Polymer flooding has proved economically and technically successful in numerous enhanced oil recovery (EOR) projects, which can often increase oil recovery from 12 to 15 % of the original oil in place. When a reservoir is flooded with viscous polymer solution, the mobility ratio between the displacing fluid (i.e., water) and the displaced fluid (i.e., oil) becomes more favorable if compared to conventional water flooding. Therefore, the volumetric sweep efficiency and correspondingly the overall oil recovery are effectively improved. Currently, there is a widespread idea that polymer flooding is inefficient in improving the microscopic oil displacement (at pore scale). However, recent research based on laboratory studies and pilot field testing has proved otherwise. It seems that the viscoelastic properties of polymeric systems indeed improve the microscopic displacement efficiency of residual oil. This paper reviews and emphasizes the recovery mechanisms that have been proposed to explain oil displacement by polymer flooding within oil reservoirs. The aim of this review is to provide a synopsis of polymer flooding which is rapidly emerging as a popular and advantageous EOR process.

A surface-active and "green" flooding agent, modified nanocellulose (NC), which is expected to be an alternative to the current flooding systems for enhancing oil recovery (EOR), was provided in this work. The physical properties of the NC samples including dispersity, rheology, phase behavior, emulsifiability, etc., as a function of mass fraction and charge density, were comprehensively studied to evaluate their EOR potential. The results indicate that this modified nanomaterial could be well dispersed in 1 wt % NaCl brine, forming a series of homogeneous nanofluids at the concentration above 0.4 wt %. Rheological analysis evidenced the viscoelastic properties and pronounced shear-thinning behavior of the nanofluids. Because of the presence of the active groups, the dynamic interfacial tension (Oil/Nanofluid) decreased to an order of 10 −1 mN/m, which accordingly promotes the microscopic recovery efficiency through an emulsification effect. It was also observed that the emulsifiability of the nanofluids was closely related to the charge density. Visual EOR experiments were conducted in a micromodel, from which two mechanisms, (1) sweep volume improvement and (2) emulsification and entrainment, were established for NC nanofluid flooding. As an eco-friendly material, this nanofluid is supposed to be a promising flooding agent in the near future.

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The petroleum industry has addressed wax problems since its inception. Every year, considerable resources are expended on wax removal, which accordingly cause significant economic loss. As one of the materials in chemical treatments, polymeric compounds referred to as ''wax-crystal modifier'', is being widely used to improve flow properties and/or combat wax deposition for waxy crude oils. This article reviews the recent achievements with regard to the flow improvement and wax inhibition of waxy oils using traditional polymeric wax crystal modifiers, such as ethylene-vinyl acetate (EVA), poly(ethylene-butene) (PEB), and polyethylenepoly(ethylene-propylene) (PE-PEP), as well as the development of novel polymers for potential use in the near future. The goal of this review is to assist people understand the advances in this topic.

In this study, a poplar high-yield pulp [preconditioning refiner alkaline peroxide mechanical pulp (P-RC APMP)] was used to produce lignin-containing cellulose nanofibril (LCCNF) dispersions through a sequential process of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation followed by high pressure homogenization. To produce LCCNF with different lignin contents, sodium hypochlorite loadings of 4−12 mmol/g fiber during TEMPO-mediated oxidation step were explored. The effect of lignin content on morphology, thermal stability, crystallinity, and rheological properties of the produced LCCNFs was investigated. The results showed that the TEMPO-mediated oxidation of cellulose was largely limited to the fiber surface. The residual lignin on the surface of LCCNF was presented as small particles. The increase of lignin content increased the thermal stability and decreased the viscosity of the LCCNF. Moreover, at higher lignin content, greater flocculation and aggregation of fibrils took place, which resulted in lower gel-like characteristics of the resultant LCCNF. The results of water contact angle determination also demonstrated that the increase of lignin content significantly increased the hydrophobicity of the LCCNF.

