Abstract

Predictions have shown that our demand for oil and gaswill continue to growin the next decade, and future supply
will becomemore reliant on tertiary recovery and from nonconventional resources.However, current reservoir characterization
methodologies, such as well logs, cross-well electromagnetic imaging and seismic methods, have their
individual limitations on detection range and resolution. Here we propose a pioneering way to use carbon quantum
dots (CQDs) as nanoparticle tracers, which can be transported through a reservoir functioning as conventional
tracers, while acting as sensors to obtain useful information. These hydrothermally produced CQDs from Xylose possess
excellent stability in high ionic strength solutions, durable absorbance and fluorescence ability due tomulti highpolarity
functional group on their surfaces. Consistency between our on-line ultraviolet–visible (UV–Vis) spectroscopy
and off-line Confocal laser scanning microscopy (CLSM) measurements confirms that CQDs have the tracerlike
migration capability in glass beads-packed columns and sandstone cores, regardless of particle concentration
and ionic strength. However, theirmigration ability is undermined in the column packed with crushed calcite grains
with positive charge. We also demonstrate that quantitative oil saturation detection in unknown sandstone core
samples can be achieved by such CQDs based on its breakthrough properties influenced by the presence of oil phase.