Systematic Calcium Carbonate Scale Risk Evaluation from Downhole toTopside Flowline

摘要

The formation of CaCO3 mineral scale is a persistent flow assurance problem in the oil and gas industry. Itdeposits at various locations with different levels from reservoir to topside flowline. It could restrict wellintervention, block flowline and reduce production. To make an effective mitigation strategy, it is essentialto understand the location and severity of scaling, and the performance of scale inhibitor under specificoperation conditions. In the work reported herein, the dynamic scale loop tests were performed to evaluate the severity of scaledeposition at different locations from the reservoir to transport flowline in the absence and in the presenceof 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 representativeof 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 pHreduces the risk of calcium carbonate formation at downhole conditions. Harsher calcium carbonatedeposition is evaluated at the conditions of phase separator/degasser units due to the higher pH of producedwater 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. Thetested phosphonate scale inhibitor provides low dose rate to effectively inhibit calcium carbonate formationat high temperature. The corrosion inhibitor could have a negative impact on the performance of scaleinhibitor, 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 inthe absence and in the presence of scale inhibitor. It contributes to the understanding of calcium carbonateformation and inhibition in the whole production system and recommends effective scale mitigationstrategies.