Publications

A discovery well in a deep-water environment within the Andaman Sub-Basin, offshore Aceh, North Sumatra, Indonesia presented several Quantitative Interpretation challenges despite an apparently simple situation of a thick shale overlying a thick sand with a clear gas-water contact (GWC). The challenges included variations in reservoir sand quality and porosity, thin shale breaks, rapid increases in elastic properties of the overlying shale with depth, and a complex AVO signature at the top of the reservoir across the field.

2D scenario modelling based on the data from the discovery well was used to set expectations for the AVO responses at the top reservoir, the GWC and for internal variations in reservoir quality resulting from variations in depth, porosity, thin shale breaks, and fluid content. These expectations were largely met by the actual seismic data except that the overlying shale was required to be anisotropic to fully reconcile the model with the seismic. Modelling also highlighted the sensitivity of the prediction of absolute porosity to the selection of an accurate datum for the depth variation of the overlying shale. With only one well available for reference, a datum was selected based on geological considerations.

An anisotropic facies-based inversion incorporating depth trends for each facies was therefore included in the quantitative interpretation workflow to successfully predict porosity, lithology, and hydrocarbon presence at a location 7 km from the original well control and in a different fault block. The results were also used to target reservoir sweet spots through a long reach side-track with remarkable accuracy.