Host-guest strategy improves rheological properties, conformational stability and oil displacement efficiency of xanthan gum.

The low cost and environmental advantages of Xanthan gum make its production and application scale exceed that of other polysaccharides. However, the temperature resistance of Xanthan gum limits its application. In this study, polysaccharide supramolecular Xanthan gum network (XG-ß-CD/AD) based on ß-cyclodextrin and adamantane was prepared for enhanced oil recovery. The structure of Xanthan gum was characterized by Fourier infrared spectroscopy, nuclear magnetic resonance spectroscopy and thermogravimetric analysis. The rheological properties of the modified polysaccharide network in aqueous solution were systematically studied. The results showed that physical cross-linking of host-guest interacion enhanced the thickening ability of the polymer. Shear rheology, extensional rheology and dynamic modulus test proved that XG-ß-CD/AD had excellent rheological properties. The micromorphology, dynamic light scattering and circular dichroism clarified the molecular conformation, the host-guest interaction can improve conformational transition temperature (Tm) and inorganic salt tolerance of Xanthan gum. Under harsh environment (90 °C, 30000 mg/L brine), the oil recovery of XG-ß-CD/AD is 6 %-11 % higher than that of XG at the same conditions, showing a better ability to improve the recovery rate. This study provides a research idea for the selection, development and application of biomacromolecular materials.

Quantitative Characterization of Adhesion Work on Shale Surfaces and Discussion on the Influence of Roughness Based on Atomic Force Microscopy (AFM).

Adhesion is an intrinsic property of rocks and liquids. Investigating the factors contributing to its formation and the mechanisms governing its action is crucial for elucidating the adhesion work between solids and liquids. The adhesion work, serving as a parameter that characterizes the energy changes during the solid-liquid contact process, is a vital tool for probing this phenomenon. However, conventional measurements of the adhesion work are significantly influenced by surface roughness and fail to differentiate local variations in the adhesion performance. This limitation obscures our understanding of the primary adsorption sites and mechanisms between solids and liquids, posing significant challenges to the study of rock surface properties. In this study, in conjunction with scanning electron microscopy and contact angle analyses, we elucidated for the first time the locations where voids form during the solid-liquid contact process, the lithological composition of rough areas, and their impact on the adhesion work between water/oil and the surfaces. Additionally, employing atomic force microscopy (AFM), we examined the variations in water/oil-solid adhesion work across different characteristic regions, thereby characterizing the overall hydrophilic/hydrophobic properties of the rock core. Specific conclusions are as follows: (1) A negative correlation exists between roughness and the contact angle adhesion work, with heterogeneity impeding liquid-rock contact; (2) By comparing the strength of water-solid/oil-solid adhesion work within localized areas, we delineated the adhesion work characteristics of samples and their primary generation sites, with oil-solid adhesion work in target blocks predominantly originating from quartz, clay minerals, and organic matter; (3) The influence of pore throat development on the overall adhesion work of samples was clarified, demonstrating that an increase in the proportion of internal rock pores enhances the surface oil-solid adhesion work; (4) A dimensionless wetting index I was established to mitigate the impact of roughness on the expression of adhesion work, exhibiting a strong correlation with traditional evaluation methods.

Spontaneous Imbibition in Nanomatrix-Fracture of Low Permeability Using Multiscale Nanofluidic Chips.

Spontaneous imbibition has garnered increasing attention as an attractive mechanism for developing tight reservoirs. Despite valuable insights from previous experiments, there remains a lack of understanding regarding the imbibition process within multiscale nanopore-fracture networks. In this work, we devised an innovative multiscale model incorporating over 105 nanochannels and integrating a microfracture network to explore the complex imbibition behavior in tight formations. Additionally, fracture-free nanomatrix models with low permeability were developed for comparative discussions. The results show that the Lucas-Washburn equation remains valid at the tremendous fracture-free nanopore networks under the confinement of 500 nm, with a relative deviation of ±6%. The nanomatrix's heterogeneity hinders the imbibition rate, resulting in a reduction of 4.6 to 10.8% in the imbibition slope. The viscosity plays a dominant role in the change of imbibition slope as temperature varies. Our experiments also found that the interactions between the nanomatrix and bulk fracture complicate the imbibition process. A single wetting front no longer applies in the nanomatrix-fracture networks. Differing fracture/microchannel connectivity leads to disparities in macroscopic patterns, saturation rates, and flow directions. The spatial arrangement of fractures significantly impacts the imbibition time. Overall, this work based on nanofluidic techniques systematically explores the effects of matrix heterogeneity, temperature, and fractures on the imbibition process. The real-time in situ visualization of fluid distribution in multiscale matrix-fracture systems has been achieved, which offers theoretical guidance for practical engineering applications.

Can Supramolecular Polymers Become Another Material Choice for Polymer Flooding to Enhance Oil Recovery?

High molecular polymers have been widely studied and applied in the field of enhanced oil recovery (EOR). At present, the focus of research has been changed to the design of polymer networks with unique properties such as anti-temperature and anti-salinity, good injection and so on. Supramolecular polymers have high viscoelasticity as well as excellent temperature, salt resistance and injection properties. Can supramolecular polymers become another material choice for polymer flooding to enhance oil recovery? The present review aims to systematically introduce supramolecular polymers, including its design strategy, interactions and rheological properties, and address three main concerns: (1) Why choose supramolecular polymers? (2) How do we synthesize and characterize supramolecular polymers in the field of oilfield chemistry? (3) What has been the application progress of supramolecular polymers in improving oil recovery? The introduction of a supramolecular interaction system provides a new idea for polymer flooding and opens up a new research direction to improve oil recovery. Aiming at the "reversible dynamic" supramolecular polymers, the supramolecular polymers are compared with the conventional covalent macromolecular polymer networks, and the challenges and future research directions of supramolecular polymers in EOR are discussed. Finally, the author's viewpoints and perspectives in this emerging field are discussed.

[Simultaneous determination of nitrapyrin and its metabolite residues in food crops by derivatization with gas chromatography-triple quadrupole mass spectrometry].

A method based on precolumn derivatization along with gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) was developed for the determination of nitrapyrin and its metabolite, 6-chloropicolinic acid, in crops. The samples were extracted by acid acetonitrile, and subjected to precolumn derivatization using a sulfoacid. The quantification of the analytes was performed by the internal standard method. Good linear relationships between the peak areas and mass concentrations of the analytes were obtained in the range of 0.025-0.2 mg/L with correlation coefficients greater than 0.995 (n=6). The limits of quantification (LOQs) were 0.05 mg/kg. The recoveries of the analytes in crops at three spiked levels (0.05, 0.1, and 0.2 mg/kg) were in the range of 80.4%-98.4%, with relative standard deviations between 1.0% and 10.1% (n=6). This new method satisfies the related regulations for the determination of nitrapyrin and its metabolite in crops.

Determination of organophosphorous pesticide phosphamidon in environmental water with luminol chemiluminescence detection.

A novel chemiluminescence method has been developed for the determination of the organophosphorous pesticide phosphamidon in environmental water samples, based on the reaction of phosphamidon with luminol-H2O2 in an alkaline medium using sodium dodecyl benzene sulfonate as the enhancer. Under optimum conditions, the increased chemiluminescence intensity was proportional to the concentration of phosphamidon in the range of 0.01-1.0 microg/mL and the detection limit was 0.0038 microg/mL (3 sigma). The relative standard deviation was <2% for 0.5 microg/mL phosphamidon (n = 11). The proposed method was applied to the determination of phosphamidon residue in an environmental water sample with satisfactory results. Further study was focused on the mechanism of phosphamidon, and a possible mechanism was proposed.