CONCENTRATION-DEPENDENT EFFECTS OF CO2 ON MICROBIAL COMMUNITIES FOR A SALINE STORAGE SITE, AN EOR SITE, AND A FRESH WATER AQUIFER

Geological carbon sequestration will likely be part of a comprehensive strategy to minimize the atmospheric release of greenhouse gasses. Carbon storage capacity and long-term carbon storage security will depend on biogeochemical processes that occur in subsurface reservoirs after CO2 injection. A critical need exists to understand the evolution of CO2 exposed microbial communities that influence the biogeochemical processes in these reservoirs. Heterogeneous flow of CO2 and a slow moving plume front will result in a gradient of dissolved CO2 concentration. The evolution of microbial ecology along this CO2 concentration gradient was investigated using fluid-slurry samples obtained from three subsurface reservoirs: a deep saline aquifer (1220 m depth, 14 MPa, 40 °C, Wellington, KS), an EOR site (490 m depth, 3.4 MPa, 40 °C, Zabata, TX), and a overlying fresh water aquifer (55 m depth, 0.5 MPa, 22 °C, Escatawpa, MS). Batch vessel experiments were conducted with samples from each site, varying pCO2 of 0% to 100% under reservoir temperature and pressure for 56 days. The microbial communities of each batch reactor were analyzed with 16S rRNA clone libraries and qPCR. In both the saline aquifer and the EOR site, DNA concentration and diversity decreased with increasing CO2 exposure. In contrast, DNA concentration and diversity of the freshwater aquifer did not display a clear trend with CO2 exposure. Batch vessel experiments with saline aquifer fluid suggest the halotolerant bacteria, Halomonas and Marinobacter, are the most tolerant of CO2 exposure. Batch vessel experiments with EOR fluid suggest Pseudomonas is the most tolerant of CO2 exposure. Batch vessel experiment with fresh water fluid suggest the well isolate, Curvibacter, is tolerant of mid CO2 exposures, and Pseudomonas is the most tolerant of high CO2 exposures (pCO2=0.5 MPa). Findings provide insight into a dynamic biogeochemical system that will alter with CO2 exposure. Adapted microbial populations will eventually give rise to the community that will impact vital bioprocesses and may lead to pore plugging, metal mobility, and sour gas production. Knowledge of the surviving microbial populations enables improved models for predicting the fate of injected CO2 and lead to better strategies for ensuring the security of carbon storage.