Long-Term High-Temperature Stability of Functionalized Graphene Oxide Nanoplatelets in Arab-D and API Brine

Research Progress in Nanofluid-Enhanced Oil Recovery Technology and Mechanism

Nanofluid-enhanced oil recovery (EOR) technology is an innovative approach to enhancing oil production in oilfields. It entails the dispersion of nanoparticles within a fluid, strategically utilizing the distinctive properties of these nanoparticles (NPs) to engage with reservoir rocks or crude oil, resulting in a significant enhancement of the oil recovery rate. Despite the notable advantages of nanofluid EOR technology over conventional oil recovery methods such as binary and ternary flooding, practical implementations continue to grapple with a range of pressing challenges. These challenges encompass concerns regarding the economic viability, stability, and adaptability of nanomaterials, which pose significant barriers to the widespread adoption of nanofluid EOR technology in the oil field. To tackle these challenges, addressing the current issues may involve selecting simpler and more readily available materials coupled with straightforward material modification techniques. This approach aims to more effectively meet the requirements of large-scale on-site applications. Within this framework, this review systematically explores commonly employed nanofluids in recent years, including inorganic nanofluids, organic nanofluids, and composite nanofluids. It categorizes the research advancements in optimizing modification techniques and provides a comprehensive overview of the mechanisms that underpin nanofluid EOR technology and its practical applications in oilfields. This comprehensive review aims to offer valuable references and serve as a solid foundation for subsequent research endeavors.

Environmental and health impacts of functional graphenic materials and their ultrasonically altered products

Graphenic materials have excited the scientific community due to their exciting mechanical, thermal, and optoelectronic properties for a potential range of applications. Graphene and graphene derivatives have demonstrated application in areas stretching from composites to medicine; however, the environmental and health impacts of these materials have not been sufficiently characterized. Graphene oxide (GO) is one of the most widely used graphenic derivatives due to a relatively easy and scalable synthesis, and the ability to tailor the oxygen containing functional groups through further chemical modification. In this paper, ecological and health impacts of fresh and ultrasonically altered functional graphenic materials (FGMs) were investigated. Model organisms, specifically Escherichia coli, Bacillus subtilis, and Caenorhabditis elegans, were used to assess the consequences of environmental exposure to fresh and ultrasonically altered FGMs. FGMs were selected to evaluate the environmental effects of aggregation state, degree of oxidation, charge, and ultrasonication. The major findings indicate that bacterial cell viability, nematode fertility, and nematode movement were largely unaffected, suggesting that a wide variety of FGMs may not pose significant health and environmental risks.

Surface modification of carbon dots with tetraalkylammonium moieties for fine tuning their antibacterial activity

The widespread of bacterial infections including biofilms drives the never-ending quest for new antimicrobial agents. Among the great variety of nanomaterials, carbon dots (CDs) are the most promising antibacterial material, but still require the adjustment of their surface properties for enhanced activity. In this contribution, we report a facile functionalization method of carbon dots (CDs) by tetraalkylammonium moieties using diazonium chemistry to improve their antibacterial activity against Gram-positive and Gram-negative bacteria. CDs were modified by novel diazonium salts bearing tetraalkylammonium moieties (TAA) with different alkyl chains (C2, C4, C9, C12) for the optimization of antibacterial activity. Variation of the alkyl chain allows to reach the significant antibacterial effect for CDs-C9 towards Gram-positive Staphylococcus aureus (S. aureus) (MIC = 3.09 ± 1.10 μg mL-1) and Gram-negative Escherichia coli (E. coli) (MIC = 7.93 ± 0.17 μg mL-1) bacteria. The antibacterial mechanism of CDs-C9 is ascribed to the balance between the positive charge and hydrophobicity of the alkyl chains. TAA moieties are responsible for enhanced adherence on the bacterial cell membrane, its penetration and disturbance of physiological metabolism. CDs-C9 were not effective in the generation of reactive oxygen species excluding the oxidative damage mechanism. In addition, CDs-C9 effectively promoted the antibiofilm treatment of S. aureus and E. coli biofilms outperforming previously-reported CDs in terms of treatment duration and minimal inhibitory concentration. The good biocompatibility of CDs-C9 was demonstrated on mouse fibroblast (NIH/3T3), HeLa and U-87 MG cell lines for concentrations up to 256 μg mL-1. Collectively, our work highlights the correlation between the surface chemistry of CDs and their antimicrobial performance.

