An organic geochemical investigation on organic rich sediments from two Neogene formations in the Klias Peninsula area, West Sabah, Malaysia

Abstract

Twenty organic rich outcrop samples from the Belait and Setap Shale formations in the Klias Peninsula area, West Sabah, were analysed by means of organic petrology and geochemical techniques. The aims of this study are to assess the type of organic matter, thermal maturity and established source rock characterization based primarily on Rock-Eval pyrolysis data. The shales of the Setap Shale Formation have TOC values varying from 0.6 wt%–1.54 wt% with a mean hydrogen index (HI) of 60.1 mg/g, whereas the shales of the Belait Formation have TOC values ranging from 0.36 wt%–0.61 wt% with a mean (HI) of 38.2 mg/g, indicating that both formations have TOC>0.5 wt% the minimum limit for hydrocarbon generation. The samples do not contain sufficient hydrogen-rich organic matter (types I, II and III) to be considered good quality source rocks. The kerogen of type II is predominantly of marine origin. This organic matter was deposited in clastic algal environments. Geochemical data (Rock-Eval, Tmax values ranging from 377–451°C for shales of the Setap Shale Formation and ranging from 466–498°C for shales of the Belait Formation, typical of high maturity), indicate variable maturation histories in both formations. The maturation level varied from the beginning to the peak stage of oil generation in the Setap Shale Formation and it has reached the over-mature level in the samples of the Belait Formation.