The application of biocides to inhibit SRB in offshore seawater injection systems has generally been controlled by budgetary requirements rather than chemical effectiveness. This has led to many systems in the North Sea becoming heavily contaminated by SRB (resulting in MIC and reservoir souring) despite the regular application of biocide chemicals over years of operation. With many platforms now remaining in production several years over their anticipated lifetime, greater emphasis is placed on preventative maintenance. As a result, operators are now looking for assurance that failures due to MIC can be minimised by effective treatment. This has resulted in an emphasis on biocide efficacy as the main criteria, although naturally cost considerations remain vitally important.

A microbiological audit performed in April 1997 showed high numbers (107 per cm2) of sessile SRB and high general corrosion rates on corrosion coupons in the Magnus water injection system. In response to this an MIC control plan was put in place, requiring a more robust biocide dosing programme. By April 2000, SRB numbers at the same location were 102 per cm2 and corrosion rates were significantly decreased. Following from this success, an attempt was made to reduce the cost of biocide treatment by reducing the frequency of additions. This project utilised the results from a biofilm monitoring device for routine sessile monitoring. An audit in April 2000 showed that planktonic SRB numbers had increased indicating biofilm formation in the deaerators. The biocide application was immediately returned to the weekly treatment.

This paper demonstrates that prior to biocide efficacy being the controlling factor, SRB inhibition was not effective. Once the emphasis was changed to biocide efficacy, SRB were inhibited and corrosion rates decreased. However, once budgetary control was reinstated, SRB numbers started to increase again.

Subject
Bacterial growth, Corrosion rate, Biocide treatment, Seawater, Biofilms, Microbiology, Bacteria, Oxygen, Deaerators, Corrosion coupons, Biocides, Microbiologically influenced corrosion, Oil
© 2002 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).
2002
Association for Materials Protection and Performance (AMPP)
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