MICROBIAL COMMUNITY CHARACTERIZATION IN WATERS ASSOCIATED WITH NATURAL CO2 ACCUMULATIONS IN THE SOUTHERN PERMIAN BASIN

The U.S. Geological Survey (USGS) is investigating naturally-occurring geologic carbon dioxide (CO₂) systems and reservoirs (>5% CO₂) to serve as analogues for anthropogenic geologic CO₂ storage. This research is aimed at determining the origin and migration pathways of naturally-occurring CO₂, evaluating CO₂ resources for enhanced oil recovery (CO₂-EOR), and characterizing geochemical and microbiological impacts on CO₂ reservoirs in hydrocarbon provinces such as the Permian Basin. Little is known about microbial communities residing in high CO₂ systems, and specifically, how differences in CO₂ concentration may impact microbial population dynamics. To evaluate whether changes in CO₂ concentrations in the Permian Basin drive differences in microbial community composition, we focused on seven field sites with associated free gas. Water and gas samples were analyzed for geochemical characteristics (chemical and isotopic composition); while waters were filtered to collect biomass for 16S rRNA gene sequencing. Sampled sites included three hot springs (36.9°C – 44.3°C, n=6) and four gas production wells (14.8°C – 24.5°C, n=4) with CO₂ concentrations ranging from 5.8% – 13.85% and 7.82% – 73.7%, respectively. All six of the hot spring samples, along with one of the four sampled gas wells, were dominated by Bacteria (>99% of total composition); while Archaea were observed at >10% in the remaining three gas wells. The total number of operational taxonomic units identified in each of the 10 water samples ranged from 20 (hydrocarbon well) to 92 (hot spring). An analysis of similarity (ANOSIM) test revealed that site type may be driving microbial community differences more than CO₂ concentration (Statistic R values of 0.913 versus 0.651, respectively), however, neither grouping produced a significant p-value; therefore, there may be other factors (e.g., temperature, water chemistry) that impact community dynamics and further investigation is needed. Studies of microbial communities within natural CO₂ systems are beneficial to gain insight on how these communities may be impacted by a long-term anthropogenic geologic CO₂ storage campaign or CO₂-EOR project.