NON-NEWTONIAN FLOW IN POROUS-MEDIA - A LABORATORY STUDY OF POLYACRYLAMIDE SOLUTIONS

Quantification of the rheological effects of polymer solutions flowing through a porous matrix must be achieved if high molecular weight pol ymers are to be used to the best effect in augmenting oil recovery. Th is investigation explores the extensional flow behaviour of polyacryla mide solutions, at dilutions around those used in oilfield practice, i n a variety of flow geometries including hexagonal-rod arrays and glas s-bead packs. Polyacrylamide solutions of 100, 250 and 500 ppm wt. wer e made up in 0, 0.05 and 3% NaCl brines to investigate the effect of p olymer concentration and salinity on elongational flow behaviour. The flow boundaries are described in geometric terms and expressions devel oped to describe the extensional strain rate experienced by the soluti ons as a function of distance travelled through these regular porous m edia. The resulting maximum extensional strain rate values were then u sed to characterise the flow and to correlate the onset point of exten sional strain viscosity in different sizes and geometries of porous me dia. The experimental results show that polyacrylamides can develop ex tensional viscosity values many times those generated under simple she ar flow for the same strain rate. Evidence of extensional behaviour wa s detected in solutions as low as 10 ppm wt. polyacrylamide. The polya crylamide principally used in these tests, Alcoflood 1175A, showed the largest effect in the 3% brine and it also showed the greatest resist ance to shear degradation in this solvent.