Papers by Manolis Veveakis
Deep-seated landslides represent one of the most devastating natural hazards on earth, typically ... more Deep-seated landslides represent one of the most devastating natural hazards on earth, typically creeping at inappreciable velocities over several years be- fore suddenly collapsing with catastrophic speeds. They can have detrimental consequences to society, causing fatalities and prone to affect transportation infrastructures. In this study, we validate that monitoring the basal temperature of a creeping landslide, and fusing it with physics-based modeling, can offer predictive and control capabilities for the landslide’s response. The study shows that physics-based models can be trained in the same phase-space, and has been applied to four case studies for its validity. We anticipate our results to be the starting point for a new era in monitoring, controlling, and forecasting deep-seated landslides, aiming at alleviating their devastating impact on society.
Springer Series in Geomechanics and Geoengineering, 2017
This paper presents a novel method to investigate shear stimulation at an injection well in Enhan... more This paper presents a novel method to investigate shear stimulation at an injection well in Enhanced Geothermal Systems (EGS). Nowadays, the technique of EGS has been extensively used for extracting thermal energy from the earth. As the intrinsic permeability of the rock is usually too low to allow an economic flow, stimulation for fractures is incorporated. The connectivity of fracture networks around boreholes dominates the system behaviour. In theory, stimulations including both tensile (mode I) and shear (mode II) fracturing are desired, so that sufficient surface area for heat exchange is produced. However, shear stimulation is considered a safer choice than tensile fracturing in terms of possibility of inducing local earthquakes. This study investigates shear fractures only, from a slip-line field point of view. The rock is modelled as elasto-viscoplastic material with damage mechanics coupled. A numerical simulator REDBACK, based on the MOOSE framework, is employed to solve this coupled multi-physics involved problem. With injection pressure imposed on the interior of a borehole, slip lines grows in the form of logarithmic spirals, indicating the potential trace of shear fractures. Imperfections are imposed on the boundary as seeding for the spirals. Cases with and without thermo-mechanical coupling are compared, indicating the essential role of shear-heating feedback in enhancing shear fractures. Bifurcation analysis for various Arrhenius numbers is performed, demonstrating a clear exponential relationship between critical injection pressure and the local temperature of host rock.
Under compressive creep, visco-plastic solids experiencing internal mass transfer processes have ... more Under compressive creep, visco-plastic solids experiencing internal mass transfer processes have been recently proposed to accommodate singular cnoidal wave solutions, as material instabilities at the stationary wave limit. These instabilities appear when the loading rate is significantly faster than the capability of the material to diffuse internal perturbations and lead to localized failure features (e.g., cracks and compaction bands). This type of solution, generally found in fluids, has strong nonlinearities and periodic patterns. Due to the singular nature of the solutions, the applicability of the theory is currently limited. Additionally, effective numerical tools require proper regularization to overcome the challenges that singularity induces. We focus on the numerical treatment of the governing equation using a nonlinear approach building on a recent adaptive stabilized finite element method. This method provides a residual representation to drive adaptive mesh refinement, a particularly useful feature for the problem at hand. We compare against analytical and standard finite element solutions to demonstrate the performance of our approach. We then investigate the sensitivity of the diffusivity ratio, main parameter of the problem, and identify multiple possible solutions, with multiple stress peaks. Finally, we show the evolution of the spacing between peaks for all solutions as a function of that parameter.
When hot and ductile rocks fail they do so with an astonishing variety. Observations from crustal... more When hot and ductile rocks fail they do so with an astonishing variety. Observations from crustal deformation show that when the fluid content is low (less than a few per cent) they form the cores of anastomosing mylonitic shear zones, which feature strong gradients in grain size towards their metamorphic fluid rich centre (Fusseis et al., 2009). In circumstances where the fluid/melt content is high they form macroscopically visible ductile fractures (Weinberg and Regenauer-Lieb, 2010) which allow melt transfer into the shallower crust forming the feeder zone of granites. We show here that all of the above phenomena are new types of instabilities well known from high temperature deformation of ceramics, i.e. materials that otherwise show brittle cleavage at cold laboratory conditions. The new failure modes boil down to a series of microscopic processes, where upon increasing temperature and decreasing applied stress failure modes transition from brittle cleavage to transgranular and...
