Microbial Diversity of a High-Temperature North Sea Oil Reservoir and Effects of Flooding

Subsurface petroleum reservoirs host indigenous microorganisms enduring extreme conditions and isolation. Microbial activity in oil reservoirs causes many deleterious effects like biodegradation and souring. Unlike the broader deep biosphere, these microbiomes in oil reservoirs are exposed to a considerable accumulation of organic substances, significant anthropogenic changes due to the introduction of novel electron acceptors, and the inoculation of foreign microbes during oil production and exploration. This study explores microbial diversity and structure in the North Sea's Edvard Grieg oil reservoir and assesses the impact of ongoing fluid injection on indigenous populations using 16S rRNA and metagenomic sequencing data. We show that the reservoir exhibits microbial variations at the regional scale, featuring low taxonomic diversity composed of an abundance of thermophilic, anaerobic, and halotolerant taxa. After fluid injections, we observed a shift in community structure, marked by a substantial increase in specific functional groups like sulfate-reducing bacteria. Notably, rather than community overprinting, we observed a homogenization of taxa within the reservoir.