Thermal stimulation of shale formations by electromagnetic heating: A clean technique for enhancing oil and gas recovery

Abstract

Electromagnetic heating has been proposed to environmentally produce shale gas, shale oil, and oil shale. Unlike hydraulic fracturing that cracks shale by tensile and shear stresses through injecting a massive amount of fracturing fluid, electromagnetic heating creates fractures by internal stress caused by the interaction between formation rocks and electromagnetic waves, which eliminates the use of water. In this study, we conducted experiments and simulations to investigate the influential factors, stimulating mechanisms, and fracturing performance of electromagnetic heating for its application in stimulating shales. First, shale samples with different compositions are subjected to electromagnetic (microwave) heating for 3 min. Then, scanning electron microscopy coupled with energy dispersive X-ray, N2-adsorption/desorption, and microscope-imaging are used to characterize pore-structure changes and fracture generation of shale samples. Finally, a finite element theoretical simulation is conducted to investigate the effects of confining pressure, electromagnetic heating power, and time on the stress distributions of the sample. Results show that both macro-fracture and micro-fractures are created after electromagnetic heating; samples either crumble into pieces or fracture into several parts, depending on their clay and pyrite contents. The stimulating mechanisms of electromagnetic heating are shrinkage of clay, and decomposition of organic content, and tensile failure by the heterogeneous expansions of minerals, which significantly enhance the pore space. Moreover, simulations show that the expansion of pyrite induces considerable tension that causes tensile failures to the shale sample, which echoes well with the experimental observations. Confinement can lower the induced tensile stress, which can be overcome by raising the electromagnetic heating power. Our study demonstrates that electromagnetic heating is a promising stimulation technique to eliminate water usage and effectively fracture the shale rock, leading to greener production of hydrocarbon resources from shale.