Organic and trace elements geochemistry of western Niger delta oils

摘要

Thirteen crude oil samples from on-shore western swamp fields in the Niger Delta were analyzed using standard organic and inorganic geochemical techniques (column chromatography, gas chromatography and inductively coupled plasma spectrophotometry) to permit their characterization. The results show that API gravity ranges from 23.5-43°; CPI ranges from 0.99-1.48; Pr/Ph ratio ranges from 1.25-2.65; Pr/nC_(17) ratio ranges from 0.41-3.90; and Ph/nC_(18) ratio ranges from 0.24-4.15. These indicate mixed organic sourcedoils. The concentration of transition metals (V, Cr, Mn, Fe, Co, Ni, Cu) in these oils ranges from 0.04-16.69 ppm. Statistical analysis of the trace metals contents and organic geochemical data enabled the correlation and classification of the oils into two groups (A & B) similar to those of earlier workers. Star diagrams and cross plots (Co/Ni versus V/Ni) confirm that the two groups of oils are genetically related with group A oils being the biodegraded equivalents of group B oils. The threshold temperature for biodegraded oils was found to be 79° C, which is in agreement with earlier published data. In general, our results support the presence of a single petroleum system in the western swamp of the Tertiary Niger Delta.