Thar Coal, Sindh, Pakistan: A Potential Candidate for Liquefaction

Abstract

The Middle to Late Palaeocene Thar coal mostly comprises matrix lithotype and falls in lignite to subbituminous C rank stage. Twenty, coal layers of variable thickness are reported at depths between 137.04 to 178.72 m beneath surface. Cumulative coal bed thickness varies from 8.08 to 36.00 m. Coal-petrography and geochemical methods were applied for characterization of Thar coal in respect of liquefaction. Rock Eval Pyrolysis data shows very high values of S1, S2 and hydrogen Index (HI). Total organic content (TOC) ranges from 31.64 to 69.5%. Sulfur content varies from 0.48 to 6% and its average content is 1.4% whereas sulfur content of the main seam averages about 1%. S1 ranges from 6.20 to 86.1 mg HC/g rock with an average of 29 mg HC/g and S2 ranges from 67.9 to 527mgHC/g rock with an average of 229.2 mg HC/g. Hydrogen Index varies from 137.4 to 838mgHC/g TOCwith an average of 409mgHC/g TOC. Extractable organic matter (EOM) yield using dichloromethane, ranges from 1397 to 10563 ppm and EOM/TOC ranges from 4.89 to 20.38 mg/g. This type of organic matter can be classified as kerogen type II and is comparable with good quality oil shale. Due to the high S1 and S2 values and the significant amount of EOM, the Thar coal can be used for liquefaction. Organic petrography examination of thirty one samples from three boreholes at Block no. 1, was carried out. Huminite is the main maceral group varying from 85 to 95%, Liptinite is the second maceral group which varies from 1.0 to 8.11% and Inertinite group ranges between 1.1 to 8.1%. Pyrite content varies up to 2.0%. Oil droplets having strong green fluorescence are observed under blue light excitation. Liptinite macerals like fluorinite, resinite and alginite also gave strong fluorescence colors. On the basis of above geochemical and petrographic results (high percentage of reactive macerals), Thar Coal seems to be a good candidate for surface gasification and liquefaction.