Pore Fluid Viscosity Research Articles

Modelling the rheology of living cell cytoplasm: poroviscoelasticity and fluid-to-solid transition

Eukaryotic cell rheology has important consequences for vital processes such as adhesion, migration, and differentiation. Experiments indicate that cell cytoplasm can exhibit both elastic and viscous characteristics in different regimes, while the transport of fluid (cytosol) through the cross-linked filamentous scaffold (cytoskeleton) is reminiscent of mass transfer by diffusion through a porous medium. To gain insights into this complex rheological behaviour, we construct a computational model for the cell cytoplasm as a poroviscoelastic material formulated on the principles of nonlinear continuum mechanics, where we model the cytoplasm as a porous viscoelastic scaffold with an embedded viscous fluid flowing between the pores to model the cytosol. Baseline simulations (neglecting the viscosity of the cytosol) indicate that the system exhibits seven different regimes across the parameter space spanned by the viscoelastic relaxation timescale of the cytoskeleton and the poroelastic diffusion timescale; these regimes agree qualitatively with experimental measurements. Furthermore, the theoretical model also allows us to elucidate the additional role of pore fluid viscosity, which enters the system as a distinct viscous timescale. We show that increasing this viscous timescale hinders the passage of the pore fluid (reducing the poroelastic diffusion) and makes the cytoplasm rheology increasingly incompressible, shifting the phase boundaries between the regimes.

Coupled DEM/CFD analysis of impact of free water on the static and dynamic response of concrete in tension regime

In this paper, the quasi-static and dynamic behavior of partially fluid-saturated concrete under two-dimensional (2D) uniaxial tension at the mesoscale is investigated numerically. It was calculated what effect the free pore fluid content (gas and water) had on the fracture process and strength of concrete in a tension regime. An improved pore-scale hydro-mechanical model based on DEM/CFD was used to simulate the behavior of fully and partially fluid-saturated concrete in quasi-static and dynamic conditions. The foundation of the fluid flow idea was a network of channels in a continuous area between discrete elements. In very porous, partially saturated concrete, a two-phase laminar fluid flow was proposed. To track the liquid/gas content, the position and volumes of the pores and cracks were considered. Numerical simulations of bonded granular specimens of a simplified spherical mesostructure that resembled concrete were carried out under dry and wet circumstances for two different strain rates. Investigations were conducted on the effects of fluid pore pressures, fluid saturations, and fluid viscosities on the strength and fracture process of concrete. The quasi-static tensile strength dropped nonlinearly with increasing fluid saturation and fluid viscosity during fluid migration through pores and cracks which contributed to a promoted fracture process. However, during rapid dynamic tensile deformation, a fracture process attenuated due to a fluid migration constraint from insufficient time to exit the pores. It caused the dynamic tensile strength to rise nonlinearly as fluid saturation and fluid viscosity increased.

Pore Fluid Dielectric Constant Effect on Geotechnical and Geo-Environmental Properties of Smectite and Kaolinite

ABSTRACT Organic compounds pose significant environmental concerns, including groundwater contamination. Clays are commonly used as liners to prevent contaminant permeation into the groundwater tables, necessitating an understanding of clay’s behavior in the presence of organic compounds. The presence of organic contaminants results in changes in the dielectric constant of pore fluid, which influences the interparticle energies and double layer thickness in the soil-pore fluid system. This study aims to elucidate the mechanisms of these changes by examining the response of smectite and kaolinite to variations in the dielectric constant. Experimental tests, including Atterberg limits, unconfined compression strength, water adsorption, sedimentation, pH, and XRD, were performed on clay samples at different concentrations of water-isopropyl alcohol mixtures. Results indicate that smectite exhibits higher Atterberg limits and water adsorption capacity compared to kaolinite. Smectite also shows more pronounced changes in response to decreasing dielectric constant. Conversely, changes in kaolinite’s behavior were attributed to variations in pore fluid viscosity and dipole moment. These findings emphasize the importance of considering viscosity and dipole moment alongside dielectric constant in predicting kaolinite behavior. Overall, this study enhances the understanding of how variations in pore fluid dielectric constant affect the geotechnical and geo-environmental behavior of smectite and kaolinite.

