Correlation of Shear and Turbulence on Scale Formation and Inhibition

Abstract

Current scale risk analysis focuses on thermodynamic calculations to determine the risk of scale, ignoring system kinetics and the impact of flow regimes on scale precipitation from mildly oversaturated systems. It is however recognised that flow regimes affect scale precipitation. Surface growth is influenced by mass transport and diffusion which are susceptible to shear stress and turbulence. Little work has been reported which examine these factors under conditions that can be readily tuned to match field production conditions. Scale inhibitor evaluation exercises therefore often rely on conventional low shear/static or laminar flow conditions which have been demonstrated in many papers to be largely inadequate for mildly oversaturated systems. This work addresses this concept and focuses on scale deposition and growth at metal surfaces as well as bulk (liquid phase) nucleation and growth in mildly oversaturated brines as a function of increasing shear. A series of controlled experiments have been conducted under “mildly oversaturated” conditions to examine the effect of; no shear conventional “static” tests, moderate shear mixed statics and much higher shear regimes including rotating cage and jet impingement approaches with calculated shear stresses up to 500 Pa and higher. This builds on previous work published by the authors in this area1 and further illustrates the importance of conducting tests at field representative shear conditions. Since shear and turbulence have a governing effect on the critical scaling tendency (the level of oversaturation below which brines remain stable under normal production conditions) the ability to correlate between shear and the propensity for scaling in mildly oversaturated systems is critically important in determining the risk of scale at different locations in the production stream. New test methods have been validated which allow the impact of shear and turbulence to be observed under conditions more representative of production conditions. These methodologies lead to scaling in mildly oversaturated brine systems without having to adjust brine chemistry or otherwise increase the scaling regime, i.e. by adjusting the flow regime to reproduce the shear expected at critical locations in the production system. Improved methodologies are therefore presented which allow more appropriate scale inhibitor qualification, taking into account the impact of shear and turbulence under field representative conditions. The work shows that this is critically important for mildly oversaturated conditions.