Enhanced rheological properties and performance of viscoelastic surfactant fluids with embedded nanoparticles

Influence of Particle Surface Charge and Shape on the Rheology and Microstructure of Worm-like Micellar Solutions

The influence of the size, shape, and surface chemistry of charged nanoparticles on the rheology and microstructure of worm-like micellar (WLM) solutions is investigated. The WLM solutions considered in this work are formulated from CTAB (cetyltrimethylammonium bromide), a cationic surfactant, and sodium nitrate (NaNO3). The addition of negatively charged particles decreased the viscoelastic properties (zero-shear viscosity and relaxation time of the micelles) of the WLM solutions. In contrast, the incorporation of positively charged particles into the micellar networks resulted in (i) an increase in zero-shear viscosity and relaxation time and (ii) an increase in the number of entanglements of the micelles. The WLM solutions are found to undergo a transition from viscoelastic fluid-like to gel-like at sufficiently high concentrations of hematite nanospheres. The association between particles and surfactant molecules is further confirmed by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) measurements. This work demonstrates that the degree of enhancement of the viscosity and relaxation time of the micelles is strongly influenced by the surface charge, shape, and surface chemistry of the added nanoparticles.

Self-Assembly Systems Based on Betaine-Type Hydrophobic Association Polymer Used in Acid Stimulation: Effects of Surfactant and Salt Ion

Hydrophobic association polymers containing various functional groups have a great deal of application potential as a self-thickening agent in carbonate acidification, while the improvement of their viscosification ability under high temperature conditions remains a significant challenge. A kind of betaine-type hydrophobic association polymer (PASD) intended for use as an acid thickener was synthesized through aqueous solution polymerization with sulfobetaine and a soluble hydrophobic monomer. The structure of PASD was characterized by FT-IR and 1H NMR. It is found that during the acid-rock reaction, the physical cross-linking between PASD and cationic surfactants (STAC) occurs through noncovalent bonding forces such as micellar interaction and electrostatic interaction, forming a self-assembly acid. The optimum conditions for the construction of the self-assembly acid and its viscosification properties, rheological properties, temperature, and salt resistance were evaluated by a six-speed rotating viscometer and a HAAK MARSIII rheometer. The results suggest that the main source of the viscosity rise of the self-assembly acid is the CaCl2 produced during the acid-rock reaction. As the acid-rock reaction progresses, the hydrodynamic radius of the self-assembly acid increases, and tighter aggregation structures form. The viscosity of the self-assembly spent acid still keeps in 140 mPa·s under 140 °C shearing for 1 h at 170 s-1, which indicates that the self-assembly acid has excellent viscosification ability and temperature resistance. Compared to PASD acid, the self-assembly acid can be used at a wider range of temperatures, and its research and development have given rise to novel ideas for the use of HAWPs as an acid thickener.

Wormlike Micellar Glycerol Solutions Formed from a Double-Tailed Surfactant with Two Quaternary Ammonium Head Groups

Herein, a quaternary ammonium surfactant with dual heads and tails, N1,N1,N1,N3,N3-pentamethyl-N3-(3-(2-tetradecylhexadecanamido)propyl)propane-1,3-diaminium dibromide, abbreviated as Di-C14-N2, was synthesized. For the first time, clear observation of aggregate structures formed by surfactants in pure glycerol systems was achieved using cryogenic transmission electron microscopy (cryo-TEM). The system's rheological properties were analyzed using both steady-state shear and oscillatory rheological measurements. The lubricating efficiency of the Di-C14-N2 glycerol solution was assessed for its tribological properties using a tribological wear tester, white light interferometer, and scanning electron microscope. In glycerol, Di-C14-N2 formed long wormlike micelles, which resulted in a glycerol solution with the zero-shear viscosity of 1013 Pa·s at 90 mM, which is the most viscous glycerol system up to now. The system displayed distinct rheological properties from the aqueous system, as evidenced by two intersections in the loss and storage moduli. The formed wormlike micelles in glycerol lead to a significant alteration in the viscoelasticity of the system, thus endowing the Di-C14-N2 glycerol solution with potential as an eco-friendly lubricant. The friction coefficient of the system was found to be 23% lower and the wear rate was 83% lower than that of pure glycerol after the addition of Di-C14-N2. This demonstrates that the addition of Di-C14-N2 greatly improves the frictional properties of pure glycerol. This study offers the possibility of directly observing the aggregate structures formed by surfactants in pure glycerol systems. It contributes to the exploration of the self-assembly behavior of surfactants in nonaqueous polar media, thereby aiding in a deeper understanding of the correlation between molecular structure, mesoscale structure, and macroscopic properties.

