Controlled Release and Effect of Calcium-Loaded Polyaramid Microspheres on Portland Cement Hydration

Summary Encapsulation-based systems can be utilized in the oil and gas industry in applications such as chemical additive preservation, small molecule release, particle delivery, and self-sealing materials. Many methods are used to encapsulate relevant chemical additives for the controlled release of contents such as polymeric capsules, inorganic shells, and mesoporous materials. Using capsules, chemical additives are delivered in cementing without requiring modification. In this way, the possibilities of formulations that comprise several capsules with various encapsulants lend to significant advancements in cementing. Here, the polymeric microcapsule (µcap) system utilizes engineered features, such as semipermeable polymeric shell walls and an empty core to house relevant chemical additives for the controlled delivery of encapsulated cargo. This new zonal isolation technology releases an accelerant into cement, enabling cement to set quickly from 15 hours without an accelerant to 4 hours with controlled release of a salt accelerant, which is a 73% decrease in nonproductive time. Slurries designed with µcaps maintain good rheological numbers at 20 Bc, with transition times from 30 Bc to 70 Bc averaging around 16.5 minutes at low 100°F and 3,000 psi. Experimental results show that a basic cement slurry design responds to the release of this encapsulant by changes in cement viscosity and set time. Thereafter, the shell walls are engineered with high-molecular-weight polymeric material akin to Kevlar that, upon release of the encapsulant in cement, emptied capsules (spent) continue to remain embedded without dissolving. Polyaramid cement using spent µcaps shows improvement in elasticity by 52% under accelerated stress tests.