Salt- and temperature-stable quantum dot nanoparticles for porous media flow

Experimental measurements and numerical simulations of the transport and retention of nanocrystal CdSe/ZnS quantum dots in saturated porous media: Effects of electrolytes, organic ligand, and natural organic matter

This study explores the transport and retention of CdSe/ZnS quantum dot (QD) nanoparticles in water-saturated sand columns as a function of electrolytes (Na+ and Ca2+), ionic strength, organic ligand citrate, and Suwannee River natural organic matter (SRNOM). Numerical simulations were carried out to understand the mechanisms that govern the transport and interactions of QDs in porous media and to assess how environmental parameters impact these mechanisms. An increase in the ionic strength of NaCl and CaCl2 increased QDs retention in porous media. The reduction of the electrostatic interactions screened by dissolved electrolyte ions and the increase of divalent bridging effect are the causes for this enhanced retention behavior. Citrate or SRNOM enhanced QDs transport in NaCl and CaCl2 systems by either increasing the repulsion energy barrier or inducing the steric interactions between QDs and the quartz sand collectors. A non-exponential decay characterized the retention profiles of QDs along the distance to the inlet. The modeling results indicated the four models containing the attachment, detachment, and straining terms - Model 1: M1-attachment, Model 2: M2-attachment and detachment, Model 3: M3-straining, and Model 4: M4-attachment, detachment, and straining - closely simulated the observed breakthrough curves (BTCs) but inadequately described the retention profiles.

Fluorescent-tagged water with carbon dots derived from phenylenediamine as an equipment-free nanotracer for enhanced oil recovery

Chemical enhanced oil recovery (EOR) through waterflooding is the most commonly used method to improve crude oil displacement and extraction however; the impact of environmental side effects may remain ambiguous. Regarding, flooding tagged water with tracers provides a better understanding of the fate of injected water and the reservoir conditions more than oil recovery. This study's main focus is the proposed carbon dots (CDs) to develop fluorescent-tagged with dual functions as a sensing and an enhancing agent for EOR operations. Different physicochemical and optical properties were obtained for CDs by tuning the surface chemistry of phenylenediamine (PD) isomers and tartaric acid (TA) via the solvothermal method which leads to green, and yellow fluorescent emissions. Size distribution and colloidal and thermal stability of the prepared nanofluids carrying CDs were controlled by atomic force microscope (AFM), transmission electron microscopy (TEM), dynamic light scattering (DLS), zeta potential, and thermogravimetric analysis (TGA). Long-time emission stability in high temperature and salinity such as conditions found in the oil reservoirs was precisely detected by fluorescence spectroscopy and a portable UV cabinet as the on-site detection method to confirm the sensing ability of CDs. While, rheological parameters of nanofluids such as viscosity, wettability alteration, and fluid/crude oil interfacial tension were evaluated to support the potential of CDs as an enhancing agent to sweep crude oil on the carbonate rock reservoirs. The oil displacement mechanism was monitored on the micromodel pattern by recording 27.8 % and 20.5 % displacement factors for the prepared nanofluids carrying 200 ppm CDs.

Intracellular Hybrid Biosystem in a Protozoan to Trigger Visible-Light-Driven Photocatalysis

Incorporating artificial photosensitizers with microorganisms has recently been recognized as an effective way to convert light energy into chemical energy. However, the incorporated biosystem is usually constructed in an extracellular manner and is vulnerable to the external environment. Here, we develop an intracellular hybrid biosystem in a higher organism protozoa Tetrahymena pyriformis, in which the in vivo synthesized CdS nanoparticles trigger photoreduction of nitrobenzene into aniline under visible-light irradiation. Integrating a photosensitizer CdS into T. pyriformis enables the photosensitizer CdS, inherent nitroreductase, and the cytoplasmic reductive substance in T. pyriformis to synergistically engage in the photocatalysis process, generating a greatly enhanced aniline yield with a 40-fold increment. Moreover, building an intracellular hybrid biosystem in mutant T. pyriformis could even grant it new capability of reducing nitrobenzene into aniline under visible-light irradiation. Such an intracellular hybrid biosystem paves a new way to functionalize higher organisms and diversify light energy conversion.

