Innovative Semi-quantitative AVO Modeling and Analysis to Reliably Predict Hydrocarbon vs. Brine Occurrence In Sand Reservoir

By

 M. Cardamone¹

(1) ENI SpA-Agip Division, S. Donato Milanese (Milan), Italy

 The case concerns an advanced AVO analysis study, carried out in an exploration area in the Mediterranean offshore, where the need of a reliable tool to rank a number of possible prospects was an issue. The request for increased reliability of the AVO method, capable of quantitatively predicting, also in terms of probability figures, the distribution and characteristics of fluids, or even the petrophysical characteristics of the reservoir was then set as a leading development goal.

This has been targeted trough a probabilistic inversion of AVO data, based upon a stochastic AVO modelling, that allow “intelligent” extrapolation of known AVO information from the wells to predict reservoir fluids in any exploration scenarios. This ENI-Agip proprietary “Fluid Inversion” methodology, is focused to estimate the probability that an assigned AVO response can be reliably ascribed to the presence of either brine, gas, oil in a sand reservoir. The developed software compares the real AVO responses at the several targets with a generalized model, which takes into account the expected variability of all the petrophysical parameters involved into the AVO phenomenon. This model is developed through a statistical analysis of all borehole data in the study area. The methodology allows an effective and powerful extrapolation of the AVO information, modelled at the well, to any new target belonging to an homogeneous geological-petrophysical scenario, even at different burial depth. The resulted fluid probability maps represent a new way to leverage pre-stack seismic information to benefit the interpretation accuracy and prospect generation process.