Utilizing Tuning/AVO Phenomena to Predict Oil Column Height in the Tui, Amokura and Pateke Fields, New Zealand

A combined tuning/AVO model was used to predict the oil column height for the Tui, Amokura and Pateke fields in the offshore Taranaki Basin, New Zealand. The Palaeocene aged Kapuni F10 reservoir sands occur at a depth of approximately 3700 mSS. The closure height and areal extents of these fields were initially mapped by converting time structure maps to depth using average velocities derived from stacking velocities. However, the traps at Tui are broad low relief features, extending up to 4 km laterally but with only limited vertical relief. This geometry means that even very small velocity variations have a significant impact on the location and extent of closure. Weak amplitude anomalies had been noted on the fields and a study was undertaken to review the tuning and AVO behaviour of the rocks in an attempt to understand the anomalies. Vp, Vs and density logs from the Tui-1 and Amokura-1 exploration wells showed that it was possible to map oil column heights using amplitudes extracted from the F10 sand seismic horizon. This modelling predicted an oil column height of 20 m at the crest of the Tui structure prior to the drilling of development well Tui-2H. In the same area a column height of about 10 m was predicted using the average velocity based depth maps. Drilling results showed a maximum column height of 21 m, confirming the validity of the modelling. This result led to the change in the direction of the next well Tui-3H. Four horizontal development wells have been successfully drilled with total estimated gross 2P reserves of 32 MMBO.