The main objective of this work is to evaluate the inclusion of nanoparticles to partially hydrolyzed polyacrylamide/resorcinol/formaldehyde gel systems to improve the stability under static and dynamic conditions. Oxide nanoparticles (<100 mgÁL −1 ) of SiO 2 , Al 2 O 3 , MgO, and Cr 2 O 3 were employed and characterized by their physicochemical properties. Gels were prepared and subsequently placed at 70 C for evaluating the nanoparticles influence in gel strength through rheological properties and syneresis measurements. Al 2 O 3 nanoparticles showed the highest potential for the reduction of the syneresis phenomena, followed by MgO and Cr 2 O 3 . The SiO 2 nanoparticles lead to a higher degradation of the gel. As the zeta potential increases, the syneresis of the gel system decreases. The nanoparticles did not significantly affect the storage modulus, describing similar gel strength than the original gel. Also, displacement tests showed an incremental of 64% of oil recovery regarding the system in the absence of Al 2 O 3 nanoparticles.Jia et al. 15 developed an experimental investigation about resorcinol/phenol-formaldehyde crosslinking HPAM (0.3 wt %) gel system and found that by varying resorcinol concentration between 10 and 30 mgÁL −1 and phenol-formaldehyde between 0.4 and 1.2 wt %, a barely flowing gel (codes D and E according to Sydansk's scale from A to I, 16 respectively) was obtained at a Additional Supporting Information may be found in the online version of this article.

During enhanced oil recovery (EOR), reservoir heterogeneities and fluids distributions promote preferential flow channels formation. Therefore, different types of gels have been proposed to improve swept efficiency on chemical flooding by plugging high permeability zones. The purpose of this article is to evaluate the effect that nanotechnology has on the inhibition of syneresis and the rheological properties of the Acrylamide Sodium Acrylate Copolymer/Chromium (III) Acetate gel system for conformance applications in mature reservoirs. Thus, a methodology is proposed in four stages: First, (I) nanoparticles synthesis, and characterization, followed by (II) bottle tests to monitor gelation kinetics and syneresis degree at 70 °C, then (III) description of the rheological evaluation on static and dynamic conditions to calculate gelation time and viscoelastic modulus (G’ and G”), and finally (IV) the displacement test with the best gel system in the presence of nanoparticles. Results showed that the best nanoparticle was the chromium oxide (Cr2O3), which represented the lesser syneresis degree and increased gelation time. Syneresis of gel samples in the presence of Cr2O3 at day 30 was under 1% for gels prepared with 4000, 6000, and 8000 mg·L−1 of polymer, and polymer to crosslinker ratio (p/c) of 40:1. Regarding SiO2, MgO, and Al2O3 nanoparticles, results show an improvement of gel strength. However, their thermal stability in terms of syneresis was lower. Displacement test in a triple parallel Slim Tube was able to recover an additional 37% of oil of the total oil present in the sandpacks, confirming the effectivity of the system when 100 mg·L−1 of Cr2O3 nanoparticles are included.

Aqueous solutions of hydroxypropyl methylcellulose (HPMC) show inverse thermoreversible gelation, i.e., they respond to small temperature variations exhibiting sol–gel transition during heating, and reversibly gel–sol transition during cooling. According to the pertinent literature on HPMC aqueous systems, at room temperature, the loss modulus (G”) is higher than the storage modulus (G’). During the heating ramp, the viscoelastic response follows a peculiar path: initially, G” and G’ smoothly decrease, then drop to a minimum and finally increase. Eventually, G’ overcomes G”, indicating the gel formation. A recent explanation of this behaviour considers a two-step mechanism: first, phase separation occurs, then fibrils form from a polymer-rich phase and entangle, leading to a three-dimensional network. Based on this, our research focuses on the rheological analysis of the different steps of the sol–gel transition of an HPMC aqueous solution. We perform different viscoelastic tests: thermal ramps, time sweeps, and frequency sweeps at selected characteristic temperatures. We couple classical analysis of the SAOS experiments with an innovative approach based on the evaluation of the activation energy (Ea), made possible by the instrument intrinsic temperature oscillations around the target value. Results show that Ea can be a valid tool that contributes to further clarifying the peculiar microstructural evolution occurring in this kind of thermoreversible gel.

Hydroxypropyl methylcellulose (HPMC) is a polymer made of a cellulose backbone with etherified methoxy and hydroxypropyl substitutions that undergoes a reversible inverse thermo-gelation upon heating. The thermo-gelation follows a two-step mechanism: first, phase separation occurs, then fibrils, formed in the polymer-rich phase, entangle to form the three-dimensional gel network. This work aims at understanding the influence of degree (DS) and molar substitution (MS) on the thermo-gelation process. DS is the number of methyl groups, and the MS is the hydroxypropyl content per anhydroglucose unit. The thermo-gelation process is here rheologically investigated for two HPMC samples, which have similar molecular weight but different MS and DS: thermal ramps are coupled with time sweep tests at selected temperatures and with frequency sweep experiments. Results show an important effect not only on the transition temperatures (beginning of the phase separation, beginning of the gelation) but also on the kinetics of the different phases of the process.