The removal of oily drilling fluid and cleaning of the annular before the cementing operation is a key point for a good cementing and hydraulic isolation between the well and formations. For that, the industry inject washers and spacers of different densities into the well. The use of microemulsions emerges as an alternative to solvent/surfactant combinations, once that these systems are capable to solubilize large volumes of oil, change the wettability of the surface and reduce the amount of surfactant used. Thus, the present work aimed to study the formulation of a microemulsion spacer fluid for removing oil-based drilling fluids. For this, a pseudo-ternary diagram was formulated with a system composed by UNT L90, kerosene, tap water and n-Butanol in order to obtain a microemulsion system and optimum point for application. After the determination of the optimum point, the microemulsion spacers were formulated with xantana gum, defoamer, baryte and microemulsions. The drilling fluid and cement paste used in this work followed the practical recommendations. Analysis of removal efficiency, compatibility and wettability change were carried out for the different formulations at room conditions. At the end of the tests it was possible to obtain results of 100% removal efficiency in less than 5 minutes, wettability change of the drilling fluid with 26% of the volume and compatibility. The results obtained with corroborate with the literature, showing a possible application of these systems. However, tests under different conditions of temperature and pressure should be carried out to assess the performance of these spacer.