Carbon dots enhanced ultra-low-density fluorescence proppants with both high-compressive strength and anti-deformation ability

The polymer ultra-low-density proppants are critical to the development of slick-water fracture technology, but which were prone to obvious deformation under high pressure in the fractures. To increase the stiffness of the styrene-divinylbenzene copolymer (SDB) and obtain desired ultra-low-density (ULD) proppants, carbon dots (CDs) were introduced in-situ considering their characteristics as the zero-dimensional carbon nanomaterial. Taking the compressive strength and axial deflection, and so forth into consideration, the synthesis conditions of CDs modified SDB microspheres (CDs-SDBs) were optimized. Taking the graphite modified SDBs (MG-SDBs) as a reference, the density of CDs-SDBs did keep almost constant at about 1.1800 similar to 1.1899 g.cm(-3) with the increase of CDs amount. The CDs-SDBs not only possess high-peak pressure (41.5 N) but also minute axial deflection (0.090 mm). The advantages of CDs-SDBs over MG-SDBs become even more pronounced under higher pressure, which can withstand closure pressure of 80 MPa with a small crush ratio of 4.47%. CDs-SDBs exhibit significant photoluminescence performances with maximum excitation and emission wavelengths of 634 nm and 554 nm. Highlights CDs-SDBs as ULD proppants with high strength and anti-deformation were developed. Advantages of CDs-SDBs become more pronounced under high-closure pressure. With increasing of CDs amount, apparent density of CDs-SDBs keep almost constant. Axial deflection of CDs-SDBs is only 0.09 mm under 41.5 N. The crush ratio is only 4.47% under 80 MPa closure pressure.

Automated summary

The development of slick-water fracture technology requires polymer ultra-low-density proppants, but these tend to deform under high pressure. To overcome this, carbon dots were introduced to increase the stiffness of the styrene-divinylbenzene copolymer (SDB) and obtain the desired ultra-low-density proppants. The synthesis conditions of carbon dots modified SDB microspheres (CDs-SDBs) were optimized, resulting in proppants with high-peak pressure and minimal axial deflection. The density of the CDs-SDBs remained constant with increasing amounts of carbon dots.