This investigations were carried out on different spent water-based muds, collected in drillings in various parts of Poland. The combined study methods included structural and phase investigations (X-ray diffractometry, infrared FTIR spectroscopy, scanning electron microscopy) and instrumental chemical determinations. The results characterize mineral and phase composition of the samples, their microstructure and chemical composition. The authors focused on the specific nature of polymer-clay complexes, which in drilling mud systems have the form of delaminated or exfoliated organic-clay polymer nanocomposites that control properties of such waste materials. Detailed recognition of properties chemistry, mineral and phase composition, microstructure of spent drilling muds have a fundamental meaning for studies on the management of these materials in the natural environmental.