Experimental study on countercurrent imbibition in tight oil reservoirs using nuclear magnetic resonance and AFM: Influence of liquid-liquid/solid interface characteristics

• Published in: Fuel (Guildford) 2024-02, Vol.358, p.130026, Article 130026
• Main Authors: Yan, Xiang, Dai, Caili, Wang, Ruoyu, Liu, He, Meng, Siwei, Jin, Xu, Hu, Yong, Wu, Yining
• Format: Article
• Language: English
• Subjects: AFM; Countercurrent imbibition; Hydraulic fracturing; NMR; Tight oil sandstones
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2023.130026

[Display omitted] •1. The effects of different types of imbibition agents on imbibition efficiency were investigated.•2. The oil migration behavior during countercurrent imbibition was studied by nuclear magnetic resonance.•3. The nanoparticle-surfactant nanofluid owned the highest imbibition oil recovery.•4. Wettability alteration was the main mechanism in enhancing imbibition oil recovery. Countercurrent imbibition of the fracturing fluid is of much significance for enhancing oil production in tight oil reservoirs during the shut-in period after hydraulic fracturing. The addition of enhanced imbibition agents such as surfactants and nanoparticles into the polymer-based fracturing fluid is conducive to oil production. How different types of imbibition agents affect oil recovery and the applicable conditions for different imbibition agents, however, still need to be clarified. In this article, we used low-field nuclear magnetic resonance (NMR) to measure the one-dimensional (1D) oil signal profiles along the imbibition direction during the countercurrent imbibition process and determine the imbibition distance and water saturation of different imbibition agents including polymer, surfactant, nano-silica (NS) and NS-surfactant complexes. Moreover, by measuring oil-water interfacial tension (IFT), and the adhesion forces between alkanes and the hydrophobic surfaces before/after the imbibition agent treatments by atomic force microscope (AFM), the IFT reduction and wettability alteration abilities of these agents were evaluated. After the NS-surfactant complexes treatment, the adhesion force which represents the force required to pull off oil from the rock surface of became the lowest (15.81 pN), merely a quarter of that of NS (73.48 pN) and surfactant (70.01 pN), indicating a superior capability of NS-surfactant to improve wettability. The imbibition efficiency of the four systems in terms of imbibition distance and oil recovery was: NS-surfactant complexes: 38.43 mm 13.2 % > nonionic surfactant: 32.15 mm 9.0 % > NS: 25.88 mm 7.6 % > polymer: 17.64 mm 4.9 %. NS-surfactant nanofluid displayed the longest imbibition distance and highest water saturation, thus possessing the highest imbibition oil recovery. Nonionic surfactant with an IFT of 4.19 mN/m could greatly reduce the IFT compared with NS (35.98 mN/m), but the recovery enhancement induced by IFT reduction was not significant. In contrast, the increase in oil recovery by wettability alteration was distin