Kinetics of calcium carbonate scaling using observations from glass micromodels

Calcium carbonate, CaCO3, is one of the most common scale components found in oilfield production wells and surface facilities. Although many computer models have been developed to predict the thermodynamic tendency of scaling, the kinetics have usually been neglected due to a lack of a reliable model to predict how fast the scale will build-up. In this work, the kinetics of calcium carbonate (calcite seeds used) precipitation have been studied by using visual observations of crystal growth within a glass micromodel. The effects of the solution composition, temperature and the presence of a gas-liquid interface on the spontaneous nucleation and the calcite crystal growth rate have been examined. From the measurements of the crystal growth kinetic data, the calcite growth rate constant as a function of temperature (25-70 degrees C) and ionic strength (up to 2 eq/kg) have been determined and an activation energy of 46.9 kJ/mol estimated. We believe that the presence of a gas-liquid interface can help spontaneous nucleation. The presence of Mg2+ at ratios of [Mg2+]/[Ca2+] between 0.1 to 0.5 causes a 50% reduction in calcite growth rate and must not be neglected in scale kinetics. (C) 1997 Elsevier Science B.V.