Application of SDS surfactant microemulsion for removal of filter cake of oil-based drilling fluid: influence of cosurfactant

After drilling oil wells using oil-based drilling fluid, there is the occurrence of a formation of a thin layer of solids adsorbed on the surface, called filter cake, which must be removed to obtain satisfactory well cementation. The present work developed microemulsion systems from sodium dodecyl sulfate, a biodegradable surfactant, with kerosene as oil phase, n-butanol as cosurfactant and distilled water, in order to evaluate its efficiency in removing the filter cake. The results showed that the microemulsion systems composed of inverse and bicontinuous micelles removed 100% of the filter cake regardless of the content of the constituents in the formulation, while the direct micelles only reached 100% with the formulation composed by 10% kerosene and cosurfactant/surfactant ratio = 4. It was observed that the cosurfactant/surfactant ratio is a determining variable for direct micelles to remove 100% of the filter cake and that they are compatible with cement, offering desirable thermal stability and improving the wettability of the rock in water.