Anaerobic microbial communities and their potential for bioenergy production in heavily biodegraded petroleum reservoirs

Most of the oil in low temperature, non‐uplifted reservoirs is biodegraded due to millions of years of microbial activity, including via methanogenesis from crude oil. To evaluate stimulating additional methanogenesis in already heavily biodegraded oil reservoirs, oil sands samples were amended with nutrients and electron acceptors, but oil sands bitumen was the only organic substrate. Methane production was monitored for over 3000 days. Methanogenesis was observed in duplicate microcosms that were unamended, amended with sulfate or that were initially oxic, however methanogenesis was not observed in nitrate‐amended controls. The highest rate of methane production was 0.15 μmol CH4 g−1 oil d−1, orders of magnitude lower than other reports of methanogenesis from lighter crude oils. Methanogenic Archaea and several potential syntrophic bacterial partners were detected following the incubations. GC–MS and FTICR–MS revealed no significant bitumen alteration for any specific compound or compound class, suggesting that the very slow methanogenesis observed was coupled to bitumen biodegradation in an unspecific manner. After 3000 days, methanogenic communities were amended with benzoate resulting in methanogenesis rates that were 110‐fold greater. This suggests that oil‐to‐methane conversion is limited by the recalcitrant nature of oil sands bitumen, not the microbial communities resident in heavy oil reservoirs

Fluvial to tidal transition zone facies in the McMurray Formation (Christina River, Alberta, Canada), with emphasis on the reflection of flow intensity in bottomset architecture

An outcrop of the McMurray Formation along the Christina River (Alberta, Canada) has been investigated to better understand depositional processes and setting. The succession is formed by large-scale tabular sets of unidirectional trough cross-stratification. Many of these sets are characterized by profusely ripple-laminated and thick, laterally persistent bottomset intervals at their base. Additionally, reactivation surfaces and infrequent set climbers occur in the foresets. The bottomsets almost entirely consist of backflow cross-lamination. Available knowledge indicates that this points to a rather strong vortex circulation and related strong and persistent main flow velocity. The observed bottomset succession is discussed within the range of variation in bottomset architecture that results from the structure and strength of the flow in the wake behind dunes and related strength of the main flow. Sets descend along a gentle slope, suggesting that dunes filled a preexisting depression, thus representing conditions of a vertically expanding and decelerating flow. This means that aggradation rate was high, which is in accordance with the thickness of the preserved sets. Systematic changes in flow strength are documented by downstream cyclic variations in organic debris, bottomset thickness, and foreset dip. The periodic increase of flow velocity is interpreted as being produced by the increased strength of the river flow during the ebbing tide on the days around spring tide. Apart from these subtle variations, the area experienced large changes in flow strength due to seasonal differences in fluvial discharge. The turbidity maximum zone was located downstream of the study site since thick slackwater mud drapes that characterize the seaward part of the fluvial to tidal transition zone are not present; only a few thin mud drapes are found at the study locality. Therefore, it is concluded that deposition took place in the most landward part of this zone. This new interpretation of this facies in the Christina River area is in line with the inferred depositional setting of the transition to the overlying thick point bar units formed by inclined heterolithic stratification

Methods for Recovery of Microorganisms and Intact Microbial Polar Lipids from Oil-Water Mixtures: Laboratory Experiments and Natural Well-Head Fluids

Most of the world’s remaining petroleum resource has been altered by in-reservoir biodegradation which adversely impacts oil quality and production, ultimately making heavy oil. Analysis of the microorganisms in produced reservoir fluid samples is a route to characterization of subsurface biomes and a better understanding of the resident and living microorganisms in petroleum reservoirs. The major challenges of sample contamination with surface biota, low abundances of microorganisms in subsurface samples, and viscous emulsions produced from biodegraded heavy oil reservoirs are addressed here in a new analytical method for intact polar lipids (IPL) as taxonomic indicators in petroleum reservoirs. We have evaluated the extent to which microbial cells are removed from the free water phase during reservoir fluid phase separation by analysis of model reservoir fluids spiked with microbial cells and have used the resultant methodologies to analyze natural well-head fluids from the Western Canada Sedimentary Basin (WCSB). Analysis of intact polar membrane lipids of microorganisms using liquid chromatography−mass spectrometry (LC−MS) techniques revealed that more than half of the total number of microorganisms can be recovered from oil−water mixtures. A newly developed oil/water separator allowed for filtering of large volumes of water quickly while in the field, which reduced the chances of contamination and alterations to the composition of the subsurface microbial community after sample collection. This method makes the analysis of IPLs (or indirectly microorganisms) from well-head fluids collected in remote field settings possible and reliable. To the best of our knowledge this is the first time that IPLs have been detected in well-head oil−water mixtures