Lead sulfide scaling in multiphase systems and co-precipitation in the presence of calcium carbonate

Undesirable precipitation of sulfide scales during hydrocarbon production, typically in sour, high temperature and high pressure systems, adds an additional level of complexity to both predicting and controlling of inorganic mineral deposition. The fundamental mechanism promoting nucleation and deposition of extremely insoluble mineral scale species such as lead sulfide (PbS) in liquid-liquid systems follows spontaneous nucleation of metal sulfide nanoparticles, and their assembly at oil-water interfaces, before oil droplets impact on surfaces leading to nanoparticle transfer and deposition. Conversely, common mineral scales such as calcium carbonate (CaCO3) possesses a higher degree of solubility, generally resulting in heterogeneous crystallization directly upon surfaces. Co-precipitation of sulfide and carbonate species is frequently encountered during production, yet the literature addressing the topic is scarce. This is the first study assessing the influence of a light oil phase on PbS–CaCO3 co-precipitation behavior. This study showed that the depositional behavior of PbS nanoparticles precipitated in a simple liquid-liquid system can be accurately predicted, based on particle wettability, oil to water ratio and the surface energy and wettability of the contact surface where nanoparticle accumulation occurs. Analysis of co-precipitation between PbS and CaCO3 highlighted differences in the precipitation mechanism between the two minerals. PbS agglomerates assembled at the oil-water interface acting as seeding points for the nucleation and growth of calcite, resulting in a strongly adsorbed PbS/CaCO3 complex that resulted in significant deposition on hydrophilic surfaces