GNGTS 2017 - 36° Convegno Nazionale

536 GNGTS 2017 S essione 3.1 Field data application. The reservoir considered in this work is located in a shale-sand sequence and is constituted by gas-bearing sands at the depth range of 900-1000 m. Borehole logs from 7 wells provide elastic and petrophysical information needed to fully characterize the reservoir rocks in terms of Vp , Vs , density, effective porosity, water saturation and shaliness. The RPM has been estimated by using a stepwise regression approach (Aleardi and Ciabarri, 2017) that yielded the following equations: (12.1) (12.2) (12.3) where Vp and Vs are expressed in m/s, density in kg/m 3 , and the petrophysical properties in percentage. As a first rough appraisal of the empirical RPM, note that the estimated equations show a physically-consistent behaviour. As expected, the Vp , and density decrease with the increase of porosity. The increase of water saturation slightly increases the three elastic property values, while an increase of shaliness determines decreases of seismic velocities and density. By focusing the attention on the numerical coefficients of Eq. 12, we observe that the porosity plays the major role in determining the elastic properties, while the shaliness, but particularly the water saturation, exert minor influences. Fig. 1a represents the smoothed seismic amplitude computed along the top reflection of the investigated reservoir and extracted from the migrated 3D seismic volume. The black dots identify the spatial locations of the seven wells that have been used to define the rock-physics model. Note that strong negative amplitude anomalies identify the transition between the cap-rock (shale) and the reservoir layers (sand). Fig. 1b shows the smoothed gradient (black arrows) derived from the amplitude image of Fig. 1a. This Fig. 1 - a) 2D map representing the smoothed seismic stack amplitude extracted along the top reflection of the investigated reservoir. b) The 2D gradient (represented by the black arrows) that was used to derive the structural regularization terms. In a) and b) the black dots represent the spatial locations of the seven wells used to define the rock-physics model.