Changes in the deep subsurface microbial biosphere resulting from a field-scale CO2 geosequestration experiment

Area of Science:

• Geomicrobiology
• Environmental Microbiology
• Carbon Capture and Storage

Background:

• Subsurface microbial communities can influence pore fluid chemistry, impacting geological storage of carbon dioxide.
• Understanding microbial responses to supercritical CO2 (scCO2) is crucial for evaluating the efficacy of geosequestration strategies.
• Previous studies lacked in situ data on microbial community dynamics during scCO2 injection events.

Purpose of the Study:

• To characterize microbial community shifts in response to scCO2 injection in a deep Australian aquifer.
• To assess the impact of geochemical changes (pH, temperature, salinity) on subsurface microbial populations.
• To evaluate a novel U-tube sampling system for in situ subsurface sampling.

Main Methods:

• Conducted a 4-day injection of 150 tons of scCO2 into the Paaratte Formation aquifer.
• Utilized a novel U-tube system for in situ groundwater sampling under pressure.
• Analyzed microbial community structure using 16S rRNA gene sequencing and performed geochemical analyses.

Main Results:

• Observed decreases in pH (2.6 log units) and temperature (5.8°C) post-injection.
• Pre-injection microbial shifts showed a transition from Firmicutes to Proteobacteria, linked to drilling fluid (PEG) removal.
• scCO2 injection led to increased relative abundances of Comamonadaceae and Sphingomonadaceae, indicating potential scCO2 tolerance.

Conclusions:

• The study successfully demonstrated an in situ sampling method for monitoring microbial changes during geosequestration.
• Specific bacterial groups, Comamonadaceae and Sphingomonadaceae, show potential for enhanced tolerance to scCO2 conditions.
• Findings contribute to understanding subsurface microbial ecology in the context of carbon capture and storage.