Rheological behavior and solution pH response properties of nanoparticle-regulated low surface tension systems

Regarding the rheological properties of fluids, certain nanoparticles can markedly modify the rheological behavior of low surface tension solutions by interacting with surfactant molecules. In this work, a low surface tension fluid with cetyltrimethylammonium chloride was prepared, and the silica nanoparticles were uniformly dispersed into it by ultrasonic dispersion. By adjusting the size, shape, and concentration of nanoparticles, the fluid behavior can be changed from Newtonian to non-Newtonian with finely tuned viscosity and characterized by a shear-thinning rheological behavior. In addition, this work explored how variations in environmental temperature and solution pH affect the rheological responses of the low surface tension suspension system. The experimental findings revealed that increasing the temperature substantially decreases the system's viscosity and induces a shear-thickening behavior. It is particularly significant that, under extreme pH conditions (either strongly acidic or alkaline), the viscosity of the nanoparticle suspensions was markedly enhanced at a particle concentration of 10 000 ppm. This interesting result coincided with a notable reduction in the zeta potential and an increase in the average particle size, suggesting an intensified aggregation of particles within the suspension system. A mechanism detailing the interaction between silica nanoparticles and surfactant micelles was proposed. This work indicates that the incorporation of nanoparticles into surfactant solutions offers a powerful approach to modulating fluid rheology across various conditions.

Self-Assembled Viscoelastic Surfactant Micelles with pH-Responsive Behavior: A New Fracturing-Displacement Integrated Working Fluid for Unconventional Reservoirs

The integrated fracturing and oil recovery strategy is a new paradigm for achieving sustainable and cost-effective development of unconventional reservoirs. However, a single type of working fluid cannot simultaneously meet the different needs of fracturing and oil displacement processes. Here, we develop a pH-responsive fracturing-displacement integrated working fluid based on the self-assembled micelles of N,N-dimethyl oleoamine propylamine (DOAPA) and succinic acid (SA). By adjusting the pH of the working fluid, the DOAPA and SA molecules can be switched repeatedly between highly viscoelastic wormlike micelles and aqueous low-viscosity spherical micelles. The zero-shear viscosity of the working fluid enriched the wormlike micelles can reach more than 93,100 mPa·s, showing excellent viscoelasticity and sand-carrying properties. The working fluid is easy to gel-break when it encounters oil, generating a low-viscosity liquid without residue. In addition, the system has strong interfacial activity, which can greatly reduce the oil-water interfacial tension to form emulsions and can achieve reversible demulsification and re-emulsification by adjusting pH. Through the designed and fabricated microfluidic chip, it can be visualized that under the synergistic effect of viscoelasticity and interfacial activity DOAPA/SA can effectively expand the swept volume of tight fractured formations, promote pore wetting reversal and crude oil emulsification, and improve the displacement efficiency. The DOAPA/SA meets the design requirements of the fracturing-displacement integrated working fluids and provides a novel method and idea for constructing the integrated working fluids suitable for fracturing and displacement in unconventional reservoirs.

