Characteristics and Influencing Factors for Forced Imbibition in Tight Sandstone Based on Low-Field Nuclear Magnetic Resonance Measurements

Spontaneous imbibition (SI) generally occurs under forced pressure (the difference between hydraulic fluid pressure and original pore pressure) during shut-in time. However, the experimental study of SI is commonly performed at atmospheric pressure and the effect of the forced pressure is often neglected. How the forced pressure influences the SI behaviors under different factors is still not clear. In this paper, low-field nuclear magnetic resonance (LF-NMR) was adopted to study the mechanism of SI in the tight sandstone rock sample under forced pressure (forced imbibition, FI). The effects of boundary conditions, initial water saturation, bedding plane (BP) direction, and fluid salinity on oil recovery were also systematically investigated. Results showed that the ultimate oil recovery (UOR) varied from different boundary conditions. An inverse correlation also exists between the water uptake and salinity. As osmotic pressure exists, more water was imbibed into core samples with the decrease of KCl salinity. The rock sample with perpendicular BP direction has a higher UOR than that with parallel BP direction. Moreover, the initial water saturation has a great effect on UOR. Higher water saturation would result in a lower UOR. This study aims to provide some insights into understanding the mechanism of FI in UOR enhancement.