Nonstationary flow of solutions of flexible-chain polymers in a porous medium

Abstract

Aqueous solutions of polyethylene oxide have been studied under the conditions of nonstationary longitudinal flow. The investigations have confirmed the deviations from Darcy's law according to the mechanism the basis for which is provided by the concepts of a strong strain action of the hydrodynamic field on coiled macromolecules.Experiments were conducted with the aim of elucidating the nature of the mechanism of an "abnormally" high degree of coverage of a porous bed with a polymer solution. The most contradictory opinions as to the nonlinearity of filtration flow of polymer solutions are being stated; most researchers believe that the nonlinearity is caused by the adsorption of macromolecules onto the porous-medium walls [1,2]. There is an opinion that the deviations from Darcy's law are due to the elastic-strain effects manifesting themselves in the case of flow of solutions of flexible-chain polymers in a porous medium [3,4]. Below, we will be dealing with experiments on checking the mechanism of an "abnormally" high degree of coverage of a porous bed with polymer solutions; the basis for this mechanism is provided by the concepts of a strong strain action of the hydrodynamic field on coiled macromolecules in filtration flow [5].The mechanism of deviations from Darcy's law lies in the self-oscillating regime of reversible processes of unrolling of macromolecules under the action of the longitudinal velocity gradients quasiregularly arising in the porous medium and in the influence of unrolling macromolecules at both the molecular and supermolecular levels on the structure of the filtration flow. The oscillation of the strains of macromolecules and dynamic supermolecular formations arising under the action of stretching flows results in the higher-than-average energy dissipation and the flow nonlinearity. The latter ensures the equalization of the front of advance and filling of inhomogeneous laminar beds with polymer fluid and hence a wider coverage of the bed.From the above mechanism of nonlinearity of the filtration of polymer solutions and from the theory of elastic-strain effects in the case of flow with extension of polymer solutions [3], it follows that the higher degree of coverage of a porous medium must be attained in nonstationary injection of a polymer solution into it. To substantiate this prediction we studied the aqueous solutions of polyethylene oxide (PEO) under the conditions of nonstationary longitudinal flow.Results and Their Discussion. In realizing the model regime of injection of a solution into a porous medium (bed), the solution under study was forced through a flow chamber (module) under the action of a constant pressure difference (see Fig. 1). This is an unusual kind of viscosimeter in which the hydroresistors are short capillaries.In the stationary regime, flow through the hydroresistors was carried out by creation of a pressure difference at the viscosimeter inlet and outlet, whereas in the nonstationary regime, it was carried out by superposition of a constant pressure differen...

Coil-Uncoiled Chain Transition of Polyethylene Oxide Solutions under Convergent Flow

“…One of the main features of the polymer solution is the ability to equalize the front of oil displacement in a reservoir with a layered heterogeneity under specific conditions [7,8]. To clarify the mechanism and conditions for the demonstration of such properties polymer solutions, it is necessary to study the features of their flow in the model conditions of a porous medium, which (in the first approximation) are realized under convergent flow [8,9]. Another practically important task with the use of polymer solutions is a water-polymer hydraulic cutting [10].…”