The Installation of Flexible Risers and Flowlines Systems With PLET on the Subsea End

Abstract

Flexible riser and flowline systems used in offshore oil and gas developments in shallow and deep water are typically terminated with vertical connectors with goosenecks or with horizontal connectors. An alternative arrangement is to terminate with PLET although it is not as commonly adopted. PLETs usually have a sizeable dimension and weight compared to the vertical and horizontal connectors hence present handling and deployment issues. A number of flexible risers and flowlines terminated with PLETs recently installed in a deepwater development in Gulf of Mexico showed that with careful engineering such deployment is viable and can be performed safely by a typical flexlay vessel. The installation engineering, installation aid requirements, the deployment methodology are presented and discussed. The observations from ensuing offshore operation showed that the flexible torsion and twist during deployment need to be carefully monitored and managed offshore. Flexibles terminated with PLETs could be potentially suitable where life of field gooseneck load may be excessive or for bigger and stiffer flexible products where making the 2nd end connections might be a challenging undertaking offshore. A PLET could also be used where an intermediate structure is required along a MEG line for example where In-Line Terminations (ILTs) are needed for flying leads plug-in. This would save on requirement for an intermediate structure and connectors.