The role of water/clay interaction in the shale characterization

Shale instability involves fully coupled chemo-mechanical phenomena, in which fundamental intermolecular surface forces are acting between the clay surfaces. These forces are function of the composition, type, amount, and microfabric of the clay content in the rock, which are responsible for the global shale behavior. Thus, the knowledge of these features is fundamental to explain their swelling behavior. This paper presents the results of water distribution analyses of seven samples of shale from different oil fields along with their X-ray diffraction, in order to establish the differences in composition and swelling behavior of such samples. The X-ray diffraction analyses clearly show the differences of swelling clay content between shale samples. Thermal gravimetric analyses also validate that a simple analysis of the water loss below 100 °C gives a good insight about the composition and swelling behavior of shales. It also shows that the water loss below 55 °C, is strongly dependent of the activity and that this dependence quickly decreases as temperature increases, which suggest that the role of activity in the swelling behavior of shale only takes place at lower temperatures.