Interaction between Deepwater Catenary Risers and a Soft Seabed: Large Scale Sea Trials

May 2001
N. Willis, P. West

Abstract The paper describes experiments completed in June 2000 as part of the STRIDE JIP – Steel Risers in Deepwater Environments 1,2.

Environments1,2 . The tests investigated the interaction between a soft clay seabed, typical of deepwater developments, and a steel catenary riser (SCR). ROV surveys of deepwater SCR’s attached to floating production vessels have shown that they can cut deep trenches into the seabed. The following objectives were set:

  1. (1) To assess the effect of seabed to SCR interface forces on local riser stresses for wave and slow drift vessel motions
  2. (2) To assess the effect of different riser trenches on local riser stresses for wave and slow drift vessel motions
  3. (3) To identify the key trenching mechanisms and rates.
  4. (4) To use the test program findings to benchmark riser FEA tools, and to adjust modelling parameters to better simulate the real case as necessary.

To achieve this, the seabed end of a deepwater SCR was simulated using a 360-ft long 6-inch diameter steel pipe, hung as a catenary across the soft seabed of a tidal harbour. A particular harbour location was found that had seabed properties similar to those of a deepwater Gulf of Mexico seabed. The top end of the pipe string was then actuated with carefully controlled wave and vessel drift motions to simulate a spar platform in 3,300-ft water depth.



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