Abstract The interplay between compaction‐driven fluid flow and plastic yielding within porous media is investigated through numerical modeling. We establish a framework for understanding the dynamics of fluid flow in deforming porous materials that corresponds to the equations describing solitary porosity wave propagation. A concise derivation of the coupled fluid flow and poro‐viscoelastoplastic matrix behavior is presented, revealing a connection to Biot's equations of poroelasticity and Gassmann's theory in the elastic limit. Our findings demonstrate that fluid overpressure resulting from channelized fluid flow initiates the formation of new shear zones. Through three‐dimensional simulations, we observe that the newly formed shear zones exhibit a parabolic shape. Furthermore, plasticity exerts a significant influence on both the velocity of fluid flow and the shape of fluid channels. Importantly, our study highlights the potential of spontaneous channeling of porous fluids to trigger seismic events by activating both new and pre‐existing faults.
Abstract Porosity waves are a mechanism by which fluid generated by devolatilization and melting, or trapped during sedimentation, may be expelled from ductile rocks. The waves correspond to a steady‐state solution to the coupled hydraulic and rheologic equations that govern flow of the fluid through the matrix and matrix deformation. This work presents an intuitive analytical formulation of this solution in one dimension that is general with respect to the constitutive relations used to define the viscous matrix rheology and permeability. This generality allows for the effects of nonlinear viscous matrix rheology and disaggregation. The solution combines the porosity dependence of the rheology and permeability in a single hydromechanical potential as a function of material properties and wave velocity. With the ansatz that there is a local balance between fluid production and transport, the solution permits prediction of the dynamic variations in permeability and pressure necessary to accommodate fluid production. The solution is used to construct a phase diagram that defines the conditions for smooth pervasive flow, wave‐propagated flow, and matrix fluidization (disaggregation). The viscous porosity wave mechanism requires negative effective pressure to open the porosity in the leading half of a wave. In nature, negative effective pressure may induce hydrofracture, resulting in a viscoplastic compaction rheology. The tubelike porosity waves that form in such a rheology channelize fluid expulsion and are predicted by geometric argumentation from the one‐dimensional viscous solitary wave solution.
<p>Fluid&#8211;rock interactions link mass and energy transfer with large-scale tectonic deformation, drive the formation of mineral deposits, carbon sequestration, and rheological changes of the lithosphere. While spatial evidence indicates that fluid&#8211;rock interactions operate on length scales ranging from the grain boundary to tectonic plates, the timescales of regional fluid&#8211;rock interactions remain essentially unconstrained, despite being critically important for quantifying the duration of fundamental geodynamic processes. Here we show that reaction-induced transiently high permeability significantly facilitates fast fluid flow through low-permeability rock of the mid-crust. Using observations from an exceptionally well-exposed fossil hydrothermal system to inform a multi-element advective&#8211;diffusive&#8211;reactive transport model, we show that fluid-driven reaction fronts propagate with ~10 cm year<sup>-1</sup><sub>,</sub> equivalent to the fastest tectonic plate motion and mid-ocean ridge spreading rates. Consequently, in the presence of reactive fluids, large-scale fluid-mediated rock transformations in continental collision and subduction zones occur on timescales of tens of years, implying that natural carbon sequestration, ore deposit formation, and transient and long-term petrophysical changes of the crust proceed, from a geological perspective, instantaneously.</p>
Abstract Focused fluid flow is common in sedimentary basins worldwide, where flow structures often penetrate through sandy reservoir rocks, and clay‐rich caprocks. To better understand the mechanisms forming such structures, the impacts of the viscoelastic deformation and strongly nonlinear porosity‐dependent permeability of clay‐rich materials are assessed from an experimental and numerical modeling perspective. The experimental methods to measure the poroviscoelastic and transport properties of intact and remolded shale have been developed, and the experimental data is used to constrain the numerical simulations. It is demonstrated that viscoelastic deformation combined with nonlinear porosity‐dependent permeability triggers the development of localized flow channels, often imaged as seismic chimneys. The permeability inside a channel increases by several orders of magnitude compared to the background values. In addition, the propagation time scale and the channel size strongly depend on the material properties of the fluid and the rock. The time‐dependent behavior of the clay‐rich rock may play a key role in the long‐term integrity of the subsurface formations.
Abstract A two‐dimensional numerical simulation of lithospheric shortening shows the formation of a stable crustal‐scale shear zone due to viscous heating. The shear zone thickness is controlled by thermomechanical coupling that is resolved numerically inside the shear zone. Away from the shear zone, lithospheric deformation is dominated by pure shear, and tectonic overpressure (i.e., pressure larger than the lithostatic pressure) is proportional to the deviatoric stress. Inside the shear zone, deformation is dominated by simple shear, and the deviatoric stress decreases due to thermal weakening of the viscosity. To maintain a constant horizontal total stress across the weak shear zone (i.e., horizontal force balance), the pressure in the shear zone increases to compensate the decrease of the deviatoric stress. Tectonic overpressure in the weak shear zone can be significantly larger than the deviatoric stress at the same location. Implications for the geodynamic history of tectonic nappes including high‐pressure/ultrahigh‐pressure rocks are discussed.
<p>Developing new numerical reactive transport models is essential for predicting and describing natural and technogenic petroleum and geological processes at different scales. Examples of such processes are pore fluid migration in subduction zones, causing seismic and volcanic activity, chemical and thermal enhanced oil recovery activities, etc. New numerical reactive transport models must be validated against analytical or semi-analytical solutions to ensure its correct numerical implementation. In this study, we construct thermo-hydro-chemo-mechanical model which takes into account multi-phase fluid flow in porous matrix associated with inter- and intra-phase chemical reactions with significant temperature and volume effect and treats porosity and permeability evolution. All equations are derived from basic principles of conservation of mass, energy, and momentum and the thermodynamic admissibility of all equations is verified. We solve the proposed system of equations both with a finite difference approach on a staggered grid and characteristic-based Lax-Friedrichs different order schemes to treat the disintegration of discontinuities.&#160; Resolving the problem of large discrepancies during the time evolution of coupled physical processes is challenging. For that, we use pseudo-iterations which force slow modes to attenuate quickly. Furthermore, we perform dimensionless analysis of the proposed model which allows us to detect proper dimensionally independent, dimensionally dependent and non-dimensional parameters. A new semi-analytical is derived which is based on a relaxation method of defining the stationary solution of system of partial differential equations, so detection specific regimes for reaction front propagation are possible. As a result, reaction front velocity dependence on Peclet, Damkohler and Lewis nondimensional parameters is obtained.</p>
