Abstract
Culture-based methods of traditional microbiology applied to microbiological processes involved in reservoir souring and microbiologically influenced corrosion (MIC) pose a risk of yielding inadequate or contradictory results. Therefore, the industry calls for more accurate and faster techniques. The need for in-situ cultivation-independent methods has over the past ten years facilitated the development of several analytical methods for determination of bacterial identity, quantity, and to some extent function, applied directly to samples of the native population. This development has so far been limited regarding practical application and it has only recently been transferred to the oil industry.
We have applied state-of-the-art molecular tools to monitor progressive corrosion attacks in an offshore oil facility in the Danish sector of the North Sea. We investigated the similarities and differences among MIC bacterial populations obtained from produced water and bacteria found in corrosion spots in a X-mas tree from a producing well.
Molecular methods proved to be a powerful tool in identifying the involved microorganisms and the most likely corrosion process. The entire population of bacteria found in the corrosion deposit was characterised and found to consist almost entirely of sulfate reducing bacteria (SRB), of which the critical species were identified. Additionally, we determined that the bacterial populations that are present in the produced water are somewhat different to those found in the corrosion deposit. Many of the bacteria in the produced water are involved in souring processes and the production of H2S.
Future research is focussing on the development of a direct and rapid method to specifically measure the critical SRB involved in MIC, both in deposits but also as a routine monitoring tool in the produced water. This new and improved microbiological approach is an important criterion in designing and testing remedial actions towards reservoir souring and MIC.
