Remediation of On-Bottom Stability (OBS) Issue During Offshore Installation of Light Weight Structure (LWS) at Malaysia Water

This technical paper presents the strategy adopted by COMPANY for Remediation of On-Bottom Stability (OBS) Issue during offshore installation of Light Weight Structure (LWS) at Malaysia Water at water depth of 54m. The knowledge sharing is based on the successful remediation work in managing the OBS issue where the substructure experience excessive tilting. The LWS is designed with minimal mudmat. In addition to that, the subsea pin pile is designed to improve substructure on bottom stability issue during substructure installation. However, during actual offshore installation of substructure, the behavior of the substructure upon setting down on seabed was not as per the intended design where the substructure tilting is observed after substructure landing onto pin pile. As mitigation, the following approaches have been implemented to safeguard the substructure from toppling: Safeguard of SubstructureRisk assessment and immediate action have been taken by temporary safe holding the substructure by connecting holdback lines between substructure and installation barge bollards.Revisit OBS engineering study and analysisRevisit on bottom stability engineering study and lifting analysis considering changes to procedure/method by increasing the initial pile length (82m) to allow for early self-penetration.Revisit pile installation and sequenceThe piles have been re-fabricated onboard installation barge by utilizing the chaser rack at DB portside.The chaser rack was fabricated at site with available surplus material onboard DB. Once the revised pile fabrication completed, the piles were installed into the substructure leg for self-penetration.Result of Remediation WorkAfter successfully securing the substructure by installing the 82m pile length at one (1) leg of substructure, it has resulted that the substructure OBS has been improved to allow the COMPANY to proceed with original installation plan sequence as per installation procedure. Ultimately, COMPANY has managed to avoid catastrophic event. Despite all the challenges, the installation of LWS were completed successfully, no damage to property and most importantly with Zero Lost Time Injury (LTI).