Publication Date:
2017-10-10
Description:
Wastewater injection into a high-rate well in the Val d'Agri oilfield, the largest in onshore Europe, has induced swarm microseismicity since the initiation of disposal in 2006. To investigate the reservoir structure and to track seismicity we performed a high-spatial resolution local earthquake tomography using 1281 natural and induced earthquakes recorded by local networks. The properties of the carbonate reservoir (rock fracturing, pore fluid pressure) and inherited faults control the occurrence and spatiotemporal distribution of seismicity. A low-Vp, high-Vp/Vs region under the well represents a fluid saturated fault zone ruptured by induced seismicity. High-Vp, high-Vp/Vs bumps match reservoir culminations indicating saturated liquid-bearing zones, whereas a very-low Vp, low-Vp/Vs anomaly might represent a strongly fractured and depleted zone characterized by significant fluid withdrawal. The comprehensive picture of the injection-linked seismicity obtained by integrating reservoir-scale tomography, high-precision earthquake locations, geophysical and injection data suggests that the driving mechanism is the channelling of pore pressure perturbations through a high permeable fault damage zone within the reservoir. The damage zone surrounds a Pliocene reverse fault optimally oriented in the current extensional stress field. The ruptured damage zone measures 2 km along strike, 3 km along dip and is confined between low permeability ductile formations. Injection pressure is the primary parameter controlling seismicity rate. Our study underlines that local earthquake tomography also using wastewater induced seismicity can give useful insights into the physical mechanism leading to these earthquakes.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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