GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 3.1 485 velocities and density together with the petrophysical properties of water saturation, porosity and shaliness. At the rightmost part of the figure it is shown the corresponding vertical facies profile derived on the basis of the petrophysical properties. Note the decrease of Vp , and density and the increase of Vs that occur passing from the shale to the gas sand at 2450 m depth. Fig. 1b shows a cross-plot of the natural logarithm of the P- and S-impedance ( Ip and Is ) for each facies. As expected for the investigated area the P-impedance progressively decreases passing from shale, to brine sand and to gas sand, whereas the Is value remains more or less constant moving from the brine to the gas sand. In particular, note the significant overlap of the Ip and Is values for the different facies but particularly for the brine sands and gas sands. This overlap can be explained taking into account the deep depth interval where the reservoir zone is located. In fact, it is known (Avseth et al., 2005) that the increasing of burial depth tends to mask the fluid effect, and makes the discrimination between different saturation conditions more problematic. For this reason the case under examination can be considered a challenging test for any classification method. Litho-fluid facies prediction from synthetic seismic data. We first show the classification results obtained on synthetic seismic data that are computed on the basis of actual well log recordings. The synthetic data have been computed by means of a 1D convolutional forward Fig. 1 – a) Example of well log data around the reservoir interval. From left to right are represented Vp, Vs, density, water saturation, porosity and shaliness. b) Cross-plot showing the distribution of the natural logarithm of P- and S- impedance for each facies.