a lower density than barite the oil and water in the used drilling fluid are present in proportionate amounts the relationship between them often being expressed as an oil to water ratio in a first embodiment shown in fig1 the apparatus 10 includes a plurality of mixers 12 20 that may be mounted to a common skid 22 oil based drilling fluid 24 is pumped from a mud plant 26 to the first mixer 12 a pump 28 may be used to introduce the drilling fluid 24 to the first mixer 12 with a predetermined pressure and flow rate a surfactant 32 is pumped into the first mixer 12 from a surfactant tank 34 the surfactant 32 may be diluted with water 30 from water tank 38 prior to its introduction to the first mixer 12 a dose pump 36 may be used to introduce the surfactant 32 to the mixer with a predetermined pressure and flow rate the surfactant 32 acts on the mud solids improving their hydrophilicity so that the polymer which is very hydrophilic and added downstream can flocculate the solids the first mixer 12 preferably is a static shear mixer including an insert not shown that provides shear to the fluid passing through the first mixer 12 sufficient to mix the surfactant 32 and the drilling fluid 24 the surfactant 32 and the drilling fluid 24 are introduced to the first mixer 12 upstream from the insert and exit the mixer 12 as a surfactant treated mud 40 a flocculant polymer 42 is stored in a flocculant storage tank 44 and ma be mixed with a base fluid 46 when necessary to form.