Application of Drilling Fluid Circulation Technology to Lifting System for Deep-Sea Mineral Resources

Abstract Various types of deep-sea mineral resources such as mud containing rare earth elements, manganese nodules, cobalt-rich crusts, and methane hydrate are found on deep-water seabeds around the world. Lifting systems for mining these resources using a gas lift approach or submersible pumps have been studied by many researchers. As an alternative to these lifting systems, this study proposes a rare earth mud lifting system using a hydraulic jet pump, like those used for artificial lifting in oil wells. The objective of this study is to investigate the design of this lifting system to maximize the mud suction rate of the hydraulic jet pump by numerical simulation. The hydraulic jet pump simulations involved two-phase flow of seawater as the working fluid and rare earth mud slurry as the production fluid. The simulation results showed that all the considered hydraulic jet pump designs could suck in highly viscous rare earth mud slurry at an ocean depth of about 7,000 m. A design with three sets of suction lines and diffusers gave the best performance and could transport a rare earth mud slurry at commercially viable combinations of flow rates and mud concentrations. At a suction line diameter of 1″, the produced mud rate exceeded the commercial reference standard, with mud recovery rates of 10,500 ton/day and 15,800 ton/day when the volumetric mud concentration of the slurry entering the pump was 20% and 40%, respectively.