Dynamic Relative Permeabilities for Partially Saturated Porous Media Accounting for Viscous Coupling Effects: An Analytical Solution

We present an analytical model to compute frequency-dependent relative permeability functions for partially saturated porous media accounting for viscous coupling effects. For this, we consider the oscillatory motion of two immiscible fluid phases and solve the Navier–Stokes equations at the pore scale using suitable interface conditions between fluids. These calculations are combined with the generalized two-phase flow Darcy equations to obtain the corresponding upscaled macroscopic fluxes. By means of an analog pore model consisting of a bundle of cylindrical capillaries in which pore fluids are distributed in a concentric manner, we find closed analytical expressions for the complex-valued and frequency- and saturation-dependent relative permeability functions. These expressions allow for a direct assessment of viscous coupling effects on oscillatory flow for all frequencies and saturations. Our results show that viscous coupling effects significantly affect flow characteristics in the viscous and inertial regimes. Dynamic relative permeabilities are affected by the pore fluid densities and viscosities. Moreover, viscous coupling effects may induce two critical frequencies in the dynamic relative permeability curves, a characteristic that cannot be addressed by extending the classic dynamic permeability definition to partially saturated scenarios using effective fluids. The theoretical derivations and results presented in this work have implications for the estimation and interpretation of seismic and seismoelectric responses of partially saturated porous media.

Lattice Boltzmann modeling of the coupled imbibition-flowback behavior in a 3D shale pore structure under reservoir condition

Imbibition and flowback of fracturing fluid usually occur in the shale matrix after hydraulic fracturing, which significantly impacts shale gas production and environmental protection. The rocks of deep shale gas reservoirs are under high-temperature and high-temperature conditions. There are rich micro-nano pores with various pore structures in deep shale. In addition, the flowback behavior is significantly affected by the imbibition behavior because the flowback begins after the end of the imbibition. Therefore, an accurate pore-scale description of the coupled imbibition-flowback behavior is crucial to understand the flowback mechanism and its impacts. In this paper, a pseudo-potential lattice Boltzmann method is employed to simulate the coupled imbibition-flowback behavior in a digital shale core, where the digital core is reconstructed by Markov Chain-Monte Carlo method based on scanning microscope images of deep shale cores. The microcosmic mechanism of the imbibition and flowback is studied under deep shale conditions. The influence of some factors, such as pore structure, fluid viscosity, wettability, and flowback pressure difference, on the flowback behavior of fracturing fluid is investigated. It is found that the fracturing fluid advances almost uniformly throughout the pore space during the imbibition process. The fracturing fluid is easy to adsorb on the pore wall, and the shale gas is located in the middle of the pore space. The viscous fingering is clearly observed during the flowback process, where shale gas flows through large pores to form a flow channel, and the fracturing fluid stays in tiny pores. The flowback rate increases gradually with the flowback time and eventually tends to be almost constant. The wettability, flowback pressure difference, and pore structure significantly influence the flowback behavior, while the fracturing fluid viscosity has a smaller effect on the flowback process.

Analytical Prediction of Coal Spontaneous Combustion Tendency: Pore Structure and Air Permeability

In previous research, many scientists and researchers have carried out related studies about the spontaneous combustion of coal at both the micro and the macro scales. However, the macroscale study of coal clusters and piles cannot reveal the nature of oxidation and combustion, and the mesoscale study of coal molecule and functional groups cannot be directly applied to engineering practice. According to our literature survey, coal is a porous medium and its spontaneous combustion is a multi-scale process. Thus, the mesoscale study of coal’s spontaneous combustion is essential. In this manuscript, the mesoscale of the coal body (such as pore size, pore volume, and specific surface area), and the meso-scale structural morphological characteristics of the coal surface are finely analyzed and characterized. On this basis, the meso-scale structure of pores and fractures are digitally reconstructed. Furthermore, velocity and pressure distributions of the flow field in the pores of the scan plane are outlined and described by numerical simulation. The results indicate that, because of the pore structure characteristics and fluid viscosity, not all fluids in the pores demonstrate flow. This conclusion well explains the source of CO gas in methane extraction pipes, which is one of the main index/indicator gases of the spontaneous combustion of coal.

