Effect of CO2${\rm CO}_2$‐Enhanced Oil Recovery on Wave Velocities in Upper Assam Basin

This study examines the impact of CO2${\rm CO}_2$ flooding on Vp${V}_p$ and Vs${V}_s$ wave velocities in the Upper Assam Basin. Laboratory experiments were conducted on 15 consolidated sandstone cores from the Naharkatiya and Rudrasagar reservoirs (>3000$>3000$ m depth) and one unconsolidated sand pack (lightweight proppant, Houston, USA). Samples, with porosities ranging from 8.03% to 47.00%, were saturated with n-C16H34${n{\text{-}}{\rm C}}_{16}{\rm H}_{34}$ before CO2${\rm CO}_2$ injection. Results indicate CO2${\rm CO}_2$ flooding reduces Vp${V}_p$ (compressional velocity, m/s) by 4–11% in consolidated samples and over 25% in the unconsolidated pack, with less pronounced but significant reductions in Vs${V}_s$ (shear velocity, m/s). These changes are influenced by pore pressure, porosity, and temperature. Higher pore pressure amplifies velocity reductions by increasing fluid density and altering the bulk modulus. In consolidated sandstones, velocity reductions diminish with increasing porosity, whereas unconsolidated sands exhibit greater sensitivity due to their lower bulk modulus. Theoretical analyses confirm that Vp${V}_p$ reductions observed in laboratory settings are representative of in situ conditions. These findings highlight the value of time‐lapse seismic monitoring in tracking CO2${\rm CO}_2$ plumes and optimizing enhanced oil recovery strategies. The integration of seismic techniques improves reservoir management while supporting carbon sequestration initiatives in the Upper Assam Basin and similar geological settings.