Insight into the Synergic Effect of Partially Hydrolyzed Polyacrylamide and Nanosilica on Sodium Silicate Sealant Gel System for Water Shutoff Applications

Production of excess water is one of the main problems leading to declined hydrocarbon production. Various techniques, including silicate gel systems, have been developed to manage water production. In this study, factors affecting the Na-silicate sealant gel system, containing polymer (PHPA) and nanosilica are investigated in terms of gelation time and syneresis. In particular, their interaction effects at varying temperatures and concentrations of activator are studied. While acid gel with hydrochloric acid, as an activator, lost more than 77% of its weight in less than a week, basic gel with calcium chloride, as an activator, was more efficient owing to its weight loss of 10% over 5 days. The syneresis increased by increasing Na-silicate concentration, activator concentration, and temperature. The proposed addition of PHPA with the aim of avoiding or delaying the syneresis was successful at temperatures below 75 °C. Below the PHPA concentration of about 0.37 g/L, the effect of calcium chloride on syneresis was lower than polymer, whereas its effect overcame at the higher concentration. The gelation time was reduced by increasing the sodium silicate, nanosilica, and calcium chloride concentrations. The gelation time increased by raising the temperature from 60 to 80 °C, whereas it decreased by increasing the temperature from 80 to 100 °C. The parameters of nanosilica, calcium chloride, PHPA, temperature, and sodium silicate had the highest to lowest effect on the gelation time, respectively. Results of gel injection into synthetic cores showed that Na-silicate gel system can be applied due to the success of effective sealing of the porous media.