| Abstract |
NEDO has been undertaking the Deep Seated Geothermal Resources Survey Project in Kakkonda (Iwate, Japan) since 1992. The pilot survey well WD-1a reached 3,729 m and over 500 degrees C in FY1995. In FY1996, NEDO drilled a sidetracking well WD-1b and hit several high permeability zones. We developed a new exploration technique using borehole to surface electro-magnetic tomography system named VEMP (Vertical ElectroMagnetic Profiling) under this project (Miura et al., 1995). We applied it to a test survey at the open-hole section (2,250 to 2,850 meters) of WD-1b in 1997. We measured magnetic fields (horizontal fields toward transmitters and vertical fields) at six frequencies (1,4,16,32,64 and 128Hz) at 13 depth levels in the hole. Signal sources were grounded-wires at six locations on the ground surface. For interpretation of the data, we are developing 2.5-D FEM nonlinear least square inversion code including robust weighting for the field data. The initial model for the inversion was based on the 2-D inversion result that was obtained by MT/CSAMT sounding in 1994 (Yamane et al., 1996). |