Petroleum data: leading the search for geothermal resources in Western Australia

Abstract

In Western Australian basins, subsurface drill-hole data, primarily from petroleum exploration, allows the identification of regions of high temperature at depth that may be potential geothermal resources. The extent and economic viability of such resources remain poorly known and require further study. Observed temperatures at depths up to 4.5 km reach 150°C in parts of the Canning, Carnarvon and Perth basins, indicating low-enthalpy resources related to regional heat flow. The greatest potential for hydrothermal resources is in the Perth Basin where subsurface temperatures of 65–85°C are reached at 2–3.5 km depth. Heat-flow modelling of 170 Perth Basin wells shows a range of 30–140 mW/m2, with the highest surface heat-flow values in the northern part of the basin. The median value of 76.5 mW/m2 for this basin exceeds the average reported for the Australian continent—64.5 mW/m2. Potential hot rocks resources are present in parts of the Canning, Carnarvon and Perth basins where the depth to 200°C is less than 5 km. Knowledge of high subhorizontal stress conditions that can enhance geothermal water flow from engineered reservoirs are based on data mostly from petroleum wells in the Perth Basin. A systematic quantitative assessment of geological, hydrogeological, geophysical, stress orientation and geochemical conditions is required to further delineate and prove these resources. Progressive compilation, validation and interpretation of subsurface data from more than 800 wells is underway, and includes temperature logs of 47 shallow water bores and 30 new thermal conductivity measurements of Perth Basin wells. Data compilation from 580 wells in the Canning, Carnarvon and Perth basins is complete. To date the greatest number of wells indicating high geothermal gradients and temperatures are in the Carnarvon Basin.