[MIS08-P10] Stress estimate and Geomechanics in seismogenic zone: Implications for NanTroSEIZE deep drilling at Site C0002
Keywords:Chikyu, Seismogenic zone, Deep drilling, Stress estimate, Petrophysics, Geomechanics
In usual case, rock strength data (unconfined compressive strength, UCS) of drilled formation is required to estimate stress magnitude based on geomechanical approach. Therefore, it is also important to estimate or measure UCS before and during a drilling operation. In order to get better UCS data and its profile with depth beneath drilling site, conventional triaxial rock strength test and precise seismic velocity model are required at least.
For ultradeep drilling of the seismogenic zones (e.g., NanTroSEIZE), stress measurement and/or estimate is certainly important to establish feasible stress measurement and/or estimate in pre-and syn-drilling phases.
In this presentation, current status of stress estimate and results from our geomechanics study at Site C0002 will be presented based on stress estimate (e.g., LOT data) and borehole observations (e.g., borehole breakout) from the previous operations (e.g., Chang et al., 2016), borehole stability analysis deduced from stress/pore pressure profile models, UCS models estimated from our triaxial test results and the reprocessed 3D seismic velocity model (Shiraishi et al., 2018). Issues to drill ahead into the plate boundary fault will be discussed for those interested on upcoming IODP Expedition 358- Nankai Seismogenic/Slow Slip megathrust.