Propagation of acoustic wave and analysis of borehole acoustic field in porous medium of heterogeneous viscous fluid

Sound field in fluid-saturated porous medium is closely related to the viscosity of fluid and the heterogeneity of porous medium. In order to improve the physical mechanism of wave propagation in porous medium and expand its application in borehole acoustic field, the shear stress of porous fluid and the heterogeneity of pore structure are considered. The wave theory in porous medium containing viscous fluid is deduced based on the Biot theory. The influence of porous medium parameters on slow shear wave is analyzed, and the dispersion and attenuation of elastic wave caused by shear stress balance in porous fluid under the influence of inhomogeneous pore structure are studied. The analytical solution of borehole acoustic field in porous medium containing viscous fluid is further derived. The phase velocity and attenuation of borehole mode waves in heterogeneous porous medium, and the waveform of borehole full wave are calculated. The influence of pore fluid viscosity on borehole full wave is analyzed. The results show that there are slow shear waves in the porous medium containing viscous fluid. The slow shear wave is characterized by low velocity and large attenuation. In heterogeneous porous medium, the balance process of shear stress related to slow shear wave not only leads to the dispersion and attenuation of fast P-wave, but also affects the propagation characteristics of borehole pseudo Rayleigh wave and Stoneley wave. In addition, the pore fluid viscosity has a great influence on the borehole Stoneley wave. The present work improves the physical mechanism of acoustic wave propagation in porous medium and provides theoretical guidance for the explanation and application of borehole acoustic waves in porous formations.

Streaming Potential in Gas Phase Discrete Unsaturated Pore

The seismoelectric effect of porous media is the main basis for seismoelectric logging. At present, most of the studies on the seismoelectric effect in unsaturated porous media adopt the model of pores with continuous distribution of gas and liquid. There is a lack of theoretical research on the micro mechanism of the seismoelectric effect of unsaturated porous media with discrete gas phase, and the existing studies do not consider the effect of the electric double layer at the gas–liquid interface on the seismoelectric effect. Based on the capillary model, this work adopted the gas phase discrete model, combined the electric double layer theory and the seepage principle, considered the effect of electric double layer at the pore wall and the gas–liquid interface, and studied the micro principle of the seismoelectric effect of unsaturated porous media. Firstly, we studied the variation of gas–water two-phase flow pattern with saturation in unsaturated pores, then proposed the equivalent principle of series circuits, deduced the effective streaming current and conductance of a pore containing multiple bubbles, and then deduced the streaming potential coupling coefficient in the unsaturated pores. We also studied the effect of pore parameters such as saturation, pore size, bubble spacing, pore fluid viscosity, and salinity on the streaming potential coupling coefficient. The results show that the streaming potential coupling coefficient first increases and then decreases with the decrease in saturation, which is the same as the trend measured in Allègre’s experiment, and provide a theoretical explanation for the non-monotonic change in the coupling coefficient with saturation in unsaturated porous media.

Frequency-dependent AVO inversion applied to physically based models for seismic attenuation

SUMMARYSeismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potentially provide high-resolution subsurface models of seismic velocities and attenuation from offset/angle seismic gathers. P- and S-wave quality factors (Q), whose inverse represent a measure of attenuation, depend on reservoir rock and pore fluid properties, in particular, saturation, permeability, porosity, fluid viscosity and lithology; however, these quality factors are rarely taken into account in seismic AVO inversion. For this reason, in this work, we aim to integrate quality factors derived from physically based models in AVO inversion by proposing a gradient descent optimization-based inversion technique to predict the unknown model properties (P- and S-wave velocities, the related quality factors and density). The proposed inversion minimizes the non-linear least-squares misfit with the observed data. The optimal solution is iteratively obtained by optimizing the data misfit using a second-order limited-memory quasi-Newton technique. The forward model is performed in the frequency–frequency-angle domain based on a convolution of broad-band signals and a linearized viscoelastic frequency-dependent AVO (FAVO) equation. The optimization includes the adjoint-state-based gradients with the Lagrangian formulation to improve the efficiency of the non-linear seismic FAVO inversion process. The inversion is tested on synthetic seismic data, in 1-D and 2-D, with and without noise. The sensitivity for seismic quality factors is evaluated using various rock physics models for seismic attenuation and quality factors. The results demonstrate that the proposed inversion method reliably retrieves the unknown elastic and an-elastic properties with good convergence and accuracy. The stability of the inverse solution especially seismic quality factors estimation relies on the noise level of the seismic data. We further investigate the uncertainty of the solution as a function of the variability of the initial models.

