Wettability and Imbibition Mechanism of the Multiscale Pore Structure of Jiyang Shale Oil Formation by NMR

Abstract

The wettability of shale pores is the key factor affecting the effectiveness of fluid–solid interaction. In this paper, two contributions were made. First, the macroscopic shale wettability of different lithofacies is evaluated by the contact angle method, and the microscopic wettability characteristics of the multiscale shale pore structure are elucidated via spontaneous imbibition and two-dimensional nuclear magnetic resonance (NMR) technology. Second, the effect of various factors, including wettability, on the imbibition efficiency of different shale lithofacies is revealed. Results show that (a) the contact angle of oil droplets is greater than 90°, indicating macroscopic hydrophilicity: block A (150.5°) > block C (149.9°) > block B (143.7°). (b) Microscale pores are hydrophilic, with a spontaneous imbibition water–oil ratio of 2.64–4.96; mesoscale pores are lipophilic, with a ratio of 0.08–0.61; macroscale pores are lipophilic, with a ratio of 0.08–0.56. (c) The higher the spontaneous imbibition water–oil ratio, the higher the imbibition recovery rate of small and large pores, and the higher the final imbibition recovery. (d) Compared with fracturing fluid, the overall recovery rate of the imbibition agent increased by 3.2%, and lithology, water–oil ratio, and micropore proportion are the main controlling factors. The research results of this article have important scientific and engineering significance for improving the recovery rate of shale oil.