Back in the 90s, offshore moorings began to regularly be conducted in waters deep enough to require a taut leg system. This of course introduced uplift into the moorings which meant that drag anchors could no longer be used. As a result, suction piles with their massive size and weight became the most viable solution in the GoM as well as other soft soil deep water areas of the world. See here how suction piles work.
Noting this change in the industry and frustrated at the time and cost required to make and install suction piles, engineers at InterMoor put their heads together and tried to figure out a better way. What they came up with was a prototype for what we now know as the SEPLA or Suction Embedded Plate Anchor.
The SEPLA is a simple plate anchor that is fixed to the end of a specifically designed suction pile called a follower and drawn into the ground. The follower is then extracted leaving the inexpensive plate anchor embedded, with only a tailing ground chain remaining above the mud to connect with a mooring line.
The first trial the SEPLA would undergo was a shallow water installation in the Gulf of Mexico in 1998. During this exercise, the installation process would be validated, and the extraction forces shown to be consistent with predictions. This success would be followed by laboratory testing that would provide InterMoor engineering with the quantitative data required to define parameters and analyse mooring locations for the suitability of SEPLA anchoring. Finally, in the early 2000s a JIP (Joint Industry Project) was conducted to codify the SEPLA for use.
For the next decade, the SEPLA would be used extensively for temporary moorings throughout the Gulf of Mexico and other parts of the world. Drilling vessel locations would be planned and SEPLAs pre-installed for their arrival. After the vessel departed the location, the anchors would be recovered and reinstalled in a new advance location. All while InterMoor engineers continued to gather reliability data and refine the SEPLA design and installation techniques.
Today, the SEPLA is used for permanent moorings as well. With nearly two decades of service in all manner of soils, InterMoor has managed to demonstrate the robustness of the system to the satisfaction of entities such as ABS and DNV. It is becoming a preferred solution for FPSOs as the build time and cost are a fraction of that required for suction piles and the twenty to thirty-year lifespan is easily accomplished with the simple design.
The SEPLA has had a successful history over the past two decades, and it continues today with the two 12leg FPSO moorings InterMoor has built in the last year. But just as in the 90s when deep water brought about the initial need for the SEPLA, the more cost-conscious environment we work in today is bringing about the expansion of the SEPLA.
Full-size floating infrastructure with its massive mooring capacity requirements has always been the domain of suction piles, but that doesn’t mean it needs to be. The SEPLA design has always been scalable and now with the input from several leading organizations in the energy industry, InterMoor is actively designing the next larger iteration of the SEPLA.
The new design will have capacities equal to current suction pile systems, but for substantially lower cost and lead times. Additionally, just as the current SEPLAs may be installed from an anchor handling vessel, the new SEPLA will be designed to utilize simpler less expensive vessels. The industry is changing and InterMoor along with the SEPLA are changing with it.