MICROBIAL COMMUNITIES IN FORMATION FLUIDS OF A CARBON SEQUESTRATION TEST WELL

A lack of data on microbes in the deep subsurface hinders our ability to predict how these microbial communities will respond to carbon sequestration. To identify microbes that could occur in reservoirs targeted for carbon sequestration, water samples were collected from potential target reservoirs in the Powder River Basin, Wyoming, and microbial communities associated with these samples were identified using 16S rRNA gene sequencing. Samples were collected at depths of 8060 ft (Lakota Formation), 8330 ft (Hulett Formation), 9380 ft (Minnelusa Formation), 9463 ft (Minnelusa Formation), and 9544 ft (Minnelusa Formation). Samples were sequenced and anions and cations measured to identify any microbial trends associated with water chemistry as a function of depth. TDS of formation fluids ranged from 61,204 - 103,327 mg/L. The 16S rRNA gene sequences identified in formation fluids were compared to those isolated from drilling muds to distinguish native microbes from those introduced via drilling processes. Microbial communities in the collected formation fluids did not simply reflect microbes present in drilling muds, as several genera, including Paracoccus and Thauera, were detected in each drilling mud at a minimum of 10% relative abundance but below 0.5% relative abundance formation fluids. A Halolactibacillus sequence was present in all sampled formation fluids ranging from 2-30% relative abundance, but was present at <0.5% relative abundance in any drilling mud. Other sequences comprised at least 5% relative abundance in only one formation fluid, such as a Clostridium sensu stricto 3 sequence only abundant in one collected sample from the Minnelusa B sand at 9463 ft. No trends in microbial community composition could be linked to formation fluid geochemistry. Therefore, considering prominent microbial species and formation fluid geochemistry alone, carbon sequestration efforts in the Powder River Basin will not impact microbial communities differently across target zones.