Thomas Poulet | CSIRO - Academia.edu (original) (raw)

Papers by Thomas Poulet

Scientific Reports, Dec 27, 2023

A suggested model to explain the episodic nature of slow earthquakes involves shear zones exhibit... more A suggested model to explain the episodic nature of slow earthquakes involves shear zones exhibiting rate-and temperaturedependent frictional behaviour hosting fluid-release chemical reactions. In this work we extend the considerations of that approach, coupling the effects of the mechanics at different faulting regimes to the chemically induced fluid pressurization inside the fault. By introducing a pressure and temperature dependence of the mechanical response in an elasto-visco-plastic model we are able to correlate the inclination angles of those specific faults with their dynamical response and enrich their faulting regimes with kinematic characterisa-tion. We retrieve that steeply dipping (normal) faults exhibit a simple response of either being locked or slip at fast seismic velocities; shallow dipping (reverse) faults on the other hand exhibit a much richer behaviour where episodic stick-slip instabilities can be encountered. When present, their magnitude depends on the (reverse) fault's angle with faults dipping at around 45 * exhibiting a maximum, whereas sub-horizontal thrusts exhibit episodic stick-slip events as low velocities and magnitude. These findings position slow earthquakes and episodic tremor and slip sequences as a natural response of shallow dipping (thrust) faults, in a regime that according to rate-and-state friction considerations is intrinsically stable.

Geothermics, Sep 1, 2021

Calibrating geothermal simulations is a critical step, both in scientific and industrial contexts... more Calibrating geothermal simulations is a critical step, both in scientific and industrial contexts, with suitable model parameterizations being optimised to reduce discrepancies between simulated and measured temperatures. Here we present a methodology to identify unaccounted physical processes in the process and overcome the problem of measurement sparsity. With an application to the Upper Rhine Graben, we demonstrate the essential need for global sensitivity studies to robustly calibrate geothermal models, showing that local studies overestimate the influence of some parameters. We ensure the feasibility of the study through a physics-based machine learning approach, reducing computation time by several orders of magnitude.

Solid Earth, Feb 18, 2021

In experiments designed to understand deep shear zones, we show that periodic porous sheets emerg... more In experiments designed to understand deep shear zones, we show that periodic porous sheets emerge spontaneously during viscous creep and that they facilitate mass transfer. These findings challenge conventional expectations of how viscosity in solid rocks operates and provide quantitative data in favour of an alternative paradigm, that of the dynamic granular fluid pump model. On this basis, we argue that our results warrant a reappraisal of the community's perception of how viscous deformation in rocks proceeds with time and suggest that the general model for deep shear zones should be updated to include creep cavitation. Through our discussion we highlight how the integration of creep cavitation, and its Generalised Thermodynamic paradigm, would be consequential for a range of important solid Earth topics that involve viscosity in Earth materials like, for example, slow earthquakes.

Springer series in geomechanics and geoengineering, Dec 13, 2022

Zenodo (CERN European Organization for Nuclear Research), Sep 15, 2021

Geological Magazine, May 30, 2022

Faulted and fractured systems form a critical component of fluid flow, especially within lowperme... more Faulted and fractured systems form a critical component of fluid flow, especially within lowpermeable reservoirs. Therefore, developing suitable methodologies for acquiring structural data and simulating flow through fractured media is vital to improve efficiency and reduce uncertainties in modelling the subsurface. Outcrop analogues provide excellent areas for the analysis and characterization of fractures within the reservoir rocks where subsurface data are limited. Variation in fracture arrangement, distribution and connectivity can be obtained from 2D fractured cliff sections and pavements. These sections can then be used for efficient discretization and homogenization techniques to obtain reliable predictions on permeability distributions in the geothermal reservoirs. Fracture network anisotropy in the Malm reservoir unit is assessed using detailed structural analysis and numerical homogenization of outcrop analogues from an open pit quarry within the Franconian Basin, Germany. Several events are recorded in the fracture networks from the Late Jurassic the Alpine Orogeny and are observed to be influenced by the Kulmbach Fault nearby with a reverse throw of 800 m. The fractured outcrops are digitized for fluid flow simulations and homogenization to determine the permeability tensors of the networks. The tensors show differences in fluid transport direction where fracture permeability is controlled by orientation compared to a constant value. As a result, it is observed that the orientation of the tensor is influenced by the Kulmbach Fault, and therefore faults within the reservoirs at depth should be considered as important controls on the fracture flow of the geothermal system.

