seismic, particularly in complexly faulted areas.
Time-slices can be used directly for fault and contour interpretation, and these aspects are illustrated by various examples.
It is vital to identify and map out potential drilling hazards. In some instances the dense 3D coverage can aid in the delineation of shallow gas anomalies and sea-bottom channels. In addition to the superior structure maps, 3D seismic could potentially be used to make detailed maps of lithostratigraphy under ideal conditions. A pilot study to map the lateral extent of a channel, seen in one of the development wells, gave encouraging results.