Contributing Microbial Communities For Microbial Enhanced Oil Recovery In Different Oil Reservoirs

Microbial enhanced oil recovery (MEOR) technique is one of the most prospectivemethods for oil recovery due to its economic, environmentally-friendly and simpleadvantages. Principally, microbes that possess functional activities and productsresulting in the increase of oil production in MEOR field trials are the key for thediscovery of MEOR mechanisms. In the present thesis, microbial communities insamples collected from oil wells during MEOR field trials carried out in six different oilreservoirs were monitored using molecular biological techniques, such as16S rRNAgene clone library and the next generation DNA sequencing. The major contents andfindings are as follows:Microbes stimulated by nutrients of molasses, corn steep liquor with N and P in thelow-temperature heavy oil reservoir of Xinjiang oil field were Pseudomonas aeruginosaand Pseudomonas stutzeri; Microbes stimulated by nutrients of corn steep powder withN and P in the mesophilic polymer flooded oil reservoir of Daqing oil field were P.aeruginosa, P.stutzeri and Bacillus halodurans; Microbes stimulated by nutirents ofcellulose bran, yeast powder and molasses with N and P in the high-temperature heavyoil reservoir of Dagang oil field were P.aeruginosa, P.stutzeri and Enterobacterhormaechei; Microbes stimulated by nutrients of molasses, corn steep liquor with N andP in the high-temperature high pour-point oil reservoir of Liaohe oil field were P.aeruginosa, P.pseudoaligenes; Microbes stimulated by nutrients of modified starch withN and P in the ultra-temperature hypersaline oil reservoir of Jianghan oil field wereP.aeruginosa, P.stutzeri, Bacillus circulans and Enterobacter hormaechei. In summary,although characteristics, field trials and nutrients of the oil reservoirs under study weresignificantly different, stimulated microbes after MEOR field trials showed significantlysimilar. Pseudomonas, Bacillus and Enterobacter were dominant in the samplescollected from the oil reservoirs after MEOR field trials, indicating that Pseudomonas,Bacillus and Enterobacter were contributing microbes for MEOR.Additionally, diversity within P.stutzeri is not limited to physiological propertiesbut is also reflected at the genetic level. P.stutzeri is a species detected frequently insamples from oil reservoirs and possessing functions for MEOR. The thesis discovered the diversity and genomovar assignment of P.stutzeri in oil reservoirs for the first time.High diversity of P.stutzeri was observed, which was exemplified in the detection ofsequences assigned to four known genomovars1,2,3,20and eight unknown genomicgroups. The frequent detection and predominance of P.stutzeri belonging to genomovar1in most of the oil reservoirs under study indicated an association of genomovars ofP.stutzeri with the oil field environments.Finally, Bacillus is a contributing group for MEOR, however diversity of Bacillusin oil reservoirs can not be well unveiled based on molecular biological methods. In thethesis, based on the advantages of both culture-dependent microbial methods andculture-independent molecular biological methods, a method for quick detection ofBacillus was invented. Many genera of Bacillus detected in the oil reservoirs understudy by the method were not reported previously, and most of sequences detected bythe method showed low similarities with cultured strains of Bacillus, which indicatedthat diversity of Bacillus in oil reservoirs was far from clear.In summary, the main innovations are concluded as follows:(1) Pseudomonas,Bacillus and Enterobacter were the main microbial communities stimulated bycomposite organic and inorganic nutrients in oil reservoirs during MEOR field trials.(2)High diversity of P. stutzeri was observed in samples from oil reservoirs, newgenomovars of P. stutzeri habiting in oil reservoirs were proposed.(3) A new method forquick detection of Bacillus in oil reservoirs was invented.