Open Geomechanics

An open source FEM code for solving coupled thermo-poroelastoplastic processes

Matthew L. McLean, D. Nicolas Espinoza — Mon, 10 Jun 2024 09:35:17 +0000

Coupled thermo-hydro-mechanical (THM) processes are ubiquitous in subsurface energy production and geological utilization and storage operations. Numerical simulation of strongly coupled THM processes is a non-trivial task, yet required to predict the performance of many applications in energy geomechanics. The majority of existing and open THM numerical codes are not user adaptable and do not include elastoplasticity coupled to mass and energy balance equations. This article presents an open source thermo-poroelastoplastic finite element numerical code with a fully-coupled monolithic solution strategy that is solved with Fenicsx computing platform. The formulation employs a mixed finite element scheme for pore pressure diffusivity equation, mean stress dependent yield surface, and non-associative plastic potential. The numerical solution is verified with small-scale conventional triaxial tests including drained and undrained compression and extension. We present example simulations reaching the yield surface induced by coupled hydromechanical and thermal loads. In addition, we present two example large-scale applications related to geothermal energy and carbon geological storage. Results show that the numerical solution accurately predicts changes of temperature, pore pressure, and stress for a wide range of model geometries and boundary conditions, including the plastic response. The code is freely available to the general community for use and modification.

Experimental investigation of the unclogging process of propped fractures with dynamic stimulation: influence of the proppant and of the dynamic signal

Youssef Fawaz, Christian La Borderie, Antoine Jacques, Gilles Pijaudier-Cabot — Wed, 16 Oct 2024 14:50:12 +0000

Dynamic excitation of reservoir systems trapping hydrocarbons is a potentially promising solution for increasing the production. At the laboratory scale, it was found that a dynamic vibration of the fluid pressure could induce an increase in permeability of fractures and improve the flow in the drainage system. This phenomenon was also confirmed on sites by the rise in water and oil well production following seismic events. In both cases, it has been hypothesized that the fluid pressure oscillations could contribute to breaking clusters of fine particles located in fractures that clog drains in the reservoir. In order to confirm such an assumption, we developed in a previous study experiments aimed at reproducing clogging in propped fractures and unclogging due to dynamic loads applied perpendicularly to the fracture (Fawaz et al., 2021). This paper built on this experimental set-up and presents a study of the major parameters governing the unclogging of propped fractures by dynamic stimulation. The influences of the proppant distribution density, proppant size, amplitude, and of the frequency of the signal were studied. After applying the dynamic load, results showed a significant increase in permeability with a high recovery rate reaching 75%.

Far-field modelling of THM processes in rock salt formations

Tue, 11 Mar 2025 11:03:18 +0000

Glaciation cycles are one aspect to be considered in assessing the safety of deep geological repository sites for long-term radioactive waste storage. This study examines the impact of time-dependent boundary conditions and thermo-hydro-mechanical (THM) couplings on geological formations under glaciation-induced stresses, pressures and temperature changes.

Using OpenGeoSys, an open-source finite element simulator, we analyzed various process couplings to understand the underlying physical processes and numerical instabilities. We simulated vertical cross-sections of geological models relevant to nuclear waste repository sites, incorporating comprehensive geological data to capture the formations' heterogeneity and structural features. A viscoplastic material model was used for rock salt strata to account for dislocation creep and pressure-solution creep. The study benefited from rigorous automation of the entire simulation workflow, making the setup suitable for evaluating actual repository sites regarding integrity criteria.

Although the modeled rock salt strata were hydraulically deactivated, results were highly dependent on hydraulic boundary conditions. Groundwater flow significantly altered the geological temperature profile via advective heat transport and influenced the temperature-dependent creep behavior. The rock salt creep law, applied over the extensive timescales at hand, approached the limits of the finite-element-method (FEM) with small-strain assumptions. Throughout the modeled glacial cycle, the salt strata exhibit low deviatoric stresses. Fluid pressure and dilatancy criteria are not violated in the repository during the modeled period.