Multibeam Surveys Around and Under Oil Platforms

In 2001-2002, Sea Surveyor conducted a series of MULTIBEAM hydrographic surveys around 16 offshore oil platforms in the Santa Barbara Channel and Santa Maria Basin of California. The objective for these multibeam sonar surveys is to identify “shellmounds” or debris piles under the platforms, and determine what factors (depth, slope, platform age, etc.) contribute to the presence of shellmounds. These surveys were conducted in support of the Minerals Management Service, Pacific Outer Continental Shelf (OCS) Program.

The seafloor under the offshore oil platforms ranged from 100’ to 1,000’ in depth. A RESON Model 8101 multibeam sonar system was used to survey the platforms in 100’-400’ water depths, and a SEABEAM Model 1180 multibeam sonar was used to survey under the platforms deeper than 400’. Survey lines were run at various orientations and distances from the platforms to ensure 100% sounding coverage under the platforms. Bathymetric contour charts and cross-sectional profiles were produced and shellmound (debris pile) dimensions were measured.