SPE Journal
Volume 15, Number 4, December 2010, pp. 977-988

Summary

In this study, the nucleation kinetics of calcium sulfate scale formation in the presence and absence of scale inhibitors has been studied. The nucleation kinetics of calcium sulfates in 0 - 3.2 M NaCl solution was measured from 0 to 200°C at various supersaturation conditions [saturation index (SI) = 0 - 1.3]. The phase behavior of these various calcium sulfate phases was monitored by X-ray diffraction (XRD). The inhibition study was performed by evaluating the inhibition efficiency of calcium sulfate precipitation at the same supersaturation and temperature ranges as those of the nucleation study. Several polyphosphonate, polymeric, and environmentally friendly inhibitors were found to be effective inhibitors. The study has shown that calcium sulfate scales are very difficult to inhibit at SI > 1. Calcium sulfate scale is inhibited most effectively by hexamethylenediamine tetra(methylene phosphonic acid) (HDTMP) if the saturation index is less than approximately 1.0. In addition, a semiquantitative model to predict precipitation kinetics of calcium sulfate as a function of temperature, pH, SI, and HDTMP concentration is established with experimental results from this study. The effect of methanol and methylene glycol (MEG) on calcium sulfate precipitation kinetics and inhibition is also presented.

© 2010. Society of Petroleum Engineers

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History

• Original manuscript received: 24 February 2009
• Meeting paper published: 21 April 2009
• Revised manuscript received: 31 December 2009
• Manuscript approved: 20 January 2010
• Published online: 18 June 2010
• Version of record: 2 December 2010