Heat flow in the Moomba, Big lake and Toolachee gas fields of the Cooper Basin and implications for hydrocarbon maturation

Abstract

Heat flow in the Moomba, Big Lake and Toolachee gas fields of the Cooper Basin is estimated from corrected bottom hole temperatures and an assumed bulk thermal conductivity of 5 ´ 10-3 cal/cm sec °C. The Moomba and Big Lake fields have heat flows of 2.61 and 2.60 microcal/cm2 sec °C. Samples of basement granite from the Moomba and Big Lake fields yield heat production of 17.5 ´ 10-13 and 24.2 ´ 10-13 cal/cm3 sec, respectively, which are sufficient to account for observed surface heat flow if the granite layer is between 7 to 10 km thick. Hydrocarbon maturation and coal rank (expressed as vitrinite reflectance) in the high heat flow Moomba-Big Lake region exhibits a different correlation to maximum palaeo-temperature and depth than in lower heat flow regimes. The degree of maturation may be dependent on the thermal energy available for metamorphism (i.e. heat flux), rather than the temperature of the basin.