Evaluation of source rocks of the Campano-Maastrichtian Nkporo group of Anambra Basin, Southeastern Nigeria

The Nkporo Group of the Anambra Basin consists mostly of dark-grey to black shales, mudstones, sandstone and siltstone. The aim of this study is to evaluate the source rocks and paleoenvironments of the Nkporo Group in the Anambra Basin. The objectives are to: determine the organic richness of the source rock and the type of organic matter (kerogen type), determine their thermal
maturity and evaluate the hydrocarbon generation potentials of the source rocks of the Nkporo Group (Nkporo Formation and Enugu Shale). The study was undertaken in three stages: desk work, field and laboratory studies. Twenty-five samples from the Nkporo Formation and Enugu Shale were analyzed using Leco CS 125 and HAWK pyrolyser for the organic geochemical parameters. This parameter was used to assess the source rock quantity and quality, type of organic matter, maturity and generating potential of the source rocks (shales). From the results of the geochemical analysis, the Total Organic Carbon (TOC ) contents of the Nkporo Formation and Enugu Shale varied from 0.41 to 2.42wt.% and 0.53 to 3.15 wt.% respectively. This shows that Nkporo Formation and Enugu Shale has fair to very good organic matter contents. The organic matter richness varies from 0.08 to 4.40mgHC /g for the Nkporo Formation and 0.36 to
3.97mgHC /g for the Enugu Shale. Hydrogen Index versus Oxygen Index plots and visual kerogen shows that the Nkporo Formation was of Type III/IV while Enugu Shale was of Type II/III kerogen. The Thermal maturity index (Tmax) of the Nkporo Formation and Enugu Shale varies from 418 to 443°C and 430 to 443°C respectively. These suggest that the Nkporo Formation is marginally
mature to mature while Enugu Shale is mature. The results of this study has shown that the source rocks of the Nkporo Formation is immature and has not generated hydrocarbon while that of the Enugu Shale is mature and has generated hydrocarbon.