Suction anchors are used in ultra-deepwater for systems requiring taut or semi-taut preset mooring systems. Delmar has installed and retrieved more suction anchors than any other offshore contractor.
This system uses a suction caisson as the anchor. The caisson is cylindrical in shape with the bottom end open. Embedment of the anchor is accomplished by using an ROV to pump water out of the top of the caisson until it is fully penetrated into the seabed. The process is simply reversed to recover the anchor.
A rig- and location-specific mooring analysis can determine the desired configuration for each system.
The suction anchor system is installed using Delmar's proprietary single vessel/single line installation method before the rig arrives, which uses one vessel with ROV capability. The anchor is overboarded, lowered, and pumped into the seabed. The preset mooring line is attached and suspended with a surface or submersible buoy, awaiting rig arrival.
Once the rig is on location, it is connected to the mooring legs by one or two anchor handling vessels (AHVs) in a short amount of time.
The recovery of the system is a simple process with the suction anchor being pumped out of the seabed and recovered over the stern of the vessel.
Delmar's suction anchor system incorporates the patented Delmar Subsea Connector (DSC), which allows the anchor to be deployed with a single line and the mooring line to be connected or disconnected at any time by an ROV.
This capability adds significantly to the flexibility of the system and reduces the cost of installation and recovery.
The advantage of the suction anchor mooring system is the anchor's ability to hold at higher uplift angles, thereby reducing the circumference of the mooring pattern and watch circle maintained by the rig. The suction anchor system provides excellent performance in ultra-deepwater and allows a rig to significantly extend its water depth capability.
Another significant advantage of the suction anchor is the ability to target an exact location, its soil-holding properties, and alignment to the rig, allowing confidence in the anchor's ultimate hold capacity. Submersible syntactic buoys in the mooring system reduce the weight of the mooring leg on the rig.
The suction anchor system is a safe and cost-effective alternative to dynamic positioning for ultra-deepwater drilling and development. The use of the Delmar Subsea Connector makes the system ideal for permanent installations where a single AHV can install and maintain the entire mooring system at a fraction of the cost required for conventional permanent mooring.