MEOR by a Newly Constructed Bacterial Oil-Displacing Consortium in Jurassic and Triassic Reservoirs: Properties Characterization, Environmental Adaptation, and Core Flooding Test

Microbial enhanced oil recovery (MEOR), a tertiary oil recovery technique, was supposed to extend the oil-producing period, and it could be a candidate for subsequent stimulation. However, reports related to MEOR were usually confined to a mild experimental setting, lacking the simulation of oilfield conditions. In this study, the indigenous oil-emulsifying bacteria were screened and evaluated for the construction of enhanced microbial oil displacement systems based on the simulation of fluid conditions in study areas (Jurassic Yan 9 and Yan 10 layers in Hujianshan oilfield and Triassic Chang 6 layer in Huaqing oilfield, Ordos Basin). The application potential of bacterial systems was evaluated through emulsification characterization and environmental adaptability, and the enhanced oil recovery of the optimal system was estimated by the core flooding test. The results showed that <i>Pseudomonas aeruginosa</i> RH1, <i>Bacillus subtilis</i> BS4, and <i>Pseudomonas stutzeri</i> PSD1 could grow at 37 °C, 55 °C, and without oxygen, reduce the surface tension (ST) of fermentation solution, and emulsify crude oil. The ST was further reduced to 26.2 mN m^-1, the oil-water interfacial tension reached 0.10 mN m^-1, and the EI₂₄ was increased to 84.33%, by the optimal bacterial oil-displacing system (<i>V</i> _RH1/<i>V</i> _BS4/<i>V</i> _PSD1 = 1:1.5:1.5), which had adaptability of temperature (4-85 °C), salinity (0-113.18 g L^-1), and pH (5-9). The core flooding tests were performed at the formation temperature and pressure of the Jurassic and Triassic study areas, indicating that oil recovery could be improved by 20.27% and 22.06% by the optimal system described above.