Synthesis and evaluation of a novel polyacrylamide functionalized nano-silica as a calcium carbonate inhibitor in upstream applications

Abstract

Calcium carbonate scale forms in production and injection wells, precipitating upon pressure and temperature changes, incompatible water mixing, and dehydration. Production shutdown is one of the most dramatic consequences caused by calcium carbonate scale formation. We synthesized, characterized, and tested a polyacrylamide functionalized nano-silica (PAM-SiO2NPs) inhibitor that prevents calcium carbonate formation at high temperatures and high brine. Positive compatibility results were confirmed before the inhibition efficiency test, whereby the efficiency was calculated by quantifying the calcium ions left in solution using ICP-OES. The inhibitor was effective at temperatures of 40, 60, and 80 C, with pH values of 7, and 9, and varying brine compositions. The inhibition efficiency increased with an increase in temperature and pH, reaching 95% after 16 h of reaction time at a temperature of 80 C, and a pH of 7 using an inhibitor concentration of 20 ppm (mg/l). A higher amount of scale formed due to an abundance of calcium ions with a cationic to anionic ratio of 80/20; however, the inhibition efficiency was higher with a ratio of 20/80, especially at lower inhibitor dosages. The collected scale in the blank and the samples with low inhibitor concentrations were characterized using SEM/EDS and TEM. The Characterization indicated that the inhibitor chelates calcium, preventing scale formation. SEM results indicated a change in scale morphology as the inhibitor was absorbed to the active crystal sites, interrupting the microcrystal growth. These findings indicate promising inhibition results at high temperatures, varying pH values, and different brine concentrations with relatively low inhibitor concentrations. Results were compared to commercial inhibitors and found to be more effective (>80%) at very low concentrations (0.2 ppm).