A Multiwalled Carbon Nanotube-Based Polyurethane Nanocomposite-Coated Sand/Proppant for Improved Mechanical Strength and Flowback Control in Hydraulic Fracturing Applications

Abstract

A novel resin-based nanocomposite-coated sand proppant is introduced to address the issue of proppant flowback in post-fracturing fluid flowback treatments and hydrocarbon production. Self-aggregation in the water environment is the most attractive aspect of these developed proppants. In this work, sand was sieve-coated with 0.1% multiwalled carbon nanotubes (MWCNTs) followed by optimized thin and uniform resin (polyurethane) spray coating in the concentration range of 2 to 10%. Quantitative and qualitative evaluations have been carried out to assess the self-aggregation capabilities of the proposed sand proppants where no flowback was witnessed at 4% polyurethane coating containing 0.1% MWCNTs. This applied resin incorporating MWCNT coating was characterized by field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy depicted the dispersed presence of MWCNTs into polyurethane resin corroborated by the presence of 38% elemental carbon on the sand substrate. Proppant crushing resistance tests were conducted, including proppant pack stress−strain response, compaction, and fines production. It was found that the proposed sand proppant decreased the proppant pack compaction by ∼25% compared to commonly used silica sand with the ability to withstand high closure stress as high as 55 MPa with less than 10 wt % fines production. The surface wettability was determined by the sessile drop method. The application of resin incorporating MWCNT coating layers changed the sand proppant wetting behavior to oil-wet with a contact angle of ∼124°. Thermogravimetric analyses revealed a significant increment in thermal stability, which reached up to 280 °C due to the addition of MWCNTs as reinforcing nanofillers.

Insight into thermo-mechanical enhancement of polymer nanocomposites coated microsand proppants for hydraulic fracturing

“…As shown in Figure 3 a, the T deg for microsand-PS-PMMA/DVB is determined to be 350 °C while that of microsand-(PS-PMMA/DVB)-(Epoxy-CG) was found to increase to 370 °C. At the same time, the T deg for microsand-epoxy is found to be only 345 °C The observed thermal stability values are found to be much higher than that of various other resin systems including furan [ 53 ], phenolic [ 54 ], polyurethane [ 33 , 53 ], polyurethane-carbon nanostructure composites [ 38 ] reported in the literature ( Table 1 ). This thermal stability enhancement of the dual-coated microsand proppants can be accredited to the improved thermal stability of the Epoxy-CG composite layer which is in turn credited to the thermal stability of graphene nanosheets.…”

“…These long-standing drawbacks of RCPs are partly resolved by coating the frac sand with polymer nanocomposites [ 35 , 36 , 37 ]. Due to their mechanical properties, the combination of these materials with other nanofillers such as carbon nanotube, graphene, and graphene oxide (GO) has been able to improve the thermo-mechanical stabilities of the proppants [ 28 , 35 , 38 , 39 ].…”

Novel Nanocomposite Coated Proppants for Enhanced Scale Inhibition Lifetime in Tight Shale Formations

“…Therefore, GNPs and MWCNTs reinforcement enhanced the stress resistance for these glass beads and sand proppants. This improvement in stress resistance can be attributed to the mechanical reinforcement provided by GNPs and CNTs to the polyurethane resin coating; indeed, nanofiber coatings (which have a high aspect ratio) provide extra mechanical strength to the resin. − In conclusion, their demonstrated stress resistance improvement makes GNPs-RCP and MWCNTs-RCP potential candidates for hydraulic fracturing operations.…”

Preparation and characterization of a self-suspending ultra-low density proppant

“… 37 Proppants appear to undergo substantial proppant pack compaction and porosity reduction due to the strong in situ confining stresses that occur underground. 38 The embedment of proppants leads to the decrease of conductivity. However, the fracture conductivity test has shown that the conductivity of UDP propped fracture is higher than that of quartz sand and ceramsite under high closing stress.…”