A perspective by Robin Lohnes, CEO, Dominion Diving Ltd.
The demands of the offshore oil and gas industry have driven the advancement of all methods of offshore diving under the restrictive limits of human physiology. Offshore air diving is the traditional method for up to 50 metres of water depth.
Saturation diving is suited for depths of up to 500 metres, thus clearly illustrating a prominent depth advantage to saturation diving. Surface Decompression Air Diving systems are relatively simple in configuration and can be mobilized to a variety of DP2 vessels in a short period of time. Charter rates for a DP2 supply vessel can be as little as 20% of the charter rate of a saturation diving vessel.
Operating consumable costs of the air diving system are limited only to fuel for compressors/generators and oxygen for surface decompression. Rapid mobilization times, reduced costs of a DP2 vessel of opportunity, and the reduced operating costs of the air diving system make air diving the common choice for emergency and short duration subsea campaigns in the shallow offshore oil and gas fields.
Saturation Diving systems are complex and are typically integrated into a saturation Dive Support Vessel (DSV). The productivity of saturation diving surpasses air diving as it provides extended bottom times and a reduction in the required amount of divers. Additionally, the use of a closed bell deployed through a moon pool in the center of the vessel allows sat divers to continue operations in adverse weather conditions well beyond the parameters of air diving systems that utilize over-the-side wet bell deployment.
As a result of the significant increase in productivity resulting from saturation diving, it is the most widely used offshore diving method for oil field construction and complex repair campaigns.
Over the past 3 decades both sat and air diving equipment and procedures have been refined to meet or exceed the demands for both increased efficiency and productivity while adhering to a strict regulatory safety culture.
Maintaining a balance between cost, productivity, safety, and efficiency is accomplished by applying the appropriate method at the correct time and place with a full understanding of the array of tools available. Cost can be misleading in either direction if not evaluated against time and safety when choosing methodology.