Using Xanthan Gum Solutions to Characterize Porous Media with the Yield Stress Fluid Porosimetry Method: Robustness of the Method and Effects of Polymer Concentration

Abstract

The yield stress fluids porosimetry method (YSM) was recently presented as a simple and non-toxic potential alternative to the extensively used mercury intrusion porosimetry (MIP). The success of YSM heavily relies on the choice of an appropriate yield stress fluid to be injected through the investigated porous medium. In previous works, xanthan gum aqueous solutions were used due to their ability to exhibit a pseudo-yield stress without substantial levels of unwanted thixotropy or viscoelasticity. Given that YSM is based on the existence of a yield stress, the accuracy of the obtained pore size distribution (PSD) crucially depends on the capacity of the injected fluid to emulate the shear rheology of a yield stress fluid. However, this capacity has still not been fully assessed in the case of xanthan gum solutions. Neither has the robustness of YSM with regard to errors in the determination of the shear-rheology parameters of the injected fluid been analysed. The shear viscosity of polymer solutions is known to be deeply influenced by polymer concentration. For these reasons, a first objective of this work is to evaluate the effect of polymer concentration on the accuracy of PSDs obtained by YSM when using xanthan gum solutions as injected fluids in laboratory experiments. To do so, xanthan gum solutions with different polymer concentrations were injected through analogous samples of a sintered silicate and the obtained PSDs were compared to the results of standard MIP. Moreover, the sensitivity of YSM to errors in the experimental determination of the shear-rheology parameters was also investigated through numerical experiments. The results of the present work permitted to gain further insight into the viability of YSM as an efficient alternative to MIP.

Numerical porosimetry: Evaluation and comparison of yield stress fluids method, mercury intrusion porosimetry and pore network modelling approaches

“…This is in contrast to ideal yield stress fluids (e.g., Hershel-Bulkley model), for which the viscosity goes to infinity as the yield stress is approached. Furthermore, this is also the case of many real pseudo-stress fluids ( Rodríguez de Castro et al, 2018 ), such as Carreau fluids with very high values of the plateau viscosities (lower Newtonian plateau). The preceding aspect may be seen as an important limitation of YSM.…”

“…The inversion algorithm consists in isolating the increase in flow rate arising from yielding of the fluid in the pores of a given size, i.e., smaller pores as the the applied pressure gradient is gradually increased. In the search for a suitable penetrant fluid with negligible degrees of viscoelasticity and thixotropy, xanthan gum aqueous solutions were proposed by Rodríguez de Castro et al (2014 ), and the polymer concentration was optimized in order to obtain accurate PSDs ( Rodríguez de Castro et al, 2018 ). Furthermore, the critical experimental issues of mechanical degradation, retention and adsorption of xanthan macromolecules were also assessed in previous research ( Rodríguez de Castro et al, 2016 ).…”

Application of Non-toxic Yield Stress Fluids Porosimetry Method and Pore-Network Modelling to Characterize the Pore Size Distribution of Packs of Spherical Beads

“…The details of the procedure followed to obtain the PSD from the raw (Q i , ∇P i ) data collected during injection of a yield stress luid in a porous sample were provided by Rodríguez de Castro et al ( , 2016Castro et al ( , 2018. For this reason, only the essential features of the method are presented in this section.…”

“…In the present experiments, a 7000-ppm xanthan gum aqueous solution was injected through the investigated packs of beads during the YSM tests. The choice of this concentration of xanthan gum solution to perform the (Q i , ∇P i ) measurements was motivated by the results presented by Rodríguez de Castro et al (2018), in which this concentration was identiied as a reliable one for the injection luid used in YSM when dealing with porous media with high-to-moderate permeability (typically > 50 mD). These concentrated aqueous solutions featured extremely high viscosity values at low shear rates, closely approaching the behaviour of ideal yield stress luids without showing signiicant thixotropy or visco-elasticity.…”

“…Moreover, polymer retention, mechanical degradation and adsorption of the macromolecules in diferent types of commonly encountered natural and synthetic porous media were experimentally assessed by Rodríguez de Castro et al (2016), concluding that none of these efects was signiicant apart from polymer retention at very low low rates in less permeable porous media. Furthermore, Rodríguez de Castro et al (2018) investigated the efects of polymer concentration of xanthan solutions on the accuracy of the PSDs provided by YSM, and the sensitivity of the method to errors in the experimental determination of the shear-rheology parameters. In the latter work, nominal values of polymer concentration were proposed for porous media with high-to-moderate permeability.…”