Technologies that serve as a bridge between renewable energy and fossil fuels are needed to meet growing energy demands and to mitigate climate change. Many reservoirs contain difficult to produce residual and/or heavily biodegraded (i.e., geochemically altered) crude oil; although there are some mechanisms to produce “heavy” oil, (e.g. thermal enhanced oil recovery) there are relatively few projects tapping these resources. Production of this residual crude oil via unconventional methods, such as enhanced oil recovery (EOR), has offset some of the decline in conventional oil production. Yet, EOR is not efficient enough to recover all of the original oil in place, and most methods are not effective for very heavy crude oils. Stimulation of in-situ microorganisms to convert the residual crude oil into natural gas (i.e., biogenic methane) is one promising strategy to “extract” these difficult-to-utilize crude oil resources. This is the one of the few regional studies investigating which microbiological communities are responsible for maximum-coupled crude oil biodegradation and microbial methanogenesis within the same formation (across a lithologically similar unit). Produced water, oil, gas, and microbial biomass samples were collected from wells completed in the Paleocene—Eocene Wilcox Group in central Louisiana. Initial results indicate relationships between the amount of crude oil biodegradation, indicators of microbial methanogenesis, microbial community diversity, and aqueous geochemistry. For example, wells exhibiting greater indicators of methanogenesis (e.g. high alkalinity values and positive δ<sup>13</sup>C-DIC values) also showed (1) greater diversity of methanogens, (2) greater amounts of crude oil biodegradation (e.g. lower API gravity values, lower pristane/phytane ratios), and (3) hydrogeochemical conditions most fit (e.g. temperature, salinity, and nutrients) for methanogens to thrive. Wells exhibiting greater amounts of biodegradation correlated to wells with the lowest temperatures, greatest bacterial diversity, and lowest salinities. Future work will include microbial cell counts and additional NextGen Illumina MiSeq sequencing; this data will hopefully help determine the microbial communities most suitable for accelerated in-situ microbial conversion of crude oil to natural gas.<br/>

Impacts of microbial community diversity on the occurrence and quantity of crude oil biodegradation and microbial methanogenesis

249th National Meeting (2015)

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