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Inspired by the viscoelastic displacement theory, a product called preformed particle gel (PPG) is developed as conformance control agent to enhance oil recovery and control excess water production. The migration law of PPG suspension in porous media is related to its deep profile control and displacement capability. Laboratory experiments indicate that PPG suspension has good viscosity increasing, and the apparent viscosity decreases with the increase of shear rate. PPG suspension is mainly elastic, and its network structure makes it have certain shear stability. PPG particles realize migration in porous media in the way of “accumulation and blockage→pressure increase→deformation and migration”. When the ratio of the PPG particle size to the pore throat diameter δ ranges from 35.52 to 53.38, the particles can match through the porous medium. When the permeability difference of the parallel model is 5, PPG suspension has the highest profile improvement rate, 69.10%. PPG suspension can adjust the planar heterogeneity, and increase the oil recovery rate by 20.75%. The PPG suspension can effectively start “cluster''、 “film” and “blind end residual oil”, and has a high oil washing efficiency. The core NMR T2 spectrum shows that PPG suspension mainly reduces oil saturation in mesopores and macropores. After PPG flooding, the EOR capacity of small pores is the highest, 39.11%.

Microalgae are potential biomass source for biodiesel production. However, their strong cell walls make efficient lipid extraction problematic. Disrupting the cell wall is a key point in enhancing lipid yield from microalgae biomass. A new type of ionic liquid (IL) has been suggested in this work as a potentially viable solvent to permeabilize the strong microalgae cell structure for the efficient extraction of lipids. Morphological changes in microalgae cells were studied before and after ionic liquid permeabilization to understand the mechanism of ionic liquid treatment. Among the three selected CO2-based alkyl carbamate ionic liquids, DIMCARP performed with the best extraction efficiency. The effects of extraction variables (temperature, time, ratio ionic liquid/Methanol, and solvent to biomass) on lipid extraction were examined via single-factor experiments coupled with response surface methodology (RSM) using a Box-Behnken design (BBD). The highest lipid yield (16.40%) was obtained after 45 min of extraction at 45 °C using a 9:1 ionic liquid to methanol and 7 mL of solvent to biomass ratio. Transesterification of lipids to make fatty acid methyl esters found that the most common fatty acids were C16:0, C18:2, and C18:3 (19.50%). The quality of the biodiesel made meets European and US standards.

A low-permeability reservoir contains many fine pore throat structures, which result in excessive injection pressure of the water injection well and difficult water injection in the production process of a low-permeability reservoir. In this study, a new silane coupling agent was synthesized via the ring-opening reaction between dodecyl amine and KH-560 (γ-propyl trimethoxysilane). The modified KH-560 was reacted with nano-SiO2 to synthesize the modified nano-SiO2 as an antihypertensive additive. Fourier infrared spectroscopy, thermogravimetric analysis and laser scattering were used to characterize this modified nano-SiO2. The results show that the particle size of the modified nano-SiO2 is less than 60 nm. The test results of the water contact angle show that the dispersion system can increase the rock contact angle from 37.34° to 136.36°, which makes the rock surface transform from hydrophilicity to hydrophobicity and reduce the binding effect of rock with water. The dispersion test shows that the modified nano-SiO2 has good dispersion stability under alkaline conditions with TX-100 (Polyethylene glycol octylphenyl ether) as the dispersant. The antiswelling test results show that the antiswelling rate of this modified nano-SiO2 is 42.9%, which can efficiently prevent the clay expansion in the formation to reduce the injection pressure. The core displacement test results show that its depressurization rate reaches 49%. The depressurization rate still maintains 46% at a 20 PV water flow rate, indicating that its depressurization effect is remarkable and it has excellent erosion resistance.

