Compared with other EOR technique like gas flooding, chemical flooding, and thermal production in heavy oil, the prominent advantages MEOR has environment-friendliness and lowest cost. MEOR has various applications not only in sandstone but also carbonate reservoirs, light oil reservoirs as well as heavy oil reservoirs.
This paper mainly reviewed progress in laboratory studies and MEOR field tests including six big successful field tests in China. Present focus on MEOR has been changed from qualitative analysis to quantitative characterization, and high-tech like 16S rDNA and advanced method has being tried to investigate its mechanism on molecular level. The mechanism of microbial effects on making oil emulsification and wettability alternation was the main interest of recent study. Application of high resolution mass spectrum (HRMS) on MEOR mechanism has revealed the change of polar compound structures before and after oil degradation by the microbial on molecular level.
MEOR could be divided into indigenous microorganism and exogenous microorganism flooding. The key of exogenous microorganism flooding, was to develop effective production strains, and difficulty lies in the compatibility of microorganism, performance degradation and high cost. Indigenous microorganism flooding, has good adaptation but no follow up process on production strains development, thus it represents the main direction of MEOR. China has some of the most complex and diversified reservoirs and was notable for the scale of MEOR field tests since there has been six big MEOR field tests since 1998 after many precious small-cale tests. All field tests have shown positive results in incremental oil and water cut reduction. The combination of indigenous microorganism and exogenous microorganism flooding was adopted because of the cost and difficulty of exogenous microorganism flooding.
MEOR screening criteria for reservoirs has been improved. The parameters include temperature, salinity, oil viscosity, permeability, porosity, wax content, water cut, and microorganism concentration in which production fluid, temperature, and salinity were the most important three parameters. MEOR was suitable in reservoirs of which temperature lower than 80°C, salinity less than 100,000 ppm, and permeability above 50 mD. MEOR experience and study in reservoirs of 120°C, salinity more than 350,000ppm and permeability of 10 mD has expanded the reservoirs range suitable to carry out MEOR.