Hydrocarbon source rock analyses of Pakawau Group and Kapuni Formation sediments, northwest Nelson and offshore South Taranaki, New Zealand

Abstract Gas‐liquid chromatographic (GLC) analysis of cuttings and outcrop of Pakawau Group and Kapuni Formation sediments from the South Taranaki Basin gave thermal maturity and provenance results consistent with previous work in the region. Explanations were sought as to the origin of hydrocarbons already discovered, and the absence of significant hydrocarbon accumulations elsewhere within the basin. GLC analysis centred on the C 15+ saturated hydrocarbon extract of rock samples, and geochemical fossil molecules were examined for their presence and relative abundance. Resulting information on the thermal maturity and provenance of the rock samples was obtained. Both Maui‐2 and Maui‐4 wells gave Odd Even Predominance (OEP) and Carbon Preference Index (CPI) values of 1.1 (±0.1) to 1.4 (±0.1), consistent with thermally mature sediments. Both showed pristane levels typical of land‐derived sediments. However, Kupe‐l well gave a CPI value of 1.7 (±0.1) which correlates with the early dry gas substage of the immature stage of hydrocarbon generation. Recent heat‐flow studies in the region agree with this result. Brunner Coal Measures proved thermally immature and the Pakawau Coal Measures indicated an increase in maturity with depth.