Abstract

In Japan, the soft sedimentary rocks of Neogene Tertiary Age are recognised as potentially good host rock for High Level Waste (HLW) disposal. In particular, the coastal soft sedimentary rock is especially thought to be one of the best candidates, since here there is no significant movement of underground water. Investigation of the hydro-geological and geo-mechanical properties of the potential host rock can be achieved by the measurement and logging of the bore hole; and is a very important way to examine the potential of the disposal candidates.

Since 2000, the CRIEPI (Central Research Institute of Electric Power Industry) has been conducting its research on controlled drilling and the logging/measurement technologies in boreholes. Based on the results of Phase 1(2000–2004), CRIEPI has been developing the drilling and logging/measurement technologies for use in fault zones. Drilling technologies for detection of fault zones, horizontal drilling, long hole drilling, coring and locality detection were developed and their applicability was confirmed while drilling. The permeability/water-sampling/imaging tool was re-engineered to apply to larger diameter boreholes and over longer measuring sections. The WL-LWD (Wire-line logging while drilling) was improved to be tougher in the hole. The borehole pressure meter and stress measurement tools were unified. Each tool necessary for the monitoring system was manufactured. The applicability of these tools and systems were verified in the borehole.

After conducting surveys for the Omagari fault system at the Kami-horonobe area at Horonobe town in Hokkaido, the drilling site and borehole trace were decided in 2005. Considering the planned trace, the bore hole was drilled to a length of 1000m with core recovery of 99.8% achieved as of FY2011. Using the borehole logging-measurement-survey method developed, the geological, hydrological, geo-mechanical, geophysical and geochemical data were collected and the Omagari fault was successfully characterized.

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