1. Introduction

The chemistry of polymers for applications in enhanced oil recovery (EOR) has been advanced to improve their stability and functionality at elevated temperatures and in brines containing high salinity and hardness concentration (i.e. harsh reservoir conditions). Therefore, a variety of functional moieties have been attached to the polymer structure including: salt-tolerant and hydrolysis-resistant moieties such as allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonate (AMPS), and/or n-vinyl pyrrolidone (n-VP) monomers; hydrophobic groups like n-alkyl (i.e. ≥C6 carbon numbers) acrylamide, and styrene; ring structures and large-rigid side groups to improve the shear stability such as styrene sulfonic acid, n-alkyl maleimide, acrylamidebase long-chain alkyl acid, and 3-acrylamide-3-methyl butyric acid, among others [1–6].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This work evaluated the generation of advanced polymer-surfactant systems built via noncovalent and host-guest interactions based on β-cyclodextrin that would be stable under harsh reservoir conditions. The aim was to formulate efficient, chemically stable, and cost-effective systems as an alternative to expensive chemical synthesis.

The SAP-AP systems were formulated in synthetic reservoir brines [16] and the effect of different concentrations of brine on the rheological properties of the SAP-AP systems was

The formulation of the SAP-AP systems was based on a molar ratio of surfactant to β-CD of 2:1 established from our previous research [17–20]. In the initial formulation of the SAP-AP system, the concentration of polymer was kept fixed at 0.5 wt% in 2.1 wt% brine. Table 2 presents the experimental design applied for the SAP-AP formulation. All the experiments were duplicated or even triplicated, and the results presented are the average of several

Self-assembly was monitored through rheology by observing the changes in the elastic (G<sup>0</sup>

the baseline associating polymers [8–10, 12, 21]. The rheological analysis was conducted using a Bohlin Gemini HR Nano Rheometer manufactured by Malvern (Worcestershire,

NaCl 1.15 1.72 3.45 5.17 6.9 MgCl2 0.03 0.04 0.09 0.13 0.18 CaCl2 0.22 0.33 0.65 0.98 1.30 Na2SO4 0.01 0.01 0.02 0.03 0.04

1.40 2.10 4.21 6.31 8.41

0 30 50 70 90 110

S/β-CD50

AP β-CD-AP β-CD-AP β-CD-AP β-CD-AP β-CD-AP

S/β-CD70

S/β-CD90

S/β-CD110

)

203

), and complex viscosity, |η\*|, relative to

Advanced Polymer-Surfactant Systems via Self-Assembling

http://dx.doi.org/10.5772/intechopen.74618

determined. Table 1 shows the compositions of the synthetic brines.

and viscous behavior (G00), loss factor (tanδ = G00/G<sup>0</sup>

Components Total concentration (wt% or TDS)

Table 1. Synthetic brine compositions.

0 Baseline-\*

\*

\*\*S: surfactant.

Surfactant (ppm) β-CD concentration (ppm)

30 \*\*S 30-AP \*\*\*SAP-AP

\*\*\*SAP-AP: self-assembling polymeric system.

Table 2. Experimental design: SAP-AP formulations.

50 S 50-AP SAP-AP

AP 30

90 S 90-AP SAP-AP

110 S 110-AP SAP-AP

70 S 70-AP SAP-AP

AP: associating polymer: AP1, AP2, or AP3 mixed at a fixed concentration of 0.5 wt%.

measurements.

Self-assembly allows the coassembly of two or more types of building blocks, resulting in increasingly structurally complex nanoassemblies that may have physical and chemical properties that are distinct from those of the original monostructures [7]. Host-guest interactions refer to the formation of supramolecular inclusion complexes based on macrocyclic molecules (i.e. host molecules) consisting of two or more entities connected via noncovalent interactions in a highly controlled and cooperative manner. These host-guest inclusions are relatively stable and provide reliable and robust connections for the fabrication of stimuli-responsive supramolecular systems [8]. Cyclodextrins (CDs) are the most used and affordable hosts in the field of inclusion chemistry [7, 9, 10].

Supramolecular β-CD-based polymer systems retain their structural stability and functionality (i.e. self-healing) after exposure to externally applied stimuli or shear forces increasing the life span of these materials [8, 7]. The self-healing capability is highly dependent on the noncovalent connections in the polymer backbone and on the decomplexation and complexation of the supramolecular system [7, 8, 11, 12]. Therefore, supramolecular chemistry built on weak and reversible noncovalent interactions has emerged as a powerful and versatile strategy to design and fabricate materials with extraordinary reversibility and adaptivity with potential applications in diverse fields [8].

In this chapter, we first discuss the steps followed during the formulation of the SAP-AP systems and their rheological analysis. Secondly, we explore the effect of ionic strength on the rheological properties of the SAP-AP systems. Next, we discuss the combined effect of shear and ionic strength on the structural stability of the self-assembling systems. Finally, we summarize the short- and long-term thermal performance of the SAP-AP systems.
