North Wales Branch Meeting

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Taranaki Basin is a moderately explored hydrocarbon province, and hosts a range of small to moderate sized oil, condensate and gas fields. It is currently the only producing basin of New Zealand, with all other sedimentary basins classed as frontier / underexplored regions. This talk will provide an overview of Taranaki reservoirs looking at changes in sediment provenance, sandstone composition and reservoir quality through time.

Clastic reservoirs occur throughout the Cretaceous-Cenozoic formations of Taranaki Basin, with discoveries in a range of terrestrial, shallow marine and deep marine facies. The oldest reservoirs are a result of Cretaceous rifting related to the breakup of eastern Gondwana, with basin fill comprising Late Cretaceous to Late Oligocene strata deposited during overall transgression. The overlying Neogene is composed of thick foreland thrust belt / back-arc deposits that record a regressive phase of basin development, related to subduction at the Australian-Pacific plate boundary. Sediments deposited during these two phases of basin history display distinct compositional characters stemming from changes in primary provenance, textural / mineralogical maturity and depositional settings.

The observed compositional and textural trends through time have had a significant impact on the quality of Taranaki reservoirs and are overprinted by a complex range of secondary (diagenetic) factors. Diagenesis is most advanced within the more deeply buried transgressive system deposits, with the type and abundance of authigenic minerals and secondary pores linked to the original sedimentary texture / composition, facies and burial / fluid history. Results from our integrated studies demonstrate how sediment provenance, depositional facies and diagenesis have all affected reservoir quality in Taranaki and are, to some degree, predictive. These approaches and techniques used in Taranaki could be applied to clastic basins in other areas in order to better understand reservoir quality and ultimately improve reservoir quality predictions.