Synergistic Hydration Mechanisms of Multiple Minerals in Carboniferous Shale from the Eastern Qaidam Basin

Shale hydration and its associated microstructural evolution play a pivotal role in wellbore stability and drilling efficiency. To clarify the dominant hydration reactions and multimineral synergistic mechanisms, systematic immersion tests were conducted on Carboniferous shale from the eastern Qaidam Basin, involving monitoring of ionic concentration in immersion solution and characterization of surface elemental distribution. Results indicate that shale hydration is dominated by sequential geochemical reactions, beginning with calcite dissolution and feldspar hydrolysis, followed by cation exchange between released cations and clay minerals (Illite and chlorite). Distinct hydration behaviors were observed across minerals: calcite dissolution exhibits a gradually decreasing reaction rate; feldspar assemblage (albite and orthoclase) exhibits heterogeneous elemental distribution and nonstoichiometric, spatially variable hydrolysis in albite, while homogeneous elemental composition and stable hydrolysis in orthoclase. K+ released from feldspar suppresses cation exchange in Illite, rendering early stage Fe3+ and Mg2+ sequential exchange in chlorite more pronounced. Hydration-induced microstructural changes predominantly include micrometer-scale dissolution pores, mineral surface exfoliation, and localized swelling. The insights into multimineral synergistic hydration mechanisms provide theoretical support for optimizing drilling fluid formulations and enhancing wellbore stability in the eastern Qaidam Basin and analogous geological settings.