Nanoscale Surface Properties of Organic Matter and Clay Minerals in Shale

Surface properties of shale play an essential role in adsorption, transport, and production of hydrocarbons from shale reservoirs. Nanoscale surface properties of kerogen and minerals of shale were examined by a series of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIRS), and atomic force microscopy (AFM). The results show that aluminosilicate is the main component of inorganic matter, while kerogen chiefly consists of carbon. FTIRS and XPS analysis indicate that the chemical bonds of the kerogen surface are O-H, C-C, C-O, pyrrolic, and so on. In contrast to kerogen, illite's bonds are mainly Si-O and Al-O. AFM results indicate that the adhesion force of kerogen is higher than that of illite in shale. In addition, at a preloading force of 2500 nN, the adhesion force of kerogen increases from 40.8 to 118.2 nN when retraction velocity increases from 500 to 2500 nm/s. The adhesion forces of montmorillonite, calcite, and muscovite are 33.7 ± 6.28, 23.8 ± 11.8, and 105.1 ± 9.1 nN, respectively. The chemical composition and bonds have a profound effect on the adhesion force of shale, which further reveals the transport and adsorption mechanism of methane in kerogen.