Impact of pore structure and clay content on the water-gas relative permeability curve within tight sandstones: A case study from the LS block, eastern Ordos Basin, China

Abstract

The water-gas relative permeability of tight sandstones governs the gas production performance and recovery efficiency in a gas reservoir. Reservoir heterogeneity cannot be neglected when we extrapolate water-gas relative permeability curves. However, efforts to determine the variation with rock types and controls of the gas and water permeability have proven insufficient. Rock composition and pore structures play an important role in the spatial variation of water-gas relative permeability and vary with diagenesis evolution. In this study, we investigated the influence of pore-throat structure, clay content and cements on the water-gas relative permeability curves within tight sandstones using casting thin sections, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), high pressure mercury injection (HPMI), and gas displacement tests on samples from the LS Block, eastern Ordos Basin, China. The results show that there is a weak relationship between the spatial variation of the water-gas relative curves and the physical properties and pore size distribution of tight sandstones. The length of the two-phase flow zone is not closely related to the porosity and permeability in tight sandstones. The gas relative permeability of the crossing point is closely related to the gas permeability, not the water phase permeability. Nevertheless, the clay content is positive to the gas saturation of the crossing point and the length of the two-phase flow. Subsequently, the water-gas relative permeability curves are divided into three types based on the simultaneous vadose region area (SVRA). Finally, the genesis of the change in the water and gas relative permeability of each type is analyzed.