Source rock characterization and hydrocarbon generation modeling of the Middle to Late Eocene Mangahewa Formation in Taranaki Basin, New Zealand

The Middle to Late Eocene Mangahewa Formation of Taranaki Basin, New Zealand, has been evaluated in terms of organic matter abundance, type, thermal maturity, burial history, and hydrocarbon generation potential. Mangahewa Formation reflects the deposition of marine, marginal marine, shallow marine, and terrestrial strata due to alternative transgressive and regressive episodes in Taranaki Basin. The sediments of the Mangahewa Formation contain type II (oil prone), types II-III (oil-gas prone), and type III kerogens (gas prone), with hydrogen index values ranging from 58 to 490 mg HC/g total organic content (TOC). Vitrinite reflectance data ranging between 0.55 and 0.8 % R-o shows that the Mangahewa Formation is ranging from immature to mostly mature stages for hydrocarbon generation. Burial history and hydrocarbon generation modeling have been applied for two wells in the study area. The models have been interpreted that Mangahewa Formation generated oil in the Mid Miocene and gas during Middle to Late Miocene times. Interpretations of the burial models confirm that hydrocarbons of Mangahewa Formation have not yet attained peak generation and are still being expelled from the source rock to present.