Lignite-derived carbonized polymer dots for oilfield tracers

Oilfield tracers are essential chemical additives in the petroleum extraction process, aiding in understanding reservoir flow characteristics, optimizing production strategies, and ultimately increasing oil recovery rates. Carbon dots (CDs), known for their tunable photoluminescent properties, ease of detection, and low toxicity, are considered promising candidates for the next generation of oilfield tracers. However, aqueous-phase oilfield tracers require CDs to possess good water solubility, high-temperature and high-salinity tolerance, low rock adsorption and detection limit, which renders many CDs unqualified for use. Currently, reports on CDs oilfield tracers are limited, with most being restricted to blue fluorescence, which has weak resistance to background fluorescence interference. In this work, by utilizing the rich organic content (17.5 wt%) of low-value lignite as a precursor, lignite-derived carbonized polymer dots (L-CPDs) exhibit green fluorescence with an absolute quantum yield (QY) of 19.78%. Comprehensive evaluations show L-CPDs offer good salt tolerance, thermal stability, and pH stability, with a detection limit reaching 1 ppb and no significant cytotoxicity. Additionally, the tracing behavior of L-CPDs is demonstrated using a microfluidic chip, highlighting their potential as alternatives to existing tracer products.