Abstract
Increasing interest in oil and gas exploration in the Nigerian inland frontier basin has
necessitated re-evaluating the once-neglected Late Cretaceous Hydrocarbon Source Rocks from
the basins. In this study, hydrocarbon generation characteristics of representative Cretaceous
outcrop source rocks and geochemical properties of their generated products are investigated
using a confined gold tube pyrolysis experiment. Conventional geochemical analyses (TOC and
Rock-eval) reveal that the source rocks are rich in organic matter and in the immature
hydrocarbon generation stage. The gold tube experiment at six (6) different temperature stages
(300°C to 500°C) indicates that the source rocks produced oil and gas in different proportions,
and the pyrolysis products contained a certain amount of C6+
liquid hydrocarbons. Observed peak oil yields of the Bida, Dahomey, and Anambra shales were 5.80, 24.09, and 6.63 mg/gTOC, respectively. The gas yields of the source rocks drastically increased with rising heating
temperatures (maturity). After exceeding 450°C (about EasyRo of 2.0%), methane and ethane gases were the dominant components in the pyrolyzates, which means that oil in the products gradually cracked into gas during the high-temperature stages. Maximum gas-to-oil ratio (GOR) of the shales ranges from 2.52 to 5.50. The δ
13C of C1, C2 and C3 from the pyrolyzates are similar to those generated from the Niger Delta and this could be a result of marine connections among the basins. This study is valuable for further exploration in the Nigerian Frontier Basins, reducing over-dependence on the Niger Delta Basin for hydrocarbon exploration.