Coal chemistry, utilization potential, and coalbed methane (CBM) assessment of some coal deposits in Central Benue Trough, north-central Nigeria

Coalbed methane (CBM), a current global legislative priority for climate change mitigation, is an unconventional and eco-friendly clean source of energy that is considered a veritable alternative to conventional fossil fuels. Despite its overwhelming advantages, CBM evaluation studies of Nigerian coals have received little or no attention. To bridge the gap in knowledge, we have for the first time in Jangwa-Shankodi and Lafia-Obi, described the potential of harnessing CBM for its gainful utilization in Nigeria using some coal deposits in its north-central region as a case study. The gas contents of the coals were determined empirically by taking account of their ultimate and proximate properties. Other coal parameters such as fuel ratio and vitrinite reflectance (Ro (%)) have also been computed and discussed. Proximate analyses of the studied coal samples show moisture contents that vary between 2.28 and 2.56%, whereas, volatile matter yield is placed in the range of 29.98–30.34%. Ash yield ranges from 7.83 to 8.64%. Fixed carbon content varies from 55.97 to 56.30%. Variation in fuel ratio shows a restricted range from 1.72 to 1.87. All the coal samples were found to be low in sulphur (< 1%) with H/C ratios that vary from 0.072 (LAF 2, 3 and 4) to 0.086 (JSK 3). Moreover, the coals were found to be of medium-volatile bituminous rank, with gas contents that range from 12.65 to 13.20 cc/g. In the current study, kerogen lies in the Type IV zone, which suggests the generation of methane gas by the studied coal samples. Also the estimated range of vitrinite reflectance (Ro) which varies between 1.073% and 1.086% indicates thermogenic gas expulsion in the coals. There is a noticeable increase in gas content with coal maturity and depth. These values are indicative of good quality coals that show antecedents for CBM production. However, considering that this work is a pilot study, we recommend that core drilling be employed in obtaining insitu measurements of the coal gas contents and thus, verify these empirical estimates. Also, detailed laboratory study on pore structure (and its distribution) and adsorption isotherm curve are recommended to better understand the coal reservoir properties and hence, consolidate the present study.