Yujun Feng

Increasing water production during the later stages of oilfield development generates large volumes of produced water with low oil content, creating challenges for efficient treatment. Downhole oil–water separation can reduce the treatment load of surface facilities but requires materials with high oil selectivity and stable performance. Herein, a hydrophobically modified melamine sponge was prepared through a simple AlCl3 immersion method. SEM-EDS, FTIR, and XPS confirmed the introduction of Al3+ onto the sponge surface and supported its interaction with electron-donating sites in the melamine framework, while the original porous structure was preserved. The modified sponge exhibited water contact angles above 130° and adsorption capacities of approximately 100 g/g for crude oil and 89 g/g for paraffin oil. TGA indicated a modest improvement in thermal stability. Oil–water separation was further evaluated through adsorption, in situ extraction, and filtration. The adsorption mode achieved nearly 100% separation efficiency, while in situ extraction reached 97.5% efficiency at a rate of 6.25 mL/s. Filtration further demonstrated the potential for polishing low-oil-content wastewater. These results highlight Al3+-modified melamine sponge as a simple and versatile material for staged oil–water separation in oilfield applications.

Hydrogels play an important role as materials in the oil and gas industry. Direct preparation of hydrogels using seawater is attractive for offshore energy production but remains challenging because conventional partially hydrolyzed polyacrylamide with a single-cross-linked network degrades rapidly via hydrolysis under high-temperature, high-salinity conditions. Here, ultrahigh-molecular-weight acrylamide (AM)/acrylic acid (AA)/2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) copolymers are combined with a Zr4+/polyethyleneimine (PEI) composite cross-linker to fabricate seawater-sourced hydrogels featuring hierarchical triple cross-linking. Upon heating, Zr4+ initially coordinates with carboxyl groups to form an ionic network. PEI subsequently undergoes chemical cross-linking with amide groups at high temperature, whereas Ca2+/Mg2+ in seawater provide additional ionic reinforcement during continuous heating. The optimized hydrogel exhibits good viscoelasticity under thermo-shear conditions from 30 to 200 °C, retaining a high viscosity of 169.5 mPa·s after the full test cycle. The long-term thermal stability experiments, elemental analysis, and density functional theory calculations reveal that AMPS-rich segments kinetically suppress amide hydrolysis and mitigate chain collapse, whereas excessive AMPS compromises network construction. This study establishes a molecular and network design strategy for water-soluble polymer-based hydrogels in extreme saline and thermal environments, enabling direct seawater fracturing in ultradeep marine reservoirs.

Carbon sequestration in saline aquifers underpins global net‑zero emission goals, yet existing CO ₂ storage capacity remains inadequate, and conventional approaches exhibit limited adaptability to reservoir environment. Here, we introduce smart, injectable soft materials based on CO ₂ ‑triggered hydrogels integrated with tailored deep eutectic solvents (DESs) to boost sequestration. The hydrogel forms upon CO ₂ ‑triggered protonation of erucamine (a C ₂₂ ‑tailed tertiary amine) within its aqueous dispersion, which promotes electrostatic interactions and hydrophobic self‑assembly. The DESs (choline chloride/polyethylene glycol‑200/boric acid) further enhance system functionality. In situ gelation and flow behavior of these soft materials is validated via visualization and rheology under simulated reservoir conditions (45°C, 10 MPa, 4500 mg·L ⁻¹ NaCl). Sequestration assays reveal that a 3.0 wt% erucamine‐based hydrogel increases CO ₂ storage by 31.8% relative to brine; incorporation of 5.0 wt% DESs to form a hybrid hydrogel further elevates storage to 52.9%. Notably, the hydrogel retains structural integrity with no detectable CO ₂ leakage throughout a 146‑day monitoring period at 45 °C. The improved CO ₂ sequestration stems from three synergistic mechanisms: erucamine‐CO ₂ reaction, hydrogel physical entrapment, and DESs‐promoted solubility. This work establishes a quantifiable and scalable soft material platform that offers a transformative route for advancing CO ₂ sequestration in saline aquifers.

