Experimental Analysis of the Effectiveness of Sodium Hexametaphosphate as Calcium Carbonate Scales Inhibitor

Abstract

Summary Offshore oil and gas production is known to present severe flow assurance issues, in particular calcium carbonate (CaCO3) scale deposition, as its formation reaction is influenced by temperature and pH changes that occur during production. This study investigated the calcium carbonate scaling process using a newly developed 1-inch diameter mesoscale loop and also the efficiency of sodium hexametaphosphate (SHMP) as a scale inhibitor for calcium carbonate under drastic conditions of temperature, flow rate, and scaling ions concentration. The relationship between flow rate, temperature, experimental time, and CaCO3 formation parameters was evaluated using a dynamic methodology designed for the mesoscale loop. Moreover, scanning electron microscopy (SEM) images and energy-dispersive spectrum (EDS) chemical analysis were used to study changes in the microstructure and the elemental composition of the deposits in the absence and presence of the scale inhibitor. The inhibition effect was found satisfactory, as CaCO3 deposition greatly decreased. The deformed structures of the CaCO3 crystals observed by SEM images and EDS analysis helped visualize the changes due to the SHMP. Finally, the temperature changes due to the accumulation of deposits through thermal images were helpful in explaining what was happening inside the pipes system during the scaling tests.