SS - Ocean Mining "Extending Deepwater Technology to Seafloor Mining"

Abstract

ABSTRACT This paper builds on the experience of designing, and building production and drilling risers for oil and gas fields and extends into deepwater mining. With the recent discovery of high grade seafloor massive sulphides (SMS) in Papua New Guinea, New Zealand and elsewhere, there is a resurgence of interest in deep ocean mining. This renewal of interest has been spearheaded by Nautilus Minerals through its Solwara 1 project; in 1,700 m of water, with a production rate of 2.0 million tons per annum. Neptune Minerals Plc also endeavors to produce SMS with a similar production rate. This paper describes the two different deepsea SMS lifting concepts being developed by the two projects and the design challenges encountered during the course of the project executions for the two mining companies. Nautilus plans to explore other adjacent fields with water depths reaching and surpassing 2500 m. It will use a riser and a lift system that utilizes a steel vertical riser combined with a bottom-suspended displacement pump for lifting the mined ore slurry. Waste water is separated from the slurry and then discharged at the seafloor. Many technical challenges have to be overcome to achieve the required performance, especially in the areas of lifting solids in a two-phase flow. Among these challenges are erosion and corrosion issues, two-phase flow assurance technology, methods of defining the system operational windows, and the overall integration of the equipment packages for the brand new industry. Separately from Nautilus, Neptune Minerals Plc commissioned an engineering scoping study for technologies for the commercial development of SMS deposits offshore New Zealand. The scope of the conceptual study was to screen options regarding subsea mining tools and strategy, alternative SMS lifting methods, and SMS processing. The SMS mining options integrated existing marine equipment and technologies, and the recommended lifting system incorporates a flexible production riser with an airlift system connected at the seafloor to an ore crusher and seafloor miner. The objective of this paper is to describe the two deepsea SMS lifting concepts and approaches to help pave the way for the future development of systems of other potential miners. Both authors have been involved extensively in the development of deep ocean production and drilling systems for the last two to three decades. Various parts of their experiences were used for the overall deepsea mining system configuration and for the evaluation of the airlift and displacement pumps for lifting SMS from the seabed to the surface. The results depicted here draw heavily upon those experiences.