This paper describes an integrated methodology to characterize shales from an engineering point of view. Shale samples from offshore Brazil were used throughout the study. The proposed methodology includes laboratory tests designed to characterize the rock individual constituents, i.e., solid particles and pore fluid, and to describe the rock microstructure. Complementary laboratory tests on the same materials indicated low potential of reactivity when in contact with saline solutions in spite of the presence of highly expansive clay minerals. The paper suggests that other elements besides simply the characteristics of the clay minerals should be considered when evaluating the potential of reactivity of shales.