Suction Caisson Anchors - a Better Option for Deep Water Applications

As offshore exploration and development of oil fields reach water depths of 1,000 to 3,000 m, novel methods of anchoring production platforms become attractive due to cost savings associated with installation. Surface production systems that are viable in these water depths include Tension Leg Platforms (TLP), spar platforms, and laterally moored ship-shaped and semisubmersible vessels. Possible anchor systems for TLP and spar platforms include the traditional driven piles, drag anchors and suction caissons. Suction caissons become better alternatives to driven piles in deepwater because of technical challenges and costs associated with the installation equipment. In addition, suction caissons also provide a greater resistance to lateral loads than driven piles because of the larger diameters typically used. Initial penetration of the suction caisson into the seabed occurs due to the self weight; subsequent penetration is by the “suction” created by pumping water out from the inside of the caisson. This paper presents a brief overview of what the current state of knowledge is regarding the design of suction caissons. In addition, the paper also documents some finite element analyses results that were conducted to determine the capacity of suction caisson anchors founded in soft clays, typical of the Gulf of Mexico.