%0 Journal Article %T Resolving hydromechanical coupling in two and three dimensions: spontaneous channelling of porous fluids owing to decompaction weakening %+ Institut des sciences de la terre [Lausanne] (ISTE) %+ Géosciences Rennes (GR) %A Räss, L %A Duretz, Thibault %A Podladchikov, Y. %< avec comité de lecture %@ 0956-540X %J Geophysical Journal International %I Oxford University Press (OUP) %V 218 %N 3 %P 1591-1616 %8 2019-09-01 %D 2019 %R 10.1093/gji/ggz239 %K Creep and deformation %K Permeability and porosity %K Geomechanics %K Non-linear differential equations %K Numerical modelling %Z Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]Journal articles %X Fingering, veining, channelling and focussing of porous fluids are widely observed phenomena in the Earth’s interior, driving a range of geo-processes across all scales. While observations suggest fairly localized flow patterns induced by fractures, the classical Darcian model predicts diffusive behaviour that leads to never-ending spreading and delocalization. We here investigate an alternative physical mechanism without the need to involve fractures. Decompaction weakening leads to the formation and propagation of localized flow-pathways in fluid-saturated porous media. We numerically solve the coupled equations using high-resolution 2-D and 3-D numerical modelling to predict non-linear porous flow in a non-linearly viscously deforming matrix. We show that high-porosity channels may be a dynamic and natural outcome of sufficiently resolved hydromechanical coupling and decompaction weakening. We propose an efficient solution strategy that involves an iterative pseudo-transient numerical method to solve the coupled system of equations in a matrix-free fashion. We discuss benefits and limitations of this approach that performs optimally on hardware accelerators such as graphical processing units and is well-suited for supercomputing. We benchmark the pseudo-transient routines against commonly used direct-iterative solving strategies and show convergence towards identical results. Furthermore, we use the fast solver to systematically study in 2-D the high-porosity channel propagation velocity as a function of bulk and shear viscosity ratios and report discrepancy between 2-D and 3-D configurations. We conclude that the fluid-flow rate in the channels is up to three orders of magnitude higher than expected by pure Darcian flow regimes and show that the high-porosity channels occurrence remains with strain rate dependant shear viscosity. We provide both the 2-D MATLAB-based direct-iterative and pseudo-transient routines for full reproducibility of the presented results and suggest our model configuration as a key benchmark case to validate the implementation of hydromechanical coupling in 2-D and 3-D numerical codes. The routines are available from Bitbucket and the Swiss Geocomputing Centre website, and are also supporting information to this paper %G English %2 https://insu.hal.science/insu-02284570/document %2 https://insu.hal.science/insu-02284570/file/Rass-GJI-2019.pdf %L insu-02284570 %U https://insu.hal.science/insu-02284570 %~ INSU %~ UNIV-RENNES1 %~ UR2-HB %~ CNRS %~ GR %~ OSUR %~ UR1-HAL %~ UR1-SDLM %~ GR-3T %~ UNIV-RENNES2 %~ TEST-UR-CSS %~ UNIV-RENNES %~ INRAE %~ UR1-ENV %~ TEST3-HALCNRS %~ TEST4-HALCNRS %~ TEST5-HALCNRS