Background The method of nuclear magnetic relaxometry to obtain molecular characteristics of the interaction of the drilling fluid aqueous component with clay-containing rocks is considered. This method allows the study of physicochemical processes of hydration of clay-containing rocks on natural core samples at the micro level. The results of evaluating the effectiveness of various non-clay drilling fluids by the inhibitory ability of their filtrates are presented. Aims and Objectives To evaluate the physicochemical interactions in the «clay - water» system by nuclear magnetic relaxometry. This method determines the quantitative assessment of the void space state during the swelling of clay-containing core material and allows us to formulate recommendations for improving the flushing fluids quality. Methods The nuclear magnetic relaxometry method is based on recording and measuring the amplitude of the spin echo signals obtained as a result of the precession of the proton system. The initial amplitude of the signal measures the amount of fluid. The volume of the core sample allows you to record the porosity of the sample. The method is based on the resonance absorption of high-frequency electromagnetic field energy by the nuclei of hydrogen fluids saturating these rocks. As a promising method for studying the pore medium, capable of objectively evaluating and supplementing the results of laboratory measurements, an NMR-relaxometer МСТ-05 of joint production of Russia and the USA was used in the work. Results To evaluate the inhibitory properties of water-based drilling fluids, the NMR relaxometry method was used. This method allows you to determine the change in the capacitive properties of clays due to the sorption of the aqueous component of the drilling fluid with a matrix of clay-containing rocks. It is possible to slow down or accelerate this process, including various ingredients in the drilling fluids formulation that are accelerators or inhibitors of the physicochemical reactions of hydration and solvation on clay surfaces. The greatest effect of suppressing the activity of clays and clay-containing rocks to swelling is achieved when washing wells with clay-free drilling mud with a complex of reagents Polysil Potassium and KLSP.