New understanding on calcium carbonate scaling kinetics

Calcium carbonate (CaCO3) is the predominate type of mineral scale formed in many industrial water processes, including oil and gas production. Comprehensive and accurate knowledge on the CaCO3 scaling mechanism is critical for effective scale management. Extensive studies have been carried out on CaCO3 formation process and prevention under various conditions of temperature, saturation state, pH, and additives. The effect of pressure is considered in scaling tendency calculation, but its potential impact on scaling kinetics has been neglected. This article presents the laboratory results of CaCO3 scaling kinetics at various pressures, 500 psi to 5,000 psi, and temperatures, 80 °C to 150 °C. Tests were conducted with a dynamic tube blocking apparatus, which measures CaCO3 scale buildup by monitoring hydrostatic pressure differential (∆P) across a capillary tubing, and the period of time for increase in ∆P to reach 1 psi was determined. Test waters were maintained at similar CaCO3 supersaturation levels at different temperature and pressure combinations by adjusting the bicarbonate alkalinity. Results show that under the test conditions, the scaling process was accelerated by both temperature and pressure. The CaCO3 scaling time was shortened by ~35% at 80 °C and > 60% at 150 °C when the pressure was increased from 500 psi to 5,000 psi. By increasing the temperature from 80 °C to 150 °C, scaling time was reduced ~45% at 1,500 psi and > 50% at 3,000 psi. This study provides a new understanding of the mineral scaling kinetics by identifying the pressure dependence of the CaCO3 scale formation process. Experimental results show that pressure, other than its impact on solubility, has an additional kinetic effect on the CaCO3 scaling rate. © 2019 Aramco Services Company. All rights reserved.