InterMoor successfully replaced (8) spiral-strand platform wires on a permanent production facility in May 2011 without requiring a platform shutdown or loss of production. The operation was completed using a single Construction Anchor-Handling Vessel (CAHV) at a significant cost savings from the traditional method involving a derrick barge.
Each mooring line consisted of unjacketed spiral-strand wire at the fairlead, two sections of jacketed spiral strand in the water column and studless chain at the seafloor. Syntactic-foam submersible buoys had been installed at each spiral-strand wire connection, so each mooring line had two buoys.
Only the platform wires were to be replaced, and the remaining mooring components including the buoys were to be reused. Protecting the existing components from damage during recovery and reinstallation posed several unique challenges. One of the main operational challenges was to design a way to bring the upper buoy and platform wire out of the water and secure them on deck so that the old platform wire could be disconnected. To accomplish this, InterMoor designed and installed a custom hang-off porch at the CAHV’s stern. The porch used a combination of pneumatic and hydraulic cylinders to manipulate and align the entire porch as each buoy connection was recovered and deployed. The porch also had separate stoppers for the socket connections and a removable cradle for the buoy. Another operational challenge was the unknown condition of the buoys themselves, particularly since they were to be reused on the replacement wires. There was no industry experience at the time in retrieving foam buoys that had remained submerged at depth for over a decade. This paper will explore these challenges and others in more detail as well as the steps that were taken to successfully overcome them.
As oil and gas developments go deeper, the risk related to lifting operations is increasing. “Existing standards and regulations don’t sufficiently meet this challenge and this is why DNV now has initiated a joint industry project to ensure a unified safety approach. Fourteen key international offshore players have joined the project,” says Robert A. Oftedal, DNV’s Business Development Leader, Cranes & Lifting.
The development of subsea cranes and lifting appliances has been driven by constant demand for increased lifting capacity, operations in greater water depths and motion compensating systems. This has introduced several technological challenges related to ensuring the reliable execution of subsea lifting operations so that objects can be safely placed on and removed from the seabed.
Ensuring proper design and correct operation, as well as regular inspection and maintenance, is crucial for not only the reliability of a lifting appliance, but also the safety of the personnel and equipment involved.
According to DNV, subsea lifting standards and regulations have not followed the steep curve of technological progress. “Instead, the required safety level has been defined by clients’ specifications, technological boundaries and manufacturers’ considerations, rather than regulatory documents acknowledged by all the stakeholders involved. Some client specifications may also be based on vessel-to-platform lifting and not subsea lifting. This situation is a challenge when contracting new equipment,” Oftedal explains.
While various measures are undertaken by different parties, implementing standards and regulatory requirements has proven to be one of the most efficient ways of reducing the risks involved in offshore operations.
“This is why DNV has invited the industry to develop a unified approach concerning important aspects of subsea lifting. The aim is to increase efficiency and safety during the equipment’s design, operation and maintenance phases,” he says.
Fourteen key industry players have joined the project and will present their conclusions in a Recommended Practice within a year. The participants are: Statoil, Petrobras, Lundin Norway, Marathon Oil Norge, Technip, Subsea7, SAIPEM, Heerema Marine Contractors, Cargotec, Liebherr Werk Nenzing, TTS Energy, Huse Engineering (incl. Rolls-Royce), SamsonRope and W. Giertsen Services.
- USA: Deep Down Inc. Receives Subsea Equipment Orders (mb50.wordpress.com)
- Norway: Statoil Orders Subsea Structures for Asgard (mb50.wordpress.com)
- Shell Awards Subsea 7 with Two Gulf of Mexico Contracts (mb50.wordpress.com)
- Ichthys: The Largest Subsea Gig for McDermott (Australia) (mb50.wordpress.com)
- UK: Talisman Selects Helix Well Ops for Subsea Works on Its Assets (mb50.wordpress.com)
- Norway: Subsea 7 Charters Island Intervention Vessel (mb50.wordpress.com)
- USA: EMAS Wins Gulf of Mexico Subsea Contract from BP (mb50.wordpress.com)