High strength glass beads coated with CNT/rGO incorporated urethane coating for improved crush resistance for effective hydraulic fracturing

Abstract

Hydraulic fracturing is a widely employed well stimulation technique in which a synthesized fracking fluid is pumped into the well bore at high pressures to propagate fractures in rock formation matrix for hydrocarbon production. Proppant being one of the essential component of fracturing fluid is used to keep the hydraulically induced fractures open and conductive by acting as a mechanically strong support particle. Hydraulic fracturing operations are gradually shifting into deeper and low permeability (tight) formation at elevated temperature and pressure conditions at which conventionally used silica sand is becoming unviable as proppant due to its crushing. For resin-coated sand (RCS), temperatures greater than 60°C under high pressures, the glass transition temperature (Tg) threshold limit of polyurethane-based resin coating is reached at which this applied coating tends to soften that results reduction in the mechanical strength of the coated sand pack. Glass beads are also considered as good contestant for proppant that were selected in this study due to their high roundness and sphericity. They were drip coated with urethane resin incorporated with three different concentrations of 0.1 wt%, 0.5 wt% and 1 wt% carbon nanotubes (CNTs) and reduced graphene oxide (rGO) nanofillers, respectively. Crush test analysis by means of Universal Testing Machine (UTM) revealed significant improvement in the mechanical strength of coated glass bead proppants. 0.5 wt% loading of CNTs into urethane resin proved to be the best optimum concentration at which the mechanical strength of the coated glass bead improved by 84% along with 40% reduction in fines generation due to its containment within the applied coating. Crush test results also further revealed that nanofillers concentration loadings greater than the optimum threshold limit into urethane resin promoted their mutual agglomeration that resulted in profound reduction in mechanical strength of coated glass beads therefore resulting in more crushing and higher generation of undesired and detrimental fine particles.