Effect of Matrix Characteristic and the Pore-Throat Limit for Water Imbibition in Early Jurassic Tight Sandstone Reservoir of the Tuha Basin

Spontaneous imbibition (SI) is a fundamental mechanism for improving the production efficiency of tight sandstone reservoirs. Matrix characteristic plays important roles in the SI process, but how these factors affect SI and the limit pore-throat size of effective driving force in the tight sandstone of the Tuha Basin has not been firmly established. Thus, a series of experiments (FE-SEM, QEMSCAN, XRD, CT, and SI) of four tight sandstone core samples were conducted under laboratory conditions in the Tuha Basin. The results show that quartz and plagioclase feldspar are the main detrital minerals, while illite and illite/smectite (I/S) are the predominant clay minerals of those sandstone samples, and they have a micro-nano (<2 μm) to meso-macro (>10 μm) pores, but the micro-nano pore performance disconnected, and during SI process, fluid enters small and meso-macro-size pores simultaneously. However, small pores play a dominant role in the initial stage (with steep imbibition slopes), while meso-macro pores predominate in the second stage (with shallow imbibition slopes), and the limit pore-throat value of the tight sandstone is around 9.1 μm in the Tuha Basin, beyond which the SI will be weakened. Though the mineral composition and its wettability will be changed with fluid environment (especially for clay minerals), the small pores (formed by clay minerals) always play a dominant role than meso-macro-size pores (mainly formed by quartz and plagioclase feldspar) in SI process. These observations can improve our understanding of fluid–reservoir interaction in the Tuha Basin’s tight sandstone reservoir and provide guidance for improving oil and gas recovery.