Wan-Fen Pu

New view on the oxidation mechanisms of crude oil through combined thermal analysis methods

In the previous study, the oxidation behavior of four Chinese crude oils (Oil 1 to 4) in the presence and absence of rock cuttings was investigated by thermogravimetry/derivative thermogravimetry (TG/DTG) techniques and oxidation tube experiments. The present work investigates the thermal behavior of these oils by combining DTG–DTA method. First, we conducted comparative analysis about mass loss rate from DTG curves and endothermic/exothermic phenomenon from DTA curves attempting to clarify the endothermic or exothermic mechanism in crude oil low-temperature oxidation. Finally, we combined the thermal analysis method with low-temperature oil oxidation tube experiment in porous media to ascertain, whether the two methods are consistent in the aspect of low-temperature oxidation mechanism of crude oil by O2 consumption rate and CO2 generating rate (carbon bond stripping reaction rate). Results show that crude oils undergo an endothermic oxidation behavior during low-temperature oxidation stage, suggesting the decomposition of hydrocarbon components. Clay can play a catalytic effect on low-temperature oil oxidation. The results of DTG–DTA tests can also better reflect oil oxidation mechanism under real conditions.

Amphoteric hyperbranched polymers with multistimuli-responsive behavior in the application of polymer flooding

Amphoteric hyperbranched polymers (AMHPMs) that respond to shear rate, temperature, salt, and pH were synthesized using a water free radical polymerization technique. The Mw of this novel polymer is much lower than that of the conventional linear hydrophobically associative polymer (HAPAM). The hydrodynamic size could be effectively tuned by adjusting the terminal functional groups of the hyperbranched monomer. In the semidilute regime, multiple hydrodynamic subchains and effective intermolecular associations between neighboring branches of polymeric chains cooperatively govern the comprehensive characteristics of AMHPMs. Rheological measurements revealed the pseudodilatant behavior in the lower shear rate region, followed by the pseudoplastic behavior of AMHPMs. Moreover, the elasticity of AMHPM-2 played a dominant role and no Gc is observed within the experimental frequency. Static experiments convincingly proved that the multiple subchains provided AMHPMs with a wider temperature-, salt- and pH-responsive region in comparison to that for HAPAM. Most importantly, the reversible hydrodynamic characteristic scale due to the mutual transformation from association to disassociation, and the excellent anti-mechanical degradation for AMHPMs in the simulative porous medium, further verified that this unique type of hyperbranched polymer is promising for the application of polymer flooding for enhanced oil recovery (EOR).

The Wettability Alteration and the Effect of Initial Rock Wettability on Oil Recovery in Surfactant-based Enhanced Oil Recovery Processes

Wettablity alteration of rock surface is an important mechanism for surfactant-based enhanced oil recovery (EOR) processes. Two salt and temperature-tolerant surfactant formulations were developed based on the conditions of high temperature (97–120°C) and high salinity (20 × 104 mg/L) reservoirs where a surfactant-based EOR process is attempted. Both the two sufactant formulations can achieve ultralow interfacial tension level (≤10−3 mN/m) with crude oil after aging for 125 days at reservoir conditions. Wettability alteration of core slices induced by the two surfactant formulations was evalutated by measuring contact angles. Core flooding experiments were carried out to study the influence of initial rock wettabilities on oil recovery in the crude oil/surfactant/formation water/rock system. The results indicated that the two formulations could turn oil-wet core slices into water-wet at 90–120°C and 20 × 104 mg/L salinity, while the water-wet core slices retained their hydrophilic nature. The core flooding experiments showed that the water-wet cores could yield higher oil recovery compared with the oil-wet cores in water flooding, surfactant, and subsequent water flooding process. The two surfactant formulations could successfully yield additional oil recovery in both oil-wet and water-wet cores. GRAPHICAL ABSTRACT

A comprehensive analysis of the properties of light crude oil in oxidation experimental studies

The analysis of light crude oil for oxidation reaction experiments is a kind of important technological for evaluating an air injection project in a reservoir. In this study, the paper comprehensively analyzes the variations of Jilin crude oil composition comparing crude oil component’s variations before and after oxidation, and investigates the effluent gas composition and hydrocarbon, analyzes the mechanism of low temperature oxidation reaction (LTO), and rebuilds the light crude oil cracking reaction of intermediate component in a new pattern. In the early stage of the oxidation reaction, firstly, oxygen is captured by forming chemical bond in liquid hydrocarbon. And then oxygen takes part in the free radical chain reaction by forming hyperoxide and decomposes to ketones, aldehydes, alcohols, and so on. Meanwhile, chain scission reaction comes up. Research result shows that the intermediate components (C7–17) of crude oil make great contribution to crude oil cracking. The experimental result shows that Jilin reservoir has the potential of implementing air injection project.

In situ catalytic upgrading of heavy crude oil through low-temperature oxidation

Abstract The low-temperature catalytic oxidation of heavy crude oil (Xinjiang Oilfield, China) was studied using three types of catalysts including oil-soluble, water-soluble, and dispersed catalysts. According to primary screening, oil-soluble catalysts, copper naphthenate and manganese naphthenate, are more attractive, and were selected to further investigate their catalytic performance in in situ upgrading of heavy oil. The heavy oil compositions and molecular structures were characterized by column chromatography, elemental analysis, and Fourier transform infrared spectrometry before and after reaction. An Arrhenius kinetics model was introduced to calculate the rheological activation energy of heavy oil from the viscosity–temperature characteristics. Results show that the two oil-soluble catalysts can crack part of heavy components into light components, decrease the heteroatom content, and achieve the transition of reaction mode from oxygen addition to bond scission. The calculated rheological activation energy of heavy oil from the fitted Arrhenius model is consistent with physical properties of heavy oil (oil viscosity and contents of heavy fractions). It is found that the temperature, oil composition, and internal molecular structures are the main factors affecting its flow ability. Oil-soluble catalyst-assisted air injection or air huff-n-puff injection is a promising in situ catalytic upgrading method for improving heavy oil recovery.

