In March and April 1984, West Japan Engineering Consultants (WJEC) was contracted by Kyushu Electric Power Company (KEPCO) to conduct field survey for a proposed mise-à-la-masse method. The survey was carried out using an exploratory well HT-8 located in the vicinity of the present production area of the Hatchobaru geothermal field in north central Kyushu, Japan. The apparent resistivity and potential maps derived from the data processing clearly indicated several promising zones of low resistivity including the present production zones where the almost all of productive wells located inside and indicated two-dimensional structure across the strike of the Komatsuike sub-fault. Two-dimensional mise-à-la-masse modeling of surface potential and apparent resistivity profiles has been developed over various bodies for multiple electrode configurations. The surface responses are obtained by the finite difference method for a horizontal body with the contrast in conductivity between the body and subsurface is 10:1, but different locations of a line sources of current electrode. A two-dimensional model has been derived to simulate results as close to observed field data across the present production zone as possible. The similarities between the observed data and the best fitted model are striking, in particular of the data for the surface potential distribution.
