Controlling sodium silicate sol-gel transition time through encapsulation of hydrochloric acid using tunable polymeric microcapsules

Sodium silicate gels are used in various applications due to their unique properties and tunable characteristics. Silicate gels can be formed by reducing the solution pH through acid activators, such as hydrochloric acid (HCl), leading to network formation. Sodium silicate gels are largely used in oil and gas production; one of the main applications is plugging fractures and high permeability zones during water injection. An efficient gel-based plugging requires precise placement of the gel, which is highly dependent on the gelation time. However, controlling gelation is challenging since it is influenced by several factors, such as pH, temperature, and ion concentration. Encapsulation and controlled release of the gelling agent (HCl) emerge as a strategy to control the start of the gelation process. This work discusses the use of polydimethylsiloxane microcapsules in controlling sodium silicate gelation by delaying the reaction inception, emphasizing the importance of microcapsule properties in this process. A new approach using a tensiometer with a Wilhelmy plate is used to measure gelation time. Results show that using encapsulated HCl in microcapsules with different shell properties, such as shell thickness and stiffness, led to different gelation kinetics. By controlling the microcapsules properties, sol-gel transition time varied from a few minutes to over 90 h.