Wettability and Its Influencing Factors of Tight Sandstones in Coal Measures in Ordos Basin, China.

With the recent development in exploration technology, extensive attention has been given to the tight sandstone gas reservoirs in coal measures. As a surface property of tight sandstone, wettability is a very important factor that controls the distribution and transport of gas and water inside the sandstone; thus, it plays a vital role in the sandstone gas-recovery process. In this study, a series of tests, namely, the Amott-Harvey wettability test, contact angle test, ζ-potential test, X-ray diffraction, thin-section analysis, scanning electron microscopy, and mercury intrusion porosimetry, were conducted to investigate the basic features of tight sandstones in coal measures and the effects of petrological characteristics, fluid properties, the underground environment, sedimentation, and diagenesis on the wetting behavior of sandstone. The impacts of three major forces, namely, the structural, electrostatic, and dispersion forces, on sandstone wettability were also discussed. The results showed that high surface roughness, high textural and compositional maturity, low organic matter content, a strong hydrodynamic sedimentary environment, weak compaction and cementation, high temperature, and high solution pH, as well as a low ionic concentration, enhance the hydrophilicity of the sandstone.