SPH-DEM modeling of the seismic response of shallow foundations resting on liquefiable sand

In this study, the seismic response of shallow foundations resting on a liquefiable soil layer is modeled using a coupled smoothed particle hydrodynamics (SPH)-discrete element method (DEM) scheme. In this framework, the soil deposit is represented by an assembly of DEM particles and the fluid domain is lumped into a set of SPH particles carrying local fluid properties. The averaged forms of Navier-Stokes equations dictate the motion of the fluid-particle mixture and the interphase forces are estimated using well-known semi-empirical equations. A saturated soil-foundation system with an average contact pressure of 50 kPa was created using the coupled scheme. The foundation block was composed of a collection of DEM particles glued together by high-stiffness bonds. No-penetration boundary condition was applied to all sides of the foundation block to allow for fluid-foundation interaction. The model was subjected to a strong base acceleration and the response was analyzed and compared to the free-field. The ground settlement in the soil-foundation system mostly originated from co-seismic deviatoric deformations while volumetric strains were the main contributing factor at the free-field. In addition, the impact of soil permeability on the seismic response of the soil-foundation system was examined by changing the pore fluid viscosity. According to the results, as the soil permeability decreased, smaller excess pore pressures developed beneath the footing thanks to the slower migration of pore fluid from the sides and bottom, and a larger magnitude of soil strength and stiffness was maintained in the expansive zone. As a result, the system with the lowest permeability experienced the smallest foundation settlement while the foundation acceleration amplitude was the highest in this case. The results also showed that the percentage of post-shaking settlement appreciably increased in the lower-permeability deposits. The results of this study were compared with the published centrifuge studies that showed good qualitative consistency. • A SPH-DEM scheme is utilized to model the seismic response of shallow foundations on liquefiable soils. • Averaged form of Navier-Stokes equations are used to describe the pore fluid motion in the mixture. • The foundation block was composed of a collection of DEM particles glued together by high-stiffness bonds. • No-penetration boundary condition was applied to all foundation sides to allow for fluid-foundation interaction. • The results of this study qualitatively agree with published centrifuge studies.

Effect of Pore–Fluid Chemistry on the Undrained Shear Strength of Xanthan Gum Biopolymer-Treated Clays

Xanthan gum (XG) biopolymer-based soil treatment is an effective soil improvement method. In this study, we explored the effect of XG on the undrained shear strength of clays (kaolinite and montmorillonite) in chemically distinct pore fluids. Among the pore fluids tested, the undrained shear strength of kaolinite was the highest in kerosene, followed by deionized (DI) water and brine. This study hypothesized that the interparticle forces and interactions dominated the undrained shear strength of the kaolinite clay. In contrast, montmorillonite showed the highest undrained shear strength with DI water, followed by brine and kerosene, likely due to the increase in thickness of the viscous double layer that reduced the undrained strength of the montmorillonite clay. XG also affected the undrained shear strength of the clays, possibly due to the increase in viscosity of the pore fluids and modification of the clay interparticle fabrics. In DI water, XG increased the undrained shear strength of kaolinite (maximum shear strength was observed in the sample with an XG-to-soil mass ratio of 0.5%) via water absorption. Simultaneously, XG decreased the undrained shear strength of montmorillonite, likely due to XG-induced particle aggregation resulting from the changes in the montmorillonite particle surface charges. In 2-M-NaCl brine, the undrained shear strength increased with the increase in XG content, regardless of the mineral types, owing to the salt-induced double-layer compression and increase in concurrent XG-induced pore–fluid viscosity. However, the unaffected and constant undrained shear strength of both clays in nonpolar kerosene suggests that hydrating XG is a prerequisite for its application in soil treatment.

