SP Monitoring for Reservoir Mass and Heat Flow Characterization

Abstract

The New Energy and Industrial Technology Development Organization (NEDO) has been developing a selfpotential monitoring technology for geothermal reservoir characterization and management since 1997. Preliminaty self-potential survey was carried out in 1998 at the Ogiri geothermal field where a geothermal power plant started operations in March 1996.

As a result of this survey, positive self-potential anomalies were observed around su~ace geothermal manifestations and the Ogiri fountains, suggesting that fluids are flowing upward. Low self-potential anomalies were observed at a reinjection zone and the vicinity of production zone. It has been interpreted that ,fluids were flowing downward at the reinjection zone and that fluids had been boiling in underground at the production zone. Consequently, self-potential anomalies reflect 4namic change, such as fluidflow and boiling.