Pore pressure and reservoir quality evolution in the deep Taranaki Basin, New Zealand

The lack of mudstone to siltstone grade lithologies within the overlying Eocene section inhibited the early or shallow onset of overpressure in the Farewell Formation. One dimensional basin modelling has shown that rapid Pliocene subsidence related to exceptionally high sedimentation rates generated overpressure through disequilibrium compaction in the overlying Oligocene to early Miocene section during the past 6 Ma. However, the late and deep (>3000 m) onset of overpressure had no effect on arresting porosity loss in the Farewell Formation. Continued compaction of Farewell Formation sandstones after dissolution of early carbonate cements of CO2 rich fluids creates zones of extremely low permeability, which have the potential to act with interbedded shales to form pressure seals as seen in the Kapuni Field.