Microbial Enhanced Oil Recovery In The Oil Reservoir After Polymer Flooding

Currently, ploymer flooding are widely used to enhance oil recovery in many oil field in China. Moisture content of the produced water rise rapidly. However, more than half of the recoverable reserves are still trapped in the oil reservoir. Currently, we are facing with many puzzles, such as the difficulty of exploitation、high-cost low-recovery. How to enhance oil recovery in oil field after polymer flooding has important historical significance. In this study,16S rDNA clone library technique was used to analyze the microbial diversity of the samples collected from the forth oil production plant of Daqing Oilfield and Gangxi of Dagang Oilfield. We analyzed the biological activity of fermentative bacteria (FMB), saprophytic bacteria (TGB) and hydrocarbon-oxidizing bacteria (HOB) and the compositions of HOB bacterial communities in the enrichment cultures inoculated with demulsifier, bactericide, flocculant and scale inhibitor. It Provide a theoretical basis for microbial enhance oil recovery after polymer flooding. A polymer-producing strain was. isolated from the samples collected from Daqing Oilfield.In this study, wo do reaserch as follows:(1)16S rDNA clone library technique was used to analyze relative abundances of compositions of bacterial community in the samples of Daqing Oilfield and Dagang Oildield. The results showed that the microbial community structure of samples from Daqing and Dagang are quite different. Pseudomonas stutzeri and Pseudomonas aeruginosa covered a dominant percentage in many samples from Daqing and Dagang.(2)16S rDNA clone library technique was used to analyze relative abundances of compositions of bacterial community in the enrichment cultures of produced water (B2-D4-P45、B2-4-P47、B2-4-P49and B2-5-51) from Bei2xi reservoir in Daqing oilfield after ploymer flooding. Results showed that the dominant polymer-producing bacteria was Paenibacillus ehimensis. In addition, polymer-producing bacteria such as Agrobacterium tumefaciens, Stenotrophomonas maltophilia、and Rhodococcus qingshengii, covered a dominant percentage in some samples. During the process of the microbial plugging; three types of polymer-producing bacteria had been stimulated. One year later, microbial diversities increased significantly, and biosurfactant-producing bacteria and petroleum hydrocarbon-degrading bacteria were activated.(3)Most probable number (MPN) method and16S rDNA clone library technique was performed in this study. The reaserch result showed that after additives for sewage treatment were added into the enrichment cultures, the biological activity of all detected bacterial group decreased. The biological activity of HOB was the most susceptible to these additives.. Obtained results of16S rDNA clone library showed hat the microbial community structure of HOB changed greatly. After the additives were added, Pseudomonas stutzeri, covered a dominant percentage in the oil well sample, was not detected in the enrichment cultures. In addtion, Pseudomonas aeruginosa, was not detected in oil well sample, became the dominant group in the enrichment cultures after demulsifier, bactericide and scale inhibitor were added. For water well sample, after bactericide was added, the only detected bacterial group was Exiguobacterium sp.. Interestingly, Thauera sp. was dominant in the water well samples before and after demulsifie, flocculant and scale inhibitor were added. Conclusion:Sewage treatment have great influence on the microorganisms, the resistance to Sewage treatment are different for different microorganisms.(4) A strain of DT-1was isolated, Phylogenetic analysis based on16S rDNA gene sequence indicated that strain DT-1was affiliated with Paenibacillus ehimensis with a similarity of99%. Crude oil before and after degradation by microorganisms was performed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), the results show that, Gas chromatograph spectrometry analysis proved that the relative percent contents decreased in aromatic hydrocarbons and non-hydrocarbons, and the composition of saturated hydrocarbons had changed a lot.