Carbon Dot Nanomaterials with High Interfacial Activity for Unconventional Reservoir Development

Abstract

Carbon dot nanomaterials (<10 nm) exhibit superior application prospects as oil displacement materials for unconventional reservoir development. However, the limited oil–water and oil–solid interfacial activity of carbon dot nanomaterials restricts their broader application. In this study, carbon dot nanomaterials (CDs) are expeditiously prepared via a microwave-assisted synthesis method utilizing urea and citric acid as precursor compounds. OAB-modified active carbon dot nanomaterials (OCDs) are prepared by grafting oleic acid amidopropyl betaine (OAB) through hydrothermal reaction at 90 °C for 5 h using CDs as a carbon dot carrier. Stability experiments show that the plentiful hydrophilic groups present on the surface of the OCD augment electrostatic repulsion among them, thereby imparting dispersibility, temperature tolerance (90 °C), and salt resistance (2.6 × 104 mg/L). Additionally, OCDs demonstrate optimal effectiveness at a concentration of 0.5 wt %. At this concentration, OCDs can reduce the interfacial tension to 0.66 mN/m and achieve the underwater oil contact angle to 126°. Within 24 h, OCDs can strip 60.6% of the oil film. OCDs show the excellent ability to enhance oil–water and oil–solid interfacial activity. Meanwhile, OCD nanofluids can effectively form emulsions with crude oil and spontaneously demulsify within 2 h in a state. Core flooding tests demonstrate that OCD nanofluids, when compared with simulated formation water, reduce injection pressure by 46.3% and enhance oil recovery by 31.1%. This study offers a promising solution for the efficient development of unconventional reservoirs with carbon dot nanomaterials.