The Campos Basin, offshore Rio de Janeiro state, is the centre of Brazil’s thriving deepwater oil and gas industry and produces approximately 80% of Brazil’s oil. Here water depths range from 80 to 3,000 metres and in order to help maintain pipelines, subsea structures and offshore rigs, divers are required to operate at depths down to 300 metres.
In the very early stages of commercial diving, it was believed that no human being could safely dive deeper than 100 metres. The narcotic effect of the nitrogen content in air at increased partial pressure can lead to impaired reactions and confusion – a condition known as nitrogen narcosis. Safe diving operations below the 100 metre depth limit resulted from new technologies, the introduction of a helium/oxygen breathing gas and new procedures.
Replacing a technique known as ‘bounce diving’ – used by divers installing the foundations of the 8 mile-long Rio-Niteroi bridge – saturation diving came to Brazil in the late 1970s with the expanding offshore oil and gas exploration industry. This method of diving allowed longer bottom time and was increasingly in demand when Petrobras made oil discoveries in the deepwater Campos Basin.
The term ‘saturation diving’ refers to the fact that the divers’ tissues absorb the maximum amount of inert gas possible, i.e. they become saturated. They are kept under pressure in a deep diving system (or saturation system) mounted on a diving vessel. A diving bell (submersible decompression chamber) is mated to the saturation system, allowing the divers to ‘transfer under pressure’; they are lowered to the underwater job site in the diving bell. The divers work in teams of two or three, with one diver always remaining in the bell to act as a rescue diver in case of difficulty.
The diving bell is connected to the surface by an umbilical which supplies breathing gases, hot water heating, lights and communications; it also sends real-time video of the diving operations to the diving supervisor at the surface. The bell is deployed for a maximum of eight hours before the divers are returned to the surface, sealed in the bell at the storage depth and pressure. They ‘transfer under pressure’ to the saturation system for a rest period whilst underwater operations are resumed by another team of divers. Following saturation, decompression can be a lengthy process – typically taking up to 11 days in the Campos Basin. The pressure is reduced gradually, following well-defined decompression tables, and the breathing mixture is changed until the divers reach the surface to breathe normal air.
Saturation divers are selected on the basis of temperament, discipline, attitude and experience. Spending up to 28 days sealed in a saturation system chamber with other divers is certainly not for everyone! Most divers in Brazil are between 30 and 60 years old and have been trained at the navy school in Rio de Janeiro. Their diving career usually begins as a shallow (air) diver where they acquire the right skills and experience before progressing to deep diving.
Fugro has saturation teams of 14 to 18 operating in water depths up to 300 metres. Three simultaneous operations were recently conducted onboard specialised diving support vessels.
Our air and saturation diving services are reinforced with dedicated dive support vessels, ROVs and surveying for subsea intervention.