To gain a better understanding the difference on microbial community structure for low permeability reservoirs in Daqing Oil Field at different days in outdoor, we constructed the 16SrDNA gene clone library for different days' samples respectively. The results showed that the dominant microbes of zero days' sample are uncultured Acinetobacter sp. (42%), uncultured Clostridia bacterium(21%) and Bacillus sp. (12%); the dominant microbes of two days' sample are uncultured Acinetobacter sp. (53%), uncultured Clostridia bacterium (13%) and Bacillus sp.(10%); the dominant microbes of four days' sample are uncultured Acinetobacter sp. (62%), uncultured Clostridia bacterium (10%), Bacillus sp.(9%) and uncultured Klebsiella sp.(8%); the dominant microbes of 6 days' sample are uncultured Acinetobacter sp. (70%) and uncultured Klebsiella sp.(10%). The numbers of uncultured Acinetobacter sp. and uncultured Klebsiella sp. are gradually increased, the numbers of uncultured Clostridia bacterium, Bacillus sp., Ochrobactrum sp. and Pseudomonas sp. are gradually decreased. It is supposed to provide a dependable basis for the importance for analysing microbial community structure of oil reservoir without delay.

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