Crude oil is the non- renewable fossil resource and energy. Currently, the oil recovery is between 30-60% worldwide. In order to increased the oil recovery, the majority of China’s oilfields experienced three enhanced oil technique applications that rely on natural energy extraction, water injection or gas injection to maintain reservoir pressure and enhanced oil recovery, including chemical flooding technology. But the technologies unable to meet the growing demand for crude oil, underground residual oil resources accounted for more than 50%, so the oilfields need more effective and environmentally friendly recovery methods. Microbial enhanced oil recovery (MEOR) currently accepted in residual oil reservoir exploitation and heavy oil reservoirs exploitation, which was one of the most effective recovery methods, the advantages including low cost, no pollution, high efficiency, simple process control, no residual metabolites, etc., and gradually become the world's remaining oil exploration techniques. Surfactant on the degradation and emulsification of crude oil, finally change the solid oil to liquid oil and further to be exploited, was the most important mechanism of MEOR technology, but there is very little industrial application, mainly because of the complex geological conditions of different oil reservoir types, the nature of crude oil with large difference each other, the strains used in petroleum production lack of enough environmental adaptability, thus the research in the microbial enhanced oil recovery mechanism and adaption performance is very important.
Researcher HUANG Zhiyong of the Lab of Microbial Community and Engineered Ecological Function, Tianjin Institute of Industrial Biotechnology, Chinese Academy sciences, screened a facultative heat tolerant microorganism named XS2, the strain can withstand high temperature (40-80℃), salinity (NaCl concentration of 5-20 %, w/v) and pH (5-9), can degrade crude oil (C9-C37 alkanes), produce bioemulsifier (withstand 40-80℃, pH5-12, NaCl concentration 1-20 % , w/v) , and the strain showed a strong industrial potential applications.
Further study of the bioactive emulsifiers showed that the E24, which presented the wax emulsifying activity, accounted for more than 68%. Aditional fermentation process optimization was carried out by controlling the dissolved oxygen, pH and fed-batch, the production of the emulsifier increased from 2.4g/L to 23g / L. Meanwhile, the active bioemulsifier has a good potential for application, can greatly improve the oil remaining after water flood recovery from 11.55% to 30.78 % by physical model.
The Task Force combined the temperature and salinity tolerance of the strain XS2 and the low surface tension of a glucolipid-producing strain (surface tension less than 25mN/m), then adding additives and nutrient salts, and the complex system can further reduce the surface tension, improve emulsifying activity and emulsion stability, By diluted in 20-fold, the surface tension and emulsifying activity of the mixed solution were maintained at a strong level. Better emulsification activity for crude oil, crude oil particle size less than 5um and can maintained more than 20h, suggesting that the complex system showed a strong potential for industrial application.
At present, the strains has been applied for patent protection, the ongoing experiment was scale production and single well stimulation in Changqing Oilfield, next research focused on further enhanced oil recovery and reduce production costs.