Degradation and enhanced oil recovery potential of Alcanivorax borkumensis through production of bio-enzyme and bio-surfactant

Microbial enhanced oil recovery (EOR) has become the focus of oilfield research due to its low cost, environmental friendliness and sustainability. The degradation and EOR capacity of A. borkumensis through the production of bio-enzyme and bio-surfactant were first investigated in this study. The total protein concentration, acetylcholinesterase, esterase, lipase, alkane hydroxylase activity, surface tension, and emulsification index (EI) were determined at different culture times. The bio-surfactant was identified as glycolipid compound, and the yield was 2.6 ± 0.2 g/L. The nC12 and nC13 of crude oil were completely degraded, and more than 40.0 % of nC14-nC24 was degraded by by A. borkumensis. The results of the microscopic etching model displacement and core flooding experiments showed that emulsification was the main mechanism of EOR. A. borkumensis enhanced the recovery rate by 20.2 %. This study offers novel insights for the development of environmentally friendly and efficient oil fields.

Toroidal micelles formed in viscoelastic aqueous solutions of a double-tailed surfactant with two quaternary ammonium head groups

Innovation in surfactant structures is an effective way to prepare new soft materials with novel applications. In this study, we synthesized a double-tailed surfactant containing two quaternary ammonium head groups (Di-C12-N2). The Di-C12-N2 solution behavior was investigated by surface tension, fluorescence, rheology, and cryo-TEM methods. Although Di-C12-N2 contained a large double-tailed hydrophobic group, the solubility of Di-C12-N2 was ∼90 mmol L-1 at 25 °C with a Krafft temperature of ∼1 °C. The increase in Di-C12-N2 concentration in the solutions led to the formation of various aggregates, including spherical micelles, worm-like micelles, multi-layered vesicles, and a rare type of small toroidal micelles. The two quaternary ammonium head groups in Di-C12-N2 led to strong electrostatic interactions between molecules, which was critical for the formation of toroidal micelles. Moreover, with an added NaCl concentration of 40 mmol L-1, the viscosity of the 5 mmol L-1Di-C12-N2 solution increased by ∼1000 times compared to the pure 5 mmol L-1Di-C12-N2 solution, revealing the high sensitivity of the unique head groups to ionic strength. This study enriches the research on the self-assembly principles of surfactants and brings new potential applications for new soft materials.

Functional Gels and Chemicals Used in Oil and Gas Drilling Engineering: A Status and Prospective

Research into functional gels and chemicals and their applications represents a cutting-edge international field of study. For example, investigating how they can be applied in oil and gas drilling (and extraction engineering) and developing novel functional chemical materials for the oil field could provide innovative solutions and technological methods for oil and gas drilling and extraction operations. Through a literature analysis, this paper presents a review of the current research status and application scenarios of different types of functional gels and chemicals, both domestically and internationally. The classification and preparation principles of various functional materials are systematically outlined and the current applications of functional gels and chemicals in oil and gas drilling and extraction engineering are introduced. These applications include drilling and plugging, enhanced oil recovery, water plugging, and profile control. The formation mechanisms and application scenarios of different types of gels and chemicals are also analyzed and summarized, with a discussion of their prospects in oil and gas drilling and extraction engineering. We broaden the scope of functional gels and chemicals by exploring new application fields and promoting the development of different types of gels and chemicals in a more intelligent direction.

Hybrid Polymer-Surfactant Wormlike Micelles for Concurrent Use for Oil Recovery and Drag Reduction

We report on the effect of a hydrocarbon (n-dodecane) on the rheological properties and shapes of the hybrid wormlike micelles (WLMs) of a surfactant potassium oleate with an embedded polymer poly(4-vinylpyridine). With and without hydrocarbon solutions, the hybrid micelles exhibit the same values of viscosity at shear rates typical for hydraulic fracturing (HF) tests, as solutions of polymer-free WLMs. Therefore, similar to WLMs of surfactants, they could be applied as thickeners in HF fluids without breakers. At the same time, in the presence of n-dodecane, the hybrid micelles have much higher drag-reducing efficiency compared to microemulsions formed in polymer-free systems since they form "beads-on-string" structures according to results obtained using cryo-transmission electron microscopy (cryo-TEM), dynamic-light scattering (DLS), and small-angle X-ray scattering (SAXS). Consequently, they could also act as drag-reducing agents in the pipeline transport of recovered oil. Such a unique multi-functional additive to a fracturing fluid, which permits its concurrent use in oil production and oil transportation, has not been proposed before.

