Molecular Structure Characterization and Interaction of a Polymer Blend of Xanthan Gum-Polyacrylamide to Improve Mobility-Control on a Mature Polymer Flood

Abstract

Abstract According to the strategy to search alternative products which can replace (partially) the use of expensive polymers in polymer-flood projects, this work helps to find the optimum combination between polymer and xanthan-gum to develop a mixture that generates viscosity in good economical and rheological conditions. The aim of this work is the characterization of the mixture of a biopolymer (xanthan gum) and a synthetic polyacrylamide in specific proportions and reservoir conditions. Both polymers are suitable for polymer flooding, but they have weaknesses on their own: the polyacrylamide is very susceptible to saline environments and mechanical degradation, while biopolymers as xanthan gum exceed these reservoir conditions but are highly degraded by some bacteria. A polymer blend of mother solutions was prepared by mechanical mixing. It is proved that a blend improves the desirable properties of mobility control if the polymers show miscibility. Several techniques were used to evidence possible interaction between the polymers. A series of tests were performed to provide complementary data regarding molecule structure, miscibility, interaction and stability of the xanthan gum-polyacrylamide mixture at 35/65 proportion in a 16,000 ppm TDS reservoir synthetic brine. The polymer mother solutions and the mixture were lyophilized in order to determine thermal events by Differential Scanning Calorimetry (DSC), Differential Thermal Analysis (DTA) and Thermo Gravimetric Analysis (TGA). Also Fourier Transform Infrared (FTIR) spectroscopic studies and Proton Nuclear Magnetic Resonance (1H NMR) were performed to obtain distinctive molecular fingerprint; and Scanning Electron Microscopy (SEM) so as to complete the morphological studies. This work shows detailed techniques of the characterization and the conclusions achieved that confirm the molecular interaction of the blend. DSC analysis at low temperatures evidence similar vitric transitions for xanthan gum and polyacrylamide mother solutions. Vitric transition temperature (Tg) is related to the polymer network packing and hydrodynamic volume, concluding that similar values means that both polymers can travel together through the porous media without being segregated. The single Tg obtained for the mixture could indicate interactions between the polymers. This interaction was also shown in the FTIR analysis: the mixture spectra showed displacement of some signals of the fingerprint zone. On the other hand, the 1H NMR spectra of the mixture did not show differences with the pure polymers ones. SEM micrographies show no surface separation: xanthan gum deposits over the continued and directional layers of polyacrylamide evidencing phase integration. Blends of bio and synthetic polymers are investigated widely in other industries due to their benefits. Up to date, there are no reports of the use of polymer mixtures in polymer flooding. The results of this work will enable the design of a pilot to be conducted during 2018 on a mature polymer-flooded area with more than 10 years of polymer-flooding (Buciak, 2013).