Efficient displacement and effective removal of oil-based mud from the wellbore prior to cementing is critical to developing an excellent bond between casing and formation. Synthetic-based muds (SBM) can leave a thin-layer of oil on the casing and the formation when displacing to cement. It’s one of the least compatible fluids with cement slurries. This oil-layer can prevent the cement slurry from forming a strong bond with the formation and the casing. The lack of good bond could lead to poor zonal isolation and leave the casing and wellbore with decreased structural integrity. Removing this oily layer is generally accomplished by running viscosified weighted spacer containing cleaning agents ahead of cement slurry. Traditional surfactants have limited performance inverting and cleaning oil-water emulsions, besides being extremely detrimental for the development of the mechanical properties of the cement.

Microemulsions (Picture 4) are an oil-external, thermodynamically stable microemulsion that can be added in water or a viscous spacer as a single additive. The additive is a microemulsion dispersion of solvents and surfactants designed to enhance compatibility with the drilling fluid, demulsify, clean and water-wet the casing and borehole surfaces for better cement adhesion. Unlike traditional surfactants and solvents utilized to improve mud removal, the proprietary microemulsion additive, provides micellular dispersions that remain uniformly dispersed in water or viscous spacers, providing greater mud removal efficiency. Laboratory data demonstrates the effectiveness of the microemulsion in removing oil or synthetic-based mud while aggressively removing the oily layer and water-wetting from the casing and the formation.

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