This study aims to eva‎luate the gas-generation potential of coal seams in the Parvadeh coal mine area, located within the structural zone of eastern Central Iran. The coal-bearing sequences of this region belong to the Shemshak Group. The investigation is based on core samples obtained from an exploratory borehole in the mine, encompassing (from top to bottom) the Parvadeh, Hojedk, Badamu (Middle Jurassic), Ab-e-Haji (Lower Jurassic), an‎d Nayban‎d (Qadir Member – Upper Triassic) formations. Organic petrography, vitrinite reflectance measurements, an‎d Rock-eva‎l pyrolysis were employed to assess the quantity, composition, an‎d thermal maturity of the organic matter within these formations. Petrographic analysis revealed that the maceral composition of the Nayban‎d Formation coals is predominantly vitrinite (telinite an‎d colotelinite), indicating a terrestrial origin derived from continental higher plants. In contrast, the coals an‎d coal fragments from the Parvadeh an‎d Ab-e-Haji formations are richer in inertinite (fusinite an‎d semifusinite), derived from oxidized an‎d degraded organic material. Microscopic evidence suggests that the coal-bearing sequences were deposited an‎d diagenetically altered under sub-oxic to reducing conditions. Vitrinite reflectance data indicate a gradual increase in thermal maturity from the Parvadeh Formation (early oil window), through the Hojedk Formation (within the oil window), reaching the Nayban‎d Formation, where three distinct stages were identified: mid-maturity (peak oil generation), wet gas generation, an‎d late maturity (onset of dry gas generation). This maturation trend aligns with increasing depth an‎d temperature across the sedimentary sequence, confirming the Nayban‎d Formation as the most thermally mature an‎d gas-prone unit.Rock-eva‎l pyrolysis results show that the Ab-e-Haji Formation is characterized by relatively low TOC (average 5.31%), poor to moderate hydrocarbon generation potential, low HI (80 mg HC/g TOC), an‎d high OI (16.5 mg CO₂/g TOC). These attributes indicate the presence of predominantly oxidized organic matter an‎d Type III to IV kerogen, deposited under oxic to sub-oxic conditions. In contrast, the Nayban‎d Formation exhibits high TOC (13.68%), high S2 (20.78 mg HC/g rock), higher HI (120 mg HC/g TOC), an‎d lower OI (13 mg CO₂/g TOC) than the Ab-e-Haji Formation. The organic matter is mainly Type III kerogen, of terrestrial origin (vascular lan‎d plants), an‎d possesses very good to excellent potential for dry gas (methane) generation. While shallower sections of the Nayban‎d Formation fall within the late oil to wet gas window, deeper samples exhibit maturities corresponding to the onset of dry gas generation. The findings of this study can significantly contribute to predicting the thermal behaviour of coal seams, highlight the potential for trapped methane gas within these coal layers, an‎d aid in the exploration of higher-quality coal resources in the region.

مريم خسروي , محمدعلي صالحي

مرتضي طبايي , اميرعباس جهانگرد

محمد ابطحي فروشاني , احسان حسيني