A bivariate statistical analysis for coal exploration within parts of the Anambra Basin in Nigeria (original) (raw)
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Appraisal of the Economic Geology of Nigerian Coal Resources
Journal of Environment and Earth Science, 2013
The coal deposits discovered so far in Nigeria are located mainly in the Lower, Middle and Upper Benue Trough. The coal deposits of the Anambra Basin in the Lower Benue Trough, located in southeastern Nigeria contain the largest and most economically viable coal resources. In the Lower Benue Trough, lignite and sub-bituminous coals occur within the Mamu Formation (Middle Campanian-Late Maastrichtian). High-volatile bituminous coals are found within the Awgu Formation (Middle Turonian-Early Santonian) in the Middle Benue Trough while the Upper Benue Trough contains lignites and sub-bituminous coals in the Gombe Sandstone Formation (Early Campanian-Late Maastrichtian). On the economic geology, the sub-bituminous coals in the Lower and Upper Benue Trough are best for combustion, power generation and chemical production and better for liquefaction while the high-volatile bituminous coals in the Middle Benue Trough, besides its best for liquefaction, are the most suitable as raw material for coke making in steel manufacture.
2017
Late Maastrichtian coal seam exposures are encountered at Eha-Alumona/Orba environs, Enugu State, Nigeria. This study aims at delineating the extent of the coal seam and estimating the tonnage, by an integrated approach. Core samples were acquired from two wells. Well 1 penetrates thick layers of sandstones of the Ajali Formation, overlying heterolithic beds of shale and siltstone, and a coal seam at a depth of 41 m, part of the Mamu Formation, Anambra Basin. Thickness of the seam is 0.6 m, equivalent to the exposure at Iyi Coal Spring, 417 m southeast of Well 1. No seam was encountered in Well 2 up to a depth of 61 m, suggesting it may have been eroded. Results from four vertical electrodes sounding (VES) and three double-dipole profile surveys show good correlation with core data. Geo-electric sections from VES 1 and VES 4 match significantly with Well 1 core data, with coal seam occurring between 40.7 – 56.6 m. Double-dipole Profile 1 shows that the seam occurs at a depth of 30 m...
International Journal of Coal Science & Technology, 2022
The petrographic composition of Cretaceous-age coals hosted in the Benue Trough, Nigeria is presented and discussed in terms of the paleodepositional settings that influenced the coal-bearing formations. The Benue Trough is a failed arm of the triple junction of an inland sedimentary basin that extends in a NE-SW direction from the Gulf of Guinea in the south, to the Chad Basin in the north. A total of twenty-nine (29) coal samples were obtained from nineteen coal localities in the Upper (UBT), Middle (MBT), and Lower Benue Trough (LBT). The high average volatile matter yield, low average ash yield, high calorific value (24.82 MJ/kg, on average), and low sulphur values indicate good quality coal deposits. The organic matter is dominated by vitrinite, reported at an average of 59.3% by volume (mineral-matter free). Variation was noted in the inertinite content across three sub-regions. Liptinite macerals were not commonly observed in the studied samples and were absent in the MBT samples. Coal facies studies decipher the paleoenvironmental conditions under which the vegetation accumulated. Indices commonly used are the gelification index (GI), tissue preservation index (TPI), ground water index (GWI and variations), vegetation index (VI), and wood index (WI). Comparing the array of coal facies models applied, the MBT samples differ from the UBT and LBT samples, concurring with the coal quality data. The UBT and LBT coals formed in an upper deltaic to drier piedmont plane depositional environment, while the MBT coal formed in a lower deltaic marsh to wet forest swamp depositional environment. All samples indicate an ombrotrophic paleomire. In view of the modified equations and the plots used, interpreting depositional environments from just a single model is not reliable.
Geochemical analysis has been carried out on coal samples from Emewe-Efopa coal in the northern Anambra Basin of Nigeria. The study was carried out mainly to determine the geochemical characteristics of the coal and its industrial potentials. Results of proximate analysis indicated that the coal contains 12.63% moisture, 5.71 % ash, 46.65 % volatile matter and 35.01 % fixed carbon. Ultimate analysis results also revealed that the coal consists of 60.99 % carbon, 5.37 % hydrogen, 1.25 % nitrogen, 13.01 % oxygen, 1.06 % sulphur and 0.013 % phosphorus. The average heating value of the coal is 11,084 Btu/1b while its free swelling index was calculated at 0.0. The results led to the conclusion that the coal is only appropriate for electricity generation, heating boilers and ovens in industrial process heating, manufacturing organic chemicals and production of gas and automotive fuel.