Synthesis and characterization of hyperbranched associative polyacrylamide

Hydrophobically modified polyacrylamide with hyperbranched structure (HDPAM) was synthesized by water free-radical copolymerization based on functional hyperbranched polyamide-modified ultrafine silica as functional monomer and methacryloxyethyl-dimethyl cetyl ammonium bromide as hydrophobic monomer. The chemical and spatial network structure of HDPAM were investigated by means of FTIR, 1H NMR, TGA and SEM, respectively. The rheological measurements indicated that the HDPAM solution was viscoelastic fluid. With the increase of HDPAM concentration, both intermolecular association efficiency of hydrophobic groups and apparent viscosity of HDPAM solution increased. HDPAM solution had good thixotropy and temperature tolerance property. Moreover, compared with HPAM, HDPAM demonstrated superior properties on the aspects of viscosification property, temperature resistance and salt tolerance.

Synthesis and evaluation of β-cyclodextrin-functionalized hydrophobically associating polyacrylamide

Modified β-cyclodextrin and N-phenethyl-methacrylamide were utilized to react with acrylamide and acrylic acid to synthesize hydrophobically associating polyacrylamide (HMPAM) via photoinitiated free-radical micellar copolymerization. HMPAM was characterized using Fourier transform infrared (FT-IR) spectroscopy, 1H nuclear magnetic resonance (1H NMR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and viscometry. Compared with partially hydrolyzed polyacrylamide (HPAM), HMPAM demonstrated superior properties on aspects of thickening ability, salt tolerance, temperature resistance and oil displacement efficiency. It was found that the apparent viscosity reached a maximum at 45 °C and the viscosity retention ratio reached 87.56% at 95 °C; at a certain range of salinity, HMPAM exhibited an evident salt-thickening phenomenon; the simulative enhanced oil recovery tests illustrated that HMPAM could remarkably enhance oil recovery by 16.4% while HPAM could enhance oil recovery by 10.8%. Moreover, the viscoelasticity and surfactant compatibility of HMPAM were investigated. The results indicated that HMPAM has potential application for enhanced oil recovery.

Synthesis of a novel comb micro-block hydrophobically associating copolymer for Ca2+/Mg2+ resistance

A comb micro-block hydrophobically associating copolymer (CBHAP), which can withstand divalent cations in harsh conditions, was successfully synthesized in this work. CBHAP showed salt-thickening and shear-thickening properties. Moreover, it showed superior tolerance to elevated concentrations of Ca2+ (10000 mg L−1) and Mg2+ (2500 mg L−1), and hence significantly outperformed commonly used salt-resistant polymers.

Degradable cross-linked polymeric microsphere for enhanced oil recovery applications

In this paper, a degradable cross-linked polymeric microsphere (DCPM) was prepared by inverse emulsion polymerization using acrylamide (AM), 2-methyl-2-acrylic amide propyl sulfonic acid (AMPS) and alpha methyl styrene (HM) as monomers, using polyethylene glycol(200) diacrylate (PEG-200 diacrylate) as labile crosslinkers. The optimized synthesis conditions of DCPM were also investigated. DCPM was characterized by Infrared spectroscopy, 1H-NMR, laser particle analyzer and elemental analysis. Mechanical stability experiments showed that DCPM processed superior anti-shear properties compared with DPM without PEG-200 diacrylate. SEM and viscosity experiments demonstrated that the degradation process of DCPM might be described from initially absorbing amount of water to swell to finally degrading into linear polymer. In addition, the effects of salinity, temperature, PEG-200 diacrylate content and DCPM content on the degradation performance of DCPM dispersed in aqueous solutions were also studied. Finally, sandpacks flooding experiments showed that DCPM initially served as a conformance control agent to plug high thief zones and subsequently acted as polymer for oil displacement within the deep reservoir to enhance oil recovery.

Study on the synthesis and properties of an eco-friendly sugar-based anionic–nonionic surfactant

An eco-friendly sugar-based anionic–nonionic surfactant (DAGA-ES) with well-established structure was successfully synthesized and characterized by electrospray ionization-time of flight mass spectrography (ESI-TOFMS), 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectrometer (FT-IR). Its adsorption morphology on surface and micelle size in aqueous solution were observed using scanning electron microscope (SEM) and a static laser scattering (SLS) instrument. The surface activities of the solution in the absence or presence of electrolyte were investigated by surface tension measurements. The properties of oil displacement including the ability of reducing oil/water interfacial tension (IFT) and wetting alteration were determined by the rotating drop and contact angle method, respectively. The enhanced oil recovery (EOR) experiment was used to evaluate displacement efficiency. The results indicated that the net-structure could be observed on the surface and the micellar diameter in aqueous solution is 197.2 nm. The fundamental parameters such as critical micelle concentration (CMC), the surface tension at the CMC (γCMC), the hydrophile–lipophile balance (HLB) values, maximum surface excess (Γmax) and minimum surface area (Amin) were obtained via surface tension measurement. In addition, the consequence of the oil displacement property showed that IFT could be reduced to 10−2 mN m−1 in an electrolyte solution without any surfactant additives. Furthermore, with the DAGA-ES concentration increasing, the hydrophilicity for both of the hydrophilic surface and lipophilic surface was gradually enhanced. Wettability reversal was achieved just on the lipophilic surface. The oil displacement experiment showed that the oil recovery increased by 16.29% using DAGA-ES versus 12.82% using AES.