The influence of basement on surface heat flow in the Cooper Basin

Abstract

This paper describes the results of an investigation into the surface heat flow distribution around GEL-99, a Geothermal Exploration Lease granted to Scopenergy Limited by the South Australian Government. I collated temperature and thermal conductivity data from a number of sources in order to construct one-dimensional thermal models of 30 petroleum industry wells. The data indicate a marked thermal conductivity contrast between the base of the Eromanga Basin sequence and the Cooper Basin sequence, resulting in a relatively high thermal gradient in the latter. Observed drill stem test temperatures support this prediction. Vertical heat flow within GEL-99 ranges from about 90 mW/m2 to over 110 mW/m2, averaging over 100 mW/m2. Heat flow drops off significantly towards and beyond the edge of the Big Lake Suite granodiorite. Observed values of heat flow cover a range of about 25 mW/m2. This variation can be attributed to a combination of a variable thickness of heat-generating material in the basement, and heat refraction through areas of relatively shallow basement.