CaCO3 Scale Surface Nucleation and Growth Kinetics in a Once-Through in situ Flow Rig as a Function of Saturation Ratio (SR)

摘要

Flow assurance issues are often as a result of scale forming on solid surfaces in components such as subsea safety control valves or in pipes. As such, understanding the scaling process and its inhibition at surfaces is incredibly important. A once through in-situ flow rig has been developed and initial results were reported in a previous paper. The rig enables the mechanisms of both bulk precipitation and surface scaling to be assessed under different conditions while keeping the saturation ratio constant. In this study the kinetics and mechanisms of CaCO3 growth are evaluated at different SR values and with Polyphosphinocarboxilic Acid (PPCA) inhibitors at 2ppm. Brines with different saturation ratios (SR) 10, 15, 25, 45 and 60 at 25°C were tested. The residence time from mixing point to sample was shorter than the induction time for bulk precipitation and as a result there are no crystals in the bulk solution as the flow passes the sample. Dynamic conditions where SR and inhibitor presence were changed were tested. The results further supported the idea that surface scaling is not always as a result of pre-precipitated crystals in the bulk solution. Surface nucleation depends on the number of active nucleation sites, a factor influenced by change in SR while the growth rate and mechanisms of surface and bulk crystals at different SR values are affected differently with inhibitors addition.