Viscoelastic Surfactant Fluids Research Articles

Performance evaluation and formation mechanism of Janus-SiO2 nanoparticles assisted viscoelastic surfactant fracturing fluids

The eco-friendly viscoelastic surfactant (VES) system, whose viscoelasticity can be enhanced by nanoparticles (NPs), is an appropriate substitute for polymer fracturing fluid. In the present study, the JA12C NPs (Janus SiO2 nanoparticles decorated with dodecyl hydrophobic carbon chain) are successfully synthesized and characterized by Fourier transform infrared spectra (FTIR), thermal gravimetric analysis (TGA), dynamic light scattering (DLS), and transmission electron microscope (TEM). The prepared JA12C NPs are separately induced into three kinds of fracturing fluids (anionic-based VES (aVES), cationic-based VES (cVES), and zwitterionic-based VES (zVES) fluids) to investigate their effects on the rheological properties of various VES fluids. It is found that additional JA12C NPs significantly enhance the viscoelasticity of cVES fluid, while hardly affecting that of aVES and zVES fluids. Then the zeta potential of mixed JA12C/surfactant dispersions and the rheological parameters of diverse VES systems are measured to explore the interaction mechanism of wormlike micelles (WLMs)/JA12C mixture. It is believed that the intensive hydrophobic interaction and the moderate electrostatic repulsion between WLMs and JA12C should be responsible for the visibly enhanced viscoelasticity of JA12C-assisted cVES (cJAVES) fluid. This work suggests the feasibility of using Janus NPs to enhance the tolerance properties of VES fluids in harsh conditions, which fills the gap in the applications of VES fracturing fluids incorporating Janus NPs.

Rheology, viscoelasticity and microstructural properties of OAPB-SDS mixtures at different temperature and pH conditions

Viscoelastic surfactant (VES) fluids are widely used in the hydraulic fracturing process to increase oil and gas productivity. Zwitterionic (carbon-18) surfactant solution, which is commonly used in VES fluids, has high critical micelle concentration, resulting in high used concentration and lack of economy. Furthermore, it is not applicable to high-temperature conditions. The oleylamidopropyl betaine (OAPB, carbon-25) with longer carbon chain has lower critical micelle concentration (CMC) and better high temperature resistance. In addition, it behaves better viscosity increasing capacity combining with anionic sodium dodecyl sulfate (SDS) surfactant. In this study, the viscoelasticity and microstructural properties of OAPB-SDS (OADS) mixtures at different temperature and pH conditions were investigated deeply. Rheology and structural morphology properties of the OADS mixed fluids were investigated by rheometer, and transmission electron cryo-microscopy. The results showed that OADS solution demonstrated elastic gel-like fluid behavior with zero shear viscosity of 3.5 × 106 mPa.s at neutral pH and room temperature, while OAPB solution demonstrated viscous fluid behavior with zero shear viscosity (ηo) of 62 mPa.s. The viscoelasticity and microstructural properties of OADS solution were influenced by concentration, pH and temperature. It was gel-like fluid at 25–40 °C, viscoelastic fluid at 60–80 °C and totally viscous fluid at 90 °C. The OADS was viscous at 0.5 wt% concentration, viscoelastic at 0.6 wt% concentration and elastic at 0.75 wt% concentration. The OADS solution showed viscous, viscoelastic and elastic behaviors at pH value of 3, 4, and 7 respectively. The fluid exhibited viscosity switch ability by reversibly altering pH values. The Cryo-TEM images confirmed that the OADS micelle experience microstructural transformed from long wormlike micelles (WLMs) to spherical micelles as the pH changes. The mixture fluid improved viscoelastic and aggregation properties than that of individual surfactant component, possessing lower used surfactant concentration. This study is useful in understanding the properties of mixed zwitterionic-anionic fluids, which is thermo-pH responsive, valuable in the fracturing.

