| Indigenous microbial enhanced oil recovery technology has been highly regarded for its unique advantages-massive in situ microbial reproduction and metabolism in reservoir, local high concentration of biomass and metabolites at the oil-water interface and nutrient adsorption being utilized by indigenous microorganism. The activation technology of functional microorganisms is the core of indigenous microbial enhanced oil recovery technology. At the same time, the research on microbial displacement mechanisms can guide the direction of numerical simulation technology, improve the prediction accuracy of simulation technology, strengthen the results of on-site application, and is the key for its industrial application. In order to lay the theoretical foundation of the industrial application, this paper focused on the researches:the indigenous microbial community, the metabolism of functional microorganisms, the screening and optimization of activation system, the evaluation of activation system, their microbial mechanisms and the analysis of field test.The structures of indigenous microbial community in formation water 6 Block were analyzed with the methods of MPN (most probable number) and high throughput sequencing. Thus, the foundation and objective for activating the indigenous microbial community were determined. The screening of activation system components was guided through the metabolic characteristics of functional bacteria. The result of these experiments revealed that the reservoir contained diverse indigenous bacteria and had a good basis for activating indigenous microorganisms. The dominant bacteria mainly were Arcobacter and the unclassified bacteria. The functional microorganisms-Pseudomonas aeruginosa and Bacillus subtilis- can produce biosurfactant and emulsify crude oil.In order to screen the activation system effectively, the evaluation indexes of screening activation system and a systematic research method of activation system were established. On the basis of these methods, an optimum activation system and its gas injection were obtained by the single factor experiment and orthogonal experiment. The function of activation system was mainly to active indigenous microorganism and emulsifies crude oil. Simulating the reservoir conditions, the activation system was evaluated. The result of these experiments revealed that the activation system can activate HOB remarkably, reduce the surface tension, and emulsify crude oil. Under the conditions of aerobic, limiting the oxygen and anaerobic, microbial community structure is changed, and functional bacteria including Pseudomonas、Bacillus and Stenotrophomonas are activated efficiently.Different gas injection volume and different forms of displacement impact on oil displacement efficiency were studied by the apparatus of microbial flooding physical simulation, and guided the field test scheme and implementation. The result of these experiments revealed that the emulsification of crude oil and the efficiency of oil displacement effect were better when gas injection and gas liquid ratio increased. The contribution rate of biomass, biosurfactant, in situ microbial reproduction and metabolism and subsequent water metabolism to improve oil displacement efficiency are approximately 6.8%,33.9% and 45.5%, respectively.After the pilot test was carried out, the related biochemical parameters were monitored. The results show: ①The indigenous bacteria were activated with the number increased 2-3,and Pseudomonas became dominant bacteria. ②The concentration of acetate ions and HCO3 increase, and the formation water pH rise. The rise of HCO3" concentration is consistent with the pH. ③The content of CO2 and CH4 in the gas of oil well changed slightly. ④After the field test, the emulsion was found 1 month later, and the effect of emulsifying crude oil was strengthened afterwards.⑤Oil production increased in wells, total oil increase was 10,104t up to Jun.,2014, and total recovery was raised by 5.2% up to Jun.,2014. |
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