Review of Synthesis and Evaluation of Inhibitor Nanomaterials for Oilfield Mineral Scale Control

Oilfield flow assurance is the subject to study the impact on the flow of production fluids due to physicochemical changes in the production system. Mineral scale deposition is among the top 3 water-related flow assurance challenges in petroleum industry, particularly for offshore and shale operations. Scale deposition can lead to serious operational risks and significant financial loss. The most commonly adopted strategy in oilfield scale control is the deployment of chemical inhibitors. Although conventional chemical inhibitors are effective in inhibiting scale threat, they have the drawbacks of short transport distance and limited squeeze lifetime due to their intrinsic chemical properties. In the past decade, as an alternative to conventional chemical inhibition, research efforts have been made to prepare functional nanomaterials with different chemical compositions to overcome the drawbacks of conventional chemical inhibitors. These synthesized nanomaterials can serve as delivery vehicles to deploy inhibitors into the target location in the production system. These nanomaterials are reported to have multiple advantages over the conventional inhibitors in terms of transportability, controlled release, and functionality, evidenced by a series of experimental studies. This review presents an overview of scale inhibitor nanomaterial development and the current methods to synthesize and to evaluate these nanomaterials in a systematic and comprehensive manner. This review focuses on the chemistry principles and methodologies underlying inhibitor nanomaterial synthesis and also the chemical instrument and strategies in evaluating the physiochemical properties of these materials in terms of inhibition effectiveness, transportability, and inhibitor return. The scale inhibitor nanomaterials (SINMs) presented in this review exemplify the continuous development in our capabilities in adopting novel nanotechnology in combating actual engineering challenges in petroleum industry.

Probing complex geophysical geometries with chattering dust

The modern energy economy and environmental infrastructure rely on the flow of fluids through fractures in rock. Yet this flow cannot be imaged directly because rocks are opaque to most probes. Here we apply chattering dust, or chemically reactive grains of sucrose containing pockets of pressurized carbon dioxide, to study rock fractures. As a dust grain dissolves, the pockets burst and emit acoustic signals that are detected by distributed sets of external ultrasonic sensors that track the dust movement through fracture systems. The dust particles travel through locally varying fracture apertures with varying speeds and provide information about internal fracture geometry, flow paths and bottlenecks. Chattering dust particles have an advantage over chemical sensors because they do not need to be collected, and over passive tracers because the chattering dust delineates the transport path. The current laboratory work has potential to scale up to near-borehole applications in the field.

Chattering dust, or chemically reactive grains of sucrose containing pockets of pressurized carbon dioxide, are used in this experimental approach to study rock fractures. The chattering dust emits acoustic shocks that can be monitored and illuminates fracture geometry.

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.

Cationic Sterically Stabilized Diblock Copolymer Nanoparticles Exhibit Exceptional Tolerance toward Added Salt

For certain commercial applications such as enhanced oil recovery, sterically stabilized colloidal dispersions that exhibit high tolerance toward added salt are desirable. Herein, we report a series of new cationic diblock copolymer nanoparticles that display excellent colloidal stability in concentrated aqueous salt solutions. More specifically, poly(2-(acryloyloxy)ethyltrimethylammonium chloride) (PATAC) has been chain-extended by reversible addition-fragmentation chain transfer aqueous dispersion polymerization of diacetone acrylamide (DAAM) at 70 °C to produce PATAC₁₀₀-PDAAM_x diblock copolymer spheres at 20% w/w solids via polymerization-induced self-assembly. Transmission electron microscopy and dynamic light scattering (DLS) analysis confirm that the mean sphere diameter can be adjusted by systematic variation of the mean degree of polymerization of the PDAAM block. Remarkably, DLS studies confirm that highly cationic PATAC₁₀₀-PDAAM₁₅₀₀ spheres retain their colloidal stability in the presence of either 4.0 M KCl or 3.0 M ammonium sulfate for at least 115 days at 20 °C. The mole fraction of PATAC chains within the stabilizer shell was systematically varied by the chain extension of various binary mixtures of non-ionic poly(N,N-dimethylacrylamide) (PDMAC) and cationic PATAC with DAAM to produce ([n] PATAC₁₀₀ + [1 - n] PDMAC₆₇)-PDAAM_z diblock copolymer spheres at 20% w/w. DLS studies confirmed that a relatively high mole fraction of cationic PATAC stabilizer chains (n ≥ 0.75) is required for the dispersions to remain colloidally stable in 4.0 M KCl. Cationic worms and vesicles could also be synthesized using a binary mixture of PATAC and PDMAC precursors, where n = 0.10. However, the vesicles only remained colloidally stable up to 1.0 M KCl, whereas the worms proved to be stable up to 2.0 M KCl. Such block copolymer nanoparticles are expected to be useful model systems for understanding the behavior of aqueous colloidal dispersions in extremely salty media. Finally, zeta potentials determined using electrophoretic light scattering are presented for such nanoparticles dispersed in highly salty media.

