DESIGN OF FIXED-TYPE OFFSHORE PLATFORM STRUCTURES UNDER IN-SERVICE CONDITIONS AND TOPPLING ANALYSIS DURING RIGS-TO-REEF DECOMMISSIONING USING THE PARTIAL REMOVAL METHOD

• Main Author: Azhari Rahim, Ilhan
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/86441
• Institution: Institut Teknologi Bandung

The oil and gas industry, in fulfilling global energy demands, requires the exploration of oil wells located in both deep and shallow waters. Offshore platforms are essential for supporting this exploration, and structural serviceability analysis is required to assess the loads acting on the structures in the field. These analyses include in-service evaluations such as in-place, seismic, and fatigue analysis. As many offshore platforms, particularly in Indonesian waters, approach the end of their operational life, decommissioning becomes necessary. One method of decommissioning is the Rigs-to-Reef process, in which inactive offshore platforms are converted into artificial reefs on the seabed. In this final project, a toppling analysis is conducted on a segment of a jacket structure as part of the rigs-to-reef decommissioning process, using tugboats as an alternative to topple and control the structure's descent. Toppling is a method of overturning offshore structures from an upright position to a horizontal position on the seabed. The analysis includes determining the rigging configuration during the toppling operation, such as the configuration for pulling the structure using slings, and the rigging configuration for controlled lifting by modeling rigging lines as the structure topples under its own weight. Analytical calculations are performed to determine the forces required by the tugboat and slings to topple the structure, as well as the forces needed from the tugboat and rigging lines to stabilize the structure during the descent. The analysis also involves checking the integrity of the jacket structure during the toppling operation, selecting appropriate slings, and calculating the necessary bollard pull capacity and brake horsepower (BHP) to recommend suitable tugboats for the operation. The analysis follows the criteria set forth in API RP-2A WSD and is conducted using SACS software and Microsoft Excel.