Nanoparticles (NPs) are widely used in the petroleum industry, particularly in upstream and downstream applications, due to their quantum effects and high surface area-to-volume ratio. However, stable dispersion and high input ratios of NPs are critical factors limiting their application. This study thus synthesizes the biopolymer nanocomposite E-Ag NPs in one step using the metabolic product exopolysaccharide (EPS) from Bacillus subtilis as both a reducing and stabilizing agent. This study explored the potential of E-Ag NPs to enhance oil recovery in low- and medium-permeability formations. Experimental results showed that the average particle size of Ag NPs synthesized using EPS ranged from 20 to 50 nm. The presence of EPS resulted in a higher Zeta potential value (−43.4 mV), indicating improved stability of the nanofluid, effectively inhibiting NPs aggregation. Interfacial tension and wettability evaluation experiments demonstrated that E-Ag NPs exhibited excellent capabilities in reducing interfacial tension and altering wettability. In the enhanced oil recovery evaluation experiments, the imbibition experiment with E-Ag NPs achieved a maximum recovery rate of 54.32%, and the core flooding experiment reached a maximum recovery rate of 16.33%. In conclusion, the biopolymer nanocomposites developed by this method offer valuable guidance and reference for oilfield development, providing a green and efficient potential solution for enhanced oil recovery.

Green-synthesized nanomaterials are anticipated to be extensively applied to inhibit sulfate-reducing bacteria (SRB) in oilfields. Using Bacillus subtilis (B. subtilis) suspension as the raw material and zinc acetate dihydrate (C₄H₆O₄Zn·2H₂O) along with silver nitrate (AgNO₃) as precursors, Ag-ZnO nanoparticles (NPs) were synthesized using a simple and environment-friendly approach. The resulting Ag-ZnO NPs showed a rough surface morphology combined with high dispersibility, showing a particle size distribution of 33–35 nm. Protease and lipopeptides were identified as potential key agents driving the synthesis of Ag-ZnO NPs. At 40 μg/mL, the Ag-ZnO nano-solution effectively inhibited SRB cell growth and reduced the corrosion rate of carbon steel materials induced by SRB. Notably, reactive oxygen species (ROS) and malondialdehyde (MDA) levels increased significantly in SRB cells treated with Ag-ZnO NPs, while cell viability declined, indicating that the nanoparticles caused irreversible damage to SRB biofilms. The inhibitory mechanisms of the NPs against SRB cells were proposed to involve physical electrostatic interactions, metal ion toxicity, cell membrane disruption, and cell lysis.