Leonhard Weixler

Preliminary Design of a Trench Cutter System for Deep-Sea Mining Applications Under Hyperbaric Conditions

Seafloor massive sulfides (SMSs) are formed as precipitation products from hot hydrothermal fluids as a result of mixing with cold seawater and are mostly found at depths between 1500 and 3600 m. These deposits are formed in tectonically active zones of oceans (midocean ridges and “back-arc” spreading systems) and are the result of the global heat transfer from the mantle in the oceanic crust. As these fluids mix with the cold surrounding seawater, metal sulfides in the water are precipitated on or in the nearby seabed. The appearance of the solid mineral occurs as cylindrical chimney structures: the so-called black and white smoker (caused mainly by the presence of iron, copper, zinc, and sulphur). Larger sulfide occurrences are mostly originated in several generations of hydrothermal cycles, and they form deposits that can range from several thousands to about million tons. SMS contains pyrite (iron), galena (lead), sphalerite (zinc), and chalcopyrite (copper). Deep-sea mining is concentrating now to exploit such deposits. So far, the only known commercial project is the one developed by Nautilus Minerals, which is based on a horizontal system. This paper describes a preliminary design of a novel cutting tool developed for a vertical mining approach. The vertical mining method is preferred when rough terrain is expected and the device is easy to relocate. Using an atmospheric and hyperbaric cutting model, the cutting energy for two selected SMS deposits has been estimated and validated with real onshore excavation sites performed with a cutting tool normally used for diaphragm wall installation (i.e., the trench cutter technology). Preliminary results suggest that the estimated cutting energy ESP is 2.9 times higher with respect to the measured one in atmospheric conditions. This could be because the model considers the worst case scenario, i.e., higher energy due to the maximum cutting forces assumed. This factor has been used to design a cutting tool which is able to work up 2000-m water depth to mine SMS deposits.

Latest Technological Developments in Offshore Deep Mixing for Piled Oil and Gas Platforms

This paper presents some recent technological developments in deep mixing for the offshore sector. Deep mixing methods comprise in-situ soil treatment technologies where binding materials are added and blended with the original soils in order to improve their mechanical properties. The MIxed Drilled Offshore Steel (MIDOS) pile is introduced in this paper, which takes advantage of such deep mixing technologies. The comparison between the API approach and CPT-based methods for the prediction of the pile capacity are provided to validate the capability of the MIDOS pile as a foundational element for oil&gas structures in different geological conditions. The theoretical calculations are intended for initial estimation of pile sizing only and are not intended as a detailed design method.Copyright

Drilling Technologies for Offshore Foundation Engineering

Offshore piles are normally installed by driving using over-water or underwater hammers. However, there are many situations where pile reaches refusal before the installation depth. This paper briefly describes the current offshore foundation practice, the BAUER technology for onshore pile installation by drilling, the BAUER experiences in the offshore foundation and geotechnical fields and a new technology for supporting offshore pile installation when refusal is prematurely reached by means of the Dive Drill.Copyright