FloaTEC's New Dry Tree Semisub Design Passes Test

FloaTEC, LLC has completed Phase-2 testing of their latest ultra-deepwater dry tree units, the Extendable Draft Semi™ (E-Semi™) and the Truss Semi™ (T-Semi™). The model test programs were conducted at the Bulgarian Ship Hydrodynamic Centre in Varna, Bulgaria and the Offshore Technology Research Center (OTRC) at Texas A&M University in College Station, Texas, respectively.

Both units are in fact low motion semis that are now qualified to support dry tree risers in ultra-deepwater up to 10,000 ft. Another significant feature is the quayside integration capability, thus eliminating the need for a heavy lift construction vessel offshore to install the topsides.

The objectives of the in-place model tests were as follows:

  • To confirm applicability of the units' design for Gulf of Mexico (GoM) post-Katrina metocean conditions.
  • To confirm that the air gap is sufficient.
  • To verify numerical predictions of in-place global responses, including platform offsets, deck accelerations, and mooring line/riser tension responses
  • To measure the forces at the truss-hull connections, and riser top/bottom tension

Although the tests were based on a unit in 4,300 feet water depth, the design can be scaled to accommodate payloads in water depths up to 10,000 feet. "I was very pleased with the tests," said John Murray, director of Technology Development for FloaTEC. "They confirmed our design tools and gave an indication of the nonlinear-type responses that can only be quantified in these model test campaigns."

Both designs utilize a modified version of FloaTEC's proprietary deep draft semi hull design and rely on hydrodynamic interaction between the heave plate and the hull to reduce motions. The draft enables quayside integration, provides for maximum flexibility when it comes to construction options; and the motions are limited to enable the use of commercially available tensioners, currently limited to under 30-ft stroke.

As many reservoirs are highly complex and will require frequent well intervention to effectively produce the reserves, particularly in the ultra-deepwater GoM, the dry tree semi offers a viable development option. Since the deepest dry tree system currently installed is in only 5,610 feet of water, extending the water depth capability of dry tree systems to 10,000 ft will enable cost effective development of many new discoveries.

The next step is to publish the results of these tests in appropriate periodicals and use the information to promote the concept. FloaTEC expects to make both designs commercially available to the market in 2009, to satisfy market demands.