A detailed study has been done on the phase behavior and rheologic al properties of Viscoelastic Surfactant (VES) bas ed fracturing fluids bearing lamellar liquid crystal structures that are developed from two surfactants (S DS and NaOA ) and three c o-surfactants (propan-2-ol, iso-amyl alcohol and 2-ethyl hexanol) in t he presence of clove oil as the organic phase and water as the aqueous phase. Lamellar liquid c rystals prepared from NaOA/2-ethyl hex anol/clove oil/water system demonstrated the best viscoelastic properties among all the developed fluids as it exhibited resistance to high temperature and shear conditions. Addition of alkali and nano-particles enhanced t he viscoelastic properties which were observed from static and dynamic rheological tests.
The rheological properties of viscoelastic surfactant (VES)-based gels prepared from a single surfactant (sodium lauryl sulfate) and mixed surfactants (cocamidopropyl betaine and sodium lauryl sulfate) are characterized and interpreted in detail with the addition of alkali. The phase diagrams were prepared to identify the gel region. These were pseudoplastic fluids with shear-thinning nature. VES fluids prepared from mixed surfactants consisting of cocamidopropyl betaine and sodium lauryl sulfate presented better rheology as analyzed. The effect of the addition of nanoparticles to this system was also studied in detail for enhancement of the thermal stability. A dynamic rheology test was also conducted to show enhancement of the storage and loss modulus with the addition of alkali and nanoparticles. A miscibility test was conducted to show the miscibility of the prepared gel with oil and water because it is one of the properties of fracturing fluid used to clean the postfractured formation.
Mixed surfactant systems have gained significant importance in the development of fracturing fluid due to polymorphism of self-assembly structures that have combined properties of the surfactants in the mixture. In this article, a comparative study on the phase behavior and viscoelastic properties of mixed surfactant based fluids, prepared from Tween 801NaOA/2-ethyl hexanol/clove oil/water and Tween 201NaOA/2-ethyl hexanol/clove oil/water quaternary system is investigated in details. The viscoelastic surfactant (VES) based fluids prepared from the former system offered superior rheological properties than the latter system. The addition of 0.1% NaOH and 500 ppm ZnO nano-particles in the VES fluids presented enhanced viscoelastic properties as concluded by static and dynamic rheological tests. Miscibility test indicated the miscibility of the VES fluids with water, unlike in the presence of diesel oil and satisfactory proppant suspension capabilities were exhibited by the developed fluids.Legend: A, water; B, (2-ethyl hexanol1water); C, (0.05% NaOH 1 2-ethyl hexanol 1 water); D, 0.1% NaOH 1 2-ethyl hexanol 1 water.
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.
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