The feasibility of enhancing oil recovery in Xinjiang oilfield with heavy oil reservoir was studied. The results showed that main microbial populations in the reservoir were saprophytic, hydrocarbon-oxidizing, nitrate-reducing bacteria, sulfate-reducing bacteria, and fermentative. Given optimized carbon and nitrogen sources, the indigenous microorganisms generated gases, which mostly were CO_2, and amount of gases could reach 1.3 times volume as nutrient solution. The effect of MEOR was evaluated by a sand pack experiment, and the oil recovery was 9.5%. The test with the injection of nutrient and air was carried out. Field performance monitoring and product ion tracking results showed: 1.the indigenous microorganisms were activated with the number increased 2-3, and microbial population structure changed apparently; 2. The content of CO_2 and CH_4 in the gas of oil well changed slightly; 3. the properties formation water were changed, the content of (HCO_3)~- in formation water varied greatly, and emulsion were found. 4. Although Indigenous Microbial Flooding Technology may be a potential technique for the development of oilfields, that biogas generated by microbes is not the primary mechanism of Indigenous Microbial Flooding Technology is determined.
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