Abstract
Subsurface petroleum reservoirs are an important component of the deep biosphere where indigenous microorganisms live under extreme conditions and in isolation from the Earth’s surface for millions of years. However, unlike the bulk of the deep biosphere, the petroleum reservoir deep biosphere is subject to extreme anthropogenic perturbation, with the introduction of new electron acceptors, donors and exogenous microbes during oil exploration and production. Despite the fundamental and practical significance of this perturbation, there has never been a systematic evaluation of the ecological changes that occur over the production lifetime of an active offshore petroleum production system. Analysis of the entire Halfdan oil field in the North Sea (32 producing wells in production for 1–15 years) using quantitative PCR, multigenic sequencing, comparative metagenomic and genomic bins reconstruction revealed systematic shifts in microbial community composition and metabolic potential, as well as changing ecological strategies in response to anthropogenic perturbation of the oil field ecosystem, related to length of time in production. The microbial communities were initially dominated by slow growing anaerobes such as members of the Thermotogales and Clostridiales adapted to living on hydrocarbons and complex refractory organic matter. However, as seawater and nitrate injection (used for secondary oil production) delivered oxidants, the microbial community composition progressively changed to fast growing opportunists such as members of the Deferribacteres, Delta-, Epsilon- and Gammaproteobacteria, with energetically more favorable metabolism (for example, nitrate reduction, H2S, sulfide and sulfur oxidation). This perturbation has profound consequences for understanding the microbial ecology of the system and is of considerable practical importance as it promotes detrimental processes such as reservoir souring and metal corrosion. These findings provide a new conceptual framework for understanding the petroleum reservoir biosphere and have consequences for developing strategies to manage microbiological problems in the oil industry.
Highlights
Despite significant efforts to reduce our dependence on energy from fossil fuels, oil, gas and coal still meet around 80% of global energy demand, and International Energy Authority projections indicate that fossil fuels will likely continue to be the dominant sources of energy and transportation fuels for many years (U.S Energy Information Administration, 2015).Petroleum reservoirs are an important component of the deep biosphere where autochthonous microorganisms live under extreme temperature and pressure conditions
The Halfdan oil field, Danish North Sea, is situated deleterious microorganisms are indigenous to the 2.1 km below the seafloor
Two distinct formation waters are present in the Halfdan oil field (Supplementary Figure S1)
Summary
Despite significant efforts to reduce our dependence on energy from fossil fuels, oil, gas and coal still meet around 80% of global energy demand, and International Energy Authority projections indicate that fossil fuels will likely continue to be the dominant sources of energy and transportation fuels for many years (U.S Energy Information Administration, 2015).Petroleum reservoirs are an important component of the deep biosphere where autochthonous microorganisms live under extreme temperature and pressure conditions. The prevalence of waters, indigenous microbial communities were methanogenic lineages (identified by 16S rRNA and driven by fermentation of complex carbon sources mcrA genes sequencing) was dependent on the and anaerobic hydrocarbon degradation potentially formation water associated with the sampled wells.
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