An intelligent micro-nano capsule green hydrogel decorated with carbon quantum dots with delayed crosslinking characteristics for enhanced oil recovery in harsh reservoir

Hydrogels are widely used in reservoir flow control to enhanced oil recovery. However, challenges such as environmental contamination from conventional crosslinkers, poor solubility of crosslinking agents, and short gelation times under high-temperature conditions (e.g., 150 °C) have hindered their practical application. Herein, we present the synthesis of amine-functionalized carbon quantum dots (NH 2 -CQDs), which act as both a nano-crosslinker and a nano-reinforcing agent within hydrogel systems. The NH 2 -CQDs-incorporated hydrogel can remain stability for 300 days under the conditions of a mineralization degree of 2.11×10 4 mg/mL and 170 °C, and has high tensile strength (371 kPa), good toughness (49.6 kJ/m 3 ), excellent viscoelasticity ( G ' = 960 Pa, G " = 460 Pa) and shear resistance. In addition, NH 2 -CQDs adds many hydroxyl groups to the hydrogel, which can be attached to the surface of various substances. At the same time, micro-nano capsules containing NH 2 -CQDs were formed by self-assembly of hydrophobic SiO 2 on water droplets, the NH 2 -CQDs solution is encapsulated in a capsule, and when stimulated by external conditions (temperature, pH, surfactant), the capsule releases the NH 2 -CQDs solution, this method greatly delays the crosslinking time between polymer and crosslinker at high temperature. Under the condition of 170 °C and pH=7, the gelation time of 10% hydrophobic SiO 2 coated hydrogel is 44 times that of uncoated hydrogel, which can be effectively used for deep formation flow control, and CQD give hydrogels fluorescence properties that can be used for underground signal tracking.