Unique Oil-in-Brine Pickering Emulsion Using Responsive Antipolyelectrolyte Functionalized Latex: A Versatile Emulsion Stabilizer

A simple and straightforward approach to synthesize oil-in-water (O/W) emulsions under high salinity and temperature using zwitterion-functionalized latexes are presented in this work. First, well-defined functionalized latexes were synthesized by emulsifier-free emulsion copolymerization in the presence of precursor sulfobetaine comonomer using brine as a continuous phase. The surface-functionalized latex particles were then characterized by DLS, SEM, TEM, XPS, and TGA. The functionalized latex exhibited antipolyelectrolyte behavior in high salinity brine and at high temperatures. The effects of salinity, temperature, and pH on the long-term stability of the particles were investigated. Further, to evaluate the potential in high salinity brine and high temperature, the saltphilic functionalized latexes were utilized to stabilize the oil/brine (O/W) interface without any other additives. The latex enabled the formation of a stable Pickering emulsion system with low solid content (<0.02% w/w) in the presence of 50% v/v n-decane. The functionalized latexes were self-assembled at the O/W interface as a spherical colloidosome in high salinity brine through hydrophobic interactions and irreversible adsorption. The supraparticles were imaged with SEM, providing an insight that the exterior of the emulsion droplets is stabilized by the saltphilic latex particles, forming a protective layer at the oil-water interface through electrostatic repulsion. The antipolyelectrolyte latex can be utilized as a novel emulsion stabilizer, which can provide a versatile alternative for applications in a complex environment such as high salinity, temperature, and low or high pH.

Ultra-Stable Silica Nanoparticles as Nano-Plugging Additive for Shale Exploitation in Harsh Environments

Owing to the harsh downhole environments, poor dispersion of silica at high salinity and high temperature can severely restrict its application as the nano-plugging agent in shale gas exploitation. The objective of this study is to improve salt tolerance and thermal stability of silica. Herein, silica was successfully functionalized with an anionic polymer (p SPMA) by SI-ATRP (surface-initiated atom transfer radical polymerization), named SiO2-g-SPMA. The grafted pSPMA brushes on silica provided sufficient electrostatic repulsion and steric repulsion for stabilizing silica in a harsh environment. The modified silica (SiO2-g-SPMA) had excellent colloidal stability at salinities up to 5.43 M NaCl (saturated brine) and standard API brine (8 wt% NaCl + 2 wt% CaCl2) for 30 days at room temperature. Simultaneously, the SiO2-g-SPMA was stable at 170 °C for 24 h as well as stable in weakly alkali environment. Furthermore, the plugging performance of SiO2-g-SPMA in water-based drilling fluids for low permeate reservoir reached to 78.25% when adding a small amount of 0.5 wt% SiO2-g-SPMA, which effectively hindered the water invasion into formation and protected the reservoir.

Stabilization of Polymer Nanocomposites in High-Temperature and High-Salinity Brines

Stabilization of polymer nanocomposites in aqueous environment with high salinity has been a constant challenge for their applications. This work aimed to improve the stability of graphene oxide (GO) polyacrylamide nanocomposites at high-temperature and high-ionic-strength brines. GO was synthesized via a modified Hummers' method and the copolymer of acrylamide (COPAM) was obtained via free-radical polymerization. The covalent functionalization of COPAM with the partially reduced GO (rGO) was successfully achieved. 1,3-Propane sultone was used to further functionalize the obtained rGO-COPAM composites to accomplish the zwitterionic character on the rGO-COPAM surface to get a material with excellent temperature stability and dispersibility in the presence of high ionic strength brines. The synthesized materials were characterized by 1H NMR, gel permeation chromatography, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy analysis, and so forth. The thermal stability of the dispersion at 80 °C for 120 days was observed by visual inspection and spectroscopic analysis. The results showed that the zwitterionic polymer produced excellent brine stability with GO nanosheets and suggested promising applications of zwitterionic polyacrylamide-GO systems especially for enhanced oil recovery.

Understanding Calcium-Mediated Adhesion of Nanomaterials in Reservoir Fluids by Insights from Molecular Dynamics Simulations

Interest in nanomaterials for subsurface applications has grown markedly due to their successful application in a variety of disciplines, such as biotechnology and medicine. Nevertheless, nanotechnology application in the petroleum industry presents greater challenges to implementation because of the harsh conditions (i.e. high temperature, high pressure, and high salinity) that exist in the subsurface that far exceed those present in biological applications. The most common subsurface nanomaterial failures include colloidal instability (aggregation) and sticking to mineral surfaces (irreversible retention). We previously reported an atomic force microscopy (AFM) study on the calcium-mediated adhesion of nanomaterials in reservoir fluids (S. L. Eichmann and N. A. Burnham, Sci. Rep. 7, 11613, 2017), where we discovered that the functionalized and bare AFM tips showed mitigated adhesion forces in calcium ion rich fluids. Herein, molecular dynamics reveal the molecular-level details in the AFM experiments. Special attention was given to the carboxylate-functionalized AFM tips because of their prominent ion-specific effects. The simulation results unambiguously demonstrated that in calcium ion rich fluids, the strong carboxylate-calcium ion complexes prevented direct carboxylate-calcite interactions, thus lowering the AFM adhesion forces. We performed the force measurement simulations on five representative calcite crystallographic surfaces and observed that the adhesion forces were about two to three fold higher in the calcium ion deficient fluids compared to the calcium ion rich fluids for all calcite surfaces. Moreover, in calcium ion deficient fluids, the adhesion forces were significantly stronger on the calcite surfaces with higher calcium ion exposures. This indicated that the interactions between the functionalized AFM tips and the calcite surfaces were mainly through carboxylate interactions with the calcium ions on calcite surfaces. Finally, when analyzing the order parameters of the tethered functional groups, we observed significantly different behavior of the alkanethiols depending on the absence or presence of calcium ions. These observations agreed well with AFM experiments and provided new insights for the competing carboxylate/calcite/calcium ion interactions.