Sustaining viscoelasticity of surfactant solutions at subzero temperatures and across extreme pH regimes remains challenging, as freezing and harsh acidic or alkaline environments inhibit aggregate growth and retard structural relaxation. This study examines microstructural evolution and rheological response of C22-tailed amine oxide (C22AO) in a 50/50 (v/v) ethylene glycol–water mixture spanning pH 2.0–13.0 and 20 °C to −20 °C. Potentiometric titration identifies an apparent pKa at 6.8, with ζ-potential declining from +18.53 mV (pH 2.0) to +2.35 mV (pH 6.8) and −1.66 mV (pH 13.0). All formulations retain thermal stability, freezing near −42.0 °C. Microscopy and scattering confirm that pH dominates aggregate morphology in 0.5 wt % C22AO solutions. Acidic conditions (pH 2.0) yield heterogeneous lamellar domains with a 57.0 nm repeat distance at 20 °C, evolving into coexisting 62.8 and 48.3 nm spacings at −20 °C. Near neutrality (pH 6.8), compact lamellar bilayers shrink from 37.0 to 31.4 nm upon cooling, whereas alkaline conditions (pH 13.0) promote disordered, entangled wormlike micelles. All samples exhibit pronounced shear-thinning and elasticity-dominated rheology. At −20 °C across these three pH values, zero-shear viscosities reach 2.45 × 106, 1.96 × 106, and 1.10 × 106 mPa·s, with corresponding elastic moduli of 65, 10, and 28 Pa at 1 rad·s–1 and loss tangent values of 0.24, 0.40, and 0.75. These findings demonstrate that pH governs aggregate morphology, while subzero cooling strengthens molecular packing and decelerates structural relaxation, enabling robust thickening and marked viscoelasticity in cryogenic extreme-pH environments.

The solution properties of charged functional polyacrylamides in saline environments are critical for their applications, yet a quantitative understanding of the effect of salt and molecular structure on their properties remains elusive. Herein, we systematically investigate the solution properties of negatively charged functional polyacrylamide, P(AM-co-AMPS), in semidilute solutions using a scaling approach, focusing on the roles of salt and AMPS molar fractions (FS). The result reveals that the excluded volume Ve decreases with increasing salt concentration and ionic valence. Concurrently, both Kuhn length b and Ve increase with FS in near-θ solvent conditions, scaling as b ∼ FS0.45 and Ve ∼ FS0.9. Molecular simulations uncover the underlying mechanism, suggesting that the chain conformation and solution properties are governed by the balance between the competition of cation–polymer electrostatic interactions and the steric hindrance of AMPS units, where the former promotes chain contraction by weakening polymer–solvent interactions and the latter favors chain extension. These findings provide molecular-level insight into the solution properties of charged functional polyacrylamides in saline environments and establish a theoretical basis for designing salt-resistant functional polymers.

Some industrial oil–water separations require in situ separation under high-temperature and high-pressure (HTHP) conditions. Although porous materials are promising for this purpose, dedicated optical cells capable of evaluating their separation performance under controlled HTHP environments remain scarce. Here, an HTHP optical cell was engineered using a 316L stainless-steel framework integrated with quartz-glass windows to enable direct visualization and performance assessment of porous materials under precisely regulated thermal and pressure conditions. The apparatus operates at up to 160 °C and 2 MPa. In representative static-holding and steady-injection validation tests, the system exhibited excellent stability, with maximum recorded deviations of 0.2 °C/0.012 MPa and 0.1 °C/0.003 MPa from the respective mean values, and no anomalous fluctuations were detected. The setup was validated using three distinct porous media, including a sponge, a membrane, and a packed powder bed, to demonstrate its broad applicability. With integrated real-time differential pressure monitoring, the system enables steady-state pressure-drop acquisition across varying flow rates, providing quantitative insight into fluid permeability resistance. It further supports flux-dependent demulsification assessment through continuous collection of the filtrate and subsequent water content analysis. By combining direct optical access with controlled thermophysical extremes, the developed cell offers a practical, robust, and versatile platform for quantitative benchmarking of porous materials in oil–water separation processes under realistic HTHP injection scenarios.

