Nitrate has been added to the injected seawater in the Halfdan field since the start of injection in January 2001 in an attempt to prevent reservoir souring.

Indications are that the treatment is successful based on analyses of fluids from backflowed injectors and from the few producers with partial seawater breakthrough. No H2S has been observed in any of the backflowed fluids from the Halfdan water injectors. The small amounts of H2S produced by the production wells reduced after seawater breakthrough to a level typically less than half the level measured prior to seawater breakthrough.

Nitrate aims to encourage the growth of nitrate utilizing bacteria (NUB) at the expense of sulfate reducing bacteria (SRB). The mechanism applicable is a combination of out-competition of SRB by NUB and inhibition / suppression of SRB activity by NUB due to the formation of nitrite. Furthermore, one strain of SRB was found to be capable of switching to nitrate reduction (thereby acting as NUB) in an environment with high sulfate concentrations.

Subject
Water, Bacterial growth, Nitrites, Sulfates, Pipelines, Seawater, Nitrates, Fluids, Bacteria, Water injection, Pigging, Sulfides, Risk reduction
Keywords:
Halfdan field, souring prevention, H2S reduction, nitrate injection, nitrate utilizing bacteria, SRB out-competition, SRB inhibition
© 2004 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).
2004
Association for Materials Protection and Performance (AMPP)
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