The oil and gas industry has been facing the challenge of minimising and optimising the control of inorganic scale formed within their facilities. Due to environmental, safety and economic reasons, it is essential to improve the current inhibition strategies. Hence, the need to understand fundaments behind mineral scale formation and deposition to surfaces.

This study focused on both crystallization mechanisms: nucleation and growth in order to assess kinetics associated to calcium carbonate (CaCO₃) scale encountered in oil and gas pipelines.

Managing CaCO₃ formation depends on chemistry of the scale, equipment design and use of appropriate techniques which enable an in-situ monitoring of the crystallization process. This highlights the need to understand both bulk and surface crystallization in order to detect the early stages of precipitation within flowing pipes. Parameters such as concentration, temperature, pressure and time were considered throughout our studies. Furthermore, a range of analytical techniques were used in-situ to detect both nucleation and growth stages of CaCO₃ formation in the bulk and surface at real time and at temperatures varying from 25^oC to 80^oC. Experiments were conducted in batch crystallization reactors and using a rotating cylinder electrode (RCE) with mixing rate of 0.01dm³/s.

Results showed that bulk induction times increased with decrease in Supersaturation and in turn decreased with increase in temperature. This certified that CaCO₃ tends to get less soluble in water as the temperature increases. Surface induction times were faster due to the fact that nucleation was heterogeneous only – whilst bulk displayed both homogeneous (high σ) and heterogeneous (low σ). Bulk interfacial energies increased with increase in temperature but ranged from 8 – 260mJ/m² were identical to prediction done in the past by Mullin.

Finally, bulk crystal’s development showed some ACC particles at very initial stages of crystallization moving then to more organized forms such as vaterite and calcite/aragonite – this has been explained in literature by the non-classical aggregation mechanism. Surface polymorphic precursor was vaterite due to the interface instability in turbulent flow.

Understanding the shape and size evolution gave a quantification of in-situ Supersaturation and possible mechanisms driving those changes. Kinetic parameters linked to nucleation and growth mechanisms are very important to create a prediction model for CaCO₃.

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