Cell wall disturbance is an important step in the downstream process of improving the efficiency of lipid extraction from microalgae. Surfactants have been proven to be efficient alternatives to organic solvents in the extraction process. In this study, an effective approach involving deep eutectic solvent (DES) (choline chloride and carboxylic acids) treatment supplemented with surfactants has been developed to disrupt the cell walls of microalgae and increase the extraction of lipids suitable for biodiesel production. A combination of polar and non-polar solvents (ethyl acetate and n-butanol) was used for the lipid extraction process. Microalgae biomass pretreated with choline chloride malonic acid supplemented with the surfactant hexadecyl trimethylammonium chloride (HTAC) showed the best results, improving lipid extraction by 12.365%. Further elucidation of the detailed mechanism behind the cell disruption of the microalga wall by DES was achieved using density functional theory (DFT) methods. The DFT calculations revealed that hydrogen bonds between the chloride ion of the DES and hydrogen bond donor (HBD) molecules are key factors dominating the destruction of the cell wall structure of Chlorella pyrenoidosa. The optimization of lipid extraction was performed through a single-factor experiment, which included the effects of different variables (time, temperature, dosage of surfactant, and ratio of n-butanol to ethyl acetate). An extraction period of 60 min at 80 °C with a surfactant concentration of 0.5% at a 1:2 ratio of n-butanol to ethyl acetate was found to produce the maximum lipid yield (16.97%). Transesterification reactions were used to obtain fatty acid methyl esters from the optimized extracted lipids. Thus, it was determined that C16:0 (20.04%), C18:2 (29.95%), and C18:3 (21.21%) were the most prevalent fatty acids. The potential for producing biodiesel from C. pyrenoidosa was validated by the high yields of C18 fatty acid methyl esters, and the properties of biodiesel are within the European and US standards.

Compounding polymer AP-P4 with high viscosity-reducing Gemini Surfactant HD, which is used as an emulsifier viscosity reduce, to improve the stability of the O/W emulsion while the viscosity reduction rate is kept. A polymeric surfactant emulsification and viscosity reduction system capable of forming a relatively stable O/W emulsion of heavy oil (0.5% HD+0.1% AP-P4) is then compounded. The system has been characterized as a high viscosity reduction rate and high stability. Meanwhile, the production liquid does not need to be added with a demulsifier and only needs to be heated to 70 °C to achieve effective demulsification. The influencing factors of the performance of the polymetric surfactant emulsification and viscosity reduction system were studied. When the oil-water ratio was 70:30 and 60:40, the viscosity reduction rate was 97.47% and 99.09%, respectively; after 15 h at 30 °C, the dehydration rates were 95.8% and 99.2%, respectively. The dehydration rate after 15 h at 70 °C was 98.1% and 99.4%, respectively; at 30 ∼ 50 °C, the water phase temperature has a greater impact on the viscosity; at 60 °C, 70 °C, the water phase temperature has little effect on the viscosity; as the temperature of the aqueous phase increased, the stability of the emulsion deteriorated. When the aqueous phase temperature was 30 °C, 50 °C and 70 °C, the dehydration rates of the emulsion after 15 h were 95.8%, 96.7% and 98.1%, respectively; As the degree of mineralization increases, the viscosity reduction rate decreases, and the stability of the emulsion deteriorates. The system has been used in field test for 2 injection wells, and the production rate of the two wells increased with a peak value of 25 m3/d and 20 t/d, respectively. Keywords: Heavy oil, Wellbore viscosity reduction, Emulsification, Polymer, Dehydration rate

Performed gels are widely used in fields to support profile modification and Enhance Oil Recovery. Previous studies of profile modification of performed gels mainly used the index of pressure, resistance factor, or residual resistance factor to represent their ability. However, there is a lack of methods available to directly study their modification ability. In this article, the preformed gels with fluorescence properties, CQDs@PPG, would provide a new way to explore the profile modification of preformed gels. This paper uses poly (acrylamide, sodium p-styrene sulfonate), carbon quantum dots, and N,N-methylenebisacrylamide to prepare the CQDs@PPG via inverse emulsion polymerization. The morphology, size distribution, structure, fluorescence characteristics, surface potential thermal stability, viscosity changes, and viscoelastic properties of CQDs@PPG were analyzed. Moreover, the fluorescence properties of CQDs@PPG under different temperature, salinity, and pH were examined. Results indicate that the CQDs@PPG have excellent stability and that pH and salinity have little influence on their fluorescence properties. Further, only the temperature would affect the fluorescence properties of CQDs@PPG, but that effect is reversible after the temperature drops. By examining the fluorescence intensity, it would be more direct for researchers to study the profile modification in further experiments.

