Coupling changes in densities and porosity to fluid pressure variations in reactive porous fluid flow: Local thermodynamic equilibrium

Abstract

Mineralogical reactions which generate or consume fluids play a key role during fluid flow in porous media. Such reactions are linked to changes in density, porosity, permeability, and fluid pressure which influence fluid flow and rock deformation. To understand such a coupled system, equations were derived from mass conservation and local thermodynamic equilibrium. The presented mass conservative modeling approach describes the relationships among evolving fluid pressure, porosity, fluid and solid density, and devolatilization reactions in multicomponent systems with solid solutions. This first step serves as a framework for future models including aqueous speciation and transport. The complexity of univariant and multivariant reactions is treated by calculating lookup tables from thermodynamic equilibrium calculations. Simplified cases were also investigated to understand previously studied formulations. For nondeforming systems or systems divided into phases of constant density, the equations can be reduced to porosity wave equations with addition of a reactive term taking the volume change of reaction into account. For closed systems, an expression for the volume change of reaction and the associated pressure increase can be obtained. The key equations were solved numerically for the case of devolatilization of three different rock types that may enter a subduction zone. Reactions with positive Clapeyron slope lead to an increase in porosity and permeability with decreasing fluid pressure resulting in sharp fluid pressure gradients around a negative pressure anomaly. The opposite trend is obtained for reactions having a negative Clapeyron slope during which sharp fluid pressure gradients were only generated around a positive pressure anomaly. Coupling of reaction with elastic deformation induces a more efficient fluid flow for reactions with negative Clapeyron slope than for reactions with positive Clapeyron slope.

Competition Between Crystallization‐Induced Expansion and Creep Compaction During Gypsum Formation, and Implications for Serpentinization

“…The net strain behavior results from the distribution of these processes throughout the entire sample, which in turn are controlled by reaction rates, movement of Ca + and SO ions through grain boundary fluid films and pore fluid as well as movement of the pore fluid itself, the local solubility of gypsum and bassanite, and the magnitude of the applied load. A sophisticated multiphysics model would be needed to evaluate the relative contribution of all these effects on the deformation behavior of hydrating porous materials (see Coussy, ; Malvoisin, Podladchikov, et al ).…”

M2Di: Concise and efficient MATLAB 2‐D Stokes solvers using the Finite Difference Method

“…In this perspective, the development of 2‐D THCM models will benefit from the presented mechanical solvers (M). The latter will be used as the main building block to further tackle studies of thermomechanical shear localization [ Duretz et al ., ] (TM coupling), two‐phase flow [ Yarushina and Podladchikov , ] leading to fluid channeling instabilities [ Yarushina et al ., ; Räss et al ., ] (HM coupling), reactive porosity waves [ Malvoisin et al ., ] (HCM coupling), or THCM coupling [ Keller and Katz , ; Weatherley and Katz , ]. Features arising from THCM coupling are often localized in space, close to material interfaces (e.g., shear zones, fluid channeling) and may depend on the local pressure field.…”

The Potential for Metamorphic Thermal Pulses to Develop During Compaction‐Driven Fluid Flow

“…The duration of these flow events are even shorter than in our current model. We note that in cold subducting lithosphere, where elasticity might play a more important role than in the orogenic core, elastic deformation in the two-phase model can greatly reduce the time scales of fluid flow (Malvoisin et al, 2015), so the general compactiondriven fluid flow still remains relevant and promising for producing episodic thermal pulses. Furthermore, given that large-scale shear zones are likely to preexist (Camacho et al, 2005), they can act as larger focusing zones into which the self-organized compaction-driven flows in this study conflux.…”

“…In brief, densities of fluid and solid phases are assumed constant, and the small porosity approximation is taken such that solid phase advection can be omitted to reduce the number of equations. Effects of nonconstant fluid/solid densities in triggering porosity waves and fluid networks during metamorphism are investigated in two recent studies (Malvoisin et al, 2015;Pl€ umper et al, 2017); this study, however, focuses on advective heat transport after porosity waves are triggered and evolve into channels. In addition, shear deformation is neglected as in previous studies to focus on volumetric compaction/decompaction (Connolly & Podladchikov, 2007;Spiegelman et al, 2001), but shear viscosity is considered because bulk viscosity depends on it via equation (6) (Hier-Majumder et al, 2006;Schmeling et al, 2012;Simpson et al, 2010).…”