Geothermal measurements in Australia

Abstract

Temperatures from exploratory diamond-drilled holes and from two oil wells were combined with laboratory determinations of thermal conductivity to give values of the surface heat flow over a large proportion of the Australian continent. Twenty-five new heat-flow values involving twenty-two different locations are presented. The mean host flow from the Western Australian portion of the Australia Precambrian Shield is 0.90 ± 0.02 μcal/cm secᴼC. This is only about half the average (2.13 ± 0.09) for the remainder of Australia. The difference in heat flow may be largely the result of a low mean concentration of radioactive material in the crust and mantle beneath the shield relative to the remainder of the continent. The results indicate the possibility of a temperature difference of 200ᴼC or more between the two regions at the M-discintinuity. A divided bar apparatus was used for most of the conductivity measurements, but a number of transient heat-flow methods was studied. A line-source method suitable for measuring the conductivity and diffusivity of cylindrical specimens of rock over a wide temperature range was developed. Several cylindrical heating probes were designed and constructed. These were suitable for measuring rock conductivities in shore boreholes of diameter 3 to 5 cm. They gave satisfactory results in straight holes under carefully controlled conditions. Divided-bar measurements of the conductivities of coarse-grained rocks were compared with transient measurements on specimens several times larger than the divided bar disks. The results of the comparison indicated that the systematic errors in conductivity values obtained from small specimens of coarse-grained rocks are not very serious. The existing data on the thermal conductivities of mineral were reviewed. New measurements on eleven specimens of feldspars indicated that their conductivities vary over a wider range than was previously expected. Show more