Nano-Composite Resin Coated Proppant for Hydraulic Fracturing

Proppant such as sand and ceramics is used in keeping the fractures open for hydrocarbon production in hydraulic fracturing operations. Its ability to withstand reservoir closure stresses and provide high conductivity is one of its key selection criteria. Sand is preferred over ceramics in unconventional plays due to its low cost and abundance. On the other hand, the lower crush strength of sand compared to ceramics limits its application to wells having lower closure stresses. Therefore, it becomes necessary to strengthen the sand as a low cost solution for demanding downhole conditions. Coating sand with resin is a long-practiced method to strengthen and control fines. One fundamental challenge with resin coated sand (RCS) lies in its overall thermo-chemo-mechanical stability at high temperature and high pressure in the presence of fracturing fluid. In this work, a nanocomposite resin has been developed to provide enhanced coating strength and chemical stability. RCS has been characterized from the perspectives of its core and coating. As received sand has been evaluated by (1) single grain crush testing, (2) optical particle size analysis for sphericity and roundness, (3) XRD for mineral content and composition, and (4) petrography analysis for microstructure, texture, and crystalline phases. Sand has been coated using phenolic formaldehyde (novolac) resin systems reinforced with nanomaterials and altered surface wetting properties demonstrating improved crush strength, chemical resistance and long-term conductivity. Loss on ignition (LOI), API proppant crush resistance test, and API long-term proppant conductivity tests have been used to evaluate RCS. Petrographic evaluation of Northern white sand shows the presence of plutonic, and monocrystalline grains having higher crush strength, whereas Texas brown sand shows abundance of polycrystalline and metamorphic grains that are relatively weaker due to impurities, and inner weak planes. The white sands are well sorted and a roundness and sphericity of >0.6 were measured by optical particle size analysis. With resin coating, the API crush resistance stress of the sand has increased by ∼200%; whereas, the API long-term proppant conductivity has increased by 41% compared to uncoated sand. The nano-composite resin coating containing a combination of nano-reinforcement materials and wettability altering agents has increased the API proppant conductivity further by 100% compared to uncoated sand. Nanomaterial used in the coating contains high surface area nanofibers with exceptionally high aspect ratio. The synergistic effect of different nanoparticles increased the strength to an even higher level by providing a barrier to the permeation of fluid in the coating thereby increasing chemical resistance. An economic and up-scalable nano-composite coating technology containing a novel combination of nanomaterials and surface wettability altering agents has been developed with improved proppant crush strength, conductivity and chemical resistance. The performance of the coated sand has not been compromised when exposed to fracturing fluid at elevated temperature making it a suitable candidate for field applications at higher stresses.