Bouncing Core Barrels: Measuring Elastic Rebound In Recovering Inner Core Barrels From 7000+ mBRT.

Abstract:

Drilling-induced damage to coring samples has been a problem ever since coring sampling began. Often this is from the fragility of certain formations (sands, for example) being sampled. Other times, the act of coring itself affects the core samples (e.g., biscuitting). One new recognized factor affecting core recovery comes from coring at extreme depths in scientific drilling.

During IODP Expedition 343, J-FAST, D/V Chikyu drilled and cored to 7760.5 mBRT. An experiment to collect borehole temperature and pressure data was attempted by running an empty inner core barrel holding 3 pressure and temperature data recorders. Although the temperature experiment failed, pressure data indicated that the inner core barrel experienced severe elastic shock when recovered by the core line winch cable.

The elastic response delay of the core line winch cable, and subsequent bouncing of the core barrel as it is being recovered to the drill floor are examined; methods of minimizing this damage are offered. This becomes more important as the Center for Deep Earth Exploration and D/V Chikyu prepare for drilling and sampling the Nankai megasplay fault/plate boundary estimated to lie at 7500 mBRT.