The future of subsea surveying unlocked

In the last 10 years, the offshore survey industry has seen the evolution of a new breed of fast remotely operated vehicles (ROVs) specifically designed for high-speed surveys and pipeline inspections. The Survey ROV, or SROV as it is commonly referred to, was in 2020 formally adopted by the rigorous standards of the Norwegian petroleum authorities (NORSOK), thereby defining the specific requirements of this new type of ROV. DeepOcean, head-quartered in Haugesund, Norway, was an early pioneer of the SROV concept, taking delivery in 2015 of the very first Superior SROV from local ROV innovator Kystdesign. In the intervening years, Superior SROV has surveyed thousands of kilometres of subsea pipelines annually and in all likelihood has the largest single-track record in pipeline inspection of any ROV globally.

The benefits of a modern SROV

Operators on the geographically extensive Norwegian Continental Shelf were quick to understand the economic advantages that a modern SROV can bring to their subsea pipeline inspection pro-grammes. They operate a vast network of oil and gas pipelines ex-tending the length of the North Sea from the shores of France and Belgium to the arctic Barents Sea, all of which requires regular external integrity assessment. Employing DeepOcean’s Superior SROV, mobilised onboard DeepOcean’s flagship survey vessel the Edda Flora, pipeline operators have realised substantial cost savings when compared with the alternative of using slow work-class ROVs configured with a survey sensor payload. Not restrict-ed to only the local Norwegian market, Edda Flora has taken Superior to the Mediterranean Sea and Black Sea for trunk line inspections to depths of 2200 m.

Superior SROV can perform pipeline inspections at up to 4 knots as a result of its array of powerful aft thrusters. To ensure highest data quality during these high-speed inspections, Superior SROV has been designed for maximum stability – its sheer size coupled with its hydrodynamic form-factor ensure that it is a superbly stable sensor platform. The SROV can carry an impressive 700 kg payload of dedicated sensors for pipeline inspection, primarily comprising dual-head multibeam echosounders (MBES), HD video cameras, side-scan sonar (SSS), INS/DVL navigation sensors, still imaging system, dissolved methane detector (for gas leak detection) and other sensors as required by the project needs.

Generating innovative digital products

Three main modes of pipeline inspection are employed using Superior SROV depending on the client requirements. Where the largest integrity risk to the pipeline is deemed to be from third party threats such as dragged anchors, trawls and such like, an operator may elect to forego collecting full visual coverage of the pipeline and instead perform a high-fly hybrid acoustic/visual inspection. Flown at about 4 m altitude, what this high-fly mode compromises in visual assessment it gains in efficiency, as there is effectively no sensor-imposed speed limit and therefore, weather depending, acquisition speed can be up to the maximum speed of the ROV which is around 4 knots. The echosounders data allows the freespan condition of the pipeline to be assessed without the traditional requirement of boom mounted video cameras imaging the pipeline/seabed interface. Additionally, the terrain model generated from the echo-sounders system is reviewed offline in parallel with the side-scan sonar data for evidence of seabed scars crossing the pipeline that might indicate possible impact and damage to the pipeline. This hybrid method includes a visual component by way of vertically mounted still imaging cameras to photograph the pipeline from above. Depending on the specific client requirements, these images can be reviewed in full to assess the visual integrity of the pipeline, or a more basic and cost effective review can be performed only visually confirming the identity of any debris items observed be-side the pipeline within the acoustic multibeam echosounder data.

The inclusion of still photographs in Superior’s armoury can generate innovative digital products, giving integrity engineers even more value from the survey. The photographs are rendered into georeferenced mosaic strips of about 50 m in length which can be useful to visualise the pipeline in a wider context. If required, the images can also be processed using photogrammetric techniques into 3D models, which can be invaluable in assessing critical anomalies.

Superior SROV can of course perform a more traditional visual pipeline inspection, only much faster. Three HD video cameras are arranged to capture full visual coverage of the pipeline. As with the high-fly mode, echosounder- and side-scan sonar data are also acquired to image scars, debris, boulders and such like outside the visual field of view of the cameras. Acquisition speed with the video cameras in close proximity to the pipeline like this tends to be capped at about 2.5 knots – it’s worth observing that this is still twice the speed of a typical WROV carrying a full survey sensor package. The limiting factors are two-fold: principally the video playback during the offline review process becomes uncomfortable for the video reviewers to watch due to the speed that the pipeline features pass through the frame, with increased risk that reportable events are missed. Secondly, at higher speeds it can become challenging to…

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Read the article online at: https://www.worldpipelines.com/special-reports/13062024/the-future-of-subsea-surveying-unlocked/