3D thermal modelling versus down-hole temperature extrapolation in the Sydney-Gunnedah-Bowen Basin and the implications for targeting potential geothermal anomalies

Abstract

Geothermal exploration programs require accurate subsurface temperature information and currently this information primarily comes from temperature maps created from shallow extrapolated down-hole temperature measurements. These extrapolations, often taken from measurements made in non-equilibrated boreholes, do not account for variations in geological structure or thermal conductivity. Here we explore temperature maps at 5km for extrapolated equilibrated and non-equilibrated bores and for modelled basin temperatures. Modelled temperatures are derived from finite element models using 3D basin geology and defined thermal properties. When 3D thermal modelling is compared to extrapolated temperatures at both shallow (500m) and deep (5km) intervals it can be shown that shallow surface temperature variations (from extrapolated measurements) are often not seen at depth. Depending on whether equilibrated or non-equilibrated temperature measurements are extrapolated, the positions of the potential target anomalies shift. In general both equilibrated and nonequilibrated extrapolated measurements either overestimate or underestimate temperatures at 5km. These extrapolated down-hole temperature measurements may even create false target anomalies, which significantly impacts on exploration.