Studies of nonlinear effects in porous media have primarily focused on oil flow in both high- and low-permeability sandstones. A limited number of studies have been conducted in carbonates with permeability of less than 0.1 µm2 and quite a few studies have been performed on the flow of polymer solutions in high-permeability reservoirs in presence of residual oil. Nonlinear pattern of the flow is attributable to non-Newtonian properties, primarily pseudoplasticity. To study nonlinear effects of the flow of polymer solutions through porous media, core flood experiments were carried out on consolidated Bobrikovian core samples of production target using the developed experimental set-up. Two sets of experiments have been conducted: 1) polymer solution flow in presence of connate water and initial oil saturation (characteristic of the initial state of the reservoir); 2) polymer solution flow in presence of residual oil saturation (characteristic of fully waterflooded state of the reservoir). Based on coreflood experiments, deviation from Darcy's linear law is observed during the flow of polymer solution both through sand-pack model and core samples at small pressure gradients regardless of fluid saturation and viscosity of polymer solution. During the flow of polymer solution through core samples pressure gradient of the transition process is substantially higher than that while flowing through the sand-pack model, especially for high-viscosity fluids. Consequently, the flow rate of polymer solution in in-situ conditions should be selected such that to take into account the ultimate pressure gradient at which the transition to linear law occurs.
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