Geophysical Monitoring with Reservoir Simulation in a Geothermal Field, Japan

Abstract

Repeat and/or continuous geophysical measurements can be used to detect subsurface changes. However, the separation of signal from noise is often a difficult task. In geothermal reservoirs, it is very useful to predict changes in geophysical observables from changing reservoir conditions, computed by reservoir simulation. We calculated changes in selfpotential based upon a three-dimensional reservoir model of the Ogiri field, which was constructed based upon various data and calibrated against the long-term gravity monitoring data. The calculated SP variation is qualitatively consistent both with a relatively long-term change obtained by repeated surveys and a short-term change detected by continuous measurements, which was associated with a field-wide shut-in of production and reinjection wells for a maintenance of the power station in spring 2003.