Three-dimensional biomechanical modeling of cylindrical bone-like porous materials subject to acoustic waves

This paper describes a three-dimensional (3D) analytical solution for the acoustic response of cancellous bone-like porous materials saturated with a viscous fluid. The effect of dynamic tortuosity, especially in clinically relevant ultrasound frequency ranges, is considered to investigate the effect of viscous interaction between the fluid and solid phases. The solution includes the effects of both fast and slow longitudinal waves as well as transverse waves propagating through the medium. The scattering operators and radial displacements are derived in terms of ultrasonic waveforms by applying the Helmholtz decomposition. The effect of different porosities, wall thickness ratios, and frequencies of incident waves on the radial displacement and scattering operators are investigated by considering various incident wave angles at forward and sideward directions. The results demonstrate that the incident wave angle has a significant effect on the radial displacement and scattering operators regardless of the porosity, wall thickness ratio, and viscosity of pore fluid. Furthermore, the distribution pattern of the radial displacement and scattering operators in relatively low frequency ranges is almost symmetric while asymmetric in relatively high frequency ranges. It is shown that the bone characterization using ultrasonic techniques is not only based on the mineral density, as used currently by electromagnetic wave-based tools, but also other biomechanical factors such as the porosity, viscosity of pore fluid, and wall thickness ratio of a cancellous bone structure. Also, the pattern of the reflected pressure can be an indicator of the state of a cancellous bone (healthy versus osteoporosis).

The Numerical study of the influence of a two-scale pore structure on the dynamic strength of water-saturated concrete

Many infrastructural concrete facilities, such as dams, bridge footings, foundations of port facilities and offshore drilling platforms, operate in a permanent contact with water. The permeable fractured-porous structure of concrete determines the water-saturated state of the surface layers of such concrete elements. Under dynamic contact loading, the pore fluid is capable of exerting a significant mechanical influence on the local stress-strain state and strength characteristics of the surface layers of concrete. This has to be taken into account when assessing the wear intensity of surface layers and predicting a concrete element’s service life. The aforesaid determines the relevance of the study aimed at identifying the influence of the pore fluid and characteristics of the concrete pore structure on the strength and fracture pattern under quasistatic and dynamic compressive loading. The present work is devoted to the theoretical study and generalization of the laws of mechanical influence of the pore fluid on the dynamic strength of high-strength concrete with a two-scale pore structure. The emphasis in the study is on analyzing the contributions of each of the pore subsystems to the integral mechanical effect of the fluid. To carry out such an analysis, a coupled hydromechanical model is developed. It takes into account the compositional structure of concrete, the presence of a pore space in a cement stone of two different scales, the interaction of a pore liquid and a solid-phase skeleton based on the Bio poroelasticity model, as well as fluid filtration in a pore space. By using the developed model were performed the numerical studies of the dependence between the compressive strength of the representative concrete volumes of the mesoscopic scale on the strain rate, the sample size, the pore fluid viscosity, and pore structure parameters. The simulation results showed the possibility of combining the obtained dependencies into a generalized (master) curve in terms of a combined dimensionless parameter, which has the meaning similar to the Darcy number. We identified two key factors that control the type and parameters of the concrete master curve of the dynamic strength. The first factor is the mobility of the pore fluid in the network of the capillary pores. It determines the rate of stress equalization in the porous skeleton due to fluid flow. The second factor is the interconnection of large micropores with the network of the small capillary pore channels. It determines the magnitude of the decrease in stress concentration in micropores by filtering the excess pore fluid into the capillary pore network. It is shown that the contributions of these two factors to the amplitude of variation of the dynamic strength of the water-saturated concrete are additive, and their total contribution reaches 25 %.

Theoretical analysis and numerical simulation of acoustic waves in gas hydrate-bearing sediments* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11974018 and 11734017) and the Strategic Pilot and Technology Special Fund of the Chinese Academy of Sciences, China (Grant No. XDA14020303).

