Mechanical Properties and Flow Behavior of Polymers for Enhanced Oil Recovery

The mechanical properties and flow behavior in porous media of three different polymer systems including a hydrophobically modified acrylamide-based copolymer (HMSPAM), a partially hydrolyzed polyacrylamide (HPAM), and a polysaccharide (xanthan gum) were evaluated to establish their functional differentiation as mobility control agents in enhanced oil recovery (EOR). The rheological properties of the polymers were described by the power-law model to investigate their non-Newtonian behavior. The first normal stress difference (N₁) and Weissenberg number (W_e) were also used to compare their elastic properties. The experimental results showed that, at comparable shear viscosity, HMSPAM exhibited significant elasticity compared to HPAM and xanthan gum. Shear resistance tests indicated that all of the polymers experienced an extra stress when converging into a capillary tube due to the “entrance effect.” Xanthan gum was the most mechanically stable polymer. Moreover, HMSPAM showed the superior reformability which was quantified by the regained viscosity with relaxation time. This could be explained by the rapid re-association of the hydrophobic interactions. Sandpack flood tests indicated that HMSPAM rendered extremely high mobility control ability during polymer flooding suggesting its potential in EOR. However, this polymer also experienced significant retention within the porous media (potential injectivity and plugging problems), which may be attributed to the formation of bulky associative polymer networks. In this work, UV spectrometry was employed to monitor the concentration of the produced polymer solutions and quantify the polymer retention within porous media. This analytical approach offers great reliability and simplicity. It was concluded that the use of a particular polymer system depends on the oil reservoir conditions and the target EOR application.     

Errata

Gelatin/1-allyl-3-methylimidazolium chloride solutions with different gelatin concentrations were prepared by using the ionic liquid 1-allyl-3-methylimidazolium chloride [AMIM]Cl as a solvent. Rheological properties of the gelatin ionic liquid solutions were investigated by steady shear and oscillatory shear measurements. In the steady shear measurements, all gelatin solutions showed a shear-thinning behavior at low shear rates, which we suggest reflect the characteristics of solvent [AMIM]Cl. In the oscillatory shear measurements, the effects of concentration and temperature on solution viscoelasticity were determined. The results show that the storage modulus G′ of gelatin solutions was essentially independent of gelatin concentration and temperature at all frequencies, while the solution viscosity greatly depended on polymer concentration and temperature. The loss modulus G″ increased with increase in concentration and decreased with rising temperature. This indicated that physical origins of elastic and dissipative behaviors were completely different. The influence of dissolved gelatin on the elasticity of solutions seemed to be minor.     

High Pressure High Temperature Dynamic Rheometry of Sulfonated Polyacrylamide Solutions in Electrolyte Media as Used for Oil Recovery Applications

Sulfonated polyacrylamide (SPAA) solutions were prepared and the effects of pressure, polymer concentration, and water temperature, pH and salinity on their rheological behavior were investigated using a concentric cylinder dynamic rheometer equipped with a high pressure cell. According to the rheological flow curves the shear stress of SPAA solutions increased less than in proportion to their shear rates; that is, a shear thinning effect occurred. For polymer solutions containing 15,000 ppm of SPAA, shear viscosity, and stress were nearly insensitive to pressure. However, the shear viscosity and stress of SPAA solutions were affected by temperature and this effect was more evident at lower pressure. The flow curves indicated the shear viscosity and stress of the samples increased with increasing SPAA concentration and pH of the water, but were decreased with increasing water salinity and temperature.     

