Study on the Evolution of Rock Pore Pressure Under Microwave Irradiation

Abstract

Microwave-assisted rock-breaking technology is a promising and innovative technique with significant potential for engineering applications. To delve into the variations in rock pore pressure after microwave irradiation, this study employs the theory of wet porous media as the foundation, using numerical simulations to analyze the evolution of pore pressure in different conditions. The research findings indicate that oil-based drilling fluids have a comparably lower influence on the effectiveness of microwave irradiation in comparison with water-based drilling fluids. Additionally, the high conductivity of a medium substantially impacts the irradiation efficacy of microwaves. Basalt exhibits superior microwave absorption and reflection properties compared to granite, limestone, and shale. Consequently, it demonstrates the highest pore pressure, while shale follows with the most rapid decrease in electric field intensity owing to its elevated conductivity. The water vapor pressure escalates with rising rock porosity. Diverse irradiation distances alter the electric field distribution pattern, resulting in various temperature hotspots on the heating surface. Optimal irradiation distances are 10 cm or 16 cm. Additionally, as microwave power rises and irradiation time lengthens, the water vapor pressure inside the rocks intensifies. The irradiation time should be selected to range from 60 to 80 s to avoid evaporative saturation phenomena, which lead to microwave energy loss. Upon microwave irradiation, the pore pressure within rocks may elevate to 4 MPa, inducing a localized imbalanced state at the irradiated surface. This results in a decrease in the rock’s triaxial strength, thereby effectively improving the rock-breaking efficiency of the drill bit.