Thermal energy storage biogel with good biodegradability for solar energy powered heavy oil recovery

For cleaner production of heavy oil with lower fossil fuel consumptions, solar thermal enhanced oil recovery (Solar TEOR) technologies are increasingly researched nowadays. However, the intermittency of solar radiation and inferior energy efficiency of steam flooding restricted industrial applications of Solar TEOR methods in oilfield. In this work, the eutectic NaCl–KCl and graphite were loaded into the biomass gelling matrix (crosslinked methylcellulose network) through supramolecular interactions. Then, a thermal energy storage biogel (NaCl–KCl)@G/MC with high thermal conductivity (2.06 W m−1·K−1), latent heat storage capacity (melting enthalpy: 112.4 J g−1 at 352.4 °C) and thermal reliability (melting enthalpy retention up to 94.4% after 30 cycles), was synthesized for improving the continuousness of solar thermal supply and energy efficiency of steam flooding. From the experimental results, the proposed oil recovery method — solar powered steam flooding in daytime + the thermal-storage biogel heated N2 flooding in nighttime — can meet the all-weather 24/7 production of heavy oil and improve energy efficiency (oil-steam ratio and thermal efficiency up to 0.56 and 62.1%). With (NaCl–KCl)@G/MC biogel assistance, energy consumption of oil production was decreased from 153.1 J·(mL oil)−1 to 9.9 J·(mL oil)−1 as the cost reduction of 19.8% in comparison with intermittent solar steaming. This study offers a candidate design to achieve a continuous thermal recovery of heavy oil entirely powered by solar energy, promoting the solar thermal technologies in oil industry operations.