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Finite element methods for thermal fracture simulation in deep underground injection processes

Deep underground injection is involved in shale gas recovery, methane hydrate extraction, geologic waste disposal, carbon sequestration, geothermal energy exploitation, and compressed air energy storage. Efficiency and impacts of these processes are still not well understood. Knowledge of the propagation of a fracture and its potential interaction with bedding interfaces is essential for better understanding of the efficiency and impacts of deep underground injection. Sophisticated fracture simulation is an effective tool to obtain this knowledge. More realistic constitutive relations are desired to increase the sophistication of a fracture model, which at the same time raise computational challenges.

In this work, thermal effects are considered for more realistic analyses of stress and pressure fields, based on the fact that massive fluid injection lasts for a long period of time with an injection temperature different from that of formation rock. More realistic 3D discrete fractures are considered in fracture propagation in order for mapping fracture geometry and propagation trajectories. To circumvent the numerical instability in the traditional finite element implementation of convective heat transfer, a stabilized finite element method is adopted; to avoid the remeshing problem in the traditional finite element implementation of fracture propagation, an extended finite element method is applied to a domain where fractures propagate or interact. Interaction between a propagating fracture and bedding interfaces can also be conveniently accounted for using this method.

Author(s):

Shunde Yin    
University of Wyoming
United States