Predicting carbonate scale in oil producers from high-temperature reservoirs

Calcium carbonate (CaCO3) scale is a common problem in the oil industry, leading to reduced well performance and obstruction of safety valves. Recent field experiences indicate that scaling may be a problem at lower saturation ratio (SR) than earlier anticipated. In a high-pressure, high-temperature scale cell, crystal growth in synthetic formation water has been studied. Induction times and growth rates have been determined by use of a microscope cell. The results have been interpreted by use of nucleation theory. The findings indicate that wells may be safely operated at SR below 2.5 at 85 degrees C. At higher temperature, crystal growth is less dependent on SR and the temperature dominates the system. Care should therefore be taken when operating wells at temperatures greater than 100 degrees C.