Numerical investigation on microwave-thermal recovery of shale gas based on a fully coupled electromagnetic, heat transfer, and multiphase flow model

Technical advances in horizontal drilling and hydraulic fracturing have significantly improved commercial shale gas development. However, current shale gas development has encountered the challenge of sustainability. Therefore, there is an urgent need to develop new technologies for shale gas production. Microwave irradiation can be used as an auxiliary technology for hydraulic fracturing to promote the sustainable development of shale gas. The temperature of the reservoir is elevated by irradiating it with electromagnetic waves, inducing complex coupling mechanisms involving rock, water, and gas in the reservoir. This study incorporated electromagnetic, heat transfer, multiphase flow, and rock deformation into a fully coupled model. Water evaporation and gas desorption owing to the increase in reservoir temperature were also considered in the proposed model. The proposed model was validated against analytical solutions from benchmark tests. Based on the model, the multiphysics coupling mechanisms during the microwave-thermal recovery of shale gas were numerically investigated. Meanwhile, the recovery efficiency of shale gas was quantitatively assessed by considering the varying parameters of microwaves and reservoirs. In addition, different waveguide layouts and irradiation schemes were designed to optimize the gas recovery schemes. This study provides necessary theoretical guidance for the field application of microwave-thermal recovery of shale gas.