Brittle To Ductile Transition In Deep Geothermal Reservoirs

Organizer: Prof. Marie Violay, EPFL

There has recently been an explosion of interest in the exploitation of high-temperature geothermal energy, largely as a result of the goings-on in Iceland. Put simply, extracting supercritical fluids from high-temperature reservoirs will yield more power for a given volumetric flow rate of stream than fluids from conventional wells. However, there is still much to learn regarding the feasibility of such operations. With increasing depth and/or temperature, rocks can undergo a transition in failure mode from localised brittle deformation to distributed ductile flow. There are also instances of localised ductile deformation, manifest as compaction bands. This transition is important for understanding the strength of the crust, seismic source mechanisms, fluid flow and pore pressure distribution in the crust, and deformation patterns at the field scale. This transition is also important to probe the viability of very deep geothermal reservoirs. Depending on material properties, environmental conditions (pressure and temperature), and imposed mechanical boundary conditions at a given scale, the brittle-ductile transition involves a change in micromechanical deformation mechanism from microcracking to a plethora of micromechanisms (cataclastic pore collapse, microcracking, granular flow, pressure solution, intracrystalline plasticity, flow by diffusive mass transfer, amongst others). An outstanding and critical challenge for our science includes evaluating the brittle-ductile transition for a range of materials (sedimentary, metamorphic, igneous, and volcanic rocks), rock attributes (low- and high-porosity rocks, grain size, microstructure etc.), and environmental conditions (pressure, temperature, pore fluids). This mini-symposium therefore provides the opportunity for contributions that discuss the brittle-ductile transition in geological materials under geological conditions. We solicit contributions on theory and simulations, instrumentation, laboratory experiments and field measurements, data analysis and interpretation, as well as inversion and modelling techniques. We particularly welcome abstracts from early career scientists.