The dynamic response of the geothermal reservoirs of Soultz-sous-Forêts (NE France) and a new sit... more The dynamic response of the geothermal reservoirs of Soultz-sous-Forêts (NE France) and a new site in Iceland are theoretically studied upon fluid injection and production. Since the Soultz case can be considered the most comprehensive project in the area of enhanced geothermal systems (EGS), it is tailored for the testing of forward modeling techniques that aim at the characterization of fluid dynamics and mechanical properties in any deeply-seated fractured cystalline reservoir [e.g. Held et al., 2014]. We present multi-physics finite element models using the recently developed framework MOOSE (mooseframework.org) that implicitly consider fully-coupled feedback mechanisms of fluid-rock interaction at depth where EGS are located (depth > 5 km), i.e. the effects of dissipative strain softening on chemical reactions and reactive transport [Poulet et al., 2016]. In a first suite of numerical experiments, we show that an accurate simulation of propagation fronts allows studying coup...
Instabilities Modeling in Geomechanics, 2021
Fifth International Conference on Fault and Top Seals, 2019
Rock Mechanics and Rock Engineering
Carbonate sediments play a prominent role on the global geological stage as they store more than ... more Carbonate sediments play a prominent role on the global geological stage as they store more than $$60\%$$ 60 % of world’s oil and $$40\%$$ 40 % of world’s gas reserves. Prediction of the deformation and failure of porous carbonates is, therefore, essential to minimise reservoir compaction, fault reactivation, or wellbore instability. This relies on our understanding of the mechanisms underlying the observed inelastic response to fluid injection or deviatoric stress perturbations. Understanding the impact of deformation/failure on the hydraulic properties of the rock is also essential as injection/production rates will be affected. In this work, we present new experimental results from triaxial deformation experiments carried out to elucidate the behaviour of a porous limestone reservoir analogue (Savonnières limestone). Drained triaxial and isotropic compression tests were conducted at five different confining pressures in dry and water-saturated conditions. Stress–strain data and X...
This release includes the functionalities to handle damage zones around faults as lower dimension... more This release includes the functionalities to handle damage zones around faults as lower dimensional elements, as well as the erosion algorithm for the microscale
International Journal of Solids and Structures, 2022
The influence of the microstructural geometry on the behavior of porous media is widely recognize... more The influence of the microstructural geometry on the behavior of porous media is widely recognized, particularly in geomaterials, but also in biomaterials and engineered materials. Recent advances in imaging techniques, such as X-ray microcomputed tomography, and in modeling make it possible to capture the exact morphometry of the microstructure with high precision. However, most existing continuum theories only partially account for the morphometry. We propose here a unifying approach to link the strength of porous materials with the necessary and sufficient microstructural information, using Minkowski functionals, as per Hadwiger's theorem. A morphometric strength law is inferred from synthetic microstructures with a wide range of porosities and heterogeneities, through qualitative 2D phase-field simulations. Namely, the damage is modeled at the microstructural level by tracking the solid-pore interfaces under mechanical loading. The strength is found to be best described by an exponential function of the morphometers, thus generalizing early works on metals and ceramics. We then show that the predictiveness of this relationship extends to real porous media, including rocks and bones.
Springer Series in Geomechanics and Geoengineering, 2017
Compaction bands are localized failure patterns that appear in highly porous rock material under ... more Compaction bands are localized failure patterns that appear in highly porous rock material under the effect of relatively high confining pressure. Being affected mainly by volumetric compression, these bands appear to be almost perpendicular to the most compressive principal stress at a stress state at the so-called "cap" of the yield surface (Issen and Rudnicki, J Geoph Res 105:21529-21536 (2000) [4]). In this study we focus on the mechanism that leads to the onset of compaction bands by using a viscoplasticity model able to describe the post-localization response of these materials. The proposed constitutive framework is based on the overstress theory of Perzyna (Adv Appl Mech 9:243-377 (1966) [7]) and the anisotropic clay plasticity model of Dafalias (Mech Res Commun 13 (6):341-347 (1986) [1]) as modified by Dafalias and Taiebat (Geotechnique 63 (16):1406-1418 (2013) [2]) which provides not only the necessary "cap" of the yield surface, but introduces a rotational hardening mechanism thus taking into account possible anisotropic phenomena. Following the analysis of Veveakis and Regenauer-Lieb (J Mech Phys Solids 78:231-248 (2015) [8]) we identify the compaction bands as "static" cnoidal wave formations in the medium that occur at a post-yield regime and we study the effect of rotational and isotropic hardening on their onset. Moreover, we determine a theoretical lower limit of confining pressure in triaxial compression tests for the compaction bands to develop.
