Medium-low maturity shale contains abundant oil resources, and in situ heating is a key technology for efficient extraction. This study systematically investigates thermal treatment effects on shale through permeability, pore structure, wettability, and adhesion force measurements. The results show that heating increases microfracture development. Both water contact angle and oil adhesion force correlate positively with total organic carbon (TOC). After thermal treatment, TOC, water contact angle, and oil adhesion force decreased by 32.7%, 46.2%, and 23.5%, respectively, indicating enhanced surface hydrophilicity due to reduced organic matter coverage and increased hydrophilic mineral exposure. A relative wettability index is proposed to characterize mixed pore wettability. Following heating, the index increases by 22.1% in small pores but decreases by 53.6% in large pores, suggesting increased hydrophilicity in small pores and increased oleophilicity in large pores, which favors oil migration into connected flow channels. These interfacial changes promote oil detachment and, combined with spontaneous imbibition, significantly enhance oil mobilization and recovery. Based on interfacial property trends, the optimal temperature range for improving oil mobility is identified as 400–450 °C. This work may provide a mechanistic basis for in situ shale oil heating development.
Bu et al. (Sun,) studied this question.