Combined Rock-Physical Modelling and Seismic Inversion Techniques for Characterisation of Stacked Sandstone Reservoir

The objective of the study is to characterise the Triassic massive stacked sandstone deposits of the Main Buntsandstein Subgroup at Block Q16 located in the West Netherlands Basin. The characterisation was carried out through combining rock-physics modelling and seismic inversion techniques. The application of inversion on time-converted PSDM stack results in better seismic impedance resolution due to better well-seismic match performance. The results show that even though the Bunter reservoir consists of lithologically uniform massive stacked sandstones, the obtained rock property volumes allow distinguishing two zones within the target unit. The upper zone - Hardegsen and Detfurth Formations - exhibits on average lower acoustic impedance, shear impedance and bulk density values compared to the lower zone - the Volpriehausen Formation. These differences are essentially attributed to changes in porosity. Larger porosities make these rock properties decrease. Moreover, it is believed that locally the entire Bunter reservoir is gas-bearing, but the Volpriehausen sandstones are tighter. Vp/Vs ratio and Poisson’s ratio are good gas-fluid indicators. Both decrease for Bunter reservoirs compared to shales of the Solling and Rogenstein Formations. Furthermore, the rock property volumes allowed improved mapping of top and base of the Bunter reservoir compared to the original seismic reflectivity volume.