EarthArXiv (California Digital Library), Mar 17, 2020

• Porosity driven by creep can be opened and sustained at high confining pressures. • There is a ... more • Porosity driven by creep can be opened and sustained at high confining pressures. • There is a direct and spontaneous physical path for single phase rocks to transition to polyphase rocks during deformation.

Zenodo (CERN European Organization for Nuclear Research), Sep 15, 2021

Advances in Water Resources

Basin Research

The Hamersley Basin in Western Australia is one of the world's largest iron ore‐producing reg... more The Hamersley Basin in Western Australia is one of the world's largest iron ore‐producing regions, hosting two types of ore in banded iron formations: the high‐grade martite‐microplaty haematite and the supergene martite‐goethite ores. With the high‐grade ores almost entirely mined in the last decade, the supergene ores have more recently become the dominant resource of interest. Consequently, understanding the genesis of these martite‐goethite deposits is a critical step for exploration. Yet, although various models exist, there is still no consensus on how these mineral resources formed, complicating the prediction of resource volume and location. Here, we show that the paleo‐stratigraphic permeability anisotropy (with higher permeability along strata than across) controls the supergene mimetic enrichment transport process and, subsequently, the mineralisation distribution. We introduce a flow model that implicitly represents strata with a potential function that orients the p...

Ore Geology Reviews, 2021

Abstract The sediment-hosted McArthur River Zn-Pb-Ag deposit is located in the southern McArthur ... more Abstract The sediment-hosted McArthur River Zn-Pb-Ag deposit is located in the southern McArthur Basin of northern Australia. 3D numerical models are used to explore the role of thermal convection in the mineral system that formed the McArthur River deposit. The model geometry is a simplified representation of the area, comprising gently dipping hydro-stratigraphic units intersected by a steeply dipping fault. An aquifer represents the source of mineralising fluid, while the fault provides a pathway for this fluid to reach the site of mineralisation, either on the seafloor (syngenetic mineralisation) or within sedimentary rocks adjacent to the fault (diagenetic/epigenetic mineralisation). Two fault permeability scenarios are investigated, representing an open fault with high permeability, and a closed fault with low permeability in the top 300 m of the model and high permeability below. In both scenarios, thermal convection occurs within the fault and aquifer due to their high permeability, with upwellings of hot fluid spaced at ∼14 to 23 km along the fault. The results show that convection results in sufficient fluid exchange between the aquifer and fault to account for known mineralisation at McArthur River (∼20 Mt Zn). In the open fault scenario, the convective upwellings provide sufficient flow of hot fluid onto the seafloor to form a 20 Mt syngenetic deposit in ∼0.4 to 0.9 Myr. Syngenetic mineralisation would be accompanied by minor diagenetic mineralisation within the sediments adjacent to convective upwellings in the fault. In the closed fault scenario, some of the hot upwelling fluid flows into sediments adjacent to the fault at ∼300 m depth, sufficient to create a 20 Mt diagenetic/epigenetic deposit in ∼2.3 Myr. The rate and temperature of fluid flowing onto the seafloor or into the host rocks increases with fault permeability and heat flux, with higher heat flux and/or permeability being required to generate a diagenetic/epigenetic deposit than a syngenetic deposit within a geologically reasonable timeframe. Geometric complexities (e.g. fault intersections, bends or offsets) and areas of anomalously high heat flow or permeability are likely to focus convective upwelling, and are therefore suggested as targets for mineral exploration.

Geophysical Journal International, Jul 14, 2017

The interaction between mechanical deformation of creeping faults and fluid flow in porous media ... more The interaction between mechanical deformation of creeping faults and fluid flow in porous media has an important influence on the heat and mass transfer processes in Earth sciences. Creeping faults can act as heat sources due to the effect of shear heating and as such could be expected to alter the conditions for hydrothermal convection. In this work, we provide a finite element-based numerical framework developed to resolve the problem of heat and mass transfer in the presence of creeping faults. This framework extends the analytical approach of the linear stability analysis (LSA) frequently used to determine the bifurcation criterion for onset of convection, allowing us to study compressible cases with the option of complex geometry and/or material inhomogeneities. We demonstrate the impact of creeping faults on the onset of convection and show that shear heating-expressed through its dimensionless group the Gruntfest number Gr-has exponential influence on the critical value of the Lewis number Le (inversely proportional to the Rayleigh number Ra) required for convection: Le c ∼ Le c0 e Gr. In this expression, Le c0 is the critical value of Le in the absence of shear heating. This exponential scaling shows that shear heating increases the critical Lewis number and triggers hydrothermal convection at lower permeability than in situations without it. We also show that the effect of shear heating in a fault significantly alters the pattern of convection in and around the fault zone.

