Wellbore integrity can be challenged with chemically corrosive environments that induce cyclic loading from geo-mechanical and geo-chemical stresses. In these harsh environments, the cement sheath and zonal isolation devices need to be designed to resist failure from deformation, fatigue, fracturing and corrosion.
Salt zones can range in width from a few feet to hundreds of feet. Besides contamination or corrosion, salt zones can flow unevenly around well casing, causing irregular external loading that can ultimately result in a partial collapse of the casing or complete well failure. The effects of loading from salt creep can be modeled using a finite element analysis tool. This analysis helps determine an optimized slurry system capable of overcoming the chemical challenge of a brine attack, while developing optimum mechanical properties for the life of the well, short and long term.
Conventional slurry systems are prone to shrinkage during curing and can be susceptible to destabilization even in the less harsh environments of dry CO2. More threatening is CO2 gas in the presence of water because it can produce carbonic acid that may contact and slowly weaken cement by a chemical conversion called carbonation. In some cases, the cement may lose enough strength to potentially impair zonal isolation integrity. Therefore, the cement system should be designed to overcome destabilization from chemically-induced corrosion at any point during the life of the well.
Halliburton has a number of corrosion-resistant cement systems that can be tailored to specific well requirements – reservoir type, reservoir properties, temperatures, pressure, and the injected gas composition are some of the factors to consider when selecting the ideal sealant. These cement systems include low- or non-Portland systems, resin blends, slurries with optimized mechanical properties.