Experimental Investigation of Hydraulic Fracturing Fluid Based on Pseudo Gemini Surfactant with Polysaccharide Addition

In the last decade, hydrogels for hydraulic fracturing based on viscoelastic surfactants have been actively studied. Interest in these systems is justified by their unique qualities: good viscoelasticity and the ability to form stable suspensions of proppant or sand, destruction without the formation of bridging agents, hydrophobization of the rock surface and metal of technological equipment, as well as oil-cleaning properties. These qualities are most often provided by a minimum set of components-a surfactant and an electrolyte. However, the absence of a polymer limits the use of these gels in formations where fluid leakoff is possible. In this article, a liquid was studied, based on a pseudo gemini surfactant (PGVES) with the addition of a water-soluble polysaccharide. The objects of study were selected based on the assumption of interactions between PGVES and the polymer; interactions which favorably influence the technological characteristics of the fracturing fluid. To confirm the hypothesis, rheological studies were carried out. These included rotational viscometry and oscillatory studies at various temperatures. The settling velocity of particles of various proppant fractions was studied and tests were carried out to assess fluid leakoff. The performed experiments show an improvement in the characteristics of the PGVES-based gel under the influence of the polysaccharide. In particular, the rheological properties increase significantly, the stability of proppant suspensions improves, and the fluid leakoff of systems decreases, all of which expands the possibility of using these fracturing fluids and makes this area of experimentation promising.

Design and Properties of Natural Rosin-Based Phosphoester Functional Surfactants

As an important forestry biomass resource, rosin has a wide range of applications in medicine, adhesives, surfactants and other fields. Using natural dehydroabietic acid as a raw material, dehydroabietic acid-based phosphorus monoester (DPM) and diester (DPD) surfactants were designed and synthesized. The chemical structures and self-assembly properties were characterized by FT-IR, NMR and TEM, and the effects of pH on critical micelle concentration, γCMC, emulsifying properties, foam properties and micelle morphology were studied. The results showed that the CMC, γCMC value and aggregate morphology had certain pH responsiveness. The γCMC value under acidic conditions was smaller than γCMC under alkaline conditions, and the foaming performance and foam stability under acidic conditions were better than those under alkaline conditions. TEM micelle morphology studies have shown that DPM and DPD surfactants can self-assemble into rod-shaped and spherical micelle morphologies with a pH change in an aqueous solution. At the same pH, the foaming and emulsification properties of DPD were better than those of DPM. The best foaming and emulsification ability of DPD were 11.8 mL and 175 s, respectively. At the same time, the foaming ability of DPD is also affected by pH. DPD has excellent foaming properties in acidic conditions, but these disappeared in neutral conditions.

Advances of supramolecular interaction systems for improved oil recovery (IOR)

Improved oil recovery (IOR) includes enhanced oil recovery (EOR) and other technologies (i.e. fracturing, water injection optimization, etc.), have become important methods to increase the oil/gas production in petroleum industry. However, conventional flooding systems always encounter the problems of low efficiency, high cost and complicated synthetic procedures for harsh reservoirs conditions. In recent decades, the supramolecular interactions are introduced into IOR processes to simplify the synthetic procedures, alter their structures and properties with bespoke functionalities and responsiveness suitable for different conditions. Herein, we primarily review the fundamentals of several supramolecular interactions, including hydrophobic association, hydrogen bond, electrostatic interaction, host-guest recognition, metal-ligand coordination and dynamic covalent bond from intrinsic principles and extrinsic functions. Then, the descriptions of supramolecular interactions in IOR processes from categories and advances are focused on the following variables: polymer, surfactant, surfactant/polymer (SP) complex for EOR and viscoelasticity surfactant (VES) for clean hydraulic fracturing aspects. Finally, the field applications, challenges and prospects for supramolecular interactions in IOR processes are involved and systematically addressed. The development of supramolecular interactions can open the way toward adaptive and evolutive IOR technology, a further step towards the cost-effective production of petroleum industry.

