Water-soluble polymers are known to be used in chemically enhanced oil recovery (EOR) processes, but their applications are limited in high-temperature and high-salinity oil reservoirs because of their inherent poor salt tolerance and weak thermal stability. Hydrophobic association of partially hydrolyzed polyacryamide (HAHPAM) complexed with silica nanoparticles to prepare nano-hybrids is reported in this work. The rheological and enhanced oil recovery (EOR) properties of such hybrids were studied in comparison with HAHPAM under simulated high-temperature and high-salinity oil reservoir conditions (T: 85 °C; total dissolved solids: 32,868 mg873 mg•L −1 ). It was found that the apparent viscosity and elastic modulus of HAHPAM solutions increased with addition of silica nanoparticles, and HAHPAM/silica hybrids exhibit better shear resistance and long-term thermal stability than HAHPAM in synthetic brine. Moreover, core flooding tests show that HAHPAM/silica hybrid has a higher oil recovery factor than HAHPAM solution.

Organic/inorganic hybrid aqueous solutions were prepared by mixing silica nanoparticle suspension and hydrophobically associating polyacrylamide (HAPAM) solution, and their rheological behaviors were examined in both pure water and brine in comparison with HAPAM. It was found that HAPAM/silica hybrid exhibits viscosity enhancement in aqueous solution and better heat-and salt-tolerances than HAPAM. Meanwhile, their long-term thermal stability is also improved. Cryo-TEM observation reveals that a reinforced threedimensional network structure of HAPAM/silica hybrid is formed. These improved properties are attributed to the formed hydrogen bond between carbonyl groups in HAPAM skeleton and silanol functionalities in silica nanoparticles in the hybrid system, and the silica nanoparticles in the hybrid act as physical crosslinkers between macromolecules.

A new type of light-switchable "smart" single-walled carbon nanotube (SWNTs) is developed by the reversible host-guest interaction between azobenzene-terminal PEO (AzoPEO) and pyrene-labeled host attached on the sidewalls of nanotubes via ππ stacking. The SWNTs hybrids not only are well dispersed in pure water, but also exhibit switchable dispersion/aggregation states upon the alternate irradiation of UV and visible light. Moreover, the SWNTs hybrids dispersion is preliminarily used as coating fl uid to form transparent conductive fi lms. The dispersant AzoPEO is removed by the contamination-free UV treatment, decreasing the resistance of the fi lms. This kind of light-switchable SWNTs hybrids, possessing a ''green'' trigger and intact structure of the nanotube, may fi nd potential applications in sensor of biomedicines, device fabrication, etc. Additionally, such a reversible hostguest interaction system may open up the possibility to control the dispersion state of SWNTs by other common polymers. Scheme 1 . The synthesis strategies for a) azobenzene-containing PEO (AzoPEO), and b) pyrene-labelled β -cyclodextrin (p-CD).

Polymer flooding represents one of the most efficient processes to enhance oil recovery, and partially hydrolyzed polyacrylamide (HPAM) is a widely used oil-displacement agent, but its poor thermal stability, salt tolerance, and mechanical degradation impeded its use in high-temperature and high-salinity oil reservoirs. In this work, a novel viscoelastic surfactant, erucyl dimethyl amidobetaine (EDAB), with improved thermal stability and salinity tolerance, was complexed with HPAM to overcome the deficiencies of HPAM. The HPAM/EDAB hybrid samples were studied in comparison with HPAM and EDAB in synthetic brine regarding their rheological behaviors and core flooding experiments under simulated high-temperature and high-salinity oil reservoir conditions (T: 85°C; total dissolved solids: 32,868 mg/L; [Ca2+] + [Mg2+]: 873 mg/L). It was found that the HPAM/EDAB hybrids exhibited much better heat- and salinity-tolerance and long-term thermal stability than HPAM. Core flooding tests showed that the oil recovery factors of HPAM/EDAB hybrids are between those of HPAM and EDAB. These results are attributed to the synergistic effect between HPAM and EDAB in the hybrid.

