Abstract

Static jar test and dynamic loop are two major test methods used for study of mineral scale formation and evaluation of scale inhibitors. In both methods, the flow is generally in the regime of laminar condition, which may not be representative of turbulent flow under field conditions. Turbulent flow in oilfield pipes is very common, especially around chokes, tubing joints, and safety values. The objective of this study is to investigate mineral scale formation and control under turbulent conditions.

A novel testing method of rotating cylinder apparatus has been developed for turbulent conditions. In rotating cylinder experiments, highly turbulent flow (up to a Reynolds number of 11,000) was created by a rotating cylinder under field temperature of 70 °C. Barite scale formation and inhibition by several typical inhibitors were investigated under different flow conditions.

During the experiments, barium concentration was measured periodically to determine scale kinetics. Barite precipitate was collected at the end of the experiment and examined by scanning electron microscope (SEM). Experimental results show 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 high turbulence. SEM images also display major difference in barite size and morphology between different flow conditions. Highly crystalline barite with an average size of 10 µm was found in laminar flow, whereas amorphous or poorly crystalline barite of only sub micrometers was formed in turbulent flow. 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.

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