Microwave-Assisted Synthesis of Carbon Nanospheres and Their Application as Plugging Agents for Oil-Based Drilling Fluids

Wellbore instability caused by the invasion of drilling fluids into formations remains a significant challenge in the application of oil-based drilling fluids (ODFs). In this study, carbon nanospheres (CNSs) were synthesized using glucose as the carbon source through a microwave-assisted method. The effects of the reaction temperature, carbon source concentration, and reaction time on the particle size of CNSs were systematically investigated. The results revealed that under optimal conditions, CNSs with an average particle size of 670 nm were successfully synthesized, exhibiting high sphericity and excellent dispersibility. CNSs demonstrated stable dispersion in mineral oil when lecithin was used as a dispersant. The plugging performance of CNSs in ODFs was evaluated through low-pressure filtration and high-temperature, high-pressure (HTHP) filtration tests. After aging at 180 degrees C for 16 h, the addition of 2% CNSs reduced the filtration volume from 10.6 mL to 2.5 mL on standard filter paper (average pore size: 3 mu m) and from 8.5 mL to 1.6 mL on microporous membranes (average pore size: 0.5 mu m). Additionally, the HTHP filtration volume decreased from 73 mL to 18 mL, and the permeability of the filter cake formed during HTHP filtration was reduced from 26.5 x 10-3 mD to 1.2 x 10-3 mD. Furthermore, CNSs improved the rheological properties and emulsion stability of ODFs. With excellent compatibility and applicability, CNSs offer a promising solution for enhancing the performance of oil-based drilling fluids.