Several commercially available and a few experimental, nonionic surfactants were identified that are capable of dissolving in carbon dioxide (CO 2 ) in dilute concentration at typical minimum-miscibility-pressure (MMP) conditions and, upon mixing with brine in a high-pressure windowed cell, stabilizing CO 2 -in-brine foams. These slightly CO 2 -soluble, water-soluble surfactants include branched alkylphenol ethoxylates, branched alkyl ethoxylates, a fatty-acid-based surfactant, and a predominantly linear ethoxylated alcohol. Many of the surfactants were between 0.02 to 0.06 wt% soluble in CO 2 at 1,500 psia and 25 C, and most demonstrated some capacity to stabilize foam. The most-stable foams observed in a high-pressure windowed cell were attained with branched alkylphenol ethoxylates, several of which were studied in highpressure small-angle-neutron-scattering (HP SANS) tests, transient mobility tests using Berea sandstone cores, and high-pressure computed-tomography (CT)-imaging tests using polystyrene cores. HP SANS analysis of foams residing in a small windowed cell demonstrated that the nonylphenol ethoxylate SURFONIC V R N-150 [15 ethylene oxide (EO) groups] generated emulsions with a greater concentration of droplets and a broader distribution of droplet sizes than the shorter-chain analogs with 9-12 ethoxylates. The in-situ formation of weak foams was verified during transient mobility tests by measuring the pressure drop across a Berea sandstone core as a CO 2 /surfactant solution was injected into a Berea sandstone core initially saturated with brine; the pressure-drop values when surfactant was dissolved in the CO 2 were at least twice those attained when pure CO 2 was injected into the same brine-saturated core. The greatest mobility reduction was achieved when surfactant was added both to the brine initially in the core and to the injected CO 2 . CT imaging of CO 2 invading a polystyrene core initially saturated with 5 wt% KI brine indicated that despite the oilwet nature of this medium, a sharp foam front propagated through the core, and CO 2 fingers that formed in the absence of a surfactant were completely suppressed by foams formed because of the addition of nonylphenol ethoxylate surfactant to the CO 2 or the brine.

Polymeric materials as anion exchange membranes (AEMs) play an essential role in the field of energy and environment. The achievement of high performance AEMs by the precise manipulation of macromolecular architecture remains a daunting challenge. Herein, we firstly report a novel rod-coil graft copolymer AEM, possessing rigid hydrophobic main chains and soft hydrophilic graft chains. The low graft density, which can alleviate the adverse influences of ioinc graft chains on the main chains, was obtained by using the living polymerization technique. Consequently, the grafted ionic groups which result in the degradation of polymer backbone was decreased to a small degree. Moreover, the relatively long graft chains induced the nanophase separation between the hydrophobic polymer chains and hydrophilic graft chains, which creates a convinient pathway for high hydroxide ion mobility. Such an accurate molecular design simultaneously improves the hydroxide ion conductivity and alkaline stability as well as dimensional stability.

Magnetorheological gels (MRGs) known as a new kind of magnetorheological material are composite gels containing magnetic particles suspended in polymer gels. In this study, a category of MR polymer gels based on polyurethane (PU) were prepared. The microstructures of these MRGs were observed with a digital microscope. Their rheological properties under both steady shear and oscillation testing were characterized by using a MR rheometer. The viscosity of the PU MRG decreased with the increment of NCO/OH ratio and increased with the increment of the weight concentration of carbonyl iron particles, molecular mass of poly propylene glycol, and applied magnetic field. The storage modulus increased gradually with the increment of applied magnetic field and weight concentration of carbonyl iron particles. The PU MRG exhibits high static shear yield stress (60.8 kPa, at 573 mT) and dynamic shear yield stress (83.9 kPa, at 573 mT) and wide variation range (static shear yield stress: 6-62 kPa, dynamic shear yield stress: 15-85 kPa). These advantages indicate that PU MRG is able to satisfy wide applications. In addition, both static and dynamic shear yield stresses of the MRG samples increase with the increment of molar mass of polypropylene glycol.