Measurement of the in Situ Thermal Conductivity of Formations in a Geothermal Field-Method and Results of Measurement

Abstract

In order to estimate thermal outputs of downhole heat exchangers or, in geophysics, to determine heat flows in the earth's crust more accurately, it is necessary to know the in situ thermal conductivities or effective thermal conductivities of formations. The authors have been proposing the Downhole Coaxial Heat Exchanger (DCHE) as a geothermal energy extraction method and carried out a field experiment with the DCHE in 1991 on the island of Hawaii using the HGP-A well. The formation surrounding the well consists only of basaltic rock. One of the purposes of the experiment was to investigate the in situ heat transfer characteristics of the formation. As a result, the heat transfer mechanism in the measurement interval was identified as almost pure conduction and the thermal conductivity corresponding to the interval was to be 1.6 The heat transfer mechanism and the thermal conductivity were concordant with the mechanism inferred from measured temperature distributions in the well and the thermal conductivity of Hawaiian basalt, respectively. Also, possible error associated with the estimated conductivity was inferred to be within a range of 0.1 to + 0.2 This indicates that measurements using the DCHE as an in situ conductivity measurement probe are quite practical.