  Two primary types of numerical instabilities often occur in low-order finite
element method (FEM) analyses of thermo-hydro-mechanical (THM) phenomena: (1)
pressure oscillations arising improper interpolation of pressure and
displacement fields; and (2) spatial oscillations induced by nonlinear
convection terms in convection-dominated scenarios. In response to these
issues, this paper proposes a novel stabilized edge-based smoothed FEM with a
bubble function (bES-FEM) for THM analysis within saturated porous media. In
the proposed framework, a cubic bubble function is first incorporated into
ES-FEM to efficiently mitigate pressure oscillations that breach the Inf-Sup
condition, and then the Streamline Upwind Petrov-Galerkin (SUPG) scheme is
adopted in bES-FEM to effectively reduce the spurious oscillations in
convection-dominated heat transfer scenarios. The accuracy of the bES-FEM with
SUPG formulation for THM coupled problems is validated through a series of five
benchmark tests. Moreover, the simulations of open-loop ground source energy
systems demonstrate the proposed method's exceptional capability in tackling
complex THM challenges in real-world applications. All the obtained results
showcase the superiority of proposed bES-FEM with SUPG in eliminating the
spatial and pressure oscillations, marking it as a promising tool for the
exploration of coupled THM issues.
