One-step synthesis of B, N co-doped carbon dot as fracturing crosslinker and fluorescent tracer in flowback and their performance

In order to deal with the problem of exploitation in low permeability reservoir and improve fracturing fluid performance, a carbon dot nano-crosslinker was developed, which has the function that the same cross-linking point can be linked with multiple guar gum molecular chains, and good stability. HRTEM and Dynamic Light Scattering(DLS) were used to observe the morphology, crystal plane(0.34 nm) and particle size distribution(1.20 nm~1.42 nm) of carbon dot crosslinker. Mapping, Fourier transform infrared spectrum(FT-IR) and X-ray photoelectron spectroscopy(XPS) were used to prove the successful doping of B, N. Then the rheological test was carried out with CDG fracturing fluid, results showed that the viscosity of CDG remained above 170 mPa·s under 120 °C and 170 s-1 shear performance better than organic boron fracturing fluid. Then, the Cole-Cole model was established for viscoelastic data at 25-120 °C, the results showed that the radius of curvature of Cole-Cole model increases with the decrease of temperature, and the system has strong compatibility. A displacement experiment was also used to characterize the fluorescence tracing properties. This proves that the preparation of carbon dots as crosslinker and fluorescent tracer are successful, also provides a new sight for the application of carbon dots.