Updating Low Frequency Model

Imprecise information about high contrast layers directly above the reservoir causes residual sidelobes and other artifacts within the reservoir, leading to incorrect imaging close to high contrast layers. We propose a method to update the P-impedance low frequency model in order to account for high contrast P-impedance layers. The updating methodology is integrated in an iterative inversion scheme in which, after a first pass inversion, information of a laterally variable high contrast P-impedance layers is interpreted and used to update the P-impedance low frequency model for a new run of the inversion. The result is a better imaging in zones close to high contrast layers. A case study is presented from a gas field located within the Dutch sector in the Southern North Sea. The Rotliegend reservoir in the gas field, which comprises high porosity Aeolian sandstones, lies just below the Top Rotliegend horizon, a marker that locally is the base of a hard Zechstein salt layer. The high impedance Zechstein Salt layer varies in thickness and is in places interleaved with shale. This causes its impedance response to vary rapidly within the seismic band width.