A large part of the fleet of platforms in Malaysian waters are ageing with the increasing demand of enhancement in view of further oil recovery and the additional development in the extended and nearby field. The enhancement process will also require development of new facilities to comply with performance and integrity requirements. The integrity issues imposed thus needs to be dealt with multi-disciplinary efforts that include a fresh regional seismic hazard mapping. To address this, a site specific assessment was carried out in 2009 for Sabah, Sarawak and West Malaysia offshore concessions in the South China Sea. The study concluded that the use of standard ISO spectral maps to be unconservative for the seismotectonic conditions offshore Malaysia. A modified spectrum shape, generally consistent with the ISO 19901–2 had been developed to match expected ground motion in each of the three blocks.
To formalize this, a new guideline has been developed for the seismic assessment of existing platforms as well as newly built fixed structures in Malaysian region.
The impact of the modified spectrum was assessed and recorded for selective platforms in these regions. This, in combination with the newly developed framework of adopting Performance Based Design, will form a complete guideline closely aligned with Petronas performance target and HSE expectations.
Fundamentally, offshore platforms shall have adequate strength against all effects influencing their structural integrity. The seismic requirements are intended to reduce risks to persons, the environment and assets to the lowest level that are reasonably practicable. The technical aspects of the developed seismic criteria can easily be implemented in future designs. However, understanding of the effect on the fitness-for-purpose of the existing structures in line with the ISO requirements are also essential. Particular emphasis to be given to the systematic inspection and subsequent integrity of topside connections of the existing facilities.