Computer Methods in Applied Mechanics and Engineering, Jun 1, 2020

Fluid injection or production in petroleum reservoirs affects the reservoir stresses such that it... more Fluid injection or production in petroleum reservoirs affects the reservoir stresses such that it can even sometime reactivate dormant faults in the vicinity. In the particular case of deep carbonate reservoirs, faults can also be chemically active; chemical dissolution of the fault core can transform an otherwise impermeable barrier to a flow channel. Due to the scale separation of the fault compared to the reservoir, implementation of highly non-linear multiphysics processes for the fault, needed for such phenomenon, is not compatible with simpler poromechanics controlling the reservoir behaviour. This contribution presents a three-scale finite element framework using the REDBACK simulator to account for those multiphysics couplings in faults during fluid production. This approach links the reservoir (km) scale-implementing poromechanics both for the fault interface and its surrounding reservoir-with the fault at the meso-scale (m)-implementing a THMC reactivation model-and the micro-scale (µm)-implementing a hydro-chemical model on meshed µCT-scan images. This model can explain the permeability increase during fault reactivation and successfully replicate fault activation, evolution and deactivation features, predicted by common fault reactivation models, yet with continuous transitions between phases. The multiscale coupling allows to resolve the heterogenous propagation of the fault slip which proves to be independent of the initial highest slip tendency location. The influence of the rock microstructure on fault and reservoir behaviour is quantified in a simulation where a hydraulically imperceptible difference in the microstructure's geometry results in a different duration of the reactivation event at the macro-scale. We demonstrate the advantage of dynamically upscaled laws compared to empirical laws as we capture permeability hysteresis during dissolution/precipitation of the fault.

Springer series in geomechanics and geoengineering, Dec 13, 2022

Geotectonic Research, Sep 1, 2015

AGU Fall Meeting Abstracts, Dec 1, 2016

Geotectonic Research, Sep 1, 2015

Scientific Reports, Dec 27, 2023

A suggested model to explain the episodic nature of slow earthquakes involves shear zones exhibit... more A suggested model to explain the episodic nature of slow earthquakes involves shear zones exhibiting rate-and temperaturedependent frictional behaviour hosting fluid-release chemical reactions. In this work we extend the considerations of that approach, coupling the effects of the mechanics at different faulting regimes to the chemically induced fluid pressurization inside the fault. By introducing a pressure and temperature dependence of the mechanical response in an elasto-visco-plastic model we are able to correlate the inclination angles of those specific faults with their dynamical response and enrich their faulting regimes with kinematic characterisa-tion. We retrieve that steeply dipping (normal) faults exhibit a simple response of either being locked or slip at fast seismic velocities; shallow dipping (reverse) faults on the other hand exhibit a much richer behaviour where episodic stick-slip instabilities can be encountered. When present, their magnitude depends on the (reverse) fault's angle with faults dipping at around 45 * exhibiting a maximum, whereas sub-horizontal thrusts exhibit episodic stick-slip events as low velocities and magnitude. These findings position slow earthquakes and episodic tremor and slip sequences as a natural response of shallow dipping (thrust) faults, in a regime that according to rate-and-state friction considerations is intrinsically stable.

Geothermics, Sep 1, 2021

Calibrating geothermal simulations is a critical step, both in scientific and industrial contexts... more Calibrating geothermal simulations is a critical step, both in scientific and industrial contexts, with suitable model parameterizations being optimised to reduce discrepancies between simulated and measured temperatures. Here we present a methodology to identify unaccounted physical processes in the process and overcome the problem of measurement sparsity. With an application to the Upper Rhine Graben, we demonstrate the essential need for global sensitivity studies to robustly calibrate geothermal models, showing that local studies overestimate the influence of some parameters. We ensure the feasibility of the study through a physics-based machine learning approach, reducing computation time by several orders of magnitude.

