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halted. Hence, they have to maintain the rheological properties ofthe OBM at different depth i.e. over a wide temperature range. Fur-thermore, OC has to minimize interaction of OBM with the bearingrocks by forming a low permeability protective cake on the borewall and developing adequate physicochemical characteristics toavoid the swelling of drilled shale rocks.In addition to OC, OBM contains also surfactants to stabilizedthe oil/water interface of droplets and several additives includ-ing polyanionic cellulose (PAC) a fluid loss reducer and differentpolymeric swelling inhibitors such as partially hydrolyzed poly-acrylamide (PHPA), sodium silicate and polyalkyleneglycols (PAGor “glycol”) to improve the stability of the drilled formation 1.Even if drilling fluids are complex formulations, the size andamount of water droplets and the dispersion state of anisotropicOC particles in the continuous phase play an important role on theviscosity so that their rheological properties seem to be governedby interactions between the three major components water/oil/OC.There is a huge number of papers in the open literature dealing withrheology of the emulsions and the rheology of swelling clay min-eral dispersions 2,3,4,5. The OC structure is extensively studiedafter dispersion in organic solvents and also in molten polymersin the aim to study the structure/properties correlation of the claypolymer nanocomposites (CPN).Recently, Rheo-SAXS studies make possible to combine struc-ture and rheology of such systems in order to link theirnon-Newtonian properties with the structure and orientation ofclay mineral particles 8,9,10. However it should be noticedthat at our knowledge, there is not any paper published on thestructure/rheology correlation with clay mineral emulsion. In thepresent work, this technique is applied to correlate the structurewith the viscosity under shear flow of OC in W/O emulsion.