First Riser Drilling Operations Undertaken in Support of Earthquake Zone Research
Riser
Drilling Operations Start as part of Nankai Trough Seismogenic Zone Experiment
(NanTroSEIZE)
Approximately
58 km southeast of Shingu City, Japan, June 26, 2009--Deep-sea Drilling Vessel CHIKYU has resumed IODP drilling
operations in the Nankai Trough Seismogenic Zone off the Kii Peninsula of Japan. The scientific drilling expedition’s first target
is located in water depths of 2,054 meters. Following sea floor surveys, the
crew began fitting riser pipe and a blow-out prevention (BOP) system into an
upper section of the first borehole to be drilled. The riser pipe and BOP (the blow-out
preventer) was successfully connected to the wellhead. After
testing the circulation of the drilling fluid, the first riser-drilling
operations for CHIKYU in the history
of scientific ocean drilling began on June 25. The British Broadcasting
Corporation (BBC) chronicled the lead-in to this historic activity, the first
media organization outside Japan to broadcast live from CHIKYU.
The
target drilling depth at the first borehole is 1,600 meters below the seafloor.
Following drilling operations, vertical seismic profiling (VSP) is expected to
begin as part of geophysical logging.
Riser
drilling involves a large marine riser pipe that connects the CHIKYU and the seafloor. The riser pipe
guides the drill pipe as it reenters the well. Drilling fluid is pumped up and
down between the riser pipe and the drill pipe. Fluid circulation and use of
the blow-out preventer (BOP) help maintain pressure balance within the borehole
and prevent it from collapsing, enabling safer and deeper drilling.
CHIKYU is the
world’s first scientific drilling vessel capable of riser drilling deep beneath
the ocean floor and in seismogenic (earthquake-producing) zones that have never
been reached before.
The
Nankai Trough subduction zone, located southwest of Japan, is one of the most
active earthquake zones on the planet, with complex geological formations
caused by tectonic plate thrusts. The scheduled drill site, the Kumano Basin, is a fore-arc basin of the Nankai Trough under the
influence of the strong Kuroshio ocean current. In combination with inclement
weather expected, due to passing typhoons, and riser drilling down to depths of
more than 2,000 meters below surface, this phase of NanTroSEIZE is considered
one of the most challenging tasks in ocean-drilling history.
The average speed of the
Kuroshio current in the surveyed area is about 1.0 knots, relatively slow for
the current speed usually observed in the Kumano Basin. Yet, fairings are to be
mounted onto to a riser pipe to smooth the hydrodynamic flow behind the riser
pipe (to reduce riser drag) and suppress the vortex-induced vibration under
high current conditions. The motion of the riser also will be monitored for
analysis, in order to use the results in future operations.
Contacts:
(For the expedition)
Takeo Tanaka,
Center for Deep Earth Exploration (CDEX)
Japan Agency for Marine-Earth Science and
Technology (JAMSTEC)
(For Publication)
Noriyuki Murata,
Japan Agency for
Marine-Earth Science and Technology
Nancy Light,
Integrated Ocean Drilling Program
Management International
Editorial Notes:
*1 IODP (Integrated Ocean Drilling Program)
The Integrated
Ocean Drilling Program (IODP) is an international marine research drilling
program dedicated to advancing scientific understanding of Earth by monitoring,
sampling, and instrumenting subseafloor environments. Through multiple
platforms, preeminent scientists explore IODP principal themes: the deep
biosphere, environmental change, and solid Earth cycles. IODP has operated
since October 2003, funded jointly by the Japan Ministry of Education, Culture,
Sports, Science and Technology and the U.S. National Science Foundation; with
additional support provided by the European Consortium of Ocean Research
Drilling; the People's Republic of China, the Republic of Korea, Australia,
India, and New Zealand.
*2 VSP (Vertical Seismic Profiling)
Vertical Seismic Profiling is a technique to obtain
information on geological formations of plate boundaries and accretionary
prisms with a great precision. It involves some 20 seismometers being lowered
from the CHIKYU into the borehole,
toward which elastic waves are fired from an air gun towered by the JAMSTEC’s
research vessel “KAIREI”.
