Protecting offshore oil terminals from wave action using innovative floating breakwaters

Loading into or unloading of oil and gas from very large crude carrier (VLCC) normally happens in the open sea, since water depth of about 18 to 22 m are needed for such vessels, and ports to accommodate such vessels are not available everywhere. For example, in Kuwait, oil loading terminal is located at a distance of 12 km from the coast at a mean water depth of 20 m. The waves at this location are predominantly approaching the mooring vessels from northwest and southwest and are moderate most of time, with wave heights less than 1.0 m for more than 85% of the time in a year. Wave height exceeds more than 2.0 m for up to 15 days in a year. During such wave climate, oil loading operation is risky. Stopping one day of oil loading operation means revenue loss of about 100 million US $ to the country. Hence it is required to reduce the wave climate around the loading terminal. Construction of any fixed wave barrier like offshore rubble mound breakwater will be out of question for few reasons. It will be prohibitively expensive (for example, each m run of the offshore breakwater will consume more than 1000 m3 of stones, which will cost about 20,000 KD/m run and hence for say 1000 m length of an offshore rubble mound breakwater, it will cost about 20 million KD); presence of such fixed structure is a navigational hazard; reorientation is not possible when the incident wave direction changes significantly from one season to another season. Kuwait Institute for Scientific Research has carried out studies on Floating breakwaters (FBW). The wave transmission and mooring forces were measured for a wide range of wave conditions. Studies were carried out on conventional pontoon breakwaters and then on FBWs with different number of skirt walls fixed at the keel of the pontoon FBWs. Wave transmission is found to be reduced significantly (to the order of 25% to 60%) by adding three or five skirt walls. However, mooring forces are increasing to an extent of 20% to 30%. A basic design and cost analysis is carried out for the floating breakwater and is compared with the rubble mound offshore breakwater. For the floating breakwater with skirt walls, the volume of material required is less than 10% of the material for rubble mound breakwater and cost saving to the tune of 50% to 70% is possible. The cost for construction and installation of such floating breakwater for 1 km length will be about 3 million KD, which is about 10% of the earnings/day of export operation. The results of this study can be used for cost effective design of floating wave barriers and loading of crude oil can be done for the whole year with less risk induced by the wave actions.