Riserless Vertical Drilling Operations using Downhole Motors in the Nankai-Trough Seismogenic Zone

The Nankai-Trough, which is located south of the main island of Honshu, Japan and extends 900 km offshore, is a<br>subduction zone with large amounts of deformed trench sediments with seismic activity and a good example of an<br>accretionary prism. At extreme ocean depths, water forms ice that has, in some instances, trapped methane in its crystalline<br>lattice, forming gas hydrates so that the Nankai-Trough contains a large amount of gas hydrate formations.