Study on suitable area selection technique for underground thermal utilization using geological data

Abstract

Three-dimensional geological structure is examined using borehole data and Mining Visualization System (MVS) software to develop a suitable area selection technique for underground thermal utilization. As there are considerable borehole data from Nagoya, central Japan, Nagoya was selected as the model field to examine three-dimensional geological structure. Geotechnical data of subsoils in Nagoya is inputted for analysis in MVS, and the needed geological information for underground thermal utilization is extracted. Since the Toriimatsu gravel bed has been used for water resources, it is expected that this bed is more permeable than others. This may be important for underground thermal utilization, because groundwater flow increases effective thermal conductivity. Deduced three-dimensional distribution of Toriimatsu gravel bed reveals not only the distribution area, but also 1) that the bed is more deeply distributed toward the west, 2) that the bed thickness is maximum in the northern part of the bed, and 3) that the distance from the surface to the top of the gravel bed becomes greater toward the west. In order to reduce the initial installation cost involved in underground thermal utilization, the area with higher thermal conductivity should be selected to save the borehole length. Because the Toriimatsu gravel bed has a shallower distribution at the eastern part of Nagoya and its bed thickness is maximum in the northern part of the bed, the northeastern part may be a suitable area for underground thermal utilization.