Enhanced oil recovery by spontaneous imbibition of nanofluid assisted low saline alkali polymer in sandstone reservoir

• Alkali and polymer effectively improve the stability of silica nanofluid . • Two different modes of spontaneous imbibition experiment. • Silica nanofluid significantly reduced the IFT and alters the wettability . • The imbibition mechanism investigated through solid–liquid interfacial force. • Silica nanofluid has potential to recover maximum oil than other flooding agents. Spontaneous imbibition plays a crucial role in enhanced oil recovery (EOR). In this work, the synergistic effect of low salinity water, alkali, polymer, and nanoparticles was explored as a potential oil recovery agent for low acid number crude oil in a sandstone reservoir. Silica nanoparticles (15 nm) at various concentrations (100–1000 ppm) were dispersed in low salinity water (lowsal) containing sodium carbonate (alkali) and polyacrylamide (PAM, polymer), referred to as low saline-alkali-polymer-nanofluid (LSAP-NFs). Interfacial tension (IFT) and contact angle measurements were performed at 50 °C to understand the impact of LSAP-NFs on EOR through spontaneous imbibition. The results showed that the larger molecular size of the polymer hindered the effect of alkali in reducing the IFT and altering the wettability . The imbibition efficiency of the LSAP-NFs was evaluated using an Amott cell at 50 °C with Berea sandstone core samples. The spontaneous imbibition results showed that the imbibition effectiveness of the LSAP-NFs was higher than that of simple alkali, LSAW, and LSAP flooding agents. The prominent mechanism of imbibition was studied by analyzing the solid–liquid interfacial force using F-D mode from Atomic Force Microscope (AFM) investigations. The interfacial mechanisms, including IFT, wettability, surface roughness, and solid–liquid interfacial forces, confirmed that the imbibition process is equally controlled by gravity and capillary forces. Further, the solid–liquid interfacial force exposed a fully hydrophilic surface with silica nanofluid, confirming that capillary force dominates imbibition. This work identifies the fundamental mechanism by which spontaneous imbibition impacts enhanced oil recovery.