Simplifying sampling

Elaine Maslin reports on Norway’s NUI newly developed seabed sampler, which will take any type of sediment while using an ROV.

The sampler during a test subsea.

Despite the best efforts by the industry to develop subsea robots capable of doing work traditionally done by divers, they continue to be needed, both on the Norwegian Continental Shelf and across the rest of the globe.

Some 2700 divers (including superintendents, air and saturation divers and support personnel) worked across the industry globally, according to 2012 figures from the International Marine Contractors Association.

While there are continuous efforts to make diving as safe as possible, there are always improvements that can be made and Norway’s NUI has come up with the latest. It has developed a solution for taking seabed sediment samples, which could be potentially contaminated from drill cuttings, produced water discharge, crude oil, mercury etc., and isolating them so that any noxious gasses in them cannot get into the diver’s quarters. The system will also mean that samples remain fully intact, between collection and the surface laboratory, with no gas leakage, to ensure analysis accurately reflects what is on the seafloor.

“Samples taken by traditional methods lose important information and might be contaminated, we have known that for years,” says Rolf Røssland, managing director at NUI, due to the way they have been collected in open samples. “The contamination [usually in the form of gases] from the seabed could seep into the bell or get onto the divers’ equipment and into the diving system.”

NUI’s subsea sampler. Images from NUI.

The consequence might be that hydrocarbons and or volatile organic compounds vaporize in the bell atmosphere, creating a narcotic effect, and contamination of atmosphere in the diving chamber system.

“The result of the sampling using traditional methods can also be questionable,” Røssland says, “as there are no standard requirements on how to take samples, where to take them, how to handle them, etc. There were also no standards for analysis.”

Changes are being made, from the top. Norwegian standards body NORSOK has introduced new standards, which stipulate that if samples are analyzed at the surface, any gases in the sample need to remain in the sample as it is transported from the seabed to the laboratory.

NUI’s response has been its seabed sampler, for taking any type of sediment, using an ROV, as well as standard procedures for collecting samples. The seabed sampler is an ROV-transportable rig, with pressure containers into which the samples are taken and, at the site, sealed until they are analyzed without being opened the laboratory.

The system has been through two pilot tests, the first with Statoil and the second with Total, both offshore Norway, using a work class ROV. The project with Total was in May 2015. After that the samplers has been operational and engaged with a client with good success. From lowering the rig, with three canisters, collecting and putting samples into each, using the ROV manipulator arm, which then closes the canister, to bringing the rig back on deck took one hour, Røssland says.

But, NUI hasn’t stopped there. Chamber systems still need to be environmentally monitored to make sure the air quality is correct for the divers. At the moment, samples are taken in 50cm-long pressurized cylinders, which have to be removed from the diver system and transported for analysis. The canisters take up space and weight and offer only a snapshot in time of the chamber atmosphere.

NUI has developed a system using absorbants to monitoring the air quality over long periods of time with testing possible in each chamber and even on individual divers, due to the small size of the carrier for the absorbents, at 11cm by 2cm deep.

NUI is owned by an association, with members including Statoil, Det norske, Repsol, Total, BP, ExxonMobil, and Gassco and has been developing and testing diving and remotely operated equipment from their facilities near Bergen since 1976.