Barite scale formation and inhibition in laminar and turbulent flow: A rotating cylinder approach

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Turbulent flow in oilfield pipes is very common, especially around chokes, tubing joints, and safety values. However the flow is generally laminar in laboratory tests for mineral scale formation and evaluation of scale inhibitors. The objective of this study is to investigate mineral scale formation and inhibition under laminar and turbulent conditions. A novel testing method of rotating cylinder apparatus has been developed to generate flow that spans from laminar to turbulent regimes (Reynolds number from 176 to 11,249) under field temperature of 70°C. Barite scale formation and inhibition by several typical inhibitors were investigated under different hydrodynamic conditions. Barite precipitation kinetics experiments showed no significant difference in precipitation kinetics between laminar and turbulent flow without scale inhibitors. However in the presence of scale inhibitors, precipitation kinetics was slower under turbulent condition. Barite precipitate was collected at the end of the experiment and examined by scanning electron microscope (SEM). SEM images display major difference in barite size and morphology between different flow regimes - highly crystalline barite with an average size of 10µm in laminar flow and amorphous barite of much smaller size in turbulent flow. Adsorption kinetics experiments of scale inhibitors on barite shows faster kinetics in turbulent flow than that in laminar flow possibly due to enhanced mass transfer in turbulence. It is proposed that the slower barite precipitation kinetics with inhibitors in turbulent flow is due to enhanced adsorption of scale inhibitor on barite crystals, and the mechanisms of enhanced adsorption include larger specific surface area and faster mass transfer rate. These results indicate that scale inhibitors may be more effective under some turbulent conditions, as opposed to previous observations. The insights presented in this work will help to understand scale control in oilfield pipes especially under turbulent conditions, and develop optimal doses of scale inhibitors with regard to flow regimes.