GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 3.1 501 Tamburriello, G., Balasco, M., Rizzo, E., Harabaglia, P., Lapenna, V. and Siniscalchi, A. Deep electrical resistivity tomography and geothermal analysis of Bradano foredeep deposits in Venosa area (Southern Italy): first results. Annals of Geophysics (2008), 51 (1), 203-212 Santilano, A., Godio, A, Manzella, A., and Dini, I.: Electrical Resistivity Structures and their Relation to Geological Features at the Larderello Geothermal Field (Italy). Proceeding of Near Surface Geoscience (2015a), Turin (Italy). 3-D geological-geophysical model and preliminary synthetic seismic reflection modelling along CROP18A line in the Larderello area R. de Franco 1 , L. Petracchini 2 , G. Caielli 1 , D. Scrocca 2 , A. Santilano 3,4 , A. Manzella 3 1 Istituto per la Dinamica dei Processi Ambientali - CNR, Milano, Italy 2 Istituto di Geologia Ambientale e Geoingegneria – CNR, Roma, Italy 3 Istituto di Geoscienze e Georisorse – CNR, Pisa, Italy 4 DIATI - Politecnico di Torino, Italy Exploration strategies of geothermal reservoirs may significantly benefit from the development of synthetic seismic reflection profiles by confirming the possibility to detect prospective features on acquired seismic reflection data and to calibrate geological-geophysical interpretation and model reconstructions. To be elaborated a synthetic seismic reflection profile requires a conceptual geological model of the subsurface structure and physical properties, which is one of the tasks of the IMAGE FP7 European project (IntegratedMethods forAdvanced Geothermal Exploration). The Larderello geothermal field is characterized by a shallow and by a deep reservoir. The latter is hosted in the metamorphic basement (Batini et al. , 2003; Bertini et al. , 1996). In seismic reflection profile, the deepest reservoir is characterized by a strong amplitude reflective signal, the well-known K-horizon, widely observed in several seismic lines (Batini et al. , 1978; Accaino et al. , 2005) and probably drilled by the San Pompeo 2 well (Gianelli et al. , 1997). In this study, geological and geophysical available data have been integrated to develop a new 3D geological-geophysical model of the portion of the Larderello geothermal field drilled by the San Pompeo 2 well. The geological-geophysical 3D modelling was performed using Petrel software. The 3D model has been used to generate a 2-D model for the synthetic seismic modelling of the main seismic units up to the k-horizon along the CROP-18A seismic reflection line acquired within the CROP project. (Scrocca et al. , 2013). The exploding reflector approach, developed in Matlab by the CREWES consortium and partly modified by us in this project, has been used to generate the synthetic seismic sections. The exploding reflector generates the seismograms for a velocity model defined by pixel (25x25 m) with constant velocity value. The positions of receivers were located at the CDP position of the line. The wavefield is propagated in depth using a finite difference algorithm, and is then convolved with the input wavelet (Ricker wavelet with 25 Hz of central frequency) to produce the seismogram at the receiver. The finite difference algorithm uses a nine-point approximation of the Laplacian operator and assumes the absorbing boundaries on the three sides of the model (bottom, right and left). The geological units defined for the velocity model are respectively the Neogene Unit, the Ligurian Flysch Complex, the Tuscan Units plus TectonicWedge Complex and the Metamorphic Units. Using the velocity ranges of the previous units reported in literature (Batini et al. , 1978, Accaino et al. , 2005), we have assigned to these units Vp values of 2700 m/s, 3850 m/s, 5500 m/s and 4800 m/s respectively (Fig. 1).