Degradation of oil is a most important part of the MEOR. This procedure can reduce the oil's viscidity and freezing point and improve the oil's fluxion in-situ. This paper shows the encouraging results of the microbial degradation on the heave oils gathered from Qihai and Xingjiang oil fields in China. The results show that the bacteria can efficiently improve the property of the oils. After microbial treatment, the gum & asphalt content of the oils are lowered at above 9% and their structure is also changed. The ΣnC21-/ΣnC22+ of the oils are enhanced through the microbial treatments and the shapes of oils in solution are changed greatly. The oils' viscidity and freezing point are reduced about 15% and 20% respectively, with production increments ranging from 8.53% additional ratio from 35.72% additional ratio and the hot oiling frequencies of oil wells reduced at least 2.3 times. The average date production of the test wells in Xingjiang oil fields from 2.39 T before the treatment to 14.196T after the treatment, the ratio of cost to output with is 3.14 time higher than that of the microbial treatment. This technology proves to be feasible and economical in these oil fields.
Heavy oils are rich in gum and asphaltene, and they have the characters of high freezing point, low flow ability, difficult oil recovery and high recovery cost [1]. Microbe can improve the physical features of heavy oil in two aspects:
by degrading the components with big molecular of heavy oil, microbe can decrease the average molecular weight of heavy oil; and
the metabolite derived from microbe, such as biological surface active substance, acid, gas and so on, can decline the viscosity of oil considerably.
Gum and asphaltene are components with biggest molecular weight and most serious polarity in heavy oils, meanwhile they are one of the main factors making the difficulty of oil recovery [2]. Usually, microbe can hardly degrade them [3]. Confronting this situation, the authors separated and bolted lots of microbe from environments rich in petroleum microbe, and through the bolting conditions control, drew out a series of mix bacteria, which can effectively degrade heavy oil, even gum and asphaltene; these microbe has been used to lower the viscosity and freezing point of heavy oil for the goal to improve physical and chemical characters of heavy oils. Several experiments of microbial enhancing oil recovery (MEOR) have been carried out in Qinghai Oilfield and Xinjiang Oilfield, China.
Samples and experimental method The effective mix bacteria bolted are mainly bud bacillus, bacillus brevis, pseudomonas and coccus[3]. In the experiments, the crude oils are mainly mentioned and analyzed from Well Xian 19, Well Qizhong 22 respectively belonging to Huayanshan Oilfield and Qigequan Oilfield of Qinghai Oilfield Corporation, and from 97 and 98 Block of Xinjiang Oilfield Corporation; the crude oils are used in repeatability experiments from Qinghai Nanyishan Oilfield, Shengli Dongxin and Jinjia Oilfield, and Liaohe Ciyutuo Oilfield; density of the oils is 0.93 to 0.96g/cm3, and the content of gum and asphaltene is more than 35%.
