Abstract

Accurate seafloor mapping is a key component of an integrated exploration and development program in the marine environment. Traditionally, bathymetry data used in the Oil and Gas Industry have been acquired using single beam echosounder technology, which although resolute with respect to water depth, leave large areas of the seafloor unmapped. Advances in multibeam sonar technology have led to laterally as well as vertically resolute seafloor mapping capabilities, providing complete and rapid coverage of the seafloor from multibeam-equipped vessels. In November 1998 Exxon acquired ? 2500km2 of proprietary multibeam data over two deepwater blocks, offshore Trinidad in an 11-day period. The data resolution and quality are impressive and clearly delineate numerous mud volcanoes or diapirs, channel systems, blowout craters, and a myriad of other fine-scale morphologic features. However, a comparison of the seafloor renderings produced from multibeam data and the seafloor image extracted from 3D seismic data revealed minimal differences.

Introduction

High-resolution bathymetry is an essential component of an integrated exploration and development program. These data have value from the earliest stages of frontier reconnaissance through the end of the development phase with applications ranging from geological modeling to pipeline routing to facilities planning and installation. Until recently, the high resolution bathymetry data available to the Oil and Gas Industry have been limited to single-beam echo sounder data acquired concurrently with 2D or 3D multichannel seismic data. The bathymetry data produced by these systems leave large areas of the seafloor virtually unmapped. In order to produce a 3D rendering, or image, of the seafloor from single beam data, it is necessary to fill in the "gaps" between widely spaced soundings by interpolating between the existing data points. The seafloor renderings generated from such data lack the fine-scale detail essential to an accurate assessment of the morphologic character of the seafloor. Multibeam Sonar (MBS) data from numerous areas worldwide have been used to produce highly detailed seafloor renderings that have revealed the morphologically complex nature of the slope environment. These renderings have played an important role in dispelling the myth that the continental slope is a quiet, low-energy environment.

Multibeam Data Products
High-resolution bathymetry.

Multibeam Sonar technology was initially developed in response to the U. S. Navy's need for high-resolution bathymetry data that could be acquired in an efficient manner. The migration of multibeam sonar technology from its origins in the military, to academia, and most recently to Industry has occurred over a period of ?25 years. Present day state-of-the-art multibeam sonar systems use sophisticated beam forming and steering techniques to acquire bathymetry data that is laterally as well as vertically resolute. The operational efficiency of these systems is excellent. In general, multibeam systems are capable of acquiring between 120 and 200 soundings per transmit pulse over a swath width of 3 to 7 times the water depth. The vessel speed during acquisition is limited only by the specified along track sounding spacing and the acoustic characteristics of the vessel such that speeds in excess of 10 kts are feasible (versus 4 - 5 kts for seismic surveying).

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