Characterization of the Lower Cretaceous Thamama Group Reservoirs through Stochastic Inversion and Rock Physics Modeling

The Lower Cretaceous Thamama Group is one of the most productive group of formations in the Middle East, containing large hydrocarbon accumulations. Thamama Group deposited along a gently sloping carbonate platform, is a thick sequence of limestone and dolomite with minor shales, with alternating reservoir and tight zones.

The reservoir characterization study encompassed classification of Thamama A-H zones and Habshan zones. As most of the Thamama reservoirs were beyond seismic resolution, Pre-stack High-Resolution Geostatistical inversion (Stochastic inversion) was performed after the deterministic AVO Pre-stack Inversion, in order to improve the understanding of heterogeneities and vertical/lateral correlation of reservoir properties (e.g. Porosity) in areas of interest under sub-seismic scales.

Geostatistical inversion could successfully separate out the thick reservoirs as well as the thin reservoirs, and capture the uncertainty associated in the model. Multiple realizations were output and the P10, P50 and P90 cases can be used as separate volume scenarios. The rock physics model predicted porosity with high confidence, using acoustic impedance and Vp/Vs. The model, generated from 31 wells, was validated using ∼600 wells and showed a good match with the well porosity.