Application of detailed molecular maturity parameters in determining thermal maturity of the Kazhdumi Formation in the Yadavaran oil field

Determining the level of thermal maturity of the organic matter (OM) is a main step in the source rock evaluation. The present study provides an example of application of three different analytical techniques including Rock-Eval pyrolysis, Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GCMS), for thermal maturity assessment of the Kazhdumi Formation in Yadavaran oil field. For this, a total of 17 cutting samples from the Kazhdumi Formation were collected systematically from three wells in this oil field. The samples were analyzed using Rock-Eval 6 apparatus and two samples (KUK-535 and HOS- 420) were selected for complementary GC and GCMS analyses. Tmax values obtained from Rock-Eval pyrolysis show a relatively narrow range of variation (421-436 °C) with an average value of 428 °C which puts the samples in the early stages of oil generation window. Maturity sensitive parameters derived from GC (CPI) and GCMS analyses [20S/(20S+20R) and

/(

+) ratios for steranes and Moretaen/Hopane and Ts/Tm ratios for terpanes] are consistent with maturation level corresponding to the main oil generation window. However, maturity parameters based on the aromatic compounds correspond to the early oil window. According to these results, the Khazhdumi Formation has experienced a relatively low level of thermal maturation and is just about to enter the main stage of hydrocarbon generation in the Yadavaran oil field. Our conclusion not only excludes the role of younger source rocks (Pabdeh and Gurpi formations) in contributing to the discovered accumulations, but also suggests other deep source layers (e.g. Sargelu and Garau Formations) as the source for hydrocarbon reserves encountered in this oil field.