The mechanism of petroleum hydrocarbon degradation by the selected bacteria Brevibacillus brevis and Bacillus cereus is studied based on the metabolite analysis. The result shows that bio-oxidation processes, especially those called unconventional subterminal oxidation, terminal and double-terminal oxidation, are the main pathway by which the bacteria will convert petroleum hydrocarbons into fatty monoacids, hydroxyl fatty acids and dicarboxylic acids. This, for the first time, makes an important correction to the prevailing opinion which says that long-chain hydrocarbon molecules can be degraded into short-chain hydrocarbon molecules instead of acid compounds. The study explains how the bacteria ingest petroleum hydrocarbons as well as the correlation between ingestion modes and the active substances present in crude oil. The pathway to produce bio-surfactants and the correlation between produced bio-surfactants and oil metabolism are also discussed in this paper.

From 2002 to 2004, Brevibacillus brevis and Bacillus cereus were applied in the microbial huff and puff as well as the Microbial enhanced waterflood test in Daqing excessively low permeability (1.0md-25md) reservoir. After bacteria injection, 44 among the 60 huff and puff wells shows a significant oil production response—the accumulative oil increment reaches 6012 tons and the input-output ratio amounts to 1: 6. The Microbial enhanced waterflood test carried out in June 2004 also provides a satisfying result. After the injection of bacteria, the pressure in the two water injectors decreased more than 2MPa, which results in an injection capacity increase. In late 2004, the fluid production of the 5 producers (the total number is 8) is increased from 29.5 tons per day (before bacteria injection) to 44.4 tons per day, and the corresponding oil production is increased from 20.8 tons per day (before bacteria injection) to 36.9 tons per day. These make MEOR a very promising oil recovery method in Daqing Oilfield.

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