Study on Thermal Change of Reservoir During in-situ Pyrolysis of Shale by Microwave Heating

The main mining method of deep oil shale is in-situ pyrolysis. Microwave heating has the advantages of high heating efficiency, fast heating rate, high controllability, high adaptability and heating in three-dimensional direction. It can be used as an ideal alternative to conventional thermal recovery methods to improve mining efficiency. In view of the thermal change of shale reservoir during microwave heating, this paper focuses on the analysis of the microwave frequency, microwave power and heating time required for the heating of Xinjiang Barkol oil shale by analyzing the heating of the reservoir and combining the strain equation, microwave power equation and energy conversion equation. Finally, the changes of porosity and permeability parameters, strain and even cracking after rock heating are predicted. The results show that when the microwave frequency is 915 MHz and the transmission power range is 10 kW~15 kW, the heating effect is the best. At about 600℃, the absorption power per unit volume of the reservoir increases, and the porosity of the reservoir also increases sharply. The rock shows obvious brittleness characteristics with the increase of temperature. It is preliminarily determined that the cracking phenomenon of Xinjiang Barkol oil shale occurs when the temperature reaches 600℃. The research can provide a theoretical basis for the in-situ pyrolysis of oil shale by microwave radiation and make the formulation of the coupling and coordination scheme of rock physical property change, cracking and mining more basis.