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.