In this paper, the effects of three cations, Ca2+, Mg2+, and Na+, on the stability of APG foams were investigated experimentally. The results show that cations can slow down the process of liquid drainage and coarsening of APG foam, which is beneficial to the stability of the foam. The salt resistance mechanism of nonionic surfactant (APG) was investigated by molecular dynamics simulation and compared with that of anionic surfactant (SDS) foam. Firstly, the distribution characteristics of cations in APG foam and SDS foam were explored. It was found that the cations in the APG foam were mainly distributed in the water layer away from the head groups, and the cations in the SDS foam were more likely to appear near the head groups. Then, the hydration of the head groups and the cation was investigated. The results show that cations have little effect on the number of water molecules in the hydration layer of APG head groups but will reduce the diffusion capacity of water molecules and increase the water retention capacity of the foam film, thereby enhancing the foam stability. The addition of cations will reduce the water retention capacity of the SDS foam film. In addition, the behavior of surfactant head and tail groups was also analyzed. It was found that the cations made the head groups of APG more inclined to be aligned perpendicular to the liquid interface, and the tail groups were more inclined to realize a cross-arrangement and cover the gas–liquid interface. This can not only slow down the gas phase mass transfer process of the adjacent foam and slow down the coarsening process of the foam but also increase the viscoelasticity and anti-disturbance ability of the foam film. The cations will weaken the staggered arrangement of the SDS molecular tail groups, and at the same time, will cause the SDS molecules to aggregate, which greatly reduces the stability of the foam.

The high-temperature stability and filtration property controlling of ultra-high-temperature water-based drilling fluids is a worldwide problem. To resolve this problem, a high-temperature-resistant quaternary copolymer (HTRTP) was synthesized based on molecular structure optimization design and monomer optimization. The physical and chemical properties were characterized by infrared spectroscopy, thermal weight, and spectrophotometry, and their temperature and salt resistance was evaluated in different drilling fluids, combined with adsorption, particle size analysis, and stability test. The results show that the thermal stability of HTRTP is very strong, and the initial temperature of thermal decomposition is above 320°C. The salt resistance of HTRTP is more than 162 g/L, and the calcium resistance is more than 5000 mg/L, which is equivalent to the foreign temperature-resistant polymer DCL-a, and is superior to the domestic metal ion viscosity increasing fluid loss agent PMHA-II for drilling fluids. It has excellent high-temperature resistance (245°C) and fluid loss reduction effect in fresh water base mud, fresh water weighted base mud, saturated brine base mud, and composite salt water base mud, which is better than foreign DCL-a (245°C) and domestic PMHA (220°C). The adsorption capacity of HTRTP on clay particles is large and firm, and the adsorption capacity changes little under the change of chemical environment and temperature. Both before and after HTRTP aging (245°C/16 h), the permeability of filter cake can be significantly reduced and its compressibility can be improved. By optimizing the particle size gradation of the drilling fluid and enhancing the colloid stability of the system, HTRTP can improve the filtration building capacity of the drilling fluid and reduce the filtration volume. The development of antithermal polymer provides a key treatment agent for the study of anti-high-temperature-resistant saline-based drilling fluid.

In this study, emulsion-free radical reaction was applied to synthesize a novel sulfomethylating hydrophobically associating copolymer (HPDS) by using acrylamide, acrylic acid, NaHSO3, HCHO, and a laboratory-made N,N-divinylnonadeca-1,10-dien-2-amine to enhance heavy-oil recovery. The structure and properties of HPDS were characterized by a range of experiments, which showed that HPDS had better stability and enhanced heavy-oil recovery capacity than hydrolyzed polyacrylamide (HPAM). One-dimensional flooding experiments illustrated that HPDS performed better in establishing resistance factor (RF) and residual RF (RRF), and approximately 19.8% oil recovery could be enhanced by injecting 1500 mg/L of HPDS solution compared with that of HPAM at only 14.1%. HPDS has a promising application prospect in enhancing heavy-oil recovery.

