Geological Structure and Underground Temperature in the Nobi Plain, Central Japan

Abstract

A study on the relationship of geothermal gradient and geological formation is performed using borehole data in the Nobi plain, central Japan. For ground-coupled heat pumps, it is better to understand the underground distribution of the effective thermal conductivity to search the areas where the deep boreholes are not necessary for heat exchange, because drilling cost in the initial cost of the geothermal heat pumps is high in Japan. In some boreholes, geothermal gradient is higher in conglomerate layers. This may suggests that groundwater flows and thermal convection is performed in conglomerate layers. In some other boreholes, however, geothermal gradient is lower in conglomerate layers. This cannot be explained by thermal convection in conglomerate layers. These indicate that thermal convection is performed in conglomerate layers but groundwater flow is also important for the formation of underground thermal distribution.