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November 2014
Arrow 05/11/2014 November Luncheon - The Challenges of Drilling a 7km Offshore Borehole to Penetrate a Seismically Active Subduction Zone

The Integrated Ocean Drilling Program (IODP) has embarked on an ambitious deep exploration project to drill a scientific borehole into the mega-splay of the Nankai Trough Subduction Zone located ~450 km SW of Tokyo, Japan.  This international project (NanTroSEIZE) is the 1st attempt to drill, test, sample and instrument an active subduction plate boundary capable of generating M8+ earthquakes.  The scientific objectives are to understand the physics of subduction earthquakes capable of generating massive tsunamis. 

Twelve transect sites have been drilled across the trench axis, primarily for sampling, establishing a regional framework of observations and commissioning many wells for in-situ real-time monitoring. Several expeditions at one of these sites have occurred with the intent to drill a 7km vertical hole that intersects the stressed fault-splay.  Expedition 348, ended in Jan 2014, after coming within 2.2 km of the mega-splay as planned.

We present a geomechanical postmortem of Exp 348 to explain the NPT encountered while drilling in this harsh environment and illustrate the process of using LWD and engineering information to design a forward well plan that delivers the borehole in a condition suitable for scientific observations in this all-important international project.

 

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