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Unraveling hydro-fracturing mechanism: Is the analysis of induced-seismicity alone sufficient?

^^ Luigi Passarelli1^^ , Antonio Pio Rinaldi2, Federica Lanza2

  • Affiliations: 1 Istituto Nazionale di Geofisica e Vulcanologia (INGV) -- Sezione di Bologna 2 Swiss Seismological Center (SED) ETH Zürich 

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 11

  • Programme No: 5.1.17

  • Theme 5 > Session 1

Abstract

In Enhanced Geothermal System (EGS) the goal is to create fluid circulation pathways for the heat production. In this respect EGS are field-lab scale of hydrothermal systems at volcanoes. Injection experiments at EGS are designed to induce hydro-shearing, where the fluid over-pressure induces either seismic and aseismic slip on pre-existing fractures; or hydro-fracturing where instead the fluid over-pressure exceeds the minimum principal stress and create tensile fracture propagating from the borehole injection point. Induced seismicity is recorded during these controlled experiments where fluids are injected following a prescribed protocol to build a reservoir via intense fracturing. However, even in designed injection experiments with a good knowledge of the stress field and rock properties, the fracturing response of the host rocks is difficult to decipher. We here have focused on the 2022 injection experiment performed at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE). We have analyzed a high-resolution catalog of earthquakes recorded during the stimulation test at FORGE 2022. We analysied the spatial and temporal features of the seismicity cloud with respect to the in-situ stress field. We additional fit to the earthquake migration front (space-time data) three mechanical model of hydroshearing or hydrofracturing.  The results indicate hydro-fracturing as the most likely underlying mechanisms driven seismcity. However, we cannot fully rule out hydro-shearing and slip on existing faults. The analysis of this controlled experiment can be a viable tool to better understand fluid circulation in natural geothermal system at volcanoes.