During CO2 flooding, serious gas channeling occurs in ultra-low permeability reservoirs due to the high mobility of CO2. The chief end of this work was to research the application of responsive nanoparticles for mobility control to enhance oil recovery. Responsive nanoparticles were developed based on the modification of nano-silica (SiO2) by 3-aminopropyltrimethoxysilane (KH540) via the Eschweiler-Clark reaction. The proof of concept for responsive nanoparticles was investigated by FT-IR, 1H-NMR, TEM, DLS, CO2/N2 response, wettability, plugging performance, and core flooding experiments. The results indicated that responsive nanoparticles exhibited a good response to control nanoparticle dispersity due to electrostatic interaction. Subsequently, responsive nanoparticles showed a better plugging capacity of 93.3% to control CO2 mobility, and more than 26% of the original oil was recovered. Moreover, the proposed responsive nanoparticles could revert oil-wet surfaces to water-wet, depending on surface adsorption to remove the oil from the surface of the rocks. The results of this work indicated that responsive nanoparticles might have potential applications for improved oil recovery in ultra-low permeability reservoirs.

To improve CO2 adsorption performance of nanoparticle absorbents, a novel tertiary amine functionalized nano–SiO2 (NS–NR2) was synthesized based on the 3–aminopropyltrimethoxysilane (KH540) modified nano–SiO2 (NS–NH2) via methylation. The chemical structure and performances of the NS–NR2 were characterized through a series of experiments, which revealed that NS–NR2 can react with CO2 in water and nanofluid with low viscosity revealed better CO2 capture. The CO2 capture mechanism of NS–NR2 was studied by kinetic models. From the correlation coefficient, the pseudo second order model was found to fit well with the experiment data. The influencing factors were investigated, including temperature, dispersants, and cycling numbers. Results has shown the additional surfactant to greatly promote the CO2 adsorption performance of NS–NR2 because of the better dispersity of nanoparticles. This work proved that NS–NR2 yields low viscosity, high capacity for CO2 capture, and good regenerability in water. NS–NR2 with high CO2 capture will play a role in storing CO2 to enhanced oil recovery in CO2 flooding.

A new type of chitosan-modified hyperbranched polymer (named HPDACS) was synthesized through the free-radical polymerization of surface-modified chitosan with acrylic acid (AA) and acrylamide (AM) to achieve an enhanced oil recovery. The optimal polymerization conditions of HPDACS were explored and its structure was characterized by Fourier-transform infrared spectroscopy, hydrogen nuclear magnetic resonance, and environmental scanning electron microscopy. The solution properties of HPDACS in ultrapure water and simulated brine were deeply studied and then compared with those of partially hydrolyzed polyacrylamide (HPAM) and a dendritic polymer named HPDA. The experimental results showed that HPDACS has a good thickening ability, temperature resistance, and salt resistance. Its viscosity retention rate exceeded 79.49% after 90 days of aging, thus meeting the performance requirements of polymer flooding. After mechanical shearing, the viscosity retention rates of HPDACS in ultrapure water and simulated brine were higher than those of HPAM and HPDA, indicating its excellent shear resistance and good viscoelasticity. Following a 95% water cut after preliminary water flooding, 0.3 pore volume (PV) and 1500 mg/L HPDACS solution flooding and extended water flooding could further increase the oil recovery by 19.20%, which was higher than that by HPAM at 10.65% and HPDA at 13.72%. This finding indicates that HPDACS has great potential for oil displacement.

To improve oil recovery significantly in low-mid permeability reservoirs, a novel modified nano-SiO2 hyperbranched copolymer (HPBS), consisting of polyacrylamide as hydrophilic branched chains and modified nano-SiO2 as the core, was synthesized via an in situ free radical polymerization reaction. The structure and properties of the hyperbranched copolymer were characterized through a range of experiments, which showed that HBPS copolymers have better stability and enhanced oil recovery (EOR) capacity and also smaller hydrodynamic radius in comparison with hydrolyzed polyacrylamide (HPAM). The flooding experiments indicated that when a 1000 mg/L HPBS solution was injected, the resistance factor (RF) and residual resistance factor (RRF) increased after the injection. Following a 98% water cut after preliminary water flooding, 0.3 pore volume (PV) and 1000 mg/L HPBS solution flooding and extended water flooding (EWF) can further increase the oil recovery by 18.74% in comparison with 8.12% oil recovery when using HPAM. In this study, one can recognize that polymer flooding would be applicable in low-mid permeability reservoirs.

