GNGTS 2018 - 37° Convegno Nazionale

64 GNGTS 2018 S essione 1.1 In this study, we present high resolution 3DVp and Vp/Vs images of the Val d’Agri carbonate reservoir and precise location of microseismicity. We analyzed about 1280 natural and induced earthquakes (M L ≤ 3) recorded between 2001 and 2014 at up to 60 stations belonging to three networks: a high performance temporary network operated by INGV from 2005 to 2006, the permanent monitoring network operated by ENI company, and the Rete Sismica Nazionale (RSN) operated by INGV. LET results integrated with subsurface information provided a comprehensive picture of the carbonate reservoir structure and the fault reactivated by injection- induced seismicity (M L ≤ 2), and pointed out the key role of inherited fault zone in the propagation of pore fluid pressure perturbations within the reservoir. 3D velocity models imaged successfully the major structural highs of the inner Apulian carbonate platform buried under the basin-bounding ridges. Ramp anticlines and pup-up structures developed during the Pliocene shortening are delineated by evident velocity bumps with ordinary Vp values for the Apulian limestone (Fig. 2-a). The correspondence between the platform structural highs and high Vp/Vs spots points to the presence of fractured liquid-saturated zones within the reservoir. 3D locations of the injection-linked earthquakes fall within low Vp and high Vp/Vs anomaly (Fig. 2-b). This anomaly points to a fractured and liquid-saturated zone in the reservoir and can be related to a fault damage zone surrounding an inherited back thrust delineated by seismic reflection data (Buttinelli et al. , 2016) and the high precision earthquake locations. Earthquake focal mechanisms and borehole breakouts data show that the inherited back-thrust is favorably oriented in the local extensional stress field. Inherited structures and imaged high Vp/Vs fluid-enriched volumes within the carbonate reservoir play an important role also in the reservoir induced seismicity linked to seasonal variations of the level of the Pertusillo lake. Accurate hypocentral locations and focal mechanisms suggest that reservoir induced events relate to active normal faults bounding the Val d’Agri basin to the west. References Buttinelli M., Improta L., Bagh, S. and Chiarabba C.; 2016: Inversion of inherited thrusts by wastewater injection induced seismicity at the Val d’Agri oilfield (Italy) . Scientific Reports, 6(1), 37165. https://doi.org/10.1038/ srep37165. Candela S., Mazzoli S., Megna A. and Santini S.; 2015: Finite element modelling of stress field perturbations and interseismic crustal deformation in the Val d’Agri region, southern Apennines, Italy. Tectonophysics, 657, 245– 259. https://doi.org/10.1016/j.tecto.2015.07.011. D’Adda P., Longoni R., Magistroni C., MedaM., Righetti F., Cavozzi C., ... and Storti F.; 2017: Extensional reactivation of a deep transpressional architecture: Insights from sandbox analogue modeling applied to the Val d’Agri basin (Southern Apennines, Italy). Interpretation, 5(1), SD55–SD66. https://doi.org/10.1190/INT-2016-0078.1. Dell’Aversana P.; 2003: Integration loop of “global offset” seismic, continuous profiling magnetotelluric and gravity data. First Break, 21(1006), 32–41. https://doi.org/10.3997/1365-2397.2003019. Improta L., Bagh S., De Gori P., Valoroso L., Pastori M., Piccinini D., … and Buttinelli M.; 2017: Reservoir structure and wastewater-induced seismicity at the Val d’Agri oilfield (Italy) shown by three-dimensional Vp and Vp/Vs local earthquakes tomography. Journal of Geophysical Research: Solid Earth, 122. https://doi. org/10.1002/2017JB014725. Fig. 1 - Traces of the velocity cross sections shown in Fig. 2. The Quaternary extensional fault systems and analyzed earthquake epicenters are also shown.