Geothermal energy prospectivity of the Torrens Hinge Zone: Evidence from new heat flow data

The Torrens Hinge Zone is a long but narrow (up to 40 km wide) geological transition zone between the relatively stable Eastern Gawler Craton a??Olympic Domaina?? to the west, and the sedimentary basin known as the Adelaide Geosyncline to the east. The author hypothesised from first principles that the Torrens Hinge Zone should be prospective for high geothermal gradients due to the likely presence of high heat flow and insulating cover rocks. A method to test this hypothesis was devised, which involved the determination of surface heat flow on a pattern grid using purpose-drilled wells, precision temperature logging and detailed thermal conductivity measurements. The results of this structured test have validated the hypothesis, with heat flow values over 90mW/m2 recorded in five of six wells drilled. With several kilometres thickness of moderate conductivity sediments overlying the crystalline basement in this region, predicted temperature at 5000m ranges between 200 and 300 C.