Accurate and Speedy Subsea Surveys Now Possible

By Khaled Aboud,
Global Business Development Manager at MCS

In the subsea world, engineers are facing severe challenges, which don’t exist onshore as the light can barely penetrate the depths, resulting in only a few metres visibility ahead, therefore engineers and surveyors have to depend on acoustic sensors to enable them to get a ‘rough estimate’ of the shape of the subsea structure that is being built or maintained.

However, these estimates often lead to inaccurate and very costly measurements of the subsea structures, which is dramatically limiting the industry’s ability to properly visualise them and therefore, to maintain them. Subsea engineering companies are often having difficulties and missing the precision accuracy needed to measure horizontal/vertical buckling of subsea pipelines for example, as the precision of the conventional methods is just not good enough.

Before MCS’ Photo Realistic 3D Cloud (PRC) technology was introduced, the industry standard was to rely on several laser-based techniques to conduct metrology jobs. However, because such methods require a lot of vessel time to be completed, this translates into very high costs. Moreover, the accuracy and precision of such methods relies on several operational conditions that can dramatically affect the quality of the job being done.

Particularly in deep waters, metrology measurements can cost as much as a staggering US$ 1 million and the preparation and deployment of the spheres and beacons on the seabed before any data acquisition phase takes place can take more than a few days. This compares to the PRC, which is one ROV mounted system, which can cover the field data acquisition in just three hours.

Reducing chartering costs
PRC is a cutting edge innovative technology to scan complete structures and pipeline sections underwater in order to create a 3D Cloud of millions of points, presenting the ‘as-built’ 3D visualisation of any scanned object, giving very accurate measurements to the nearest millimetre.

The essential requirements of this new technique were to be strong enough to work reliably in the harsh, restrictive subsea environment and to be even more accurate, if not better than the current acoustic methods.

Put simply, MCS’ PRC is a way to gain ‘the ability to see’. It allows engineers to precisely visualise the subsea infrastructure and it has the ability to measure to fabrication accuracy, but with the same simplicity as if the engineers are sat behind their desks ashore.

Additionally, while conventional methods are based on a ‘Static Mode’ from a tripod on the seabed, which then needs to be transferred from one location to the other to cover the required area, the PRC is used on ‘Dynamic Mode’, covering all the required area with no limitations of the altitude, speed or the area to be surveyed.

No limitations in altitude or speed
There are several applications for PRC, for example construction companies, can use it for Out-of-Straightness Surveys. Here it is possible to measure accurately up to a centimetre in both the vertical and horizontal 
dimensions to determine the pipeline shape.

Other applications include: pipeline lateral and vertical buckling surveys, spool measurements, subsea construction, decommissioning, repairs, free span identification, FPSO inspection and for onshore/offshore topside facilities.

PRC was recently used to carry out pipeline inspections for Zakum Development Company (ZADCO), which owns the Upper Zakum (UZ) offshore field located in the Arabian Gulf, 84 km from Abu Dhabi.

32 pipelines inspected
ZADCO has initiated the Upper Zakum Field Development (UZFD) programme, which is aimed at achieving a target oil production plateau rate of 750 K BPD from the UZ field. As part of Phase 1, ZADCO awarded the EPC contract to the National Petroleum Construction Company (NPCC) and Technip France Abu Dhabi Consortium.

As part of the contract, NPCC installed 32 pipelines. These had to undergo ROV surveys to make sure there was no damage to any pipelines or sleepers, lateral or vertical movements of the pipelines at the crossings, or examine if any pipelines are positioned very close to the edge of a sleeper. Additionally, the surveys had to inspect and report the type of support / bags [Mono Tunnel support bags, Grout mattress, Pyramid bags, sand-cement bags/ temporary supports etc.] and see if any gaps with the pipelines were evident.

An Observation Class ROV (Class II), Sea Eye Panther/Panther plus with two booms and three cameras were used for the survey and the software module package was provided by MCS. PRC was used for the first time in the ROV survey, replacing conventional MCS software.

After the ROV surveys using PRC, ZADCO then carried out spot inspections using divers to verify the ROV reports. Observations found that there was a variation of only 3 – 7 cm when it came to the difference in the crossing clearance measurements. Therefore, the PRC reading was verified and approved, and ZADCO felt there was no requirement for additional verification of the crossing height by divers as the PRC measurements were deemed accurate. The measurement of the Mono Tunnel grout bags from the edges were nearly the same and the free span length reported by the ROV was also acceptable.

‘Accurate and cost effective’
Overall, ZADCO was satisfied with the results and recommended using PRC software in future ROV surveys as it ‘proved accurate and cost effective because of the remarkable savings made in surveying time’.

And although PRC substantially increased the speed of inspections during this first surveying project for ZADCO, the company expects surveys to get even faster as everyone gets used to the new technology.

The Industry Contribution is a new section in which the subsea industry companies share their project endeavors or analyses. This article was produced by MCS and does not necessarily reflect the view of Subsea World News. No member of the editorial team took part in creation of this article. Please contact us at [email protected] for inquiries.