Project: Unravelling the complexity of the Brittle-ductile transition in the crust: implications for deep hydro-geothermal circulation
Funding: SNF
Dates: 01.01.2022 – 31.12.2025
This project is a request for four years funding for 1 PhD students, three years fundingfor a postdoc, technical support, and funding for the setup of experimental equipmentand analytical expenses required for their work. Most of the equipment to carry out theproposal is already available at EPFL (high pressure and temperature rig calledTARGET, but needs to be upgraded), UNIL and UNIGE (analytical facilities).This project aims at quantifying how the failure mode at the brittle-ductile transitioncontrols the hydraulic properties of newly formed fractures in low porosity – fresh andaltered rocks -, and how they vary with time and fluid type. The outcome will improveour ability to assess heat transfer between magmatic intrusions and high-enthalpyhydro-geothermal systems, to model the migration of fluids through nominally ductilefractures, to enhance permeability in such environment and, more generally, will aid inunderstanding the nature of permeability as a function of depth in the earth’s crust.Previous experiments were conducted far from in-situ conditions, mostly at roomtemperature and low confining pressure. We will experimentally study the evolution ofboth the hydraulic properties and seismic properties during brittle to ductiledeformation at confining pressure up to 200 MPa and temperature up to 800°C andwith relevant pore pressure. Experiments will be conducted on both fresh and alteredrocks, and with either inert, low, or high reactive fluids, to understand how each ofthese elements will affect the underlying deformation mechanism
Project: THE INFLUENCE OF TEMPERATURE ON THE COMPACTION OF POROUS VOLCANIC ROCK
Funding: Germaine de Staël
Project dates: 01.07.2021-30.06.2023
Volcanoes are inherently unstable structures. First, they are haphazardly built from a combination of en-dogenous growth and the exogenous accumulation of the products of effusive and explosive eruptions, and are therefore characterised by materials with disparate physical and mechanical properties. Second, their haphazard construction, coupled with endogenous forcing resulting from dyke emplacement and magma accumulation (cryptodome formation), results in oversteepened and unstable slopes. As a result, volcano deformation (such as volcano spreading; e.g., Borgia et al., 2000) and mass wasting events (such as partial flank collapse with the emplacement of debris avalanche deposits, lahars, rockfalls, and debris flows; e.g., Roverato et al., 2021) are commonplace at many volcanoes worldwide. Catastrophic collapse resulting from volcano spreading (e.g., van Wyk de Vries and Francis, 1997) and mass wasting events present a significant volcanic hazard, and can also trigger hazardous laterally-directed explosions and devastating—both economically and in terms of loss of life—high-energy pyroclastic density currents (e.g., Glicken, 1996; Cole et al., 2015). Indeed, in the last 10,000 years, partial flank collapses at about 200 vol-canoes have resulted in at least 20,000 fatalities (Siebert et al., 2010). As a result, stability assessments at volcanoes are an essential component of volcano monitoring and volcanic hazard mitigation.
Project: FRIGEO
Funding: Climact
Project dates: 01.11.2021 – 31. 10.2022
The primary objective of Project FRIGEO is to assess the influence of failure on the hydraulic characteristics of recently formed fractures within low porosity fresh rock formations. Additionally, the project aims to investigate how these characteristics evolve over time and in response to interactions between fluids and rock. The anticipated results of this endeavor will significantly enhance our capacity to evaluate thermal aspects within high-enthalpy geothermal systems. Moreover, the findings will contribute to the development of models pertaining to fluid migration through ostensibly brittle fractures, particularly in the context of CO2 sequestration. This will also encompass strategies to augment permeability under such specific conditions.
Prior research endeavors predominantly transpired under conditions considerably removed from in-situ settings, often encompassing room temperature and minimal confining pressure. Our approach involves a comprehensive experimental exploration of how both hydraulic and seismic attributes transform during instances of brittle deformation. This investigation spans confining pressures reaching up to 200 MPa and temperatures of up to 200°C. Our study will encompass various rock types, including sandstones and carbonates, in conjunction with inert, low-reactive, and highly reactive fluid mediums.
Project: Testing the feasibility of engineered geothermal system beyond the brittle-ductile transition
Project dates: 16.01.2023 – 01.05.2023
Our research project seeks to address fundamental questions regarding the behavior of low porosity rocks at the transition from brittle to ductile deformation. Specifically, we aim to elucidate the role of fluid pressure and the interplay between fluid and rock properties in influencing the failure mode within these rocks. We are investigating the intricate strain partitioning mechanisms that govern fault slip as well as broader bulk deformation processes, encompassing both plastic and cataclastic mechanisms.
Furthermore, our inquiry delves into the evolution of porosity and permeability over time and under varying strain rates, focusing on conditions representative of the brittle to ductile transition and characterized by high temperature and high pressure. We intend to unravel the complex relationship between porosity, permeability, and strain, shedding light on how these properties evolve under extreme geological conditions.
In semi-brittle reservoirs, the enhancement of permeability is a critical challenge. Our research aims to identify strategies for effectively increasing permeability in such reservoirs. We are dedicated to determining the optimal stimulation parameters required under these specific conditions, thus offering insights into the methodology necessary to achieve successful permeability enhancement.
An additional aspect of our investigation concerns the potential for inducing seismicity through fluid injection in environments characterized by elevated temperature and pressure. By conducting rigorous experiments and analyses, we aim to understand the conditions under which fluid injection could trigger seismic events and discern the underlying mechanisms driving such seismicity.
