The behaviour of low-viscosity, pressure-driven compressible pore fluid flows in
viscously deformable porous media is studied here with specific application to gas
flow in lava domes. The combined flow of gas and lava is shown to be governed by
a two-equation set of nonlinear mixed hyperbolic–parabolic type partial differential
equations describing the evolution of gas pore pressure and lava porosity. Steady state
solution of this system is achieved when the gas pore pressure is magmastatic and
the porosity profile accommodates the magmastatic pressure condition by increased
compaction of the medium with depth. A one-dimensional (vertical) numerical
linear stability analysis (LSA) is presented here. As a consequence of the pore-fluid
compressibility and the presence of gravitation compaction, the gradients present in
the steady-state solution cause variable coefficients in the linearized equations which
generate instability in the LSA despite the diffusion-like and dissipative terms in the
original system. The onset of this instability is shown to be strongly controlled by the
thickness of the flow and the maximum porosity, itself a function of the mass flow
rate of gas. Numerical solutions of the fully nonlinear system are also presented and
exhibit nonlinear wave propagation features such as shock formation. As applied to
gas flow within lava domes, the details of this dynamics help explain observations of
cyclic lava dome extrusion and explosion episodes. Because the instability is stronger
in thicker flows, the continued extrusion and thickening of a lava dome constitutes
an increasing likelihood of instability onset, pressure wave growth and ultimately
explosion.
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Elastic Properties of Confined Fluids from Molecular Modeling to Ultrasonic Experiments on Porous Solids
Fluids confined in nanopores are ubiquitous in nature and technology. In recent years, the interest in confined fluids has grown, driven by research on unconventional hydrocarbon resources -- shale gas and shale oil, much of which are confined in nanopores. When fluids are confined in nanopores, many of their properties differ from those of the same fluid in the bulk. These properties include density, freezing point, transport coefficients, thermal expansion coefficient, and elastic properties. The elastic moduli of a fluid confined in the pores contribute to the overall elasticity of the fluid-saturated porous medium and determine the speed at which elastic waves traverse through the medium. Wave propagation in fluid-saturated porous media is pivotal for geophysics, as elastic waves are used for characterization of formations and rock samples. In this paper, we present a comprehensive review of experimental works on wave propagation in fluid-saturated nanoporous media, as well as theoretical works focused on calculation of compressibility of fluids in confinement. We discuss models that bridge the gap between experiments and theory, revealing a number of open questions that are both fundamental and applied in nature. While some results were demonstrated both experimentally and theoretically (e.g. the pressure dependence of compressibility of fluids), others were theoretically predicted, but not verified in experiments (e.g. linear scaling of modulus with the pore size). Therefore, there is a demand for the combined experimental-modeling studies on porous samples with various characteristic pore sizes. The extension of molecular simulation studies from simple model fluids to the more complex molecular fluids is another open area of practical interest.
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- Award ID(s):
- 1944495
- NSF-PAR ID:
- 10230277
- Date Published:
- Journal Name:
- Applied physics reviews
- ISSN:
- 1931-9401
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0024114
