8 results on '"Monachesi, Leonardo"'
Search Results
2. Groundwater response to tidal fluctuations in wedge-shaped confined aquifers
- Author
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Cuello, Julián E., Guarracino, Luis, and Monachesi, Leonardo B.
- Published
- 2017
- Full Text
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3. Bayesian inversion of joint SH seismic and seismoelectric data to infer glacier system properties.
- Author
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Macchioli‐Grande, Franco, Zyserman, Fabio, Monachesi, Leonardo, Jouniaux, Laurence, and Rosas‐Carbajal, Marina
- Subjects
MONTE Carlo method ,MARKOV chain Monte Carlo ,DATA logging ,PROBABILITY density function ,MARGINAL distributions ,SEISMIC waves ,GLACIERS ,MODULUS of rigidity - Abstract
In glacial studies, properties such as glacier thickness and the basement permeability and porosity are key to understand the hydrological and mechanical behaviour of the system. The seismoelectric method could potentially be used to determine key properties of glacial environments. Here we analytically model the generation of seismic and seismoelectric signals by means of a shear horizontal seismic wave source on top of a glacier overlying a porous basement. Considering a one‐dimensional setting, we compute the seismic waves and the electrokinetically induced electric field. We then analyse the sensitivity of the seismic and electromagnetic data to relevant model parameters, namely depth of the glacier bottom, porosity, permeability, shear modulus and saturating water salinity of the glacier basement. Moreover, we study the possibility of inferring these key parameters from a set of very low noise synthetic data, adopting a Bayesian framework to pay particular attention to the uncertainty of the model parameters mentioned above. We tackle the resolution of the probabilistic inverse problem with two strategies: (1) we compute the marginal posterior distributions of each model parameter solving multidimensional integrals numerically and (2) we use a Markov chain Monte Carlo algorithm to retrieve a collection of model parameters that follows the posterior probability density function of the model parameters, given the synthetic data set. Both methodologies are able to obtain the marginal distributions of the parameters and estimate their mean and standard deviation. The Markov chain Monte Carlo algorithm performs better in terms of numerical stability and number of iterations needed to characterize the distributions. The inversion of seismic data alone is not able to constrain the values of porosity and permeability further than the prior distribution. In turn, the inversion of the electric data alone, and the joint inversion of seismic and electric data are useful to constrain these parameters as well as other glacial system properties. Furthermore, the joint inversion reduces the uncertainty of the model parameters estimates and provides more accurate results. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
4. Seismic wave propagation in coupled fluid and porous media: A finite element approach.
- Author
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Bucher, Federico, Zyserman, Fabio I., and Monachesi, Leonardo B.
- Subjects
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POROUS materials , *THEORY of wave motion , *SEISMIC waves , *POROELASTICITY , *FLUIDS - Abstract
We present a numerical method to simulate seismic wave propagation in coupled fluid and porous media. We developed a numerical finite element–based algorithm to approximate solutions to viscoacoustic and Biot's equations, considering the open pore conditions at the interfaces between both media. The algorithm architecture allows to simulate arbitrary distributions of viscoacoustic and poroelastic regions, facilitating the modelling of heterogeneous systems involving complex geometries. The algorithm includes a double parallelization scheme whose efficiency in terms of computing time and memory requirements was tested for different core distributions and mesh sizes. We validate our proposal by performing a comparison between its results and those obtained with a well‐known freely available code. We test its capabilities by studying two different scenarios with geophysical interest: a lake with an irregular bottom and a fractured porous medium. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
5. A generalized effective anisotropic poroelastic model for periodically layered media accounting for both Biot’s global and interlayer flows
- Author
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Milani, Marco, Monachesi, Leonardo Bruno, Sabbione, Juan Ignacio, Rubino, Jorge German, and Holliger, Klaus
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Physics::Fluid Dynamics ,Mathematical formulation ,Attenuation ,Anisotropy ,Geofísica ,Meteorología y Ciencias Atmosféricas ,CIENCIAS NATURALES Y EXACTAS ,Ciencias de la Tierra y relacionadas con el Medio Ambiente ,Physics::Geophysics ,Rock physics - Abstract
We present a generalized effective poroelastic model for periodically layered media in the mesoscopic scale range, which accounts for both Biot’s global and interlayer wave-induced fluid flow, as well as for the anisotropy associated with the layering. Correspondingly, it correctly predicts the existence of the fast and slow P-waves as well as quasi and pure S-waves. The proposed analytical model is validated through comparisons of the P-wave and S-wave phase velocity dispersion and attenuation characteristics with those inferred from a one-dimensional numerical solution of Biot’s poroelastic equations of motion. We also compare our model with the classical mesoscopic model of White for a range of scenarios. The results demonstrate that accounting for both wave-induced fluid flow mechanisms is essential when Biot’s global flow prevails at frequencies that are comparable or smallerwith respect to those governing interlayer flow. This is likely to be the case in media of high permeability, such as, for example, unconsolidated sediments, clean sandstones, karstic carbonates, or fractured rocks. Conversely, when interlayer flow occurs at smaller frequencies with respect to Biot’s global flow, the predictions of this model are in agreement with White’s model, which is based on quasi-static poroelasticity., Facultad de Ciencias Astronómicas y Geofísicas
