Microencapsulation of Acids by Nanoparticles for Acid Treatment of Shales

Abstract

Acid treatment is one of the common well-stimulation techniques to improve the production in tight carbonates or calcite-rich shale reservoirs. Because the reaction rates are often too large at the reservoir temperatures, retarded acid systems such as emulsified acids, foamed acids, and polymer-gelled acids are used. The retarded acids also minimize damage to the wellbore and propagate acids long-distance from the wellbore in fractured shales. In this work, a novel encapsulation method of highly concentrated acid (∼10 wt % HCl) is reported as an alternative retarded acid system. Microencapsulation of these acids is performed using highly hydrophobic silica nanoparticles. The mixing of these particles with acid under high shear rates results in the formation of acid-in-air powders. The release of acid from these powders could be triggered by external stimuli such as mechanical pressure or surfactant addition. The thermal stability, corrosion inhibition efficiency, and shale surface reactivity are compared ...