Effects of a counter-ion salt (potassium chloride) on gemini cationic surfactants with different spacer lengths

Improvement of the Rheological Behavior of Viscoelastic Surfactant Fracturing Fluids by Metallic-Type Nanoparticles

The use of nanotechnology in the field of acidizing, particularly in fracturing fluids, has garnered significant attention over the past decade. Viscoelastic surfactants (VESs) are utilized as one of the most effective fracturing fluids, possessing both elasticity and viscosity properties. These fluids are crucial additives in acidizing packages, enhancing their performance. However, various factors, such as salinity, temperature, pressure, and concentration, can sometimes weaken the efficacy of these fluids. To address this, the integration of nanoparticles has been explored to improve fluid retention in reservoirs and enhance the efficiency. This study focuses on investigating the impact of the main metallic-type nanoparticles on the rheological behavior of VES fluids. Iron oxide, magnesium oxide, and zinc oxide nanoparticles were utilized, and the microscopic-scale rheological behavior of the fluids was thoroughly evaluated. The highest performance for enhancing fluid gelation, stability, and rheological characteristics of VES fluids was found for Fe2O3 nanoparticles at an optimum concentration of 500 ppm. At this concentration and shear rate of 100 s-1, the viscosity of the fluid reached 169.61 cP. For iron oxide nanoparticles at a concentration of 500 ppm, by increasing the temperature from 25 to 85 °C, the gelation state of the fluid increased from 7 h and 50 min to 17 h and 45 min. This improvement is attributed to their high surface area and the increased density of entanglement points within the micelles, leading to a more interconnected structure with enhanced viscoelastic properties. Furthermore, iron oxide nanoparticles significantly enhance gelation by physically connecting the micelles, thereby improving stability and structure. The absorption of surfactant molecules by the nanoparticles additionally contributes to micelle reconstruction and shape alteration. The presence of iron oxide nanoparticles helps maintain the gel structure even at elevated temperatures, preventing rapid viscosity decrease. Our findings may provide new insights for development of high-performance, economical, and environment-friendly fracturing fluids used in well stimulation operations.

Use of Betaine-Based Gel and Its Potential Application in Enhanced Oil Recovery

In this paper, a betaine-based gel containing 2.0% erucamide propyl betaine (EAPB), 0.5% oleic acid amide propyl betaine (OAPB), and 0.1% KCl was prepared for use as a fracturing fluid. The performance evaluation showed that KCl may improve the temperature resistance and increase the viscosity of the optimized fracturing fluid. At 80 °C, the apparent viscosity of the viscoelastic surfactant (VES)-based fracturing fluid was approximately 50 mPa·s. Furthermore, the gel had high shear resistance, good viscosity stability, and high sand-carrying performance. After being sheared at 170 s−1 for 60 min, the reduction in viscosity was 13.6%. The viscosity of the gel was relatively stable at room temperature (27 °C) for one week. In a suspension containing 10% sand (particle size < 0.45 mm, density = 2.75 g cm−3), the settling velocity of proppant particles was 1.15 cm h−1. In addition, we detected that the critical micelle concentration of this gel was approximately 0.042 wt%. The viscosity could be reduced to <5 mPa·s at 60 °C within 1 h when 6.0% crude oil was present, and oil displacement experiments showed that the broken fracturing fluid can enhance the oil displacement rate up to 14.5%. This work may facilitate research on fracturing fluids and oil recovery.

Gemini Surfactant with Unsaturated Long Tails for Viscoelastic Surfactant (VES) Fracturing Fluid Used in Tight Reservoirs

The high dosage of surfactant terribly restrains the extensive application of viscoelastic surfactant (VES) fracturing fluid. In this study, a novel gemini surfactant (GLO) with long hydrophobic tails and double bonds was prepared and a VES fracturing fluid with a low concentration of GLO was developed. Because of the long tails bending near the double bonds, there is a significant improvement of the surfactant aggregate architecture, which realized the favorable viscosity of the VES fluid at a more economical concentration than the conventional VES fracturing fluids. Fourier transform infrared spectrometry (FT-IR), nuclear magnetic resonance spectrometry (1H NMR, 13C NMR), and high-resolution mass spectrometry (HRMS) were employed to study the formation of the product and the structure of GLO. The designed GLO was produced according to the results of the structure characterizations. The formula of the VES fracturing fluid was optimized to be 2.0 wt % GLO + 0.4 wt % sodium salicylate (NaSal) + 1.0 wt % KCl based on the measurements of the viscosity. The viscosity of the VES fluid decreased from 405.5 to 98.7 mPa·s as the temperature increased from 18 to 80 °C and reached equilibrium at about 70.2 mPa·s. The VES fluid showed a typical elastic pseudoplastic fluid with a yield stress of 0.5 Pa in the rheological tests. It realized a proppant setting velocity as low as 0.08 g/min in the dynamic proppant transport test carried by GLO-based VES fracturing fluid. Compared to the formation water, the filtrate of the VES fracturing fluid decreased the water contact angle (CA) from 56.2 to 45.4° and decreased the water/oil interfacial tension (IFT) from 19.5 to 1.6 mN/m. Finally, the VES fracturing fluid induced a low permeability loss rate of 10.4% and a low conductivity loss rate of 5.4% for the oil phase in the experiments of formation damage evaluation.

