Analysis On Indigenous Microbial Community And Functional Bacteria Of Typical Block In Xinjiang Oilfield

Microbial enhanced oil recovery technique is an enhanced technique to increase the recovery efficiency of water flooding oil field and to focus on research on microcosmic mechanism. Research on microbes in oil pool and efficient functional bacteria are the key contents in this technique. Through investigation on the status quo of microbial enhanced oil recovery technique, this paper researches microbial community structure in oil pool, and learns the distribution law of microbes in each block in Xinjiang Oilfield; it also builds complex microbial community which can stabilize the emulsified crude oil, so as to better serve microbial enhanced oil recovery technique.In this research, firstly, a method of molecular ecology is optimized and selected on the basis of the oil pool environment. The researchers optimize DNA extraction method as well as the primer, gel concentration and electrophoresis time of denaturing gel gradient electrophoresis (DGGE) method, and select restriction enzyme of Terminal-restriction fragment length polymorphism (T-RFLP) method. By comparing the prices of application conditions of traditional DGGE and T-RFLP and emerging 454 pyrosequencing technique in oil pool environment, the researchers conclude that PCR-DGGE method is very sensitive when distinguishing communities with close genetic relationship; however, it is prone to causing errors in the experimental results since the information content it carries is not large; therefore, it needs to be applied in coordination with other methods. Although T-RFLP method has high accuracy and good repeatability, it cannot directly identify the genus information of the microbes because of incomplete data in RDP database; therefore, it is applicable to comparing the changes of microbial community structure.16SrDNA clone library method and 454 pyrosequencing method both have high accuracy, and the two methods can mutually verify each other. However, limited by the workload of picking cloning, generally, clone library method can only detect the relative dominant bacteria with the abundance larger than 1%; 454 pyrosequencing method can detect micro bacterial genus with the abundance of only 0.03% or even lower. To save the costs,16SrDNA clone library method shall be used when detecting simple microbial community structure in the oil pool, such as activated microbial community, which can obtain the detection results which can explain the problems.Then the researchers detect the four groups of water samples from the oil pools in different blocks in Xinjiang Oilfield by means of different methods of molecular ecology.1) The researchers compare the changes of community structure in the produced liquid from T6190 oil well in Liuzhong area after microbial flooding by combining DGGE method and clone library technique, and they find that dominant bacteria in T6190 in different periods concentrate upon Pseudomonas, arcobacter and Clostridium. The results show the diversity of the microbial community structure in the characterization of produced liquid. With the increasingly reduced nutritional agents injected on site, it will appear negative correlation with the daily output of the oil well.2) The researchers compare the community structures in the produced liquids from the oil well and the injected water from injection well in Luliang block by means of clone library. They find that the bacteria contents in the injected water are in average, where bacterial genus abundance of Pseudomonas accounts for 72% in the produced liquid, the abundance of Pseudomonas accounts for 10%, with obvious dominance; aromatic index of the injected water is larger than that of the produced liquid in the oil well.3) The researchers analyze the potential functional bacteria in the produced liquids from 10 oil wells in 6 different blocks in Xinjiang Oilfield by means of clone library method; they find that Rhodobacteraceae, Pseudomonadaceae and Bacillaceae which have the functions of hydrocarbon degradation and biosurfactant generation universally exist in the 10 water samples.4) The researchers determine the bacteria and archaea community structures in Luliang, Liuzhong area and Qizhong area in Xingjiang Oilfield by means of 454 pyrosequencing method; they find that in the same block, when the mineralization of the water sample is less than 12000mg/L, the diversity of the bacterial community structure largely appears the positive correlation with mineralization. The bacterial structures in the three blocks are featured by inter-block similarities and specificities within blocks; while such law is not found in archaea structure. Meanwhile, the sequencing results find that under natural selection condition, most of the bacteria which can adapt to the oil pool conditions and which are brought in by the injected water are the dominant bacteria in the original injected water. In Liuzhong area block where the oil pool environment is artificially changed, such conditions is in the contrary, where those which can survive in the oil pool are the inferior bacteria in the original injected water. While such law is not found in archaea structure; and all the bacteria detected in the produced liquid which mutually exist in the injected water all belong to relative dominant bacteria. Meanwhile, the experiments also find that the abundance of OUT which exists in archaea in the injected water and produced liquid is larger than that of bacteria in both the injected water and produced liquid in the three blocks. This indicates that compared with bacteria, more archaea in the injected water can adapt to oil pool environment; moreover, most of them in the oil pool are brought in by the injected water as estimated.Finally, through nine generations of acclimatization in the laboratory, the researchers get the stable microbial community composed of Bacillus licheniformis, Bacillus subtitlls and Bacillus amyloliquefaciens; three bacterial strains of bacillus are abstained through screening and cultivation in the laboratory. Comparison on emulsifiability and flooding effects of the stable microbial community and single bacterial strain shows that the stable microbial community can reduce the surface tension to 27mN/m from 72mN/m, so that it can increase the oil recovery rate by 8.22% under the condition that recovery rate by water flooding reaches 44.13%; the comprehensive effects is slightly superior to that of bacillus subtitlls, while the emulsifiability and flooding effects of bacillus licheniformis and bacillus amyloliquefaciens are comparatively weak. In the experiment, the four strains of single bacteria of Rhodococcus, Geobacillus, Brevibacillus and Pseudomonas are commonly cultivated with the stable microbial community respectively. Inspection is carried out on the growth conditions of each strain by means of T-RFLP method, which finds that rhodococcus and brevibacillus cannot commonly grow with the stable microbial community, while pseudomonas and geobacillus grow well after being commonly cultivated with acclimated microbial community, and their abundance ratio with acclimated microbial community can reach 1.2:1 and 1.3:1. Test is carried out on the surfactant yield, degradation property and flooding effects of the complex microbial community which is the common culture of acclimated microbial community and pseudomonas, geobacillus, which finds that the emulsifiability of complex microbial community culture of acclimated microbial community and geobacillus is weak; the emulsification effect, stability of emulsion and the surfactant yield of the complex microbial community composed of acclimated microbial community and pseudomonas are all superior to that of acclimated microbial community. The recovery rate can be finally increased by 9.01%. This shows that pseudomonas can generate synergistic effect with microbial community to metabolize crude oil.In conclusion, this research compares several molecular methods and finds out the most suitable application ranges and conditions. Moreover, it is used for subsequent sample analysis and gets the distribution laws of microbial community in oil pool subject to microbial flooding or without microbial flooding. An acclimated strain with excellent emulsification effect is finally obtained, and it is found to be able to form synergistic effect with pseudomonas, so as to better metabolize the biosurfactant generated on the surface of crude oil, thus increasing flooding efficiency.