GEOCHEMICAL CHARACTERISTICS AND DEPOSITIONAL ENVIRONMENT OF SOURCE ROCKS FROM SEM WELL, SOUTHEASTERN NIGER DELTA BASIN, NIGERIA.

An integrated petroleum-geochemical investigation was conducted to assess the source-rock potential, kerogen characteristics, thermal maturity, organic-matter provenance, and depositional conditions of shale samples from the SEM well, Niger Delta Basin. Rock-Eval pyrolysis indicates high organic richness, with total organic carbon (TOC) contents of 3.77–3.95 wt.% and S2 values of 10.77–12.18 mg HC/g rock. S1 values of 7.52–10.58 mg HC/g rock and genetic potential (S1 + S2) of 19.22–21.64 mg HC/g rock indicate excellent to very good hydrocarbon-generating potential. Hydrogen Index (HI) values of 275–323 mg HC/g TOC characterize the organic matter as predominantly Type II to mixed Type II/III kerogen, with significant oil- and gas-prone potential. Biomarker distributions indicate mixed marine algal, bacterial, and terrigenous organic-matter inputs, while V/Ni and Ni/Co ratios suggest a dominant marine contribution. Tmax values of 429–430°C, supported by sterane and aromatic biomarker maturity parameters, indicate thermally mature organic matter within the oil-generation window. Trace-element and biomarker proxies collectively suggest predominantly oxic to suboxic siliciclastic deposition with intermittent reducing conditions. The geochemical characteristics therefore identify the SEM well shales as organically rich, oil- and gas-prone source rocks with effective hydrocarbon-generation potential, deposited in a fluctuating fluvial-deltaic to deltaic setting associated with the Akata–Agbada transition zone of the Niger Delta Basin