Carbon quantum dots with tracer-like breakthrough ability for reservoir characterization

Predictions have shown that our demand for oil and gas will continue to grow in the next decade, and future supply will become more reliant on tertiary recovery and from nonconventional resources. However, current reservoir characterization methodologies, such as well logs, cross-well electromagnetic imaging and seismic methods, have their individual limitations on detection range and resolution. Here we propose a pioneering way to use carbon quantum dots (CQDs) as nanoparticle tracers, which can be transported through a reservoir functioning as conventional tracers, while acting as sensors to obtain useful information. These hydrothermally produced CQDs from Xylose possess excellent stability in high ionic strength solutions, durable absorbance and fluorescence ability due to multi high-polarity functional group on their surfaces. Consistency between our on-line ultraviolet-visible (UV-Vis) spectroscopy and off-line Confocal laser scanning microscopy (CLSM) measurements confirms that CQDs have the tracer-like migration capability in glass beads-packed columns and sandstone cores, regardless of particle concentration and ionic strength. However, their migration ability is undermined in the column packed with crushed calcite grains with positive charge. We also demonstrate that quantitative oil saturation detection in unknown sandstone core samples can be achieved by such CQDs based on its breakthrough properties influenced by the presence of oil phase.

Synthesis of salt-stable fluorescent nanoparticles (quantum dots) by polyextremophile halophilic bacteria

Here we report the biological synthesis of CdS fluorescent nanoparticles (Quantum Dots, QDs) by polyextremophile halophilic bacteria isolated from Atacama Salt Flat (Chile), Uyuni Salt Flat (Bolivia) and the Dead Sea (Israel). In particular, a Halobacillus sp. DS2, a strain presenting high resistance to NaCl (3-22%), acidic pH (1-4) and cadmium (CdCl2 MIC: 1,375 mM) was used for QDs biosynthesis studies. Halobacillus sp. synthesize CdS QDs in presence of high NaCl concentrations in a process related with their capacity to generate S2- in these conditions. Biosynthesized QDs were purified, characterized and their stability at different NaCl concentrations determined. Hexagonal nanoparticles with highly defined structures (hexagonal phase), monodisperse size distribution (2-5 nm) and composed by CdS, NaCl and cysteine were determined by TEM, EDX, HRXPS and FTIR. In addition, QDs biosynthesized by Halobacillus sp. DS2 displayed increased tolerance to NaCl when compared to QDs produced chemically or biosynthesized by non-halophilic bacteria. This is the first report of biological synthesis of salt-stable QDs and confirms the potential of using extremophile microorganisms to produce novel nanoparticles. Obtained results constitute a new alternative to improve QDs properties, and as consequence, to increase their industrial and biomedical applications.

Continuum-based models and concepts for the transport of nanoparticles in saturated porous media: A state-of-the-science review

Environmental applications of nanoparticles (NP) increasingly result in widespread NP distribution within porous media where they are subject to various concurrent transport mechanisms including irreversible deposition, attachment/detachment (equilibrium or kinetic), agglomeration, physical straining, site-blocking, ripening, and size exclusion. Fundamental research in NP transport is typically conducted at small scale, and theoretical mechanistic modeling of particle transport in porous media faces challenges when considering the simultaneous effects of transport mechanisms. Continuum modeling approaches, in contrast, are scalable across various scales ranging from column experiments to aquifer. They have also been able to successfully describe the simultaneous occurrence of various transport mechanisms of NP in porous media such as blocking/straining or agglomeration/deposition/detachment. However, the diversity of model equations developed by different authors and the lack of effective approaches for their validation present obstacles to the successful robust application of these models for describing or predicting NP transport phenomena. This review aims to describe consistently all the important NP transport mechanisms along with their representative mathematical continuum models as found in the current scientific literature. Detailed characterizations of each transport phenomenon in regards to their manifestation in the column experiment outcomes, i.e., breakthrough curve (BTC) and residual concentration profile (RCP), are presented to facilitate future interpretations of BTCs and RCPs. The review highlights two NP transport mechanisms, agglomeration and size exclusion, which are potentially of great importance in controlling the fate and transport of NP in the subsurface media yet have been widely neglected in many existing modeling studies. A critical limitation of the continuum modeling approach is the number of parameters used upon application to larger scales and when a series of transport mechanisms are involved. We investigate the use of simplifying assumptions, such as the equilibrium assumption, in modeling the attachment/detachment mechanisms within a continuum modelling framework. While acknowledging criticisms about the use of this assumption for NP deposition on a mechanistic (process) basis, we found that its use as a description of dynamic deposition behavior in a continuum model yields broadly similar results to those arising from a kinetic model. Furthermore, we show that in two dimensional (2-D) continuum models the modeling efficiency based on the Akaike information criterion (AIC) is enhanced for equilibrium vs kinetic with no significant reduction in model performance. This is because fewer parameters are needed for the equilibrium model compared to the kinetic model. Two major transport regimes are identified in the transport of NP within porous media. The first regime is characterized by higher particle-surface attachment affinity than particle-particle attachment affinity, and operative transport mechanisms of physicochemical filtration, blocking, and physical retention. The second regime is characterized by the domination of particle-particle attachment tendency over particle-surface affinity. In this regime although physicochemical filtration as well as straining may still be operative, ripening is predominant together with agglomeration and further subsequent retention. In both regimes careful assessment of NP fate and transport is necessary since certain combinations of concurrent transport phenomena leading to large migration distances are possible in either case.