Solid Earth, Feb 18, 2021

In experiments designed to understand deep shear zones, we show that periodic porous sheets emerg... more In experiments designed to understand deep shear zones, we show that periodic porous sheets emerge spontaneously during viscous creep and that they facilitate mass transfer. These findings challenge conventional expectations of how viscosity in solid rocks operates and provide quantitative data in favour of an alternative paradigm, that of the dynamic granular fluid pump model. On this basis, we argue that our results warrant a reappraisal of the community's perception of how viscous deformation in rocks proceeds with time and suggest that the general model for deep shear zones should be updated to include creep cavitation. Through our discussion we highlight how the integration of creep cavitation, and its Generalised Thermodynamic paradigm, would be consequential for a range of important solid Earth topics that involve viscosity in Earth materials like, for example, slow earthquakes.

Springer series in geomechanics and geoengineering, Dec 13, 2022

Zenodo (CERN European Organization for Nuclear Research), Sep 15, 2021

Geological Magazine, May 30, 2022

Faulted and fractured systems form a critical component of fluid flow, especially within lowperme... more Faulted and fractured systems form a critical component of fluid flow, especially within lowpermeable reservoirs. Therefore, developing suitable methodologies for acquiring structural data and simulating flow through fractured media is vital to improve efficiency and reduce uncertainties in modelling the subsurface. Outcrop analogues provide excellent areas for the analysis and characterization of fractures within the reservoir rocks where subsurface data are limited. Variation in fracture arrangement, distribution and connectivity can be obtained from 2D fractured cliff sections and pavements. These sections can then be used for efficient discretization and homogenization techniques to obtain reliable predictions on permeability distributions in the geothermal reservoirs. Fracture network anisotropy in the Malm reservoir unit is assessed using detailed structural analysis and numerical homogenization of outcrop analogues from an open pit quarry within the Franconian Basin, Germany. Several events are recorded in the fracture networks from the Late Jurassic the Alpine Orogeny and are observed to be influenced by the Kulmbach Fault nearby with a reverse throw of 800 m. The fractured outcrops are digitized for fluid flow simulations and homogenization to determine the permeability tensors of the networks. The tensors show differences in fluid transport direction where fracture permeability is controlled by orientation compared to a constant value. As a result, it is observed that the orientation of the tensor is influenced by the Kulmbach Fault, and therefore faults within the reservoirs at depth should be considered as important controls on the fracture flow of the geothermal system.

EarthArXiv (California Digital Library), Mar 17, 2020

• Porosity driven by creep can be opened and sustained at high confining pressures. • There is a ... more • Porosity driven by creep can be opened and sustained at high confining pressures. • There is a direct and spontaneous physical path for single phase rocks to transition to polyphase rocks during deformation.

Zenodo (CERN European Organization for Nuclear Research), Sep 15, 2021

Advances in Water Resources

Basin Research

The Hamersley Basin in Western Australia is one of the world's largest iron ore‐producing reg... more The Hamersley Basin in Western Australia is one of the world's largest iron ore‐producing regions, hosting two types of ore in banded iron formations: the high‐grade martite‐microplaty haematite and the supergene martite‐goethite ores. With the high‐grade ores almost entirely mined in the last decade, the supergene ores have more recently become the dominant resource of interest. Consequently, understanding the genesis of these martite‐goethite deposits is a critical step for exploration. Yet, although various models exist, there is still no consensus on how these mineral resources formed, complicating the prediction of resource volume and location. Here, we show that the paleo‐stratigraphic permeability anisotropy (with higher permeability along strata than across) controls the supergene mimetic enrichment transport process and, subsequently, the mineralisation distribution. We introduce a flow model that implicitly represents strata with a potential function that orients the p...

