Abstract
Cement sheaths are designed to protect the integrity of oil and gas wells by mitigating movement of formation fluids and leaks. A failure of the cement sheath can result in the loss of zonal isolation, which can lead to sustained casing pressure. Gas migration through a cement sheath in the annulus is one of the main challenges that compromises zonal isolation. Failure in cement-casing bonding and micro annulus creation are other huge issues that compromises wellbore integrity. Even though some past studies have shown the application of nanomaterials, very few have conducted full scale tests measuring the compressive strength, thickening time and gas transition time of these materials.
In this study, nanosynthetic graphite with designed expansive properties has been introduced to fresh cement slurry. The expansive properties of nanosynthetic graphite were achieved by controlling the preparation conditions. The material was made from synthetic graphite and has a surface area ranging from 325-375 m2/gram. Several tests including compressive strength, rheology, and thickening time were performed. An addition of only 0.5% nanosynthetic graphite with appropriate reactivity was sufficient to maintain expansion in the cement system, leading to an early compressive strength development. It has excellent thermal and electrical conductivity and can be used to design a cement system with short and long-term integrity. Rheology and thickening time tests confirmed its pumpability. Controlling the concentration of the additive is a promising method that can be used to mitigate gas migration in gas bearing and shallow gas formations.
