Total has completed the first large-scale inspection survey in the deep offshore using an autonomous underwater vehicle (AUV) instead of a remotely operated vehicle (ROV). It's an uncommon choice, ordinarily reserved for acquiring subsea geophysical data. Equipped with next-generation sensors, the AUV performed a comprehensive inspection survey of 502 kilometers of pipeline in Block 17 in Angola. It was a novel, bold approach that enables us to create a new strategy for managing subsea pipeline integrity.
Imagining Another Way to Use AUVs
In deepwater environments, inspecting subsea infrastructure is paramount to assess the condition of installations and ensure the integrity of assets subjected to strong geoenvironmental stresses. But the number of pipelines has soared since the first deep offshore developments in the late 1990s, leading to increasingly costly and time-consuming inspections by remotely operated underwater vehicles (ROVs).
To optimize its strategy for managing the integrity of subsea infrastructure, Total E&P Angola developed an innovative inspection approach using an autonomous underwater vehicle, or AUV. Although normally reserved for geophysical data acquisition, AUVs have a significant advantage: they can collect data for one-quarter the cost, in one-fifth the time.
High-Resolution Equipment to Perform the Most Common Inspections
Besides conventional sensors — multibeam echo sounders, side scan sonar, sub bottom profilers — the AUV includes new sensors such as a subsea laser and a high-resolution optical camera. Such tools are widely used in the oil industry, but never before for large-scale subsea applications. They help offset AUV technological shortcomings compared to ROVS, producing high-resolution, micro-bathymetric, hydrographic data that is suitable for 3D modeling and photomosaic images.
A number of navigation sensors are also integrated to optimize AUV position, such as an Inertial Navigation System (INS) and Doppler Velocity Log (DVL). All data are georeferenced and then published in a customized geographic information system (GIS). This allows end users (inspectors, pipeline engineers, geotechnicians) to view and analyze all the collected data in a single interactive window display.
So an AUV can provide a baseline for subsea facilities. Additionally, it can identify particular points of interest requiring detailed investigation or mitigation measures. AUV pipeline inspection surveys will not fully replace conventional ROV inspection surveys, because cathodic protection measurements from dynamic AUVs are not currently feasible. But results are far higher in quality than the standard method.
AUV payload for pipeline inspection survey
Perspective views of a pipeline 3D laser point cloud
Perspective views of an in-line tee 3D laser point cloud.
Photomosaic of a pipeline section
AUV GIS data reviewer allows users to “play” through multiple datasets along the pipeline
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