In this work we present an inversion framework to identify material properties defining the plast... more In this work we present an inversion framework to identify material properties defining the plastic behaviour of pore collapse modeled by thermo-hydro-mechanical simulations. This framework is built on the finite element REDBACK numerical simulator, which is capable of solving a multi-physics problem in a tightly coupled, massively parallel manner. We demonstrate the approach by matching the stress-strain response of an Adamswiller sandstone in a drained triaxial experiments.
A Finite Element implementation is presented to solve for Stokes flow on a deformable rock matrix... more A Finite Element implementation is presented to solve for Stokes flow on a deformable rock matrix reconstituted from a stack of computerized tomography images. Tightly coupling this flow solution with a mechanical deformation model exhibits the hydro-mechanical evolution of permeability in a fully saturated rock under compression. The scope of the presented micro-scale computation of permeability is demonstrated through a multi-scale simulation of pore pressure progression within a petroleum reservoir under production.
On the thermo-poro-mechanics of chemically active faults Shear zones in outcrops and core drillin... more On the thermo-poro-mechanics of chemically active faults Shear zones in outcrops and core drillings on active faults commonly reveal two scales of localization, with centimeter to tens of meters thick deformation zones embedding much narrower zones of mm-to cm-scale. The narrow zones are often attributed to some form of fast instability such as earthquakes or slow slip events. Surprisingly, the double localisation phenomenon seem to be independent of the mode of failure, as it is observed in brittle cataclastic fault zones as well as ductile mylonitic shear zones. In both a very thin layer of chemically altered, ultra fine grained ultracataclasite or ultramylonite is noted. We present an extension to the classical solid mechanical theory where both length scales emerge as part of the same evolutionary process of shearing the host rock. We highlight the important role of any type of solid-fluid phase transitions that govern the second degree localisation process in the core of the shear zone. In both brittle and ductile shear zones chemistry stops the localisation process caused by a multiphysics feedback loop leading to an unstable slip. The microstructural evolutionary processes govern the timescale of the transition between slow background shear and fast, intermittent instabilities in the fault zone core. The fast cataclastic fragmentation processes are limiting the rates of forming the ultracataclasites in the brittle domain, while the slow dynamic recrystallisation prolongs the transition to ultramylonites into a slow slip instability in the ductile realm.
In any geological formation, faults play an important role as they can range from impermeable sea... more In any geological formation, faults play an important role as they can range from impermeable seals to fluid pathways. At geological time scales, faults can exhibit steady creep and basins have been known to deform quite considerably. The study of fault mechanics has been widely studied and has been recently shown to play a role in affecting the behavior of fluid dynamics, namely the geometry of hydrothermal convection cells. Whilst the onset of hydrothermal convection has been extensively studied for more than a decade, little is known about the effects of mechanical deformation of faults (expressed as shear heating) on hydrothermal convection. With the need to solve for tightly coupled thermo-hydro-mechanics, we investigate these effects using a new open-source numerical multiphysics simulator, REDBACK. This simulator is specifically designed to study material instabilities in a tightly coupled manner. Using a linear stability analysis and the implementation of a pseudo-arclength ...
In this paper, we show the impact of Thermo-Hydro Mechanical couplings (THM) on the stability of ... more In this paper, we show the impact of Thermo-Hydro Mechanical couplings (THM) on the stability of a saturated fault gouge under shear. By resorting to Cosserat continuum mechanics, that allows to take into account rotational degrees of freedom, we regularize the problem of localisation and we predict the thickness of a shear band. A linear stability analysis of the homogeneous state is performed and then the system of equations is integrated using a Finite Element (FE) analysis. These analyses can be used for studying the evolution of the thickness of the principal slip zone in a fault under undrained adiabatic shear. Good agreement is found between theoretical predictions and field observations.
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Papers by Manolis Veveakis