Development of a Novel Surfactant-Based Viscoelastic Fluid System as an Alternative Nonpolymeric Fracturing Fluid and Comparative Analysis with Traditional Guar Gum Gel Fluid

Surfactant-based viscoelastic (SBVE) fluids have recently gained interest from many oil industry researchers due to their polymer-like viscoelastic behaviour and ability to mitigate problems of polymeric fluids by replacing them during various operations. This study investigates an alternative SBVE fluid system for hydraulic fracturing with comparable rheological characteristics to conventional polymeric guar gum fluid. In this study, low and high surfactant concentration SBVE fluid and nanofluid systems were synthesized, optimized, and compared. Cetyltrimethylammonium bromide and counterion inorganic sodium nitrate salt, with and without 1 wt% ZnO nano-dispersion additives, were used; these are entangled wormlike micellar solutions of cationic surfactant. The fluids were divided into the categories of type 1, type 2, type 3, and type 4, and were optimized by comparing the rheological characteristics of different concentration fluids in each category at 25 °C. The authors have reported recently that ZnO NPs can improve the rheological characteristics of fluids with a low surfactant concentration of 0.1 M cetyltrimethylammonium bromide by proposing fluids and nanofluids of type 1 and type 2. In addition, conventional polymeric guar gum gel fluid is prepared in this study and analyzed for its rheological characteristics. The rheology of all SBVE fluids and the guar gum fluid was analyzed using a rotational rheometer at varying shear rate conditions from 0.1 to 500 s^-1 under 25 °C, 35 °C, 45 °C, 55 °C, 65 °C, and 75 °C temperature conditions. The comparative analysis section compares the rheology of the optimal SBVE fluids and nanofluids in each category to the rheology of polymeric guar gum fluid for the entire range of shear rates and temperature conditions. The type 3 optimum fluid with high surfactant concentration of 0.2 M cetyltrimethylammonium bromide and 1.2 M sodium nitrate was the best of all the optimum fluids and nanofluids. This fluid shows comparative rheology to guar gum fluid even at elevated shear rate and temperature conditions. The comparison of average viscosity values under a different group of shear rate conditions suggests that the overall optimum SBVE fluid prepared in this study is a potential nonpolymeric viscoelastic fluid candidate for hydraulic fracturing operation that could replace polymeric guar gum fluids.

Synthesis and Enhanced Oil Recovery Potential of the Bio-Nano-Oil Displacement System

Nanoparticles (NPs) have attracted great attention in the tertiary oil recovery process due to their unique properties. As an economical and efficient green synthesis method, biosynthesized nanoparticles have the advantages of low toxicity, fast preparation, and high yield. In this study, with the theme of biotechnology, for the first time, the bio-nanoparticles reduced by iron-reducing bacteria were compounded with the biosurfactant produced by Bacillus to form a stable bio-nano flooding system, revealing the oil flooding mechanism and enhanced oil recovery (EOR) potential of the bio-nano flooding system. The interfacial properties of the bio-nano-oil displacement system were studied by interfacial tension and wettability change experiments. The enhanced oil recovery potential of the bio-nano-oil displacement agent was measured by microscopic oil displacement experiments and core flooding experiments. The bio-nano-oil displacement system with different nanoparticle concentrations can form a stable dispersion system. The oil-water interfacial tension and contact angle decreased with the increase in concentration of the bio-nano flooding system, which also has a high salt tolerance. Microscopic oil displacement experiments proved the efficient oil displacement of the bio-nano-oil displacement system and revealed its main oil displacement mechanism. The effects of concentration and temperature on the recovery of the nano-biological flooding system were investigated by core displacement experiments. The results showed that the recovery rate increased from 4.53 to 15.26% with the increase of the concentration of the system. The optimum experimental temperature was 60 °C, and the maximum recovery rate was 15.63%.

