METHANOGENIC CRUDE OIL BIODEGRADATION IN FOSSIL ENERGY RESERVOIRS: IMPROVED UNDERSTANDING THROUGH MICROBIAL, METABOLIC, AND METAGENOMICS ANALYSES (Invited Presentation)

Deep subsurface crude oil reservoirs harbour diverse microbial communities that can both positively and negatively affect energy recovery operations. For example, the methanogenic consortia inhabiting reservoirs have likely biotransformed light oil to heavy oil over geological time, a detrimental process that devalues crude oil. At the same time, such consortia can also biodegrade crude oil to methane in real time, a potential ‘green’ strategy for improving the sustainability of fossil fuel extraction with lower environmental and health impacts. To this end, we have aimed to better understand the reservoir conditions under which anaerobic crude oil biotransformation occurs, the metabolic pathways involved, and the microorganisms facilitating these processes. Using produced water fluids from a low temperature, low salinity, heavy oil reservoir, we established long term methanogenic incubations and sampled over time to monitor for changes in microbial community composition and known metabolites and genes indicative of anaerobic biodegradation. Over the course of 17 months, we observed the transient accumulation of fumarate addition metabolites and genes, along with fluctuations in the abundances of microbial community members. Progressive enrichment of select organisms including Desulfotomaculum, methanogenic archaea, and candidate phyla such as Atribacteria suggested their involvement in hydrocarbon biodegradation. This has recently been supported through metagenomics sequencing efforts. Draft genomes of Desulfotomaculum and Atribacteria were found to contain several fumarate addition genes, as well as downstream hydrocarbon metabolic pathways and genes predicted to facilitate syntrophic interactions. Draft genomes of other organisms have also been curated and are currently under investigation. Other enrichments established using saline, produced water from hot crude oil reservoirs are also revealing evidence of crude oil methanogenesis under these more extreme conditions. Ongoing characterization of these enrichments will help to determine whether similar microbial interactions and metabolic pathways occur under diverse environmental pressures.