An Analytical Model for Estimating Terrain Influence on Reservoir Pressures- Implications for Hohi Thermal Area

Abstract

When geothermal fields are found in mountainous areas, it is usually observed that natural discharge points (hot springs) are located in regions of relatively low ground surface elevation. In the natural state, it is sometimes possible to correlate stable undergroundreservoir pressures with the local ground surface elevation (in addition to correlation with absolute elevation with respect to sea level). That is, underground pressure at a fixed elevation will be higher under mountains than under valleys. A simplified linearized analytical model for these phenomena is presented. Observations of hot spring discharge rates and underground pressures may be used in connection with this model to obtain approximate regionally averaged horizontal and vertical rock permeabilities. The method is illustrated by application to the Hohi thermal region located on Kyushu Island. Japan.