Wells in the same basin have unique properties and microbial communities
Wells at mesophilic temperatures and moderate depths [1500-3000 ft, 457-914 m] are promising sites for successful MEOR applications29–31 within the Illinois basin. We selected five such wells from this basin that were all approximately 27 ˚C (80 ˚F) in order to hold the temperature constant between trials and simplify cross-well comparisons (Table 1). The wells had depths of 1336-2258 ft (407-688 m) while the pH remained fairly neutral (pH 6 – 7). DNA was extracted from the produced water (effluent) of each well to assess the native microbial community composition via 16S rRNA gene profiling (Supplemental Figure 1 ). We found that each well had a distinct microbial composition with various sulfur-reducing (H2S-producing) and MEOR-relevant9,19,31 archaea and bacteria. Common bacteria phyla include Proteobacteria, Bacteroidota, Firmicutes, Synergistota, Spirochaetota, Verrucomicrobiota, Desulfobacterota and Campilobacterota, of which the latter three are prominent sulfur-metabolizing bacteria.32–35 These populations were distinct from others in the literature,36,37 a finding that is not unexpected given that each community is driven by different environmental conditions such as temperature, salinity, pH, nutrient availability, and oil gravity among other factors.19 However, there is no known correlation between native microbial community and MEOR success. Therefore, we pursued in vitro functional screening to evaluate candidate wells for MEOR top-down microbiome engineering.
Table 1 Characteristics of candidate wells from the Illinois basin