Numerical simulation of the physical response of shale oil reservoirs under microwave and steam synergy and single heating methods

This article is the first to simulate the changes in temperature, porosity, permeability, and displacement of oil shale reservoirs under microwave followed by steam and steam followed by microwave and to analyze the oil shale reservoirs under single steam and microwave in comparison, aiming to find out the most suitable way for in-situ exploitation of oil shale among the four types of heating methods. From the results of COMSOL Multiphysics field software, the average temperatures of the reservoir under 600 W single microwave heating, 650 °C single steam heating, steam followed by microwave heating, and microwave followed by steam heating were 570.15, 528.53, 725.66, and 524.36 °C, respectively, at a heating time of 500 days; the average porosity was 16, 18.692, 19.52, and 17.744%, respectively; the average permeability was 4.343 × 10^-16, 2.05 × 10^-11, 1.738 × 10^-11, and 1.09 × 10^-11 m², respectively; and the average displacement of the reservoir was 3.3 cm, 3.11 cm, 3.38 cm, and 2.65 cm, respectively. The temperature of the oil shale reservoir increases with time for four heating methods, and the heating distance becomes larger. The reservoir's porosity, affected by steam followed by microwave and single steam, showed a decreasing then increasing trend over 100 days and leveled off after 300 days, while with single microwave and microwave followed by steam, it showed a linear increase. Permeability exhibits minimal variation at reservoir temperatures ranging from 200 to 300 °C but experiences a significant increase above 300 °C. The displacement of the reservoir gradually increases under the four applied methods. The oil shale reservoir treated with steam followed by microwave outperforms the other three methods in heating speed, range, pore connectivity, and oil and gas circulation, offering a new method for future research on oil shale in-situ extraction technologies.