Development of the Gemini Gel-Forming Surfactant with Ultra-High Temperature Resistance to 200 °C

In order to broaden the application of clean fracturing fluid in ultra-high temperature reservoirs, a surfactant gel for high-temperature-resistant clean fracturing fluid was developed with a gemini cationic surfactant as the main agent in this work. As the fracturing fluid, the rheological property, temperature resistance, gel-breaking property, filtration property, shear recovery performance and core damage property of surfactant gel were systematically studied and evaluated. Results showed the viscosity of the system remained at 25.2 mPa·s for 60 min under a shear rate of 170 s⁻¹ at 200 °C. The observed core permeability damage rate was only 6.23%, indicating low formation damage after fracturing. Due to micelle self-assembly properties in surfactant gel, the fluid has remarkable shear self-repairability. The filtration and core damage experimental results meet the national industry standard for fracturing fluids. The gel system had simple formulation and excellent properties, which was expected to enrich the application of clean fracturing fluid in ultra-high temperature reservoirs.

Experimental Study on the Stability of a Novel Nanocomposite-Enhanced Viscoelastic Surfactant Solution as a Fracturing Fluid under Unconventional Reservoir Stimulation

Fe3O4@ZnO nanocomposites (NCs) were synthesized to improve the stability of the wormlike micelle (WLM) network structure of viscoelastic surfactant (VES) fracturing fluid and were characterized by Fourier transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Then, an NC-enhanced viscoelastic surfactant solution as a fracturing fluid (NC-VES) was prepared, and its properties, including settlement stability, interactions between NCs and WLMs, proppant-transporting performance and gel-breaking properties, were systematically studied. More importantly, the influences of the NC concentration, shear rate, temperature and pH level on the stability of NC-VES were systematically investigated. The experimental results show that the NC-VES with a suitable content of NCs (0.1 wt.%) shows superior stability at 95 °C or at a high shear rate. Meanwhile, the NC-VES has an acceptable wide pH stability range of 6-9. In addition, the NC-VES possesses good sand-carrying performance and gel-breaking properties, while the NCs can be easily separated and recycled by applying a magnetic field. The temperature-resistant, stable and environmentally friendly fracturing fluid opens an opportunity for the future hydraulic fracturing of unconventional reservoirs.

Novel Trends in the Development of Surfactant-Based Hydraulic Fracturing Fluids: A Review

Viscoelastic surfactants (VES) are amphiphilic molecules which self-assemble into long polymer-like aggregates-wormlike micelles. Such micellar chains form an entangled network, imparting high viscosity and viscoelasticity to aqueous solutions. VES are currently attracting great attention as the main components of clean hydraulic fracturing fluids used for enhanced oil recovery (EOR). Fracturing fluids consist of proppant particles suspended in a viscoelastic medium. They are pumped into a wellbore under high pressure to create fractures, through which the oil can flow into the well. Polymer gels have been used most often for fracturing operations; however, VES solutions are advantageous as they usually require no breakers other than reservoir hydrocarbons to be cleaned from the well. Many attempts have recently been made to improve the viscoelastic properties, temperature, and salt resistance of VES fluids to make them a cost-effective alternative to polymer gels. This review aims at describing the novel concepts and advancements in the fundamental science of VES-based fracturing fluids reported in the last few years, which have not yet been widely industrially implemented, but are significant for prospective future applications. Recent achievements, reviewed in this paper, include the use of oligomeric surfactants, surfactant mixtures, hybrid nanoparticle/VES, or polymer/VES fluids. The advantages and limitations of the different VES fluids are discussed. The fundamental reasons for the different ways of improvement of VES performance for fracturing are described.

Networks of Micellar Chains with Nanoplates

Abstract

Nanocomposite networks of surfactant micellar chains and natural bentonite clay nanoplates are studied by rheometry, small-angle neutron scattering, and cryogenic transmission electron microscopy. It is shown that, in an aqueous medium in the presence of a small part of an anionic surfactant, sodium dodecyl sulfate, the molecules of a biodegradable zwitterionic surfactant, oleyl amidopropyl dimethyl carboxybetaine, form micron-length living micellar chains which entangle and form a network possessing well-defined viscoelastic properties. It is found that addition of negatively charged clay nanoplates leads to an increase in viscosity and relaxation time by an order of magnitude. This is explained by the incorporation of the nanoplates into the network as physical multifunctional crosslinks. The incorporation occurs via the attachment of semispherical end-caps of the micelles to the surface of the particles covered with a surfactant layer, as visualized by cryogenic transmission electron microscopy. As the amount of nanoplates is increased, the rheological properties reach plateau; this is associated with the attachment of all end parts of micelles to nanoplates. The developed nanocomposite soft networks based on safe and eco-friendly components are promising for various practical applications.

