PETROLEUM POTENTIAL OF CRETACEOUS SHALES IN THE UPPER BENUE TROUGH, NIGERIA

A geochemical study of the argillaceous sequences of Turonian-early Santonian age penetrated by ten shallow boreholes in the Upper Benue Trough was carried out. The-average total organic carbon contents of the sampled sections of the Bima, Yolde, Pindiga, Sukuliye and Jessu Formations were 0.30. 1.40, 0.85, 0.60, and 0.54%, respectively. Apart from the Bima Formation, all exceed the minimum value (0.5% TOC) normally required for a petroleum source rock. In spite of the moderate TOC, however, the content of soluble organic matter (SOM) and saturated hydrocarbons (SHC) was generally low. In terms of organic-matter type. a predominantly marine facies with some terrigenous input is inferred for the Sukuliye and Pindiga Formations. This indicates that open-marine conditions might not have been established during the Turonian marine transgression, which deposited these units. Within the updip sector of the basin. the organic matter is thermally immature. The most promising zones seem to be located south of the study area, where source rocks that have attained optimum levels of maturity for hydrocarbons occur.