Abstract

Static jar and dynamic loop tests are two major test methods used in the oilfield scale industry to evaluate the performance of scale inhibitors. The minimum inhibitor concentration (MIC) under the test conditions can be determined, but with a certain amount of assumptions and theoretical analysis of the mechanism of scale inhibition, especially for scale inhibitors with dispersive effects.

Unlike these traditional test methods, a newly developed test method, using an ultrasonic technique along with turbidity measurement, has been used to evaluate scale inhibitors and understand the inhibition mechanisms. In comparison with traditional test methods, this test method provides a quick and effective way to understand the scale inhibitors, including the effect of scale inhibitors on the induction, nucleation and growth stages of scale formation, and also the dispersion functions of scale inhibitors.

Several typical commercial scale inhibitors, including phosphonate and polymer based chemistries have been tested using this newly developed test method. Different scale inhibitors demonstrated different inhibition mechanisms and will be addressed in detail in this paper.

Results showed a polymer based scale inhibitor has good inhibition on the induction time of scale formation and a phosphoric based scale inhibitor showed a major dispersive effect on scale inhibition. The combined formulation based on these two inhibitors has been evaluated and a synergistic effect was observed and later confirmed by both the traditional static jar test and dynamic loop test, where the mixture of 75% polymer based scale inhibitor and 25% phosphoric based scale inhibitor showed much better performance than both neat scale inhibitors.

In this paper, this newly developed test method will be introduced in detail and the benefits and limitations will also be discussed. By understanding the mechanism of the scale inhibitors, this technique might provide a new and alternative route of developing and formulating scale inhibitors.

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