Study on Steady Shear Rheological Behavior of Concentrated Suspensions of Sulfonated Polyacrylamide/Na-Montmorillonite Nanoparticles

Concentrated suspensions of sulfonated polyacrylamide (SPA)/Na⁺-montmorillonite (Na-MMT) were prepared and their stability and steady shear rheological properties were described as a function of nanoparticle and polymer concentration and temperature. The results showed that the Na-MMT nanoparticles suspensions were stable in the absence and presence of SPA and no sedimentation was seen. The Z-average particle sizes for the SPA/Na-MMT suspensions increased in the presence of SPA. Rheological investigations showed that the SPA solutions and SPA/Na-MMT suspensions displayed non-Newtonian behavior in almost the whole range of shear rate. All the suspensions exhibited a shear-thinning flow character as shear rate increased. The flow curves indicated the shear viscosity and stress of the samples were decreased with increasing nanoparticles concentration up to 1.5 wt%, but for Na-MMT loading greater than 1.5 wt% there was an increase in shear viscosity and stress of the suspensions. Increasing of SPA concentration had more effect on increasing the rheological properties of SPA/Na-MMT suspensions than increasing of nanoclay content. Shear viscosity and stress of the suspensions increased with increasing SPA concentration and decreased with increasing temperature from 50°C to 70°C.     

Structural Orientations of Cellulose Acetate Phthalate/Ethyl Cellulose Blends in Solution

Cellulose acetate phthalate/ethyl cellulose blends were investigated by means of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetry/differential thermal analysis (TGA-DTGA), shear viscosity and oscillatory shear tests. The studies showed a higher thermal stability, induced by the occurrence of hydrogen bonding, more predominant in ethyl cellulose and blends with higher content of ethyl cellulose. The effect of solution concentrations in N,N-dimethylacetamide, blend compositions and shear rate on the rheological functions generated regions with properties typical for liquid crystalline solutions in the shear field. These studies are suggested to be useful in identification of liquid crystal properties, required in some electrotechnical applications.     

Gelation Rheology and Water Absorption Behavior of Semi-Interpenetrating Polymer Networks of Polyacrylamide and Carboxymethyl Cellulose

Gelation rheology and swelling behavior of novel semi-interpenetrating polymer network (semi-IPN) hydrogels based on polyacrylamide are described. These hydrogels were prepared by solution cross-linking of partially hydrolyzed polyacrylamide and carboxymethyl cellulose (CMC), using chromium triacetate. Effects of CMC content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels increased with increasing CMC content. Enhancement of storage modulus was more than two times for the semi-IPN gels containing 50 wt% CMC. It was also found that increasing the CMC content decreased the loss factor, indicating that the elastic properties of this gelling system increase more strongly than the viscous properties. The swelling ratio of the semi-IPN gels in tap water, NaCl and CaCl₂ solutions, and synthetic oil reservoir water slightly decreased as the concentration of the CMC increased. The improved storage modulus and slightly decreased swelling capacity in oil reservoir water make these semi-IPN hydrogels potentially good candidates for excess water treatment in oil recovery applications.     

Electrospun PLA: PCL composites embedded with unmodified and 3-aminopropyltriethoxysilane (ASP) modified halloysite nanotubes (HNT)

Electrospinning is a simple and versatile fiber synthesis technique in which a high-voltage electric field is applied to a stream of polymer melt or polymer solution, resulting in the formation of continuous micro/nanofibers. Halloysite nanotubes (HNT) have been found to achieve improved structural and mechanical properties when embedded into various polymer matrices. This research work focuses on blending poly(ε-caprolactone) (PCL) (9 and 15 wt%/v) and poly(lactic acid) (PLA) (fixed at 8 wt%/v) solutions with HNT at two different concentrations 1 and 2 wt%/v. Both unmodified HNT and HNT modified with 3-aminopropyltriethoxysilane (ASP) were utilized in this study. Fiber properties have been shown to be strongly related to the solution viscosity and electrical conductivity. The addition of HNT increased the solution viscosity, thus resulting in the production of uniform fibers. For both PCL concentrations, the average fiber diameter increased with the increasing of HNT concentration. The average fiber diameters with HNT-ASP were reduced considerably in comparison to those with unmodified HNT when using 15 wt%/v PCL. Slightly better dispersion was obtained for PLA: PCL composites embedded with HNT-ASP compared to unmodified HNT. Furthermore, the addition of HNT-ASP to the polymeric blends resulted in a moderate decrease in the degree of crystallinity, as well as slight reductions of glass transition temperature of PCL, the crystallization temperature and melting temperature of PLA within composite materials. The infrared spectra of composites confirmed the successful embedding of HNT-ASP into PLA: PCL nanofibers relative to unmodified HNT due to the premodification using ASP to reduce the agglomeration behavior. This study provides a new material system that could be potentially used in drug delivery, and may facilitate good control of the drug release process.     