Smart Fluids and Their Applications in Drilling Fluids to Meet Drilling Technical Challenges

This article presents extensive analysis and review on recent developments in smart fluids as well as future opportunities of smart drilling fluids utilization in oil and gas well drilling while focusing on the following smart fluids: smart nanoparticles, electrorheological, magnetorheological, and viscoelastic surfactant (VES) fluids. The distinctive properties of nanoparticles such as tiny particle sizes, high specific surface area, mechanical strength, and thermal stability make them suitable for utilization in drilling fluids. In bentonite water-based drilling fluid systems, this review suggests that charged nanoparticles are capable of displacing exchangeable ions in between bentonite clay platelets, thereby forming intercalates which can interact with clay surfaces through electrostatic attraction or repulsion. In improving wellbore stability, it is presented in this review that nanoparticles are able to invade and plug ultratiny pore spaces in shale formations, thereby further enhancing shale formations’ mechanical strength and wellbore stability. According to this review, the magnitude of changes in properties of smart electrorheological and magnetorheological fluids largely depends on the intensity of applied electric and magnetic fields. The intensity of smart fluids properties alteration due to applied field would equally depend on wt.% concentration and chemical compositions of particles susceptible to electric and magnetic fields. Based on review carried out on VES smart fluids, attractive and repulsive forces in the smart VES fluids solution result in the formation of micelles which can cause changes in viscoelastic property of the formulated smart viscoelastic fluids. The more the concentration of charged ions in the base fluid which VES fluids come in contact with, the higher the viscoelasticity of the smart VES fluids. According to this review, utilization of smart materials in drilling fluids can result in meeting oil and gas well drilling technical challenges including enhancing wellbore stability, improving hole cleaning performance, lost circulation control, fluid loss control, enhancing rate of penetration, pressure drop control, and easing cutting carrying efficiency of drilling fluids. This review equally suggests that the utilization of smart fluids such as smart magnetorheological and electrorheological fluids would facilitate drilling automation and real-time data acquisition processes, which is the future technology in oil and gas drilling.

Enhancing the Oil Recovery from Naturally Fractured Reservoirs Using Viscoelastic Surfactant (VES) Flooding: A Field-Scale Simulation.

A viscoelastic surfactant (VES) has the combined properties of a surfactant and a polymer. Injection of VES fluids into naturally fractured reservoirs (NFRs) can control the mobility of the injected fluid and enhance the total oil recovery. This paper presents a field-scale simulation to evaluate the performance of a noble VES fluid in enhancing the oil recovery from a naturally fractured reservoir. In this work, the results of coreflooding, computerized tomography (CT)-scan, rheology, interfacial tension (IFT), and adsorption measurements were used to build and calibrate a lab-scale model. Thereafter, a chemical enhanced oil recovery (EOR) modeling simulator developed by a computer modeling group (CMG-STARS) was used to build a field-scale simulation. Real seismic data, permeability and porosity distributions, and operating conditions were utilized to develop and evaluate the simulation model. The results show that VES can outperform the surfactant-polymer (SP) flooding and waterflooding in NFRs; VES improved the oil recovery by 10% and reduced the water cut by 47%, at the same conditions. VES reduced the IFT by two orders of magnitude (100 times) compared to waterflooding. Also, VES altered the rock wettability to a more water-wet status, leading to reduce the relative permeability to water (Krw) by a factor of 10, on average. Finally, the simulation study indicated that applying waterflooding after VES flooding leads to a minor increase in the oil recovery. Overall, this study provides a detailed comparison between VES flooding, SP flooding, and conventional waterflooding in NFRs. Sensitivity analysis was performed to study the impact of treatment parameters on the oil recovery from naturally fractured reservoirs. Using actual NFR data, the optimum VES flooding was determined, which will help in conducting VES flooding for real EOR operations.

Impact assessment of nanoparticles on microstructure and rheological behaviour of VES fracturing fluid formulated with mixed surfactant system