Polymer injection for viscous oil displacement has proven effective and gained interest in the recent years. The two general types of EOR polymers available for field applications, synthetic and biological, display different rheological properties during flow in porous media. In this paper, the impact of rheology on viscous oil displacement efficiency and front stability is investigated in laboratory flow experiments monitored by X-ray. Displacement experiments of crude oil (~500cP) were performed on large Bentheimer rock slab samples (30×30cm) by secondary injection of viscous solutions with different rheological properties. Specifically, stabilization of the aqueous front by Newtonian (glycerol and shear degraded HPAM) relative to shear thinning (Xanthan) and shear thickening (HPAM) fluids was investigated. An X-ray scanner monitored the displacement processes, providing 2D information about fluid saturations and distributions. The experiments followed near identical procedures and conditions in terms of rock properties, fluxes, pressure gradients, oil viscosity and wettability. Secondary mode injections of HPAM, shear-degraded HPAM, xanthan and glycerol solutions showed significant differences in displacement stability and recovery efficiency. It should be noted that concentrations of the chemicals were adjusted to yield comparable viscosity at a typical average flood velocity and shear rate. The viscoelastic HPAM injection provided the most stable and efficient displacement of the viscous crude oil. However, when the viscoelastic shear-thickening properties were reduced by pre-shearing the polymer, the displacement was more unstable and comparable to the behavior of the Newtonian glycerol solution. Contrary to the synthetic HPAM, xanthan exhibits shear thinning behavior in porous media. Displacement by xanthan solution showed pronounced viscous fingering with a correspondingly early water breakthrough. These findings show that at adverse mobility ratio, rheological properties in terms of flux dependent viscosity lead to significant differences in stabilization of displacement fronts. Different effective viscosities should arise from the flux contrasts in an unstable front. The observed favorable "viscoelastic effect", i.e. highest efficiency for the viscoelastic HPAM solution, is not linked to reduction in the local Sor. We rather propose that it stems from increased effective fluid viscosity, i.e. shear thickening, in the high flux paths. This study demonstrates that rheological properties, i.e. shear thinning, shear thickening and Newtonian behavior largely impact front stability at adverse mobility ratio in laboratory scale experiments. Shear thickening fluids were shown to stabilize fronts more effectively than the other fluids. X-ray visualization provides an understanding of oil recovery at these conditions revealing information not obtained by pressure or production data.

Thermo‐reversible phase behaviors and rheological properties of a pentablock terpolymer solution, poly(N‐isopropylacrylamide)‐b‐poly(ethylene oxide)‐b‐poly(propylene oxide)‐b‐poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) (PNIPAM150‐PEO136‐PPO45‐PEO136‐PNIPAM150), are investigated in comparison with its precursor, PEO136‐PPO45‐PEO136 (F108). It is found that the critical gelation concentration of the terpolymer solution is only about 11 wt %, which is significantly lower than that of F108 solution (∼22 wt %). The 11 wt % terpolymer solution displays higher viscosity, stronger gel strength, and fast thermo‐responsive behavior compared with the 22 wt % F108 solution. The 11 wt % terpolymer solution shows a typical Newtonian fluid behavior at 30 °C due to the presence of individual spherical micelles, and presents an elastic gel property at 41 °C because of the formation of the close‐packed micelle aggregates. Cryogenic transmission electron microscopy (cryo‐TEM) and variable‐temperature 1H NMR results demonstrate that the sol–gel phase transition mechanism is mainly related to the hydrophilic/hydrophobic transition of PPO and PNIPAM groups by external temperature stimulus. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1335–1342

A simple way to develop single‐walled carbon nanotube (SWNT) hybrids with ‘smart’ light‐switchable properties is demonstrated by Y. Feng and co‐workers. On page 5010, they decorate SWNT surfaces with pyrene‐containing cyclodextrins via π–π stacking. After adding azobenzene‐modified poly(ethylene oxide), the SWNT hybrids are not only well dispersed in pure water through host‐guest interactions, but also exhibit switchable dispersion/aggregation states upon alternating irradiation of UV and visible light.

Thermosetting resin is gaining more acceptances in Plug and Abandonment due to its excellent mechanical properties after set and ability for placement in locations cement cannot reach. A thorough understanding of its curing behavior such as gel time is essential to ensure safe placement and a good seal. This paper investigates the pressure-sensitive gelation behavior of polymer resin under in-situ conditions, and the pressure effect on the gel time of thermosetting resin was evaluated. An innovative assessment methodology named CAPT (Consistency under Applied Pressure Test) was created to assess the curing process of thermoset resins in a pressurized consistometer. A series of resin samples were tested at temperatures ranging from ambient to 120°C with applied pressures up to 10,000 psi. The consistency was initially used to indicate the gel structure development of the resin while it was gelling. Based on the consistency data, the relationship between applied pressure and gel time of resins was studied and a new approach of modeling the curing process with the influence factor of pressure was proposed. The primary observation was the confirmation that the gelation process of thermosetting resin under applied pressure was faster than that under atmospheric pressure. However, the gel time had big variations. The pressure sensitivity mainly depended on the initiators and it was only partly dependent on the temperature. There was a threshold value for the pressure effect on the gel time. Below the threshold, the gel time only decreased by around 5%. Above the threshold, the pressure effect was much larger where the gel time decreased by 20% - 30%. This could be mainly attributed to the thermodynamic effect caused by pressure accelerating the polymerization process, resulting in a shorter gel time. Meanwhile, these results help explain why the curing behavior of thermosetting resin placed underground where high pressure is encountered often differs from the laboratory-predicted performance. Besides indicating the relative strength development, consistency analysis could also be used to assess the pressure effect on the gelation process of a resin sample in down-hole operations with applied pressures. Thus, CAPT would be more suitable than a conventional reactivity test to propose a new approach of modeling the gel time of thermosetting resin systems with the influence factor of pressure. CAPT is a novel method to accurately evaluate the curing process of thermosetting resin and indicate its relative strength development. This helps engineers reach a good balance between designing proper operations and preserving mechanical properties in the plug and abandonment process.