Community structure and distribution of endogenous microorganism in water flooding reservoirs of Shengli Oilfield

16S rDNA clone and sequencing were carried out to determine the community structure of the endogenous microorganism in 10 different water flooded reservoirs of Shengli Oilfield,which were screened according to temperature(55 ~91℃).salinity (3 000 -20 000 mg/L),permeability((207 ~6 900)×10~(-3)μm~2)and some other factors.The results show that the communities of the endogenous microorganism consist of diverse bacteria and archaea.114 kinds of bacteria are detected,which are dominated by Proteobacteria (Gammaproteobacteria 41.4%,Betaproteobacteria 25.0%).There are 14 kinds of archaea.As a whole,all kinds of micro-organism required for microbial oil displacement are included,such as hydrocarbon-degrading microorganism,surfactant producing microorganism and methane producing microorganism,etc.Achromobacter and Arcobacte for hydrocarbon degrading can be found almost in all the investigated reservoirs.The community structures of endogenous microorganism are influenced by temperature,salinity,permeability and water flooding time.In the reservoirs with higher temperature,there are more archaea and thermophile bacteria such as Thermus, Thermincola,Thermanaeromonas.Especially in 90℃reservoir,thermophile bacteria content reaches to 23%,and there is extreme thermophile Geoglobus.In the reservoirs of higher salinity( 10 000 mg/L),halotolerant bacteria content is about 30%,which is about as two times as that in the reservoirs of lower salinity.But strict anaerobic and denitrification strain doesnt take advantages under higher salinity.Besides,higher permeability and longer water flooding time could increase the diversity of the communities,and the number of the communities can increase by above one times.It is concluded that all the investigated reservoirs contain abundant endogenous micro-organism, and in them all there is biological basis for microbial enhanced oil recovery.But there is difference in microorganism community structure in different environmental reservoirs.So the formula design and the injection technology of microbial flooding should be optimized according to specific reservoir environment.