Coal dots synthesized from coal tar pitch as a novel oil displacement agent for enhanced oil recovery: Performance, mechanisms, and implications for sustainable resource development

Carbon quantum dots (CQDs) are a class of zero-dimensional carbon nanomaterials recognized for their unique fluorescent properties, demonstrating significant potential across various fields. However, their application in the petroleum industry has not been adequately explored. This paper synthesized coal-based CQDs (coal dots) using a chemical oxidation method, achieving a mass yield of over 90 %. The coal dots had an average diameter of 2.4 nm and carried hydroxyl and carboxylic acid groups, making them hydrophilic and negatively charged. Their potential application as an oil displacement agent for enhanced oil recovery (EOR) was examined, resulting in an incremental oil recovery of 12.0 % in low-permeability rocks and 4.5 % in tight rocks. Our exploration of solid-fluid and fluid-fluid interactions suggested that wettability alteration, driven by the repulsive structural forces within the framework of surface forces, contributed to the EOR achieved with coal dots. The integration of coal dots into EOR can lead to the effective and sustainable development of both petroleum and coal resources.