Effect of reservoir composition and structure on spontaneous imbibition: a case study of Shahejie Formation shale in Zhanhua Sag, Bohai Bay Basin

Abstract

Spontaneous imbibition has a certain impact on the oil and gas recovery of shale reservoirs. However, the current research on the influence of mineral composition and pore structure on spontaneous imbibition is not sufficiently comprehensive and lacks quantitative evaluation. Therefore, this study employed experimental methods combining X-ray diffraction, scanning electron microscopy, high-pressure mercury intrusion, nuclear magnetic resonance, and spontaneous imbibition to qualitatively and quantitatively characterize the influence of mineral composition, content, and pore structure characteristics on spontaneous imbibition. The results indicate that the relationship between quartz, calcite, and clay minerals and the imbibition slope exhibits a two-stage distribution (with critical values of 25%, 40%, and 20%, respectively). With the increase in mineral content, the imbibition slope first increases and then decreases. Additionally, pore structure parameters such as average pore throat radius, sorting coefficient, and structural coefficient show a positive correlation with the imbibition slope. Furthermore, small pores contribute significantly during the early imbibition stage, while medium to large pores serve as the main flow channels during the diffusion stage. This study quantitatively evaluates the relationship between fluids and minerals, providing a theoretical basis for understanding the complex interaction between fluids and minerals.