9:45 AM - 10:00 AM
[MIS16-04] Estimation of under-seafloor fluid on temperature and volume from the logging-while-drilling data in an active hydrothermal field
Keywords:Okinawa Trough, Seafloor hydrothermal Deposit, Cross-ministerial Strategic Innovation Promotion Program (SIP), Logging-while-drilling
At C9012 and C9016, the arcVISION clearly detected temperature anomaly at 234 meter below the seafloor (mbsf) and 80 mbsf, respectively. Temperature quickly increases at that depth and it would reflect the existence of high-temperature heat source. During the drilling, however, drilling water was continuously circulated at high flow-rate (2600L/min) as stated above. Thus the measured temperature is not exactly in-situ temperature, but the profile of the temperature reflects the temperature variation of each stratigraphic layer of the bore hole.
To investigate the detail of the heat source, such as in-situ temperature and quantity of heat, we performed numerical analyses of thermal fluid and energy-balance assuming injection of high-temperature fluid. We combined pressure loss theory of double cylinders and temperature equation to replicate the fluid flow and its temperature between borehole wall and drilling pipe during the thermofluid injection. As the result, we estimated the temperature and the volume of injected fluid to be 115oC~ and 17.3 m3, respectively (at C9012) from the calculation. This temperature is lower than that of a hydrothermal vent which had been found near the hole (300oC). We will present preliminary results of the calculation for the newest cruise (CK16-01).