A caliper survey of the horizontal well MFF-25A in the Dan field showed that the tubing was severely corroded with several fully penetrating holes. This study investigated whether the accelerated corrosion was caused by microorganisms.

The number and nature of microorganisms in samples of downhole deposits was determined using quantitative polymerase chain reaction (qPCR). Furthermore, wavelength dispersive X-Ray fluorescence spectroscopy (WDXRF) was conducted for elemental composition analysis of corrosion products. Produced water samples were also collected and analyzed with qPCR.

The results showed that corrosion products and MIC-promoting SRB, SRA and methanogens were all present in high numbers in the well, and therefore probably contributed to the ongoing corrosion. Methanogens were particularly abundant, constituting 47-67% of all prokaryotes in the solid samples.

Test results of downhole solids and produced water from MFF-25A revealed that SRB and methanogens were strongly underrepresented in planktonic relative to sessile populations. This must be taken into consideration when assessing MIC risk in wells based on analysis of water samples. Also, MIC risk assessment was performed in adjacent wells based on microbial numbers in planktonic water samples.

It was concluded that SRA and methanogens should be included in future MIC monitoring and corrosion risk assessment together with the SRB.

Subject
Water, Methanogens, Metal surfaces, Solids, Calipers, Risk assessment, Seawater, Tubing, Produced water, Deposit corrosion, Microorganisms, Microbiologically influenced corrosion, Samples
Keywords:
sulfate-reducing Bacteria (SRB), sulfate-reducing Archaea (SRA), sulfate-reducing prokaryotes (SRP), methanogens, microbiologically influenced corrosion (MIC), quantitative polymerase chain reaction (qPCR), Dan oil field
© 2011 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2011
Association for Materials Protection and Performance (AMPP)
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