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

Abstract

Subsurface microorganisms may respond to increased CO2 levels in ways that significantly affect pore fluid chemistry. Changes in CO2 concentration or speciation may result from the injection of supercritical CO2 (scCO2) into deep aquifers. Therefore, understanding subsurface microbial responses to scCO2, or unnaturally high levels of dissolved CO2, will help to evaluate the use of geosequestration to reduce atmospheric CO2 emissions. This study characterized microbial community changes at the 16S rRNA gene level during a scCO2 geosequestration experiment in the 1.4 km-deep Paaratte Formation of the Otway Basin, Australia. One hundred and fifty tons of mixed scCO2 and groundwater was pumped into the sandstone Paaratte aquifer over 4 days. A novel U-tube sampling system was used to obtain groundwater samples under in situ pressure conditions for geochemical analyses and DNA extraction. Decreases in pH and temperature of 2.6 log units and 5.8°C, respectively, were observed. Polyethylene glycols (PEGs) were detected in the groundwater prior to scCO2 injection and were interpreted as residual from drilling fluid used during the emplacement of the CO2 injection well. Changes in microbial community structure prior to scCO2 injection revealed a general shift from Firmicutes to Proteobacteria concurrent with the disappearance of PEGs. However, the scCO2 injection event, including changes in response to the associated variables (e.g., pH, temperature and salinity), resulted in increases in the relative abundances of Comamonadaceae and Sphingomonadaceae suggesting the potential for enhanced scCO2 tolerance of these groups. This study demonstrates a successful new in situ sampling approach for detecting microbial community changes associated with an scCO2 geosequestration event.

Microbial Growth under Supercritical CO 2

“…Indeed, the King Island core, which yielded the highest number of scCO 2 -tolerant isolates, was unconsolidated sandstone and fully penetrated by drilling fluid based on tracer data. Notably, drilling fluid characterized by Mu et al (22) was dominated by sequences of Bacilli.…”

“…Furthermore, high-pressure incubations to simulate reservoir conditions with elevated (but not supercritical) CO 2 have demonstrated activity of acetoclastic methanogens (under 49.3-atm pressure with 86.4 mM CO 2 ) (19) and homoacetogens (under 395-atm total pressure with 126 mM CO 2 ) (20). Recently, field studies at the Ketzin CO 2 sequestration site in Germany and the Otway Basin site in Australia provided evidence that changes in microbial community composition occur following CO 2 injection, suggesting that a combination of processes, including differential survival and possibly growth, occurs in the subsurface after exposure to near-and supercritical levels of CO 2 (21,22).…”

“…We performed a series of experimental enrichment cultures inoculated with subsurface fluid filtrate or well core samples from three subsurface environments targeted for CO 2 sequestration: the Frio-2 site near Liberty, TX (29); the Otway Basin site in southeastern Australia (22,30,31); and the King Island site near Stockton, CA (32). These three sites are geologically attractive as prospective CO 2 injection zones because they consist of high-porosity/permeability sandstone formations overlaid by low-permeability sealing layers capable of structurally trapping buoyant scCO 2 in the underlying zone.…”

Isolation and characterization of a CO2-tolerant Lactobacillus strain from Crystal Geyser, Utah, U.S.A.

“…Because recharge to Crystal Geyser may be seasonal, the microbial community of the site is likely dynamic and this could explain why CG-1 was not detected by Emerson et al (2015). Nevertheless, the detection and cultivation of CG-1 validates the findings of Morozova et al (2011), Mu et al (2014, Emerson et al (2015), Mu and Moreau (2015) showing that organisms present in CO 2 environments are viable and can potentially impact geochemistry.…”

“…Other field studies have also been performed at CO 2 injection sites, all examining microbial community profiles using molecular techniques (Morozova et al, 2011;Mu et al, 2014;Mu and Moreau, 2015) and showing that microbial community changes will occur as a result of CO 2 perturbation into the subsurface sytem.…”