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.

The effect of sonication on the ion exchange constant, KXBr of CTABr/chlorobenzoates micellar systems

The ion exchange constant, KXBr (for the case of cetyltrimethylammonium bromide, CTABr, in this study) is a method dependant characterization of ion exchange process by counterions, X and Br with different relative binding ratios. In this report, the ion exchange constant, KXBr values for micelle systems irradiated under 2 min of sonication at 120 W power using a probe sonicator with 1 cm tip were determined to be 85.2, 125.6 and 122.4 when X  = o-, m- and p-chlorobenzoates, respectively. The values were quantified using a semiempirical kinetic method coupled with Pseudophase Micellar model, and later compared to the same system in the absence of sonication. The sonication was found to amplify the KXBr values by ~ 13-fold for X  = o-chlorobenzoate and ~ 2.5-fold for X  = m- and p-chlorobenzoates. This is due to the improvement of ion exchange process by the oscillation of bubbles generated by acoustic cavitation. An active ion exchange process indicates better stabilization of the micelle aggregational structure by the penetration of the introduced counterions, X into the micelle Stern layer leading to the growth of the micelle. This is supported by the remarkable increase in the viscosity of the micelle system by > 7-fold for X  = o-chlorobenzoate and by > 2-folds for X  = m- and p-chlorobenzoates. Sonication was also found to induce maximum viscoelasticity at lower concentration ratio of [CTABr]:[X]. The ability of ultrasound to induce micelle growth and exhibiting viscoelasticity at lower concentration of counterionic additive will be very useful in technologies where viscoelastic solution is desired such as in oil drilling and centralized heating and cooling system.

pH-Responsive aggregates transition from spherical micelles to WLMs induced by hydrotropes based on the dynamic imine bond

In recent years, the use of dynamic chemical bonds to construct stimulus-responsive micelle systems has received increasing attention. However, current reports focus on the construction of dynamic covalent bond surfactants using dynamic chemical bonds, and the method of applying dynamic covalent bonds to hydrotropes has not been reported yet. In this study, a novel pH-responsive worm-like micelle system was constructed by mixing cetyltrimethylammonium bromide (CTAB), 4-hydroxybenzaldehyde (HB) and p-toluidine (MB) at the molar ratio of 60 mM : 40 mM : 40 mM. The formation mechanism of the dynamic covalent bond hydrotropes and the rheological behavior of the micelles were investigated via rheology, 1H-NMR spectroscopy and Cryo-TEM. The results show that as the pH increases, the viscosity of the solution first decreases and then increases rapidly. The microscopic aggregates in the solution transition from spherical micelles to worm-like micelles (WLMs), and the solution changes from a water-like fluid without viscosity to a gel system that can withstand its own weight. The transformation of the aggregates and their rheology can be attributed to the formation of MB-HB-, which is a type of hydrotrope with dynamic covalent bonds. Moreover, the transition from spherical micelles to worm-like micelles in this system is reversible.

Experimental Investigation and Performance Evaluation of Modified Viscoelastic Surfactant (VES) as a New Thickening Fracturing Fluid

