Geochemical Evaluation of Offshore Western Niger Delta Shale

Akinsehinwa Akinlua¹ and Nelson Torto^2
1Department of Chemistry, Obafemi Awolowo University, Ile-Ife, Nigeria
²Department of Chemistry, University of Botswana, Gaborone, Botswana

A geochemical evaluation of shale samples obtained from three offshore fields; MJ, MF and ML fields was carried out. Offshore oil samples and onshore oil samples were studied for correlation. The gas chromatographic data showed that the three offshore fields studied exhibited, different and unique geochemical signatures. Shale samples from MJ field are thermally mature, n-alkane and their isoprenoid hydrocarbon distribution indicated that the organic matter was of marine and terrestrial origin. The organic matter appeared to have a significant marine contribution and deposited in alternating oxic and anoxic environments. In MF field, sedimentation of the organic matter in the shallow depths was under reducing environment while that of the deeper depth horizons was under oxidizing environments. The organic matter of this field had contributions from both marine and terrestrial sources. The geochemical data indicate that organic matter from ML field is strongly terrestrial and was deposited under oxidizing conditions. Most of the shale samples from this field are thermally mature but some are immature. Geochemical plots showed good geochemical correlations between the oils from onshore field and oils from offshore fields. There are some differences between the rock extracts from the three offshore fields and oils from the onshore field. Rock extracts and oils from the offshore fields are correlative to an extent but the correlation is not strong.

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