Abstract
Compared with other enhanced oil recovery (EOR) techniques like gas flooding, chemical flooding, and thermal production, the prominent advantages of microbial enhanced oil recovery (MEOR) include environment-friendliness and lowest cost. Recent progress of MEOR in laboratory studies and microbial flooding recovery (MFR) field tests in China are reviewed. High biotechnology is being used to investigate MFR mechanisms on the molecular level. Emulsification and wettability alternation due to microbial effects are the main interests at present. Application of a 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 the 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 the microorganism, performance degradation, and high cost. Indigenous microorganism flooding has good adaptation but no follow-up process on production strain development; thus, it represents the main development direction of MEOR in China. More than 4600 wells have been conducted for MEOR field tests in China, and about 500 wells are involved in MFR. 47 MFR field tests have been carried out in China, and 12 field tests are conducted in Daqing Oilfield. MFR field test’s incremental oil recovery is as high as 4.95% OOIP, with a typical slug size less than 0.1 PV. The input-output ratio can be 1 : 6. All field tests have shown positive results in oil production increase and water cut reduction. MEOR screening criteria for reservoirs in China need to be improved. Reservoir fluid, temperature, and salinity were the most important three parameters. Microbial flooding technology is mature in reservoirs with temperature lower than 80°C, salinity less than 100,000 ppm, and permeability above 5 mD. MFR in China is very close to commercial application, while MFR as quaternary recovery like those in post-polymer flooding reservoirs needs further study.
Highlights
Oil and gas remain the main primary energies in the world
Tertiary recovery is known as enhanced oil recovery (EOR), which includes polymer flooding, surfactant flooding, gas flooding, thermal production, and microbial enhanced oil recovery (MEOR)
Different from previous studies focused on microbial huff and puff, or cycle microbial recovery (CMR), which are not real microbial flooding tests, this paper focuses on real microbial flooding recovery (MFR) to show what progress and experience have been made in China
Summary
Oil and gas remain the main primary energies in the world. Enhanced oil recovery involves how to recover as most original oil in place (OOIP) as possible economically. The EOR process has two basic features: (a) effectiveness of recovery of more oil and (b) relatively low cost. To increase the sweep efficiency, the most important way is to reduce the mobility ratio, which can be attained by increasing the water phase viscosity, or reducing the oil viscosity, or improving the relative permeability. This is the key idea of mobility control, which is of vital importance in all EOR techniques. MEOR follows the basic EOR principle of enlarging the sweep efficiency and increasing the capillary number. It could be applied to sandstone [17], carbonate [18, 19], light oil, heavy oil [11, 20, 21], and medium/high-permeability and low-permeability reservoirs [20, 22, 23]
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