Solution Behavior of Hydrophobic Cationic Hydroxyethyl Cellulose

The hydrophobic cationic hydroxyethyl cellulose (HEC-g-DA) was prepared by grafting HEC with various alkyl ammonium chlorides (DA) in order to improve the thickening properties of cationic hydroxyethyl cellulose. The solution behavior of HEC-g-DA was studied, and showed that the apparent viscosity of HEC-g-DA increased with polymer concentration, and there existed a critical association concentration (Cp*). The alkyl chain length of DA had a great influence on Cp*, which decreased with increasing alkyl chain length; however, too long an alkyl chain of DA reduced the water solubility of the polymer, resulting in a slight increase of Cp*. The effect of temperature and electrolyte concentration on the thickening properties of HEC-g-DA was investigated; the value of viscous flow activation energy (E_a) was minimum for the sample of HEC-g-DA16 (glycidyl-N-hexadecyl–N,N-dimethyl-ammonium chloride), indicating the weakest sensitivity of the viscosity to temperature. In the whole range of shear rate investigated, the solutions of HEC-g-DA displayed the shear thinning behavior of a pseudoplastic fluid. The values of viscous index (n) from the Ostwald model simulation decreased with polymer concentration, indicating an improvement of the shear thinning property of the solution, whereas the increase of the consistency coefficient (k) indicated the enhancement of the thickening behavior of the polymer. With increasing polymer concentration, the molecular association of HEC-g-DA16 became strong, and high-shear stress was required to remove the association, while the difference between G′ and G″ became small, indicating that the elasticity of the system was enhanced at high polymer concentration. The amphiphilic structure of the HEC-g-DA16 molecules contributed to the low surface tension of the polymer.     

Modified Single-Mode Leonov Rheological Equations for Polymer Melts and Solutions

The shear viscosity and the normal stress coefficients are important parameters in the flow of polymer melts and polymer solutions. Based on the Leonov model, modified single-mode rheological equations are presented by introducing relaxation time and temperature functions, and the shear viscosity and the normal stress coefficients are predicted. Without a complex statistical simulation, the experimental data of a low-density polyethylene melt, a poly(ethylene oxide) solution and a mixed decalin/polybutene oil solution were compared to verify the modified equations in very wide range of deformation rates. Furthermore, based on the equations, the relationship between the stress overshoot and the temperature is discussed. In addition, the predicted shear thinning behavior for the modified equations is also compared with other single-mode models.     

Study on the Dynamic Rheometry and Swelling Properties of the Polyacrylamide/Laponite Nanocomposite Hydrogels in Electrolyte Media

Polyacrylamide/laponite/chromium triacetate nanocomposite (NC) hydrogels were prepared by incorporation of the laponite nanoparticles in partially hydrolyzed polyacrylamide followed by cross-linking of their aqueous solutions with chromium triacetate. Influence of nanoparticle, cross-linker, polymer concentrations, and gelation media (water) temperature, salinity, and rheometer frequency on the viscoelastic behavior of the NC hydrogels were studied by probing the network properties. In addition, swelling behaviors of these NC gels in tap and oil reservoir water were evaluated. According to dynamic rheometry of the gelation process, the limiting storage modulus of the NC gels increased with increasing laponite content. The addition of laponite into the polyacrylamide gelling system increased their viscous properties more strongly than the elastic properties. The ultimate elastic modulus of the NC gels increased with increasing water salinity and temperature. Increasing rheometer frequency during gelation retarded the sol–gel transition and decreased the ultimate elastic modulus. The equilibrium swelling ratio of the NC hydrogels in tap water decreased with increasing laponite content. The salt sensitivity of the NC gels in oil reservoir water slightly decreased with increasing laponite content. These results suggest the superiority of the hydrolyzed polyacrylamide (HPAM)/chromium acetate/laponite NC hydrogels for water shut-off applications in oil reservoirs as compared with unfilled HPAM gels.     

