Experimental Study of Nanosilica for Remediating Wellbore Cement Leakages in Co2 Storage

Abstract

During CO2 storage process, a major risk is anticipated when fixing wellbore cement micro-annuli leakage. The leakage of CO2 from these pathways has smaller aperture size and requires a low-viscosity sealant that can provide strong and resilient sealing performance. Nanosilica dispersion particles possess unique properties such as small particle size, enabling them to easily penetrate deep into small crevices and narrow fracture widths. In this paper, the use of nanosilica as a sealant for remediating CO2 leakage from wellbore cement fractures was investigated. Silica gel was formed as sodium ions was introduced in the nanosilica dispersion. The generated gel displayed excellent stability under high pressure and high temperature of CO2. Core flooding tests indicated the nanosilica sealant could generate a high holdback pressure barrier to prevent CO2 leaking through the fracture. Factors such as nanosilica concentration and fracture width effect on the holdback pressure were investigated. As the particle concentration increased from 15% to 25%, the holdback pressure increased from 300 psi to 900 psi. On the contrary, the holdback pressure decreased from 400 psi to 250 psi as the fracture width increased from 0.05 inch to 0.15 inch. Further studies indicated that the nanosilica gel had the self-healing capability, in which the holdback pressure could recover after CO2 broke the gel.

Keywords: CO2 Leakage, Sealing Pressure Gradient, Nanosilica Gel Strength, Sealing Regenerative, Leaching Effect, Leakage Pressure Gradient