Experimental and Numerical Exploration of Electromagnetic-Induced Fracturing of Clay-Shale
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2022-09
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Abstract
The rapid electromagnetic (EM) heating of saturated clays and shales offers a potential means of selectively fracturing interbedded shales, and thereby enhancing oil production while maintaining the caprock integrity of shaley oil sand reservoirs during thermal production process. It is hypothesized that fracturing will occur in an extremely low permeability porous medium due to a large increase in pore fluid pressure by electromagnetic wave heating. As opposed to classical resistive heating, the EM heating of saturated clays/shales is mainly achieved by the interaction between radiating electromagnetic waves and polar water molecules. The above provides the backdrop for the thesis which aims at understanding the underlying fracture and thermal stress mechanisms of EM heating in a geomaterial. As such, comprehensive laboratory experiments are conducted in a specially designed EM heating apparatus. Challenges of the experimental endeavor are highlighted, given the susceptibility of measurement sensors with electromagnetic radiation. Four scenarios of tests are performed on kaolinite clay samples, a surrogate for clay-shale, whose basic properties are measured prior to EM heating. The use of kaolinite samples allows for the conduct of repeatable tests and provides a benchmarking for future tests on actual clay-shale core samples. Results of undrained tests at different confining conditions show that the clay will lose its structural integrity when the thermally induced excess pore pressure in the sample is higher than its tensile strength plus confining pressure. Alongside with the above lab experiments, a two phase (water-steam) fully coupled Multiphysics (EM wave propagation/thermal/fluid/mechanics) model is developed to study the major mechanisms of rapid EM heating. The finite element method is employed with a segregated numerical strategy to solve this highly nonlinear problem using a commercial software COMSOL Multiphysics. The simulation results indicate that pore water pressures develop mainly due to the high contrast between the fluid and solid phase coefficients of thermal expansion. Numerically predicted zones of fracture initiations and patterns are verified against experimental observations using a Mohr-Coulomb failure envelope combined with a tension cutoff.
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Chen, X. (2022). Experimental and numerical exploration of electromagnetic-induced fracturing of clay-shale (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.