Rotating viscous-fluid cosmologies with scalar field and heat flux

Rotating cosmological models under the influence of both shear and bulk viscosity, together with scalar field and heat flow, are studied. Exact solutions of the field equations are obtained. The solutions have nonzero expansion, shear, and rotation. The properties of the solutions are studied and the temperature distribution is also given explicitly.     

Flow Characteristics of Partially Hydrolyzed Polyacrylamides during Converging into a Capillary

Partially hydrolyzed polyacrylamides (HPAMs) are the most widely used polymers in enhanced oil recovery (EOR). This study presents capillary flow measurements of three different molecular weight HPAMs in synthetic brine. Polymer solutions having similar viscoelasticity were forced to flow through a 0.23 mm (radius) stainless steel capillary to investigate their flow characteristics including mobility reduction (apparent viscosity) and mechanical stability, represented by the extent of mechanical degradation (DR). The results indicated that the apparent viscosity of the polymer solutions markedly dropped with increasing flow rate until 5 mL/min, corresponding to the shear rate of 8,730s^?1; after that a slight viscosity decrease was observed. The high-molecular-weight HPAMs (6.5 and 8.0 × 10⁶ g/mol) began to have slightly greater apparent viscosity than the low-molecular-weight HPAM (1.0×10⁶ g/mol) above the shear rate of 26,180 s^?1; this might result from the occurrence of the coil-stretch transition. All the HPAMs experienced very similar percentages of mechanical degradation (10%) at shear rates between 1750 and 8730 s^?1; however, above 8730s^?1 the high-molecular-weight HPAMs exhibited a steep increase in mechanical degradation (DR). On the other hand, in the case of the low-molecular-weight HPAM, the DR curve almost leveled off at 12%. Therefore, low-molecular-weight HPAMs are generally suggested for EOR applications. These results, we suggested, should be useful to improve the efficiency of polymer EOR by minimizing mechanical degradation.     

Effect of Added Monosodium Glutamate on Characteristics of Polyamide Dope Solutions

Formic acid (FA) solutions prepared with various concentrations of polyamide 66 (PA 66) and monosodium glutamate (MSG) were evaluated in terms of properties, such as density, viscosity, and cloud point. The influence on density was insignificant, whereas the viscosity was strongly affected by the amount of PA 66 and MSG additive. The solutions were further evaluated by casting them in a flat film form and determining the demixing time in a humid atmosphere. The considered cases at lower polymer concentrations at various MSG amounts, indicated that the demixing time increased with increase in polymer concentration. The time for demixing, however, decreased for a given higher amount of polymer when the amount of additive was increased in the dope solution. Membranes were prepared at various coagulant bath temperatures. The tensile strength and degree of adsorption (DOA) of these membranes were found. The tensile strength was higher when the membranes were prepared at higher temperature. The DOA, on the other hand, was higher for the membranes formed at lower temperature.     

