Drilling and workover rigs on Floating Production Systems (FPSs) are typically tied down or fastened to the decks of offshore structures by ‘sea fastenings’ to prevent movement during hurricanes. During Hurricane Ivan, a number of drilling or workover rigs shifted. These movements are being assessed along with the current design philosophy and criteria for storm sea fastenings, rig and storm sea fastening installation practices, and onboard storm operational practices to ready FPSs for a hurricane. Results will provide information that can be used to assess any needs to revise tiedown criteria or practices to avoid future damage.
Drilling and workover rigs on Floating Production Systems (FPSs) are typically tied down or fastened to the decks of offshore structures by 'sea fastenings' to prevent movement during hurricanes. These sea fastenings can include large diameter bolts, weldments, braces, or other means.
During Hurricane Ivan, a number of drilling or workover rigs shifted. Possible factors that could contribute to these movements could include:
adequacy of design criteria for the storm sea Fastenings
proper design and installation of storm sea fastenings
operational practices to secure the rigs as a hurricane Advances
the intensity of hurricane Ivan loads on the storm sea fastenings significantly exceeding the design criteria
This project is being conducted in two Phases. Phase 1, being sponsored by the Minerals Management Service, is focusing on
Collecting information and data on Floating Production Systems (FPSs) in the path of Hurricane Ivan that had platform drilling or workover rigs.
Assessing this information to determine probable causes for the rig movements.
Assessing success cases where rigs sustained Hurricane Ivan forces without movement.
Completing an example case study comparing the actual behavior of a rig that moved during Hurricane Ivan with estimated rig loads and sea fastening capacities
Completing case studies of failures and successes of rig sea fastening systems during hurricane Ivan
Evaluate tie-down design options to prevent observed movements during storms
Review practices for exchanging rig/floating system information needed for sea fastening design
Document results and findings.
Figure 1 shows the locations of FPSs that were exposed to Hurricane Ivan. Table 1 lists FPSs exposed during Ivan, and indicates whether rigs were on board and if there was movement. There were four instances reported in which drilling rigs or rig related equipment on FPSs moved. Movements were reported to have occurred on
Ram Powell TLP
Horn Mountain Spar
Devils Tower Spar