Performance of colloidal silica grout at elevated temperatures and pressures for cement fracture sealing at depth

Hydrocarbon well decommissioning requires the long-term sealing of abandoned wells. Current plug and abandonment (P&A) operations are not always able to address all potential fluid migration pathways, resulting in possible upwards hydrocarbons from formations penetrated by wellbore. The development innovative materials improve remains a major challenge. This paper presents proof concept for use colloidal silica (CS)-based grout performance P&A operations. CS is non-toxic suspension nanoparticles (<100 nm) undergoing gelation upon destabilisation. Due its excellent penetrability controllable gel time, has repairing fine-aperture cracks within cement sheath, at cement/casing interface, or plug, where penetration cementitious grouts restricted due their relatively large particle size. In this study, suitability deployment up 1500 m depth was successfully demonstrated. Firstly, range mixes were investigated test feasibility emplacement considering timescale 2 h pumping surface depth. Secondly, investigate performance, injected into fractured cores (0.2 0.5 mm fracture aperture) exposed pressure temperature conditions simulating downhole scenarios (based on gradients North Sea, UK). Fracture permeability water injection assessed pre- post-treatment. work found that values after treatment reduced three orders magnitude, thus confirming cracks.