The behaviour of polymer solutions in extension-dominated flows, with applications to Enhanced Oil Recovery

Abstract

Abstract:The rheometry and flow behaviour of aqueous solutions of polyacrylamide and xanthan gum are discussed, with the expectation that the results will be of use in Enhanced Oil Recovery (EOR). The rheometrical study gives particular prominence to the dramatically high values of extensional viscosity which are possible in aqueous solutions of flexible polymers such as polyacrylamide. The effect of such factors as polymer concentration, salt concentration and mechanical degradation on rheometrical properties is outlined. Reference is also made to the qualitatively-different rheometrical behaviour experienced by comparable solutions of xanthan gum.Further evidence is advanced that some dilute polymer solutions of potential use in EOR experience abnormally high resistance in flows which are dominated by extension. Since flow through a porous medium involves a substantial extensional component, it is argued that there is justification for studying the effect of this high extensional-viscosity behaviour in a number of idealized geometries of relevance to EOR conditions. The resulting experiments indicate that, at low flow rates, shear viscosity is the dominant influence, but that, after a critical set of conditions, extensional-viscosity considerations can become all important and the observed pressure losses are against any expectation based on conventional fluid mechanics.Flow visualization studies support the pressure-drop measurements in emphasising the strong influence of high extensional viscosities in flows through tortuous geometries.

Viscoelastic flow past a confined cylinder of a polyisobutylene solution

“…Dhahir and Walters (1989) visualized streamlines for the planar flow past an asymmetrically confined cylinder and observed that for a (elongational thickening) viscoelastic liquid more material flows through the broader gap, compared with a Newtonian liquid. Jones andGeorgiou et al (1991) found the same effect in the flow of several types of liquids through an antisymmetric array of confined cylinders. It is considered as a manifestation of the extensional viscosity: molecules entering the narrow gap must elongate more strongly than those entering the broad gap, which results, for elongational thickening liquids, in a locally higher flow resistance in the narrow gap.…”

“…The effect is demonstrated experimentally by Walters and coworkers [Dhahir and Walters (1989), Cochrane er al. (1981) Jones and Walters (1989), Georgiou et al (1991)]. Cochrane et al (1981) observed that the streak lines for a viscoelastic fluid were much more sensitive for a small asymmetry in the constraining of the cylinder than for a purely viscous, Newtonian fluid.…”

“…This is also predicted by the four-mode PTT and Giesekus models which are fitted adequately with data measured in simple shear flow. The use of a model fluid that is more sensitive for elongational flows will give more drastic viscoelastic effects, see for example the results of Walters and co-workers with polyacrylamide solutions [Dhahir and Walters (1989), Cochrane et al (1981), Jones andWalters (1989), Georgiou et al (1991)]. …”

Characterizing Porous Media with the Yield Stress Fluids Porosimetry Method

“…Xanthan gum is a commonly used viscosifier (Garcia-Ochoa et al 2000;Abidin et al 2012), especially in manufacturing food grade products (Palaniraj and Jayaraman 2011), as well as in polymer flooding technics for "Enhanced Oil Recovery" (Jones and Walters 1989;Abidin et al 2012). Its chemical composition, structure and other physicochemical properties can be referred to, for example, Song et al (2006).…”

“…Xanthan gum solutions are one of the main examples of inelastic, shear-thinning fluids in contrast to linear flexible polymers as polyacrylamide (Jones and Walters 1989;Sorbie 1991a) which are highly viscoelastic. Due to the stiffness of its molecule, xanthan semidilute aqueous solutions develop a high viscosity level and a very pronounced shear-thinning behavior.…”