Characterization of Source Rocks from Off-shore Niger Delta Basin, Nigeria

Rock samples from the offshore Niger Delta basin, Nigeria were characterized by the predominance of C₂₆ 20R + C₂₇ 20S TAS peak using GC-MS. Among the compounds identified in m/z 245 mass chromatograms, C₂₁ methyltriaromatic steroids, C₂₂ methyltriaromatic steroids and C₂₇, 4-methyltriaromatic steroid + C₂₉, 4-methyl-, 24-ethyltriaromatic steroid were the dominant compounds in the rock samples from MJI oilfield while the rock samples from MJO oilfield were characterized by higher abundance of aromatic dinosteroids. All the compounds identified in the m/z 245 mass chromatograms of rock extracts from OKN were relatively low compared to the rock samples from MJI and MJO oilfields. The source rocks were found to be formed from mixed origin (terrestrial and marine) but with significant contribution of dinoflagellates to the organic matter and deposited in freshwater-brackish/saline lacustrine environment. The source rocks were found to have immature to early oil window maturity status based on the distributions and abundance of triaromatic steroids in the source rocks and this was further supported by well-established maturity parameters based on the saturate and aromatic biomarkers. This study showed that the abundance and distribution of triaromatic steroids and triaromatic dinosteroids can be used to assess the origin, depositional environments and thermal maturity of source rocks in the Niger Delta Basin.

Keywords
Triaromatic steroids; Aromatic dinosteroids; Source rocks; Niger Delta.