Corresponding states principle for newtonian viscosities-temperature effects

In the first part of the paper a superposition method for the polymer solution zero shear rate viscosity η_o as a function of concentration c is reviewed. The method was successful in numerous systems, but it partially failed in four, the worst case being polyisobutene in isooctane, where data were available over the full concentration range and molecular weights (MW) ranged from 900 to 2.5 × 10⁶. It was postulated that the possible cause for this is either MW dependence of T_g which would result in a faster than expected increase in η_o for higher MW samples, or a difference in flow mechanism between the solutions at low and high concentration. In the second part, a new theory for the temperature effect on η_o is proposed. The theory permits linearization of η_o (T) results both for small molecules and for polymeric liquids. In systems where a transition occurs, the linearized plot shows a sharp break. The theory was extended to the concentration dependence of the polymer solution viscosity.

It permits linearization of η_o (c) data, compensates for the MW dependence of T_g, and allows detection of transition points. The theory was tested on solutions of polyisobutene and polydimethyl-siloxane. In both cases, the data were superimposed on a single master curve.     

Investigation into ferrofluid magnetoviscous effects under an oscillating shear flow

The use of ferrofluid seals in mechanical systems can lead to viscous damping that affects their dynamic behavior. This paper describes an investigation into local viscous properties in the case of an axial harmonic force. The influence of magnetic field level, shear stress amplitude and frequency are studied. Even for ferrofluid particles in a highly saturated magnetic field, it is shown that viscosity increases with magnetic intensity, decreases with the frequency of harmonic excitation and is not sensitive to shear rate amplitude. Viscosity is lower for oscillatory flows than for steady flows.     

高压对食品胶溶液流变特性的影响

 经高压处理后,卡拉胶、琼胶、高甲氧基果胶、海藻酸钠、黄原胶和瓜尔豆胶等六种食品胶溶液的粘度变化不同。卡拉胶和琼胶溶液的粘度显著增加,高甲氧基果胶、海藻酸钠和瓜尔豆胶溶液的粘度变化较小,而黄原胶溶液的粘度明显降低。动态粘弹性测量表明,卡拉胶和琼胶溶液的贮藏模量（G′）在高压处理后明显减小,而且G′变得小于G″,这表明卡拉胶和琼胶溶液的弹性变小。高甲氧基果胶、海藻酸钠和瓜尔豆胶溶液的损耗正切值（tan δ=G″/G′）在处理后几乎没有变化,黄原胶溶液的tan δ略微减小。高压处理后食品胶溶液流变特性的不同变化表明,高压处理对食品胶的影响因其种类、胶分子的结构和胶在水溶液中的构象而异。文中对造成这些变化差异的可能原因进行了探讨。     

Effect of molecular weight on the ultrasonic degradation of poly(vinyl-pyrrolidone)

The ultrasonic degradation of poly(vinyl-pyrrolidone) (PVP) of different initial molecular weights was studied at a fixed temperature. The effect of solution concentration on the rate of degradation was investigated. A method of viscometry was used to study the degradation behavior and kinetic model was developed to estimate the degradation rate constant. The results were indicated that the rate of ultrasonic degradation increased with increasing molecular weight. It was found that rate constant decreases as the concentration increases. The calculated rate constants correlated in terms of inverse concentration and relative viscosity of PVP solutions. This behavior in the rate of degradation was interpreted in terms of viscosity and concentration of polymer solution. With increasing solution concentration, viscosity increases and it causes a reduction in the cavitation efficiency thus, the rate of degradation will be decreased. The experimental results show that the viscosity of polymers decreased with ultrasonic irradiation time and approached a limiting value, below which no further degradation took place. This study confirms the general assumption that the shear forces generated by the rapid motion of the solvent following cavitational collapse are responsible for the breakage of the chemical bonds within the polymer. The effect of polymer concentration can be interpreted in terms of the increase in viscosity with concentration, causing the molecules to become less mobile in solution and the velocity gradients around the collapsing bubbles to, therefore, become smaller.     

