Horizontal drilling has experimented a large increase in last years. In Brazil, two horizontal wells were drilled in Fazenda Belem and Carmopolis Fields. The first one reached a final measured depth of 1128 m and the horizontal length was 533 m. The drilling fluid program was elaborated after a large number of laboratory tests, in order to get a composition that best fitted the drilling requirements, mainly the desirable lubricity. The idea of using a water-base fluid instead of an oil-based, known as more suitable in this case, arose because the Company is interested in drilling this kind of well offshore, in deep water, where the use of oil-base muds is forbidden. Different compositions of water base muds were developed and tested in laboratory and the results led to low-solids salt fluids having a lubricant in its composition. The lubricity coefficients of these fluids are similar to those obtained with oil-base muds. 9-FZB-446D-CE well was drilled with the chosen fluid and high values of torque and drag were not registered, being the operation a total success. (author) 10 tabs.