Geology, geochemistry and biomarker evaluation of Lafia-Obi coal, Benue Trough, Nigeria
Fuel, 2002
La®a-Obi coals from four boreholes were investigated in this study to ascertain their sedimentological and geochemical characteristics. This data enables the proper evaluation of their oil source rock potential and industrial utilization. The La®a-Obi area is underlain by rhythmic sequences of shale, sandstone and limestone with varying thicknesses of interbedded coal, inferring deposition under shallow marine conditions. The ash and moisture contents of the coal are high suggesting good potential for use in the steel industry. The relatively low volatiles and high vitrinite/inertinite contents indicate that the coal has an appreciable coking quality. Although the total organic carbon content exceeds the kerogen threshold of 0.5 wt% for generation of crude oil, the high vitrinite re¯ectance values (R 0 . 1.0%) and several geochemical maturity indices indicate mature to overmature facies. The bitumen compositions also re¯ect full maturity. The geological and geochemical characteristics of the La®a-Obi coals are compared and contrasted with those of Enugu coals, with emphasis on the possible economic applications of the former. q
SOURCE ROCK EVALUATION OF COALS FROM THE LOWER MAASTRICHTIAN MAMU FORMATION, SE NIGERIA
Journal of Petroleum Geology, 2007
ABSTRACT The Lower Maastrichtian Mamu Formation in the Anambra Basin (SE Nigeria) consists of a cyclic succession of coals, carbonaceous shales, silty shales and siltstones interpreted as deltaic deposits. Sub-bituminous coals within this formation are distributed in a north-south trending belt from Enugu-Onyeama to Okaba in the north of the basin.Maceral analyses showed that the coals are dominated by huminite with lesser amounts of liptinite and inertinite. Despite high liptinite contents in parts of the coals, an HI versus Tmax diagram and atomic H/C ratios of 0.80-0.90 and O/C ratios of 0.11-0.17 classify the organic matter in the coals as Type III kerogen. Vitrinite reflectance values (%Rr) of 0.44 to 0.6 and Tmax values between 417 and 429°C indicate that the coals are thermally immature to marginally mature with respect to petroleum generation. Hydrogen Index (HI) values for the studied samples range from 203 to 266 mg HC/g TOC and S1+S2 yields range from 141.12 to 199.28 mg HC/ g rock, suggesting that the coals have gas and oil-generating potential. Ruthenium tetroxide catalyzed oxidation (RTCO) of two coal samples confirms the oil-generating potential as the coal matrix contains a considerable proportion of long-chain aliphatics in the range C19-35.Stepwise artificial maturation by hydrous pyrolysis from 270°C to 345°C of two coal samples (from Onyeama, HI=247 mg HC/g TOC; and Owukpa, HI=206 mg HC/g TOC) indicate a significant increase in the S1 yields and Production Index with a corresponding decrease in HI during maturation. The Bitumen Index (BI) also increases, but for the Owukpa coal it appears to stabilize at a Tmax of 452-454°C, while for the Onyeama coal it decreases at a Tmax of 453°C. The decrease in BI suggests efficient oil expulsion at an approximate vitrinite reflectance of ∼I%Rr. The stabilization/decrease in BI is contemporaneous with a significant change in the composition of the asphaltene-free coal extracts, which pass from a dominance of polar compounds (∼77-84%) to an increasing proportion of saturated hydrocarbons, which at >330°C constitute around 30% of the extract composition. Also, the n-alkanes change from a bimodal to light-end skewed distribution corresponding to early mature to mature terrestrially sourced oil.Based on the obtained results, it is concluded that the coals in the Mamu Formation have the capability to generate and expel liquid hydrocarbons given sufficient maturity, and may have generated a currently unknown volume of liquid hydrocarbons and gases as part of an active Cretaceous petroleum system.
