This tentative method results from 6 year research on CO2 corrosion. In this study, the real physical chemistry of the corrosive media is analysed in detail, as well as the specificity of the proper notion of corrosivity in oil and gas wells. In our Company, wells are thus considered corrosive when and only when additional work overs would be naturally required for the purpose of corrosion.

With this definition, the corrosivity of wells appears to be closely linked to the presence of localized forms of corrosion.

Independent of the influence of flow effects, mechanisms of localized corrosion are proposed. They have been verified in the laboratory in nearly stagnant media. Localized attacks are shown to be due to the existence of stable galvanic couples, between small corroding anodes and unattacked cathodic surroundings. The stability and therefore the existence of the couple originates in the chemical composition of water. On the other hand, the initiation of the couple may have many different causative processes (turbulence, non metallic inclusions, caliper tracks or any other heterogeneity).

The waters produced by corrosive oil and gas wells appear to have a signature of their own, in an appropriate "corrosion diagram", built from about 60 analyzed case histories. For new fields, soon after their discovery, the recognition of this signature enables the future corrosivity of wells to be predicted.

Examples are given where this method has been used for deciding very early whether the equipment of future wells will be made of standard or stainless steel.

Subject
Anions, Water, Corrosion rate, Corrosivity, Couplings, Oil wells, Partial pressures, Acidity, Corrosion attacks, Tubing, Steel, Localized corrosion, Erosion corrosion
© 1985 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).
1985
Association for Materials Protection and Performance (AMPP)
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