In hydraulic fracturing, fracturing fluids are used to create fractures in a hydrocarbon reservoir throughout transported proppant into the fractures. The application of many fields proves that conventional fracturing fluid has the disadvantages of residue(s), which causes serious clogging of the reservoir’s formations and, thus, leads to reduce the permeability in these hydrocarbon reservoirs. The development of clean (and cost-effective) fracturing fluid is a main driver of the hydraulic fracturing process. Presently, viscoelastic surfactant (VES)-fluid is one of the most widely used fracturing fluids in the hydraulic fracturing development of unconventional reservoirs, due to its non-residue(s) characteristics. However, conventional single-chain VES-fluid has a low temperature and shear resistance. In this study, two modified VES-fluid are developed as new thickening fracturing fluids, which consist of more single-chain coupled by hydrotropes (i.e., ionic organic salts) through non-covalent interaction. This new development is achieved by the formulation of mixing long chain cationic surfactant cetyltrimethylammonium bromide (CTAB) with organic acids, which are citric acid (CA) and maleic acid (MA) at a molar ratio of (3:1) and (2:1), respectively. As an innovative approach CTAB and CA are combined to obtain a solution (i.e., CTAB-based VES-fluid) with optimal properties for fracturing and this behaviour of the CTAB-based VES-fluid is experimentally corroborated. A rheometer was used to evaluate the visco-elasticity and shear rate & temperature resistance, while sand-carrying suspension capability was investigated by measuring the settling velocity of the transported proppant in the fluid. Moreover, the gel breaking capability was investigated by determining the viscosity of broken VES-fluid after mixing with ethanol, and the degree of core damage (i.e., permeability performance) caused by VES-fluid was evaluated while using core-flooding test. The experimental results show that, at pH-value (6.17), 30 (mM) VES-fluid (i.e., CTAB-CA) possesses the highest visco-elasticity as the apparent viscosity at zero shear-rate reached nearly to 106 (mPa·s). Moreover, the apparent viscosity of the 30 (mM) CTAB-CA VES-fluid remains 60 (mPa·s) at (90 ∘C) and 170 (s−1) after shearing for 2-h, indicating that CTAB-CA fluid has excellent temperature and shear resistance. Furthermore, excellent sand suspension and gel breaking ability of 30 (mM) CTAB-CA VES-fluid at 90 (∘C) was shown; as the sand suspension velocity is 1.67 (mm/s) and complete gel breaking was achieved within 2 h after mixing with the ethanol at the ratio of 10:1. The core flooding experiments indicate that the core damage rate caused by the CTAB-CA VES-fluid is (7.99%), which indicate that it does not cause much damage. Based on the experimental results, it is expected that CTAB-CA VES-fluid under high-temperature will make the proposed new VES-fluid an attractive thickening fracturing fluid.

Effects of sodium chloride on rheological behaviour of the gemini-like surfactants

The gemini-like surfactants have been constructed by compounding N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and o-phthalic acid (o-PA), m-phthalic acid (m-PA), or p-phthalic acid (p-PA), and are denoted as o-EAPA, m-EAPA, and p-EAPA, respectively. It is well known that inorganic salts have significant effects on surfactant aggregates, and herein the effects of sodium chloride (NaCl) on gemini-like surfactants is explored by rheological and dynamic light scattering measurements, and cryo-TEM. It is found that the viscoelasticity of the EAPA systems first increases and then decreases with an increase of the NaCl concentration. And the optimal NaCl concentrations for these three systems are in the order of o-EAPA < m-EAPA < p-EAPA due to different spacer distances between the two carboxyl groups in the phthalic acid. Similar trends in the N,N-dimethyl oleoaminde-propylamine (DOAPA) and o-PA, m-PA, or p-PA systems were also observed. The results show that an appropriate NaCl concentration will promote gemini-like surfactants to form wormlike micelles (WLMs). Upon further increasing the NaCl concentration, the WLMs transform into vesicles. Excessive NaCl concentration will cause the surfactant systems to reach their cloud point and make the surfactants precipitate out. The mechanism of the effects of NaCl is that Cl- reduces the electrostatic repulsion between the headgroups of the surfactants. This work is helpful in understanding the effects of inorganic salts on the surfactants and this study is useful for exploring the practical applications of gemini-like surfactants.

