Abstract
The Risha field is one of the Jordan's most important gas fields, but little has been known about the origins and the underlying formation mechanism(s) of its gases. Hence, we carried out studies to determine the origin and formation mechanism of the natural gas in the Risha field, Jordan. The integrated carbon and hydrogen isotope compositions reveal that the Early Silurian Mudawwara Formation is the main source for Risha gases that are dry gases with some condensates. The content of methane ranges from 90.2 to 91.7% with small amounts of ethane, propane, and non-hydrocarbon gases (CO2, N2). They are thermogenic gases from marine organic matter which were formed from secondary cracking of the oil and gases of primary cracking at highly mature stages (Ro = 1.40–1.84%). The carbon isotope compositions show a partial reversal trend of δ13C1 > δ13C2< δ13C3< δ13C4 due to further high thermal evolution effect on isotope signatures.
•The genetic origin of Ordovician natural gas in Risha gas field were defined.•Natural gas from Risha gas field is generated from marine sapropelic organic matter.•It displayed partial reversal between methane and ethane (δ13C1 > δ13C2).•Risha natural gas is highly mature thermogenic from highly mature source rocks.