The Evaluation On Oil Displacement Eiffciency Of Bio-surfactant And Application In Pubei Oilfield

Bio-surfactant is the microbial metabolin with surfactivity, which yield is animportant indicator for measuring that microbe enhances oil recovery. There areseveral kinds of bio-surfactants, such as glycolipid, lipopolysaccharid, lipopeptid,neutral lipid derivatives, and so on. Bio-surfactant can significantly reduce thesurface tension and improve interface properties. Comparing with chemicalsurfactant, bio-surfactant has many advantages of good selectivity, low dosage,non-toxicity, bio-degradability, no pollution. It can also introduce new functionalgroups which is difficult to be synthesized by chemical methods.In this paper, bio-surfactant formulation which appropriate for Block Pubei wasselected and optimized. The adaptability of rhamnolipid surfactant to Pubei field wasresearched. The evaluation on oil displacement efficiency of bio-surfactant andparameter values of field trials were studied through indoor core floodingexperiments. According to the results of applying in field tests, series of problemswere solved such as complex process, difficult operation and environmentalpollution, and we deepened the understanding of bio-surfactant displacementmechanism.1. Selection and optimization of bio-surfactant for Pubei oilfieldAccording to the specific characteristics of Pubei reservoir, it was necessary forthe mixture of chemical surfactants and rhamnolipid to achieve ultra-low interfacialtension without alkali conditions. After several rounds of screening and testing, achemical surfactant synergized with rhamnolipid was selected. The interfacialtension of the surfactant which concentration was lower than0.1%(wt) can form10-1mN/m magnitude with a wide concentration range of0.1%(wt)～0.01%(wt).The bio-surfactant composite system possesses good stability of interfacial tensionand dynamic interfacial tension balance.2. The adaptability of rhamnolipid surfactant composite system for Pubei oilfieldThe adaptability of rhamnolipid surfactant composite system was studied forPubei oilfield through aspects of reservoir temperature, pressure, permeability. The conclusions are as following:（1）The oil layer temperature of Pubei reservoir is40-50℃, and the optimizedcomposite systems can achieve ultra-low interfacial tension.（2）Through the rational design of viscosity and injection rate of floodingsystems, the pressure showed important guiding significance to improve andenhance the oil displacement efficiency of the bio-surfactant flooding.（3）Permeability affect the pass capacity of injecting the rhamnolipid surfactantcomposite systems.3. The indoor evaluation on oil displacement efficiency of the bio-surfactantThe concentration of bacterial solution was optimized, according to therelationship of the amount of bio-surfactant and oil displacement efficiency. Theexperimental concentrations were0.5%,1.0%,2.0%, and the suitable bio-surfactantconcentration was ultimately determined at1.0%. Meanwhile, the effect of differentslug composite on the oil displacement efficiency was analyzed, throughpre-polymer slug design of profile control, determination of polymer molecularweight and concentration.4. The field test application of bio-surfactant on Pubei AreaAccording to three principles of improving reservoir sweep efficiency, reducingthe flow of fluid into the bypass furthest and taking full advantage of the floodingperformance of injecting fluid, personalized program was designed and siteconstruction was carried out. Yield increase was significant and stable. Until to theend of September2010, the amount of incremental oil was1315tons. Evaluation onPubei area had been recognized as:(1) Dynamic changes of injecting wellsThe injection pressure decreased, and apparent injectivity index of water wellsincreased0.9m3/d MPa, which value was from6.3m3/d MPa to7.2m3/d MPa.(2) Dynamic changes of production wellsThe amount of Rhamnolipid was measured qualitatively from the produced fluidof connection wells. The results showed that bio-surfactant was obtained in9testwells. Water content generally decreased and the oil displacement efficiency wasimproved in all of9production wells. The average water content decreased from93.66%to90.24%. In Pubei oilfield, the main change for the quality of oil production was the increasing of the content of non-hydrocarbon and asphaltene. The salinity ofproduced fluid and the content of the ion Cl-increased also.