Probing the Formation of Wormlike Micelles Formed by Cationic Surfactant with Chlorobenzoate Derivatives

The energy released when tetradecyltrimethylammonium bromide (C₁₄TAB) is combined with different derivatives of chlorobenzoates in an isothermal titration calorimeter (ITC) allows a direct evaluation of the spontaneity of the threading of the aromatic anions into the micellar palisade. The comparison between the enthalpimetric curves with the ones for viscosity of the solutions, hydrodynamic radii of the aggregates (dynamic light scattering experiments), and the fraction of aromatic anions incorporated (diffusion-ordered spectroscopy experiments) allows the establishment of the variations of enthalpy with formation, growth, and decrease of the wormlike micelles (WLMs). The formation of WLMs with C₁₄TAB is very favored (very exothermic) for titrations of chlorobenzoate derivatives which present the chlorine atom in positions 3 or 4 of the aromatic ring. However, the aggregation is highly unfavorable if chlorine is at position 2 of chlorobenzoate. According to the results, the high potential of the ITC to determine critical concentrations and the energies associated with the aggregation of a cationic surfactant and aromatic anions for the formation of WLMs was demonstrated.

pH-Switchable IFT variations and emulsions based on the dynamic noncovalent surfactant/salt assembly at the water/oil interface

Additional HCl can facilely control the dynamic noncovalent interaction between anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and additional organic matter, 4,4'-oxydianiline (ODA), at the water/oil interface. At low HCl concentration (ODA/HCl molar ratio (r) = 1 : 1.5, [ODA] = 250 mg L-1), the ODA+ ions effectively enhanced the SDBS ability to reduce the water/oil interfacial tension (IFT) by about two orders of magnitude, while the (SDBS)2/ODA2+ gemini-like surfactants could be constructed at a relatively high HCl concentration (r = 1 : 4, [ODA] = 250 mg L-1), which could largely reduce the IFT to 1.19 × 10-3 mN m-1. Molecular simulation was employed to explore the interfacial activity of ODAn+ (ODA+/ODA2+) ions and the SDBS/ODAn+ interaction. The control experiments used another three surfactants to verify the proposed model. The pH-switchable gradual protonation of amino groups in ODA molecules determined the SDBS/ODA interfacial assembly, which was responsible for the reversal of IFT variations and the related emulsion behaviors.

Study on the effect of the organic acid structure on the rheological behavior and aggregate transformation of a pH-responsive wormlike micelle system

A worm-like micelle (WLM) system can be obtained by mixing long-chain cationic surfactants and polybasic organic acids in an aqueous solution. However, the effect of different organic acid structures on the rheological behavior of WLM systems has not been researched. Herein, a novel pH-responsive wormlike micelle system (EATA) was constructed by the complexation of N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and benzene tricarboxylic acid (TA) at a molar ratio of 3 : 1. UC22AMPM/citric acid (EACA) was also prepared to perform a comparison. The rheological behavior, aggregate transformation and thickening mechanism of EATA solutions were investigated by using rheological measurements, cryo-TEM, DLS, surface tension and 1H NMR. The results show that, at low pH, spherical micelles were formed and the EATA solution exhibited a lower viscosity than the EACA system due to the strong hydrophobicity of the phenyl groups of TA molecules, but the viscosity reaches 106 mP s at pH 4.80. Because of the lower pKa value of TA than CA, the viscosity of the EATA system drops sharply with the appearance of precipitates caused by the isoelectric point when the pH is greater than 4.80. In addition, by circularly changing the pH value several times, the wormlike micelles could maintain their original viscoelasticity without being weakened in the slightest.

Responsive morphology transition from micelles to vesicles based on dynamic covalent surfactants

