Because many fundamental questions concerning the dynamics of the Earth and itsstructure remain unanswered, the Integrated Ocean Drilling Program (IODP) hasrecently completed a feasibility study for drilling and coring a hole 500meters (1,640 feet) through the Mohorovicic seismic discontinuity into theupper mantle of the oceanic crust from three candidate locations in the PacificOcean (Cocos Plate, Baja California, and offshore Hawaii). The main challenges discussed in this paper are threefold. First, drilling withriser in ultra-deepwater environments with water depths around 4,000 meters(13,120 feet) which will set a new world record. Secondly, drilling and coringin very high temperature igneous rocks with bottom-hole temperatures that areestimated to be as high as 250°C (480°F). Finally, drilling and coring a verydeep hole with a total drilled and/or cored interval around 6,000 meters(19,685 feet) in the oceanic crust below the Pacific Ocean seafloor in order toreach the upper mantle which will constitute a major achievement for theworldwide scientific community. This paper presents detailed analyses and several discussions concerning marinedrilling riser options by first reviewing the capabilities of the current riserconfiguration that is onboard the IODP scientific drilling drill-ship Chikyuand then evaluating alternative designs such as titanium riser, hybridtitanium-steel riser, slim-riser and lighter buoyancy modules. Furthermore, thedeepwater subsea equipment, drill-pipe design, wellbore design, down-holetools, drilling fluids, circulating temperature, cementing methods and variousadvanced technologies that would be required for this type of operation arealso reviewed. In addition, operational time and cost estimations for differentscientific drilling cases are provided (borehole continuously cored to totaldepth, continuous cores only across the major lithologic and geophysicaltransition intervals, spot coring and when only the mantle section iscored). Finally, this study helps evaluate critical issues in terms of current andtrending technologies in oilfield and geothermal industries that need to beresolved before embarking upon such a challenging project. The results of thiswork show that drilling to the mantle is certainly feasible, and that there areexisting solutions to many of the technological challenges based on work beingdone in the oilfield, offshore and geothermal industries.
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