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

Abstract

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.