Synthesis of erucic amide propyl betaine compound fracturing fluid system

Identifying and prioritizing organic toxicants in treated flowback and produced water from shale gas exploitation sites using an integrative effect-directed analysis and nontarget screening method

The use of hydraulic fracturing in shale gas exploitation has generated substantial amount of flowback and produced water (FPW), and ecological risk of these highly complex chemical mixtures has raised worldwide concern. Herein, an integrative effect-directed analysis (EDA) and nontarget screening (NTS) workflow was developed to identify and prioritize main toxicants in the treated FPW (T-FPW). The workflow included sample extraction and fractionation, zebrafish embryo toxicity tests, target and nontarget chemical analyses, and toxicity prioritization and confirmation using toxicological priority index (ToxPi). Results showed that less hydrophobic compounds (log Kow < 3.7) which were used in fracturing fluid and their degradation products were the potentially high-risk toxicants in T-FPW. Thirty-nine target compounds identified in toxic fraction explained 4.82% of the mortality. Additional 584 nontarget contaminants were annotated by NTS. Risk prioritization was achieved for 470 identified contaminants with ecotoxicity data available using a ToxPi method. Six nontarget toxicants were identified with higher ecological risks than all target contaminants, and their presence in FPW were confirmed using reference standards. A principal component analysis of NTS features revealed that EDA fractionation reduced mixture complexity and focused toxicant screening, which significantly improved NTS efficiency, highlighting advantages of integrative EDA and NTS for mixture risk assessment.

Influence of tail group length, amide functionality and added salt ion identity on the behaviour of betaine surfactants

Hypothesis The behaviour of surfactants in solution and at interfaces is governed by a combination of steric and electrostatic effects experienced by surfactant molecules as they interact with solvent, other species in solution, and each other. It would therefore be anticipated that highly interacting groups would significantly influence surfactant behaviour. The widely used amide functionality has polar H-bond donor/acceptor properties, and therefore its inclusion into a surfactant structure should have a profound effect on surface activity and self-assembly of that surfactant when compared to the equivalent molecule without an amide linker. Further, chaotropic or kosmotropic salt ions that affect water structuring and hydrogen bonding may provide opportunities for further tuning surfactant interactions in such cases. Experiments A library of betaine surfactant with tail lengths n=14-22 both with and without an amidopropyl linker were synthesised to study the effect of the amide functionality on surfactant properties. Characterisation of the molecules interfacial properties were performed using pendant drop tensiometry and their solution state formulation properties were probed using small-angle neutron scattering (SANS) and rheological measurements. Findings Presence of an amidopropyl linker had little effect on aggregation propensity (as evidenced by critical micelle concentration) and aggregate morphology of betaine surfactants, but did increase the Krafft temperature of these surfactants. SANS analysis indicated that aggregate morphology of alkyl betaine surfactants could be influenced by the addition of sodium salts with chaotropic counterions (I- and SCN-), but they were insensitive to more kosmotropic anions (SO42-, F- and Cl-), providing unique and novel solution control methods for this (supposedly salt-insensitive) class of surfactants.

Synthesis and Properties of Exceptionally Thermo-Switchable Viscoelastic Responsive Zwitterionic Gemini Surfactants in Highly Saline Water

Viscoelastic surfactants (VESs) have significant importance for stimulation of low-permeable reservoirs and acid diversion applications to effectively enhance hydrocarbon productivity. VESs offer lower residues, complete gel production, and lower formation damage that make them suitable candidates for hydraulic fracturing applications. In this research work, the synthesis of two new zwitterionic gemini surfactants 1 and 2 together with previously known amidosulfobutaine (C₁₈AMP3SB) has been achieved. Evaluation of viscosity behavior of neat surfactants in CaCl₂ solutions at varied temperatures and shear rates did not show any upsurge in their viscosities. Nevertheless, a mixture of surfactants 1 and 2 in combination with C₁₈AMP3SB displayed a significant increase in viscosity, transforming the solution into a highly viscous gel. At a fixed shear rate of 35 s^-1 and under different temperatures, solutions of the mixture of surfactants 1 and C₁₈AMP3SB displayed viscosities ranging from 4.34 to 354.3 cPs (81-fold enhancement). Likewise, viscosities of formulations based on mixing 2 and C₁₈AMP3SB under identical experimental conditions ranged from 3.89 to 290 cPs (74-fold enhancement). The viscofying stability tests at 90 °C at a shear rate of 35 s^-1 of mixed surfactant formulations revealed no appreciable change in their viscosities for up to 1 h. Moreover, temperature-dependent experiments suggested an increase in the viscosity with an increase in temperature. Thermogravimetric analysis revealed that these surfactants are thermally stable, with no appreciable loss of mass up to 300 °C. The viscoelastic properties of these surfactants suggest their potential and utility in well stimulation for enhanced oil recovery.

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.

