Microbial community composition of a hydrocarbon reservoir 40 years after a CO2 enhanced oil recovery flood

Abstract

Injecting CO2 into depleted oil reservoirs to extract additional crude oil is a common enhanced oil recovery (CO2-EOR) technique. However, little is known about how in situ microbial communities may be impacted by CO2 flooding, or if any permanent microbiological changes occur after flooding has ceased. Formation water was collected from an oil field that was flooded for CO2-EOR in the 1980s, including samples from areas affected by or outside of the flood region, to determine the impacts of CO2-EOR on reservoir microbial communities. Archaea, specifically methanogens, were more abundant than bacteria in all samples, while identified bacteria exhibited much greater diversity than the archaea. Microbial communities in CO2-impacted and non-impacted samples did not significantly differ (ANOSIM: Statistic R = -0.2597, significance = 0.769). However, several low abundance bacteria were found to be significantly associated with the CO2-affected group; very few of these species are known to metabolize CO2 or are associated with CO2-rich habitats. Although this study had limitations, on a broad scale, either the CO2 flood did not impact the microbial community composition of the target formation, or microbial communities in affected wells may have reverted back to pre-injection conditions over the ca. 40 years since the CO2-EOR.

Genome-Resolved Meta-Analysis of the Microbiome in Oil Reservoirs Worldwide

“…One of them was affiliated with the Thermovirgaceae family. Members of this family were found in a hydrocarbon reservoir that was submitted to a CO 2 enhanced oil recovery flood 40 years ago [ 54 ]. In terms of the archaeal community, this oil reservoir metagenome was characterized by the predominant presence of members of Halobacterota (8) phylum, followed by Thermoplasmota (2) and Euryarchaeota (1).…”

“…These were classified as Methermicoccus shengliensis and the hyperthermophilic sulfide producing Archaeoglobus fulgidus [ 59 , 79 ], belonging to the Halobacterota phylum, and as the CO 2 /H 2 -reducing methanogen Methanothermobacter thermautotrophicus and the sulfide-producing Thermococcus sibiricus , members of the Euryarchaeota phylum. The last two are frequently found in oil thermophilic oil reservoirs [ 54 , 56 , 57 , 76 , 79 ]. Seven genomes belonging to Firmicutes phylum were recovered: Thermoanaerobacter pseudethanolicus (2), Caldanaerobacter subterraneus (1), Thermoacetogeniales (1), Ammonifexales (1), and Moorellia (2), which are known to be syntrophic and fermentative bacteria [ 75 , 84 , 85 , 86 ].…”

Rapid microbial methanogenesis during CO2 storage in hydrocarbon reservoirs

“…5 ). These were sampled from the formation water in two wells within each field alongside previous microbiology analysis of these fields 37 . Co-occurrence of both methanogenic and methanotrophic Archaea shows the potential for conversion of CO 2 to CH 4 and vice versa, consistent with isotopic signatures at intramolecular and intermolecular equilibrium.…”

Microbiome Assessment of Global Oil Reservoirs Reveals Site-Specific Hydrocarbon Degradation Functional Profiles

“…One of them was affiliated to the Thermovirgaceae family. Members of this family were found in a hydrocarbon reservoir that was submitted to CO2 enhanced oil recovery flood 40 years ago [54]. In terms of the archaeal community, this oil reservoir metagenome was characterized by the predominant presence of members of Halobacterota (8) phylum, followed by Thermoplasmota (2) and Euryarchaeota (1).…”

“…These were classified as Methermicoccus shengliensis and the hyperthermophilic sulfide producing Archaeoglobus fulgidus [59,79], belonging to the Halobacterota phylum, and as the CO2/H2-reducing methanogen Methanothermobacter thermautotrophicus and the sulfide-producing Thermococcus sibiricus, members of the Euryarchaeota phylum. The last two are frequently found in oil thermophilic oil reservoirs [54,56,57,76,79]. Seven genomes belonging to Firmicutes phylum were recovered: Thermoanaerobacter pseudethanolicus (2), Caldanaerobacter subterraneus (1), Thermoacetogeniales (1), Ammonifexales (1) and Moorellia (2), which are known to be syntrophic and fermentative bacteria [75,[84][85][86].…”