From spud to plug, the ability for cement to provide an adequate seal with the casing is of paramount importance in preventing the migration of fluids along the wellbore and to the environment. No matter the extremity of a cements compressive or even tensile strength, when debonding between the cement body and steel wall occurs, a micro-annulus is formed and acts as a direct flow path between previously isolated formation fluids. Recent studies using slightly unconventional methods have shown that adding small concentrations of nanoparticle barite and magnetite to a heavy; field ready, class H cement; present an increase in the potential bond strength of the cement.

To show this, laboratory evaluations on the shear and tensile bonding strength of the cement/steel interface were completed for nanoparticle barite and magnetite concentrations of 1%, 3%, and 5% by weight of cement using specially made apparatuses. Each apparatus was designed such that the cement slurry was allowed to set on top of a steel coin that was finely sandblasted to insure that each sample had a similar binding surface and each test used the same displacement rate for consistent loading across each of its samples. The shear bond strength was completed using a modified split core setup that imposed the desired failure plane along the cement/steel interface depending on its orientation. Tensile loading of the samples was applied using a threaded connection point adhered to the top of the set cement sample and connected to the load frame using a specially designed set of brackets.

Using the modified split core setup, it was seen that nanoparticle concentrations of as little as 1% by weight of cement increased the bond strength substantially when compared to the base case for both additives. Additionally, testing of the tensile bond strength further confirmed that the presence of nanoparticles have a significant effect on the cements ability to stay bonded with the inner wall of steel casing. The improvement observed is likely due to the coupled impact of the nanoparticles that act as both a mechanical reinforcement, and a means to reduce the presence of large Calcium Hydroxide (CH) crystals in the hydrated cement body whose irregular shape and fragile nature make it poorly suited for bonding to steel.

Altogether, the addition of nanoparticle barite and magnetite has been seen to introduce new strength to the binding potential of wellbore cement to the steel casing. This translates to a more resilient seal at the cement/steel interface which increases the overall barrier integrity. Whether implemented as a plug or primary cement, the need for an impermeable barrier is absolute.

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