In this paper work we characterize clay minerals that are used in the preparation of ecological drilling fluids. The chemical composition of the clay minerals is determined by emission spectral analysis and by atomic absorption spectrophotometry. To characterize the clay minerals from the mineralogical and structural point of view we used thermal analysis, IR spectral analysis and X-ray diffraction method. The analysis’ result is a criterion for choosing clay minerals that have to ensure a good stability to ecological drilling fluids.
