Green carbon quantum dots applied as tracer for petroleum reservoir characterization

Abstract

This work aimed to synthesize environmentally friendly Carbon Quantum Dots (CQDs) using biowaste for application as tracer fluids in hydrocarbon reservoirs. Banana-da-terra peels (Musa spp), pear orange (Citrus sinensis) and kapok pods (Ceiba pentandra), were the raw materials used in the hydrothermal carbonization synthesis methodology of CQDs, due to their high availability and low cost and the efficiency of the method. The materials were characterized by MET, FTIR, UV–vis, PL and Quantum Yield. In the performance analyses of CQDs in carbonate rock, an optical tensiometer was used, and their compatibility in a simulated porous media with silica micro pearls and sand. The infrared results showed that the common functional groups present in both the CQDs, and carbonate rock samples were OH, NH and CN, indicating the favourability of solubility in water and a degree of interaction between the nanoparticles and the medium. All three synthesized CQDs showed excellent optical properties such as high emission intensity, good stability and long lifetime. The calculated Quantum Yield (QY) proved to be higher than 50 %, a value above the average for green materials. The contact angle of the fluid-rock interaction, in carbonate rock soaked by oil, showed that in the rock with oil the angles were greater than 90° for all samples, and decreased over time. For pure rock (without oil) it was noted that at the beginning, all CQDs angles were lower than 90°, suggesting high wettability. In compatibility tests, the CQDs did not interact with the oil and did not form additional phases. Furthermore, the increase in temperature does not have a significant impact on the emission, suggesting that these studied materials would have a high potential for application as tracers in reservoirs.