Seismic inversion of a 3D seismic data set covering the Dan Field using the ISIS software package

摘要

Part of a 3D seismic survey has been inverted for both acoustic impedance and porosity. The inversion area covers the Dan Field in the Danish part of the North sea. The inverted seismic data comprise every in-line from 300 to 1000 and every x-line from 100 to 750, giving a total of 456,351 traces. The seismic inversions were carried out in the time window 1.500-2.500 seconds two-way travel-time (s TWT) using the ISIS global seismic inversion software. The main inversion results consist of: 1. An acoustic impedance volume with low- frequency information. 2. A porosity volume with low-frequency information. Sonic logs, density logs, porosity logs, and check-shot data from seven wells within the inversion area were available. The wavelet used for the seismic inversion for acoustic impedance was estimated from well M-9x by using the lest squares method. The wavelet is near constant phase and of normal polarity (a positive reflection coefficient corresponds to a white through on the seismic data). The wavelet used for the seismic inversion for porosity was derived by scaling the wavelet used for the acoustic impedance inversion. Low-frequency components of the acoustic impedance variations are not present in the seismic data. Since this information is essential to the interpretation, it should be accounted for in the seismic inversion. A low-frequency model was constructed by extrapolating the low-pass filtered acoustic impedance logs from all wells except M-10x. The acoustic impedance volume determined by the inversion accounts for approximately 97.7% of the seismic energy of the data volume. The porosity volume determined by the inversion accounts for approximately 97.4% of the seismic energy of the data volume. The match between the porosity volume and the porosity logs is not as good as the match between the acoustic impedance volume and the acoustic impedance logs. (EG)