ORGANIC GEOCHEMICAL EVALUATION OF THE MAASTRICHTIAN COAL AND SHALE FACIES OF GOMBE FORMATION, GONGOLA BASIN, NIGERIA
The organic geochemical results show that the organic carbon content of the coals is high (62.75-65.29 wt %) and moderate (1.78-2.99 wt %) for the shales. S2 values for the coals are high (57 to 103.21 HC/g rock) and relatively low (less than 3 HC/g rock) in the shales. The HI less than 200mgHC/gTOC for all the samples (29-64 mgHC/gTOC and 90-140mgHC/gTOC for shale and coal respectively) suggest Type III kerogen and plant contributions from terrestrial sources. Consequently, gaseous hydrocarbon potential is exhibited in the source beds. This is supported by the PI (< 0.1) and the ratio of S2/S3 ranging from (0.6-5.5).
The Tmax ranging from 425 to 430 0C and 416 to 422 0C for the shales and coals respectively (and generally less than 4350C) indicate pre oil window stage in spite of the high organic matter concentration. Plot of production Index PI versus Tmax based maturity indicate low level organic matter conversion. In conclusion, the samples constitute good source rock and have potential for gas but the kerogens are not thermally mature to generate oil.