An electrostatic model is developed to model the pH, temperature, and ionic strength dependence of phosphonate ionization and complex formation. Using the approach, two calcium phosphonate precipitates have been studied. The initial calcium phosphonate phase formed is an amorphous material. Using a dialysis process, the amorphous solid gradually transforms into a crystalline solid via removal of phosphonate. The solubility product of the amorphous phase is 10−49.4. The crystalline material is three orders' magnitudes less soluble than the amorphous phase. The pH, temperature, and ionic strength dependence of the precipitation is discussed. The transformation between the two solids is a function of both temperature and solution to solid ratio. The precipitation--solid transformation--dissolution process can be used to model the retention and release of phosphonate following an inhibitor squeeze in oil and gas fields. Inhibitor squeezes and returns of five different oil and gas wells of widely different geological, physical, and chemical conditions are compared using this mechanistic interpretation.

Subject
Acids, Hydrogen concentration, Phosphonates, Solids, Solubility, Calcium, Oil and gas, Acidity, Constants, Chemical inhibition, Metals, Corrosion inhibitors, Brines
Keywords:
phosphonate, precipitation, scale inhibitor, transport, inhibitor squeeze
© 1993 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).
1993
Association for Materials Protection and Performance (AMPP)
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