A novel bound water occurrence model for tight sandstone

[Display omitted] •A novel bound water occurrence model was proposed.•Water-film has a negligible impact on the minimum pore/throat radius for gas charging but greatly impact permeability.•I/S-mixed layer and illite exert the most significant influence on bound water saturation. Understanding the occurrence state and microscopic distribution of bound water, as well as the factors governing bound water saturation and its impact on natural gas flow within nano-scaled pore networks, holds significant importance for reservoir evaluation, productivity prediction, and production. However, the complexity of pore structure poses a challenge in quantitatively characterizing these aspects, and currently, no effective method exists to achieve this characterization. This study takes the Bashijiqike tight sandstone of the Kuqa Depression of the Tarim Basin as an example; by integrating physical property test, XRD, microscopic observation with casting thin section and SEM, HPMI, NMR, and NMR-supervised gas-charging experiment, proposed a novel bound water occurrence model to depict the microscopic distribution of bound water in nano-scaled pore space. Furthermore, the impact of bound water on gas-flowing behaviors was thoroughly examined and the complex relationships between bound water saturation and reservoir macroscopic and microscopic parameters were explored. In addition, based on the grey relational analysis, the critical controlling factor on bound water saturation were screened out. The bound water in the pore space of tight sandstone comprises two components: capillary-bound water within small pores (