This paper presents an alternative method for decommissioning offshore wellhead platform using converted flat top barge as decommissioning barge. The barge shall have capability to self-decommissioning topside and jacket and transportation to disposal premises. The key advantage for this propose new concept is to eliminate using of heavy derrick-crane vessel for all decommissioning activities, this can help to reduce cost for decommissioning in significant magnitude and also reduce marine hazards due to heavy lift handling. The barge will be installed with accommodation module, special tools and equipment such as mooring system, reverse float-over lifting with heave-compensation system & skidding appliances, jacket bottom lifting appliances and etc. in order to perform decommissioning activities under opensea environment with only minimal assist from marine support vessel. The decommissioning barge concept is designed to suit with various sizes of wellhead platform. Extensive engineering study has been performed in term of naval architect and structure engineering to proof feasibility of decommissioning barge concept and the existing platform located in Gulf of Thailand where is prone to Typhoon extreme sea condition. The study result shows that modify barge is feasible to perform decommissioning of various sized wellhead platforms. Applicable worldwide offshore and Southeast Asian fields, present many similar platforms where this innovative tools can be used to make an economy of scale in the removal operations. The feasibility study also include scope of explore opportunity to further improvement in term of flexible operation and cost saving. The following two options are performed the high level feasibility study and cost sensitivity with positive result outcomes.
Option 1 -Decommissioning barge with self-propelled system
Option 2 -Decommissioning barge with self-propelled with control stationkeeping capabilities
In term of cost saving, sensitivity study to compare the cost with conventional method is perform. Based on decommissioning execution over an entire service life, the decommissioning barge can gain cost saving over 23%.