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Mizunami Underground Research Laboratory
Deep borehole investigations (MIZ-1 Borehole)

Location and projected trace of the planned the MIZ-1 borehole

The MIZ-1 borehole is being drilled in an overall southwesterly direction from the northeast part of the MIU construction site. The inclination or plunge will vary with depth, based on the inclination control plan described below, which will enable the borehole investigation program to be optimized.

- Drill vertically from surface to approximately 250mabh.
- From 250mabh to 460mabh, using controlled directional drilling, the borehole will curve in a southwesterly direction, with inclination decreasing from vertical in increments of 0.67 degrees every 12mabh. The inclination target is 12 degrees from vertical.
- From 460mabh to 1,350mabh, drill to southwest at 78 degrees inclination from horizontal.

This controlled directional drilling results in an offset from the borehole collar of about 207m at the bottom and a true vertical depth of about 1,329m.
Status of activities

CHD-134 wireline drilling with drilling mud was finished at a depth of 1300mabh on August 31.




Geological model prediction
(depth along
borehole axis)

(predicted geological intersections)
104mabh

:Unconformity (Mizunami G./Toki Gr)
104-105mabh

:Weathered zone
104-138mabh

:Jointed zone
104-400mabh

:Upper highly fractured domain(UHFD)
400-1350mabh

:Lower sparsely fractured domain(LSFD)
747-756mabh

:IMF11
906-908mabh

:IMF10
1145-1170mabh

:IMF03
The following restrictions and requirements were considered in planning the location and layout of the MIZ-1 borehole.

Restrictions:
- Borehole must be within the MIU construction site and cannot cross the site boundary at any depth.
- Obstruction to the MIU facility construction work should be avoided.

Requirements:
- Attempt to intersect inferred major faults considered to exist in the Toki granite at the MIU construction site and to study their geological properties.
- Less fractured, relatively hard granite is more amenable to controlled directional drilling than is highly fractured or soft rock. Therefore, for this technical reason, intersection of faults during the controlled directional drilling should be avoided.
- The true vertical depth must be over 1,000m to acquire information on the deep geological environment.
For more details

Working Program for MIZ-1 Borehole Investigations(PDF)
This document mainly describes the plannde working program for MIZ-1 borehole investigations including associated laboratory programs during and after drilling.