Replacement of SPM Buoy Moorings – Engineering Challenges

Abstract For FPSOs/cargo ships with higher drafts, it is necessary to have a dedicated facility at offshore to load/unload petroleum products since it is impossible to approach shore due to shallow water depths near shore. This dedicated facility which is called as Single Point Mooring (SPM) buoy can handle extra-large vessels at offshore. SPM buoy is a floating buoy anchored offshore to allow handling of liquid cargo for FPSOs/cargo ships. SPM buoys serve as a link between shore facilities and the tankers. Considering the importance of SPM buoys in providing liquid cargo services to various ships, it is crucial to inspect and maintain the mooring components which holds the SPM buoy in position. Replacement and maintenance of mooring components needs to be carried out periodically. NMDC Energy, one of the leading EPCI contractors in Middle East recently was engaged in a project for the replacement of mooring components for an SPM buoy in Arabian waters. Mooring components adopted in the project includes anchor chains and piles and related hardware. Since the buoy was operational, replacement of its mooring accessories required considerations of tanker berthing and slack periods. Superimposing the tanker berthing schedules to the construction activities for the replacement provides realistic duration of the project and required multiple mobilizations. The sequential installation of anchor piles and subsequently the mooring chains for SPM buoy demand meticulous planning and engineering. The challenge gets compounded when multiple vessel types such as self-elevating platform and DP vessel are used. The establishment of clear sequence of operations and logistics are essential to initiate engineering feasibility assessments. This paper provides comprehensive discussion of all factors that needs to be accounted for seamless installation of piles and chains.