The geochemistry of formation waters in the molasse basin of upper Austria

Membrane Lipids as Indicators for Viable Bacterial Communities Inhabiting Petroleum Systems

Microbial activity in petroleum reservoirs has been implicated in a suite of detrimental effects including deterioration of petroleum quality, increases in oil sulfur content, biofouling of steel pipelines and other infrastructures, and well plugging. Here, we present a biogeochemical approach, using phospholipid fatty acids (PLFAs), for detecting viable bacteria in petroleum systems. Variations within the bacterial community along water flow paths (producing well, topside facilities, and injection well) can be elucidated in the field using the same technique, as shown here within oil production plants in the Molasse Basin of Upper Austria. The abundance of PLFAs is compared to total cellular numbers, as detected by qPCR of the 16S rDNA gene, to give an overall comparison between the resolutions of both methods in a true field setting. Additionally, the influence of biocide applications on lipid- and DNA-based quantification was investigated. The first oil field, Trattnach, showed significant PLFA abundances and cell numbers within the reservoir and topside facilities. In contrast, the second field (Engenfeld) showed very low PLFA levels overall, likely due to continuous treatment of the topside facilities with a glutaraldehyde-based antimicrobial. In comparison, Trattnach is dosed once per week in a batch fashion. Changes within PLFA compositions across the flow path, throughout the petroleum production plants, point to cellular adaptation within the system and may be linked to shifts in the dominance of certain bacterial types in oil reservoirs versus topside facilities. Overall, PLFA-based monitoring provides a useful tool to assess the abundance and high-level taxonomic diversity of viable microbial populations in oil production wells, topside infrastructure, pipelines, and other related facilities.

Tracing fluid sources and interactions

Methods of evaluating possible sources and interactions of ancient and modern fluids are being significantly improved by the development of new isotopic and geochemical microprobe techniques. Applications of O, C, and S isotopes are benefiting from the development of laser ablation methods capable of 0.1 permil precision on submilligram samples and ion microprobe methods capable of permil precision on nanogram regions of rock sections. The noble gases are proving themselves useful conservative tracers of fluid processes. The ubiquitous presence of air saturated water patterns testifies to the dominance of water originating at the Earth's surface, while the presence of radiogenic isotopes and 3 He quantify interactions with crust and m antle respectively. The use of resonance ionisation has increased sensitivity for Xe and Kr analyses to the single atom level. Examples of fluid regimes currently under study are described.