Rheology and Adsorption of Aqueous Polymer Solutions

Abstract

ABSTRACT Studies were made of the apparent solution viscosities, temperaturest ability, adsorption and transport in porous media of two partly hydrolizedpolyacrylamide polymers, Nos. 500 and 700. Apparent solution viscosities were measured for polymer solutions with 0.25,0.20, 0.15, 0.10, 0.05, 0.025, 0.015 and 0.005 per cent weight per volumeconcentration in solvents of 2, 1, 0.5, 0.1, 0.01 and 0.001 per cent NaCl anddistilled water using capillary tube viscometers. The polymer solutions arepseudoplastic and, to describe the viscosity-shear rate relations, measurements were made with shear rates ranging from 7 to 2,000 sec. It was found thatpolymer solution viscosities are higher at low shear rates and NaCl concentrations. For the two polymers studied, the higher molecular one developsgreater viscosities at a given concentration and shear rate. If the pH of the polymer solution is adjusted by the addition of small volumes of HCI, the viscosity drops with decreasing pH. The viscosity reduction is relatively small for a pH range of 9.8 to 7, but drops sharply for more acidic solutions. Both polymers were found to degrade if heated to 275–300°F, even though they were heated in oxygen-free at- mosphere. Polymer adsorption was determined for six different polymer solutions and three different adsorbents in batch- typeexperiments. Adsorption was found to range from a low of 30 to a high of 880ug/g. In consolidated cores and sand packs, adsorption was significantly less, ranging from 35 to 160 ug/g. This is tentatively interpreted as meaning that the injected polymer solution cannot invade pores smaller than some criticalsize. The small pores have a larger surface area per unit volume than larger pores; hence, the greater part of the surface area was not avail- able to thepolymer. INTRODUCTION MANY RESEACHERS have shown that the use of dilute aqueous polymer solutionscan recover more oil than is recoverable by ordinary water flood from linearand radial flow models in the laboratory. The added recovery by polymer flooding is small in linear water floods in rather homogeneous porous media ifthe oil viscosity is less than 60 cp. For more viscous oils, the additionalrecovery becomes greater. If the flow model is heterogeneous, for example, composed of layers with different permeabilities polymer flooding is more efficient than water flooding in two ways: the oil recovery is greater and thewater-oil ratios are lower. Flow studies in five-spot Berea sandstone and Hele-Shaw models have shown the principal mechanism of increased recovery to beimprovement in the sweep efficiency. Theoretical studies have confirmed theexperimental findings. In field applications, it appear, 4 that polymers haverecovered more oil than conventional water flooding, but an accurate assessment of the benefits of the process is not possible because one is unable to make acomparison with controlled water floods. The mechanism by which polymers reduce the mobility to water is notcompletely understood. The mobility reduction has been shown to be due in partto an increase in the viscosity of the water and in part to a reduction of the permeability of the porous medium after the polymer has flowed through it. Polymer solutions are non-Newtonian, and a number of theories have been advanced to explain their flow characteristics The present study deals with therheological characteristics and adsorption of two partly hydieolyzedpolyacrylamide polymers, Nos. 500 and 700.