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Reservoir pressure is a key factor affecting the degree of spontaneous imbibition. In this work, the oil distribution characteristics in core samples were simulated before and after spontaneous imbibition using nuclear magnetic resonance (NMR) technology. Specifically, four core samples were selected and subjected to spontaneous imbibition experiments at 0.1, 5, 10, and 15 MPa, respectively. Furthermore, the imbibition efficiency and imbibition rate at different pressures can be quantitatively calculated using the NMR T2 spectrum. The results indicate that the imbibition efficiency of smaller and larger pores has no obvious trend in the initial stage of spontaneous imbibition (0–72 h). After 72 h of spontaneous imbibition, there was a significant positive correlation between the imbibition efficiency and experimental pressure. Moreover, the imbibition rate of smaller pores increased monotonically with the increase in experimental pressure at 72–216 h in the four core samples. The imbibition rate of the smaller pores in core sample #4 at an experimental pressure of 15 MPa reached a maximum of 0.245%/h. However, the imbibition rate of larger pores in the four core samples has no significant correlation with pressure. In the overall analysis, the imbibition efficiency and imbibition rate of the four core samples have a positive correlation with the experimental pressure. At the same time, it was found that because of the greater number of smaller pores in tight sandstone, the degree of influence of experimental pressure on the spontaneous imbibition effect in smaller pores determines its influence on the overall spontaneous imbibition in the tight sandstone reservoir.
Wang et al. (Mon,) studied this question.