The Maastrichtian Mamu and Nsukka Formations in the Anambra Basin (SE Nigeria) consists of a cyclic succession of coals, carbonaceous shales, silty shales and siltstones interpreted as deltaic deposits. Subbituminous coals within these formations are distributed in a north-south trending belt from Enugu-Onyeama to Okaba in the north of the basin. Coals from these formations have been characterized by petrological and geochemical techniques. The aims of this study were to assess the quality of its organic matter, evaluate its thermal evolution and highlight its potential as a source rock. The total organic carbon (TOC) (67.21wt%) of the coal constitutes that of a good source rock with gas-prone kerogen indicated by Rock-Eval S 2 /S 3 (21.0). The high oxygen index (OI) (15.72 mgCO 2 g -1 TOC) and pr/ph (7.93) suggest deposition in a shallow marine environment. Maceral analyses showed that the coals are dominated by huminite with lesser amounts of liptinite and inertinite. Despite high liptinite contents in parts of the coals, the n-alkane distribution dominated by n-C 24 -n-C 31, an HI versus T max diagram and atomic H/C ratios of 0.80-0.90 and O/C ratios of 0.11-0.17 classify the organic matter in the coals as Type III kerogen. Vitrinite reflectance values (%Rr ) of 0.44 to 0.59% and T max values between 414 and 432 o C indicate that the coals are thermally immature to marginally mature with respect to petroleum generation. Hydrogen Index (HI) values for the studied samples range from 183.09 to 344.53 mg HC/g TOC and S 1 +S 2 yields range from 120.5 to 242.04 mg HC/g rock, suggesting that the coals have gas and oil-generating potential. This thermal evolution is thought to account for its current hydrogen index (250.24 mgHCg -1 TOC). Generated petroleum may not have reached the threshold for hydrocarbon expulsion but a review of petroleum system elements in the basin will stimulate high prospects in the Anambra basin.
2021
The petrographic composition of coals hosted in the Benue Trough, Nigeria are presented and discussed in terms of paleodepositional setting that influenced the coal-bearing formations. The Benue Trough is a failed arm of the triple ‘RRr’ junction of an inland sedimentary basin that extends in a NE-SW direction from the Gulf of Guinea in the south, to the Chad Basin in the north. A total of twenty-nine (29) coal samples were obtained from 19 coal localities in the Upper (UBT), Middle (MBT), and Lower Benue Trough (LBT). The proximate data indicates the coal samples have a high volatile matter content, low ash yield, and high calorific value (24.82 MJ/Kg, on average). The sulphur values are generally low (average of 0.94 %). The coal samples are generally high in vitrinite, with an average of 59.3% by volume (mineral-matter free). Variation was noted in the inertinite content for the three sub-region samples. Liptinite macerals were not commonly observed in the studied samples and are...
Journal of Geography, Environment and Earth Science International, 2021
Detailed geologic mapping and geochemical analysis of coal samples around Abocho area, northern Anambra Basin, Nigeria was conducted in order to assess the quality of the coals in the area. Proximate and ultimate analyses were carried out on coal samples from the Mamu Formation to determine its chemical characteristics. Physical analysis was also carried out on the coal samples to determine the specific gravity, density and hardness. Geochemical analysis was also carried out on the associated rocks in the study area (Abocho), particularly Shales and Clays to determine their major oxides composition. The area is composed of the Maastrichtian Mamu Formation overlain by the Ajali Sandstone of the same age both dipping between 16°E and 19°E. The geologic mapping of Abocho area revealed two mappable lithologic units: The Mamu Formation and the Ajali Sandstone. The Proximate analyses indicates that the coal contains an average 7.15%, 35.53%, 36.24% of moisture content, volatile matter an...
Petroleum & Coal, 2011
The hydrocarbon potential of the Upper Cretaceous units (Maastrichtian Mamu Formation) of the Anambra Basin, Southeastern Nigeria was assessed by Rock-Eval pyrolysis. The total organic carbon (TOC) values range from 0.07 to 61.42 wt. % (averaging 8.54 wt. %). The genetic potential (GP) and hydrogen index (HI) values range from 0.05 to 332 mg HC/g rock and 40 to 771 mg HC /g respectively. These values indicate that the sediments have gas and oil generating potential. The organic matter is predominantly gas prone (mostly type III and mixed type III/II). The level of thermal maturity deduced from the production index (0.02 to 0.63), calculated vitrinite reflectance of 0.47 to 0.78 %Ro and T max values between 338 and 441 o C suggest that the coal and shale samples are thermally immature to marginally mature with respect to petroleum generation.