Three-Dimensional Thermo-Poroelastic Modeling and Analysis of Flow, Heat Transport and Deformation in Fractured Rock with Applications to a Lab-Scale Geothermal System

Abstract

Fractures and other discontinuities, such as bedding planes, and faults, usually act as highly permeable flow paths, dominating subsurface fluid and heat transport, which is of importance in developing underground energy resources. We investigate coupled transport and fracture deformation/propagation within the framework of the theory of thermo-poroelasticity. A 3D finite element method is developed and utilized to discretize the governing equations. To simulate the thermo-hydro-mechanical behavior of the fracture/matrix system, a special zero-thickness interface element is implemented based on the cohesive zone model (CZM), to simulate both tensile and shear failure. The fluid flux/heat exchange between the fractures and the surrounding permeable rock matrix is determined by fluid/heat transfer coefficients satisfying mass and energy balance across the interior boundaries, and allowing for temperature and pressure drop across the interface. Numerical analyses are performed to verify the model and to illustrate fundamental phenomena observed in the laboratory. Lab-scale fracturing and circulation experiments are studied in detail, revealing the role of hydro-thermo-mechanical properties and coupled processes.