Correlation: thermal conductivity – compressional wave velocity on rocks

N. Gegenhuber1

1Montanuniversität, Austria

Keywords: correlation
property: thermal conductivity, comprespressional wave velocity
material: rocks

Thermal conductivity is one of the key properties of geothermal studies and many other applications [1]. Due to difficult measurements of the thermal conductivity in boreholes, only laboratory values are available. Therefore the knowledge of correlations between thermal conductivity with other properties measurable in wells or from the surface could deliver it indirectly.

Our approach was to correlate thermal conductivity with compressional wave velocity for magmatic (granites, gneiss and basalts/gabbros/diorites) and sedimentary rocks (sandstones).

Velocity was determined with an ultrasonic laboratory device. Thermal conductivity was measured using the Tk04 thermal conductivity meter from TeKa (Berlin, Germany) which is a transient method.

Two models are applied, a defect and an inclusions model, described by Berryman (1995) [2], Schoen (1996) [5] or Mavko et al (1998) [4]. Both in a first step consider the solid mineral composition and implement as a second step, defects and inclusions.

Inclusion models can be applied on elastic and thermal properties. For the elastic properties Budiansky and O'Connell [3]derived equations for penny-shaped cracked medium with a self-consistent method. For thermal conductivity calculation the Clausius-Mossotti relation [2] can be applied.

The basic idea of the defect model [5] is a defect in a solid matrix block. It is characterized by its relative length (defect parameter).

Correlations worked well for the selected rocks. They show the two important factors that influence thermal conductivity and velocity: the effect of mineral composition and cracks/fractures. Derived equations allow the transformation of elastic wave velocities from borehole measurements into a thermal conductivity estimate for geothermal applications.

  1. Abdulagatova, Z., Abdulagatov, I.M., Emirov, V.N. International Journal of Rock Mechanics and Mining Science, 46, 1055-1071 (2009)

  2. Berryman, J. A, in Handbook of Physical Constants (American Geophysical Union, Ed.), 205 – 228 (1995)

  3. Budiansky, B. and O’Connell R.J. Int. Journ. Solids Struct., 12, 81-97 (1976)

  4. Mavko, G., Mukerji, T., Dvorkin, J., The Rock Physics Handbook, Cambridge University Press (1998)

  5. Schoen, J. H., Physical properties of rocks: Fundamentals and Principles of Petrophysics (Handbook of Geophysical Exploration Series) - Pergamon Press London (1996)

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