Characterization of Coal Formations in the Middle Benue Trough and Anambra Basin, Nigeria Using Rock-Eval Pyrolysis

Abstract

Global energy demand has increased exponentially in the twenty first century with over dependence on few energy sources. These sources comprise oil and gas, renewable and nuclear energy. Nigeria suffers from acute energy deficiency especially in electric power availability; which has to a great extent, left the country behind in industrial and technological advancements. This has been attributed to huge dependence on few energy sources by a rapidly growing population. This study therefore evaluates the geochemical properties of coal deposits in the Middle Benue Trough and Anambra Basin, Nigeria as a strategy for addressing the energy shortfall in the country. Twenty five (25) coal samples from the study area were analyzed using Rock Eval Pyrolysis at the Federal Institute for Geosciences and Natural Resources, Hannover, Germany while combustion tests were carried out at the Ibrahim Badamasi Babangida University, Lapai, Nigeria. Results show that Okaba coal has an average TOC of 62.98%, HI of 278.22HC/gTOC, OI of 19.26mgCO /gTOC and Tmax of 420oC while Ogboyaga coal has average TOC of 63.4%, HI of 235.02HC/gTOC, OI of 38.47mgC2 O /gTOC and Tmax of 424oC. Omelehu coal on the other hand has an average TOC of 48.34%, HI of 224.74HC/gTOC2, OI of 28.362mgCO /gTOC and Tmax of 421.8oC while Owukpa coal has an average TOC of 38.98%, HI of 234.2HC/gTOC, OI of 20.572mgCO /gTOC and Tmax of 427oC. The Lafia-Obi coal has an average TOC of 35.9%, HI of 56.12HC/gTOC, OI of 30.61mg2CO /gTOC and Tmax of 451oC. Combustion test 2 revealed that Okaba, Ogboyaga, Omelehu, and Owukpa coals took 10.00, 10.35, 11.37 and 13.22 minutes to boilequal volume of water respectively. Lafia-Obi coal did not bring the water to boiling point. Juxtaposing Rock Eval and combustion results revealed that Okaba coals have efficient combustion attributes of relatively high HI and low OI which resulted to fast boiling time and minimal smoke emission while the Lafia-Obi coals have the least combustion attributes with very low HI which made it difficult to combust. Ogboyaga coals have a good combustion attribute of high HI but the OI is also high. This explains the smoky combustion. Van Krevelen plot [HI versus OI] characterize the kerogens in Okaba, Ogboyaga, Omelehu, and Owukpa coal deposits as transitional Type II/III while Lafia-Obi coal as Type III. HI versus Tmax plot also characterize Okaba, Ogboyaga, Omelehu, and Owukpa coal deposits as immature for oil and gas generation although they possess relatively high HI while the Lafia-Obi coal as mature in the gas window although they have very low HI. Okaba, Ogboyaga, Omelehu, and Owukpa coal deposits show good prospect for clean bio-fuel extraction while Okaba coal can be used in its natural state to generate energy for industries with minimal smoke emission.