Numerical Simulation of Oil Shale Retorting Optimization under In Situ Microwave Heating Considering Electromagnetics, Heat Transfer, and Chemical Reactions Coupling

Oil shale constitutes an important proportion of unconventional resources, and its efficient exploitation helps alleviate the Chinese oil shortage situation. Nowadays, microwave heating is a promising method for in situ development of oil shale. However, the corresponding numerical simulation lacks in guiding the retorting optimization under microwave heating. A novel pseudo three-dimensional model, considering electromagnetics, temperature field, and chemical reactions coupling was developed and implemented to investigate oil shale reservoirs’ retorting performance under microwave heating based on the finite element method (FEM). The effects of microwave power, antenna number, and antenna position were analyzed creatively to optimize the microwave heating parameters. Numerical results showed high microwave power increased the maximum reservoir temperature quickly near the heating well, but the thermal conductivity of oil shale dominated the temperature of distal formation. For a typical case of two antennas at 0.9 m spacing and 500 W, the maximum temperature can reach 443 °C at 100 days, and the kerogen near the wellbore quickly converts to hydrocarbon products. Moreover, increasing antennas can improve the heating rate, and the specific distance between two antennas should be designed based on the microwave power and oil shale properties.