Experimental Study on the Drag Reduction Performance of Clear Fracturing Fluid Using Wormlike Surfactant Micelles and Magnetic Nanoparticles under a Magnetic Field

This paper examines a new study on the synergistic effect of magnetic nanoparticles and wormlike micelles (WLMs) on drag reduction. Fe₃O₄ magnetic nanoparticles (FE-NPs) are utilized to improve the performance of viscoelastic surfactant (VES) solutions used as fracturing fluids. The chemical composition and micromorphology of the FE-NPs were analyzed with FT-IR and an electron microscope. The stability and interaction of the WLM-particle system were studied by zeta potential and cryo-TEM measurements. More importantly, the influences of the temperature, FE-NP concentration, magnetic field intensity, and direction on the drag reduction rate of WLMs were systematically investigated in a circuit pipe flow system with an electromagnetic unit. The experimental results show that a suitable content of magnetic nanoparticles can enhance the settlement stability and temperature resistance of WLMs. A magnetic field along the flow direction of the fracturing fluid can improve the drag reduction performance of the magnetic WLM system. However, under a magnetic field perpendicular to the direction of fluid flow, an additional flow resistance is generated by the vertical chaining behavior of FE-NPs, which is unfavorable for the drag reduction performance of magnetic VES fracturing fluids. This study may shed light on the mechanism of the synergistic drag reduction effects of magnetic nanoparticles and wormlike micelles.

The one-step synthesis of B,N co-doped carbon dots as a fracturing crosslinker and fluorescent tracer in flowback fluid and their performance

The carbon dot crosslinker has a unique crosslinking mechanism, that each crosslinking point can crosslink multiple guar gum molecular chains.

Disruption of Cationic/Anionic Viscoelastic Surfactant Micellar Networks by Hydrocarbon as a Basis of Enhanced Fracturing Fluids Clean-Up

Studies of the effects produced by the solubilization of hydrophobic substances by micellar aggregates in water medium are quite important for applications of viscoelastic surfactant solutions for enhanced oil recovery (EOR), especially in hydraulic fracturing technology. The present paper aims at the investigation of the structural transformations produced by the absorption of an aliphatic hydrocarbon (n-decane) by mixed wormlike micelles of cationic (n-octyltrimethylammonium bromide, C8TAB) and anionic (potassium oleate) surfactants enriched by C8TAB. As a result of contact with a small amount (0.5 wt%) of oil, a highly viscoelastic fluid is transformed to a water-like liquid. By small-angle neutron scattering (SANS) combined with cryo-TEM, it was shown that this is due to the transition of long wormlike micelles with elliptical cross-sections to ellipsoidal microemulsion droplets. The non-spherical shape was attributed to partial segregation of longer- and shorter-tail surfactant molecules inside the surfactant monolayer, providing an optimum curvature for both of them. As a result, the long-chain surfactant could preferably be located in the flatter part of the aggregates and the short-chain surfactant—at the ellipsoid edges with higher curvature. It is proven that the transition proceeds via a co-existence of microemulsion droplets and wormlike micelles, and upon the increase of hydrocarbon content, the size and volume fraction of ellipsoidal microemulsion droplets increase. The internal structure of the droplets was revealed by contrast variation SANS, and it was shown that, despite the excess of the cationic surfactant, the radius of surfactant shell is controlled by the anionic surfactant with longer tail. These findings open a way for optimizing the performance of viscoelastic surfactant fluids by regulating both the mechanical properties of the fluids and their clean-up from the fracture induced by contact with hydrocarbons.