- Published
- 2016
6. An analytical study of seismoelectric signals produced by 1-D mesoscopic heterogeneities.
- Author
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Monachesi, Leonardo B., Rubino, J. Germán, Rosas-Carbajal, Marina, Jougnot, Damien, Linde, Niklas, Quintal, Beatriz, and Holliger, Klaus
- Subjects
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SIGNAL processing , *MESOSCOPIC systems , *FLUID dynamics , *POROUS materials , *FLUID flow , *PETROPHYSICS - Abstract
The presence of mesoscopic heterogeneities in fluid-saturated porous rocks can produce measurable seismoelectric signals due to wave-induced fluid flow between regions of differing compressibility. The dependence of these signals on the petrophysical and structural characteristics of the probed rock mass remains largely unexplored. In this work, we derive an analytical solution to describe the seismoelectric response of a rock sample, containing a horizontal layer at its centre, that is subjected to an oscillatory compressibility test. We then adapt this general solution to compute the seismoelectric signature of a particular case related to a sample that is permeated by a horizontal fracture located at its centre. Analyses of the general and particular solutions are performed to study the impact of different petrophysical and structural parameters on the seismoelectric response. We find that the amplitude of the seismoelectric signal is directly proportional to the applied stress, to the Skempton coefficient contrast between the host rock and the layer, and to a weighted average of the effective excess charge of the two materials. Our results also demonstrate that the frequency at which the maximum electrical potential amplitude prevails does not depend on the applied stress or the Skempton coefficient contrast. In presence of strong permeability variations, this frequency is rather controlled by the permeability and thickness of the less permeable material. The results of this study thus indicate that seismoelectric measurements can potentially be used to estimate key mechanical and hydraulic rock properties of mesoscopic heterogeneities, such as compressibility, permeability and fracture compliance. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
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7. Including poroelastic effects in the linear slip theory.
- Author
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Germán Rubino, J., Castromán, Gabriel A., Müller, Tobias M., Monachesi, Leonardo B., Zyserman, Fabio I., and Holliger, Klaus
- Subjects
SEISMIC wave studies ,ROCK deformation ,POROELASTICITY ,FLUID dynamics ,MATRICES (Mathematics) - Abstract
Numerical simulations of seismic wave propagation in fractured media are often performed in the framework of the linear slip theory (LST). Therein, fractures are represented as interfaces and their mechanical properties are characterized through a compliance matrix. This theory has been extended to account for energy dissipation due to viscous friction within fluid-filled fractures by using complex-valued frequency-dependent compliances. This is, however, not fully adequate for fractured porous rocks in which wave-induced fluid flow (WIFF) between fractures and host rock constitutes a predominant seismic attenuation mechanism. In this letter, we develop an approach to incorporate WIFF effects directly into the LST for a ID system via a complex-valued, frequency-dependent fracture compliance. The methodology is validated for a medium permeated by regularly distributed planar fractures, for which an analytical expression for the complex-valued normal compliance is determined in the framework of quasistatic poroelasticity. There is good agreement between synthetic seismograms generated using the proposed recipe and those obtained from comprehensive, but computationally demanding, poroelastic simulations. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
8. Effective Pore Fluid Bulk Modulus at Patchy Saturation: An Analytic Study.
- Author
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Monachesi, Leonardo B., Wollner, Uri, and Dvorkin, Jack
- Subjects
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PORE fluids , *BULK modulus , *ELASTIC waves , *MODULUS of rigidity , *DATA analysis - Abstract
A patchy saturated two‐layered porous rock, with each layer filled with a different fluid, is examined. We assume that this system is probed by an elastic wave having a wavelength much larger than the layers' thicknesses. We also assume that the diffusion length is smaller than the thickness of an individual layer, which implies hydraulic disconnection between layers. In the context of Gassmann's fluid substitution theory, we analytically derived an exact expression for the effective fluid bulk modulus assuming that both layers have the same porosity, dry frame, and mineral matrix properties. In addition we derived an approximate solution that works well at relatively high porosities. Both solutions are expressed as a weighted average of the arithmetic and harmonic averages of individual bulk moduli of the pore fluid. These weights are explicitly given as functions of the porosity, the fractional thicknesses of both layers, and the elastic moduli of the constituents. For the approximate solution, one does not require explicit knowledge of the shear modulus of the rock. The comparison with laboratory data showed that, in the case where a porous, isotropic rock is filled with water and gas, the approximate solution can be used to model the measured data for high values of water saturation. Key Points: We derive exact and approximate analytic solutions to model the effective fluid bulk modulus of patchy saturated porous rocksWe compare and validate the solutions with stochastic simulation and laboratory data [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
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