Systematic Calcium Carbonate Scale Risk Evaluation from Downhole to Topside Flowline

Abstract

Abstract The formation of CaCO3 mineral scale is a persistent flow assurance problem in the oil and gas industry. It deposits at various locations with different levels from reservoir to topside flowline. It could restrict well intervention, block flowline and reduce production. To make an effective mitigation strategy, it is essential to understand the location and severity of scaling, and the performance of scale inhibitor under specific operation conditions. In the work reported herein, the dynamic scale loop tests were performed to evaluate the severity of scale deposition at different locations from the reservoir to transport flowline in the absence and in the presence of scale inhibitors under dynamic conditions. The tests are carried out at various temperatures (20-130°C) and pH (6.0-8.3), which are major factors contributing to calcium carbonate formation and representative of the operating conditions at different locations from reservoir to topside flowline. The results showed low calcium carbonate risk from reservoir to wellhead under tested conditions. Although the high reservoir temperature favors calcium carbonate formation in downhole, the low pH reduces the risk of calcium carbonate formation at downhole conditions. Harsher calcium carbonate deposition is evaluated at the conditions of phase separator/degasser units due to the higher pH of produced water after released CO2 from fluid. Calcium carbonate scale can also deposit in transport flowline, especially at high temperature during summer in the desert area, along with higher pH of the produced water. Calcium carbonate scale prevention and mitigation treatments are required to inhibit scale deposition. The tested phosphonate scale inhibitor provides low dose rate to effectively inhibit calcium carbonate formation at high temperature. The corrosion inhibitor could have a negative impact on the performance of scale inhibitor, and this must be considered when designing the scale inhibitor treatment. This paper gives a comprehensive study of scaling risk evaluation from downhole to topside flowline in the absence and in the presence of scale inhibitor. It contributes to the understanding of calcium carbonate formation and inhibition in the whole production system and recommends effective scale mitigation strategies.