Reservoir Characterisation in Offshore Gulf of Thailand: Distinguishing Reservoir Sands Through Elastic Inversion

Distinguishing between reservoir sands and shales is frequently challenging, due to the common problem of the Acoustic Impedances of these lithologies overlapping. In this paper we show the successful characterisation of reservoir sands by the application of Extended Elastic Impedance to 3D seismic data from Block B8/38 offshore Gulf of Thailand. Gradient Impedance vs Acoustic Impedance crossplots were used to identify the optimum Chi angle for the separation of lithologies, and it was found that an angle of 16 degrees separated reservoir sand from shale throughout the intervals of interest, with an angle of 10 degrees separating the highest quality reservoir sand. Enhanced Coloured Inversion was applied to intercept and gradient volumes, then these were combined to produce weighted volumes by applying the calculated Chi angle rotation. These volumes predicted a sand distribution in agreement with the well data. Further manipulation of the data was carried out to identify fluid fill. The far stacks were colour inverted, then multiplied with the final EEI volume. This combination of inverted elastic properties generated a volume which highlights the presence of hydrocarbons.