Non-Newtonian flow in porous media-a laboratory study of polyacrylamide solutions

Abstract

Quantification of the rheological effects of polymer solutions flowing through a porous matrix must be achieved if high molecular weight polymers are to be used to the best effect in augmenting oil recovery. This investigation explores the extensional flow behaviour of polyacrylamide solutions, at dilutions around those used in oilfield practice, in a variety of flow geometries including hexagonal-rod arrays and glass-bead packs. Polyacrylamide solutions of 100, 250 and 500 ppm wt. were made up in 0, 0.05 and 3% NaCl brines to investigate the effect of polymer concentration and salinity on elongational flow behaviour. The flow boundaries are described in geometric terms and expressions developed to describe the extensional strain rate experienced by the solutions as a function of distance travelled through these regular porous media. The resulting maximum extensional strain rate values were then used to characterise the flow and to correlate the onset point of extensional strain viscosity in different sizes and geometries of porous media. The experimental results show that polyacrylamides can develop extensional viscosity values many times those generated under simple shear flow for the same strain rate. Evidence of extensional behaviour was detected in solutions as low as 10 ppm wt. polyacrylamide. The polyacrylamide principally used in these tests, Alcoflood 1175A, showed the largest effect in the 3% brine and it also showed the greatest resistance to shear degradation in this solvent.