Design and Installation of Coupled Mooring System for Tender-Assisted Drilling at a Deepwater TLP

Abstract

Abstract The first Tension Leg Platform (TLP) in Malaysian waters was installed in 2016 at a water depth of about 500 m. It is notable in being the 2nd deep water platform in Malaysia with tender-assisted drilling (TAD) feature. The semisubmersible TAD vessel was connected to the platform using nylon hawser ropes which together with chain-polyester-wire moorings on the TAD and TLP allow for station-keeping during drilling operations. This paper describes the planning and execution of the mooring installation campaign. The paper also brings up key learnings from the campaign that may be useful to consider for risk reduction in future projects of similar nature. Mooring system was purpose-designed for the TAD vessel with ground chain and polyester segments connecting to rig wire for each of its 8 mooring lines. Installation plan was based on pre-installing suction piles and pre-laying ground-chain and polyester. These pre-laid moorings were then retrieved for hook up to the TAD at site. One of the major challenges was identifying suitable pre-lay routes for the lines due to widely prevalent geo-hazards and exclusion zones on the seafloor. Close attention was also given to installation methods of hawsers between the TLP and TAD with emphasis on minimizing personnel exposure to risks of working under tensioned lines and over water. The installation campaign involved several vessels in the field simultaneously operating in the field and was closely coordinated with efficient SIMOPS plan and execution. Early engagement with various disciplines and stakeholders is crucial in minimizing risks. Interfaces with engineering contractors, geomatics and geotechnical teams, component suppliers and installation contractors were instrumental in safe and injury-free installation and hook-up campaign of the TLP-TAD system currently under operation. One question that is brought up is to do with risks versus values of load-testing synthetic mooring lines in field. While the need for such tests is well known, operational and safety risks require close attention.