Based on Carcione–Leclaire model, the time-splitting high-order staggered-grid finite-difference algorithm is proposed and constructed for understanding wave propagation mechanisms in gas hydrate-bearing sediments. Three compressional waves and two shear waves, as well as their energy distributions are investigated in detail. In particular, the influences of the friction coefficient between solid grains and gas hydrate and the viscosity of pore fluid on wave propagation are analyzed. The results show that our proposed numerical simulation algorithm proposed in this paper can effectively solve the problem of stiffness in the velocity–stress equations and suppress the grid dispersion, resulting in higher accuracy compared with the result of the Fourier pseudospectral method used by Carcione. The excitation mechanisms of the five wave modes are clearly revealed by the results of simulations. Besides, it is pointed that, the wave diffusion of the second kind of compressional and shear waves is influenced by the friction coefficient between solid grains and gas hydrate, while the diffusion of the third compressional wave is controlled by the fluid viscosity. Finally, two fluid–solid (gas-hydrate formation) models are constructed to study the mode conversion of various waves. The results show that the reflection, transmission, and transformation of various waves occur on the interface, forming a very complicated wave field, and the energy distribution of various converted waves in different phases is different. It is demonstrated from our studies that, the unconventional waves, such as the second and third kinds of compressional waves may be converted into conventional waves on an interface. These propagation mechanisms provide a concrete wave attenuation explanation in inhomogeneous media.

Dynamic response analysis of fluid-saturated porous rectangular plates

Abstract Based on Biot’s model for saturated porous media, the governing equation of fluid-saturated porous rectangular plates is presented, in which the compressibility of solid particles and fluid and the viscosity of pore fluid is taken into account. A series solution is given for simply-supported fluid-saturated porous plates. The accuracy of the solution is validated by degenerating the fluid-saturated porous rectangular plates into single-phase solid rectangular plates. As a numerical example, the free vibration characteristic and the dynamic response under harmonic loads are analysed. The influence of surface infiltration conditions, porosity, pore fluid permeability coefficient and loading frequency on the free vibration frequency is discussed.

Surface-erosion behaviour of biopolymer-treated soils assessed by EFA

Exocultured biopolymers are ecofriendly soil-stabilisation agents with superior particle bonding, hydrogel-formation characteristics and zero endoculture duration. However, the use of exocultured biopolymers for enhancing soil resistance against surface erosion by water flow is yet to be investigated. Using erosion function apparatus (EFA) in combination with an ultrasonic P-wave reflection monitoring device, the effect of exocultured biopolymers on the erosion parameters of critical shear stress and the erodibility coefficient was examined in this study in soils with different particle distributions. In this way, biopolymer soil treatment showed a ten-fold increase in critical shear stress along with a 90% reduction in erodibility coefficient; results which could be attributed to enhanced particle-to-particle contact and increased pore-fluid viscosity and pore clogging. The results of this study demonstrate the feasibility of using exocultured biopolymers in mitigating surface erosion of erosion-prone soils.

A dynamic elastic model for squirt-flow effect and its application on fluid-viscosity-associated velocity dispersion in reservoir sandstones

Velocity dispersion is a common phenomenon for fluid-charged porous rocks and carries important information on the pore structure and fluid in reservoir rocks. Previous ultrasonic experiments had measured more significant non-Biot velocity dispersion on saturated reservoir sandstones with increasing pore-fluid viscosity. Although wave-induced local squirt-flow effect could in theory cause most of the non-Biot velocity dispersion, its quantitative prediction remains a challenge. Several popular models were tested to predict the measured velocities under undrained conditions, but they either underestimated the squirt-flow effect or failed to simultaneously satisfy P- and S-wave velocity dispersions (especially for higher viscosity fluids). Based on the classic double-porosity theory that pore space is comprised of mainly stiff/Biot’s porosity and minor compliant porosity, an effective “wet frame” was hypothesized to account for the squirt-flow effect, whose compliant pores are filled with a hypothesized fluid with dynamic modulus. A new dynamic elastic model was then introduced by extending Biot theory to include the squirt-flow effect, after replacing the dry-frame bulk/shear moduli with their wet-frame counterparts. In addition to yielding better velocity predictions for P- and S-wave measurements of different fluid viscosities, the new model is also more applicable because its two key tuning parameters (i.e., the effective aspect ratio and porosity of compliant pores) at in situ reservoir pressure could be constrained with laboratory velocity measurements associated with pore-fluid viscosities.

