Organic geochemical signatures of source rocks and oil-source correlation in the Papuan Basin, Papua New Guinea

Abstract

The Papuan Basin is the largest petroliferous basin in Papua New Guinea (PNG), where developed several sets of potential source rocks (SRs). The Jurassic SRs are clay-rich shales, whose organic matter (OM, mainly type Ⅱ 2 -Ⅲ) is predominantly derived from terrestrial higher plants deposited in a more oxic environment with relatively high maturity (0.35% < Ro < 2.03%). The Cretaceous SRs contain mixed inputs of terrigenous and marine OM (type Ⅱ 2 -Ⅲ) formed in sub-oxidized to oxidized depositional conditions with moderate maturity (0.33% < Ro < 1.58%). Whereas the Paleocene-Miocene SRs are predominant marine calcareous shales with subsidiary terrigenous OM inputs. These SRs containing type Ⅲ kerogen are mostly immature (0.21% < Ro < 0.70%). The Papuan Basin oils were classified into three distinct genetic families based on biomarkers and stable carbon isotopes. Family A oils, with heavy carbon isotopes, low Pr/Ph ratios, C 29 /C 27 ααα 20 R sterane <1.0, are likely originated from autochthonic Paleogene-Neogene mature marine OM. Family B oils have the characteristics of high Pr/Ph, moderate carbon isotopes, the dominance of C 29 ααα 20 R sterane, and are predominantly derived from autochthonous Jurassic SRs. Family C oils in the Eastern Papuan Fold Belt (EPFB) can be further subdivided into three subtypes by more subtle differences in specific biomarkers. Type C 1 oils, most likely stemmed from the Lower Cretaceous SRs, are characterized by light stable carbon isotopes, Pr/Ph > 2, the mild dominance of C 29 ααα 20 R sterane and the absence of oleanane ± lupane. Type C 2 oils can be clearly distinguished from Type C 3 by C 19 /(C 19 + C 23 ) tricyclic terpane <0.5, while the latter ones have higher abundances of oleanane ± lupine and diahopanes as well as C 24 tetracyclic/C 23 tricyclic terpane ratios. Type C 2-3 oils are originated from calcareous SRs that deposited in Late Cretaceous or younger age. • The organic geochemical signatures of the Papuan Basin SRs were elaborated. • Biomarkers, stable carbon isotopes, n -alkanes and iso-alkanes were used. • The oil samples in the Papuan Basin can be classified into three genetic families. • The likely origin of diverse oil families in the Papuan Basin were discussed.