Microbiological monitoring of samples collected from oilfield operations is crucial for understanding microbial impacts on metal infrastructure. As many oilfields and related infrastructure are in remote locations, the time between sample collection, shipping to laboratory and sample processing for microbiological analysis can vary from days to weeks. Hence, robust sample handling and preservation methodology to arrest microbiological activity at the time of sample collection is needed.
To identify the best preservation methodologies that can be adopted for solids, oily sludge samples were collected twice from the nose of the same pig trap during a routine pipeline pigging operation of a crude oil transmission pipeline over a span of two years. Samples were chemically preserved at the time of sample collection (with different alcohols or commercially available nucleic acid preservation reagents) or remained unpreserved, and all samples were stored either at 4°C or at room temperature following collection. Samples were assessed using 16S rRNA gene sequencing to determine microbial community composition at day 0 (time of sample collection) and at different intervals for up to 50 days of storage, and comparisons in microbial community composition were made to the day 0 results.
A substantial shift in microbial community composition was observed in samples that were not chemically preserved or not kept cold at 4°C in as little as 7 days following sludge collection. In addition, greater microbial diversity and community shift was observed in samples kept at room temperature compared to cold storage. Chemical preservation reagents showed varying efficacies at preserving microbial community composition with increased lengths of storage. These results emphasize the need for careful sample preservation and handling of sludge samples for accurate monitoring of microbial communities, an analysis that can play a pivotal role in the early identification of potentially corrosive microorganisms during the routine inspection of pipelines.
