Characterization and Evaluation of the Sengan Field, Japan, Using a Large Set of Physical Property Data Obtained for Core Holes

Abstract

Using a large number of bulk density and thermal conductivity data carefully obtained on core samples from deep holes together with temperature log data and other geophysical information and studying their relation to geology in the area, it has become possible to evaluate the energy and fluid transport phenomena in the upper crust of a representative high-heat-flow spot, Sengan-Hachimantai geothermal area, Japan. The primary factor which controls the density and thermal conductivity values in a geological environment of volcanic rocks has been found to be porosity, based on very closely spaced measurements of the two properties of those core samples. It is shown that hydrothermal convection cells are localized within narrow fractured zones, for example in the Yakeyama sub-area, and that temperatures in the poorly fractured zones are controlled by thermal conduction. Estimation of the resource potentiality of the area is made using the temperature and physical property data obtained in this work.