Interfacial and Aggregation Behaviour of Sodium Dodecyl Sulphate Induced by Ionic Liquids

Aggregation studies of anionic surfactant sodium dodecyl sulphate (SDS) was investigated in aqueous 1-butyl-3-methylimidazolium chloride [bmim]Cl and N-butyl-N-methyl pyrrolidinium tetrafluoroborate [bmp]BF₄ ionic liquid (IL) solutions respectively. Systems were studied by surface tension, conductance, UV-VIS absorption/emission spectroscopy and dynamic light scattering. Critical micelle concentration (CMC) values gradually decreased with increasing IL concentration which indicates synergistic interaction between ILs and SDS. Gibbs free energy change results demonstrated spontaneous micellization induced by ILs; however the effect of ILs were not similar to the corresponding regular salts (NaCl and NaBF₄). Aggregation number (n) of micelles, determined by fluorescence quenching method, indicate that the 'n' values increase with increasing ILs concentration, induced by the oppositely charged IL cation. Size of the micelles, determined by dynamic light scattering studies, increased with increasing ILs concentration, which were due to the formation of larger aggregates; the aggregates are considered to be comprised of the anionic surfactant with a substantial proportion of ILs cation as the bound counter ions. Such studies are considered to shed further light in the fundamentals of IL induced micellization as well as in different practical applications.

Mechanistic Aspects of Simultaneous Extraction of Silver and Gold Nanoparticles across Aqueous-Organic Interfaces by Surface Active Iron Oxide Nanoparticles

Surface active iron oxide nanoparticles (NPs) were used for the simultaneous extraction of water soluble Ag and Au NPs across an aqueous-organic interface from aqueous bulk. The surface activity of iron oxide NPs was achieved by using cationic Gemini surfactants of different architectures during the in situ synthesis of iron oxide NPs in hydrothermal synthesis. Aqueous bulk solubility of Ag and Au NPs was achieved by stabilizing them with conventional surfactants of different polarities such as SDS, CTAB, and DDM. The amphiphilic nature of iron oxide NPs demonstrated their remarkable ability to extract Ag and Au NPs through both hydrophilic and hydrophobic interactions. The mechanism of extraction from aqueous bulk was monitored by placing different amounts of surface active iron oxide NPs on the aqueous-organic interface and was studied with the help of UV-visible, DLS, and IR measurements. XPS and TEM measurements were used for the quantitative estimation of efficiency of extraction. Extraction was facilitated when both hydrophilic and hydrophobic interactions were participating simultaneously. Results may help in designing a suitable method for purification of industrial effluents contaminated with metal particulates simply by applying an external magnetic field rather than going through a complicated conventional filtration process.

Application of a Zwitterionic Hydrophobic Associating Polymer with High Salt and Heat Tolerance in Brine-Based Fracturing Fluid

ZID₁₆PM, a zwitterionic hydrophobic associating polymer, has equivalent positive and negative charges and some hydrophobic monomers with twin-tailed long hydrophobic chains. It exhibits a great heat resistance and salt tolerance to the common salt in formation brine (MgCl₂, CaCl₂, NaCl, and KCl), which is attributed to its anti-polyelectrolyte effect and strong association force. High-salinity water (seawater or formation water) can be prepared as a fracturing fluid directly. In this paper, the formation water of the West Sichuan Gas Field is directly prepared into fracturing fluid with a concentration of 0.3% ZID₁₆PM (Fluid-1), and the seawater of the Gulf of Mexico is directly prepared into fracturing fluid with a concentration of 0.3% ZID₁₆PM (Fluid-2). Finally, rheological measurements, proppant suspension tests, and core matrix permeability damage rate tests for the Fluid-1 and Fluid-2 are conducted. Results show that after 120 min of shearing at 140 and 160 °C, respectively, the viscosity of Fluid-1 remains in the range of 50–85 mPa·s, and the viscosity of Fluid-2 remains in the range of 60–95 mPa·s. And the wastewater produced by an oilfield in Shaanxi, Xinjiang, and Jiangsu are also prepared into fracturing fluids with a concentration of 0.3% ZID₁₆PM, the viscosity of these fracturing fluids can remain 32, 42, and 45 mPa·s, respectively, after 120 min of shearing at 160 °C. All results demonstrate that the polymer ZID₁₆PM displays prominent performance in fracturing fluids.