Organic Geochemistry, Petrography, Depositional Environment and Hydrocarbon Potential of the Eocene Coal Deposits of west Daranggiri Coalfield, Meghalaya

Abstract

The Eocene coal deposits of west Daranggiri coalfield of Meghalaya is hosted in the Tura Formation. The coals are perhydrous in composition, rich in organic matters and poor in mineral content. The organic matters are dominantly represented by Type III kerogens contributed by terrestrial plants. Petrographic analysis confirms dominance of vitrinite with subordinate amounts of liptinite and inertinite. Maturity parameters like vitrinite reflectance, Rock-Eval Tmax, volatile matter content etc. indicate low thermal maturity of the coal within lignite to subbituminous rank. The coals are immature to act as petroleum source rock despite having high-quality organic matters. However, perhydrous nature of the organic matters and significant amount of liptinite macerals suggest that despite low thermal maturity, the coals might have some capacity to generate liquid hydrocarbon. High liptinite and perhydrous vitrinite contents of the coal may result in suppression of vitrinite reflectance, thus, underestimation of maturity. Presence of exsudatinite in the coal also points to generation of some liquid hydrocarbon. The coal deposits possess excellent potential for hydrogenation industry. The coals are characterized by very high rate of conversion from coal to oil and high oil yield. Indices of facies critical maceral association indicate the origin of the coal in wet swamps under mildly oxic to the anoxic environment with moist hydrodynamic condition. The high sulphur content of the coal, association of marine palynological assemblage and presence of limestone beds at the top of the Tura Formation point to nearshore environment of deposition.

Organic geochemistry and petrology of the coals in the Laisong Formation, Naga Schuppen Belt, NE India: Inferences on hydrocarbon potential and depositional environment

“…The liptinite content in the Jaintia coals is higher than that of Laisong coals (Singh & Singh, 2000). The rank of the Laisong coal (lignite to sub-bituminous type 'C') is found to be overlapping or slightly lower than the Jaintia coals that ranges from sub-bituminous type 'C' to high volatile bituminous type 'C' (Gogoi et al, 2020;Singh, 2018).…”

“…Collotelinite is the most dominant vitrinite maceral in both coal deposits (Singh et al, 2013). The vitrinite reflectance of the Laisong (Gogoi, Kumar, & Phukan, 2020;Singh, 2018). The liptinite content in the Jaintia coals is higher than that of Laisong coals (Singh & Singh, 2000).…”

Hydrocarbon generation potential evaluation via petrographic and geochemical analyses of El-Maghara coal in Sinai, Egypt

“…The thermal maturity is measured using the procedures of ASTM 49 to calculate the vitrinite reflectance (R o %). The maceral content, especially reactive macerals (RM), can be used to determine oil yield and conversion of coal into hydrocarbon 50 , 51 using the following formulas 52 . …”

Rock-Eval Pyrolysis and Petrographic Characteristics of Coals of Chintalapudi Sub-Basin, Pranhita-Godavari Basin, Southern India: Implication to Depositional Environment

“…Organic petrography deals with the microscopically visible organic matter present in rocks and is the most effective method for determining the depositional environment, the source vegetation,and the maturation level of coal and its gas generation potential (Diessel, 1983;Flores, 2002;Kalkreuth , 1991;Latif , 2021). Many researchers have provided a thorough study of several geochemical parameters in evaluating the richness, maturity and quality of source rocks, vitrinite reflectance, maceral analysis, total organic content measurement, rock-eval pyrolysis, associations between maturity and hydrocarbon generation, as well as the depositional environment (Dow, 1977;Tissot and Welte, 1978;Thompson-Rizer, 1993;Law, 1999;Vandenbroucke and Largeau, 2007;Gogoi , 2008;Salleh , 2008;Sahoo and Gogoi, 2011;Phukan , 2013;Jahan, 2016;Sharma , 2016;Singh , 2016aSingh , -b, 2017aMathews , 2020;Gogoi , 2020Gogoi , , 2021Singh and Kumar, 2020;Singh , 2022;Kar , 2022). Quantitative and qualitative analyses of different kerogen types with the geochemical study of organic matter provide a better understanding of the generating potential (GP) of source rocks (Thompson and Dimbicki, 1986;Isabel, 2012).…”