GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.1 83 After the datuming we applied a gapdeconvolution on CROP-18Aand -18B with an operator length of 140 ms and a lag of 12 ms. On CROP-03, an operator length of 70 ms, lag of 4 ms, was used in the window from 0 to 1600 ms TWT, and an operator length of 160 ms, lag of 12 ms, in the window from 1600 to 6500 ms TWT. We applied a trimmed mean-dynamic filter and fx-deconvolution on the CROP-03 and CROP-18B data. After sorting the data in CDP gather, we interactively performed the velocity analysis for dynamic corrections and residual statics applications. We applied a time-variant filter and a time-variant trace mixing for enhancing identified signals, defining a lateral window of 5 traces weighted by a symmetrical weighting function towards the central trace on the stacked data. At the end, a post-stack Kirchoff time migration was applied for all seismic lines, smoothing and reducing stacking velocities and limiting the aperture. Results and discussion. Our study points out that the application of advanced techniques allows obtaining better seismic images, also for old data. The presence in the upper crust of more horizons with large difference in acoustic impedance (high reflectivity) is confirmed in all the seismic sections. These reflections are sometimes bright as the previously recognized K-horizon, considered as the principal marker of the investigated area. The new images set give constraints to more precise interpretation procedures of the underground structures. The length of the profiles will help in the construction of new geological models of the geothermal province. In the following part, we present the sections to which an overly has been added to underline the continuity of the main reflecting markers adding transparency and leaving visible the seismic data in the background. Part of CROP-18A migrated profile is presented as example in Fig. 2. The profile shows a rather continuous horizon, which we marked with dots from Massa Marittima, at around 1 s TWT, to the NW-termination where it reaches 2.2 s. It corresponds to the H-horizon, drilled by the well S. Pompeo-2, positioned in the section according to Batini et al. (1983). The improvement obtained with the new processing can be recognized by comparison with the old published profile CROP-18A. In conclusions, improving the signal to noise ratio and preserving the reflection amplitudes, the distinct seismic units were differentiated, offering a direct image of the variable lithology and petrophysical properties characterizing the upper crust of the Tuscany Geothermal Province. Fig. 2 – Part of the CROP-18A post-stack time-migrated section. Interpreted reflections are highlighted by gray dotted lines. The well S. Pompeo-2 indicates the position of the H horizon at about 1 s TWT (after Batini et al. , 1983). It can be followed almost over the whole section. The datum plane is fixed at the sea-level for all the sections given in the paper.