Imaging Geothermal Fractures by CSAMT Method at Takigami Area in Japan

Abstract

Controlled Source Audio-frequency Magneto-Telluric (CSAMT) survey was carried out in Takigami geothermal field. Staions were closely taken with regular grid spacing of 150 m. The purpose of the measurements is to delineate a detailed resistivity structure and location of electrical discontinuities that may reflect a possible faults and fractures correlated with a promising reservoir.

The interpretation results based on 2-D inversion analysis show that there are some electrical discontinuities are found in the orth-South and West-East directions, which correlate with the trend of some faults where geothermal reservoir exist. The electrical discontinuity Fd in N-S direction correlates with Noine fault zone, which divides the subsurface into eastern and western parts according to the characteristics of electrical resistivity, permeability, temperature and depth of reservoirs. The electrical discontinuity Fa in W-E direction corresponds to the Teradoko fault where the major production wells have been drilled in the Takigami area.