A dynamic covalent bond is widely used to fabricate stimuli responsive systems due to its reversible molecular recognition properties. In this study, we developed a pH-responsive morphology transition system based on a mixture of a cationic surfactant CTAB and two nonamphiphilic precursors, 4-hydroxybenzaldehyde (HB) and octylamine (OA), at a molar ratio of 100 : 60 : 60 (CTAB/HB/OA). The morphology transition of CTAB/HB/OA was characterized by 1H NMR spectroscopy, Fourier transform infrared spectroscopy, macroscopic appearance observation, dynamic light scattering, and rheological and cryo-TEM measurements. The phase behavior of CTAB/HB/OA solutions underwent transition from a water-like fluid to a transparent gel-like solution and then converted into a turbid low-viscosity solution upon increasing the pH. Upon increasing the pH from 4.93 to 7.99, the morphology was transformed from spherical micelles to wormlike micelles. Upon further increasing the pH to 12.02, the wormlike micelles gradually disappeared with the formation of vesicles. Thus, a morphology transition from micelles to vesicles can be triggered by varying the pH of CTAB/HB/OA solutions. This drastic variation in morphology behavior was attributed to the pH dependent ionization and formation of the anionic surfactant HB-OA-. Besides, over 3 cycles of morphological alternation among spherical micelles, wormlike micelles and vesicles of the CTAB/HB/OA solutions can be obtained by adjusting the pH.

Ion-selective molecular inclusion of organic dyes into pH-responsive gel assemblies of zwitterionic surfactants

The pH-Responsive sol–gel transition of a surfactant gel took place along with ion-selective capture and release of dye molecules.

A responsive anionic wormlike micelle using pH-directed release of stored sodium based on polybasic acids

Responsive wormlike micelles are very useful in a number of applications, whereas it is still challenging to create dramatic viscosity changes in anionic surfactant systems. Here a differential pH-responsive wormlike micelle based on sulfonic surfactants was developed, which is formed by mixing sodium dodecyl trioxyethylene sulphate (SDES) and ethylenediaminetetraacetic acid tetrasodium (EDTA4-·4Na+) at the molar ratio of 1 : 1. The phase behavior, aggregate microstructure and viscoelasticity of the SDES/EDTA4-·4Na+ solution were investigated via macroscopic observation, cryo-TEM and rheological measurements. It was found that the phase behavior of the SDES/EDTA4-·4Na+ solution undergoes transitions from a water-like fluid to viscoelastic upon decreasing the pH. On decreasing the pH from 12.01 to 3.27 by adding HCl, the viscosity of the transparent solutions with wormlike micelles was increased rapidly and reached ∼3100 mPa s. Furthermore, on increasing the pH by adding NaOH, the viscosity was slightly increased due to the addition of Na+. However, the increase in the concentration of Na+ is much smaller than the theoretical addition. The same phenomenon was noted in the sodium citrate solution, but does not exist in the sodium formate system. The viscosity of the micellar solution has a sensitive response to inorganic acids and tolerance to inorganic bases due to the characteristics of polybasic acids.

Rheological behavior and mechanism of pH-responsive wormlike micelle variations induced by isomers of phthalic acid

Responsive wormlike micelles (WLMs) constructed by different carboxylic acids are fascinating. However, it is unknown how the position of the carboxylic groups alters the stimuli-response of wormlike micellar systems. Herein, three pH-responsive WLMs based on Gemini-like surfactants (named o-EAPA, m-EAPA, and p-EAPA) were formed and studied through the complexation of N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and o-phthalic acid (o-PA), m-phthalic acid (m-PA), or p-phthalic acid (p-PA) at the molar ratio of 2 : 1. The viscoelasticity, phase behavior and aggregate microstructure were separately explored by rheological, appearance observation and cryo-TEM methods. The results show that all phthalic acids can protonate UC22AMPM, thereby forming WLMs. However, with the shorter spacer distance between two carboxyl groups in phthalic acid, o-EAPA exhibits the longer length scale of aggregates and a more efficient thickening ability compared to the other two systems. Similar results in the N,N-dimethyl oleoaminde-propylamine (DOAPA) and o-PA, m-PA, and p-PA systems further verify the applicability of this mechanism. Furthermore, the phthalic acid based WLMs are found to exhibit intriguing reversible pH-responsive behaviors, which include promptly switching between a high elastic system and a low viscosity fluid by pH control. The o-EAPA system possesses a larger viscosity maximum, which produces more precipitous viscosity changes as the pH varies. This study is beneficial for the formation of pH-responsive WLMs and to determine their advantages for applications.