Abstract
Feasibility of carbon quantum dots as tracers in petroleum industry was explored in this study to provide diversified options for reservoir evaluation. A kind of water-soluble fluorescent carbon quantum dots (CA-CQDs) with high fluorescence quantum yield and an average particle size of ca. 5.6 nm was successfully prepared with citric acid as carbon source and ethylene diamine as nitrogen source by controlling hydro thermal temperature and time. Fluorescence test results demonstrated that CA-CQDs were easy to sample and analyse and present outstanding fluorescence performance at 10~(-6) g L~(-1). The stability, adsorption, compatibility and fluidity of CA-CQDs were comprehensively evaluated. Results showed that optical properties of CA-CQDs present excellent stability because they minimally changed under different temperatures, salt solutions and pH conditions. Adsorption effect of different minerals on CA-CQDs was small, and concentration retention rate was stable at above 90% after 5 days of adsorption. CA-CQDs showed satisfactory compatibility with formation water samples, and concentration deviation was maintained within 2%. It was convenient for real-time monitoring and analysis because CA-CQDs presented evident breakthrough-elution process with strong migration capacity but weak retention and adsorption capacities when flowing in the pipeline. The results of this study proved that CA-CQDs demonstrated high application potential as tracers in oilfields.
NSTL