Abstract: The Hangjinqi area in the northern margin of the Ordos Basin has been explored for natural gas for about 40 years.However, it wasn't until a decade ago that a systematic investigation of gas reservoiring conditions in this area has been initiated.As a result, exploration breakthrough had been made here after aiming at the large-scale lithological traps.The Permo-carboniferous tight clastic rocks were found to contain more than 700 billion m³ of gas-in-place.A comprehensive study shows that large-scale gas fields in the area were mostly formed within the pervasive near-source layered petroleum system in the transitional sequences at the lower Permo-Carboniferous.This petroleum system has widely-distributed coal-measure source rocks in the Upper Carboniferous, huge Lower Permian channel sandstone reservoirs, short distance between the source and the reservoirs, massive hydrocarbon generation and charging during the Early Cretaceous and large area of Upper Permian cap rocks.The Upper Paleozoic gas reservoirs in the area feature in lithological traps, large gas-bearing area and low abundance of reserves.As newly found reservoirs are mostly tight and low-permeability, how to locate sweet spots to realize a highly effective gas discovery is a challenge for all those engaging in petroleum industry.

Key words: reservoiring factor, near-source accumulation, large gas field, Hangjinqi area, Ordos Basin