60 Geophysics in Geothermal Exploration Figure 2.3 Relationship between attenuation and petrophysical parameters (after Morlier and Sarda, 1971).Top: laboratory measurements on cores with constant specific surface. Bottom: laboratory measurements on cores with variable specific surface Theoretically, the effective specific surface S can be calculated from the porosity ϕ and the Klinkenberg permeability k (given in m2 in equation (2.5) but typically reported in mD) using Kozeny’s equation (Kozeny, 1927) k = Ck(ϕ3/S2) (2.5) Sg = S/(1 – ϕ) (2.6) with ϕ: porosity, S: Specific surface, Sg: Specific surface with respect to grain volume, Ck: Kozeny’s factor The Kozeny’s factor can be calculated from the porosity via a simple model of linear 3D interpenetrating tubes (Mortensen et al., 1998). The specific surface Sg with respect to the bulk volume is given in 1/m in equations (2.5) and (2.6) but typically reported in m2/cm3. Fabricius et al. (2007) have found that the specific surface with
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