A Vertical Mining System Concept Using DTH for Seafloor Mining

摘要

In the concept of subsea mining field development, a subsea crawler generally has a big drill and scrapesrnthe mineral deposit horizontally. In this “Horizontal Mining System (HMS)”, ores vary in size and largernchunks should be crushed into transportable particles. So the Subsea Crushing and Feeding Unit (SCFU)rnmust be required for efficient slurry transportation to use the traditional riser system. In this paper, wernintroduce and discuss our “Vertical Mining System (VMS)” concept, which consists of a Down-The-HolernDrill (DTH) unit mounted on a jack up platform. This vertical mining system can be used for bothrnexploration and production of the subsea mineral deposit.rnThe DTH unit makes the mineral deposit into powder-like particles while it digs into the hole. Wernexecuted drilling experiments on land with a granite rock using a DTH unit. The result showed the drilledrnparticle size were less than 1mm, which indicates that this method allows us to transport the ore slurryrndirectly through the traditional riser/pump system.rnBecause the ore particle is even and small enough, the Subsea Crushing Unit (SCU) can be eliminated.rnSo we believe the total project cost and period can be reduced compared to the HMS concept. Thernmaximum drill length can be from 30 to 50 m. The mining speed per a DTH is determined by the drillrndiameter and the drilling speed depending on the rock strength. At present, in our granite experiments, thernDTH drilling speed was around 3.0 cm/sec. The desired production amount is achieved by installing pluralrndrilling units.rnWe deploy the jack up platform instead of a crawler considering several reasons. The priority is wernneed to keep the xy coordinate of the drilling unit precisely controlled for efficient field layout. Thernsecond reason is we should keep the drill stem vertically even though the seabed has a slope or it isrnuneven. It is a gravity type jack up with 4 legs and has a set of xy horizontally sliding actuators whichrnenables us to position the drill units automatically on the seabed. The horizontal size of the jack up isrnaround 15 m times 15 m. The position of the platform will be changed continuously by suspending it withrnthe support vessel’s crane after it digs the 10 meters square seabed area. A subsea ore separator will bernsettled near the platform to select high-grade ore from low-grade ore on the seabed, which reduces notrnonly the transportation cost/time but also the amount of marine disposal from the surface facility.