Play Systems

The geothermal play systems approach is designed to be a conceptual approach to help facilitate the use of existing geoscience datasets to predict temperature. Several key parameters, outlined in more detail below, have been identified from the equation for temperature and from Darcy’s law, which predicts fluid flow rates through rock. Each of these parameters may be linked to available Geoscience Australia datasets to help estimate them.

Equation for temperature

T equal integral fraction numerator A subscript z space plus space Q subscript m over denominator italic lambda end fraction d subscript z ;

where T is temperature; Az = heat contribution from sources in the crust; Qm = heat contribution from the mantle; λ = thermal conductivity; and dz is depth.

Darcy’s Law

Q space equal fraction numerator minus italic kappa italic capital alpha open parentheses increment italic capital rho close parentheses over denominator italic mu L end fraction

where Q is the fluid flow rate, κ is the permeability of the rock the fluid is flowing through, µ is the viscosity of the fluid, ΔP is the pressure drop across which the fluid is flowing, and L is the distance over which the fluid is flowing.

Key parameters

Thermal conductivity or the ability of the rock to transmit heat. This is influenced by composition, porosity, temperature, pressure, and in some rocks, grain size. Datasets that could be useful in estimating these parameters include surface geology maps, and geophysical datasets such as gravity and seismic.

Heat production rate. The main source of heat from within the crust is radioactive decay of naturally occurring uranium, thorium and potassium. Measurements of the concentrations of these elements in rock samples can be used to estimate the heat production rate of different rock types.

Mantle heat flow or heat flow into the base of the crust. This can be estimated from existing heat flow measurements together with estimates of heat production in the crust.

Crustal thickness. This can be estimated using information from geological maps or geophysical datasets.

Permeability of potential reservoir rocks. This can be directly measured, or estimated from rock descriptions and from geophysical datasets.

Application

This approach was used in the Assessment of the uranium and geothermal potential of north Queensland.

Topic contact: energy@ga.gov.au Last updated: April 2, 2013