Dynamic variations of oil components and microbial communities during indigenous microbial stimulation pilot study in low-permeability reservoirs

Abstract

Indigenous microbial stimulation is considered as a highly promising technology for enhanced oil recovery (EOR) of low-permeability reservoirs. In this paper, oil components and microbial communities of indigenous microorganisms before and after bio-stimulation in the largest low-permeability oil field of China were discussed. The results showed that Pseudomonas aeruginosa was dominant in the original samples, followed by some sulfate-reducing bacteria (SRB) and iron-reducing bacteria (IRB), such as Desulfovibrio oxyclinae, and Methylopila capsulata, Deferribacter abyssi. After bio-stimulation, the species of microorganisms gradually decreased, the content of Pseudomonas aeruginosa reached 2∼3 times than that of the original samples. The harmful bacteria, such as SRB and IRB, gradually disappeared. The Pr/Ph of the oil decreased, whereas the Pr/nC 17, Ph/nC 18, and ∑nC 21−/∑nC 22+ increased. The average molecular weight of oil decreased after the microorganisms were stimulated, in which the contents of N1-containing compounds increased, and that of O1-containing compounds decreased. The contents of biphenyls, naphthalene, and its derivatives decreased. Whereas those of aromatic compounds, such as phenanthrene, quaternary, fluorene, and their homologs increased. Pilot study was applied in LD field block, the average water cut of 27–47 well group decreased from 87.60% to 74.86%, the oil production increased from 12.18 t/d to 29.58 t/d.