Downflank hydrocarbon potential identified using seismic inversion and geostatistics: Upper Maastrichtian reservoir unit, Dan Field, Danish Central Graben

Abstract

Porosities considerably higher than anticipated from porosity/depth trend models are encountered in a Maastrichtian reservoir unit on the western flank of the Dan Field. Because there is a good correlation between seismic impedance and well log porosity, inverted seismic data are used to infer that highly porous zones are widely distributed. The distribution of these high porosity zones is predicted using geostatistical methods based on the inverted seismic data. These predictions contradict the general assumption that porosity deteriorates with depth in the study area. Annealing cosimulation is applied using inversion-derived seismic impedances as soft data and well log porosities as hard data. The sensitivity of the porosity characterization to hydrocarbon in-place estimates is investigated through the calculation of water saturations using height above free water level and simulated porosity as input parameters. Multiple realizations show that calculated hydrocarbon in-place estimates are more sensitive to the location of the free water level than to uncertainties related to the geostatistical reservoir characterization.