Geochemical evaluation of the carbonaceous shale of the upper cretaceous Anambra Basin for potential gas generation, Nigeria

• Published in: Arabian journal of geosciences 2021-03, Vol.14 (6), Article 456
• Main Authors: Akintola, George Oluwole, Ikhane, Phillips Reuben, Amponsah-Dacosta, Francis, Adeagbo, Ayoade Festus, Mhlongo, Sphiwe Emmanuel, Edokpayi, Joshua Nosa, Oladipo, Vincent Olajide, Jegede, Ademola Oluborode, Akintola, Akintunde Isaac, Adebisi, Niyiola Olaonipekun
• Format: Article
• Language: English
• Subjects: Aliphatic hydrocarbons; Anoxia; Anoxic conditions; Boreholes; Cell walls; Cretaceous; Earth and Environmental Science; Earth science; Earth Sciences; Hydrocarbons; Kerogen; Low concentrations; Macerals; Natural gas; Natural gas industry; Ocean basins; Organic matter; Original Paper; Parameters; Plant extracts; Plant tissues; Pristane; Saturated hydrocarbons; Sedimentary basins; Sedimentary rocks; Sediments; Shale; Shale gas; Shales; Terrestrial environments; Thermal evolution; Total organic carbon; Woody plants
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-021-06813-0

The rise in demand for natural gas has spurred the need to investigate the inland sedimentary basin for more potential sources. In response, the petrophysical parameters of the carbonaceous shale samples from two deep boreholes of Anambra Basin were evaluated. The gas-prone nature of Nkporo shale showed a thermal evolution of a Type III kerogen with initial HI value between 650 and 800 mgHC/gTOC, S2/S3 < 1, a maximum T max value of 488°C and have a low hydrocarbon generation potential ranging from 0.07 to 0.15. However, the average TOC content (2.21 wt%) indicated a good source rocks for hydrocarbon since it exceeds threshold limit of 0.5%. The plot of HI against T max shows that the organic matter belongs to the Type-III kerogen which reflects the capability of the Npkoro Formation to generate more natural gas than oil compared to Type-II kerogen. The high values (>3) of pristane/phytane ratio in both wells indicated that the organic matter belongs to terrigenous source deposited under anoxic condition which is typical of non-marine shale. The presence of Oleanane content in the Cretaceous shale sediments indicated the contribution of cell wall and woody plant tissues from the terrestrial higher plant. The low concentrations of extractable organic matter (EOM) present in form of isoprenoid and aliphatic hydrocarbon indicated little or no bitumen extract from the studied shale. Considering the high carbon preference indices (CPI) value greater than 1, the preponderance of vitrinite organic macerals and other favourable aforementioned petrophysical parameters, the non-marine Npkoro Shale Basin has significant potential to generate and expel natural gas apart from the current marine basins.