Experimental Research on the Correlation of Spontaneous Imbibition–Hydration Damage–Ion Diffusion in Shale Gas Reservoirs

The interaction between shale gas reservoirs and fracturing fluid triggers water–rock reactions, such as spontaneous imbibition, hydration damage, and ion diffusion, restulting in low flowback rate and high salinity, which have a huge impact on fracturing results and shale gas production. Currently, research on these water–rock reactions has been conducted. However, spontaneous imbibition, hydration damage, and ion diffusion simultaneously occur, and the research on relations among these water–rock reactions is not enough. As a result, it is not beneficial for a deep understanding of the interaction between fracturing fluid and shale and the optimization design of fracturing. Therefore, based on laboratory experiments, the law and influence factors of shale spontaneous imbibition, hydration damage, and ion diffusion with various conditions were determined. Investigations of quantitative correlation and interaction mechanisms among shale spontaneous imbibition, hydration damage, and ion diffusion were completed. Results indicated that these reactions had synchronous response features and were all strong in earlier stages and gradually became stable. Spontaneous imbibition and hydration damage exhibited mutual promotion, increasing shale imbibition amount. With the increment in imbibition amount, ion diffusion grew, pushing more saline ions into fracturing fluid and reducing the activity of fracturing fluid. Consequently, shale spontaneous imbibition and hydration degree were restricted. The outcomes deepen the understanding of the interaction between fracturing fluid and shale, providing theoretical support for efficient hydraulic fracturing in shale gas reservoirs.