Organic geochemistry and basin modeling of the Eocene Mangahewa source rock system in the Pohokura oilfield, Taranaki Basin (New Zealand) and their indication of oil and gas potential

ABSTRACT: The importance of organic geochemistry and basin modeling is widely recognized and used to understand the source rock potential and hydrocarbon generation history of the Mangahewa Formation, and thereby given the foundational role in the petroleum exploration. This study utilized the total organic carbon (TOC) content and hydrogen index (HI) to investigate the dominant kerogen type and hydrogen richness for the significance of petroleum generative potential. The Mangahewa coals and carbonaceous shales exhibit an excellent source rocks, with high total organic content (TOC) of more than 22%. The coals and carbonaceous shales were also characterised by Type II–III kerogen with Type III kerogen, promising oiland gas-prones. The Mangahewa Formation reached the main oil generation, with vitrinite reflectances between 0.53% and 1.01%. Vitrinite reflectance was also used in developing themal models and reveal the transformation (TR) of 10–50% kerogen to oil during the Late Miocene. The models also showed that the Mangahewa source rock has a significant oil generation and little expulsion competency, with a TR of up to 54%. These findings support the substantial oil-generating potential in the Taranaki Basin's southern graben and can be used as a guide when developing strategies for an oil exploration program.