Abstract: Based on lots of laboratory work, three groups of bacteria that can live in reservoir condition were picked to be applied to five wells in Qinghai Oilfield to improve oil production. These bacteria can change the oil’s properties and enhance the oil re-covery in Lab flooding experiment. All the five wells, which
produced sand and a mass of paraffin precipitated, produced more oil after microbial treatment with average increment by 8.35% through 35.72%. In the same time, the interval of hot oil cycling go beyond 2.3 times, The ratio of cost to return reached 1∶4.5, which indicate the prosperous future of applica-
tion of microbial method for improving oil production to Qinghai Oilfield.

Key words: microorganism, oil displacement test, single well, Huayanshan Oilfield, Qigequan Oilfield