Hyper-branched structure-an active carrier for copolymer with surface activity, anti-polyelectrolyte effect and hydrophobic association in enhanced oil recovery

Herein, a hyper-branched polymer h-PMAD with, simultaneously, surface activity, an anti-polyelectrolyte effect and a hydrophobic association was prepared via aqueous solution free radical polymerization, and characterized by IR, NMR, TG-DTG and SEM. The polymer h-PMAD provided excellent comprehensive properties in terms of surface activity, thickening, water solubility, rheology and aging, which were compared with studies of HPAM and the homologous linear polymer PMAD. Specifically, the IFT value was 55.40 mN m-1, 789.24 mPa s apparent viscosity with a dissolution time of 72 min, 97.72, 90.77 and 105.81 mPa s with Na+, Ca2+ and Mg2+ of 20 000, 2000 and 2000 mg L-1, respectively. Meanwhile, the non-Newtonian shear thinning behavior had a 96.33% viscosity retention while the shear rate went from 170 s-1 to 510 s-1 and then returned to 170 s-1 again and 0.12 Hz curve, with an intersection frequency of G' and G''. Also, it had 33.51% and 50.96% viscosity retention in formation and deionized water at 100 °C and a low viscosity loss in formation water at 80 °C over 4 weeks. Moreover, the h-PMAD had an EOR of 11.61%, was obviously higher than PMAD with 8.19% and HPAM with 5.88%. Most importantly, the better EOR of h-PMAD over that of PMAD testified that the hyper-branched structure provided an active carrier for copolymers with functionalized monomers to exert greater effects in displacement systems, which is of an extraordinary meaning.

Poly(sodium 4-styrenesulfonate) Stabilized Janus Nanosheets in Brine with Retained Amphiphilicity

Maintaining colloidal stability in unfriendly environments while retaining surface chemical properties is challenging for fundamental science and crucial for many applications. Here, we report for the first time that by using a low concentration of poly(sodium 4-styrenesulfonate) (PSS), graphene-based amphiphilic Janus nanosheets (AJNs) can be stabilized in high salt brine (3 wt % NaCl and 0.5 wt % CaCl₂), whereas the interfacial behavior of the nanosheets is not affected. The adsorption of PSS on the hydrophilic and hydrophobic surfaces of AJNs in brine was investigated experimentally and by molecular dynamics simulations. Simulations further showed that the spatial configuration of absorbed PSS molecules with sulfonate functional groups facing outward favored the generation of electrosteric repulsive interactions. Calculations of the interaction energy between PSS molecules and the nanosheet revealed surface charge as a key parameter to stabilize AJNs in the salt environment, as demonstrated by the case of graphene oxide with higher surface charge. Simulations were also used to examine the interfacial behavior of graphene-based AJNs in biphasic systems. The AJNs, which exhibited asymmetry in surface wettability, remained at the oil/brine interface because of PSS detachment from the hydrophobic surface. The results were subsequently experimentally confirmed, consistent with our previously reported graphene-based AJN fluid prepared in fresh water. The process was thermodynamically supported by the demonstrated negative change of Gibbs free energy. We believe that such a strategy could benefit for the stabilization of other AJNs with surface chemical accessibility under harsh conditions.

Highly Ordered and Multiple-Responsive Graphene Oxide/Azoimidazolium Surfactant Intercalation Hybrids: A Versatile Control Platform

To produce graphene materials with better controllability, a new graphene oxide (GO) intercalation hybrid is fabricated with the incorporation and functionalization with the azoimidazolium (AzoIm⁺) surfactant. The hybrid exhibits a highly uniform lamellar structure in which a few layers of GO are stacked with AzoIm⁺ alternatively. Simultaneous control of the mesoscopic structures, aggregation properties, and electrochemical behavior of the hybrid is achieved by inheriting the photo, thermal, and mechanical responsiveness of azoimidazolium. Ultraviolet (UV) treatment produces a well-dispersed GO/AzoIm⁺ suspension aggregate and a precipitate, whereas the specific capacitance of the final hybrid decreases. The lamellar stacking becomes anisotropic by uniaxial stretching on a soft polymer. With a liquid crystal unit inserted between the layers, the d spacing of the lamella passes through transformation, disordering, and finally recovery stages, associated with the increasing and decreasing temperature. The explosive release of heat generated by the thermal reduction of GO is reduced in the GO/AzoIm⁺ intercalation hybrid. The release of heat is tunable by varying the relative quantity and UV treatment of AzoIm⁺. The physical properties of the hybrid allow the controlled preparation of ultrasmall Au nanodots between the GO layers. This represents a major step toward multiple-responsive integrated graphene applications.

Synthesis of graphene oxide/polyimide mixed matrix membranes for desalination

Graphene oxide (GO) was incorporated into polyimide (PI) to fabricate GO/PI mixed matrix membranes (MMMs), which show a high water flux (36.1 kg m⁻² h⁻¹) and a high salt rejection (99.9%) for desalination of 3.5 wt% seawater at 90 °C.