Of Co <sub> 2 </ Sub> - Microbial Alternately Flooding Experimental Research

The oil recovery by water flooding is low in china's oil fields because most are continental sediments and they have complicate formation conditions. In recent years most oil fields in East China have entered into their later high water cut period. Tertiary oil recovery technology such as gas injection, chemical and microbial methods is widely applied there. However, every kind of oil recovery method has its own limitation. Research on effective and economical ways to recover the large amount of residual oil has been carried out by many experts and specialists.The essay connects gas injection with microbial method and suggests a new model to enhance oil recovery that is CO₂-microbe compound flooding. The new method can not only make use of gas but also exert the microbe function. The injection of CO₂ into oil can make the viscosity and interfacial tension low. At the same time the chosed microbe that can break up the organic matter with high weight can help to solve the sedimental problem during the gas injection and its products also can reduce viscosity and interfacial tension. So the compound flooding can greatly enhanced oil recovery. But that the fact is or not true needs confirming by experiment like long-core test.The essay chooses seven kinds of impure microbes and analyzes their characteristics. The oil used in long-core test is from Niu 20-15 well of Shengli field without gas and the experimental condition set is: temperature 60℃and pressure 15MPa. Three long core tests are designed: microbial flooding, CO₂-water alternate injection and CO₂-microbe alternate injection. At last some knowledges and results are acquired.The results show that(1) The hydrocarbon composing has changed obviously after the microbe is injected into oil, and the short chain alkylate is increased and long-chain alkylate is relatively reduced, so the chosed microbe can effectively decompose the oil;(2) The oil recoveries of the three tests are all higher than water flooding and the oil recovery factors are respectively 55.25%, 58.06% and 67.07%. The injected fluid can effectively drive out oil;(3) The recovery of gas-microbe alternate injection is the highest of all the experiments;(4) Water cut is greatly declined after gas breaks through.