Experimental Study on Effect of hydrophobicity on Polymer Conformations, Rheology and Flow in Porous Media
Creators: Patel, Viralkumar
Publisher: name: University of Alberta Library
Year: 2023

<p>Typically, polymer screening for enhanced oil recovery operations is done based on viscosity, viscosity dependent molecular weight correlations, and concentration. However, direct measurement of molecular weight and Molecular Weight Distribution (MWD) along with the other conformational parameters can provide better insights into the molecular characteristics of polymer molecules. In this work, we emphasize the need for incorporating MWD, radius distributions, and conformational characteristics of polymer solutions over the conventional screening criteria or enhance oil recovery operations. In particular, the hydrophobicity and concentration-dependent polymer conformations affect the polymer network formations at the molecular level in the aqueous and salinity environments is studied, and how they relate to polymer flow in the porous media. Due to limitations of gel permeable chromatography, direct measurement of polymer molecular weight, MWD, radius distributions, and conformations are measured using fluid flow fractionation (FFF) method. The effect of hydrophobicity on the rheological properties, shear rheology, and extensional rheology is also explained. Furthermore, the flow behavior of the polymer solutions in the consolidated and unconsolidated porous media in terms of Resistance Factor (RF) and Residual Resistance Factor (RRF) is justified by using the viscoelastic properties and polymer conformation.<br>
The results show that the average molecular weight increased with polymer concentration and hydrophobicity in both, aqueous and saline environments. However, narrow MWDs were observed for the polymer solutions with brine salinity. The average radius increased with the polymer concentration. However, these values decreased with hydrophobicity in aqueous media and increased with hydrophobicity in a saline environment due to the charge screening effect. The domination of intermolecular networks only seems to occur above the critical aggregation<br>
concentration. The polymer conformations changed from randomly coiled Hookean to the compacted sphere Non-Hookean as the hydrophobicity, concentration, and salinity increased. This corresponded to the higher resistance and residual resistance factors. The MWDs along with different types of confirmations were not able to differentiate the shear rheological behavior at the identical polymer concentration. However, the higher apparent extensional viscosity justifies the formation of an intermolecular network eventually responsible for forming Hookean randomly coiled polymer conformations.<br>
The polymer conformational properties measured using FFF and apparent viscosity profiles are used to explain how the hydrophobicity of polymer affects the polymer resistance and retention in the porous media, especially when shear and extensional rheology fails to explain the flow behavior in the porous media. The results showed that higher hydrophobic polymer was able to form non-Hookean rigid spherical structures that increase the hydrodynamic trapping. Whereas, at the low hydrophobicity, the formation of soft randomly coiled polymer conformations offers ease of injectivity even at the higher injection rates. Additionally, the proposed interaction mechanism of the coiled conformations on the rock surface is an important criterion for the prediction of polymer retention in the porous media. At the higher polymer concentration, the polymer retention in the porous media increased due to the domination of gel retention in the porous media. Combining concentration and hydrophobicity-dependent structure formations allow for optimizing the operation parameters like flow rate, pre-shearing, and filtration conditions.</p>