First riser-drilling operations in earthquake zone off Japan successfully completed

Posted By: Staff
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Washington, July 31 (ANI): The deep-sea drilling vessel CHIKYU, for the first time in the history of scientific ocean drilling, successfully conducted riser-drilling operations to drill down to a depth of 1,603.7 meters beneath the seafloor, off the coast of Japan.

Engaged in the Integrated Ocean Drilling Program (IODP) Expedition 319, the CHIKYU is drilling deep into the upper portion of the great Nankai Trough earthquake zone to gain insights into geological formations and stress-strain characteristics.

The CHIKYU is operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) a partner in the IODP.

The Kumano Basin drilling and sampling operations began on May 12. The science party, which includes Co-Chief Scientist Lisa McNeill of the National Oceanography Centre, Southampton (UK), is expected to complete the first drill site on or about August 1.

Riser-drilling technology was used from about 700 meters below the seafloor to the bottom of the hole.

Riser-drilling involves the circulation of drilling fluid that helps maintain pressure balance within the borehole.

Cuttings were recovered from the circulated drilling fluid and analyzed to gain a better overall picture of downhole changes in lithology and age.

Core samples also were collected between depths of 1,510 and 1,593.3 meters below the seafloor.

According to Co-Chief Scientist Lisa McNeill, a member of the University of Southampton's School of Ocean and Earth Science based at the National Oceanography Centre, "This state-of-the-art technology enables scientists to access an unknown area. It will provide a lot of important information about what has happened in the seismogenic zone in the past and its present condition."

Following drilling operations that included 'measurement-while-drilling' to obtain real-time geophysical characteristics, wireline logging instruments were lowered into the borehole to measure formation temperature, resistivity, porosity, density, gamma ray, and borehole diameter.

The riser-drilling technology enabled dynamic formation testing using the logging instrumentation for the first time during IODP scientific ocean drilling operations.

This instrumentation is designed to measure stress, water pressure, and rock permeability.

Co-Chief Scientist Timothy Byrne of University of Connecticut emphasizes the importance of the Nankai Trough experiment results.

"These two parameters, stress magnitude and pore pressure, are both important to understanding earthquake processes," he said.

Operations at this drill site are expected to conclude after casing the borehole to the bottom of the hole and capping it with a corrosion cap for future installation of a long-term borehole monitoring system (LTBMS). (ANI)

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