Ore Geology Reviews, 2021

Abstract The sediment-hosted McArthur River Zn-Pb-Ag deposit is located in the southern McArthur ... more Abstract The sediment-hosted McArthur River Zn-Pb-Ag deposit is located in the southern McArthur Basin of northern Australia. 3D numerical models are used to explore the role of thermal convection in the mineral system that formed the McArthur River deposit. The model geometry is a simplified representation of the area, comprising gently dipping hydro-stratigraphic units intersected by a steeply dipping fault. An aquifer represents the source of mineralising fluid, while the fault provides a pathway for this fluid to reach the site of mineralisation, either on the seafloor (syngenetic mineralisation) or within sedimentary rocks adjacent to the fault (diagenetic/epigenetic mineralisation). Two fault permeability scenarios are investigated, representing an open fault with high permeability, and a closed fault with low permeability in the top 300 m of the model and high permeability below. In both scenarios, thermal convection occurs within the fault and aquifer due to their high permeability, with upwellings of hot fluid spaced at ∼14 to 23 km along the fault. The results show that convection results in sufficient fluid exchange between the aquifer and fault to account for known mineralisation at McArthur River (∼20 Mt Zn). In the open fault scenario, the convective upwellings provide sufficient flow of hot fluid onto the seafloor to form a 20 Mt syngenetic deposit in ∼0.4 to 0.9 Myr. Syngenetic mineralisation would be accompanied by minor diagenetic mineralisation within the sediments adjacent to convective upwellings in the fault. In the closed fault scenario, some of the hot upwelling fluid flows into sediments adjacent to the fault at ∼300 m depth, sufficient to create a 20 Mt diagenetic/epigenetic deposit in ∼2.3 Myr. The rate and temperature of fluid flowing onto the seafloor or into the host rocks increases with fault permeability and heat flux, with higher heat flux and/or permeability being required to generate a diagenetic/epigenetic deposit than a syngenetic deposit within a geologically reasonable timeframe. Geometric complexities (e.g. fault intersections, bends or offsets) and areas of anomalously high heat flow or permeability are likely to focus convective upwelling, and are therefore suggested as targets for mineral exploration.

Geophysical Journal International, Jul 14, 2017

The interaction between mechanical deformation of creeping faults and fluid flow in porous media ... more The interaction between mechanical deformation of creeping faults and fluid flow in porous media has an important influence on the heat and mass transfer processes in Earth sciences. Creeping faults can act as heat sources due to the effect of shear heating and as such could be expected to alter the conditions for hydrothermal convection. In this work, we provide a finite element-based numerical framework developed to resolve the problem of heat and mass transfer in the presence of creeping faults. This framework extends the analytical approach of the linear stability analysis (LSA) frequently used to determine the bifurcation criterion for onset of convection, allowing us to study compressible cases with the option of complex geometry and/or material inhomogeneities. We demonstrate the impact of creeping faults on the onset of convection and show that shear heating-expressed through its dimensionless group the Gruntfest number Gr-has exponential influence on the critical value of the Lewis number Le (inversely proportional to the Rayleigh number Ra) required for convection: Le c ∼ Le c0 e Gr. In this expression, Le c0 is the critical value of Le in the absence of shear heating. This exponential scaling shows that shear heating increases the critical Lewis number and triggers hydrothermal convection at lower permeability than in situations without it. We also show that the effect of shear heating in a fault significantly alters the pattern of convection in and around the fault zone.

Computer Methods in Applied Mechanics and Engineering, Jun 1, 2020

Fluid injection or production in petroleum reservoirs affects the reservoir stresses such that it... more Fluid injection or production in petroleum reservoirs affects the reservoir stresses such that it can even sometime reactivate dormant faults in the vicinity. In the particular case of deep carbonate reservoirs, faults can also be chemically active; chemical dissolution of the fault core can transform an otherwise impermeable barrier to a flow channel. Due to the scale separation of the fault compared to the reservoir, implementation of highly non-linear multiphysics processes for the fault, needed for such phenomenon, is not compatible with simpler poromechanics controlling the reservoir behaviour. This contribution presents a three-scale finite element framework using the REDBACK simulator to account for those multiphysics couplings in faults during fluid production. This approach links the reservoir (km) scale-implementing poromechanics both for the fault interface and its surrounding reservoir-with the fault at the meso-scale (m)-implementing a THMC reactivation model-and the micro-scale (µm)-implementing a hydro-chemical model on meshed µCT-scan images. This model can explain the permeability increase during fault reactivation and successfully replicate fault activation, evolution and deactivation features, predicted by common fault reactivation models, yet with continuous transitions between phases. The multiscale coupling allows to resolve the heterogenous propagation of the fault slip which proves to be independent of the initial highest slip tendency location. The influence of the rock microstructure on fault and reservoir behaviour is quantified in a simulation where a hydraulically imperceptible difference in the microstructure's geometry results in a different duration of the reactivation event at the macro-scale. We demonstrate the advantage of dynamically upscaled laws compared to empirical laws as we capture permeability hysteresis during dissolution/precipitation of the fault.

Springer series in geomechanics and geoengineering, Dec 13, 2022

Geotectonic Research, Sep 1, 2015

AGU Fall Meeting Abstracts, Dec 1, 2016

Geotectonic Research, Sep 1, 2015