117Complex structures, e.g., granulated media or vis coelastic fluids, are known to exhibit the property of an anomalously slow transition to an equilibrium state. If the internal state of the medium is character ized by some parameter ξ (order parameter, defectiv ity, etc.), it is usually assumed that, at the initial Δξ deviation from the equilibrium state the order parameter returns to its equilibrium value according to the exponential law = + . Here, τ is the relaxation time, i.e., one more internal parame ter describing the medium. The known theory of relaxation absorption of sound is constructed based on this approach (see, e.g., [1], p. 435). In complex media at large relaxation times, another dependence in real ized instead of the exponential law, namelyIn particular, the authors of [2] observed such variations in the modulus of elasticity in rock during natural relaxation of defects. An analogous dependence of viscosity on time was observed in acoustic experiments with a drilling fluid in [3,4]. A slow evolution of sound passage through a granulated medium was studied in [5].This study gives the results of experimental investi gations of the time dependence of viscoelastic shearmoduli for crude oil specimens at a known composi tion of the tested specimens. Viscoelastic moduli of elasticity were determined using the method of rota tional rheometry in the mode of shear harmonic deformations with a small amplitude. The model the oretical description of an anomalously slow variation in the parameters of the analyzed medium in time is proposed.Crude oil specimens denoted as no. 1 and no. 2 were used as test subjects. The composition of these oils (Table 1) was determined with the help of the sat urate, aromatic, resin, and asphaltene (SARA) tech nology.This technology is based on separation of degassed oil into SARAs according to their solubility and polarity.In elastic media, the shear stress σ is proportional to the shear strain ε.Let the strain change according to the harmonic law where ε 0 is the amplitude of strain harmonic oscillations and ω is the oscillation frequency. By combining the contributions from elas tic and viscous components, let us write the equationAbstract-The results of experiments on the observation of the slow evolution of viscoelasticity moduli of crude oil are presented. Measurements were carried out continuously for 72 h at frequencies of 0.5, 5, and 50 Hz at different temperatures. Based on the Boltzmann statistical approach to determination of the velocity of transition into an equilibrium state, a model differential equation describing slow kinetics of variations in the internal medium parameters is derived. As distinct from the accepted exponential time dependence, the slow kinetics is shown to yield a logarithmic time dependence of perturbation damping.
