Geostatistical AVO Inversion on a Deepwater Oil Field

Seismic inversion is usually treated as a deterministic problem. However, since the seismic amplitude data contains noise and the frequency resolution is limited, high and low frequencies will be uncertain. For a consistent treatment of these uncertainties, a geostatistical inversion method can be used.<br><br>We have used a Bayesian linearised AVO inversion method for a turbiditic channel system reservoir containing two offset stacks. In this Bayesian approach, the earth model parameters Vp, Vs, and ρ are given by a multi-normal distribution where spatial coupling is imposed by correlation functions. A linearised relationship between the model parameters and the AVO data, allows us to obtain the posterior distribution for the earth model parameters analytically.<br><br>The posterior distribution represents a laterally consistent seismic inversion where the solution in each location depends on the solutions in all other locations. The distribution contains the best estimate of the model parameters as well as their associated uncertainties. Using kriging, full frequency information from well data are spread in a volume around the wells; and from the posterior uncertainty we generate full frequency solutions for the entire volume.<br><br>The Bayesian approach is fast and the inversion gave good match with well log data.