Systematic Study of Viscoelastic Properties During Polymer-Surfactant Flooding in Porous Media

Abstract

Based on the currently discussed ability of HPAM-polymer to increase displacement efficiency due to viscoelastic properties, a comprehensive evaluation of the possible impact on the design of polymer-surfactant mixtures is presented in this investigation. This assessment includes a comprehensive analysis of laboratory experiments. Experimental data was obtained from different sources and furthermore crosschecked, such as: rheological characterization, flooding through microfluidics devices, and core flooding experiments. First, solutions were characterized by the analysis of different rheological techniques. Second, flooding experiments were performed in a microfluidic device which has a hyperbolical contraction-expansion geometry, capable to provide apparent extensional viscosity. Third, single phase core flooding experiment was conducted using Bentheimer core plugs to evaluate the flow behavior of polymer and surfactant in porous media. Finally, flow paths of polymer-surfactant mixtures were described using streamline visualization techniques. The latter was performed injecting the solutions at different flow rates in a Glass-Silicon-Glass (GSG) micromodel generated from a micro CT scan images of a real porous media. Polymer-surfactant mixtures depicted a pseudoplastic behavior with an increasing in polymer's apparent viscosity due to the presence of a surfactant. Polymer extensional viscosity has been slightly improved due to the addition of Polyethylene oxide (PEO) at 0.5wt% and 1.5wt% using a solvent of 4.0 g/l TDS. Increasing in the measured extensional pressure drops suggested that the viscoelastic properties are improved by using polymer-surfactant combination at apparent rates below 720s-1. Shear rate coefficients resulted in an acceptable match between the rheometer and the core flooding measurements. At a critical value of adjusted shear rates (40-50 S-1), viscosity of three solutions was almost the same value of 30 mPa.S (Critical apparent viscosity). After this critical value, HPAM with no PEO and with 0.5wt% PEO showed shear thickening behavior, while with 1.5wt% PEO showed shear thinning behavior till shear rate value of 95 S-1, after this rate, it was dominated by shear thickening behavior. Moreover, different flow regimes were observed through the streamline visualization in GSG micromodels; a zone mainly considered by laminar flow in case of HPAM with 0.5wt% PEO, remarkable vortex was observed in an open pore geometry and crossing streamlines especially in the wall areas in case of HPAM with no PEO. This evaluation leads to understanding the viscoelastic behavior in porous media when polymer and surfactant flooding are applied in combination and provide a proper understanding to complement the few literature resources available about this topic.

A Comprehensive Combination of Apparent and Shear Viscoelastic Data during Polymer Flooding for EOR Evaluations

“…Viscoelastic polymers exhibit shearthinning behavior during rotational rheometry experiments whereas, when flowing through porous media the same polymer solution depicts shear thickening behavior-at a certain medium/high shear rates [4] [5] [6]. Core flood experiments have confirmed apparent viscosity dependence on shear rate [6], [7].…”

On the Role of Polymer Viscoelasticity in Enhanced Oil Recovery: Extensive Laboratory Data and Review

“…Shear-thickening behavior can be observed after the polymer flow has reached the second critical shear rate as shown in Figure 5 . A remarkable observation that can be made from this plot is that shear thickening is only encountered in porous media during polymer flooding and not in rotational rheometer measurements [ 8 , 20 , 26 , 27 , 63 , 65 , 66 , 67 , 68 ]. It is believed that the missing shear thickening is the result of the missing flow motion, since the viscosity increase is commonly explained with a distinctive stretching of the polymer molecule [ 27 , 69 ].…”

“…These are commonly measured by the use of state-of-the-art rotational rheometer, but the moduli, for example, can also be measured using the dynamic light scattering (DLS) technique developed by Duffy et al [ 102 ] and in detail explained by Hincapie [ 8 ]. For measurement of extensional viscosity, the small sample viscometer (mVROC™) or the extensional viscometer-rheometer-on-a-chip (eVROC™) as presented by Pipe et al [ 103 ] and Elhajjaji et al [ 65 ] can be used. In this study, based on the results obtained from preliminary experiments prior to this work, it is assumed that the extensional viscosity—often discussed as the additional viscosity in shear thickening—is not the reason for the viscosity increase in porous media seen after the second critical shear rate (see Section 3.2.2 and Section 3.2.3 ), but the onset of elastic turbulence.…”