Adding available nitrogen and carbon can improve the efficiency of oil displacement with indigenous bacterial flooding
In this study, simulated oil displacement tests were performed to investigate the effects of addition of readily available nitrogen and carbon nutrients on indigenous bacterial growth and crude oil displacement. The displacement efficiency of indigenous bacterial flooding was determined using simulated formation water (CaCl2-type, control) supplemented with NH4NO3 (N), glucose (G), or both (N + G). The results showed that NH4NO3-containing treatments (N and N + G) promoted indigenous bacterial growth in oil sand tubes by up to 704-fold compared with controls, whereas the G treatment inhibited growth by 91.1%. The cumulative displacement efficiencies of N, G, and N + G treatments were 102.9%, 22.1%, and 64.6% higher than those of controls, respectively. The corresponding relative quantities of 230 °C vaporizable fractions in residual oil were 35.8% higher, 64.2% lower, and 141.1% higher than those of controls. The levels of saturates, asphaltenes, and other materials in residual oil from the upper portion of oil sand tubes respectively decreased by 13.4%, 22.3%, and 31.9% in NH4NO3-containing treatments compared with controls. The pH and surface tension of displaced fluid were respectively 36.8% and 23.7% lower than those of the injected fluid. These results suggest that adding appropriate nitrogen and carbon sources can improve the efficiency of oil displacement with indigenous bacterial flooding via biological degradation, pore plugging and surface and interface interactions.