Study of oilwell cements by solid-state NMR

The prime objective of the plug-and-abandon operations is to provide zonal isolation for infinite time. Cement-based materials are generally used as plugging materials. Therefore, it is important to understand physical and chemical processes causing cement degradation in downhole environment. In this study, we have characterised two cement formulations at different ageing conditions using NMR and XRD techniques. In particular, we evidence that an increase in pressure and temperature leads to more polymerised calcium silicate hydrates (C-S-H). In the low permeability cement samples, it was shown that the pozzolanic activity of silica fumes increases with temperature and pressure and leads to the consummation of all the portlandite released during cement hydration. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.