Japan reports first coring operations of CHIKYU

The deep-sea scientific drilling vessel CHIKYU, owned by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and provided to the Integrated Ocean Drilling Program–jointly funded by Japan and the United States–has recently undergone successful testing operations, according to JAMSTEC-CDEX Director-General Asahiko Taira. Successful performance results are now available for the Blow Out Preventer (BOP) handling System Integration Test (SIT). Dr. Taira also reported successful piston-coring operations (part of the BOP-SIT), including recovery of two piston cores, i.e. cylindrical sediment samples taken from strata using a hydraulically actuated piston corer (Hydraulic Piston Coring System: HPCS). HPCS is used for sampling mud and sand from geological layers beneath the seafloor.

JAMSTEC conducted ship-steering training using the Dynamic Positioning System (DPS), as well as training in deploying and retrieving transponder signals, the acoustic locator off Nagasaki, Suruga Bay, and Boso Peninsula. During two test periods (Oct. 10–Dec. 1, off Shimokita Peninsula, and Dec. 4–Dec. 12, off Suruga Bay), the following CHIKYU systems/equipment were tested to confirm performance:

• A) Off Shimokita Peninsula
• 1) Drilling equipment performance test (drillpipe handling test)
• 2) Mud system performance test (Circulation test and mixing test for high-density drilling mud)
• 3) Dynamic Positioning System (DPS) test
• 4) Piston coring by HPCS
• B) Off Suruga Bay 5) BOP handling test

“These results confirm the basic performance of the drilling equipment and that the CHIKYU’s systems meet our expectations and are ready for upcoming, full-scale drilling operations,” declared Dr. Taira. “Testing enabled us to acquire new information to facilitate CHIKYU’s safe and smooth operation. Our plan is to move CHIKYU to Sukumo Bay in Kochi as a base port to conduct more tests, especially ship positioning.”

The piston coring test was performed 60 kilometers to the east off Shimokita Peninsula from Nov. 22-28. Two piston cores, 50 meters and 70 meters long, respectively, were retrieved by HPCS from 1,200-meter water depths. JAMSTEC also conducted performance tests for research and core analysis systems onboard, using the recovered cores. To confirm the strength of strata for BOP supporting/landing during upcoming riser drilling in FY2006, measurements were made of whole 50-meter core share strength. As a result, said Taira, “We are confident that the strength of strata around this area is sufficient for BOP landing and successful riser-drilling.”

Judging from the recovered cores, Taira identified the following features in the surface sediments at the drill site:

1) Sediment samples (50 meters, 70 meters beneath the seafloor) are olive-grey, diatomecious mud with frequently observed ash layers. The origin of sediments is mud and sand by river discharge, ocean plankton and volcano eruption.
2) This kind of mud, containing many plankton bodies, is distributed widely not only in the sea near Japan, but also along the land’s edge. This mud is meant to absorb the organic material (carbon), and it has been thought that it controls the CO2 density levels in the atmosphere and ocean, and relates to climate changes as well.
3) There is a possibility that the palaeoclimatic changes of Tohoku district during the last 20,000 to 30,000 years would be revealed by analysis of this piston cores.