Geochemical characteristics and source rock of Ordovician gas reservoir, Changqing Gasfield

摘要

Carbon isotopic composition of methane in Ordovician gas reservoir in the Changqing Gasfield can reflect the dominance of Upper Paleozoic coal-type gas despite its high mature de- Gree. The ~12C-rich ethane in the Ordovician reservoir(δ~13C_2 < -29/100), known as a marker as Oil-type gas, does not indicate the Ordovician marine carbonate as main source rock, it is be- Cause of the relative less ethane content in coal-type gas than in oil-type gas due to generation And migration. The way of Upper Paleozoic coal-type gas migrating into the Ordovician reservoir Is widely through the unconformity instead of only through the erosion groove in the weathering Crust.