Record-Setting AUV Pipeline Inspection in Deepwater West Africa

Abstract In deepwater environments the inspection of subsea infrastructure (including pipelines, wellheads and anchors) is paramount for assessing "life of field" and for ensuring the integrity of assets subject to geo-environmental constraints. Following the first deepwater development in the late 1990s, the number and length of pipelines has significantly increased, leading to time-consuming and costly conventional Remotely Operated Vehicles (ROV) inspections. Based on these technical and economical constrains, an Autonomous Underwater Vehicle (AUV) based solution, technology routinely used for seabed and sub-seabed geophysical data acquisition, has been considered. This paper presents the application of such methods to deep offshore fields in West Africa. The availability of new AUV mounted high resolution sensors (Laser, subsea camera) in addition to conventional sensors (Multi Beam Echo Sounder, Side Scan Sonar, Sub Bottom Profiler) has expanded over the past years, providing Operators with a new set of tools for baseline surveys, field monitoring and inspection purposes. Through the deployment and application of these innovative sensors, already developed in the industry but never used for deep water large scale operations, this new approach was an opportunity to fill technological gaps for pipeline inspection using an AUV instead of an ROV. At an altitude of 5 to 7 meters above the seabed facilities, a detailed and accurate inspection survey conducted with subsea laser and high resolution camera was performed. Micro-bathymetry and high-resolution hydrographic data allow detailed mapping of subsea facilities and surrounding seabed as well as a large-scale overview of the developed areas. Integrating processed data from conventional and new AUV sensors in a Geographical Information System (GIS), creates a new decision-making tool for the life-of-field integrity. It allows the Operator to establish a high resolution baseline of the installation and to identify particular points of interest requiring further detailed investigations. The quality of results far exceeds the standard methods and helps to identify equipments requiring mitigation measures or detailed investigations as requested by pipeline engineers. The final dataset could be used as a subsea engineering reference to conduct repeated AUV acquisitions and to identify/monitor changes over time. Due to its speed and limited maneuverability, AUV could not fully replace conventional ROV inspection. The combination of both methods and technologies offers a large panel of solutions to optimize pipeline inspection surveys. The development of new sensors specifically adapted to AUV payload leads to considering AUVs not only as a site-investigation tool used for geohazard assessment prior subsea installation but shall nowadays be considered far beyond their original design, allowing a step forward to subsea monitoring and inspection surveys.