Journal of Colloid and Interface Science 286 (2005) 7–13 www.elsevier.com/locate/jcis An improved predictive correlation for the induction time of CaCO 3 scale formation during flow in porous media E. Stamatakis a,b,c,∗ , A. Stubos b , J. Palyvos a , C. Chatzichristos c , J. Muller c a School of Chemical Engineering, National Technical University of Athens (NTUA), Greece b National Centre for Scientific Research Demokritos (NCSRD), 15310 Agia Paraskevi, Attica, Greece c Institute for Energy Technology (IFE), P.O. Box 40, NO-2027 Kjeller, Norway Received 14 May 2004; accepted 13 December 2004 Available online 21 February 2005 Abstract The induction time, t ind , of calcium carbonate precipitation in porous rocks was experimentally measured under dynamic conditions at temperatures from 25 to 120 ◦ C with the use of a radiotracer technique, where the gamma-emitting nuclide 47 Ca was used as a tracer in order to monitor the scale deposition at real time. Based upon nucleation theory and experimental observations, the following improved correlation is proposed: log t ind (min) = 3.2 − 3.0 SI − 959.8 T + 1849.9 SIT . This equation predicts satisfactorily the induction time of calcium carbonate scale formation under specific dynamic (flow) conditions in the near-well region (T is the absolute temperature in K, and SI is the saturation index, SI = log SR, where SR is the saturation ratio).  2005 Elsevier Inc. All rights reserved. Keywords: Induction time; Scale formation; Calcium carbonate; Porous media 1. Introduction The formation of mineral scales from produced wa- ter/brines in oil/gas wells and pipelines constitutes an old but persistent problem for the oil industry. The sparingly solu- ble CaCO 3 may form when a solution is supersaturated, that is, when the product of the concentrations of the precipitat- ing ions (Ca 2+ , CO 2− 3 ) exceeds the solubility product K sp , which is the equilibrium constant for a reaction, in which a solid ionic compound dissolves to give its constituent ions in solution. The reasons for the creation of a supersaturated solution are related to a number of mechanisms [1]. However, many waters that have become oversaturated and scale-prone do not always produce scale. Supersaturated calcium carbonate * Corresponding author. Fax: +47-63811168. E-mail address: manos@ife.no (E. Stamatakis). can be metastable in a solution for some time before precip- itating. Thus, a period of time usually elapses between the attainment of supersaturation and the appearance of crys- tals. This time lag, generally referred to as the induction time, t ind , is considerably influenced by the level of supersat- uration, state of agitation, presence of impurities, viscosity, etc. [2]. As the induction time can be affected by many exter- nal factors, it cannot be regarded as a fundamental property of a system. Nor can it be fully relied upon to yield ba- sic information on the process of nucleation. Nevertheless, despite its complexity and uncertain composition, the in- duction time has frequently been used as a measure of the nucleation event, under the simplifying assumption that it can be considered to be inversely proportional to the rate of nucleation, J [2]: (1) t ind ∝ J −1 . 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2004.12.040