Middle-phase microemulsions have garnered increasing attention for enhanced oil recovery (EOR) owing to their capacity to achieve ultra-low oil-water interfacial tension (IFT). However, the quantitative correlations between surfactant concentration (CS), middle-phase volume (jM), optimal salinity, and oil recovery factor remain inadequately explored, impeding the rational design of cost-effective formulations. In this study, model microemulsions were fabricated using a surfactant pair of sodium dodecyl benzene sulfonate and alkyl propoxy sulfate, with paraffin oil serving as a crude oil surrogate. Salinity scans, 100-day phase behavior tracking, and core flooding tests were conducted across a CS range of 0.5–14.0 wt% to establish key parametric relationships. Results show that elevating CS shifts the middle-phase salinity window from 10.5–13.0 wt% to 9.0–12.0 wt% NaCl, while optimal salinity decreases linearly. At optimal salinity, a linear relationship emerges between CS and equilibrium jM: . The microemulsion flooding recovery factor (EM) obeys an exponential relationship with CS: , rising from 7.8% to 48.1% as CS increases from 0.5 wt% to 8.0 wt%. Recovery enhancement is governed predominantly by IFT reduction at low concentrations (0.5–2.0 wt%) and by the synergistic effect of sweep efficiency and ultra-low IFT at higher concentrations (2.0–8.0 wt%). These integrated relationships provide a practical framework for balancing technical performance with economic viability in field-scale EOR deployment.

Ultralong-chain quaternary ammonium surfactants serve as promising clean fracturing-fluid thickeners owing to their facile formation of wormlike micelles (WLMs) in salt solution. However, the ion-specific effects of common inorganic counterions on the formation of WLMs still remain unclear. In this study, we investigate the aqueous solution of docosyl(trimethyl)azanium chloride (DCTAC) with NaBr, NaNO₃, or NaI at temperatures of 60 °C and above through steady/oscillatory rheology, small-angle neutron scattering (SANS), and cryogenic transmission electron microscopy (cryo-TEM). By integrating the results of previous research, we found that the four comparable counterions, namely Cl^-, Br^-, NO₃^-, and I^-, can induce a sphere-to-wormlike transition and result in a pronounced maximum viscosity. Nevertheless, the optimal counterion-to-surfactant ratios for rheological properties vary significantly (80, 6, 3, and 1 eq. for Cl^-, Br^-, NO₃^-, and I^-, respectively). Counterion binding affinity to DCTAC plays a crucial role in determining the self-assembly behavior and rheological properties. The effects of these four counterions precisely adhere to the Hofmeister series, i.e., Cl^- < Br^- < NO₃^- < I^-. SANS and cryo-TEM verify the emergence of elongated cylindrical micelles. Meanwhile, rheology demonstrates that I^- ions generate substantially stronger micellar networks with excellent temperature resistance, which can be attributed to its strong affinity for the micellar interior. These findings establish a connection between counterion affinity, WLM growth, and thermal robustness, offering practical guidance for the design of high-temperature cationic viscoelastic surfactant fluids in complex brines.

Thermoresponsive macromonomers with tunable lower critical solution temperature (LCST) are pivotal building blocks for heat- adaptive polymer systems. However, rational modulation of their phase transition behavior remains challenging due to the intricate coupling between macromolecular architecture and environmental triggers. In this work, a series of multi-responsive poly(acrylamide-co-N-(1,1-dimethyl-3-oxobutyl)-acrylamide) (poly(AM–co–DAAM)) macromonomers were synthesized via a two-step route and systematically characterized using 1H NMR and gel permeation chromatography. UVvis spectroscopic measurements demonstrate that their LCST can be continuously programmed across a broad temperature range of 12–80 °C by modulating molecular composition and solution conditions. This versatile thermoresponsive profile originates from architecture- reliant hydration–association balance: elevated DAAM content facilitates segmental dehydration and thermally induced aggregation, whereas AM-enriched chains sustain robust hydration stability. The macromonomer concentration yields a nonmonotonic U-shaped LCST response, signaling a shift from concentration- facilitated interchain association to overlap-driven multichain clustering. NaCl monotonically depresses LCST through the salting-out effect, while pH variation triggers a V-shaped thermal response by reversibly adjusting the hydration of amide and carbonyl groups, as well as DAAM-dominated local chain interactions. Variable-temperature 1H NMR analyses capture the gradual emergence of DAAM-rich thermoaggregated domains during heating, with nearly 72 mol% of the DAAM units involved in thermal assembly. These findings establish a predictive structure–environment co-regulation paradigm, enabling the rational design of customizable LCST precursors for thermoviscosifying and diverse thermoresponsive polymer materials.