The nature and type of fracturing fluid play a vital role in a successful hydraulic fracturing job. The desired fracturing fluid should have non-damaging characteristics and an effective proppant carrying capacity. Though viscoelastic surfactant (VES) fluid has started to replace the polymer-based fluids for the fracturing of specific formations owing to its non-damaging characteristics; however, its wider application to high-temperature formation is still a challenge to the operators. Incorporation of nanoparticle has been able to extent the thermal stability of VES fluid. The current study examined the impacts of different nanoparticles at different concentrations on rheological and structural properties of VES fluid prepared from mixed surfactant system which is composed of NaOA/tween 80, Co-surfactant, oil and water. Nano-enhanced VES fluids were formulated using SiO2, Fe2O3, MgO, and ZnO nanoparticles at varied concentrations, ranging from 250 ppm to 1000 ppm. The rheological and morphological variations of VES fluids were studied at different shear rates and temperatures. MgO and Fe2O3 enhanced VES at 500 ppm concentration fluid showed excellent rheological characteristics with 3529 cp and 2817 cp viscosity at a shear rate of 100 S−1, temperature 35 °C, which is much above the required viscosity value. Zeta potential and surface area of nanoparticles both play an important role in the rheological enhancement of VES fluid. MgO enhanced VES fluid with a surface area (83.7 m2/g) and zeta potential (−15.9, mV) of MgO nanoparticles showed better rheological properties than silica enhanced VES gel with surface area (127.8 m2/g) and zeta potential (–33.8, mV). It was also observed that increasing the nanoparticle concentration improved VES fluid's rheological properties; however, the rate of increment decreased after 500 ppm concentration. The cryo-FESEM images clearly indicate the distict change in the lamellar structure of VES fluids on the addition of nanoparticles compared to that of in its absence. The dynamic rheology tests further confirmed the compact structure and stronger entanglement of micelles in the presence of nanoparticles.All the developed nano-enhanced VES fracturing fluids showed desired viscosity up to the temperature of 150 °C. Among all nano-enhanced fracturing fluid, MgO enhanced VES fracturing fluid showed excellent viscosity (i.e., 200 cP) with respect to time at 100 °C temperature and a shear rate of 100 S−1. All the nano-enhanced VES fluid was miscible with formation water & there were no residues observed. A static column test was also done to check the proppant carrying capacity of VES gel. The MgO enhanced VES gel has also showed lowest proppant settling velocity of 0.305 cm/min which is much lower than the maximum permissible proppant settling velocity of 5 cm/min. The findings of this study can help for a better understanding of nano-enhanced VES fracturing fluid in mitigating the constraints associated with hydraulic fracturing jobs in formation with high temperatures. Thus, the knowledge about the functional characteristics of different nanoparticles in enhancing the fracturing fluid properties will help us to select suitable nanoparticle-surfactant combinations for a particular field.

Organic Acid-Enhanced Viscoelastic Surfactant and Its Application in Fracturing Fluids

Viscoelastic surfactant (VES) fracturing fluids, with the advantages of low residues, complete gel breaking, and low formation damage, have received considerable attention in hydraulic fracturing techniques. However, the complicated synthesis process and high costs limit the widespread application of VESs. Herein, a VES fracturing fluid composed of wormlike micelles was developed by coupling an ultralong hydrophobic chain surfactant N-erucamidopropyl-N,N-dimethylamine (EA), with p-phthalic acid (p-PA), which behaved as a “Gemini-like” surfactant via noncovalent interactions. The macroscopic appearance and viscosity of this fluid were responsive to the regulation of pH values. Then, the related fracturing performance of this fluid was systematically investigated, from which it could be concluded that the VES fluid exhibited good temperature and shear resistance, excellent proppant-carrying and gel-breaking abilities and also caused less damage to core permeability and low corrosion of steel under acidic conditions. Finally, the rheological properties of the VES fluid could be switched multiple times without any decay by changing the pH values, indicating its excellent reusability for fracturing procedures. Consequently, this study demonstrates potential applications of reusable VES fracturing fluids based on supramolecular pH-responsive surfactants.

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.

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.

Development of Selective Acidizing Technology for an Oil Field in the Zechstein Main Dolomite

This paper presents laboratory studies based on which a stimulation technology for an oil field located in the Zechstein Main Dolomite was investigated. A large number of oil wells in the Main Dolomite produce significant amounts of reservoir water. Matrix acidizing using conventional acid solutions in such wells has caused a significant increase in water cut, because of their affinity for water. The purpose of this cooperation between the Oil and Gas Institute–NRI and the Brenntag Polska was to develop an acid treatment technology that would not increase the water cut after acidizing treatment in wells where oil production is accompanied by the production of reservoir water. Therefore, a series of tests were performed, including the selection of a suitable viscoelastic surfactant that was sensitive to crude oil. The contact of the gel of the viscoelastic surfactant fluid with crude oil resulted in the reduction of its viscosity The tests described herein include dissolution/dispersion tests, rheological tests, acid sludge tests, compatibility tests, core flow experiments, and corrosion tests, which allowed recipes to be developed for the preflush, diverter, and acidizing liquid. Then, recommendations were established for using these liquids in matrix acid treatment. A series of treatments performed according to this technology allowed the removal of near-wellbore damage without increasing the water cut.

