Pyrolytic and provenance evaluation of organic matter from the tertiary niger delta basin, nigeria: implication on hydrocarbon generation.

Abstract

The present work deals with evaluation of organic matter based on detailed Rock-Eval pyrolysis techniques studies to evaluate hydrocarbon generation potential of source rocks by collecting twenty- nine shale samples from well cuttings in the Tertiary Formations of the Niger Delta, Nigeria. The values of vitrinite reflectance (0.57–0.74%Ro) and maximum (Tmax: 420–445°C) confirmed that samples are at early maturity to matured stage enough to generate liquid and gaseous hydrocarbon. The cross-plot between hydrogen index (HI) and oxygen index (OI) atomic ratio indicates that samples were predominant in the bituminous rank and having kerogen Type III makes it suitable for hydrocarbon generation. Rock-Eval pyrolysis analysis (Types II-III and Type III kerogen) on shale samples from the Niger Delta reveals organic matter of predominantly terrestrial origin based on type III kerogen. The organic matter (OM) assemblages suggests a marine setting but dominated by terrestrial inputs likely related to fluvial processes which is function of most delta system. Based on high total organic carbon (TOC) value of 5.42wt% and Type III kerogen made the shale an excellent source rock, with gas-prone kerogen. The high OI, low total sulphur (TS) suggests terrestrially derived OM and deposition in an oxic and dysoxic shallow marine environment. In addition, HI and Tmax values describe the samples as a characteristic Type III dominant kerogen and potential to generate oil and gases while the Tmax, consistently indicate an immature to mature on the shale organic matter.