INTEGRATED ANALYSIS USING 3D SEISMIC SURVEY IN THE YAMAGAWA GEOTHERMAL FIELD, SOUTHWESTERN JAPAN

Abstract

Most of the geothermal reservoirs in Japan are composed of steeply dipping faults or fracture zones. Gravity survey is commonly conducted to identify the reservoir structures. However, the resolution of the gravity survey is much broader than the size of faults or fracture zones and we cannot locate the fault/fracture zones by only the gravity survey. To resolve this problem, we focused our attention on the 3D seismic method, which reveals the detailed reservoir structure with higher spatial resolution, and applied it to geothermal reservoir exploration in order to verify the efficacy on that and obtain experimental solutions. The 3D reflection seismic survey and the refraction survey were conducted in Yamagawa geothermal field in Japan.
In this study, we addressed a variety of advanced analyses. Full waveform inversion (FWI) depicted a complicated velocity structure of the volcanic region and Ant-tracking enhanced planar structures of indications from the coherence analysis. Geophysical models from seismic, magnetotelluric and gravity surveys, as well as well information, were integrated with geostatistical techniques, joint/simultaneous inversion and multi-attribute analysis. As a result from the integration flow, we built 3D lithofacies and temperature models which would be useful for geothermal exploration. We also found that interpolation processing is effective and useful to compensate the lack of data, which encouraged us to conduct seismic surveys in mountainous areas where limited number of survey lines and seismic data are available.