In the current coring system, there are two main methods: a Hydraulic Piston Coring System (HPCS) mainly used for relatively shallow and soft sedimentary layers which utilizes piston action movements to thrust the core barrel into the seafloor to recover core samples and the Rotary Core Barrel (RCB) which is mainly used for hard formations, rotating the core barrel to retrieve cores. A core bit is mounted to the tip of the core barrel to drill into the rocks and a wireline enables the recovery of the inner tube within which the scraped cores are stored. Cores can thus be recovered continuously and stably, even with variations in the layers, by a Wireline Coring System.

Mr. Shinmoto holding the plate of the Best Paper Award.

　Even with such advanced coring equipment, cores of high quality are not always recovered. In some cases, the cores are damaged or sand and gravel layers are washed away by drilling fluid from the coring tool, leaving only gravel. We are now working on improvements to the core bit to address these problems. First, the number of bid blades was reduced so that the cores would not be damaged from contact with the blades. The tip was sharpened to prevent cores from being washed away and also to ensure that drilling fluid would not flow into the core side, preventing core jam. When the core bit was thus improved, these problems could be resolved, enabling recovery of cores in good condition even from sandstone or mudstone. The paper describing this improved core bit by Yuichi Shinmoto, Technical Engineer of the CDEX Engineer Department, was awarded Best Paper at the 15th Formation Evaluation Symposium of Japan.

　The main objective of the deep-sea drilling vessel, CHIKYU, is to carry out scientific drilling and eventually reach the Earth’s mantle. However, temperatures at the mantle exceed 250°C with pressures of 1000 atm. The mantle is also expected to be extremely hard so that a durable, efficient system will be required to drill for extended periods under the most extreme conditions.