Experimental Evaluation of Carbon Dots Stabilized Foam for Enhanced Oil Recovery

Foams are used as divergent fluids for conformance control in enhanced oil recovery (EOR) operations. It is created by mixing a surfactant and a gas in situ in high-permeability reservoirs (e.g., surfactant alternating gas or SAG). Foams exhibit instability issues at reservoir conditions with a highly complex pore network, high pressure, high temperature, and high salinity. Here, we examine the stability and efficacy of foams formed with and without the addition of carbon nanoparticles (or nanodots). Carbon particles have demonstrated stability, mobility, and scalability for harsh reservoir environment use and application as a tracer technology. In this study, we investigate the feasibility of using inexpensive carbon dots as “foam boosters.” The experiments involved using different levels of brine salinities (ranging from seawater to formation connate water), different concentrations of the nanodots (ranging from 5 to 500 ppm), different types of surfactants (anionic, cationic, and nonionic) and gases (CO₂, N₂, and air), and different levels of temperature (ranging from 27 to 100 °C) to target representative conditions of Saudi Arabian reservoirs. In addition, we examined both foam structure, such as the gas–liquid interface, and liquid film lamella to better understand the mechanisms contributing to foamability and foam stability. The study highlights and unravels the complex interrelationship of the different influencing components on the stability of foam with the addition of the carbon particles. The bulk and porous media stabilities of the foams are analyzed using a static foam analyzer and an HP/HT core-flood system, respectively. Foam stability is assessed in terms of type and amount of modified/functionalized carbon particles, surfactant, and gas. We observed that the bulk foam containing only trace amounts (5–10 ppm) of carbon nanodots shows improved stability in a high-salinity medium. The particles improved the foam stability maximum by 70% and more than doubled the foam half-life for some foams. Confocal microscopy images of the foam structure of systems containing an increased concentration of carbon particles reveal an increased thickness of the lamellae and a decreased average bubble size. This is a clear indication of the enhanced foam stability. Carbon dots decreased the drainage rate of the lamellae and delayed the bubble rupture point or coalescence. The particles improved the foam stability by preferentially positioning itself in the lamella and preventing liquid drainage and film thinning.