chemical wash the rotor was rotated for 10 minutes at 100 rpm the rotor when then removed from the chemical wash and left to drain for two minutes the bottom of the rotor was wiped clean and weighed w 2 the naf removal efficiency r was then determined by eq 1 the tests were repeated at least twice and the results were averaged to obtain a final result it is desirable to achieve an r value higher than 75 in the present examples the non aqueous naf drilling fluid was rheliant u2122 available from m i swaco houston tex usa the rheliant u2122 formulation was based on synthetic oil lao 16 18 from ineos oligomers with a 75 25 oil water ratio the drilling fluid was weighted with barite to a density of 1500 kg m 3 12 5 lbm gal the following surfactant solvent blend was prepared in a beaker with a magnetic stirrer and agitated until the solution was homogeneous 100 wt of a blend of ethoxylated alcohols with hlbg values between 8 and 16 and butoxyethanol available from schlumberger rotor tests conducted with the drilling fluid had the following result r 60 the following surfactant solvent blend was prepared in a beaker with a magnetic stirrer and agitated until the solution was homogeneous 50 wt of a blend of ethoxylated alcohols with hlbg values between 8 and 16 and butoxyethanol available from schlumberger 50 wt butoxyethanol rotor tests conducted with the drilling fluid had the following result r 62 the following surfactant solvent blend was prepared in a beaker with a magnetic stirrer and agitated until the solution was homogeneous 50 wt of a blend of ethoxylated alcohols with hlbg values between 8 and 16 and butoxyethanol available from.