Geothermal reservoir monitoring with absolute gravimetry

Abstract

A miniaturized absolute gravimeter, the FG5L was tested at Ogiri geothermal field. One day of measurements at a site provided a gravity value with an error of about 10 microGal. However, the fluctuations in the daily values greatly exceeded the daily estimated error. The FG5L is far from being useful for geothermal reservoir monitoring. The FG5, which was upgraded from the FG5L, was tested at Yanaizu-Nishiyama geothermal field. The FG5 requires only a few days to provide useful results at each survey location. Therefore one FG5 gravimeter can be used at all the geothermal fields in Japan that are being monitored. We have already used it at the 5 existing gravity networks.