Can coal generate commercial quantity of liquidhydrocarbon? A case study from the coaly ShemshakFormation NE Iran

摘要

Generation of gaseous hydrocarbon from humic coals has long been accepted by petroleumgeologists while generation of liquid hydrocarbon in commercial quantity from coal is still a matter ofdebate. In present study an attempt has been made to evaluate the quantity of liquid hydrocarbongenerated and expelled from coaly Shemshak Formation, NE Iran. The Shemshak Formation isextensively distributed in Eastern Alborz region ranging in thickness from 1500m to more than 2000m.It consist of shale, sandstone and conglomerate interbedded with several coal layers of variousthickness. Based on the petrographic studies of various coal layers it was inferred that considerableamount of oil prone liptinitic organic matter are associated with these layers. Vitrinite reflectancevalues varies from 0.7 to1.5% indicating catagenetic stage of thermal maturation corresponding to oilgeneration window. This is further supported by reliable Tmax values. Amount and nature ofhydrocarbon generated were determined using initial petroleum potential, petroleum generation index,petroleum expulsion efficiency, coal density, effective thickness and areal distribution of coal layers.Petroleum potential varies from 0.07 to 69.4 mgHC/g rock indicating high potentiality of these layersto generate liquid hydrocarbon. Petroleum expulsion efficiency and petroleum generation index varyfrom 0.08 to1 and 0.01 to 0.08 respectively. Considering the large areal extent and great thickness ofShemshak Formation together with thermal maturation of organic matter it was concluded thatcommercial quantity of liquid hydrocarbon has been generated from this formation.