Evaluating the changes of sorption and diffusion behaviors of Illinois coal with various water-based fracturing fluid treatments

The water-based fracturing stimulation is commonly used for low permeability coalbed methane (CBM) reservoirs. The influence of various fracturing fluids on the gas sorption and diffusion behaviors were experimentally studied in the work. The Illinois basin coal was selected for the experimental measurements. We used slickwater, guar gel and viscoelastic surfactant (VES) fracturing fluids to treat the coal. The sorption and diffusion behaviors were measured and quantified by the volumetric sorption experiments. The microscope was employed for the coal sample surface observation to qualitatively characterize the coating and residue behavior of fracturing fluids. It was found that all types of fracturing fluids can significantly influence the gas sorption capacity of coal. Apart from the low concentration of polyacrylamide (0.1% and 0.3%) slickwater, all other fracking fluids damage the gas sorption capacity. For most fracturing fluids, the sorption capacity can be recovered closely back to its virgin coal condition with extensive water washing. For the coal samples treated by the VES fracturing fluid, both the Langmuir volume and Langmuir pressure were dramatically increased. The adverse effect of fracturing fluids on coal is apparent and all diffusion coefficients decrease with the treatment. Even with extensive washing, the diffusion coefficient cannot recover for slickwater and VES fluids. But guar gel fluid has the best diffusion recovery because of the easy removal of the guar gel. This study provides a preliminary data set for fracturing fluid selection for Illinois coal in terms of sorption and diffusion.

Effects of moving contact line on filament pinch-off dynamics of viscoelastic surfactant fluids

Experiments illustrate that the moving fluid contact line can significantly affect the extensional rheology of viscoelastic surfactant solutions. A scaling analysis is provided to rationalize the effects of contact-line spreading on extensional rheology of viscoelastic fluids.

Application of pH‐Responsive Viscoelastic Surfactant as Recyclable Fluid at High Temperature

AbstractA pH‐responsive amphiphilic surfactant stearic amide 3‐(N,N‐dimethylamino)propylamide (SAA) was synthesized and served as a thickener in aqueous solution to construct a switchable viscoelastic surfactant fluid (VES fluid). The structure of SAA was studied by 1H NMR, and the viscoelastic behavior of VES fluid was studied in detail by rheological measurements. The viscosity of this VES fluid can be switched reversibly from low to high immediately by adjusting system pH value. Even at high shear rate (170 s−1) and high temperature (90 °C), excellent viscoelastic behavior of this VES fluid can be observed, which is a key performance for fracturing applications. Meanwhile, the recycled VES fluid can still maintain good pH‐responsive behavior even after more than three cycles. These unique performances of this VES fluid not only enhanced our understanding of the transformation of wormlike micelles at high temperature, but also enriched a large potential of VES fracturing fluid in the development of oil and gas reservoirs.

Reduction of clean fracturing fluid filtration loss by viscosity enhancement using nanoparticles: Is it feasible?

Fracturing fluid filtration loss is a significant research topic related to fracture propagation, formation damage and the cost of hydraulic fracturing. To reduce the loss, nanoparticles have been used to enhance the fracturing fluid properties such as viscosity and well-building ability. In this work, silica nanoparticles (NPs) with different concentrations (0, 0.01, 0.03 wt%) were added into the viscoelastic surfactant (VES) fluid composed of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal). A micro pore-throat structure was applied to investigate the flow characteristics of those three fracturing fluids with Deborah numbers (De) spanning from 1.52 to 73.2, and a Newtonian fluid was set as the control group. It was found that the flow patterns of VES solutions performed as the convergent flow similar to those of the Newtonian fluid at upstream, and turned into divergent flow with the gathering of streamlines at downstream. Surprisingly, the flow characteristics between VES solution with no nanoparticles and nanoparticle-enhanced the VES solution showed an insignificant difference with high flow rates (5 and 20 ml/h). The nanoparticle was unable to enhance or influence the properties of VES fluid when flowing through convergence–divergence and divergence–convergence structure. Neither the breakage nor the recombination of wormlike micellar were barely affected by the nanoparticle.

A smart recyclable VES fluid for high temperature and high pressure fracturing

The visco-elastic surfactant (VES) fluid has acquired great attention in the development of tight oil & gas reservoir due to low damage to the formation. However, the high cost and undesirable viscosity reduction at high temperature have seriously restricted the development of the VES fluids. In this paper, a functional VES fracturing fluid with good viscoelastic switchability under high temperature and high pressure was designed and constructed by CO2 responsive surfactant, erucamidopropyl dimethylamine (abbreviated as EA). It was interestingly found that this VES fluid can exhibits excellent rheological properties even at high temperatures in the presence of supercritical CO2 or CO2, and the rheological property can be reclaimed more than three times without reduction. The shear viscosity of 4 wt% EA + NaSal solution under 120 °C can meet the requirement of fracturing application in presence of CO2 pressure, and it is significantly rare in the literature where the surfactant solution is capable of withstanding such temperature. Cryogenic scanning electron microscopy (cryo-SEM) was used to study the aggregation structure. The self-assembly mode and the self-healing mechanism of this VES fluid was proposed to further understand its mechanism from the molecular level. The results of tests demonstrate that this functional VES fluid provides potential in the application of smart VES fracturing fluid.

