ABSTRACT

Rock-Eval pyrolysis has been widely accepted as a standard method of analyzing sedimentary rocks especially coals for hydrocarbon prospectiveness. This method was used to analyse twenty-one samples from the Benue Trough of Nigeria. Four samples from the Mamu Formation, fourteen samples from the Agwu Formation, Two samples from the Lamja Sandstone, and one sample from the Gombe Sandstone within lower, middle and upper Benue Trough respectively. The four samples from the Mamu Formation have an average TOC of 44.03wt.%, an average S1 of 2.14mg/g, an average S2 of 133 mg/g and an average Tmax of 431oC. The HI is very high, ranging from 266 to 327 mgHC/gTOC. The mean HI from S2 versus TOC plot is about 363 (r2 = 0.9877) mgHC/gTOC. This figure places these coals into type II organic matter that can generate oil and gas. The Tmax values suggest an onset of oil generation. The fourteen samples from the Agwu Formation have an average TOC of 46.23 wt.%, S1 of 172 mg/g and Tmax of 452oC. Agwu 1, Agwu 6 and Agwu 7 show exceptionally low HI, S1 and S2 but the Tmax values for these samples fall within the optimal temperature for hydrocarbon generation. HI for the rest of the samples ranges from 120 to 267 mgHC/gTOC. All the samples from the Agwu Formation have an average HI of 280 mgHC/gTOC from S2 versus TOC diagram. On HI versus OI plot, the samples plotted on all the organic matter types’ tracks. The HI value of 182 mgHC/gTOC from S2 versus TOC plot implies that coals from the Upper Benue Trough have type III organic matter with gas and oil source potential. The Tmax of 438oC indicates that the samples from the Lamja Sandstone are within early to middle oil window while the Tmax of 423oC from sample of the Gombe Sandstone implies immaturity.