Microbial enhanced oil recovery through deep profile control using a conditional bacterial cellulose-producing strain derived from Enterobacter sp. FY-07.

BACKGROUND: Heterogeneity of oil-bearing formations is one of major contributors to low oil recovery efficiency globally. Long-term water flooding will aggravate this heterogeneity by resulting in many large channels during the exploitation process. Thus, injected water quickly flows through these large channels rather than oil-bearing areas, which ultimately leads to low oil recovery. This problem can be solved by profile control using polymer plugging. However, non-deep profile control caused by premature plugging is the main challenge. Here, a conditional bacterial cellulose-producing strain, namely Enterobacter sp. FY-0701, was constructed for deep profile control to solve the problem of premature plugging. Its deep profile control and oil displacement capabilities were subsequently identified and assessed. RESULTS: The conditional bacterial cellulose-producing strain Enterobacter sp. FY-0701 was constructed by knocking out a copy of fructose-1, 6-bisphosphatase (FBP) encoding gene in Enterobacter sp. FY-07. Scanning electron microscope observation showed this strain produced bacterial cellulose using glucose rather than glycerol as the sole carbon source. Bacterial concentration and cellulose production at different locations in core experiments indicated that the plugging position of FY-0701 was deeper than that of FY-07. Moreover, enhanced oil recovery by FY-0701 was 12.09%, being 3.86% higher than that by FY-07 in the subsequent water flooding process. CONCLUSIONS: To our knowledge, this is the first report of conditional biopolymer-producing strains used in microbial enhance oil recovery (MEOR). Our results demonstrated that the conditional bacterial cellulose-producing strain can in situ produce biopolymer far from injection wells and plugs large channels, which increased the sweep volume of injection water and enhance oil recovery. The construction of this strain provides an alternative strategy for using biopolymers in MEOR.

Microbial abundance and community composition influence production performance in a low-temperature petroleum reservoir.

Enhanced oil recovery using indigenous microorganisms has been successfully applied in the petroleum industry, but the role of microorganisms remains poorly understood. Here, we investigated the relationship between microbial population dynamics and oil production performance during a water flooding process coupled with nutrient injection in a low-temperature petroleum reservoir. Samples were collected monthly over a two-year period. The microbial composition of samples was determined using 16S rRNA gene pyrosequencing and real-time quantitative polymerase chain reaction analyses. Our results indicated that the microbial community structure in each production well microhabitat was dramatically altered during flooding with eutrophic water. As well as an increase in the density of microorganisms, biosurfactant producers, such as Pseudomonas, Alcaligenes, Rhodococcus, and Rhizobium, were detected in abundance. Furthermore, the density of these microorganisms was closely related to the incremental oil production. Oil emulsification and changes in the fluid-production profile were also observed. In addition, we found that microbial community structure was strongly correlated with environmental factors, such as water content and total nitrogen. These results suggest that injected nutrients increase the abundance of microorganisms, particularly biosurfactant producers. These bacteria and their metabolic products subsequently emulsify oil and alter fluid-production profiles to enhance oil recovery.

Dynamic processes of indigenous microorganisms from a low-temperature petroleum reservoir during nutrient stimulation.

Compared to medium-high temperature petroleum reservoirs (30°C-73°C), little is known about microbial regulation by nutrients in low-temperature reservoirs. In this study, we report the performance (oil emulsification and biogas production) and community structure of indigenous microorganisms from a low-temperature (22.6°C) petroleum reservoir during nutrient stimulation. Culture-dependent approaches indicated that the number of hydrocarbon-oxidizing bacteria (HOB), nitrate-reducing bacteria (NRB) and methane-producing bacteria (MPB) increased by between 10- and 1000-fold, while sulfate-reducing bacteria (SRB) were observed at low levels during stimulation. Phylogenetic analysis of the 16S rRNA gene indicated that Pseudomonas, Ochrobactrum, Acinetobacter, Halomonas and Marinobacter, which have the capability to produce surfactants, were selectively enriched. Methanoculleus, Methanosaeta, Methanocorpusculum and Methanocalculus showed the largest increase in relative abundance among archaea. Micro-emulsion formed with an average oil droplet diameter of 14.3 µm (ranging between 4.1 µm and 84.2 µm) during stimulation. Gas chromatographic analysis of gas production (186 mL gas/200 mL medium) showed the levels of CO2 and CH4 increased 8.97% and 6.21%, respectively. Similar to medium-high temperature reservoirs, HOB, NRB, SRB and MPB were ubiquitous in the low-temperature reservoir, and oil emulsification and gas production were the main phenomena observed during stimulation. Oil emulsification required a longer duration of time to occur in the low-temperature reservoir.

Nutrients and oxygen alter reservoir biochemical characters and enhance oil recovery during biostimulation.

Biostimulation of petroleum reservoir to improve oil recovery has been conducted in a large number of oilfields. However, the roles and linkages of organic nutrients, inorganic salts and oxygen content during biostimulation have not been effectively elucidated. Therefore, we investigated the relationships between carbon source, nitrogen source, phosphorus source, oxygen content, and microbial stimulation, oil emulsification, and oil degradation. The organic nutrients (molasses) accelerated microbial growth, and promoted oil emulsification under aerobic conditions. The added molasses also promoted metabolites production (CO2, CH4 and acetic acid) and microbial anaerobic hydrocarbon degradation under anaerobic conditions. (NH4)2HPO4 improved gases production by neutralizing the acidic production and molasses. NaNO3 could also improve gases production by inhibiting sulfate-reducing bacteria to adjust pH value. Oxygen supply was necessary for oil emulsification, but bountiful supply of oxygen aggravated oil degradation, leading the entire ranges of alkanes and some aromatic hydrocarbons were degraded. Core-flooding experiments showed an oil displacement efficiency of 13.81 % in test with air package injected, 8.56 % without air package injection, and 4.77 % in control test with air package injection and 3.61 % without air package injection. The results suggest that the combined effect of organic nutrients, inorganic salts and oxygen content determines microbial growth, while production of metabolites, oil emulsification and biodegradation alter the reservoir biochemical characters and influence oil recovery during stimulation.