In summary, our research project is a comprehensive exploration of the complex interactions between fluid pressure, rock properties, deformation mechanisms, porosity, permeability evolution, and seismicity in low porosity rocks at the brittle to ductile transition. Through meticulous experimentation and analysis, we aspire to contribute valuable insights to the field of geology and reservoir engineering.
Project: RAISE
Funding: OFEN
Project dates: 01.01.2020 – 31.12.2021
Raise is a project between SFOE and LEMR at EPFL to develop safe stimulation protocols for EGS. To optimize stimulation and minimize seismic risk, the role of fluid injection in earthquake physics needs to be understood. However, the effect of acid fluid on fault mechanics is still not clear, with implications for matrix acidizing stimulation. Here we aim at investigating earthquake nucleation and propagation in the presence of acid fluids. We propose an experimental approach designed to achieve the following specific objectives: 1) the characterization of the frictional parameters (rate-and-state parameters) of faults saturated with fluids characterized by different acid concentration, 2) the characterization of the dynamic weakening during earthquake rupture propagation in the presence of fluids characterized by different acid concentration 3) the characterization of the evolution of the fault hydraulic properties during shearing in the presence of fluids characterized by different acid concentration.
Project: BEFINE
Funding: EU ERC starting grant
Project dates: 01.01.2017 – 01.01.2021
Fluids play an important role in fault zone and in earthquakes generation. Fluid pressure reduces the normal effective stress, lowering the frictional strength of the fault, potentially triggering earthquake ruptures. Fluid injection induced earthquakes (FIE) are direct evidence of the effect of fluid pressure on the fault strength. In addition, natural earthquake sequences are often associated with high fluid pressures at seismogenic depths. Although simple in theory, the mechanisms that govern the nucleation, propagation and recurrence of FIEs are poorly constrained, and our ability to assess the seismic hazard that is associated with natural and induced events remains limited. This project aims to enhance our knowledge of FIE mechanisms over entire seismic cycles through multidisciplinary approaches, including the following:
– Set-up and installation of a new and unique rock friction apparatus that is dedicated to the study of FIEs.
– Low strain rate friction experiments (coupled with electrical conductivity measurements) to investigate the influence of fluids on fault creep and earthquake recurrence.
– Intermediate strain rate friction experiments to investigate the effect of fluids on fault stability during earthquake nucleation.
– High strain rate friction experiments to investigate the effect of fluids on fault weakening during earthquake propagation.
– Post-mortem experimental fault analyses with state-of-art microstructural techniques.
– The theoretical friction law will be calibrated with friction experiments and faulted rock microstructural observations.
These steps will produce fundamental discoveries regarding natural earthquakes and tectonic processes and help scientists understand and eventually manage the occurrence of induced seismicity, an increasingly hot topic in geo-engineering. The sustainable exploitation of geo-resources is a key research and technology challenge at the European scale, with a substantial economical and societal impact.
Project: Hydro Mechanical Couplings in Enhanced Geothermal Reservoir
Funding: SNF/AP Energy Grant
Project dates: 01.06.2015 – 30.09.2020
The objective of this project is to provide better understanding of the various couplings between hydraulic and mechanical interactions in enhanced geothermal systems. In particular, this project provides a detailed study of how the friction properties control the transport properties of reactivated fractures for low porosity rocks. Previous experiments were conducted far from in-situ reservoir conditions, mostly at room temperature and low confining pressure. Here, we will experimentally study the evolution of both the fluid transport properties and seismic properties during deformation (seismic and aseismic) at pressure up to 200 MPa and temperature up to 400°C. These data will provide new constraints on the permeability evolution during the creation of geothermal reservoirs. Importantly, our results will shed new light on the physics of induced earthquake mechanisms by combining deformation experiments with the registration of the micro seismicity at high temperature and confining pressure, simulating geological conditions in the reservoirs.
Project: EDGAR
Funding: OFEN
Project dates: 01.03.2017 – 01.09.2020
Engineered geothermal systems (EGS) projects have attempted to apply hydraulic, acid and thermal stimulations to improve the transmissivity between wells and create a network of fractures that allows for sustainable extraction of heat stored in the solid rock matrix. So far, the stimulation procedures have not been fully designed, and consequently induced seismicity is still a risk. Within this project, we investigate the role of fluid and in particular fluid viscosity in the context of induced seismicity due to geothermal reservoir stimulation. In particular, we developed a new experimental apparatus able to reproduce geothermal in situ conditions. Moreover, we performed several series of experiments to address the role of fluid viscosity in the entire seismic cycle (i.e. earthquakes reactivation, earthquakes nucleation and earthquakes propagation). The fluid viscosity property showed an ambiguous behavior in our experimental results: the increase of fluid viscosity trapped on the slip surface promotes the earthquake nucleation, but under some condition of slip velocity and fault roughness, it increases the energy necessary for earthquakes propagation.
The complexity of the analyzed problem and the uncertainties of state of stresses, geometry and lithologies of the fractures in real geothermal systems do not allow us to establish universal and general rules for the injection of viscous fluids in field operations.
However, the results of this project answer fundamental questions about the role of viscous fluids on faults and fractures behavior. Further research, especially in pilot project for fluid injection at intermediate scale, can build on and benefit from the presented results. In particular, the results of this pilot project showed that also the rheology of the used fluids in the field operation can have an impact on the seismic risk linked to stimulation and production phases of geo-reservoirs.