Spontaneous Imbibition in Synthetic Clay-Rich Shale Considering Hydration-Induced Pore-Structure Evolution

Summary

Spontaneous imbibition is a critical mechanism controlling fluid transport and fracturing fluid retention in shale reservoirs. Especially in continental shale with high clay content, the pore structure changes induced by hydration swelling make this process highly complex. In this study, synthetic shale samples simulating the Da'anzhai Member were prepared to explore these mechanisms. By incorporating the unique flow characteristics of brittle mineral pores, clay mineral pores, and organic matter pores, a comprehensive analytical expression that accounts for various pore types for imbibition has been derived. Meanwhile, digital image correlation (DIC) technology was utilized to dynamically monitor changes in pore structure during the imbibition process, revealing significant apparent pore volume (PV) change due to clay hydration swelling effects, which were then used to improve the imbibition model. The results indicate a positive correlation between clay content and imbibition capacity, with dynamic pore structure evolution caused by clay hydration swelling significantly enhancing imbibition mass. The phenomenon of the imbibition exponents exceeding 0.5 can be attributed to changes in porosity caused by clay hydration swelling. The proposed model integrates experimentally measured physical parameters with DIC-constrained apparent porosity evolution parameters, thereby improving its interpretability for analysis of fluid imbibition and dynamic pore-structure evolution in clay-rich shale-like porous media.