Flow Patterns of Viscoelastic Fracture Fluids in Porous Media: Influence of Pore-Throat Structures.

Viscoelastic surfactant (VES) fluid and hydrolyzed polyacryamide (HPAM) solution are two of the most common fracturing fluids used in the hydraulic fracturing development of unconventional reservoirs. The filtration of fracturing fluids in porous media is mainly determined by the flow patterns in pore-throat structures. In this paper, three different microdevices analogue of porous media allow access to a large range of Deborah number (De) and concomitantly low Reynolds number (Re). Continuous pore-throat structures were applied to study the feedback effect of downstream structure on upstream flow of VES fluid and HPAM solution with Deborah (De) number from 1.11 to 146.4. In the infinite straight channel, flow patterns between VES fluids and HPAM solution were similar. However, as pore length shortened to 800 μm, flow field of VES fluid exhibited the triangle shape with double-peaks velocity patterns. The flow field of HPAM solution presented stable and centralized streamlines when Re was larger than 4.29 × 10−2. Additionally, when the pore length was further shortened to 400 μm, double-peaks velocity patterns were vanished for VES fluid and the stable convergent flow characteristic of HPAM solution was observed with all flow rates.

Cryogenic viscoelastic surfactant fluids: Fabrication and application in a subzero environment

HypothesisCurrent viscoelastic surfactant (VES) aqueous solutions quickly freeze and thus, lose their viscoelasticity and flowability at subzero temperatures, limiting their practical use in cold environments. Therefore, it is highly desirable to develop cryo-VES fluids with freezing point far below 0 °C. Since addition of alcohol antifreeze greatly reduces the freezing point of water, cryo-VES fluids might be generated in the presence of alcohols. ExperimentsThe self-assembly behavior of a C22-tailed surfactant, erucyl dimethyl amidopropyl betaine (EDAB), in eight alcohol/water cosolvents from 20 to −20 °C was studied by pyrene fluorescent probe, cryo-TEM imaging and cryo-SNAS characterization, and the solution properties of the mixtures were investigated by rheological test. FindingsIt is found that the alcohol molecular structure, content and temperature play crucial roles dominating EDAB self-assembly behavior. Monohydric alcohols are unfavorable for micelles formation and growth, thus VES fluids cannot be obtained in the presence of 50 vol% monohydric alcohols even at subfreezing temperatures. On the contrary, dihydric and trihydric alcohols with short alkyl chain show less negative effect on EDAB micellization. Thus, cryo-VES fluids can be formed in the presence of 50 vol% ethylene glycol, 1,3-propanediol or glycerol due to the formation of wormlike micelles. These cryo-VES fluids with different alcohols exhibit different temperature-sensitivity and rheological properties, furnishing them with potential applications in anti-freeze hydraulic fracking fluids and aircraft deicing/anti-icing fluids.

A novel CO2 and pressure responsive viscoelastic surfactant fluid for fracturing

Hydraulic fracturing is playing a more and more important role in rapid shale oil and gas recovery development. Meanwhile, damage to the reservoir fracture and environmental contamination caused by fracturing fluid flowback water has raised serious concerns. In this study, a CO2-responsive surfactant, erucamidopropyl dimethylamine (EA), was synthesized and used as the thickening agent to develop a novel viscoelastic surfactant (VES)-based fracturing fluid. This fluid was responsive to the presence and pressure of CO2. It was not only rock formation friendly and environment benign but also readily reusable attributed to a gelling-breaking process that can be easily controlled by manipulating CO2 gas conditions. The viscoelastic behaviors of this VES fluid were investigated through rheological measurements under ambient and elevated temperature and pressure. The fluid-rock interaction was studied in core flooding tests. Results showed a good CO2-responsiveness, switchable viscoelastic performance, high shear tolerance, thermal stability, good salinity tolerance, and low core damage of the fluid. The switchable rheological behavior implies this fracturing fluid can readily be reused. It is expected that this fluid finds applications not only in enhanced oil and gas recovery, but also in other areas such as CO2 sequestration reservoir leakage sealing.

