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The present work reports 3D-cross-linked polymer network-based coating onto frac sand prior to the epoxy coating to prepare dual-coated sand proppants with very high-stress resistance. The 3D-cross-linked poly(styrene-methyl methacrylate)/divinyl benzene) (PS-PMMA/DVB) coatings have been successfully prepared by the in-situ one-step bulk polymerization method with AIBN as an initiator at 70 °C. The 3D-polymer networks coated sand particles were then added with a mixture of epoxy resin and cure (4:1) along with commercial graphene (CG) and cured at 150 °C for 5 min. Interestingly, the roundness and sphericity of the sand particles have been retained even after the dual coating. The elasticity (E), hardness (H), and the fracture toughness (K c) of the dual coating (PS-PMMA/DVB)-(Epoxy-CG) have been reached a maximum of 7.78 GPa, 0.34 GPa, and 3.22 MPa m1/2 respectively. The mechanically and thermally reinforced dual-coated sand particles with very high-stress resistance up to 12,000 psi will be successful proppants for hydraulic fracture operations. • Mechanically reinforced (3D-(PS-PMMA/DVB))-(Epoxy-Graphene) coated proppant. • The stress resistance of the proppant is as high as 12,000 psi. • The fracture toughness of (3D-(PS-PMMA/DVB))-(Epoxy-Graphene) is 3.22 MPa m1/2. • Elasticity and hardness of the coating shells are 7.78 GPa and 0.34 GPa. • The thermal stability is as high as 368 °C. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is a process that enhances the production of hydrocarbon using fracking fluids in the presence of proppant (sand or man-made), causing the unconventional oil and gas wells to fracture. This, in turn, allows the trapped hydrocarbons to flow through and be recovered. However, the hydrocarbons are situated at high temperature and high pressure (HTHP) environment, which could damage the proppant. As an alternative, coating the proppant with HTHP resistant materials has proven to enhance the properties of the proppant, leading to higher production of hydrocarbons. It is important to note that understanding the material's chemical, mechanical, and thermal properties before coating the proppant is the most important step. Hence, this comprehensive review addresses (1) currently available proppants and their properties, (2) the chemical, thermal and mechanical properties of polymer nanocomposites with 2D-nanofillers and epoxy nanocomposites with potential for frac sand applications and (3) highlight the interaction between the sand and the nanocomposites. • Mechanically robust proppants under HTHP conditions. • Epoxy nanocomposites coated frac sand proppants. • Incorporation of 2D-nanofillers strengthened the polymer coated sand. • Highlights the interaction between sand and polymer nanocomposites. [ABSTRACT FROM AUTHOR]

Herein, we report mechanically reinforced dual-coated sand proppants for hydraulic fracturing operations. The dual-coated sand proppants were prepared by sequential surface modifications. The sand particles were firstly coated with polystyrene-polymethyl methacrylate copolymer (PS-PMMA) composite with commercial graphene (CG) (first composite layer) and subsequently coated with epoxy-CG composite (second composite layer). The copolymer-CG coating onto sand particles was carried out by mixing 1:1 styrene (S) and methyl methacrylate (MMA) monomers with the initiator AIBN along with CG followed by adding the mixture to sand particles with vigorous stirring and subsequent polymerization at 70 °C. The PS-PMMA-CG coated sand particles were then mixed with epoxy resin and a cure in a ratio of 4:1 along with CG and cured at 150 °C for 5 min. Chemical, mechanical, thermal, and morphological characterizations for the composite layers and dual-coated sand proppants were investigated in detail by Fourier transform-infrared spectroscopy (FT-IR), nano-indentation, thermogravimetric (TGA), optical, and scanning electron microscopic (SEM) techniques. The FT-IR results revealed that the successful formation of PS-PMMA-CG copolymer composite and cross-linked epoxy-CG composites. The XRD results indicated that the successful surface coverage of the dual composites coating onto the sand. The optical and SEM results revealed that the roundness and sphericity of the reinforced proppant particles were greater than 0.6. Interestingly, elasticity (E), and hardness (H) of the coating shells have reached a maximum of 3.97 GPa and 0.144 GPa, respectively. The thermal stability of the (PS-PMMA-CG)-(epoxy-CG) dual composite shell has reached as high as 363 °C. Furthermore, the stress resistance of the optimized dual-coated sand proppant (Sand-(PS-PMMA-CG)-(epoxy-CG)) reached as high as 10000 psi with a fine production of <10 wt%. The mechanically reinforced dual-coated sand including the most desirable characteristics of roundness and sphericity to be greater than 0.6, high-stress resistance with excellent thermal and mechanical stabilities confirmed its great potential to be applied as successful proppants in oil and gas upstream applications. Image 1 • Mechanically reinforced ((PS-PMMA)-Graphene)-(Epoxy-Graphene) dual-coated sand. • Elasticity and hardness of the coating shells are 3.97 GPa and 0.144 GPa. • The thermal stability is as high as 363 °C. • The stress resistance of the proppant is as high as 10000 psi. [ABSTRACT FROM AUTHOR]