Heat flow modelling: a generalized two-dimensional diffusive and convective numerical model for the Exmouth Plateau, offshore Northwest Australia

Abstract

The surface heat flow pattern for the Exmouth Plateau region offshore Northwest Australia has been defined. The average surface heat flow is 59 mW/m 2, which is the expected level for continental crust. The heat flow frequency has a Gaussian (bell shaped) distribution about this mean within the range of 19 mW/m 2 to 106 mW/m 2. Overall the areal heat flow variation is rather smooth, and there is a gradual trend from high heat flow, in the order of 100 mW/m 2, from a confined region in the southeast, to average heat flow values on the plateau. It is within this background (average) heat flow on the plateau that a single region of low heat flow is situated. The area of the heat flow low, which has levels below 40 mW/m 2, is about 4000 km 2 and the centre of the low is about 230 km from the heat flow high. Conduction alone cannot give rise to this low heat flow so a conduction and convection analysis needs to be undertaken. The mathematics for two-dimensional non-linear heat and mass transfer in a heterogeneous and anisotropic porous medium that is applicable to the geological environment has been developed. The equations governing fluid motion are coupled to the diffusive and convective heat equation, so enabling an emphasis on free or natural convection rather than forced convection. A numerical model, based on the Alternate Direction Implicit method, has been developed around the mathematical formulation to simulate heat and mass transfer in a porous medium. It is concluded that lateral variations in rock thermal conductivity give rise to horizontal temperature gradients that are the major driving force of natural convection at the Exmouth Plateau region.