Rapid measurement of transient velocity evolution using GERVAIS

Rapid velocity measurements using GERVAIS (Gradient Echo Rapid Velocity and Acceleration Imaging Sequence), an EPI (Echo Planar Imaging) based technique capable of measuring velocity over an observation time of several milliseconds, are performed on a wide-gap Couette Rheo-NMR cell for the first time. A variable delay time between a control signal to initiate a transition in flow and the start of the measurement sequence is incorporated to allow investigation of the transient evolution of the velocity field following a step change in rotation rate. Both the commencement and the cessation of imposed shear stress are investigated for (i) a shear banding micellar solution of CPyCl (cetylpyridiniumchloride)/NaSal (sodium salicylate) in brine and (ii) a low molecular weight PDMS (polydimethylsiloxane) oil. With respect to the micellar solution, an elastic shear wave is seen to propagate across the cell following the commencement of shear stress whilst an oscillatory ‘recoil’ is observed following the cessation of shear stress; neither of these phenomena were observed for the PDMS oil which exhibited a purely viscous response as expected for an incompressible Newtonian fluid. This technique has potential applications across a wide range of transient rheological investigations, particularly with respect to optically opaque materials.     

Ultrasound effect used as external stimulus for viscosity change of aqueous carrageenans

Ultrasound (US) serves as a stimulus to change shear viscosity of aqueous polysaccharides of ι-carrageenan, κ-carrageenan and, agar. The US effect was compared in their aqueous solutions at 60 °C for the US frequency of 23, 45, and 83 kHz. Under the US condition with 50 W at 45 kHz, the shear viscosity of each aqueous solution was decreased significantly. Subsequently, when the US was stopped, the shear viscosity returned back to the original value. In addition, the US showed different effects of the US frequency over the viscosity change in the three kinds of polysaccharides. When the US frequency was changed, the US effects were less at 83 kHz and 28 kHz for the shear viscosity change. In addition, as NaCl was present in the aqueous solution, the viscosity change decreased by the US exposure. These results suggest that the US effect on the viscosity reduction was influenced by the condition of polymer coil conformation, which was expanded or shrank by electrostatic repulsion of the SO₃^? groups. FT-IR analysis supported that the hydrogen bonds of carrageenans were broken during the US exposure. Using Fourier self-deconvolution for the FT-IR spectra without and with US exposure suggests that the US influenced the hydrogen bonds of water and the OH group of polysaccharides.     

Effects of Monomer Feed Amounts on Solution Properties and Solution Morphologies for a Comb-like Ter-polymer

An acrylamide(AM)-based ter-polymer (PAAB) containing sodium 2-acrylamido-2-methylpropane sulphonate (NaAMPS) and p-vinylbenzyl-terminated octylphenoxy poly(ethylene oxide) (VBE, polymerization degree: 24) was synthesized by an aqueous free-radical copolymerization. In order to obtain a PAAB polymer with both good thickening properties and surface and interfacial properties in brine solutions for enhanced oil recovery (EOR), the influences of the NaAMPS and VBE feed amounts on the intrinsic and apparent viscosities and the surface and interfacial tensions of the PAAB polymer in aqueous solutions were investigated. The optimum NaAMPS feed amount was 9 mol%; an excessive feed amount interfered with the aggregations of the PAAB macro-molecules in aqueous solutions and on the surfaces of aqueous solutions and the interfaces between aqueous solutions and kerosene. In addition, for this NaAMPS feed concentration, the PAAB polymer showed the highest apparent viscosities and the lowest surface and interfacial tensions in 5 g L^?1 NaCl for a VBE feed amount of 1.1 mol%. The mechanism giving rise to the solution properties for this polymer was examined. For this purpose, the effect of the polymer concentration on the supra-molecular structures of the PAAB polymer in water and in 5 g/L NaCl, were investigated by ultraviolet spectral analysis using pyrene as a probe. A transmission electron microscope (TEM) was also used to observe the morphologies of the associated structures in aqueous solutions to explore the correlation between the solution properties and solution structures for PAAB; expanded polymer chain bundles were formed at a polymer concentration of 0. 4 g L^?1, higher than the critical micelle concentration (0. 3 g L^?1).