Diving and ROV Services are used for a number of subsea construction, installation, inspection, repair and maintenance activities throughout the exploration, development and production oil and gas lifecycle. Depending on the type, complexity and water depth of the task different approaches may be used to carry out the work at hand. The approaches can be broken down into 3 sub-categories;
- Air or Mixed Gas Diving
Air or mixed gas diving is used at depths no greater than 75msw depending of the mix of gas used. At any greater depth than 50msw saturation diving is preferred to avoid the risks of decompression sickness and allow divers to work at depth for longer.
Air or mixed gas diving relies on the supply of breathing gas from the surface. Gases used may be oxygen, or a mixture of oxygen and nitrogen (Nitrox) or oxygen and helium (Heliox). Oxygen and nitrox is used a shallower depths (50msw) with heliox and provide a bottom time of no more than 50 minutes at such depth. Like wise, Heliox may be used down to 75msw however with only 30 minutes bottom time. Depending on the working depth divers may be lowered to depth in a basket or a wet bell.
- Saturation Diving
"Saturation'' simply refers to the fact that the diver's tissues have absorbed the maximum partial pressure of gas possible for that depth as a result of the diver having been exposed to breathing gas at pressure for a prolonged period. This is significant because once the tissues become saturated, the time to ascend from depth and to decompress safely will not increase with further exposure. This means that SAT diving enables divers to live and work at depths greater than 50 m for days or even weeks at a time. It is a type of diving that allows for greater economy of work and enhanced safety for the divers, since, after working in the water, the divers can rest and live in a dry pressurized habitat on the ocean floor at the same pressure as the work depth. The diving team is compressed to the working pressure only once, and decompressed to surface pressure once.
- ROV Services
Due to the inherent risks involved in traditional manned diving, technology advances continue to allow more and more underwater tasks to be performed using Remote Operated Vehicles (ROV's). ROV's are underwater robots of different sizes and capabilities that are operated from the surface by special trained ROV-pilots. These robots can be fitted with cameras, manipulators, survey sensors, and other tools for specific construction and inspection tasks, and are used for offshore and inshore projects.
Each approach utilises a floating base, most often a vessel of some sort, although barges or fixed platforms may be used. As will be shown in more detail below, depending on the nature of the task, the depth and approach selected vessel selection may include modified AHTS, PSV or Multipurpose Platform Supply Vessels (MPSV's) as well a specialised Dive Support Vessels (DSV's) tailor made to support the diving activities.