Abstract

The use of Autonomous Underwater Vehicles (AUVs) for offshore surveying has progressed rapidly in the last year from vision to reality. After a period of development lasting over 10 years, Maridan - the Danish developer and manufacturer of AUVs - has been operating its MARIDAN 600 series of AUVs successfully for the past year.

In 2001, Maridan teamed with UK survey company Gardline Surveys to perform integrated offshore surveys with its MARIDAN 600 AUV, using this cutting edge survey technology for BP in the Central North Sea in tandem with shallow geotechnics.

The paper illustrates the benefits and constraints of using AUV technology on a number of site survey and pipeline projects in the Central North Sea. Examples of the high quality survey data acquired by the AUV's multibeam, sidescan and sub-bottom profiler sensors will be discussed. The systems dead-reckoning navigation performance is assessed. The HSE and operational issues for the MARIDAN 600 are described. Attention is drawn to the deployment, reliability and performance monitoring issues, which presented themselves. Also the flexibility of the AUV to survey in areas close to and within offshore structures was highlighted.

The paper also examines the key success factors required by the industry to make potential AUV productivity gains a reality.

Background and Objectives

In October 2001, Gardline Surveys were contracted by BP Exploration to carry out a series of Autonomous Underwater Vehicle (AUV) surveys, a geotechnical coring programme and ROV inspections in shallow water conditions of the Central North Sea. Water depths were approximately 100m. The purpose of having the ROV onboard was to identify features observed by sonar or swathe bathymetry within the area of survey or on the pipeline routes from previous surveys. Gardline contracted the AUV operation to Maridan AS, a Danish AUV manufacturer, who sub-contracted De Beers to carry out the AUV surveys using a MARIDAN 600 vehicle built specifically for shallow water, high resolution, diamond prospecting surveys offshore Southern Africa. This is the first commercial AUV produced by the company. The vehicle had been in operation for some 5 months prior to relocation to NW Europe.

Figure 1 : Maridan 600 AUV(Available in full paper

The support vessel employed was MV Ocean Seeker, a 77m hydrographic and geotechnical survey ship owned and operated by Gardline. All operations were conducted from the foredeck of the vessel.

The AUV solution was seen to provide potential benefits over conventional survey methods-the following key objectives were identified for this project :-

  • To evaluate the potential benefits of AUV technology over conventional methods, in terms of data resolution and cost efficiencies

  • Operations within 500m exclusion zones at fixed installations, where conventional methods are constrained by vessel access restrictions and environmental conditions

  • Simultaneous AUV based geophysical and vessel based geotechnical data acquisition under certain conditions

  • Extent to which the AUV required close support from the "mother vessel"

A key objective of the project was to evaluate the performance and safe operations of the Maridan AUV in a variety of typical North Sea operating situations and weather conditions.

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