Abstract
Management of geohazard risks and lowering the costs can only be achieved by adopting an out-of-the box thinking for the development of novel techniques. To meet the expectations innovative lay analysis has been developed for laying of umbilical and flexible flowlines of Jangkrik Complex Project. The complex comprises subsea wellheads in water depths down to 430m, tied back to the FPU via 9 flowlines and 7 umbilical's resting on a seabed along routes including major escarpment areas with undulous terrain while descending mountains at angle up to 50 degrees, seabed surface varying from soft clay & silty sands to weak coral area, and passing through large boulders area.
The new approach is based on dynamic continuous lay method used in installation analysis. This method is an improvement to the normal static steps lay analysis method that produces unrealistic results in steep slopes. The discrepancies occur as by laying of product and moving of vessel forward in each static step, software solves for the static equilibrium position by iterating to achieve zero out of balance force thus affecting the friction force in equilibrium and residual tension at TDP. This new method remembers line motion history to capture the correct frictional effects and residual tension at TDP.
The most significant benefit of this novel technique is in reducing the overall cost of the project by reducing the offshore installation complexity by minimising seabed intervention work and speeding up the operational time. This method has significantly reduced the required length of protection such as the Uraguard™ and VIV strakes along the span section by identifying only the critical free spans. This paper introduces the dynamic continuous lay method and compares it with the conventional method, and further validates the accuracy level of this technique by comparison of obtained results with offshore survey data. High accuracy level in defining of residual lay tensions leading to predict correct free spans on uneven seabed and has proven to be vital cost saving for similar projects.
