Prediction and Evaluation of Calcium Carbonate Deposition at Surfaces

Abstract

Mineral scaling is one of the main flow assurance problems facing the oil and gas sector and imposes severe constraints on the economic and safe operation of many fields. During the last decades, operators, in conjunction with the chemical manufacturers and oilfield service companies have focused on understanding, predicting and mitigating scale formation. Even though progress towards better management of scale formation continues, scale precipitation is still a significant flow assurance problem, caused by changes in temperature and pressure conditions or by mixing incompatible waters (produced water, seawater, aquifers) especially at high water cuts. One of the most frequently depositing scale types in the oil production process is calcium carbonate. To date, the overwhelming amount of research has been on the thermodynamics that drive the precipitation of calcium carbonate in an aqueous system, with little attention given to actual surface deposition. Therefore, to improve scale management practices, the kinetics that dominate CaCO3 surface formation need to be understood. The work presented in this paper, has as its main focus the deposition of CaCO3 at a stainless steel surface. The data from the surface is presented in conjunction with the findings from bulk phase experiments. A small bore flow rig and a quartz crystal microbalance were used for monitoring the induction time and the real time deposition of CaCO 3. Calcium carbonate deposition was examined at a range of conditions with emphasis given to different saturation ratios (SR). The results are discussed in correlation with the theoretical calculations based on a scale prediction software. The data collected from the CaCO3 surface experiments contribute to understanding at which level the saturation ratio becomes a threat with respect to scale formation at surfaces. This paper describes steps towards predicting the induction time of calcium carbonate at surfaces, when the main input is the saturation ratio.