Reservoir property analysis from well log data of north cape formation, Taranaki Basin, New Zealand

Abstract

Taranaki basin is the petroleum production basin along the western side of New Zealand. The main production fields have been along the marginal zone with Cenozoic reservoirs. However, the Cenozoic fan reservoirs are restricted to the offshore zone which is the majority of the basin. Therefore, Cretaceous sandstones in the North Cape Formation which deposited in sub-basin at the initial phase of basin formation might be the target reservoir in the deepwater block. Nonetheless, the Cretaceous reservoir is still in its infancy due to the limitation of the data. In this study, well log data were used to reveal the North Cape Formation characteristic. The petrophysical interpretation was used to identify depositional environment and reservoir properties. The result gives evidence of reservoir properties of sandstone in the North Cape Formation. The porosity is between 10% and 27% while permeability is up to 700 mD. The porosity of sandstones in wells located near the peninsular is lower than wells located in the offshore zone. The porosity might be controlled by compaction as a result of overburden sedimentary successions. This hypothesis relates to seismic data showed progradation of sediment from the Taranaki peninsular and proportion of clay minerals which referred to the degree of compaction. Another factor controlling the porosity is depositional environment. Barrier bar sandstone shows the highest porosity compared with channel and tidal flat sandstone. In conclusion, the North Cape Formation sandstone has potential to become a reservoir especially in the deepwater field, and the main factors controlling reservoir properties are depositional environment and degree of compaction.