CT-Based Investigation and Numerical Modeling of Wettability Alteration During Spontaneous Imbibition

This study explores the effect of brine salinity on spontaneous imbibition (SI) in oil-wet carbonate rocks, with a particular focus on the enhancement of oil recovery through wettability alteration. Co-current (COSI) and counter-current (COUSI) spontaneous imbibition tests were performed using carbonate core samples saturated with oil and connate water. The experiments involved the use of low salinity water (LSW) and high salinity water (HSW) as imbibing fluids under controlled boundary conditions in Amott cells. High-resolution X-ray computed tomography (CT) was employed to monitor in-situ water saturation profiles at different stages of the tests. The findings demonstrate that LSW significantly improves the efficiency of SI compared to HSW. LSW led to a more uniform and faster penetration of the imbibition front, indicating stronger capillary-driven displacement and effective wettability alteration toward a water-wet state. In contrast, HSW resulted in slower and more limited imbibition with sharper saturation fronts, revealing weaker wettability modification. Quantitative comparisons based on CT imaging and numerical simulations confirmed a stronger wettability shift in LSW-treated cores, with the calculated wettability index increasing from moderately water-wet to strongly water-wet conditions. The integration of experimental observations and perturbation-based numerical modeling enabled dynamic tracking of wettability alteration over time. Simulation results showed good agreement with experimental data, with less than 10% error in most cases. These outcomes highlight the effectiveness of LSW in modifying rock-fluid interactions and improving oil displacement in tight, oil-wet carbonate reservoirs. The results offer a valuable framework for designing optimized low salinity EOR strategies in naturally fractured formations where SI plays a critical recovery role. • New counter-current and co-current solutions for 1D spontaneous imbibition by the Perturbation method were validated using experimental data. • CT scanning techniques have been used to measure in-situ water saturation profiles during SI process for nonwatery-wet carbonate rocks in oil-water system. • CT imaging reveals faster, more uniform imbibition fronts using LSW, indicating stronger capillary-driven displacement and effective wettability alteration. • Perturbation-based numerical modeling closely matches experimental observations, validating dynamic wettability alteration with less than 10% error.