Centrifuge modelling of static liquefaction in submarine slopes: scaling law dilemma

The scaling laws for the centrifuge modelling of the initiation and propagation of static liquefaction in submerged slopes are investigated in this paper. A theoretical model is developed to analytically determine the scaling factor of fluid viscosity in simulating the onset of static liquefaction by detailed analysis of the hydromechanical processes at the grain scale. Based on this, a fluid with a viscosity of [Formula: see text]-times that of water ([Formula: see text]-fluid) is suggested, where N is the geometrical scaling factor in centrifuge modelling. A fluid with a viscosity of N-times that of water (N-fluid) was adopted for simulating dynamic events in the centrifuge; N-fluid is used and suggested by previous researchers. Centrifuge tests were designed to examine and verify the scaling factors for pore fluid viscosity in simulating the onset of static liquefaction and the post-liquefaction behaviour of subaqueous landslides. These tests were performed at 10g, 30g, and 50g conditions, with [Formula: see text]-fluid, N-fluid or water, where g is the Earth’s gravitational acceleration. Results confirm that the correct scaling factors (prototype/model) for pore fluid viscosity are [Formula: see text] and 1/N for investigating the onset of static liquefaction and the post-failure behaviour of the submarine slopes, respectively.

Wave propagation characteristics at the welded interface of double-porosity solid and double-porosity dual-permeability materials

ABSTRACT In the present study, propagation characteristics (reflection/refraction phenomena) at the welded interface of two dissimilar double-porosity media are investigated. Both the double-porosity materials behave dissipative to wave propagation due to the presence of viscosity in pore fluid. All the waves (i.e. incident, reflected and refracted) are considered as inhomogeneous (i.e. different directions of propagation and attenuation). Reflection and refraction coefficients are calculated theoretically in the form of eight inhomogeneous linear equations. Reflected and refracted waves energy shares are represented with two different energy matrix. For the incidence of and SV waves, the partition of incident energy among various reflected and refracted waves is calculated numerically for particular numerical examples. The impacts of various physical properties (like, pore-fluid viscosity, double-porosity structure, wave-induced fluid flow and permeability) of double-porosity dual-permeability materials on the partition of incident energy are depicted graphically at each angle of incidence. Numerically, the conservation of incident energy during the reflection/refraction process is obtained at each angle of incidence.

A simple and general macroscopic model for local-deformation effects in fluid-saturated porous rock

SUMMARYWave-induced fluid flows (WIFF) can be viewed as cases of broader local-deformation (LD) phenomena and represent the principal causes of seismic-wave attenuation in fluid-saturated porous rock. Most existing WIFF models refer to greatly simplified microstructures and specific flow patterns, such as planar divergent flows within thin cracks (squirt flows, SF) or flows within patchy-saturation zones. However, such microstructures represent only idealized mathematical models that may be impossible to consistently identify within a given rock. At the same time, most details of such microstructures are insignificant for seismic waves, which are only sensitive to averaged properties of the medium. To perform microstructure-independent modelling of LD effects, we develop a simple yet general approach based entirely on a macroscopic local-deformation variable. This variable is broadly analogous to Biot's fluid content and is illustrated for two specific microstructural models. The macroscopic model is Biot-consistent and uses only time- and frequency-independent material properties. Both local and global (Biot's) pore flows and all types of waves and deformations are explained in a rigorous and consistent manner. The model allows constraining a minimal set of material properties responsible for all observed elastic and anelastic effects in porous rock. Because of making no assumptions about the microstructures and their spatial scales, this approach should comprise at least some of the existing WIFF models. In particular, this model accurately reproduces all attenuation and velocity dispersion spectra predicted by a broadly used SF model. The model also contains effects not considered previously, such as bulk viscosity of pore fluid and viscous coupling between the rock frame and fluid-filled pores. The model offers straightforward extensions to multiple porosities and cases of viscous fluids in primary pores. Based on the resulting differential equations, physically consistent schemes for numerical modelling of seismic wavefields can be developed for porous rock with arbitrary LD effects.