Steric stabilization of nanoparticles with grafted low molecular weight ligands in highly concentrated brines including divalent ions

Whereas numerous studies of stabilization of nanoparticles (NPs) in electrolytes have examined biological fluids, the interest has grown recently in media with much higher ionic strengths including seawater and brines relevant to environmental science and subsurface oil and gas reservoirs. Given that electrostatic repulsion is limited at extremely high ionic strengths due to charge screening, we have identified ligands that are well solvated in concentrated brine containing divalent cations and thus provide steric stabilization of silica nanoparticles. Specifically, the hydrodynamic diameter of silica nanoparticles with grafted low molecular weight ligands, a diol ether, [3-(2,3-dihydroxypropoxy)propyl]-trimethoxysilane, and a zwitterionic sulfobetaine, 3-([dimethyl(3-trimethoxysilyl)propyl]ammonio)propane-1-sulfonate, is shown with dynamic light scattering to remain essentially constant, indicating lack of aggregation, at room temperature and up to 80 °C for over 30 days. An extended DLVO model signifies that steric stabilization is strongly dominant against van der Waals attraction for ∼10 nm particles given that these ligands are well solvated even in highly concentrated brine. In contrast, polyethylene glycol oligomers do not provide steric stabilization at elevated temperatures, even at conditions where the ligands are soluble, indicating complicating factors including bridging of the ether oxygens by divalent cations.

Responsive Stabilization of Nanoparticles for Extreme Salinity and High-Temperature Reservoir Applications

Colloidal stabilization of nanoparticles under extreme salinity and high temperature conditions is a key challenge in the development of next generation technologies for subsurface reservoir characterization and oil recovery. Polyelectrolytes have been investigated as nanoparticle stabilizers, but typically fail at high ionic strengths and elevated temperatures due to excessive charge screening and dehydration. We report an approach to nanoparticle stabilization that overcomes these limitations, and exploits the antipolyelectrolyte phenomenon, in which screening of intrachain electrostatic interactions causes a polyzwitterion chain to undergo a structural transition from a collapsed globule to a more open coil-like regime with increases in ionic strength and temperature. Small-angle neutron scattering on a model zwitterionic polymer in solution indicated an increase in both radius of gyration and excluded volume parameter of the polymer with increases in ionic strength and temperature. The model zwitterion was subsequently incorporated within a polymeric stabilizer for nanoparticles under harsh reservoir conditions, and used to functionalize hydrophilic (silica) as well as hydrophobic (polystyrene) nanoparticles. Long-term colloidal stability was achieved at salt concentrations up to 120,000 mg/dm3 at 90 °C, approximately twice the stability limit previously reported in the literature. The approach can be broadly generalized to a large class of synthetic polyzwitterions, and can be adapted to a wide variety of other colloidal systems in which demands placed by extreme salinity and temperature conditions must be met.

Photopatterned oil-reservoir micromodels with tailored wetting properties

Micromodels with a simplified porous network that represents geological porous media have been used as experimental test beds for multiphase flow studies in the petroleum industry. We present a new method to fabricate reservoir micromodels with heterogeneous wetting properties. Photopatterned, copolymerized microstructures were fabricated in a bottom-up manner. The use of rationally designed copolymers allowed us to tailor the wetting behavior (oleophilic/phobic) of the structures without requiring additional surface modifications. Using this approach, two separate techniques of constructing microstructures and tailoring their wetting behavior are combined in a simple, single-step ultraviolet lithography process. This microstructuring method is fast, economical, and versatile compared with previous fabrication methods used for multi-phase micromodel experiments. The wetting behaviors of the copolymerized microstructures were quantified and demonstrative oil/water immiscible displacement experiments were conducted.