Delmar Systems, Inc., used multiple mooring techniques to successfully moor a semi-submersible drilling rig for BP at its Gulf of Mexico “Mad Dog III” location. Due to the sloping nature of the sea floor, Delmar moored Diamond Offshore’s Ocean Victory at the 4,300-foot location using a combination of the rig’s on-board mooring equipment and three preset mooring legs. The preset mooring legs were installed on location using Delmar’s patented Subsea Connector and single-vessel installation procedure.
The rig’s mooring system consists of conventional chain and wire segments attached to high-holding capacity anchors. The Delmar suction anchor legs consist of two suction anchors—one 9½-foot diameter by 60-foot long and the other 9½-foot diameter by 50-foot long. These suction anchors were connected to 3,000-foot x 3¼-inch sections of chain and 6,000-foot x 3 ½-inch sections of wire rope. Additionally, Delmar had preset a 15-MT Bruce anchor and subsequently connected the rig to this system upon arrival at location. Conventional anchor handling operations and connection to preset moorings were completed in an efficient 28 hours.
“Given the severe seafloor conditions, the ‘Mad Dog III’ location presented numerous design challenges in developing a sound mooring system,” said Evan Zimmerman, Delmar Chief Engineer. “Delmar modified and fabricated suction anchors from one of our standard designs to accommodate site-specific soils and loading requirements. Delmar’s suction anchor technology, efficient installation method and patented connector proved to be not only the most time efficient mooring system for ‘Mad Dog III’, but also the most cost-effective.”
Delmar’s suction anchor technology is expanding the field in which moored drilling rigs can operate. Until recently, only dynamically positioned vessels were able to operate in areas with highly varying bottom slopes.
“These same fields are now economically and technically feasible for moored vessels,” Zimmerman said. “With Delmar’s high level of suction anchor experience, mooring options are opening vast acreage in the Gulf of Mexico for conventional drilling rigs.”