The Upper Jurassic Penglaizhen Formation gas pool in Chengdu sag is a secondary gas pool with its gas being sourced from the Upper Triassic source rocks over 3 km beneath the reservoirs.Due to the long vertical distance between the reservoir and source rocks

the gas migration path and mechanism are assumed to be of particular importance.The gas-bearing sandstones are widely distributed in the Penglaizhen Formation and have great heterogeneity

thus study of the principal controlling factors on gas accumulation is critical to understanding its heterogeneity.Analyses of gas sources

original gas compositions

isotopic compositions

dry coefficient

and iC

4

/nC

4

demonstrate that the major hydrocarbon migration pathways are source-rock-connected faults and permeable carrier beds through which gas is capable of migrating with high efficiency.Hydrocarbon exploration and exploitation indicate that source-rock-rooted faults and good-quality reservoirs.The existence of source rock-rooted faults is the indispensable condition for gas accumulation in the Penglaizhen Fm in Chengdu sag.The rational combination between the source rock-rooted faults and reservoirs and the poroperm charateristics of reservoirs further influence the enrichment of gas.Gas is highly enriched in the downdip areas where the sandstones have good poroperm characteristics and are connected with or near to the source rock-rooted faults.The study results are valuable for gas exploration and development and can increase success rate in drilling prolific and commercial wells.