<> "The repository administrator has not yet configured an RDF license."^^ . <> . . . "Coupled multi-phase hydromechanical modeling of induced seismicity associated with geo-energy applications"^^ . "Industrial activities to extract deep underground energy resources can induce earthquakes. Such induced seismicity can jeopardize the public acceptance of associated\r\nindustrial projects and, with increasing size, cause damage to infrastructure and pose a\r\nrisk to the population. It is therefore necessary to develop methods to better control\r\nand mitigate the seismicity. In order to achieve this, the physical mechanisms leading to\r\ninduced earthquakes need to be studied more accurately. For instance, it is known that\r\nthe injection or withdrawal of fluids causes changes in stress and pore pressure in the\r\nsubsurface, which can lead to the reactivation of faults. However, various processes are\r\nstill poorly understood, especially when multiple fluid phases are present. Since most\r\nof the processes are hidden underground, physics-based numerical models can help to\r\nimprove the understanding of the interactions between rock and fluids underground.\r\nIn this thesis, we use numerical models to simulate the physical processes involved in\r\ndifferent geo-energy projects. Firstly, we model gas extraction from a compartmentalized\r\nreservoir intersected by a fault to more accurately understand the processes leading to\r\nproduction-induced seismicity. The results show that gas production causes poroelastic\r\nstress changes and gas flow promoting fault reactivation. Simulations aimed at avoiding\r\ninduced earthquakes indicate that shut-in of the production well and gas reinjection\r\ninto the depleted reservoir compartment can stabilize the fault, while injection into\r\nthe adjacent compartment may not be successful in preventing the fault from being\r\nreactivated.Secondly, we numerically model the induced seismicity in the deep geothermal\r\nproject in St. Gallen, Switzerland, conducted in 2013 . After a stimulation phase, a gas\r\nkick forced the operators to inject fluids to combat the kick, followed by hundreds\r\nof minor seismic events and a ML 3 . 5 earthquake. The induced seismicity occurred\r\nseveral hundreds of meters away from the well and may have been influenced by multi-\r\nphase fluid interactions during the gas kick, which precludes a simple interpretation\r\nof the occurrences. We first attempt to determine the predominant mechanism that\r\nled to fault reactivation: poroelastic or direct pressure effects. The results show that\r\nchanges in Coulomb stress can be three orders of magnitude greater in the case of a\r\npermeable hydraulic connection, i.e., when the injected fluid directly pressurizes the\r\nfault. In combination with multiple independent observations, we conclude that the\r\ndirect pressure effect was the predominant mechanism in the St. Gallen reservoir. We\r\nthen model the gas kick, the subsequent injection and the induced seismicity. Assuming\r\nthe gas to be initially sealed by the fault and released after fault reactivation, our model\r\nis successful in reproducing the spatio-temporal evolution of the induced seismicity.\r\nThe model suggests that the gas could have contributed significantly to enhance the\r\ninduced seismicity.Although the interaction between gas flow and seismicity is certainly specific in\r\nSt. Gallen, the release of overpressurized gas has been suggested as a cause of after-\r\nshocks in naturally occurring earthquake sequences. Therefore, thirdly, we simulate\r\nthe effect of single- and multi-phase overpressurized in-situ conditions on the timing\r\nand magnitude of induced earthquakes. On the one hand, the results show that such\r\nconditions can lead to earlier fault reactivation. On the other hand, while the size of\r\nthe induced earthquakes increases when overpressurized gas prestresses the fault, an\r\ninitially overpressurized reservoir does not result in a larger event.\r\nThe overall results of the thesis show that multi-phase fluid flow can have a strong\r\ninfluence on induced earthquakes during both fluid injection and production operations.\r\nTherefore, in future geo-energy projects, the potential influence of gas should be\r\nadequately taken into account."^^ . "2020" . . . "ETH Zurich"^^ . . . "., ETH Zurich"^^ . . . . . . . . . "Dominik"^^ . "Zbinden"^^ . "Dominik Zbinden"^^ . . "ETH Zurich"^^ . . . . . . "HTML Summary of #2289 \n\nCoupled multi-phase hydromechanical modeling of induced seismicity associated with geo-energy applications\n\n" . "text/html" . . . "Other-additional study" . . . "St. Gallen" . . . "Geothermal energy production" . .