The thermal, mechanical, electrical and transport properties of rocks are determined by their mineralogical composition, chemistry and texture. Several experimental studies have demonstrated correlations between the simple petrology and chemical composition of rocks and some of their petrophysical properties (Contreras et al. 1994, Viggiano and Gutiérrez 1988). The interrelationships between chemical characteristics and petrophysical properties of rocks are extremely complex, poorly understood and hard to model, from both a theoretical and practical point of view. Heterogeneities in the fractured matrix allow us to consider the mechanisms of interaction among different matrix blocks, fractures, microfractures and faults with different porosities and permeabilities. The effective treatment of heterogeneities is achieved using special averages at the contact interfaces.