Foam Stabilization Mechanism of a Novel Non-cross-linked Foam Fracturing Fluid

Traditional foam hydraulic fracturing fluids used guar cross-linking technology. However, major production problems, such as high friction and difficulty to accurately control the cross-linking time, have influenced the large-scale application of cross-linked guar foam fracturing fluids. In this study, we developed a novel non-cross-linked foam fracturing fluid using a series of polymers synthesized with acrylamide and hexadecyl trimethylallyl ammonium chloride as monomers and improved the stability of foam by forming structures in solution through association. The results showed that the hydrophobic groups were the key factors that affect the foam stability, and the hydrolysis degree had a significant effect on the elasticity of the polymer solution. The model association polymer with 0.75% hydrophobic group content and 56% hydrolytic degree was optimal. The stability of our proposed foam was comparable to that of the cross-linked guar gum foam. The adsorption of associating polymers on the gas and water interface resulted in a high-stability foam. Our study demonstrates a new avenue to develop high-stability foams to satisfy the current hydraulic fracturing scheme.

Heads or tails? The synthesis, self-assembly, properties and uses of betaine and betaine-like surfactants

Betaines are a key class of zwitterionic surfactant that exhibit particularly favorable properties, making them indispensable in modern formulation. Due to their composition, betaines are readily biodegradable, mild on the skin and exhibit some antimicrobial activity. Vital to their function, these surfactants self-assemble into diverse micellar geometries, some of which contribute to increased solution viscosity, and their surface activity results in strong detergency and foaming. As such, their behavior has been exploited in various applications from personal care (including shampoos and liquid soaps) to specific industrial fields (such as enhanced oil recovery). This review aims to inform the reader of the diverse range of different betaine and betaine-like surfactants that have been actively researched over the past three decades. Synthesis as well as both chemical and physical characterization of betaine surfactants are discussed, including small-angle scattering studies that indicate self-assembly structures and rheological data that demonstrates texture and flow. Stimulus responsive systems and exotic betaine analogs with enhanced functionality are also covered. Crucially, the connection between surfactant molecular architecture and function are highlighted, exemplifying precisely why zwitterionic betaine and related surfactants are so uniquely functional.

Synthesis and Characterization of Surfactant for Retarding Acid-Rock Reaction Rate in Acid Fracturing

Acid fracturing is an effective method to develop ultra-low permeability reservoirs. However, the fast reaction rate reduces the effect of the acid fracturing and increases the near-well collapse risk. Therefore, it is necessary to retard the acid–rock reaction rate. In this work, we synthesized an acid-resistant Gemini zwitterionic viscoelastic surfactant (named VES-c), which has good performances such as temperature resistance, salt resistance, and shear resistance. Besides, a low concentration of VES-c increases the viscosity of the acid solution. The CO₂ drainage method was used to measure the reaction rate between the dibasic acid and dolomite/broken core. We find that the dibasic acid containing 0.3% VES-c retards the dolomite reaction rate of 3.22 times compared with only dibasic acid. Furthermore, the dibasic acid containing 0.3% VES-c exhibits uniform distribution and is not easy to adhere to the solid surface. The VES-c also is favorable to reduce the formation of amorphous calcium carbonate. Retarding the rate of acid–rock reaction and enhancing the acidification are mainly attributed to VES-c's salt-tolerance, anti-adsorption, and the property of increasing the viscosity of the solution. Hopefully, this kind of surfactant retarding reaction rate is applied to other acid–rock reactions.

pH-responsive viscoelastic supramolecular viscosifiers based on dynamic complexation of zwitterionic octadecylamidopropyl betaine and triamine for hydraulic fracturing applications

Viscosity modifying agents are one of the most critical components of hydraulic fracturing fluids, ensuring the efficient transport and deposition of proppant into fissures. To improve the productivity index of hydraulic fracturing processes, better viscosifiers with a higher proppant carrying capacity and a lower potential of formation damage are needed. In this work, we report the development of a novel viscoelastic system relying on the complexation of zwitterionic octadecylamidopropyl betaine (OAPB) and diethylenetriamine (DTA) in water. At a concentration of 2 wt%, the zwitterionic complex fluid had a static viscosity of 9 to 200 poise, which could be reversibly adjusted by changing the suspension pH. The degree of pH-responsiveness ranged from 10 to 27 depending on the shear rate. At a given concentration and optimum pH value, the zwitterionic viscosifiers showed a two-orders-of-magnitude reduction in settling velocity of proppant compared to polyacrylamide solution (slickwater). By adjusting the pH between 4 and 8, the networked structure of the gel could be fully assembled and disassembled. The lack of macromolecular residues at the dissembled state can be beneficial for hydraulic fracturing application in avoiding the permeation damage issues encountered in polymer and linear-gel-based fracturing fluids. The reusability and the unnecessary permanent breakers are other important characteristics of these zwitterionic viscosifiers.

Viscosity modifying agents are one of the most critical components of hydraulic fracturing fluids, ensuring the efficient transport and deposition of proppant into fissures.