To address the problem regarding poor shear resistance of commonly employed polymers for oil displacement, modified nano-SiO2/AA/AM copolymer (HPMNS) oil displacement agents were synthesized using acrylic acid (AA), acrylamide (AM), and modified nano-SiO2 of different modification degrees as raw materials. HPMNS was characterized by means of infrared spectroscopy (IR), nuclear magnetic resonance (1H-NMR, 13C-NMR), dynamic/static light scattering, and scanning electron microscope. A comparative study of the shear resistance properties for partially hydrolyzed polyacrylamide (HPAM) and HPMNS was conducted. Compared to HPAM, the introduced hyperbranched structure endowed HPMNS with good shear resistance, which was quantified from the viscosity retention ratio of the polymer solutions. From the perspective of rheological property, HPMNS also showed great shear stability after shearing by a Mixing Speed Governor and porous media shear model. Furthermore, with a higher degree of modification, HPMNS-2 had better shear stability in terms of viscosity and rheological property than HPMNS-1. The phenomena were due to its lower hydrodynamic radius, weight-average molecular weight, and better flexibility of its molecular chains. In addition, upon the indoor displacement test, the resistance factor and residual resistance factor values of HPMNS-2 were higher than those of HPAM. This behavior is beneficial for increasing oil recovery.

A novel hyperbranched polymer was synthesized using acrylamide (AM), acrylic acid (AA), N-vinyl-2-pyrrolidone (NVP), and dendrite functional monomer as raw materials by redox initiation system in an aqueous medium. The hyperbranched polymer was characterized by infrared (IR) spectroscopy, 1H NMR spectroscopy, 13C NMR spectroscopy, elemental analysis, and scanning electron microscope (SEM). The viscosity retention rate of the hyperbranched polymer was 22.89% higher than that of the AM/AA copolymer (HPAM) at 95°C, and the viscosity retention rate was 8.17%, 12.49%, and 13.68% higher than that of HPAM in 18000 mg/L NaCl, 1800 mg/L CaCl2, and 1800 mg/L MgCl2·6H2O brine, respectively. The hyperbranched polymer exhibited higher apparent viscosity (25.2 mPa·s versus 8.1 mPa·s) under 500 s−1 shear rate at 80°C. Furthermore, the enhanced oil recovery (EOR) of 1500 mg/L hyperbranched polymer solutions was up to 23.51% by the core flooding test at 80°C.

A novel copolymer containing nano-SiO2 was synthesized by free radical polymerization using acrylamide (AM), acrylic acid (AA), and nano-SiO2 functional monomer (NSFM) as raw materials under mild conditions. The AM/AA/NSFM copolymer was characterized by infrared (IR) spectroscopy, 1H NMR spectroscopy, elemental analysis, and scanning electron microscope (SEM). It was found that the AM/AA/NSFM copolymer exhibited higher viscosity than the AM/AA copolymer at 500 s−1 shear rate (18.6 mPa·s versus 8.7 mPa·s). It was also found that AM/AA/NSFM could achieve up to 43.7% viscosity retention rate at 95°C. Mobility control results indicated that AM/AA/NSFM could establish much higher resistance factor (RF) and residual resistance factor (RRF) than AM/AA under the same conditions (RF: 16.52 versus 12.17, RRF: 3.63 versus 2.59). At last, the enhanced oil recovery (EOR) of AM/AA/NSFM was up to 20.10% by core flooding experiments at 65°C.

The corrosion inhibition properties and mechanisms of quinoline quaternary ammonium salt (QA) and L-methionine (LM) on pre-corroded Q235 carbon steel in 1wt% HCl solution were studied using the weight loss method and molecular simulation technology. The degree of pre-corrosion of steel will affect the corrosion inhibition performance of the corrosion inhibitor. QA and LM compete to adsorb to the iron surface to form a film, and the repulsion between the corrosion product and the film reduces the slow-release performance. [ABSTRACT FROM AUTHOR]