GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 3.1 493 PPD associated with each inverted CMP gather. The MAP solution pertaining to the posterior distribution of facies p(F|d) and the corresponding probability of occurrence of each facies are represented in Fig. 3b. The maps represented in Figs. 3a and 3b evidence that the exploration well has intersected a sand channel with high porosity and low water saturation and shaliness values. Moreover, these maps clearly depicts the later extension of the gas sand channel intersected by the well at 2.46 s and also the complex depositional structure of the investigated area with both interconnected and isolated sand channels surrounded by shale intervals. Conclusions. I described a target-oriented, non-linear, MCMC algorithm for litho-fluid facies identification and petrophysical properties estimation. The algorithm has been applied for reservoir characterization in offshore Nile Delta. This approach, although its relatively high computational cost, reliably estimates the non-uniqueness of the solution that is the uncertainties affecting the estimated subsurface characteristics (both in terms of litho-fluid facies and petrophysical properties), taking into account the uncertainties in the prior information, the uncertainties in the estimated rock-physics model and the uncertainties in the observed AVA response. The field data application shows that the shaliness and particularly the porosity are the best resolvable parameters, whereas the water saturation is poorly resolvable due to its minor influence on the AVA response in the range 0%-95%. The petrophysical properties estimated for the CMP gather closest to the well show a close match with the well log information thus confirming the reliability of the final results. The 2D maps of litho-fluid facies and petrophysical properties estimated along the interpreted top of the reservoir show a very complex depositional Fig. 2 – a) Left: close-up around the target time interval for the CMP gather closest to the position of an exploration well. Right: the AVA response extracted from the CMP shown on the left and associated to the target reflection. b) Inversion results obtained for the CMP illustrated in a), showing a comparison between prior and posterior distributions for litho-fluid facies and petrophysical properties.