Quantitative characterization of spontaneous and forced imbibition during soaking process in tight oil reservoirs

During the soaking process after hydraulic fracturing in tight reservoirs, the imbibition between matrix and fracture is an important mechanism for enhancing oil recovery. The soaking pressure acts on the matrix-fracture system in the form of external pressure difference to establish a dynamic-imbibition process. In this study, a core-scale numerical model is developed based on experimental data to study the dynamic-imbibition mechanism under non-zero initial water saturation quantitatively. The simulation results show that the enhancement extent of capillary pressure to the matrix oil mobilization is more significant under conditions of higher external pressure difference. Furthermore, the contributions of spontaneous imbibition (SI) and forced imbibition (FI) to the mobilization of matrix oil are 8.74% and 91.24% respectively. Then, effects of the oil-water viscosity ratio (VROW), matrix initial water saturation (MIWS), and fracture on SI and FI are analyzed in depth. As the MIWS increases from 0.27 (bound water) to 0.3, SI and FI decrease by 64.43% and 10.01%. The increase of VROW, MIWS, and fracture number tends to enhance the contribution of FI. This work is pivotal for gaining profound insights into imbibition and improving tight oil recovery through hydraulic fracturing development.