Flow of viscoelastic surfactants through porous media

We compare the flow behavior of viscoelastic surfactant (VES) solutions and Newtonian fluids through two different model porous media having similar permeability: (a) a 3D random packed bed and (b) a microchannel with a periodically spaced pillars. The former provides much larger flow resistance at the same apparent shear rate compared to the latter. The flow profile in the 3D packed bed cannot be observed since it is a closed system. However, visualization of the flow profile in the microchannel shows strong spatial and temporal flow instabilities in VES fluids appear above a critical shear rate. The onset of such elastic instabilities correlates to the flow rate where increased flow resistance is observed. The elastic instabilities are attributed to the formation of transient shear induced structures. The experiments provide a detailed insight into the complex interplay between the pore scale geometry and rheology of VES in the creeping flow regime. © 2017 American Institute of Chemical Engineers AIChE J, 64: 773–781, 2018

Nanoparticle-Enhanced Hydraulic-Fracturing Fluids: A Review

Summary Hydraulic-fracturing fluids are used to break down subterranean formations where oil and gas are trapped. Pad or prepad fluids are first pumped into the formation to generate the fracture geometry. Once the fracture geometry is created, additional fluid containing proppant is used to transport these solid particles into the fractures. Then, the hydraulic pressure is released and the fracture will tend to close. At that stage, the proppant prevents fracture closure and provides a conductive channel for hydrocarbons to flow into the wellbore. Biopolymers, synthetic polymers, foams, viscoelastic surfactant (VES) fluids, and slickwater are all used as fracturing fluids, each with properties that are beneficial under certain conditions. Today, their formulations are well-developed, and more recently, may incorporate small-sized particles in the nanometer size range. Such nanoparticles have addressed certain technological limitations of fracturing fluids. For example, VES fluids were reported to suffer high leakoff rates in moderate permeability reservoirs (200 md) and were limited in temperature (beyond approximately 220°F, viscosity was diminished significantly). Another challenge is the pressure-dependent behavior of borate-crosslinked gels, where the viscosity was found to drop significantly under high pressures. Also, in high-temperature reservoirs (>350°F), it is very challenging to design a fluid that can sustain enough viscosity for a required period of time. Synthetic polymers (mainly acrylamide-based polymers) are commonly used and have been reported to be used at high concentrations. These high-concentration requirements are imposed by the need for a stable viscosity under high-temperature conditions. High polymer loading increases the potential of formation damage caused by the fluid residue. These challenges, which can be addressed by nanotechnology, could have a major impact on hydraulic-fracturing applications. For instance, the working temperature limit of VES-based fluids was improved from 200 to 250°F (93 to 121°C) by adding zinc oxide (ZnO) and magnesium oxide (MgO) nanoparticles. The borate-crosslinked gels were found to maintain their viscosity at pressures up to 20,000 psi when using boronic acid-functionalized nanolatex silica particles as crosslinkers, while under such high pressures, conventional borate crosslinkers showed more than 80% reduction in viscosity. Moreover, the rheological properties of mixed VES/polymer fluids were enhanced when using nanoparticles. Use of foams can reduce the amount of water consumed in hydraulic fracturing. Alfa olefin sulfonate (AOS) surfactant can be foamed by use of carbon dioxide (CO2). Aluminum oxide nanoparticles were found to stabilize the foams created by AOS, VES, and CO2. This has a potential application in waterless fracturing. This review paper will capture all of these aspects and summarize the most recent experience of nanoparticle usage in hydraulic-fracturing fluids design.

EFFECTS OF NANOPARTICLES AND SURFACTANT CHARGE GROUPS ON THE PROPERTIES OF VES GEL

Abstract - Application of viscoelastic surfactant (VES) fluids in hydraulic fracturing is still in the development stage, though shear thinning behavior and water solubility are the two important characteristics behind increasing interest in their use in fracturing jobs. Effects of ionic characteristics and the concentration of different surfactants on the rheological properties of VES fluid have been investigated in detail in the present study for a number of surfactant systems. Phase behavior of the system was studied and the gel region was identified. Effects of alkali on the viscosity, thermal stability, and miscibility (in water) of the developed gel were also investigated. Dynamic rheological study was carried out to determine the storage modulus and loss modulus. This study shows that mixed anionic-anionic system gives improved rheology compared to single anionic and mixed anionic-zwitterionic surfactant systems. Keywords : Hydraulic Fracturing; Viscoelastic gel; Surfactant based fluids; Rheology; Nanoparticles.