Â鶹ÒùÔº

The Integrated Ocean Drilling Program (IODP) has announced completion of a feasibility study of drilling and coring activities that would be conducted in an ultra-deepwater environment into very high temperature igneous rocks to reach the upper oceanic mantle.

This initial feasibility study focuses on future requirements for planning, drilling and coring a hole through the 6 km-thick oceanic crust and the crust-mantle interface or "Moho", then 500 meters into the mantle from three candidate locations in the Pacific Ocean (Cocos Plate, Baja California and Hawaii) and to point out some of the critical issues that need to be resolved before embarking upon such a challenging project. The document was prepared by Blade Energy Partners, U.S. upon request by the IODP-MI.

Challenges of the mantle drilling project include drilling into very hard igneous rocks at extremely high temperatures (i.e., 200-250 °C) using coring tools that are routinely used in less extreme conditions and drilling in deepwater environments (i.e., >4000 meters). Both of these challenges push the limits of current drilling technologies. The main challenges discussed in this study are as follows:

• Drilling with riser in ultra-deepwater environments with water depths around 4000 meters which will set a new world record.
  
• Drilling and coring in very high temperature igneous rocks with bottom-hole temperatures that are estimated to be as high as 250°C which will also set a new world record.
  
• Drilling and coring a very deep hole with a total drilled and/or cored interval around 6000 meters in the oceanic crust below the Pacific Ocean seafloor in order to reach the upper mantle which will be a major achievement for the worldwide scientific community.

The report includes discussions and analyses concerning environmental data, marine drilling riser options, deepwater subsea equipment, drill-pipe design, wellbore design, down-hole tools, drilling fluids, various advanced technologies and operational time and costs estimations. The analysis concluded that there are existing available technologies, equipment, and materials in the ultra-deepwater industry that could enable the IODP drilling vessel Chikyu, operated by the Center for Deep Earth Exploration (CDEX) of Japan Agency for Marine-Earth Science and Technology (JAMSTEC), to conduct operations at the candidate locations.

The results of this study show that drilling/coring a scientific hole into the upper mantle is certainly feasible, and that existing solutions are currently available to many of the technological challenges based on work being done in the commercial industries. In addition, technologies and techniques are continuously advancing, and can be expected to continue to close the gap between what is required and what is currently possible.