Bayesian Seismic Inversion Delivers Integrated Sub-Surface Models

Abstract

We introdu ce a new open-source toolkit for model-based Bayesian seismic inversion called Delivery. This inversion code uses a layer -based prior model with rock physics information taken from log analysis as the basic structure that generates reflection seismic data. The model allows for uncertainty in both the fluid type and saturation in reservoir layers: variation in seismic responses due to fluid effects are taken into account via Gassman’s equation. Multiple stacks are supported, so the software implicitly performs a full AVO inversion using the Zoeppritz equations. Uncertainties and irresolvabilities in the inverted models are captured by the generation of multiple stochastic models from the Bayesian posterior, all of which acceptably match the seismic data, log data, and rough initial picks of the horizons. Post -inversion analysis of the inverted stochastic models then facilitates the answering of commercially useful questions, e.g. the probability of hydrocarbons, the expected reservoir volume and its uncertainty, and the distribution of net sand. The Delivery software is java -based and thus platform independent. Input and output is driven via XML, Seismic Unix 1 (SU) and BHP_SU 2 data formats, and the output interfaces naturally with the free INT viewer 3 . The ass umption of independent traces means that the inversion can be massively parallelized, and distributed across cluster computing systems.