Water adsorption on kaolinite and illite after polyamine adsorption

Polyamine (PA) is a novel inhibitor applied to water-based drilling fluid in order to reduce clay hydration. In this paper, water adsorption behavior on kaolinite and illite after PA adsorption (PA-kaolinite, PA-illite) was characterized by X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and adsorption isotherms tests using water, benzene, and heptane. After PA adsorption, water adsorption on kaolinite was enhanced while water adsorption on illite was reduced. Water vapor adsorption affinity on kaolinite in an entire range was significantly increased due to H-bonds between the ammonium groups of PA and water molecules. As a result, kaolinite surface tension was increased. Water adsorption affinity on illite in the low relative humidity (RH) regimes was decreased after PA adsorption and illite surface tension decreased because fewer water molecules could adsorb on tetrahedral (SiO₄) of illite. Therefore, PA can be used as inhibitor while drilling shale formations mainly composed of illite, not kaolinite.