Deep-sea mining : dewatering plumes, vortex-induced vibrations and economic modelling

Abstract

Deep-sea mining activities are expected to commence in the next decade; the International Seabed Authority (ISA) has already issued twenty nine exploration licenses for polymetallic nodules, polymetallic sulphides and polymetallic crusts. The ISA is seeking to approve the exploitation regulations for polymetallic nodules in the next two years, but there are significant research and knowledge gaps that still have to be explored. The discharge of dewatering plumes, the analysis of the effect of vortex-induced vibrations (VIV) on mining risers, and the development of updated and detailed economic models -which are among the most pressing ones - are addressed in this thesis. PLUMEX field studies were conducted in the Pacific Ocean to create and monitor six dewatering plumes. The data obtained from the experiments will be used to validate analytic and numeric plume models that will help to assess the environmental impacts. Additionally, a preliminary VIV analysis of a simple riser configuration was conducted to show the significant impact of VIV on the fatigue life. The results showed that the fatigue life could be reduced to less than one year. Lastly, an independent and thorough economic model is being developed at MIT to allow the simulation of different scenarios and forecast the economic result of a polymetallic nodule exploitation. The ISA will consider the results from the model to determine the royalties and fees that will be paid by future contractors in order to share their benefit with the humankind.