WP1

Experimental characterization of complex rheologies

Coordinators: D. Mainprice (CNRS-GM) & C. Spiers (UU) 

This WP groups 5 projects centred on the experimental characterization of rheology in the laboratory.

ESR1. Rheology of the lithospheric mantle. Supervisors: S. Demouchy, D. Mainprice (CNRS-GM). Secondments : Univ. Durham & Schlumberger
Objectives: Constrain the rheology of the lithospheric mantle through deformation experiments on olivine single crystals and aggregates at 800-1100°C and pressure ~ 300MPa via deformation experiments in a Paterson Press
Expected Results: Flow laws for the lithospheric mantle; experiments performed to variable finite strain will allow to analyse the hardening behaviour and the strain localization due to interactions between the crystal anisotropy and the boundary conditions. Microstructural characterization by SEM-EBSD (Montpellier) and TEM (coll. P. Cordier, Univ. Lille) will permit correlation of the mechanical behaviour with the evolution of the intracrystalline strain fields and dislocation structure. In-situ analysis of microseismicity during the experiments will allow characterizing the ductile-brittle transition.

ESR2. Effects of fault rheology on microseismicity. Supervisors : A. Niemeijer, H. Paulssen (UU). Secondments : Univ. Bristol & Baker Hughes
Objectives: Assess potential hazards associated with induced seismicity by (1) investigating the effects of fault rheology on microseismic (acoustic emission) signatures in the laboratory, focusing on the factors that control nucleation of aseismic versus microseismic rupture at low slip velocities; (2) comparing laboratory-scale microseismicity with records of reservoir-scale seismicity from oil, gas and geothermal fields
Expected Results: Identification of the factors controlling the transition from aseismic to (micro)seismic slip on fault rock materials relevant to the oil, gas and geothermal energy industry. Develop a better understanding of the scaling relations for seismic events from the laboratory to the reservoir scale.

ESR3. Quantifying the role of coupled solution transfer and frictional/brittle processes in controlling the rheology, transport and containment properties of rocksalt . Supervisors: C. Spiers, S. Hangx (UU). Secondments : UCL & AkzoNobel
Objectives: This project aims a) to develop mechanism-based models describing porosity-permeability development in deforming salt due to competition between fluid-assisted crack growth and crack healing/sealing processes, b) to determine the influence of these processes on creep, and c) to determine how fluid-phase additives can be used to manipulate the mechanical and transport properties of salt. The results obtained will be relevant to better predicting the stability and containment capacity of solution-mined storage caverns in rocksalt, the flow properties of granular salt products and the behaviour of crustal rock and fault systems under hydro- or geothermal conditions.
Expected Results: New, quantitative, mechanism-based constitutive models describing the rheological behaviour, transport properties and containment capacity of rocksalt in the regime where fluid-assisted microcracking and crack healing/sealing compete, and where pressure solution and sintering (neck growth) effects compete with frictional granular flow.

ESR4. The role of diffusion creep mechanisms, activated at seismic slip rates by frictional heating, in controlling dynamic fault weakening and earthquake propagation. Supervisors: N. De Paola, S. Nielsen, R.E. Holdsworth (UDUR) Secondments : Geosciences Montpellier & Geospatial Research Ltd.
Objectives: Preliminary results from high velocity friction experiments, performed in the Rock Mechanics laboratory at Durham, show that superplastic flow may control the strength of fine-grained rocks deforming at high strain rates and temperatures. This project aims to: 1) Describe the friction of earthquake faults by experiments at seismic slip rates; 2) Constrain strain rates and temperatures leading to activation of diffusion creep by microstructural analyses on the nanoscale material of experimental and natural slip zones; 3) Model the flow stresses predicted by diffusion creep constitutive laws, using natural and experimental slip zones parameters, and compare them with those values measured in the laboratory. The results obtained will be used to test whether the activation of grain size-sensitive diffusion creep mechanisms can account for the weakening of faults observed in experiments performed at seismic slip rates.
Expected Results: A better understanding of earthquake propagation processes in the upper crust by the proposition of a new, mechanism-based model to explain the observed weakening of faults, when deforming at seismic slip rates, by the activation of grain size-sensitive, diffusion creep mechanisms. The expected results may impact on seismic risk assessments.

ESR5. Rheology and deformation of glass under extreme conditions. Supervisors: B. Kaus (JGU) & C. Kunisch (Schott).Secondments : Geosciences Montpellier
Objectives: The rheology of glass is essentially measured by indentation tests at room temperature, but the present picture is too coarse, as the deformation is heterogeneous and the actual pressure and temperature beneath the indentor tip cannot be measured. The proposed association of numerical models and experiments at elevated temperatures (below the glass transition temperature) and moderate pressure with precise determination of both strain and stress will allow to determine the influence of pressure on the glass mechanical behaviour. This will lead to a better understanding of how glass interacts with other materials (such as metals) and open the possibility to use glass for new (and extreme) industrial applications.
Expected Results: Constrain the rheology of various glass types under high pressures

ESR10 . Creep of granular materials: from fault gouge to reservoir rocks. Supervisors: N. Brantut, T.M. Mitchell, P.G. Meredith (UCL). Secondments: Univ. Utrecht & Geospatial research Ltd
Objectives: (1) Characterization of the microphysical deformation processes associated with creep of granular aggregates (quartz and phyllosilicates) under pressure and temperature conditions commensurate with those at depth in the brittle crust.  (2) Quantification of the evolution of associated physical and transport properties; compressional and shear wave velocities, acoustic emission statistics and locations, and permeability.  (3) Development of a physics-based rate-dependent constitutive deformation model to enable extrapolation of experimental data to crustal spatial and timescales
Expected Results: New and unique holistic datset describing rate dependent deformation of granular aggregates. A fully coupled fluid flow and deformation model. Model outputs describing granular deformation in fault zones and reservoirs.

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