New ways for research and development using a deep-sea hydrothermal vent system in the Okinawa Trough

JAMSTEC has an international patent for the environmentally-friendly cultivation system of offshore hydrothermal chimneys as the accessory product of scientific drilling program in the Okinawa Trough at deep water of 1,100 mbsl. This cultivation system was inspired by rapid growth of precipitated minerals (sulfide chimney) on the drilled hole. We introduce in this paper, the achievement from the riserlesss drilling campaign in Iheya North field in 2010 as IODP Exp. 331 and in 2014 as SIP Okinawa. After the IODP Exp. 331, the major findings were the massive continuous hydrothermal fluid supply from the drilled hole and the rapid growth of the precipitated minerals (sulfide chimney). The flow rate estimated from the installed producer is around 300 - 500 liter per minute through 3.5 inch pipe in diameter. The Cu-Pb-Zn-rich sulfide chimney having average concentrations of 4.5 wt% Cu, 6.9 wt% Pb, 30.3 wt% Zn and 8.7 wt% Fe at the outlet of the drilled hole was rapidly grown to be from 2 m to 8 m in 6 months. In Exp. 331 two temporary wells are and 5-1/2” tubing pipe were installed and those are producing the hydrothermal fluid. JAMSTEC are planning to install two new monitoring wells in Feb 2016 at Iheya North field and at Noho field. Those wells are sensing and logging flow rate, temperature and pressure. It can capture the precipitated minerals from hydrothermal fluid and those data by retrieving monitoring cell by ROV. The system was built and tested in March 2015. LWD operation was performed in 2014 as a part of SIP program. 7 wells are drilled with LWD for the depth of 200 - 350 mbsf in only 9 days in riserless drilling throughout the risk of 350 deg.C thermal fluid by applying continuous circulation system. The continuous circulation system successfully suppresses the hydrothermal fluid pressure by the circulation back pressure and the maximum downhole temperature recorded at LWD was only 85 deg.C in a short period. At the last our future plan is discussed focusing on our present concerns.