Kinetics of Transformation and Inhibition of Calcium Carbonate Scale Formation in Mixed Oil Fractions

Abstract

Abstract The thermodynamic and kinetic uncertainities created by the mixing together of various fluids during oil processing and transportation will affect scaling tendency of facilities and the efficiency of inhibitors to combat scaling. The most severe operational challenges with pipeline transportation are flow assurance issues due to scale formation, which often lead to blockage of pipelines, and related to the flow of multiphase fluids. There is therefore the need for an understanding and assessment of the mechanisms and kinetics of scale formation in multiphase systems containing mxture of oil phases. This work studies the mechanisms and behavior of precipitation of calcium carbonate scale in mixed oil fractions. Experiments were conducted in both single and multiphase systems for SR 211 at 30°C and SR 198 at 60°C. The mixed oil fractions include 50ml cyclohexane, 30ml kerosene, 20ml toluene and 0.01% asphaltene, fully dissolved in toluene. Homogeneous dispersion in the two-phase mixture was achieved using the Rotating Cylinder Electrode (RCE) with an overhead impeller blade stirring at 520 rpm to create The fouling process was investigated in the presence of a chemical scale inhibitor, polyphosphinocarboxylic acid (PPCA) at below the Minimum Inhibitor Concentratio (MIC). Samples are collected and analysed using the Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Atomic Absorption Spectroscopy (AAS) techniques to evaluate the morphology, polymorphic transformation and calcium ion concentration respectively at different time intervals. The study shows that the presence of an organic phase has a major effect on CaCO3 polymorphic abundance, slowing down the initial rapid transformation of vaterite to calcite. Injection of inhibitor below MIC combined with the presence of asphaltene do not prevent the bulk scaling but has an effect on the relative distribution as well as stability of the metastable vaterite. This could provide further insights for the development of inhibition and control strategies to deal with CaCO3 scale formation in multiphase systems.